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o ume Eitors Bernar Ferminí BiritT. Pries

3 Topics in Medicinal Chemistry

Editorial Board: P. R. Bernstein · A. Buschauer · G. J. Georg · J. A. Lowe · H. U. Stilz

Ion Channels

Volume Editors: Bernard Fermini · Birgit T. Priest

With contributions by B. Fermini · A. Gerlach · F. Van Goor · P. Grootenhuis · S. Hadida L. Kiss · D. S. Krafte · J. Krajewski · A. Lagrutta · B. T. Priest J. J. Salata · M. Suto · Z. Wang

123

Drug research requires interdisciplinary team-work at the interface between chemistry, biology and medicine. Therefore, the new topic-related series should cover all relevant aspects of drug research, e.g. pathobiochemistry of diseases, identification and validation of (emerging) drug targets, structural biology, drugability of targets, drug design approaches, chemogenomics, synthetic chemistry includ- ing combinatorial methods, bioorganic chemistry, natural compounds, high-throughput screening, pharmacological in vitro and in vivo investigations, drug-receptor interactions on the molecular level, structure-activity relationships, drug absorption, distribution, metabolism, elimination, toxicology and pharmacogenomics. In references Topics in Medicinal Chemistry is abbreviated Top Med Chem and is cited as a journal.

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ISBN 978-3-540-79728-9 e-ISBN 978-3-540-79729-6 DOI 10.1007/978-3-540-79729-6

Topics in Medicinal Chemistry ISSN 1862-2461

Library of Congress Control Number: 2008930785

c 2008 Springer-Verlag Berlin Heidelberg

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Volume Editors

Dr. Bernard Fermini

Pfizer Inc. MS 4083 Groton Laboratories Eastern Point Road Groton, CT 06340 USA Bernard.Fermini@pfizer.com

Dr. Birgit T. Priest

Department of Ion Channels Merck Research Laboratories Mail Code RY80N-C31 PO Box 2000 Rahway, NJ 07065 USA birgit_priest@merck.com

Editorial Board

Dr. Peter R. Bernstein

AstraZeneca Pharmaceuticals 1800 Concord Pike Fairfax Research Center B313 PO Box 15437 Wilmington, DE 19850-5437 USA

Prof. Dr. Armin Buschauer

Inst. f. Pharmazie Universität Regensburg Universitätsstr. 31 93053 Regensburg

Prof. Dr. Gunda J. Georg

University of Minnesota Department of Medical Chemistry 8-101A Weaver Densford Hall Minneapolis, MN 55455 USA

Prof. John A. Lowe

Pfizer Inc. MS 8220-4118 Eastern Point Road Groton, CT 06340 USA

Dr. Hans Ulrich Stilz

Aventis Pharma Deutschland GmbH Geb. G 838 65926 Frankfurt a.M.

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Preface to the Series

Medicinalchemistryisbothscienceandart.Thescienceofmedicinalchemistry offers mankind one of its best hopes for improving the quality of life. The art of medicinal chemistry continues to challenge its practitioners with the need for both intuition and experience to discover new drugs. Hence sharing the experience of drug discovery is uniquely beneficial to the field of medicinal chemistry.

The series Topics in Medicinal Chemistry is designed to help both novice and experienced medicinal chemists share insights from the drug discovery process. For the novice, the introductory chapter to each volume provides background and valuable perspective on a field of medicinal chemistry not available elsewhere. Succeeding chapters then provide examples of successful drug discovery efforts that describe the most up-to-date work from this field.

The editors have chosen topics from both important therapeutic areas and from work that advances the discipline of medicinal chemistry. For exam- ple, cancer, metabolic syndrome and Alzheimer’s disease are fields in which academia and industry are heavily invested to discover new drugs because of their considerable unmet medical need. The editors have therefore prioritized covering new developments in medicinal chemistry in these fields. In addition, important advances in the discipline, such as fragment-based drug design and other aspects of new lead-seeking approaches, are also planned for early vol- umes in this series. Each volume thus offers a unique opportunity to capture the most up-to-date perspective in an area of medicinal chemistry.

