CRTh2: Can Residence Time Help ? RSC-SCI Cambridge Medicinal Chemistry Symposium Churchill College, Cambridge 8-11 September 2013 Rick Roberts Almirall Introduction Paul Ehrlich, The Lancet (1913), 182, 445 “A substance will not work unless it is bound” 100 years on: “What a substance does may depend on how long it is bound” 2 In a nutshell …. Introduction “Applications of Binding Kinetics to Drug Discovery” D. Swinney, Pharm. Med. (2008), 22, 23-34 3 Energetic concept of Residence Time kon Standard model [R] + [L] [RL] k unbound off bound Energy ‡ Binding process (kon) is (R·L) determined by the energy barrier Ea E Ligand concentration a Unbinding process (koff) is determines the number of Ed determined by the energy attempts to get over this barrier Ed barrier [R] + [L] G = Ed -Ea [RL] Reaction coordinate Potency (Ki) is determined by the difference in these energies koff Ki = kon 4 K , k , k i on off -1 -1 kon M s Potency (nM) vs kon vs koff Very fast association 108 10 1 0.1 0.01 0.001 107 100 10 1 0.1 0.01 0.001 fast association 106 1000 100 10 1 0.1 0.01 0.001 105 10 M 1000 100 10 1 0.1 0.01 0.001 slow association 104 10 M 1000 100 10 1 0.1 0.01 Very slow association 103 10 M 1000 100 10 1 0.1 “inactive” 102 10 M 1000 100 10 1 10 10-1 10-2 10-3 10-4 10-5 10-6 10-7 s-1 koff Energy A simple binding measurement gives no clue to how fast the association and dissociation are (R·L)‡ Very slow associating compounds that are very slow dissociating (R·L)‡ slow associating compounds that are slow dissociating Are all fast associating compounds that are fast dissociating equipotent Very fast associating compounds that are very fast dissociating [R] + [L] If we can control the transition state energy, we can control the binding kinetics [RL] Reaction coordinate 5 What is the transition state (R·L)‡ ? entropy Protein conformational Partial changes desolvations Energy-lowering steps to get to Fleeting final bound state existence A physical process Partial electrostatic interactions Solvated Solvated Calculate G and Ligand Receptor hence potency A calculated process + interaction + interaction - 10 × from ligand + Van der Waals interaction - 6 × from receptor - Entropy of ligand +/- etc Water molecules - Molecular orbital orientation Molecular interaction points +/- etc 6 Why bother to control Binding Kinetics ? Residence time / Dissociation half-life seconds minutes hours days level PD PK time Mechanistic Surmountable Insurmountable Pharmacodynamic Potency has little influence over these behaviours Partial agonism ↔ Full agonism Functional efficacy relates to off-rate .M3 agonists Mol. Pharmacol. (2009), 76, 543-551 .A2A agonists Br. J. Pharmacol. (2012), 166, 1846-1859 7 Why bother to control Binding Kinetics ? Residence time / Dissociation half-life seconds minutes hours days level PD PK time Mechanistic Surmountable Insurmountable Pharmacodynamic Efficacy depends on substrate concentration Enzyme inhibitors can cause a build-up of substrate .Lovastatin, an HMG-CoA reductase inhibitor is sensitive to HMG- CoA build-up .Candasartan, an ACE inhibitor is insensitive to AT1 build-up Mechanism-based toxicity Dopamine D2 antagonists .Clozapine as a rapidly reversible D2 antagonist .Haloperidol is insurmountable and blocks basal D2 activity GI Toxicity of COX-1 inhibitors. Lett. Drug Design Disc. (2006), 3, 569 .Celecoxib is surmountable and free of GI ulceration .Aspirin is irreversible and carries use warnings 8 Why bother to control Binding Kinetics ? Residence time / Dissociation half-life seconds minutes hours days level PD PK time Mechanistic Surmountable Insurmountable Pharmacodynamic Pharmacodynamics outlasts Pharmacokinetics Ester hydrolysable M3 antagonists .Ipratropium is dosed 2 puffs, 4 times a day .Aclidinium and Tiotropium are twice and once daily respectively Kinetic selectivity M3 over M2 selectivity .Aclidinium bromide safety profile. J. Pharm. Exp. Ther (2009), 331, 740-751 9 On rates by mechanism – also independent of potency Simple fit Induced fit kon k1 k3 [R] + [L] [RL] [R] + [L] [RL] [RL*] koff k2 k4 . If the off rate is slow, . The first on and off rates are quicker the on rate is also slow . Some kind of internal change takes place once bound . The final off rate is macroscopically the slowest Energy Energy ‡ (R·L)‡ (RL) (R·L)‡ slow Ea Ed [R] + [L] [R] + [L] quick [RL] [RL] [RL*] Reaction coordinate Reaction coordinate 10 On rates by mechanism Simple fit kon [R] + [L] [RL] koff . If the off rate is slow, the on rate is also slow Simple fit model Once “on”, the ligand behaves as an 100 insurmountable antagonist 80 However, the time to 60 “get on” is about 6 h. 40 Before this time the 20 ligand is a partial % Receptor Occupancy antagonist 0 6 121824 Time (h) Simulation: Dissociation half-life 24 h