Apeksha Khatiwada

Characterization of Allosteric Modulators of Glutamate Transporters:

Selectivity and Potency Screening

Implications for Drug Development and for Understanding Allosteric Modulation of

Glutamate Transport

APEKSHA KHATIWADA

AUGUST 2018 A Dissertation Presented to Faculty of Drexel University College of Medicine In partial fulfilment of the Requirement for the Degree of Masters of Science in Drug Discovery and Development

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ACKNOWLEDGMENTS I would like to acknowledge everyone who believed in me and has been a constant motivator throughout my journey. Firstly, I would like to extend my sincere gratitude to my mentor, Dr. Andreia Mortensen for her guidance, support and encouragement towards my work. She has been so nice to me and taught all the laboratory techniques, helped me improved my presentation and critical thinking skills. I feel so fortunate to have this wonderful opportunity to do my master’s thesis under her supervision.

This project would not have been possible without Dr. Joseph Salvino. All the synthetic analogs used for the project has been synthesized in medicinal chemistry lab under his supervision. I would also like to thank Dr. Wagner F. Santos (University of São

Paulo, Brazil) for kindly providing us additional compound for my study.

I would like express my heartfelt thanks to members of my thesis committee: Dr. Ole

Mortensen, Dr. Joanne Mathiasen, and Dr. Joseph Salvino for their time and support. Every suggestions and feedbacks from them has been a tremendous tool towards making my work as best as possible.

I would also like to thank Dr. Paul McGonigle and Dr. Joanne Mathiasen for making the Drug Discovery and Development program so interesting and for all the valuable feedbacks, interactions and words of encouragement.

I would also like to thank Dr. Ole Mortensen for his insights and knowledge that really helped me understand the neuropharmacology and for stimulating the discussions during presentations that helped me build my confidence. iv

I would also like to thank previous lab members Ryan Wretz, Romulo Falcucci and

Srawastie Sarker for their contributions toward the project. I would also like to thank

Rafaela Scalco, an exchange student from Brazil who trained me with all the basic skills for my project.

I would like to thank my current lab member Jennifer Green for her support and contribution towards my work. I would also like to thank Stacia Lewandowski, Caitlyn Rice and Shaili Agarwal and Xiaonan Liu for their useful inputs and suggestions towards my work. They have been amazing support to me.

I would also like to thank the Meucci lab for providing some of the animals for my study, the Hu lab for providing the dissection hood and the front office for being so kind and cooperative all the time.

There is nothing greater than family’s love and support and I feel extremely blessed to have amazing family and super supportive husband Pratic. They have always always believed in me and encouraged me to do better. I would never be able to achieve what I have without their support. I owe them a huge thanks.

Contents

List of Figures and Tables ...... vii Abstract ...... ix 1. INTRODUCTION ...... 1 1.1. GLUTAMATE AND GLUTAMATERGIC SYNAPSE ...... 1 1.2. GLUTAMATE RECEPTORS ...... 3 1.3. GLUTAMATE TRANSPORTERS: LOCALIZATION AND MOLECULAR FUNCTIONING ...... 5 1.4. GLUTAMATE EXCITOTOXICITY ...... 10 1.5. PREVIOUS STRATEGIES TO TREAT THE HARMFUL EFFECTS OF GLUTAMATE EXCITOTOXICITY AND THEIR LIMITATIONS ...... 12 1.6. TARGETING GLUTAMATE TRANSPORTERS: AN EMERGENT STRATEGY...... 14 1.7. ALLOSTERIC MODULATION ...... 16 1.8. IDENTIFICATION OF PAMs OF EAAT2: PREVIOUS STUDIES ...... 17 1.9. PROGRESSION OF COMPOUNDS: FIRST TO THIRD GENERATION ...... 19 2. AIMS ...... 21 3. MATERIALS AND METHODS ...... 22 3.1. MATERIALS ...... 22 3.2. EQUIPMENT ...... 24 3.3 Synthesis of compounds and workflow chart ...... 24 3.4. Experiments with COS-7 cells ...... 27 3.4.1. Transfection of COS-7 cells ...... 27 3.4.2. Glutamate uptake assays in COS-7 cells ...... 27 3.5. Experiments with primary cultures of glia ...... 29 3.5.1 Glia dissection and plating ...... 29 3.5.2 GLUTAMATE UPTAKE ASSAYS IN GLIA ...... 31 3.6 DOSE RESPONSE ASSAYS IN OTHER TYPES OF NEUROTRANSMITTER TRANSPORTERS 33 3.6.1 DOSE RESPONSE ASSAYS IN GABA (GAT-1) and GLYCINE (Glyt1, Glyt3) TRANSPORTERS ...... 34 3.6.2 DOSE RESPONSE ASSAYS IN MONOAMINE TRANSPORTERS (hDAT, hNET and hSERT) ...... 35 3.7. IN VITRO NEUROPROTECTION STUDIES ...... 35 3.8. DATA ANALYSIS ...... 36 vi

4. RESULTS ...... 38 4.1. DOSE RESPONSE ASSAYS IN COS-7 CELLS ...... 38 4.1.1. Validation of previous results ...... 38 4.1.2 Non-selective stimulators of glutamate uptake ...... 39 4.1.3. Stimulators of glutamate transport: selective to EAAT1 and EAAT2 ...... 42 4.1.4. Stimulator of glutamate transport: selective to EAAT2 only ...... 45 4.1.5. Inactive compounds ...... 46 4.1.6. Inhibitor compounds ...... 47 4.2. DOSE RESPONSE ASSAYS IN GLIA ...... 52 4.3. KINETICS STUDIES ...... 56 4.3.1 KINETICS STUDIES IN COS-7 CELLS ...... 56 4.3.2 KINETICS STUDY IN GLIA ...... 60 4.4 DOSE RESPONSE ASSAYS IN OTHER TYPES OF NEUROTRANSMITTER TRANSPORTERS 64 4.4.1 DOSE RESPONSE IN GABA AND GLYCINE TRANSPORTERS ...... 64 4.4.2 DOSE RESPONSE IN MONOAMINE TRANSPORTERS ...... 65 4.4. IN VITRO NEUROPROTECTION STUDIES ...... 67 4.4.1 NEUROPROTECTION STUDIED IN EXCITOTOXIC GLUTAMATE INSULTS ...... 67 4.4.2 NEUROPROTECTION STUDIED AFTER OXYGEN/GLUCOSE INSULTS ...... 69 5. CONCLUSIONS ...... 72 6. DISCUSSION AND FUTURE DIRECTIONS ...... 81 7. REFERENCES ...... 88

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List of Figures and Tables

Figure 1. Glutamatergic synapse showing release of glutamate from presynaptic neurons and expression of ionotropic receptors and transporter on the glial membrane...... 2 Figure 2. Model of a glutamatergic synapse demonstrating the localization of EAATs 1-4. .. 8 Figure 3. Transmembrane domains of the glutamate transporter indicating scaffolding and transporting domains ...... 9 Figure 4. Glutamatergic synapse under physiological conditions (a) and excitotoxic conditions (b)...... 10 Figure 5. Diagram showing the allosteric site in EAAT2, the in silico screening approach that lead to the identification of GT949, and a dose response curve of GT949 in glutamate uptake assay performed in transfected COS-7 cells...... 18 Figure 6. Workflow chart proposed to identify a lead compound predictive of in vivo efficacy...... 26 Figure 7. Effect of DA-023 on glutamate uptake in EAAT2 transfected COS-7 cells...... 39 Figure 8. Effect of NA-005 on glutamate uptake in transfected COS-7 cells...... 40 Figure 9. Effect of VY-3-285 on glutamate uptake in transfected COS-7 cells...... 41 Figure 10. Effect of VY-3-286 on glutamate uptake in transfected COS-7 cells...... 42 Figure 11. Effect of DA-050 on glutamate uptake in transfected COS-7 cells...... 43 Figure 12. Effect of DA-058 on glutamate uptake in transfected COS-7 cells...... 44 Figure 13. Effect of PWX-10 on glutamate uptake in transfected COS-7 cells...... 45 Figure 14. Effect of NA-014 on glutamate uptake in transfected COS-7 cells...... 46 Figure 15. Effect of DA-040 on glutamate uptake in transfected COS-7 cells...... 47 Figure 16. Effect of VY-3-209 on EAAT2 mediated glutamate uptake in transfected COS-7 cells...... 48 Figure 17. Effect of VY-3-171 on EAAT2 mediated glutamate uptake in transfected COS-7 cells...... 49 Figure 18. Effect of NA-010 on EAAT2 mediated glutamate uptake in transfected COS-7 cells...... 50 Figure 19. Effect of DA-055 on EAAT2 mediated glutamate uptake in transfected COS-7 cells...... 51 Figure 20. Effect of VY-3-136 (A) and VY3-136(2) (B) on EAAT2 mediated glutamate uptake in transfected COS-7 cells...... 52 Figure 21. Effect of DA-050 on glutamate uptake in cultured glial cells...... 53 Figure 22.Effect of PWX-10 on glutamate uptake in cultured glial cells...... 54 Figure 23. Effect of NA-005 on glutamate uptake in cultured glial cells...... 55 Figure 24. Effect of NA-014 on glutamate uptake in cultured glial cells...... 56 Figure 25. Effects of NA-014 on the kinetics of EAAT2...... 57 Figure 26. Effects of PWX-10 on the kinetics of EAAT1...... 58 Figure 27. Effects of PWX-10 on the kinetics of EAAT2...... 59 Figure 28. Effect of NA-014 on the kinetics of glutamate transport in glia cells...... 61 Figure 29. Effect of PWX-10 on the kinetics of glutamate transport in glia cells...... 62 viii

Figure 30. Effect of NA-009 and VY-3-209 on the kinetics of glutamate transport in glia cells...... 63 Figure 31. Effect of NA-014 on GABA and Glycine uptake in transfected COS-7 cells...... 64 Figure 32. Effect of PWX-10 on GABA and Glycine uptake in transfected COS-7 cells...... 65 Figure 33. Effect of NA-014 on monoamine uptake in transfected COS-7 cells...... 66 Figure 34. Effect of PWX-10 on monoamine uptake in transfected COS-7 cells...... 67 Figure 35. Representative images of mixed neuron-glia cultures (control and insult with glutamate)...... 68 Figure 36. Neuroprotective effects of NA-014 after excitotoxic insults in mixed neuron/glia cultures...... 69 Figure 37. Representative images of mixed neuron-glia cultures (control and subjected to 35 min OGD insults)...... 70 Figure 38. Neuroprotective effect of NA-014 in cortical mixed cultures after OGD insult. . 71

Table 1: Previous strategies evaluated to treat harmful effects of glutamate excitotoxicity, mechanism and their limitations...... 12 Table 2: Comparison of Efficacy and Potency of DA-023 In EAAT2 Mediated Glutamate Uptake Between Previous Study And Current Study...... 72 Table 3: Effect of Third Generation Compounds on Glutamate Uptake Assays Performed On COS-7 Cells Transfected with EAAT1, EAAT2 and EAAT3...... 73 Table 4: Effect of Selective Compounds on glutamate uptake performed in Glia ...... 75 Table 5: Effect of NA-014 (10, 100 and 500 nM) on the Vmax and Km values from kinetics study on COS-7 cells transfected with EAAT2...... 76 Table 6: Effect of NA-014 (10,100 and 500 nM) on the Vmax and Km values from kinetics study on Glia...... 77 Table 7: Effect of PWX-10 (10,169 and 500 nM) on the Vmax and Km values from kinetics study on COS-7 cells transfected with EAAT2 ...... 77 Table 8: Effect of PWX-10 (100 and 500 nM) on the Vmax and Km values from kinetics study on Glia ...... 78 Table 9: Effect on NA-014 and PWX-10 on GABA, Glycine and Monoamine transporters. .. 79

Abstract

Characterization of Allosteric Modulators of Glutamate Transporters:

Selectivity and Potency Screening

Implications for Drug Development and for Understanding Allosteric Modulation of

Glutamate Transport

Glutamate excitotoxicity is the result of increased extracellular glutamate levels, which causes overactivation of post synaptic neurons, excessive calcium influx and further downstream signaling resulting in cell death. Excitotoxicity is associated with a number of acute and chronic CNS disorders such as stroke, traumatic brain injury (TBI), epilepsy,

Huntington’s disease, Parkinson's disease, mental illness, Alzheimer’s disease, neuropathic pain and drug addiction. Excitatory amino acid transporter 2 (EAAT2) is responsible for rapid removal of the majority of extracellular glutamate, thus maintaining the glutamate homeostasis and preventing excitotoxicity. Therefore, enhancing the function of this transporter could be a promising approach towards preventing or treating the harmful effects of excitotoxicity. Previous studies have identified a compound from a spider venom that enhanced the function of EAAT2 and displayed neuroprotective properties. Later, the site of interaction of this compound on the transporter was identified, and this information was employed to generate a pharmacophore, that in turn was used to perform a virtual screening of a large library of compounds. This approach identified novel compounds that were characterized as positive allosteric modulators (PAM) of EAAT2, in glutamate uptake assays in transfected COS-7 cells and in glial cultures. Nonetheless, the compounds derived x

from the virtual screening had poor drug-like properties. To address this issue and

progress the studies toward drug development, several analogs were designed and

synthesized in collaboration with a medicinal chemistry lab. The purpose of this study was

to screen these compounds for efficacy, potency and selectivity in glutamate transport

assays. Additionally, a compound derived from Parawixia bistriata venom, Parawixin10

(PWX-10) was also studied. Our goal was to identify a lead compound that is an EAAT2

PAM with good drug-like properties that can progress to in vivo studies. In structure

activity relationship (SAR) studies, compounds were first screened in assays in

overexpressing COS-7 cells (transfected with EAAT1, EAAT2 and EAAT3 respectively) and

in cultured astrocytes. The selectivity of stimulatory compounds were confirmed through

dose response assays in other types of neurotransmitter transporters (GABA, Glycine and

monoamine transporters) and the mechanism of allosteric modulation was confirmed

through kinetic studies by comparing the Vmax and Km values. Selected stimulatory

compounds were studied for their neuroprotective properties in in vitro models in neuron/glia cultures subjected to excitotoxic insults by application of glutamate and by deprivation of oxygen and glucose. Using this approach, we have identified three non- selective PAMs of EAAT1-3 transporters: VY-3-285, VY3-286 and NA-005, three PAMs of

EAAT1 and EAAT2: DA-050, DA-058, PWX-10, and a few inactive compounds and negative allosteric modulators (NAMs) of glutamate transporters. Moreover, we identified one selective EAAT2 PAM, NA-014, with good efficacy and potency and, importantly, remarkable neuroprotective properties in two in vitro models of excitotoxicity. Future directions include examining the effects compound NA-014 in in vitro and in vivo models, such as TBI, neuropathic pain and epilepsy. The NAMs of EAAT2 and other subtypes of xi transporters identified can be used in future studies to understand mechanisms of allosteric modulation of glutamate transport.

