András Varró Department of Pharmacology and Pharmacotherapy University of Szeged, Hungary Albert Szent-Györgyi Medical Center 2007 The importantance of cardiac repolarization reserve in safety pharmacology Clinical significance of drug induced QT- prolongation and related syndromes: an update

Developmental cost Withdrawal cost: ~ 800 million USD ~ ? million USD Withdrawn drugs Terfenadine Astemizole Grepafloxacin Cisapride None approval or suspended development several Complicated approval Moxifloxacin Ziprasidone Approved with QT cautions in labeling numerous Re-labeling Thioridazine Droperidol Due to Torsades de pointes: Torsades de pointes RARE: with terfenadine 1/50000 „If you remember, I did mention possible side-effects.” „QT interval prolongation, with the potential for fatal arrhythmias, has been the single most common cause of withdrawal or relabeling of marketed drugs in the last decade” (Roden et al. J.Clin.Invest. 115: ; 2005)

Drugs That Prolong the Q-T Interval and/or Induce Torsades de Pointes Raymond L. Woosley, MD, Ph.D. Arizona CERT (Center for Education and Research on Therapeutics) Information from the FDA-approved drug labeling and the medical literature.

Closed and last revised: 03/01/2006

Primary drug effect (I Kr I HERG blockade) Secondary risk factors (effect amplifiers) –High doses or rapid administration –Metabolic inhibition –Impaired elimination –Bradycardia –Hypokalemia ; hypomagnesemia –Heart disease (CHF, LVF, diabetes) –Female gender 70 % –Concomittant ion-channel modifier –Undetected ion channel polymorphisms or mutation( LQT) Moxifloxacin (fluroquinolone) as positive control 6 – 10 ms QT prolongation E. Kevin Heist et al. Heart Rhythm 2005;2:S1–S8 Current clinical view of drug induced torsade pointes arrhythmia

QT lengthening Important antiarrhythmic mechanism Sign of dangereous side effect of various drugs

Gaborit et al. J Physiol (2007) pp 675–693 Regional differences

regular heart beat ERP 5 extrasystole 2

CONTROL 100 nM L-735, mV 200 ms 0 mV CONTROL 10 µM CHROMANOL 293B 0 mV PURKINJE FIBERVENTRICULAR MUSCLE The effect of I Ks block on the APD in dog right ventricular muscle and Purkinje fiber 50 mV 200 ms 0 mV Varro et al. J Physiol. 2000;523: Experimental demonstration of the repolarization reserve

TIME (min) APD (ms) nM L-735, ms 50 mV 0 mV nM L-735,821 E VERATRINE CONTROL APD CHANGE (%) 1 µM E µg/ml VERATRINE n=7 *  n=8 * The effect of I Ks block in pharmacologically lengthened APD in dog right ventricular muscle Varro et al. J Physiol. 2000;523: Experimental demonstration of the repolarization reserve

Conclusion in 2000 Varro et al. J Physiol. 2000;523:67-81.

Role of I Ks in the repolarization reserve in the human ventricle Jost et al., Circulation. 2005; 112:

Bilicki et al. Br J Pharmacol 2002; 137: mV 200 ms 0 mV CL = 5000 ms I Ks 0 mV 50 mV 200 ms I Kr I Kr + I Ks 0 mV 50 mV 200 ms CL = 5000 ms I K1 200 ms 50 mV 0 mV I Kr I Kr + I K1 200 ms 50 mV 0 mV EAD Multiple K + channel block and repolarization reserve Chromanol 293B Dofetilide + Chromanol 293B BaCl 2 Dofetilide + BaCl 2

Repolarization Reserve

200 ms I k1 CURRENT I NCX I Kr (H)ERG+miRP1 I Ks KvLQT1+minK Kir 2.1 (Kir2.x) I to Kv4.3+Kv1.4 KChIP2 CHANNEL PROTEIN I Ca Cav1.2+Cav  2  1 NCX I Na Nav1.5+Nav  1

Kääb et al. 2003; Eur Heart Journal Sotalol test The role of repolarization reserve in patients