Concentration of [L] at 10 × IC50 Sufficient PK levels needed for sufficient time to ensure receptor becomes saturated 11 On rates by mechanism Induced fit k1 k3 [R] + [L] [RL] [RL*] k2 k4 The ligand binds quickly (Total RO%) However at this point it behaves as a classical surmountable ligand Induced fit model Once “on”, the ligand behaves as an 100 insurmountable antagonist 80 Total RO% 60 RL*% 40 RL% 20 % Receptor Occupancy 0 6 121824 Time (h) Simulation: k4 Dissociation half-life 24 h Concentration of [L] at 10 × IC50 Sufficient PK levels needed for sufficient time to ensure receptor becomes saturated 12 The CRTh2 Programme 13 Brief introduction to CRTh2 Real name: .Chemoattractant Receptor- homologous molecule expressed on T-Helper 2 cells .Also known as DP2 CRTh2 activation: .induces a reduction of intracellular cAMP and calcium mobilization. .is involved in chemotaxis of Th2 lymphocytes, eosinophils, mast cells and basophils. CRTh2 and DP1 review. Nat. Rev. Drug Disc. (2007), 6, 313 .inhibits the apoptosis of Th2 lymphocytes CRTh2 antagonism: .stimulates the production of IL4, IL5, and .Should block pro-inflammatory PGD2 effects on IL13, leading to: key cell types . eosinophil recruitment and survival . mucus secretion .Potential benefit in: . airway hyper-responsiveness . asthma . immunoglobulin E (IgE) production . allergic rhinitis . etc . atopic dermatitis. 14 Why Long Residence Time in CRTh2 ? Indole acetic acids Cl HO O HO O N F N S S N O O NH ? O Oxagen-Eleventa AstraZeneca Actelion Novartis Merck Pulmagen-Teijin OC-459 AZD-1981 Setipiprant R = CF3 QAV-039 MK-7246 ADC-3680 Phase III Phase II Phase III R = H QAW-680 Phase I Phase II Phase II/II Aryl acetic acids ? Indomethacin Weak agonist Boehringer Array Roche BI671800 ARRY-502 RG-7581 Phase II Phase II Phase I Phenoxyacetic acids HN N O HO O CF3 OMe AstraZeneca Panmira Panmira Amgen AZD-5985 or AM461 AM211 AMG-853 AZD-8075 Phase I Phase I Phase II Phase I/I 15 PK of carboxylic acids PK Half-life vs Volume 10 2. Ideal CRTh2 Acid 3. zone Zwitterion 1 Human PK profiles of Total body water volume 150 carboxylic acids 0.1 Adapted from Obach, Total plasma volume Drug.Metab.Disp. 4. 1. (2008), 36, 1385 Volume of distribution (L/kg) 0 6 12 18 24 Human terminal half-life (h) Techniques used to avoid rapid clearance: 1.Very high plasma protein binding (e.g. Diflunisal >99%) 2.Zwitterionic tissue distribution (e.g. Trovafloxacin, Vss 1.3 L/kg) 3.Organ distribution (e.g. Pravastatin, t½ 0.5 h, but concentrated in the liver) 4.Be small, be ignored by the liver (e.g. Probenecid, 80-90% renal excretion) O O F O OH HO O H N N N OH OH O H F H N OH 2 H F Diflunisal Trovafloxacin Pravastatin Probenecid PK t½ 10h PK t½ 11h PK t½ 0.5h PK t½ 5.9h 16 Our internal programme We want to find a once a day, oral, low dose (≤ 10 mg) CRTh2 antagonist for mild-moderate asthma . All antagonists are acids. Acids generally have poor PK . Clinical dosing of first CRTh2 antagonists – high dose and twice daily . Therefore, we chose to deliberately look for slowly dissociating CRTH2 antagonists: . to maintain receptor occupancy beyond normal PK and extend duration of action . to reduce the pressure of finding a carboxylic acid with desirable PK properties . to add the possibility of extra protection due to insurmountability against PGD2 burst release Residence time / Dissociation half-life seconds minutes hours days level PD PK time Mechanistic Surmountable Insurmountable Pharmacodynamic 17 Are there slow-dissociating CRTh2 antagonists? O HO H N F N S O O Ramatroban TM-30642 TM-30643 TM-30089 (CAY-10471) Structure not disclosed Merck Amira Pulmagen MK-7246 PGD2 AM432 ADC-3680 Dissociation Compound Potency Reference half-life* Ramatroban pA2 36 nM 5 min Mol. Pharmacol. (2006), 69, 1441 TM-30642 pA2 20 nM 8 min --- / / --- TM-30643 pA2 4 nM (12.8 years) --- / / --- TM-30089 pA2 (13.5 years) --- / / --- MK-7246 Ki 2.5 nM 33 min Mol. Pharmacol. (2011), 79, 69 PGD2 KD 11 nM 11 min Bioorg. Med. Chem. Lett. (2011), 21, 1036 AM432 IC50 6 nM 89 min --- / / --- ADC-3680 Ki 1.6 nM 20 min American Thoracic Society (ATS), May 17-22, 2013 18 In vitro dissociation assays CRTh2 GTPS binding Compound PDG2 .Membranes over-expressing human CRTh2 35 3 h .PGD2 agonism produces allows [ S]-GTPS binding, detected by radioactivity Ramatroban 0 → 10 µM Readout time 5000 Readout 4000 1 h 3000 Classical Surmountable 2000 Readout inhibition Ramatroban 1000 0 0.1 nM 10 nM 1 µM 100 µM PGD2 Concentration 1000 800 Readout Classical 15 min 600 Insurmountable 400 inhibition Readout TM-30089 200 (CAY-10471) 0 0.1 nM 10 nM 1 µM 100 µM PGD2 Concentration CAY-10471 0 → 5 µM 19 In vitro dissociation assays CRTh2 Surmountability vs Insurmountability Compound PDG2 .Membranes over-expressing human CRTh2 35 3 h .PGD2 agonism produces