1. INTRODUCTION

1.1. GLUTAMATE AND GLUTAMATERGIC SYNAPSE

Glutamate is the principal excitatory amino acid neurotransmitter in the brain. It is the

mediator of synaptogenesis, sensory information, learning, motor coordination, emotions

and cognition, including memory formation and memory retrieval (McEntee & Crook, 1993;

Ohgi, Futamura, & Hashimoto, 2015; Riedel, Platt, & Micheau, 2003; Wozniak, Rojas, Wu, &

Slusher, 2012). Glutamate is synthesized in the brain by the process of transamination of an

intermediate from the tricarboxylic (TCA) cycle and is also synthesized from the precursor

glutamine, which is released by glial cells (Schousboe, Scafidi, Bak, Waagepetersen, &

McKenna, 2014). Glial cells are widely distributed in the brain and they surround the

neurons acting as a glue (Jakel & Dimou, 2017). Glutamate homeostasis is very critical as the increased extracellular concentration of this amino acid is involved in the pathology of neurodegenerative disorders, psychiatric illness and substance abuse (Brendan, 2001;

D'Souza, 2015; Lewerenz & Maher, 2015). This implies that understanding of glutamatergic

synapse is very essential to identify therapeutic approach towards treating the above-

mentioned disorders. 2

Figure 1. Glutamatergic synapse showing release of glutamate from presynaptic neurons and expression of ionotropic receptors and transporter on the glial membrane.

From (Attwell & Gibb, 2005).

Glutamate is stored in the vesicles in the presynaptic neurons and its release form the vesicles is stimulated upon the arrival of the action potential, as shown in figure 1.

Glutamate then activates the receptors in the post synaptic neurons which leads to activation of downstream signaling. The clearance of glutamate from the synapse is crucial since high concentrations could be toxic to the neurons. To accomplish this, there are a group of transporters involved in rapid removal of extracellular glutamate, known as excitatory amino acid transporters (Kanner & Schuldiner, 1987; Niciu, Kelmendi, &

Sanacora, 2012). Excitatory amino acid transporters (EAATs) are the main regulators of glutamate homeostasis and are classified into five subtypes: EAAT1, EAAT2, EAAT3, EAAT4 and EAAT5. Localization and molecular functioning of these subtypes will be further discussed in section 1.3. 3

The glutamate taken up by glial cells is then converted into glutamine and recycled into the presynaptic neuron to be converted it to glutamate (Schousboe et al., 2014; Yelamanchi et al., 2016). The transport process is electrogenic as the influx is driven via Na+/K+ ATPase by cotransport of three sodium ions and the counter-transport of a potassium ion (Amara &

Fontana, 2002). The proper functioning of the Na+/K+ pump and availability of ATP

required for this secondary active transport is critical for EAATs mediated clearance of

glutamate (Kanner, 1983; Lingrel & Kuntzweiler, 1994).

1.2. GLUTAMATE RECEPTORS

The postsynaptic glutamate receptors can be classified into ligand gated ionotropic receptors and G-protein coupled metabotropic receptors (Traynelis et al., 2010). The ionotropic glutamate receptors (iGluRs) family consists of three subtypes: NMDA, AMPA, kainate receptors. Each subtype has specific functions and their own pharmacological profile (Sprengel, 2013).

NMDA receptors are heterotetrameric proteins with high calcium permeability. The

NMDA receptors are activated upon binding of glycine and L-glutamate, which leads to influx of Na+ and Ca++, and efflux of K+ (Zito & Scheuss, 2009). NMDA receptors are

comprised of three subunits GluNR1, GluNR2, and GluNR3 and these subunits provide unique biophysical, pharmacological and signaling properties to the receptor (Paoletti,

Bellone, & Zhou, 2013). NMDA receptors are under voltage gated Mg++ block at resting

membrane potential, and this block is removed after AMPA receptor activation, which leads

to depolarization and thus removal of the blockade. The NMDA receptor is more permeable 4

to Ca++ than Na+, and causes Ca++ influx upon activation, which in turn results in further

physiological signaling (Paoletti et al., 2013; Zito & Scheuss, 2009). NMDA receptors are

implicated in learning, memory, and neuroplasticity and therefore, abnormal NMDA

receptor function is associated with various neurological disorders and cognitive defects

(Duguid IC & Smart TG, 2009).

AMPA receptors are tetrameric, ligand-gated, cation-selective ion channels responsible

for modulating cell excitability by gating the flow of Ca+2 and Na+ ions into the cell (Wallach,

Colestock, & Adejare, 2017). AMPA receptors are the main drivers in mediating synaptic

transmission and plasticity (Barrow & McAllister, 2013). The activation of AMPA receptors cause initial depolarization mainly due to Na+ influx and this leads to activation of NMDA

receptors by removing the voltage dependent Mg++ blockade of NMDA receptors (Banerjee,

Borgmann-Winter, Ray, & Hahn, 2016). The number and functions of AMPA receptors are

altered with cognitive decline and its overall regulation i.e. synthesis to degradation is very

critical for memory formation and storage (Henley & Wilkinson, 2013).

Kainate receptors are ionotropic glutamate receptors, heterotetramers of subtypes

GluR5–7 and/or KA 1–2. These receptors share similar permeability properties like AMPA

receptor i.e. more permeable to sodium ion and less permeable to calcium ions

(Gleichmann & Mattson, 2009). Kainate receptors mediate fast excitatory neurotransmission and are expressed in both pre and post synaptic neurons (Ofengeim,

Miyawaki, & Suzanne zukin, 2011). The receptor selective compounds, UBP 296 (specific kainate receptor antagonist) and (RS)-2-amino-3(3-hydroxy-5-tert-butylisoxazol-4-

yl)propanoic acid (ATPA) (kainate receptor agonist) were used to confirm the role of 5

kainate receptors in long term potentiation (Läck, Ariwodola, Chappell, Weiner, & McCool,

2008). The kainate receptor mediated depression of glutamate release requires G-protein

activation; however, the presynaptic kainate receptor mediated stimulatory effect of

glutamate release does not involve G-protein activation. The stimulatory effect is seen as a

consequence of increased levels of cytosolic calcium ions which stimulates adenylyl cyclase

and thus induces glutamate release (Andrade-Talavera et al., 2012; Sihra, Flores, &

Rodríguez-Moreno, 2013).

1.3. GLUTAMATE TRANSPORTERS: LOCALIZATION AND MOLECULAR FUNCTIONING

The family of excitatory amino acid transporters (EAATs) are responsible for rapid

removal of glutamate from the synapse and thus maintaining the extracellular glutamate

concentration, playing a very crucial role in the glutamate homeostasis (Danbolt, 2001) and belong to the solute carrier 1 (SLC-1) family of proteins. As stated in section 1.2., five different EAATs cloned from human and can be classified as EAAT1, EAAT2, EAAT3, EAAT4 and EAAT5 and the corresponding nomenclature in rat are GLAST, GLT-1 and EAAC1.

EAAT4 and EAAT5 have not been distinctively named in rats.

EAAT1-EAAT2 are present in astrocytes, therefore these glial carriers EAAT1 and

EAAT2 have a significant role in the removal of glutamate from the synapse. EAAT3 and

EAAT4 are found in postsynaptic membranes and EAAT5 is found in photoreceptor cells of the retina. EAAT5 are low affinity glutamate transporters and do not have a significant role in bulk clearance of extracellular glutamate form synapse (Danbolt et al., 1998; Divito &

Underhill, 2014; Hubbard & Binder, 2016). 6

The EAAT1/GLAST (human/rat nomenclature) transporter is primarily found in the

astrocytes of the cerebellum and plays a role in glutamate clearance from the synapse but

to a lesser extent that EAAT2. Upon investigation of GLAST expression in peripheral organs,

it was found to be expressed primarily in epithelial cells, cells of the macrophage-lineage,

lymphocytes, fat cells, interstitial cells, and salivary gland acini (Berger & Hediger, 2006).

Among these five transporter types, EAAT2/GLT-1 (human/rat nomenclature) is the one responsible for major amount of glutamate uptake and accounts for more than 90% of glutamate clearance from the synapse (Bar-Peled et al., 1997; Suchak et al., 2003). EAAT2 is

expressed throughout the brain and spinal cord and its downregulation has been

associated with various pathological conditions (Kim et al., 2011). Since EAAT2 is

responsible for more than 90% of glutamate uptake, it is expected that any abnormality in the expression or function of this transporter could lead to increased extracellular glutamate concentration leading to neuronal death. Therefore, targeting this transporter could be a potential therapeutic approach towards maintain glutamate homeostasis and preventing disorders due to increased glutamate concentration.

The EAAT3/EAAC1 (human/rat nomenclature) transporter is located throughout the brain, especially cortex, hippocampus, cerebellum and basal ganglia. It is expressed predominantly in post synaptic neurons, however, it has also been found in oligodendrocytes and, in the injured brain, in microglia. Along with glutamate transport, this transporter is also responsible for cystine transport (Hubbard & Binder, 2016; Kim et al., 2011). The expression of EAAT3 in presynaptic glutamatergic terminal is very low and therefore it does not have a significant role in glutamate-glutamine shuttle unlike EAAT2 7

which is responsible in shuttling glutamine to presynaptic neuron where it is resynthesized

into glutamate (Bjorn-Yoshimoto & Underhill, 2016). EAAT3 on postsynaptic neuron is

located near to mGluR5, and transporter activation could lead to receptor activation and

might have unwanted liabilities as a consequence of downstream signaling (Jong, Kumar, &

O'Malley, 2009; Jong & O’Malley, 2017).

The EAAT4 transporter is predominantly expressed in Purkinje cells of the cerebellum,

and it is also found in other neurons at significantly lower levels (Divito & Underhill, 2014).

EAAT4 is also present in astrocytes of mouse forebrain and spinal cord and in retinal

astrocytes of the rat (W. H. Hu, Walters, Xia, Karmally, & Bethea, 2003; Ward, Jobling,

Puthussery, Foster, & Fletcher, 2004; J.-H. Yi, Herrero, Chen, & Hazell, 2007).

The EAAT5 transporter is expressed in rod and cones photoreceptor terminals and in axon terminals of rod bipolar cells of the retina (Wersinger et al., 2006). It is co-expressed in photoreceptor terminals with GLT-1c, which is a splice variant of EAAT2. The rate of glutamate uptake is very low than EAAT2 (Arriza, Eliasof, Kavanaugh, & Amara, 1997;

Schneider et al., 2014).

The localization of EAATs in glial and presynaptic and postsynaptic neuronal membrane is shown in Figure 2. Glutamate is synthesized and stored in vesicles of post synaptic neurons and is released during stimulation of pre-synaptic neuron into the synapse. EAAT1 and EAAT2 are predominantly present in glial membrane and expression of EAAT2 is greater than EAAT1, making it responsible for major amount of glutamate uptake. EAAT3 and EAAT4 are distributed in post synaptic membrane near with NMDA,

AMPA, kainate receptors. 8

Figure 2. Model of a glutamatergic synapse demonstrating the localization of EAATs 1-4. EAAT1 (green) and EAAT2 (red) are localized to glial membranes. EAAT3 (blue) and EAAT4 (magenta) are localized to post-synaptic membranes (Divito & Underhill, 2014).

The understanding of structural and functional properties of transporters is crucial

to have better knowledge about glutamate transport mechanism. This information could

open doors to identify novel approaches to regulate glutamate homeostasis. The first study

of glutamate transporters structure was performed using crystallization of a glutamate transporter ortholog from the bacteria Pyrococcus horikoshii, GltPh (Yernool, Boudker, Jin, &

Gouaux, 2004). GltPh was identified as a trimer that consisted of eight transmembrane

domains and two hairpin loops, HP1 and HP2, (Yernool et al., 2004). The transmembrane 9 domains serve as a scaffold surrounding C terminal core domain, involved in transport mechanism as shown in Figure 3. The key functional regions of the transporter HP1 and

HP2 are both helix turn helix structure and the substrate binding site is located between the tips of these two hairpin loops (Yernool et al., 2004).

Figure 3. Transmembrane domains of the glutamate transporter indicating scaffolding and transporting domains (A. C. K. Fontana, 2018).