Ibutilide test Kilborn et al. Circulation : II-673 Change in QTc (msec) Number of Subjects The role of repolarization reserve in patients Ibutilide test

Decreased repolarization reserve due to ventricular electrophysiological remodelling  Pharmacogenetics (LQT syndrome, ion-channel polymorphysm etc.)  Gender  Ischaemia  Renal failure  Diabetes  Drugs  Heart failure

Cumulative mortality Years QTc < 454ms QTc > 454ms QTc < 454ms QTc > 454ms QTc Interval as Guide to Select Those Patients With Congestive Heart Failure … Brendorp et al. Circulation 2001; 103: Placebo-treated patients Dofetilide-treated patients DIAMOND-CHF Trial and repolarization reserve

Rodriguez et al. JAMA 2001, Vol 285: Repolarization reserve and gender

Liu et al. Circulation. 2005;112: Cisapride rescues misprocessed mutant (LQT3) sodium channel trafficing

How to predict torsades de pointes arrhythmia ? HERG assay ? Action potential duration in dog Pf ? QTc ? QT dispersion ? APD triangularization (SCREENIT system – Hondeghem) ? QT/APD short term variability ?

Variability of Repolarization What does it mean? temporal beat-to-beat spatial Purkinje fiber, M-cell, Subendocardial, Subepicardial,Basal, Apex

How to measure? Varriability index Short-term beat-to-beat varriability Brennan et al. IEEE, 2001; 48: QT or APD Berger et al., Circulation, 1997 Poincaré plot

Thomsen et al, Circulation. 2004; 110: Different effects of sotalol and amiodarone – two drugs lengthening QT – on the short term repolarization variability

Combined I Kr plus I Ks block in the ventricular myocyte: beat-to-beat variability of repolarization Volders et al. Circulation. 2003;107:

TdP – TdP + Control Dofetilide (0.025 mg/kg) Dofetilide (0.025 mg/kg) + HMR-1556 (1 mg/kg) QT-interval n-1 (s) QT-interval n (s) Dog QT-interval n-1 (s) Dog QT-interval n-1 (s) Dog QT-interval n-1 (s) Dog QT-interval n-1 (s) Dog QT-interval n-1 (s) QT-interval n (s) Dog QT-interval n-1 (s) Dog QT-interval n-1 (s) Dog 8 Effects of I Kr -blocker dofetilide and I Ks -blocker HMR-1556 on QT-interval variability in conscious dogs Lengyel et al. Br J of Pharmacol 2007; advance online publication

* * Controls (n = 11) Heart failure patients (n = 11) QTQTcQT-STV ms QTQTcQT-STV Percentage change (%) Changes in cardiac repolarization in patients with heart failure * QTQTcQT-STV ms Controls (n = 41) Psychiatric patients (n = 54) * QTQTcQT-STV Percentage change (%) Changes in cardiac repolarization in patients treated with antipsychotic drugs

Drug indrustry Development of life saving drugs (antiarrhythmics, cardiotonics, AIDS drugs etc.) Endpoint: mortality Development of quality of life improving drugs (pl. antihistamins, CNS and GI drugs etc.) Endpoint: not mortality „I guess we should have tried it on the rats first.”

General conclusion 1.We should first reach a concensus what degree or any kind of mortality can be tolerated. 2.Before treatment we should assess the susceptability of the patients regarding possible QT lengthening (repolarization reserve) 3.In the future during drug development, to design and control safety pharmacology studies deeper cardiac electro- physiological background and further basic research is required. ”Are you coming hunting, or are you gonna sit around here all day inventing?”

Specific conclusion considering the role of repolarization reserve 1.Cardiac muscle has strong safety margin of repolarization („REPOLARIZATION RESERVE”). Decrease of this repolarization reserve does not necessarily lead to marked change of repola- rization but makes hearts susceptible to arrhythmias. 2.Multiple K + channel block can result excessive repolarization lengthening by eliminating the repolarization reserve and therefore it can associate with increased proarrhythmic risk. “Are you sure about this, Dave? It seems odd that a pointy head and long beak is what makes them fly.” REPOLARIZATION RESERVE