Potassium Channelopathies: Consequences and Impact on Treatment December 4, 2010

Karen S. Wilcox, Ph.D. Department of Pharmacology & Toxicology Anticonvulsant Drug Development Program University of Utah

American Epilepsy Society Annual Meeting Disclosure

No Conflicts to Disclose

Funding: NINDS: RC1 NS069033 (KSW & JAW), NS41673 (KSW), NS44210 (HSW); Dumke Foundation (KSW) , Primary Children’s Research Foundation (KSW)

American Epilepsy Society Annual Meeting Potassium Channelopathies and Epilepsy

Ø Variety of seizure disorders and syndromes Ø Inherited channelopathy Ø De novo channelopathy Ø Acquired or transcriptional channelopathy Ø Loss AND gain of function mutations Inward Rectifier Family –KCNJ1•6, 8•16 KCNJ10 EAST Syndrome KCNJ11 DEND Syndrome

6 Transmembrane K+ Channels Twin Pore Channels –KCNK1•7, 9•18

S1S0S2 S3 S4 S5 S6

KCNN1•4 KCNT1•2 2+ + + + Voltage•Activated K+ Channels Ca •Activated K Channels Na •Activated K Channels

Shaker•related Family Eag•related family KvLQT•related family Slo•related family KCNA1•7, 10 (Shaker) KCNH1•8 KCNQ1•5 KCNMA1 Ca2+ and Voltage Activated KCNB1•2 (Shab) Channels KCNC1•4 (Shaw) KCNU1 pH sensitive channel KCNQ1•LQTS/SUDEP? KCND1•3 (Shal) KCNQ2, KCNQ3 • KCNMA1 • Benign Familial Neonatal Generalized Epilepsy and Convulsions KCNA1 Episodic Ataxia 1, Partial Paroxysmal Dyskinesia Seizures, SUDEP? KCND2 Temporal Lobe Epilepsy Brenner and Wilcox, in press Mutations in KCNQ2 and KCNQ3 Benign Familial Neonatal Convulsions (BFNC)

S1S0S2 S3 S4 S5 S6

Ø Generalized and partial seizures Ø Onset usually within first few days and can be as late as 13 months Ø Incomplete penetrance Ø Can also occur de novo Ø Spontaneous resolution Ø(with or without anticonvulsant treatment) Ø Normal psychomotor skill, development, and learning ability in most, but not all patients ØGreatly increased risk of developing adult onset epilepsy –BENIGN???? Seizure susceptibility gene?

(Singh et al, Charlier et al*) (Biervert et al, Schroeder et al, Lerche et al) KCNQ2 and KCNQ3 Subunits Co• Assemble to Form the M•channel

• Unique channel that is gated by voltage and GPCRs • Muscarinic ACh receptor activation will close channel and depolarize cell • Helps set and maintain resting membrane potential • Influences action potential firing rates Cooper, E. C. et al. Arch Neurol 2003;60:496•500. • Mechanism of action for retigabine (Ezogabine®) 69 Mutations in KCNQ2 Have Been Identified in Families with BFNC

Y284C N258S 283insGT E119G S122L 195insT,195del10insA A196V L243F R207W A306T R207Q 129splice M208V D212G Del E3•E11, R214W V250G Dup E3•E12 S247W G271V S247X W269X S105del3 R333Q,R333W Q323X Q78delC Del E9•3'utr L339R P387insC 372 splice K69insC 398del2 R353G 405splice Del E9•E17 T359K P410fs12X R153del1 H228Q R448X 416splice Del E13•E15 K21delGGTG E509splice E526D 522del13 M1V,M1T,Del E1•E5 544splice R553Q 867ins K554N 653del1 GGGCC 644delT 562ins5bp R588spliceL637R V589X R581X 866delG Singh et al., in Animal Models of Epilepsy: Methods and Innovations, Ed. S. C. Baraban, (2009) 709delT Only Four Mutations Have Been Identified in the KCNQ3 Gene in Families with BFNC

Singh et al., in Animal Models of Epilepsy: Methods and Innovations, Ed. S. C. Baraban, (2009) KCNQ2 Is Highly Concentrated at the Axon Initial Segment (AIS)

Pan et al., J Neurosci 26:2599 –2613, 2006 Neurons in Mice With a Kcnq2 Haploinsufficiency Are More Excitable

B6 control Szt1

S1S0S2 S3 S4 S5 S6

1.0 Szt1 control 0.8 B6 control 0.6 0.4 * 0.2 normalized frequency normalized 0.0 1 2 3 4 5 6 7 8 9 10 Otto et al, J.Neurosci., (2006) interstimulus interval number Retigabine Is Not as Effective in Mice With a Kcnq2 Haploinsufficiency

B6 wildtype Szt1 S1S0S2 S3 S4 S5 S6

10 uM RGB

10 uM RGB control 15 pA control 15 pA 150 ms 150 ms

140 pA

400 ms Otto et al, J.Neurosci., (2006) Retigabine Is Less Potent In Mice With a Kcnq2 Haploinsufficiency