The HP1 act as an inner gate and HP2 act as an outer gate for the glutamate transport and occluded state is formed when both the gates are closed. The four different conformational state that have been identified are i) outward facing open (OFOp), (ii) outward facing occluded (OFOc), (iii) the inward facing occluded (IFOc) and (iv) inward facing open. The opening of HP2 leads to exposure of the substrate binding site and it closes again once the glutamate and other ions bind. At this point, the transporter remains in an occluded, outward-facing conformation. The inner gate HP1 opens when the whole core domain approaches the cytosol resulting in an occluded inward facing conformation. 10

The binding of potassium to the carrier then facilitates outward facing state (Grazioso et al.,

2012; Jiang & Amara, 2011).

1.4. GLUTAMATE EXCITOTOXICITY

Glutamate excitotoxicity is the result of increased extracellular glutamate levels,

which causes overactivation of post synaptic neurons, excessive calcium influx that in turn

activates a number of enzymes, including phospholipases, endonucleases, and calcium

activated proteases, causing cell death as shown in figure 4 (de Cabo de la Vega &

Carrascosa-Romero, 2014; Manev, Favaron, Guidotti, & Costa, 1989).

Figure 4. Glutamatergic synapse under physiological conditions (a) and excitotoxic conditions (b). (A. C. Fontana, 2015)

Glutamate excitotoxicity is associated with pathogenesis of number of central

nervous system disorders like traumatic brain injury (TBI) (J. H. Yi & Hazell, 2006), stroke

(Grewer et al., 2008), epilepsy (Chapman, 2000), and amyotrophic lateral sclerosis 11

(ALS)(Dunlop, Beal McIlvain, She, & Howland, 2003), Alzheimer’s disease(Campos-Peña &

Meraz-Ríos, 2014), Huntington’s disease(Lievens et al., 2001), Parkinson's disease(Ambrosi, Cerri, & Blandini, 2014; Blandini, Porter, & Greenamyre, 1996), mental illness (Brendan, 2001), drug addiction (D'Souza, 2015) and neuropathic pain (Osikowicz,

Mika, & Przewlocka, 2013).

The molecular mechanisms behind excitotoxicity include altered calcium buffering, nitrogen free radicals formation, production of reactive oxygen species, mitochondrial membrane depolarization and neuronal death (Dong, Wang, & Qin, 2009). The NMDA receptor is very permeable to calcium and upon continuous activation, causes huge increase in intracellular calcium levels and catabolic enzyme activities. This increased calcium level and enzymatic activity triggers a cascade of events that causes apoptosis or necrosis (Prentice, Modi, & Wu, 2015). AMPA receptors are also involved in generation of excitotoxicity and this is attributed to their calcium permeability and the increases in the calcium permeability can lead to neuronal damage as a consequence of downstream signaling (Dong et al., 2009; Van Damme et al., 2007).

Additional mechanisms involved in glutamate excitotoxicity include mitochondria dysfunction, leading to production of reactive oxygen species (Nicholls, 2004; Nicholls,

Johnson-Cadwell, Vesce, Jekabsons, & Yadava, 2007) and oxidative stress (Chen, Guo, &

Kong, 2012; Fonnum & Lock, 2004).

1.5. PREVIOUS STRATEGIES TO TREAT THE HARMFUL EFFECTS OF GLUTAMATE

EXCITOTOXICITY AND THEIR LIMITATIONS

As stated above, there are many important players contributing towards glutamate excitotoxicity at various stages. Glutamate receptors, calcium influx, and overall post synaptic over activation have been considered as targets to treat the harmful consequences of glutamate excitotoxicity. However, there is no single therapeutic agent to date with remarkable clinical effect. Some of these previous strategies and their limitations have been summarized in Table 1.

Table 1: Previous strategies evaluated to treat harmful effects of glutamate excitotoxicity, mechanism and their limitations.

Strategy Drug / Mechanism Limitations

NMDA receptor blockage Ketamine is a non- Ketamine is associated with competitive NMDA severe side effects, such as NMDA receptors are very receptor antagonist and psychotomimetic actions, and permeable to calcium and inhibit Na+ and Ca2+ influx also exhibited abuse potential therefore its modulation through these channels. It (Krystal et al., 1994; Lodge & could ameliorate the interacts with the Mercier, 2015). neurotoxic downstream Phencyclidine binding site, signaling associated with located within the NMDA increased calcium influx receptor-associated ion into post synaptic neurons. channel. Ketamine is found to have neuroprotective NMDA antagonists like effects in an in-vivo model ketamine and of cerebral ischemia phencyclidine prevent the (Church, Zeman, & Lodge, calcium influx associated 1988) and neuro- with their activation and regenerative effects in an in thus prevent the activation vitro model of neuronal of proteases and injury in rat hippocampal endonuclease as a part of neurons (Himmelseher, Pfenninger, & Georgieff, 13

downstream signaling 1996). resulting in neuroprotective effects (Lodge & Mercier, Memantine, a NMDA 2015; Petrovic, Horak, receptor antagonist, is Memantine was found to be Sedlacek, & Vyklicky, 2005). approved for use in ineffective in treating Alzheimer’s disease by the hypoxia-induced FDA, but it is not neurodegeneration, seizure associated with and audiogenic myoclonic psychotomimetic side jerks. (Tai & Truong, 2013). effects like ketamine. This This indicates that difference is due to the fact uncompetitive, low affinity that memantine does not blockers of NMDA receptor, block the physiological such as memantine, are likely activity of NMDA, which is not effective in treating essential for normal neurodegenerative diseases. neuronal functioning, but it blocks the open-channel conformation and mediates the effect when the receptor is over stimulated, i.e., only during excitotoxicity (Lipton, 2005).

Inhibition of presynaptic Riluzole, a drug that Exact mechanism behind this release of glutamate works by inhibiting inhibitory action on presynaptic release of glutamate release is still Since excessive release of glutamate, prevented over unclear (Deflorio et al., 2014; glutamate causes greater excitation of post synaptic Xie et al., 2011). The most amount of receptor neurons and thus calcium common adverse effect of activation and higher influx. Riluzole was shown riluzole is nausea, asthenia as calcium influx leading to to have neuroprotective a result of blockade of muscle excitotoxicity, inhibition of effects by modulating the sodium channels or glutamate releases at the glutamate acetylcholine receptor earlier stage could be a good neurotransmission and is channels (Bahram, Nicolas, way to prevent further approved for use in ALS Reinhard, & Johannes, 2002). damage and control (Cheah, Vucic, Krishnan, & excessive release and thus Kiernan, 2010; Miller, binding to receptors at the Mitchell, & Moore, 2012; postsynaptic neurons. Shaw & Ince, 1997; Vucic et al., 2013).

Calcium channel blockage T-type calcium channel This class of compounds is blockers like Flunarizine Not very selective and their Calcium is one of the main and zonisamide have neuroprotective effects may 14

drivers of excitotoxicicty been extensively studied be due to other overlapping and is responsible trigger and found to have mechanisms, such as the downstream signaling neuroprotective inhibition of monoamine leading to neuronal death. properties in vivo and in oxidase. Despite of having Therefore, blocking calcium vitro models(Kopecky, neuroprotective properties, channels could also be one Liang, & Bao, 2014). they have side effects like approach to prevent nausea, vomiting, headache, excessive calcium load in mental status changes, the cytosol. neuropathy, and change in weight (Kopecky et al., 2014).

Caspase/calpain Calpain inhibitor-1 (CAI- This strategy is not an ideal as inhibitors 1), caspase-3 inhibitor it targets the proteases that and Ac-DEVD-CHO were come into action at much These are cysteine studied for the later stages in the glutamate proteases that are involved neuroprotective effects in mediated excitotoxicity. Also, in pathogenesis of neuronal ischemia and spinal cord cysteine proteases are not the apoptosis following spinal injury. They were found to only proteases associated cord injuries and show significant with cell death, there are also neurodegenerative diseases neuroprotection (Perrin, other endonuclease (Momeni, 2011; Ray, Hogan, Ecarnot-Laubriet, Vergely, phospholipase and protease & Banik, 2003). Therefore, & Rochette, 2003; Ray et involved in induction of cell inhibition of these protease al., 2003) death. Therefore this strategy could be one of the not very effective (J. N. Berry, approach to prevent cell Sharrett-Field, Butler, & death. Prendergast, 2012).

1.6. TARGETING GLUTAMATE TRANSPORTERS: AN EMERGENT STRATEGY

In light of the several limitation of the above-mentioned strategies, more effective strategies have yet to be explored and identified. In this sense, an other promising and

emergent strategy to treat excitotoxicity is to target the glutamate transporters, specifically

to enhance its expression and/or function. Increases in glutamate uptake would reflect in

decreased extracellular concentration of glutamate and therefore prevent the

overstimulation of post synaptic glutamate receptors. 15

The strategy to increase EAAT2 expression has been explored for over a decade. The

beta-lactam antibiotic ceftriaxone was the first drug identified to increase the expression of

this protein by accelerating gene transcription (Rothstein et al., 2005). Ceftriaxone has

been shown to have neuroprotective effects in various in vitro and in vivo models of neurodegenerative disorders like TBI(Cui et al., 2013), stroke(Lipski et al., 2007), ischemia

(Y. Y. Hu et al., 2015), Parkinson’s(Chotibut et al., 2014) and ALS(Beghi, Bendotti, &

Mennini, 2006; J. D. Berry et al., 2013; Lee et al., 2008). Despite showing promising results in preclinical studies, ceftriaxone failed to show clinical efficacy in phase 3 study for ALS

(Cudkowicz et al., 2014).

The development of a translational enhancer of EAAT2 is one of the recent advancements in this approach. LDN/OSU-0212320 is a small molecule stimulator of glutamate transporter EAAT2 translation. This compound was shown to have neuroprotective effects in primary neuron-glia co-cultures subjected to glutamate induced excitotoxicity, in a in vivo model of pilocarpine-induced temporal lobe epilepsy model and in an animal model of ALS (Kong et al., 2014). LDN/OSU-0212320 was also demonstrated to have a good pharmacokinetic profile including good brain penetrance and does not have the side effects like the marketed NMDA antagonist Ketamine, making this compound a promising lead for drug development (Limpert & Cosford, 2014).

Despite showing neuroprotective effects to some extent, none of the above- mentioned strategies have successfully translated to clinic. LDN/OSU-0212320 is still under study; therefore, it is too early to comment on its clinical efficacy. The rationale for targeting EAAT2 and increasing its function is promising, as EAAT2 is the transporter subtype responsible for the majority of glutamate uptake in the brain (Suchak et al., 2003). 16

Therefore, increasing its function is a fast mechanism, when compared to translational/transcription enhancers that need a long time for synthesis of protein, and thus could be developed for a therapy for acute disorders (such as TBI and stroke) and also for neurodegenerative disorders (in which prolonged episodes of excitotoxicity are frequent).

In this sense, allosteric modulation emerges as potential strategy for EAAT2 modulation. Allosteric modulation would not disturb the normal physiological function of the transporter (explained in more detail below in section 1.7.); therefore, this is an attractive strategy for drug development.

The development of positive allosteric modulators (PAMs) of glutamate transporter

EAAT2 is one of the research focus of our lab and the basis of my project presented herein.

1.7. ALLOSTERIC MODULATION

Allosteric modulation is a phenomenon of modulating the effect of a protein via binding of an allosteric modulator/ligand at a site distinct from its endogenous agonist- binding site (which is the orthosteric site). Allosteric modulators bind to an allosteric site and mediate their effects in the presence of the endogenous agonist. The major advantage of allosteric modulation is that it does not interfere with agonist binding to the orthosteric site and therefore, the normal function and interaction of agonist and orthosteric site remains intact i.e. the affinity of the transporter remains unchanged with profound effect in efficacy. Therefore, it is predicted that positive allosteric modulation would result in fairly less side effects than other classes of compounds described in section 1.5. 17

Allosteric modulation can be classified into stimulatory, meaning, increasing the functional efficacy of the transporter or inhibitory, meaning decreasing the functional efficacy. Here we define allosteric modulators inducing stimulatory effects as positive allosteric modulators (PAM) and the ones inducing inhibitory effects as negative allosteric modulators (NAM).

1.8. IDENTIFICATION OF PAMs OF EAAT2: PREVIOUS STUDIES

Previous studies have shown that the venom of the spider Parawixia bistriata actively stimulates glutamate uptake in rat brain synaptosomes, and exerted neuroprotective effects in a model of ischemia in rat retina (A. C. Fontana et al., 2003)

Upon studies of its kinetics properties, it was found that the venom did not altered the affinity for glutamate (KM), but increased by ~70% the Vmax of glutamate transport, suggesting that it acted via allosteric modulation. Further studies identified the site of interaction for the active compound from the venom, Parawixin1, on the EAAT2 transporter (Mortensen, Liberato, Coutinho-Netto, Dos Santos, & Fontana, 2015). In these studies, chimeric and mutant transporters were generated and the interaction site was identified to be comprised of amino acid residues M86, L295, P443, and W472 in transmembrane domains TM2, TM5, and TM8. This study also suggested that an interaction between transport and scaffolding domains facilitated the movement of transport, which in turn enhanced the uptake process (Mortensen et al., 2015). Subsequently, this information was employed to generate a pharmacophore, that was used to perform a virtual screening of a large library of compounds (Kortagere et al., 2018). The GltPh structure was used as a 18

model for this approach, as human EAATs 3-D structures were not know at that time. The

structure of human EAAT1 was recently elucidated through the use of competitive and non-competitive inhibitors (Canul-Tec et al., 2017).