Dr. Peter R. Bernstein Prof. Dr. Armin Buschauer Prof. Dr. Gunda J. Georg Dr. John Lowe Dr. Hans Ulrich Stilz

Preface to Volume 3

The history of ion channel research is one that is rich and fascinating. It spans many different disciplines (biology, physiology, biophysics, bioelectricity, etc.), extends over more than two centuries, and today represents a mature and excit- ing field. Because of their prevalence and the critical role they fulfill in virtually all tissue types and organs, ion channels play a vital role in basic physiological functions, including muscle contraction, CNS signaling and hormone secre- tion among many. Not surprisingly, ion channels are drug targets for a number of therapeutic agents. At the other end of the spectrum, several human dis- eases have been linked to mutations or dysfunction of ion channels. In some cases, elucidating the specific ion channel dysfunction underlying the disease phenotype may provide a target for therapy. The recognized importance of ion channels in health and disease, combined with the potential to develop a broad range of new drugs for the treatment of ion channel-related diseases, has fu- eled the need to develop more suitable screening technologies accounting for their complex structure and function, and has led to a dramatic increase in the number of medicinal chemistry programs directed at ion channel targets.

Accordingly, this volume was written to introduce medicinal chemists to the field of ion channels. Its aim is to review recent advances in the field of ion channel-related diseases, and is meant to be accessible to graduate students, teachers, biologists, chemists and many other disciplines. Following an overview chapter summarizing the current state of ion channel screening technologies, five topics covering areas such as cancer, cardiac arrhythmias, cystic fibrosis, and pain have been selected, and the current state of knowledge ispresentedbyleadingexpertsintheirfieldinawaythatisaccessibletoall.Each chapter is structured to cover the biological rational for the target, the current status in the development of agents to treat the disease, and future perspective and challenges facing each therapeutic area. Hopefully, this effort will help to foster enhanced communication and collaborations between chemists and ion channel experts. Whether we are at the verge of a golden age for ion channel drug discovery remains to be determined, but what unfolds over the coming years should be of utmost interest for anyone involved in drug development.

May 2008 Bernard Fermini Birgit Priest

Contents

Recent Advances in Ion Channel Screening Technologies B.Fermini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Role of Kv7 and Cav3 Ion Channels in Pain D.S.Krafte·J.Krajewski·A.Gerlach·M.Suto . . . . . . . . . . . . . . 27

Potassium Channels: Oncogenic Potential and Therapeutic Target for Cancers Z.Wang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Pharmacological Rescue of Mutant CFTR Function for the Treatment of Cystic Fibrosis F.VanGoor·S.Hadida·P.Grootenhuis . . . . . . . . . . . . . . . . . . 91

On the Process of Finding Novel and Selective Sodium Channel Blockers for the Treatment of Diseases B.T.Priest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Kv1.5 Potassium Channel Inhibitors for the Treatment and Prevention of Atrial Fibrillation A.Lagrutta·L.Kiss·J.J.Salata . . . . . . . . . . . . . . . . . . . . . . 145

Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Recent Advances in Ion Channel Screening Technologies

Bernard Fermini

Pfizer Global Research and Development, Exploratory Safety Differentiation, Eastern Point Road, Mail Stop 4083, Groton, CT 06340, USA Bernard.fermini@pfizer.com

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Ion Channels as Drug Targets . . . . . . . . . . . . . . . . . . . . . . . . . 3

3 Historical Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Methods for Evaluating Ion Channels . . . . . . . . . . . . . . . . . . . . . 11 4.1 Radioligand Binding Assays . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 Fluorescence Assays Using Membrane Potential Dyes . . . . . . . . . . . . 12 4.3 Ion Flux Assays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

5 Automated Electrophysiology Technologies . . . . . . . . . . . . . . . . . . 15 5.1 Automated Electrophysiology–Planar Patch Technology . . . . . . . . . . . 15 5.2 IonWorks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.3 The IonWorks Quattro – Population Patch Clamping . . . . . . . . . . . . 19 5.4 PatchXpress 7000A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.5 QPatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.6 Port-A-Patch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.7 Non-planar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6 Future Perspectives and Challenges . . . . . . . . . . . . . . . . . . . . . . 22

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Abstract Ion channels play a vital role in basic physiological functions such as generation of electrical activity in nerves and muscle, control of cardiac excitability, intracellular signaling, hormone secretion, cell proliferation, cell volume regulation, and many other biological processes. Because of their prevalence and the critical role they play in virtually all tissue types and organs, ion channels are also involved in a number of pathophys- iological conditions. The recognized importance of ion channels in health and disease, combined with the potential to develop new drugs targeting ion channels in a broad range of diseases, has fueled the need to develop more suitable screening technologies account- ing for their complex structure and function. Ion channels have been neglected as drug discovery targets because of the inability to study large number of compounds or validate large numbers of unknown or mutant ion channel genes using traditional ion channel screening technologies. Therefore, several efforts were undertaken to automate and im- prove the throughput of electrophysiological methods. In this chapter, we will review a number of the more standard ion channel screening technologies currently used, in- cluding: (1) radioligand binding assays, (2) fluorescent assays using membrane potential dyes, and (3) ion flux assays, and emphasize some of the advantages and shortcomings of