Otto et al, Epilepsia, (2004) Therapeutic Implications of Mutations in KCNQ2 and KCNQ3

ØIncreased seizure susceptibility ØAre patients at risk following insults? ØAltered pharmacology has implications for clinical trials ØThe right compound for the right patient: Øpharmacogenomics Potassium Channelopathies and Sudden Unexplained Death in Epilepsy (SUDEP)

KCNQ1 (Kv 7.1): expressed in heart and CNS KCNA1 (Kv 1.1): expressed mainly in CNS

S1 S2 S3 S4 S5 S6 S0 SUDEP

ØPatients with epilepsy die unexpectedly at a rate up to 24 times greater than the general population ØSUDEP may account for up to 18% of all deaths in patients with epilepsy ØAES & EFA Joint Task force recommends discussing SUDEP with patients and families ØClinical risk factors for SUDEP: Øearly onset intractable epilepsy Ømales, aged 20•40 years Øgeneralized seizures Øexposure to multiple anticonvulsant medications Øpoor compliance with medications Potential Mechanisms Hypothesized to Result in SUDEP

Ø Intrinsic cardiac problem, e.g. LQTS mutations

Ø Cardiac failure mediated by autonomic dysregulation

Ø Apnea due to central respiratory depression Loss of Function Mutations in KCNQ1 Result in Long QT Syndrome and Cause Seizures in Mice

T311I

S1 S2 S3 S4 S5 S6< A340E S0

Ø Slow delayed rectifier potassium current (IKS) in human cardiac myocytes

Ø Not thought to be expressed in CNS KCNQ1 Potassium Channels and Seizures in Mouse Forebrain

Goldman et al., Sci Trans Med, 2009 KCNQ1 Potassium Channels in Mouse Vagal Nerve Nuclei

n. X

n.XI

Cortical Discharges Often Trigger Cardiac Asystole

Goldman et al., Sci Trans Med, 2009 KCNQ1 Potassium Channel Mutations in Heart and Brain

Ø Hundreds of LQTS mutations have been identified for KCNQ1 Ø Loss of function

Ø Seizure disorders have been observed with greater than expected frequency in patients with LQTS

Ø Excessive autonomic activity can influence cardiorespiratory function T311I

S1 S2 S3 S4 S5 < A340E S0 S6 Loss of Function Mutations in KCNA1 (Kv1.1) Can Result in Epilepsy

T226R A242P Ø T226R and A242P mutations in KCNA1 result in partial epilepsy S1 S2 S3 S4 S5 S0 S6 Øreduce expression or trafficking of channels Ø Kcna1 knockout mice have seizures and die prematurely Ø Enhanced excitability related to axonal repolarization and propagation EEG–ECG Recordings Reveal Interictal and Ictal Cardiac Abnormalities in Kcna1•/•

Glasscock, E. et al. J. Neurosci. 2010;30:5167•5175 KCNA1 Is Present In Vagus Nerve Axons: Enhanced Parasympathetic Activity in Knockout Mice?

Glasscock, E. et al. J. Neurosci. 2010;30:5167•5175 Therapeutic Implications of Potassium Channelopathies and SUDEP

ØScreen for heart rhythm disorders to reduce the risk ØFollow up with genetic screening and pharmacotherapy where indicated KCNJ11 (KIR 6.2; KATP) Channelopathy: Delay, Epilepsy, and Neonatal Diabetes (DEND) Syndrome

ØGain of function mutation Ø Neonatal•onset diabetes Ø Developmental delay Ø Neonatal seizures Ø Infantile spasms Shimomura, K. et al. Neurology 2007;69:1342•1349 Ø Intractable seizures KATP Gating

Shimomura, K. et al. Neurology 2007;69:1342•1349 Treatment for DEND with Glibenclamide

Ø Binds to the SUR receptor Ø Closes the channel Ø Depolarizes cells in pancreas and allows insulin release Ø Seizures come under control J Physiol 572.3 (2006) 617–624 Ø Development resumed

Shimomura, K. et al. Neurology 2007;69:1342•1349 Potassium Channelopathies: Consequences and Impact on Treatment

Ø A large number of familial and de novo channelopathies in potassium channels underlie, or are associated with, many types of epilepsy

Ø Both loss of function and paradoxically, gain of function mutations: Ø Missense/nonsense Ø Splicing mutations Ø Small and gross deletions Ø Small and gross insertions Ø Indels Potassium Channelopathies: Consequences and Impact on Treatment

Recent advances in genetics and animal models provide information to guide treatment Ø Reduce risk of SUDEP Ø Identify seizure susceptibility genes ØMany forms of epilepsy likely to be multifactorial Ø Novel drug targets and personal pharmacogenomics Ø Basic mechanisms underlying epilepsy ARS question to be placed here (if applicable)