The virtual screening approach identified several molecules that interacted with the

pharmacophore in the transporter (Kortagere et al., 2018). Ten of these compounds were

evaluated for their glutamate uptake activity in COS-7 cells transfected with EAAT1, EAAT2

or EAAT3 and in primary cultures of glia. Among them, compounds GT949, GT951, and

GT939 were found to increase the activity of EAAT2 selectively, with no effect on EAAT1

and EAAT3. Moreover, they increased the Vmax of transport, without changes in the affinity

for glutamate, indicating that they are PAMs of EAAT2 (Kortagere et al., 2018). Figure 5 shows three-dimensional view of the glutamate transporter, where we can see the allosteric site and the orthosteric site and the binding of compound GT949. The dose response of this compound in the glutamate uptake assays is also shown where the compound stimulatory activity of compound is selective to EAAT2 and does not have any stimulatory activity through EAAT1 and EAAT3.

Figure 5. Diagram showing the allosteric site in EAAT2, the in silico screening approach that lead to the identification of GT949, and a dose response curve of GT949 in glutamate uptake assay performed in transfected COS-7 cells.

(Kortagere et al., 2018). 19

1.9. PROGRESSION OF COMPOUNDS: FIRST TO THIRD GENERATION

Even though GT949 was shown to be a potent PAM of EAAT2 (Kortagere et al.,

2018), and to have neuroprotective properties (previous studies in the lab, not shown), it needed improvement in their drug-like properties. To this end, we established a

collaboration with a medicinal chemistry lab at The Wistar Institute, under the supervision

of Dr. Joseph Salvino. Several analogs were designed and synthetized, with the goal of

identifying analogs with efficacy, potency, selectivity and kinetics properties similar to

GT949, but with better water solubility, better brain penetrance, lower molecular weight,

improved metabolic stability and that had neuroprotective properties, to progress to

translational studies. These compounds therefore belong to a second generation of compounds, and were studied by previous lab members in glutamate uptake assays in COS-

7 cells and cultured astrocytes. Additionally, selectivity studies in other subtypes of neurotransmitter transporters and in vitro neuroprotection studies resulted in the emergence of DA-023 as a promising lead compound with good properties i.e. efficacy, potency, selectivity and in vitro neuroprotection. However, this compound still needed further optimization to have better a drug-like pharmacokinetic profile (Molecular weight

< 500 Da, LogP <3, total polar surface area 60-70) and water solubility. Therefore, more analogs were designed and synthetized, giving rise to the third generation of compounds.

My project was based on the study of this third generation of glutamate transport modulating compounds.

Additionally, a compound isolated from Parawixia bistriata venom, Parawixin10, was also included in my project. Parawixin10 was previously shown to increase glutamate 20

uptake in rat cortex synaptosomes. In order to have anti-convulsing properties in an in vivo

epilepsy model (Fachim et al., 2011; Fachim, Mortari, Gobbo-Netto, & Dos Santos, 2015).

However, its selectivity for different subtypes of EAATs and other neurotransmitter transporters was unknown. Therefore, this compound was incorporated into my studies of efficacy, potency, selectivity and kinetics properties.

2. AIMS

The overall aim of present study is to screen the third generation analogs for their efficacy, potency and selectivity of action on neurotransmitter transporters.

One goal of these studies is to identify the most promising positive allosteric modulators of glutamate transporter EAAT2; as such class of compound could be further developed. Another goal is to understand allosteric modulation of glutamate transport. In this sense, the structure-activity relationship studies performed could also help us further our understanding of the mechanisms of negative allosteric modulation (NAMs) of glutamate transport and to use this information in synthesis of useful analogs.

To accomplish these goals, the synthetized compounds were examined for their glutamate transport activity in overexpressing cells and cultured glial cells. The selectivity for the transporters was examined in cells expressing different neurotransmitter transporters including EAATs, GABA, Glycine and monoamine transporters. The mechanism of allosteric modulation was confirmed through kinetic studies and compounds were classified into different categories as per their activity. The most promising lead to enhance glutamate transport is progressed into in vitro neuroprotection studies, pharmacokinetic analysis and then into appropriated in vivo models for further assessment of their activity.

3. MATERIALS AND METHODS

3.1. MATERIALS

The third generation compounds included 27 compounds reffered to as: VY-3-133,

VY-3-136, VY-3-171, VY-3-207, VY-3-209, VY-3-215, VY-3-218, VY-3-246, VY-3-285, VY-3-

286, DA-006,DA-029,DA-040, DA-046, DA-050, DA-052, DA-055, DA-056, DA-057, DA-058,

DA-066, NA-005, NA-008, NA-009, NA-010, NA-014 and NA-019. The structures of these

compounds are not shown herein due to intellectual property restrictions.

Apart from these synthetic analogs, a compound derived from Parawixia bistriata

venom, Parawixin10, was also included in this project. This compound was isolated by the

lab of Dr. Wagner F. Santos (University of São Paulo, Brazil) and kindly provided to us.

COS-7 cells used for transient transfection of transporters were obtained from ATCC

(Manassas, VA). The transfection reagent used was from Mirus TransIT®-LT1 Transfection

Reagent (Mirus Bio LLC, Madison, WI).

MDCK cells were also obtained from ATCC (Manassas, VA) and were stably transfected with hDAT, hNET and hSERT by colleagues of the lab.

Trypsin, T-75 and T-150 flasks, 24 well plates and Scintillation fluid (Ecolite) were purchased from Thermo Fisher Scientific (Waltham, MA).

The cell culture media used for COS-7 cells was High glucose Dulbecco’s Modified

Eagle Medium (DMEM) from Invitrogen (Carlsbad, CA) containing 10% Fetal Bovine Serum

(from VWR, Radnor, PA) and 1% Penicillin/Streptomycin (from Thermofisher Scientific,

Waltham, MA). 23

For MDCK cells culture the media used was similar to COS-7 cells media with the

addition of 50 g/mL blasticidin (Invitrogen, San Diego, CA).

μ Radiolabeled [3H]-glutamic acid (51.1 Ci/mmol), glycine, [2-3H] (48.7 Ci/mmol),

-[2,3-3H(N)] (80.8 Ci/mmol), [3H]-Dopamine (32.6 Ci/mmol),

5Aminobutyric-Hydroxy Tryptamine, Acid (GABA), [3H] γ- (23.9 Ci/mmol) and Norepinephrine Hydrochloride, DL-[7-

3H(N)] (14.9 Ci/mmol) were purchased from Perkin Elmer (Boston, MA, USA).

Dissection tools for glia preparation were purchased from Biomedical Research

Instruments (Silver Spring, MD, USA).

Glia culture media is DMEM (Thermofisher Scientific, Waltham, MA) media with

10% Fetal Bovine Serum (Hyclone, South Logan, UT, USA), and 50 g/mL gentamicin

(Thermofisher Scientific, Waltham, MA) added. μ

Primary neuron/glia cultures were grown in Neurobasal Medium with B27

supplement, glutamine and gentamicin. Additionally, glucose-free DMEM (for

oxygen/glucose deprivation insults) was used. All reagents were purchased from

Thermofisher Scientific (Waltham, MA).

Horse serum for neuronal cultures was purchase from Hyclone (South Logan, UT,

USA). DL-threo- -Benzyloxyaspartic acid (TBOA) was purchased from Tocris (Bristol,

United Kingdom).β

Poly-lysine coated 96-well plates and phosphate-buffered saline (D-PBS) were

purchased from Corning (NY, USA).

3.2. EQUIPMENT

A Tri-Carb 3100TR liquid scintillation counter (PerkinElmer, Waltham, MA) was

used for measuring radioactivity from cell lysates of experiments performed in the 24-well

plate format.

A plate washer Elx50® from Biotek (Winooski, VT, USA) was used for transport

assays in 96-wells microplates (for glia and MDCK cells).

The radioactivity measurement was done using a Microplate Scintillation and

Luminescence Counter from Wallac (Shelton, CT, USA).

A Sorvall Legend XT centrifuge from Thermo Scientific® (Waltham, MA, USA) was

used for centrifugation of bacterial preparation for DNA extraction.

Nanodrop ND-1000 spectrophotometer (Wilmington, DE, USA) country) was used

for measuring DNA concentration.

Olympus SZ51 Stereo Microscope 0.8x - 4x (Japan) was used for dissection of newborn rat brains.

3.3 Synthesis of compounds and workflow chart

Previous studies performed in the lab demonstrated that the first generation compounds, GT949, GT951 and GT939, selectively stimulated EAAT2 mediated glutamate uptake and had neuroprotective properties (Falcucci, 2016). However, these compounds lacked good drug-like properties to advance as drugs. Therefore, several structural modifications were carried out and new analogs were synthetized in collaboration with a medicinal chemistry lab, giving rise to the second generation of compounds. These 25 compounds were also previously studied in the lab for their efficacy, potency, selectivity and neuroprotective properties and DA-023 was identified as a promising analog with good efficacy, potency, selectivity and neuroprotective properties. However, this compound still had poor brain penetration and water solubility. Therefore, further optimization was required, and this resulted in the synthesis of 27 compounds that belong to the third generation of analogs. The study of this third generation compounds is the focus of my project.

Figure 6 is a representation of work flow chart of my project.

Synthesis of 27 analogs Additional compound from Parawixia bistriata venom,

(Medicinal chemistry lab) Parawixin10

Dose response assays for glutamate transport in transfected COS-7 cells

(Selectivity, Efficacy and Potency)

Compounds with stimulatory effect on either EAAT2 or both EAAT2 and EAAT1 progress to next step

Dose response assay for glutamate transport in

cultured glia (endogenous system)

(Efficacy and Potency)

Only the compounds with stimulatory effects

in glia (and COS-7 cells) progress to next step

Kinetics studies in COS-7 cells and cultured glia

Determination of Vmax and KM

Selectivity studies in other neurotransmitter transporters

GABA (GAT-1 and GAT-3) and Glycine (GlyT1) transporters

Monoamine transporters (hDAT, hNET, hSERT)

In-vitro neuroprotection studies Pharmacokinetic Studies In-vivo neuroprotection studies (Parallel studies in lab) (Outsourced) (Parallel studies in lab)

Figure 6. Workflow chart proposed to identify a lead compound predictive of in vivo efficacy. 27

3.4. Experiments with COS-7 cells

3.4.1. Transfection of COS-7 cells

COS-7 cells were cultured at 37 C in T-150 flasks with DMEM media (with 10% fetal bovine serum and 100 units/mL of penicillin).˚ Before transfection, cells were checked for confluency, and media was aspirated and cells were washed with phosphate buffer saline

(PBS). The cells were then trypsinized using 2ml of 0.05% trypsin and incubated for 15-20 min at 37 C, then DMEM media was added to inactivate trypsin and the cell suspension was collected˚ in a 15 ml tube, leaving behind 1 ml cells to regrow in the flask. The cells were counted using a hemocytometer. In 50 ml tubes, Opti-MEM, Mirus TransIT®-LT1

Transfection reagent and the DNA of interest (EAAT1 or EAAT2 or EAAT3 or empty vector

CMV) were added ( in a 24 well plate). To this tube, cell suspension (50,000 cells per well) was added0.5μg perand well DMEM media was used to make up the final volume (500 L per well). The solution was then plated in 24 well plates and incubated at 37 C for two daysμ prior to glutamate uptake assays. For each plate, first six rows were plated˚ with cells transfected with empty vector (CMV) and remaining 18 wells were plated with either

EAAT1 or EAAT2 or EAAT3 in three different plates, for dose response curves. For kinetic experiments, the design of the plating was modified to plate one full individual 24 well plate for each DNA (empty vector and EAATs).

3.4.2. Glutamate uptake assays in COS-7 cells

All of the synthetic compounds were dissolved in DMSO to 10mM stock solutions, and stored at -20oC freezer. 28

a) Dose response assays

On the day of the assays, stocks were used to prepare different dilutions required

for dose response assays (from 10 to 0.00006 , in a logarithm serial dilution, prepared

in buffer). In addition, 150nM 3H-L-glutamateμM was prepared using 24.3 M of the stock solution from Perkin Elmer. Transfected cells were washed with PBS-CMμ (PBS with the addition of 0.1 mM CaCl2 and 1 mM MgCl2) and then or vehicle were

added. The plate was then incubated with the200 compounds μL of compounds and vehicle for 10 min

150nM 3H-L-glutamateat 37 was ˚C added to each well and allowed to incubate

atand room then temperature100 μL of for 10 min, where the uptake reactions would take place. The cells

were then washed twice with PBS-CM and 4 of lysis buffer (1% SDS, 0.1N NaOH) was

added to each well. The plates were then 00μLplaced over shaker for 20 min and the cell

homogenates were collected and added into vials containing 3 ml scintillation liquid. The

radioactivity was counted using scintillation counter.

All dose-response assays were performed at least three times for each compound.

b) Kinetic assays

The kinetics experiments were performed to confirm the activity through allosteric

modulation of the transporter and determination of Vmax and Km (affinity) of the transporter. The compounds that stimulated the EAAT1 and/or EAAT2 mediated glutamate uptake in COS-7 cells and in glia were progressed to kinetics studies. COS-7 cells were transfected with the DNA of interest (EAAT1 or EAAT2) or empty vector CMV in 24 well plates respectively as per section 3.4.1. For kinetics study, different concentrations (3.9 nM- -radiolabeled

500μM) of glutamate solution were prepared using of a mixture of non 29

and radiolabeled glutamate (99.8%:0.2%). Compounds of interest were diluted to 10, 100

and 500nM final concentrations. One 24-well plate transfected with empty vector CMV was

-CM) per well and

used as a background and were treated with 200 μL or vehicle EAAT2 (PBS was also treated with vehicle,incubated while for additional 10 min at plates 37˚C. transfected One plate withwith EAAT1EAAT1 or EAAT2 were treated with the

thiscompound pre- of interest in different concentrations,ion of and varying incubated concentration for 10 min (to at result 37 ˚C. in After final concentrationsincubation, of 3.9 100 nM μL- of glutamate) were added solut in triplicates to each plate. Uptake reactions were allowed to happen at500μM RT for 10 min. The plates were then washed with PBS-CM twice

dded to each well. The plates were then placed over shaker

and allowed400 μL lysis to shake buffer to were20 min. a Cell homogenates were collected and transferred into vials

containing 3 ml of scintillation liquid and the radioactivity was counted using scintillation

counter.

All kinetic assays were performed at least three times for each selected compound.

3.5. Experiments with primary cultures of glia

3.5.1 Glia dissection and plating

Sprague-Dawley rats, E16-17 time pregnant, were purchased from Charles Rivers

Laboratories, Inc. Animals are delivered to the ULAR animal facility and are housed

singlely in cages, in compliance with the Drexel University guidelines for animal care and

use, in a controlled environment at 72 ± 2 degrees Fahrenheit with standard 12:12 h light:

dark cycle, with ad libitum access to food and water. 30

2-4 days old rat pups were used for dissecting brains for glia culturing, according to previous reports (Shimizu, Abt, & Meucci, 2011). Pups were decapitated using a large scissor and a small scissor was used to cut through the head and isolate the brain. The brain was removed and placed in a 60 mm dish containing 4mL of cold dissection media

(16mM glucose, 22mM sucrose, 10mM HEPES, 135mM NaCl, 5mM KCl, 1mM Na2HPO4,

0.22mM KH2PO4, ph. 7.4, Osm 300-310). The No.1 and No. 5 tweezers were used for peeling the meninges and then the cortices were isolated from the midbrain. Cortices were transferred into another 60 mm dish containing 4 mL of cold dissection media and further minced with curved scissors. The minced samples were collected and placed in a 15mL tube with 2.5% trypsin. The 15mL tube was then wrapped with parafilm and placed in a

37°C water bath for 15 min and was shaken slightly every 5 min. The suspension was then transferred to a fresh 15mL tube by minimizing the amount of trypsin-containing media. To the same tube, was resuspended 20-30 times using pipette. The largeDNAse pieces (60μg/mL)of tissue were was allowed added to and settle to the bottom of the tube and 80% of the supernatant was transferred into a 50 ml tube. About 3 ml glia media was added to the tube with large tissues then resuspended and 80% of supernatant was collected and transferred to the 50 ml tube. The cell suspension in the 50 mL tube was diluted in 40 ml

Glial media (DMEM media, 10% centrifuged for 15 min at 280g.Fetal Supernatant Bovine Serum, was andaspirated, 50 μg/mL and gentamicin)the pellet was and resuspended in 3 ml glia media. Cells were plated in a 150 cm2 flask and media was added to a total of 20 ml per flask. This flask was then placed in the incubator at 37 C for 10 days and media was changed after 24 h and then every 3 days. ˚

The T-150 flasks containing primary glia were washed with PBS and then trypsinized with 0.05% trypsin for 15-20 mins in a 37°C incubator. Glia media was then added to the flask, resuspended and cell suspension was collected and added to a 50mL conical tube.

This sample was then centrifuged for 15min at 280g. The supernatant was aspirated and the pellet was resuspended in a 3 mL of glia media. The cells were counted using a hematocytometer and the suspension was diluted with glia media. Glial cells were plated at a concentration of 10,000 cells per well in a Poly-lysine coated 96 well plates. The plates were incubated at 37°C for 14 days (14 DIV).

3.5.2 GLUTAMATE UPTAKE ASSAYS IN GLIA

96 well plates containing 14 DIV glia were used for glutamate uptake assays. The

compounds that were determined to stimulate glutamate uptake through EAAT1 or EAAT2

or both in transfected COS-7 cells were also studied in this approach. Dose response assays

were performed, with different concentration of compounds freshly prepared from a 10 mM stock solution.

a) Dose response assays

On the day of the assays, stocks were used to prepare different dilutions required

for dose response assays (from 10 to 0.00006 , in a logarithm serial dilution, prepared

in PBS-CM buffer). In addition, 150nM 3H-L-glutamateμM was prepared using 24.3 M of the

stock solution from Perkin Elmer. Plates were washed with PBS-CM using a plateμ washer

and 100 L of varying concentrations of compounds (or vehicle) were added per well, in

triplicatesμ. Several wells were also included to be incubated with the non-selective EAAT 32 inhibitor DL-TBOA (for obtaining the non-specific background) and were pre-incubated in the plates for 10 min at 37oC. Then 50 L of 150 nM 3H-L-glutamate was added to each well, and reactions were allowed to occurμ for 10 min at 37°C. After 10 mins, the plates were washed with PBS-CM using the plate washer and then 100 L scintillation liquid was added to each well. The radioactivity was counted using Microplateμ Scintillation and

Luminescence Counter.

b) Kinetics assays

For kinetic studies, we also used glia plated in 96 well plates and grown 14 DIV at 37 C.

The compounds and glutamate solutions were prepared as in section 3.4.2 (b). The plate˚ was divided for four treatments each: the first treatment group was vehicle, the second was non-selective EAATs inhibitor TBOA (background), and the third and fourth treatment groups were compounds that showed stimulatory effects in dose response glutamate uptake assays in COS-7 cells and glia.

The cells were washed with PBS-CM using a plate washer and then either 100 L of vehicle (PBS-CM), TBOA or selected compounds at indicated concentrations were addedμ to each well and incubated at 37 C for 10 min. Then, 50 L of varying concentrations of glutamate (3.9 nM – 1000 µM, of˚ a mixture of radiolabeledμ and non-radiolabeled glutamate

(99.8%:0.2%) were added in quadruplicate. Reactions occurred for 10 min at RT, and plates were washed with PBS-CM twice using the plate washer. 100 liquid was added to each well and the radioactivity was counted usingμL of a scintillationMicroplate

Scintillation and Luminescence Counter. 33

All dose-response assays and kinetic assays were performed at least three times

for each compound.

3.6 DOSE RESPONSE ASSAYS IN OTHER TYPES OF NEUROTRANSMITTER

TRANSPORTERS

Dose response assays of selected compounds were performed to investigate an

effect in GABA (GAT-1, GAT-3), Glycine (Glyt1) and monoamine transporters (human

dopamine, human nor-epinephrine and human serotonin, (hDAT, hNET, hSERT,

respectively). These assays further examined the selectivity of selected compounds that

were determined to be PAMs in glutamate uptake assays in transfected COS-7 cells and glia.

For GABA and glycine uptake assays, COS-7 cells were transfected with pcDNA3.1

(as the empty vector) and GAT-1, GAT-3 or Glyt1 in 24 well plates. Following the

transfection procedure, as described in section 3.4.1, plates were incubated at 37 C for two

days prior to dose response assays. ˚

For monoamine transport assays, stable hDAT, hNET, hSERT transfected Madin-

Darby Canine Kidney (MDCK) cells were used, as well naïve MDCK cells for obtaining the

background. Stable transfections were performed previously in the lab and the cells were

kindly provided to us for these studies.

The cells were washed with PBS, trypsinized with 0.25% trypsin and then

resuspended in DMEM media (with 10% fetal bovine serum and 100 units/mL of penicillin,

0.05 units/mL of blasticidin). The cell suspensions were collected and counted using 34

hemocytometer and the final volume is adjusted with DMEM media to plate well

(50,000 cells per well) in 96 well plates. The plates are incubated at 10037 C μL and per dose response assays are performed the next day. ˚

All assays were performed at least three times for each compound.

3.6.1 DOSE RESPONSE ASSAYS IN GABA (GAT-1) and GLYCINE (Glyt1, Glyt3) TRANSPORTERS

Compound

stock solutions of 10s were mM. diluted to varying concentrations (10 μM to 0.00006 μM) from

A radioactive GABA solution was prepared from 12 of radioactive GA

BAto 10 nM, and 20nM glycine solution .3 μM stock of radioactive

glycine. The cells were first washed withwas PBSprepared-CM and from then 18.7 varying μM stock concentration of

compounds (in a 200 L volume) or vehicle were added in quadruplicate. The plates were

then incubated at 37 Cμ for 10 min, and then 100 L of 10 nM radiolabeled GABA solution or

20 nM radiolabeled ˚glycine solution was addedμ in each well. Uptake assays were carried

out for 10 min, and reactions were stopped by washing twice with PBS-CM.

buffer was added in each well, and after shaking for 20 min, cell homogenate400 μLs werelysis

collected and transferred into vials containing 3 ml scintillation liquid. The radioactivity

was counted using scintillation counter, as described above. All assays were performed at

least three times for each compound.

3.6.2 DOSE RESPONSE ASSAYS IN MONOAMINE TRANSPORTERS (hDAT, hNET and

hSERT)

Stable hDAT, hNET, hSERT transfected MDCK cells were used for monoamine

uptake assays. Cells were plated in 96 well plates and incubated for a day at 37 C. Then,

plates were washed with PBS and the treated with varying concentrations˚ (10 to

0.00006 of compounds prepared from stock 100solution μL of of 10 mM for 10 min at 37 C.

Rows containingμM ) hDAT and hNET received 150nM 3H-dopamine solution prepared˚ from 3H-dopamine50μL of

150 nMstock 3H -solution of 31.25μM , and rows containing hSERT3H-5HT received and allowed 50μL toof rest for 10 5HTmins solution at RT. preparedThe compounds from stock and solutionmonoamine of 31.25μM solutions were diluted in the

working buffer (comprised of PBS-CM containing 0.0005% RO water (reverse osmosis water) to inhibit catechol-o-methyltransferase from metabolizing monoamines and

0.00005% ascorbic acid to prevent oxidation of monoamines). After 10 min incubation, the

plates were washed with PBS-CM added to

each well. The radioactivity was countedtwice, and using then Microplate 100 μL scintillation Scintillation liquid and Luminescence was

Counter. All dose-response assays were performed at least three times for each compound.

3.7. IN VITRO NEUROPROTECTION STUDIES

A potential neuroprotective effect of selected compounds was studied in vitro in mixed culture of neurons and glia. Specifically, compounds with a stimulatory effect of COS-

7 cells and glia were further examined for neuroprotective effects by subjecting the 36

cultures to two types of insults i) excitotoxic glutamate insults: exogenous glutamate was

applied for 24h, in presence of the compound, vehicle or controls. After 24h cells were fixed

for immunocytochemistry and analysis, and ii) oxygen-glucose deprivation (OGD), which is

a model of in vitro ischemic stroke(Lipski et al., 2007): the cultures were subjected to OGD

for varied times, from 5 min-1 h, and then OGD media was replaced with fresh growth

media, along with compounds to be tested and controls. 24 h later, cells were fixed and

immunocytochemistry was performed to determine neuronal survival.

Neuronal survival was assessed by performing immunocytochemistry against MAP-

2 (neuronal specific protein) and GFAP (glia specific protein) to examine cellular

morphology, 24 h after the treatments. These assays were carried out by other members in

the lab and kindly provided to us for inclusion in this document.

3.8. DATA ANALYSIS

The data analysis was performed using GraphPad Prism version 5.03 (GraphPad

Software, La Jolla, CA).

For glutamate uptake assays in COS-cells and glia, data was fitted to dose-response curves by non-linear regression analysis. Data was normalized to percent of control (vehicle), and the EC50 was obtained. The EC50 represents the concentration of compound that results in

50% of observed stimulation or inhibition. The efficacy was calculated as function of

maximum uptake observed as compared to control, in percentage. Data was given as means

± SD of three independent experiments for the selectivity, efficacy and potency of

compounds for each transporter. 37

For kinetic analysis of compounds, the nonspecific uptake (from empty vector, CMV transfected cells) was subtracted and the data were analyzed considering Michaelis-

Menten kinetics. Data was converted to pmol/well/min, and kinetic parameters Vmax and

KM values were estimated. Statistical analysis on the values of Vmax and KM were performed using the Student’s t-test for paired data and One-way analysis of variance (ANOVA) followed by Dunnett’s multiple-comparisons posthoc test with vehicle as control. The values were considered to be significantly different when p <0.05.

For neuroprotection studies, the neuronal survival was expressed as % of neuronal death comparing control, insult and treatments. Statistical significance was assessed using One- way analysis of variance (ANOVA) followed by Dunnett’s multiple-comparisons posthoc test with vehicle as control (* p <0.05), or Newman-Keuls posthoc test for multiple comparisons (# p <0.05).

4. RESULTS

4.1. DOSE RESPONSE ASSAYS IN COS-7 CELLS

The third-generation compounds were analyzed for glutamate uptake assays in COS-7 cells transfected with EAAT1, EAAT2 and EAAT3. In this result section, the compounds were grouped depending upon their selective activity through each transporter type, into five groups: i) non-selective stimulator of glutamate uptake, ii) Stimulator of glutamate selective to EAAT1 and EAAT2, iii) Stimulator of glutamate selective to EAAT2 only, iv)

Inactive compounds and v) Inhibitor of glutamate uptake through EAAT1/EAAT2 or both.

4.1.1. Validation of previous results

The second-generation compounds were studied by previous lab members and DA-023 was identified as most selective, efficacious and potent EAAT2 PAM compound. To validate these results, a dose-response curve assay in EAAT2- mediated glutamate uptake in COS-7 cells was performed. Figure 7A shows the dose-response curve for DA-023 from one experiment that is representative of three experiments previously performed. Figure 7B shows a similar experiment performed by me, in which we can conclude that results were reproducible, validating previous data, as the EC50 and efficacy values previously obtained were very similar (0.16 ± 0.08 nM and 157±35% vs 0.5 nM and 261%, respectively).

Figure 7. Effect of DA-023 on glutamate uptake in EAAT2 transfected COS-7 cells. A. Previously performed. B. Current results. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle).

4.1.2 Non-selective stimulators of glutamate uptake

After validation of previous results, testing for all compounds belonging to the third

generation was performed. Compounds that stimulated glutamate uptake mediated by all

three transporters i.e. EAAT1, EAAT2 and EAAT3, were NA-005, VY-3-285 and VY-3-286.

Figure 8 shows dose response curves for NA-005 from one experiment that is representative of three experiments. The potencies and efficacies are expressed as Mean ±

SD of all three experiments. The results show that NA-005 stimulates the glutamate uptake through these three transporters, with the effect on EAAT3 being the most potent and efficacious in comparison with the effect on EAAT1 and EAAT2-mediated uptake, as shown by the values of EC50 and efficacy.

Figure 8. Effect of NA-005 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 9 shows dose response curves for VY-3-285 from one experiment that is representative of three experiments. The potencies and efficacies are expressed as Mean ±

SD of all the experiments. The compound stimulates glutamate uptake through all three transporters and it has comparable efficacy and potency for all three transporter types.

Figure 9. Effect of VY-3-285 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 10 shows dose response curves for VY-3-286 from one experiment that is

representative of three all experiments. The potencies and efficacies are expressed as Mean

± SD of all the experiments. The compound stimulated glutamate uptake through all three transporters. However, the effect of VY-3-286 on EAAT1 and EAAT2 mediated uptake is more efficacious, when compared to the effect on EAAT3 mediated uptake but the potencies remain similar throughout all the transporters.

Figure 10. Effect of VY-3-286 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

4.1.3. Stimulators of glutamate transport: selective to EAAT1 and EAAT2

We identified a group of compounds that only stimulated glutamate uptake through

EAAT1 and EAAT2 and did not show any effect on EAAT3-mediated uptake. These compounds were DA-050, DA-058 and Parawixin10 (PWX-10). Figure 11 shows dose response curves for the effect of DA-050 from one experiment that is representative for all experiments. The potencies and efficacies are expressed as Mean ± SD of all the experiments. The compound stimulated glutamate uptake through all EAAT1 and EAAT2 only and there was no effect in EAAT3 mediated glutamate uptake. The compound was 43

found to be most potent and efficacious towards EAAT2 mediated uptake as represented by

the blue curve below.

Figure 11. Effect of DA-050 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 12 shows dose response curve for DA-058 from one experiment that is representative for all experiments. The potency and efficacy is expressed as Mean ± SD of all the experiments. The compound stimulated glutamate uptake through all EAAT1 and

EAAT2 only and there was no effect in EAAT3 mediated glutamate uptake. The compound was found to have similar efficacy and potency in EAAT1 and EAAT2 mediated glutamate uptake. 44

Figure 12. Effect of DA-058 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 13 shows a dose response curve for PWX-10 from one experiment that is representative for all experiments. The potency and efficacy is expressed as Mean ± SD of all the experiments. The compound stimulated glutamate uptake through EAAT1 and

EAAT2 only, with no effect on EAAT3- mediated glutamate uptake. The compound was found to have similar efficacies in EAAT1 and EAAT2 mediated glutamate uptake. However,

PWX-10 was found to be more potent in EAAT1 mediated glutamate uptake, as shown by the EC50 values 45

EAAT1 EC50= 5.80 ± 5.93 nM Efficacy= 162 ± 11.31 %

EAAT2 EC50= 5.25 ± 2.47 nM Efficacy = 160.87 ± 9.36 %

250 EAAT3 No effect 200

150 EAAT1

100 EAAT2

50 EAAT3 % L-glutamate uptake (Normalized to control) 0 -10 -8 -6 -4 -2 0 2 PWX-10 log [µM]

Figure 13. Effect of PWX-10 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

4.1.4. Stimulator of glutamate transport: selective to EAAT2 only

The only compound that stimulated glutamate uptake in COS-7 cells selectively

through EAAT2 was NA-014. This compound did not show any effect in EAAT1 and EAAT3

mediated glutamate uptake. Figure 14 shows dose response curves for NA-014 from one

experiment that is representative for three experiments. The potency and efficacy is

expressed as Mean ± SD of all the experiments. This compound is potent and efficacious

stimulator of EAAT2 glutamate uptake. 46

Figure 14. Effect of NA-014 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

4.1.5. Inactive compounds

There were eight compounds that did not show any activity in EAAT2 mediated uptake: VY 3-207, VY-3-218, VY-3-246, NA-008, NA-009, NA-019, DA-040, DA-052, DA-057,

DA-066, VY-3-133 and DA-056. These compounds were classified as inactive compounds.

Figure 15 shows a representative dose response of compound DA-040 on glutamate uptake mediated by all three transporter types, showing lack of effect. 47

Figure 15. Effect of DA-040 on glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle).

4.1.6. Inhibitor compounds

There were four compounds that inhibited EAAT2 mediated glutamate uptake in

COS-7 cells: VY-3-171, VY-3-209, DA-055, VY3-136, VY-3-136(2) and NA-010. Figure 16 shows dose response curves for the VY-3-209 on EAAT2 mediated glutamate uptake. This compound did not show any effect on EAAT1 and EAAT3 mediated glutamate uptake (data not shown). 48

Figure 16. Effect of VY-3-209 on EAAT2 mediated glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 17 shows a dose response curve for the VY-3-171 on EAAT2 mediated glutamate uptake. This compound inhibited on EAAT1 mediated glutamate uptake and did not affect EAAT3- mediated glutamate uptake (data not shown).

Figure 17. Effect of VY-3-171 on EAAT2 mediated glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 18 shows a dose response curve for the NA-010 on EAAT2 mediated glutamate uptake. This compound did not affect EAAT1 and EAAT3- mediated glutamate uptake (data not shown).

Figure 18. Effect of NA-010 on EAAT2 mediated glutamate uptake in transfected COS- 7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 19 shows a dose response curve for the DA-055 on EAAT2 mediated glutamate uptake. This compound did not affect EAAT1 and EAAT3 mediated glutamate uptake (data not shown).

Figure 19. Effect of DA-055 on EAAT2 mediated glutamate uptake in transfected COS- 7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

Figure 20 shows a dose response curve for the VY-3-136 and VY-3-136 (2) on

EAAT2 mediated glutamate uptake. Both the compound inhibited EAAT1 mediated glutamate uptake (data not shown) and did not affect EAAT3. 52

Figure 20. Effect of VY-3-136 (A) and VY3-136(2) (B) on EAAT2 mediated glutamate uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as mean ± SD of three independent experiments.

The compounds with stimulatory activity on dose response assays in COS-7 cells as well as

in glia were studied in kinetics assays. The results for kinetics are shown is section 4.3.

4.2. DOSE RESPONSE ASSAYS IN GLIA

The compounds that had stimulatory effects on COS-7 cells were further studied for their glutamate uptake activity in cultured glia, to validate these results in a more endogenous system. VY-3-285, VY-3-286 and NA-005 stimulated glutamate uptake in COS-

7 cells transfected with EAAT1, EAAT2 and EAAT3. DA-050, DA-058 and PWX-10

stimulated glutamate uptake in EAAT1 and EAAT2 transfected COS-7 cells. NA-014 53

selectively stimulated glutamate uptake in EAAT2 transfected COS-7 cells. Therefore, all

these stimulatory compounds were studied in glia.

Only compounds NA-005, NA-014 and PWX-10 had stimulatory effects on glutamate uptake in glial cultures. Compounds DA-050, DA-058 did not show any effect in glutamate uptake in glia. The compounds VY-3-285 and VY-3-286 had variable activity among individual experiments in glial culture i.e. stimulatory once but no effect most of the time.

Figure 21 shows a dose response curve for DA-050 from one experiment that is representative for all experiments. This compound did not show any effects on glutamate uptake assays performed in glial cells despite of showing stimulatory effects on COS-7 cells.

Curves for DA-058, DA-050, VY-3-285 and VY3-286 were similar to this curve showing no activity (lack of effect).

Figure 21. Effect of DA-050 on glutamate uptake in cultured glial cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle). 54

Figure 22 shows a dose response curve for PWX-10 from one experiment that is representative for all experiments. The potency and efficacy is expressed as Mean ± SD of all the experiments.

EC50 = 22 ± 7.07 nM Efficacy= 313.94 ± 25.64 %

400

300

200

100 % L-glutamate uptake (Normalized to control) 0 -10 -8 -6 -4 -2 0 2 PWX-10 log [µM]

Figure 22.Effect of PWX-10 on glutamate uptake in cultured glial cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as Mean ± SD of all the experiments.

Figure 23 shows a dose response curve for NA-005 from one experiment that is representative for all experiments. The potency and efficacy is expressed as Mean ± SD of all the experiments.

Figure 23. Effect of NA-005 on glutamate uptake in cultured glial cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as Mean ± SD of all the experiments.

Figure 24 shows a dose response curve for NA-014 from one experiment that is representative for all experiments. The potency and efficacy is expressed as Mean ± SD of all the experiments.

Figure 24. Effect of NA-014 on glutamate uptake in cultured glial cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with 50 nM 3H-L-glutamate. Results are normalized to percentage of control (vehicle) and expressed as Mean ± SD of all the experiments.

4.3. KINETICS STUDIES

4.3.1 KINETICS STUDIES IN COS-7 CELLS

The compounds NA-014 and PWX-10 were the only compounds that stimulated glutamate

uptake in dose response assays performed in COS-7 cells as well as glia. Therefore, kinetics

studies were performed to confirm the allosteric modulation of the transporter, looking at

the Vmax and Km values obtained from the experiments.

Fig. 25 shows glutamate uptake kinetic analysis of the effect of different concentration of NA-014 (10nM, 100nM and 500 nM) in EAAT2 transfected cells.

Vehicle NA-014 NA-014 NA-014 (10 nM) (100 nM) (500nM)

Vmax(pmol/well/min) 133 ± 13.89 175.4 ± 9.93 403.3 ± 35.82 *** 706.4 ± 8.38 ***

KM (µM) 47.66 ± 28.78 46.92 ± 11.04 98.50 ± 29.68 67.57 ± 8.38

Figure 25. Effects of NA-014 on the kinetics of EAAT2. Graphs illustrate kinetic analysis of L-glutamate uptake in transfected COS-7 cells pre- incubated with 10, 100 and 500 nM of NA-014. Vmax and KM were calculated, and the values are presented in the table; KM was not statistically different between the varying concentrations of compounds analyzed in this study. Vmax of compound at 10 nM concentration was not statistically different from that of vehicle. *** p < 0.05, Vmax of compound compared (100nM, 500nM) to vehicle.

Fig. 26 shows glutamate uptake kinetic analysis of the effect of different concentration of PWX-10 (10nM, 169nM and 500 nM) in EAAT1 transfected cells.

Vehicle PWX-10 PWX-10 PWX-10 (10 nM) (169 nM) (500nM)

Vmax (pmol/well/min) 127 ± 14.60 168.3 ± 7.34 312.8 ± 33.3 *** 783.0 ± 23.27 ***

KM (µM) 52.51 ± 29.46 48.95 ± 8.78 92.90 ± 34.10 52.37 ± 6.70

Figure 26. Effects of PWX-10 on the kinetics of EAAT1. Graphs illustrate kinetic analysis of L-glutamate uptake in transfected COS-7 cells pre- incubated with 10, 169 and 500 nM of PWX-10. Vmax and KM were calculated, and the values are presented in the table; KM was not statistically different between the varying concentrations of compounds analyzed in this study. Vmax of compound at 10 nM concentration was not statistically different from that of vehicle. *** p < 0.05, Vmax of compound compared (169 and 500nM) to vehicle.

Fig. 27 shows glutamate uptake kinetic analysis of the effect of different concentration of PWX-10 (10nM, 169nM and 500 nM) in EAAT2 transfected cells. 59

Vehicle PWX- PWX-10 PWX-10 (500nM) (10 nM) (169 nM) Vmax 133.25 ± 14.02 170 ± 9.20 309.4 ± 18.99 *** 797.2 ± 26.41 *** (pmol/well/min)

KM (µM) 47.68 ± 21.20 50.50 ± 11.15 81.68 ± 18.32 49.56 ± 6.72

Figure 27. Effects of PWX-10 on the kinetics of EAAT2. Graphs illustrate kinetic analysis of L-glutamate uptake in transfected COS-7 cells pre- incubated with 10, 169 and 500 nM of PWX-10. Vmax and KM were calculated, and the values are presented in the table; KM was not statistically different between the varying concentrations of compounds analyzed in this study. Vmax of compound at 10 nM concentration was not statistically different from that of vehicle. *** p < 0.05, Vmax of compound compared (100nM, 500nM) to vehicle.

4.3.2 KINETICS STUDY IN GLIA

The compound that selectively stimulated EAAT2 mediated glutamate uptake,

NA014, and the compound stimulating EAAT1 and EAAT2 mediated glutamate uptake,

PWX-10, were studied in glia as well to confirm the results in a more endogenous system.

Apart from the stimulatory compounds NA-014 and PWX-10, the inactive compound NA-

009 and inhibitory compound VY-3-209 were also studied to validate the mechanism of allosteric modulation of transporters by these third generation compounds.

Figure 28 shows that Vmax of glutamate transport is increased in glial cells when incubated in presence of NA-014 (100 and 500nM).

Vehicle NA-014 NA-014 (100 nM) (500nM) Vmax (pmol/well/min) 20.01 ± 1.53 42.35 ± 1.44 *** 72.76 ± 3.67 ***

KM (µM) 53.53 ± 13.30 52.50 ± 5.82 49.84 ± 8.30

Figure 28. Effect of NA-014 on the kinetics of glutamate transport in glia cells. Graphs illustrate kinetic analysis of L-glutamate uptake in cultured glia cells pre-incubated with vehicle, 100 nM, 500 nM of NA-014. Vmax and KM were calculated and values are presented in the table; KM was not statistically different between the compounds analyzed in this study. *** p < 0.05, Vmax of drug compared to vehicle.

Figure 29 shows that Vmax of glutamate transport is increased in glial cells when

incubated in presence of PWX-10 (100 nM and 500nM).

Vehicle PWX-10 PWX-10 (100 nM) (500nM) Vmax 19.70 ± 1.28 38.23 ± 1.29 *** 59.44 ± 3.29 *** (pmol/well/min) KM (µM) 42.62 ± 9.49 41.69 ± 4.85 49.09 ± 9.02

Figure 29. Effect of PWX-10 on the kinetics of glutamate transport in glia cells. Graph illustrate kinetic analysis of L-glutamate uptake in cultured glia cells pre-incubated with vehicle, 100 nM, 500 nM of PWX-10. Vmax and KM were calculated, and values are presented in the table; KM was not statistically different between the compounds analyzed in this study. ***p < 0.05, Vmax of drug compared to vehicle.

Figure 30 shows that Vmax of glutamate transport is not significantly changed in glial cells when incubated in presence of NA-009 (100 nM), and the Vmax of glutamate transport is decreased in glial cells when incubated in presence of VY-3-209 (100 nM).

Vehicle NA-009 VY-3-209 (100 nM) (100nM) Vmax 18.44 ± 1.08 20.15 ± 1.46 10.89 ± 0.67 *** (pmol/well/min)

KM (µM) 41.41 ± 8.43 49.18 ± 11.81 44.82 ± 9.37

Figure 30. Effect of NA-009 and VY-3-209 on the kinetics of glutamate transport in glia cells. Graphs illustrate kinetic analysis of L-glutamate uptake in cultured glia cells pre-incubated with vehicle, 100 nM NA-009 and 100 nM VY-3-209. Vmax and KM were calculated, and values are presented in the table; KM was not statistically different between the compounds analyzed in this study. ** p < 0.05, Vmax of compound VY3-209 compared to vehicle. Vmax of NA-009 is not significantly changed.

4.4 DOSE RESPONSE ASSAYS IN OTHER TYPES OF NEUROTRANSMITTER TRANSPORTERS

4.4.1 DOSE RESPONSE IN GABA AND GLYCINE TRANSPORTERS

COS-7 cells were transfected with GAT-1, GAT-3 for GABA transport and Glyt1 for glycine

transport and dose response of NA-014 and PWX-10 were performed. Figure 31 shows the

dose response of NA-014 on GABA and Glycine uptake in transfected COS-7 cells.

Figure 31. Effect of NA-014 on GABA and Glycine uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with radiolabeled GABA and Glycine respectively. Results are normalized to percentage of control (vehicle).

Figure 32 shows the dose response of NA-014 on GABA and Glycine uptake in transfected

COS-7 cells.

Figure 32. Effect of PWX-10 on GABA and Glycine uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with radiolabeled GABA and Glycine respectively. Results are normalized to percentage of control (vehicle).

4.4.2 DOSE RESPONSE IN MONOAMINE TRANSPORTERS

MDCK cells stabled transfected with hDAT, hNET or SERT were used for dose response of

NA-014 and PWX-10 on dopamine, norepinephrine and serotonin uptake, respectively.

Figure 33 shows these dose response curves of NA-014 on monoamine uptake, demonstrating lack of effect. 66

Figure 33. Effect of NA-014 on monoamine uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with radiolabeled dopamine/norepinephrine/serotonin respectively. Results are normalized to percentage of control (vehicle).

Figure 34 shows the dose response of PWX-10 on monoamine uptake in stabled transfected

MDCK cells.

Figure 34. Effect of PWX-10 on monoamine uptake in transfected COS-7 cells. Cells were incubated with varied concentrations of compound for 10 min at 37oC and 10 min with radiolabeled dopamine/norepinephrine/serotonin respectively. Results are normalized to percentage of control (vehicle).

4.4. IN VITRO NEUROPROTECTION STUDIES

4.4.1 NEUROPROTECTION STUDIED IN EXCITOTOXIC GLUTAMATE INSULTS

The compounds with stimulatory effects in COS-7 cells and glia were further examined for neuroprotective effects by subjecting the cultures to excitotoxic glutamate insults. Figure

35 shows representative images of mixed cultures at 14 DIV treated with vehicle (control) or 100 µM L-glutamate for 24 h. Immunocytochemistry was performed against neuron specific MAP-2, glial specific GFAP, and DAPI was used for nuclear staining. 68

Figure 35. Representative images of mixed neuron-glia cultures (control and insult with glutamate). Representative images from 14-DIV neuron/glia cultures, obtained from prefrontal cortices from late embryonic stage (E17) rat embryos and plated at a density of 35,000 cells/coverslip in 12-well plates. Vehicle (control), cells treated with application of 100 µM L-glutamate for 24 h and with co-treatment with 100nM NA-014 are indicated. Immunostaining against neuronal marker MAP-2 (green), glial maker GFAP (red), and nuclear marker DAPI (blue). Images taken with 30x magnification with a confocal microscope.

Figure 36 shows the quantification data, where a neuroprotective effect was evaluated by comparing the percentage of surviving neurons among treatments with 100 µM L- glutamate, glutamate incubate in presence of NA-014, in presence of NA-014 and TBOA

(non-selective competitive inhibitor of EAATs), and in presence of NMDA antagonist APV.

The level of neuronal survival decreased to about 25% after application of 100 M glutamate, and was reverted to ~100% when co-incubated with 100 nM NA-014. Thμis neuroprotective effect was reverted by co-application of glutamate transport inhibitor

TBOA, suggesting its action is dependent on the transporter activity. The neuroprotective effect was comparable to positive control NMDA antagonist and APV. Additionally, negative control NA-009 did not affect the level of neuronal survival. 69

Figure 36. Neuroprotective effects of NA-014 after excitotoxic insults in mixed neuron/glia cultures. Each bar in the graph represents mean ± S.D. Data compared and normalized to control. ***p<0.001, one-way Anova, Dunnett’s multiple-comparisons posthoc test with vehicle as control. ###p<0.001, Newman-Keuls test for multiple comparisons. Courtesy of Srawasti Sarker, A. Mortensen lab.

4.4.2 NEUROPROTECTION STUDIED AFTER OXYGEN/GLUCOSE INSULTS

Compound NA-014, which was shown to have stimulatory effect of COS-7 cells and glia, was further examined for neuroprotective effects by subjecting the cultures to oxygen/glucose deprivation (OGD) insults Figure 37 shows representative images of cultures either under control conditions or OGD insult for 35 min, demonstrating that the insult results in 70 decreased neuronal density, when compared to control, as shown as less MAP-2 (green) staining.

Figure 37. Representative images of mixed neuron-glia cultures (control and subjected to 35 min OGD insults). Representative images from 14-DIV mixed cultures. Cells were obtained from prefrontal cortices from E17 rat embryos and plated at a density of 35,000 cells/coverslip in 12-well plates. Immunostaining against neuronal marker MAP-2 (green), glial maker GFAP (red), and nuclear marker DAPI (blue). Images taken with 30x magnification with a confocal microscope. Courtesy of Srawasti Sarker, A. Mortensen lab.

Figure 38 shows the quantificative data from the OGD assays. The insult resulted in ~26%, of cell survival, whereas co-incubation with 100 nM NA-014 reverted this level to control levels. Co-incubation with positive control APV also resulted in survival levels comparable to control conditions.

Figure 38. Neuroprotective effect of NA-014 in cortical mixed cultures after OGD insult. NA-014 displays neuroprotection in mixed cultures exposed to OGD for 35 min. Immunocytochemistry for MAP-2 and GFAP was performed and neuronal survival was assessed by blind counting of 5-10 random fields/ coverslip and 4 coverslips/treatment.***p<0.001 One Way Anova, Dunnett’s multiple-comparisons posthoc test with vehicle as control, ###p<0.001, One Way Anova, Newman-Keuls test for multiple comparisons.

Potential effects of Parawixin10 after L-glutamate and OGD insults in this model are currently under study.

5. CONCLUSIONS

The main aim of this study was to identify the most promising positive allosteric

modulators of glutamate transporter EAAT2. The first and second generation compounds

were studied by previous lab members, leading to the identification of compound DA-023

as a promising Lead that selectively stimulated EAAT2 mediated glutamate uptake.

However, DA-023 need improvement in its poor drug like properties and therefore a third

generation compounds was developed and studied as a part of my project. Before studying

the third generation compounds, it was essential to confirm the effect of DA-023 on EAAT2

mediated glutamate uptake assay. Therefore, the dose response curves of DA-023 were

compared from previous study and current study. The EC50 values and efficacy were

comparable supporting the validity of the experiment.

Table 2: Comparison of Efficacy and Potency of DA-023 In EAAT2 Mediated Glutamate Uptake Between Previous Study And Current Study.

Compound EC50, Efficacy

DA-023 (Previous study) 0.16 ± 0.08 nM, 152± 35%

DA-023 (Current Study) 0.5 nM, 261%

The third-generation compounds were then studied for their glutamate uptake in COS-7

cells transfected with EAAT1, EAAT2 and EAAT3. The dose response curves from these

studies enabled the identification of efficacy, potency and selectivity of these compounds.

The compounds that stimulated glutamate uptake in EAAT1 and/or EAAT2 transfected

cells were further studied in cultures of glia to confirm the activity in an system that

endogenously expressed the transporters The compound having EAAT3 mediated 73 stimulatory effect on glutamate uptake was not studied further because of potential liabilities associated with modulation of EAAT3, as discussed in section 1.3.

Table 3: Effect of Third Generation Compounds on Glutamate Uptake Assays Performed On COS-7 Cells Transfected with EAAT1, EAAT2 and EAAT3. Green color represents activator compound (PAM) and red color means inhibitor compound (NAM). COMPOUNDS EAAT1 EAAT2 EAAT3

EC50 / IC50 (Mean±SD) EC50 / IC50 (Mean±SD) EC50 / IC50 (Mean±SD)

Efficacy (Mean±SD) Efficacy (Mean±SD) Efficacy (Mean±SD)

NA-005 57.95 ± 77.8 nM 10.3 ± 11.2 nM 4.33 ± 7.5 nM

189 ± 9.89% 151.5±51.2% 233.5 ± 55.86%

VY-3-285 2.75 ± 3.18 nM 0.73 ± 0.94 nM 2.54 ± 3.47 nM

222 ± 55.72% 156 ± 4.24% 188.2 ± 5.09%

VY-3-286 2 ± 1.41 nM 0.95 ± 0.07 nM 1.55 ± 2.05 nM

160.25 ± 27.22% 186.5±24.7% 130.5 ± 2.12%

DA-050 46 ± 36.76 nM 0.5 ± 0.56 nM No Effect

150 ± 21.21% 261.5±40.3%

DA-058 2.24 ± 1.07 nM 0.4 ± 0.42 nM No Effect

186 ± 41.01% 200.5 ± 58.6

NA-014 No Effect 3.5 ± 4.4 nM No Effect

167.3 ± 8.3%

VY-3-207,

VY-3-208,

VY-3-246, All these compounds were grouped as inactive compounds as they had no

NA-008, effect on any of the transporters. 74

NA-009,

NA-019,

DA-040,

DA-056,

DA-052,

DA057,

DA-066

VY-3-133

VY-3-209 21.5 ± 11.73 nM

32.55 ± 10.6%

VY-3-171 95.5 ± 68 nM

35 ± 31 %

NA-010 3121 ± 12.02 nM

58.5 ± 11.31%

DA-055 34.45 ± 5.02 nM

37.91 ± 11.45%

VY-3-136 591.50 ± 176.84 nM

38.10 ± 10.32%

VY-3-136(2) 924.50 ± 24.74 nM

20.55 ± 2.75%

PWX-10 5.80 ± 5.93 nM 5.25 ± 2.47nM No Effect

162 ± 11.31 % 160.87 ± 9.36%

The dose response studies on transfected COS-7 cells enabled to categorize the compounds into four different groups i) Non-selective stimulator, ii) Compounds selective to EAAT1 and EAAT2, iii) Compounds selective to EAAT2 only, iv) inactive compounds and v) inhibitor compounds. The compounds with stimulatory effects were progressed to further studies in secondary cultures of glia. Therefore, VY-3-285, VY-3-286, DA-050, DA-058, NA-

005, NA-014 and PWX-10 were studied in glia.

A number of inhibitory compounds (NAMs) were also identified in this study, namely VY-3-209, VY-3-171,VY-136,VY-3-136(2) NA-010 and DA-055. These compounds

can be used in the future studies to understand mechanisms of negative allosteric

modulation of glutamate transport.

Table 4: Effect of Selective Compounds on glutamate uptake performed in Glia

Compounds Effect

VY-3-285 Variable activity among different

experiments

VY-3-286 Variable activity among different

experiments

DA-050 No effect

DA-058 No effect

NA-005 EC50=17.5 ± 24 nM

Efficacy= 186 ± 70 % 76

NA-014 EC50=13.4 ± 10.2 nM

Efficacy= 186 ± 70 %

PWX-10 EC50=22 ± 7.07 nM

Efficacy= 313.94 ± 25.64 %

The compounds NA-005, NA-014 and PWX-10 stimulated glutamate uptake in glia and the other compounds i.e. DA-050, DA-058, VY-3-285 and VY-3-286 failed to show any stimulatory effects. Even though NA-005 had stimulatory effect, it was not progressed for further studies due to its EAAT3 mediated stimulatory effect as it could lead to side effects.

Therefore, only NA-014 and PWX-10 were progressed for Kinetics studies. The kinetics studies were performed in COS-7 cells and Glia to confirm the allosteric modulation by comparing the Vmax and Km values from kinetics experiments. The increase in Vmax shown by 100 nM and 500 nM of NA-014 and PWX-10 indicates the increased efficacy of transporter and no change in Km represents that the affinity remains unchanged supporting

the allosteric modulation. Table 5 shows the percentage change in Vmax at varying

concentration of NA-014 in kinetics studies performed on COS-7 cells transfected with

EAAT2.

Table 5: Effect of NA-014 (10, 100 and 500 nM) on the Vmax and Km values from kinetics study on COS-7 cells transfected with EAAT2.

Parameters EAAT2 + 10 nM EAAT2 + 100 nM EAAT2 + 500 nM

NA-014 NA-014 NA-014

Vmax No significant Vmax increased by Vmax increased by

change in 203% in 431.1% in 77

comparison to comparison to comparison to

EAAT2 + vehicle EAAT2 + vehicle EAAT2 + vehicle

Km No significant change in comparison to EAAT2 + vehicle

Table 6 shows the percentage change in Vmax at varying concentration of NA-014 in kinetics studies performed on Glia.

Table 6: Effect of NA-014 (10,100 and 500 nM) on the Vmax and Km values from kinetics study on Glia.

Parameters Glia + 100 nM NA-014 Glia + 500 nM NA-014

Vmax Vmax increased by 106.6 % in Vmax increased by 263.6% in

comparison to Glia + vehicle comparison to Glia + vehicle

No significant change in comparison to Glia + vehicle

Table 7 shows the percentage change in Vmax at varying concentration of PWX-10 in kinetics studies performed on COS-7 cells transfected with EAAT1 and EAAT2.

Table 7: Effect of PWX-10 (10,169 and 500 nM) on the Vmax and Km values from kinetics study on COS-7 cells transfected with EAAT2 78

Parameter EAAT1 + EAAT1 + EAAT1 + EAAT2 + EAAT2 + EAAT2 +

s 10 nM 169 nM 500 nM 10 nM 169 nM 500 nM

PWX-10 PWX-10 PWX-10 PWX-10 PWX-10 PWX-10

Vmax in No Vmax Vmax No Vmax Vmax comparison significant increased increased significant increased increased

to vehicle change in by 145 % by 516% change in by 132 % by 498 %

compariso in in compariso in in

n to compariso compariso n to compariso compariso

vehicle n to n to vehicle n to n to

vehicle vehicle vehicle vehicle

No significant change in comparison to vehicle

Table 8 shows the percentage change in Vmax at varying concentration of PWX-10 in kinetics studies performed glia.

Table 8: Effect of PWX-10 (100 and 500 nM) on the Vmax and Km values from kinetics study on Glia

Parameters Glia + 100 nM Glia + 500 nM

PWX-10 PWX-10

Vmax Vmax increased by 94 % in Vmax increased by 201.7% in

comparison to Glia + vehicle comparison to Glia + vehicle 79

Km No significant change in comparison to Glia + vehicle

The compounds NA-014 and PWX-10 were further studied for their selectivity and therefore dose response assays were performed in COS-7 cells transfected with GABA and

Glycine transporters and stable transfected human dopamine, human norepinephrine and human serotonin transporters. The compounds did not show any effect on other type of transporters.

Table 9 shows the effect of NA-014 and PWX-10 on other type of neurotransmitter transporters.

Table 9: Effect on NA-014 and PWX-10 on GABA, Glycine and Monoamine transporters.

Compounds GAT-1 GAT-3 GlyT1 hDAT hNET hSERT

NA-014 No Effect No Effect No Effect No Effect No Effect No Effect

PWX-10 No Effect No Effect No Effect No Effect No Effect No Effect

These compounds were further studied for neuroprotective effects and were found to have

neuroprotective activity in both excitotoxic glutamate insult and OGD. The neuroprotective effect was evaluated by comparing the % of surviving neurons among different treatment groups. NA-014 was found to have remarkable neuroprotective effect as shown by increased percentage of surviving neurons in presence of NA-014, which was comparable to NMDA antagonist APV and this effect was reverted in presence of TBOA, suggesting that 80 the neuroprotective effect is dependent upon the transporter activity. Similar kind of neuroprotective effect was seen in OGD model, where the neuronal survival significantly dropped after 35 mins of OGD and this effect was reverted after the application of NA-014 suggesting its neuroprotective effects.

In conclusion, we have progressed the development of previously identified EAAT2

PAMs in two in vitro models, have performed structure-activity relationship (SAR) studies on three chemical series and identified two promising compounds: NA-014 and PWX-10, to be examined for their pharmacokinetic profile.

Compound NA-014 is currently being investigated for its potential neuroprotection in in vivo models of TBI and neuropathic pain.

6. DISCUSSION AND FUTURE DIRECTIONS

My studies started with performing dose response assay of second generation compound DA-023, previous identified in the lab, to be a promising compound that stimulated EAAT2 mediated glutamate uptake. The purpose of repeating the dose response assay was to validate the previous data and to compare the reproducibility of the experiment. My project included third generation compounds (synthetic analogs) and an additional compound Parawixin10, isolated from Parawixia bistriata spider venom.

The initial screening studies for selectivity, efficacy, and potency in transfected COS-7 cells identified compounds with different actions, which were grouped into classes of stimulators, inhibitors or inactive compounds. The stimulator compounds were further classified into non-selective stimulators, selective stimulators of EAAT1 and EAAT2 and selective stimulators of EAAT2 only. The major focus was towards the compound that could stimulate the glutamate uptake through EAAT2. However, the compound stimulating

EAAT1 mediated glutamate uptake could also be acceptable for progression of drug development, as EAAT1 is also located in the glia (however, its contribution to the level of glutamate uptake in the brain is much smaller than EAAT2(Rothstein et al., 1994; Storck,

Schulte, Hofmann, & Stoffel, 1992). The reason for focusing on EAAT2 is that it is the transporter responsible for 90% of the glutamate uptake in the brain, so targeting this subtype of transporter would likely translate in the most efficacious effect on glutamate clearance. The compounds stimulating glutamate uptake through EAAT3 were not further studied as EAAT3 is present in the neurons in proximity with mGLURs and is thought to 82

activate these receptors upon, which could have unwanted effects as a result of

downstream signaling (Jong et al., 2009; Jong & O’Malley, 2017).

The compounds that stimulated EAAT1 and EAAT2 were studied in secondary cultures

of glia to confirm the stimulatory activity in a native environment. Not all the stimulatory compounds in transfected COS-7 reproduced this effect in in glia and therefore, those

compounds were not studied further (such as VY3-285, VY-3-286, DA-050 and DA-058).

We suggest that in cells transfected with only a subtype of transporter a clear response of

the compound can be observed. However, in a native system like glia, the expression of

transporters subtypes is likely variable among preparations. The glial preparations used in this study express EAAT1, EAAT2 and EAAT3 (supplemental data of (Kortagere et al.,

2018). This heterogeneity is likely to affect the response of the compound on glutamate uptake. The overexpressing cells are transfected with human EAATs; however, glia

expresses GLAST, GLT1 and EAAC1 respectively. The COS-7 cells could be transfected with transporters that have been cloned in rats in order to compare the glutamate uptake and differences observed among overexpressing cells and in glia.

The compounds that stimulated glutamate uptake in transfected COS-7 cells, as well in glia, were NA-005, NA-014 and PWX-10. Two compounds were progressed further to selectivity studies, kinetic and subsequently neuroprotection studies, NA-014 and PWX-10,

since they were efficacious (~170 % increase in the rate of glutamate transport) and

potent (with EC50 for stimulation of EAAT2-mediated uptake in the nM range). NA-014 is

selective stimulator of EAAT2, and PWX-10 a stimulator selective to EAAT1 and EAAT2. On

the other hand, compound NA-005 did not progress to further studies due to its non- 83

selective modulatory activity on EAAT3. As stated before, activation of EAAT3 transporter

could lead to mGLUR5 receptor activation and lead to downstream signaling, and that

could be associated with liabilities, such as psychotic effects (Kinney et al., 2005;

Niswender & Conn, 2010).

The remaining EAATs, i.e. EAAT4 (expressed in cerebellum) and EAAT5 (expressed in

retina) are not expressed well in COS-7 cells. However, studying role of PAMs on these transporters is also important. For that purpose, electrophysiology studies could be performed in future to study the currents associated with transport and the effect of the

PAMs on these currents.

Our studies also identified a number of inhibitory compounds (NAMs). It is worth noting that these NAMs are not as potent or efficacious as inhibiting glutamate transport as the PAMs identified here are at stimulating transport. The meaning and relevance of these findings are still under discussion. One possible application could be understanding the role of these NAMs in cognition. Glutamate being essential for learning, memory and cognition, its rapid removal from synapse could have some effect on cognition. This could be studied through animal behavior assays.

Subsequently to dose-response assays, which resulted in the selection of a few compounds, we next performed kinetic experiments to confirm the allosteric mechanism of transporter modulation. Therefore, kinetics studies were performed in COS-7 cells as well as in Glia and the Vmax and Km values were compared. A significant increase in Vmax in

EAAT2-mediated uptake assays was seen with the incubation of 100 and 500 nM of NA-

014. Additionally, PWX-10 incubation increased Vmax on EAAT1 and EAAT2-mediated 84

uptake kinetic assays. The increased Vmax shows the enhanced efficacy of the transporter.

We have also compared Km values and saw no significant changes among groups, meaning

that the affinity of the transporter was not changed, which is an evidence of allosteric

modulation of the transporter.

The major advantage of allosteric modulation is that it does not interfere with agonist

binding to the orthosteric site and therefore, the normal function and interaction of agonist

and orthosteric site remains intact and therefore, are expected to have no side effects in

comparison to previous compounds explored in the past to target harmful effects of

excitotoxicity like Ca2+ channel blockers and NMDA receptors blockers.

Compound NA-014 was then studied on other types of neurotransmitter transporters including GABA (GAT-1, GAT-3), Glycine (Glyt1) and monoamine transporters

(hDAT, hNET and hSERT). The dose response assays showed that the compounds did not

affect GABA, glycine and monoamine uptake, supporting the selectivity towards EAATs.

Selectivity of PWX-10 was studied on the monoamine transporters, showing lack of effect

of this compound on them. Selectivity studies of PWX-10 was also performed on GABA and

glycine transporters and this compound did not affect GABA and glycine uptake. The

results from these selectivity studies suggested that the compound is selective to EAAT1

and EAAT2 only.

After confirmation of efficacy, potency, selectivity and allosteric modulation, the

next step was to study potential neuroprotective effects of the compound. The selected

compounds were examined by my colleagues in lab for neuroprotective effects by

subjecting the cultures to two types of insults i) excitotoxic glutamate insults and ii) 85 oxygen-glucose deprivation (OGD), which is a model of in vitro ischemic stroke. Compound

NA-014 was found to have neuroprotective activity in both excitotoxic glutamate insult and

OGD. Also, the neuroprotective effect of the compound was not seen in presence of the non- selective glutamate transporter inhibitor TBOA, supporting the fact that this compound works through the modulation of transporters and are inactive when the transporter itself is blocked. The neuroprotective effects were also seen pronounced in OGD model, where the percentage neuronal survival was very low after 35 min of OGD and this effect was shown reverted by the compound and the neuronal survival was comparable to that of the control group.

These results show that NA-014 is the most promising compound of the third generation compounds for progression to drug development. One concern associated with this positive allosteric modulation is whether it could lead to any undesirable effect on cognition due to excessive glutamate uptake. However, the drug memantine that is an

NMDA antagonist is prescribed to Alzheimer’s patients to enhance cognition. Therefore, the effect of PAMs like NA-014 could only be predicted depending upon the behavior assays for learning and memory. It would be interesting to see whether the compounds would have enhancing effects on cognition like memantine or it would decrease the cognitive abilities because of rapid glutamate clearance.

Our next interest is to understand which structural chemical modifications result in selective or non-selective stimulatory effects, inhibitory effects, or lack of activity. Changes were made in order to reduce lipophilicity, polarity, reduce size and H-bonding, with the goal of improving CNS penetration and metabolic stability. Unfortunately, we cannot 86 display specific information on the chemical modifications designed, due to intellectual properties restrictions, so a thorough discussion on this matter is not possible.

PWX-10 also emerged as a promising compound for drug development, due to its selective actions towards EAAT1 and EAAT2 and allosteric mechanism. Potential neuroprotection properties of this compound are currently being pursued and structure- activity relationship (SAR) studies with PWX-10 analogs will be performed in the future to understand ways of engaging these transporters.

Furthermore, one goal of these studies was to provide SAR information about among our group of biologists and medicinal chemists, and we are confident that we have made progress to understand how to the modifications in the different functional group affects the selectivity and efficacy of the compounds effect on the transporters.

Future goals of the project could be divided into immediate goals and long-term goals. The immediate goal is to study the pharmacokinetic profiles of NA-014 and PWX-10 and to progress these compounds to in-vivo neuroprotection studies. The long term goal is to identify the most promising PAM selective to EAAT2 with good drug like properties that could be progressed as a lead compound towards clinical trials and serve as a therapeutic intervention to target harmful effects of glutamate excitotoxicity. These compounds are in the form of racemic mixtures and the next step in further understanding their engagement with EAAT2 could be separating these racemic mixtures and study the effect of individual enantiomers on EAAT2 mediated uptake. There are compounds that fail in clinical trials despite of having good efficacy in in-vivo studies, like ceftriaxone. Ceftriaxone has been shown to have neuroprotective effects in various in vitro and in vivo models of 87 neurodegenerative disorders but failed in phase 3 studies of ALS. This draws attention towards increasing the efficacy via multiple therapy approach. The transcriptional enhancer of EAAT2, ceftriaxone, could be combined with compound increasing functional efficacy, PAMs, in order to have enhanced effects and could be successfully translated to clinic.

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