DISCOVERY AND CHARACTERIZATION OF G PROTEIN-GATED, INWARDLY-RECTIFYING, POTASSIUM CHANNEL MODULATORS By Krystian Andrzej Kozek Dissertation Submitted to the Faculty of the Graduate School of Vanderbilt University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Pharmacology October 31, 2018 Nashville, Tennessee Approved: C. David Weaver Ph.D. (Mentor) Jerod S. Denton Ph.D. (Committee Chair) Corey R. Hopkins Ph.D. Danny G. Winder Ph.D. Charles C. Hong M.D., Ph.D. This work is dedicated to my loving wife Lindsay and my adorable son. Their love, unconditional support, and endless encouragement make my life an absolute joy. ii ACKNOWLEDGMENTS I would like to thank the Vanderbilt Medical School for the fantastic education during the preclinical years leading up to my graduate studies. It was during this time that I became acutely aware of just how phenomenal the concept of ions moving between cellular structures to generate electrical activity truly is. I am extraordinarily grateful to Dr. David Weaver for providing me the opportunity to study this phenomenon in his laboratory and alongside him at the bench. I am thankful for all the time he has taken to share his mind and for all his efforts to bring drug screening to Vanderbilt University, making it a world-class academic neuroscience drug screening campus. Dr. Weaver is the greatest example of an expert scientist among many diverse, challenging, and interesting fields. He wears multiple metaphorical hats each day as he pushes the boundaries of ion channel mechanisms, fluorescent probe development, optical imaging technology, and small- molecule development for targeted modulation of ion channels. Nevertheless, he always keeps his door open for questions from his students, and his patient words demonstrate a deep understanding of the mentorship he provides. The Weaver Laboratory is home to an incredible group of scientists with whom I am forever grateful to have studied. They have supported me throughout many of the most important events in my life and have been incredible lab mates, friends, critics, and professional colleagues. They all contributed to making the high-throughput screen I describe a reality and supported my scientific efforts often. They are all incredible and driven scientists. Thank you to Francis J. Prael III for your discussions about science and for bringing new techniques to the lab. Thank you to Dr. Brittany Spitznagel for lending a hand anytime times get tough in the lab. Thank you to Dr. Brendan Dutter, Dr. Susan Ramos-Hunter, and Dr. Kristopher Abney for their support throughout the many facets of research. Finally, thank you to Dr. Yu (Sunny) Du, who is always smiling and iii makes every day extra exciting through sharing of results, discussing philosophy, helping design experiments, and being an inspirational parent and role model. I have learned a lot from the people in the Weaver Laboratory, and I will never forget my time with you. I would like to thank Dr. Paige Vinson for her work in making the Vanderbilt High- Throughput Screening Core Facility an indispensable resource at Vanderbilt. Thank you to Corbin Whitwell, Emily Days, and all the High-throughput Screening Core Facility colleagues that have made an immense number of compounds available to researchers like myself. I would like to thank the Laboratory of Dr. Jerod Denton for developing and sharing the many ion channel-expressing cell lines, especially Dr. Sujay Kharade for his work and collaboration. I would like to thank the Laboratory of Dr. Corey Hopkins for the synthesis of analogs of the molecules described within. Thank you to the Vanderbilt Department of Pharmacology for creating one of the best places to study pharmacology, with a rich curriculum and cutting-edge roster of speakers, teachers, and students. Thank you also to the Vanderbilt Medical Scientist Training Program and its leadership team, past and present, for creating one of the best places in the world to train as a physician scientist. Special thanks to Dr. Chris Williams, Melissa Krasnove, Dr. Megan Williams, Dr. Terry Dermody, Dr. Michelle Grundy, Dr. Jim Bills, Dr. Larry Swift, and Dr. Lourdes Estrada. You have all helped shape the person I am today, and I am grateful. I would also like to thank my committee members, Drs. Jerod Denton, Danny Winder, Corey Hopkins, and Charles Hong for their support, guidance, and collaboration, all of which was essential to the completion of this body of work and my graduate studies. Thank you to Dr. Denton for serving as my committee chair and for his expertise in inwardly-rectifying potassium channels and his work developing models to study these channels. Thank you to Dr. Hopkins for his expert insight and guidance surrounding the development of analogs of compounds discovered through iv screening. Thank you to Dr. Winder for his support throughout my scientific efforts and for creating a vibrant community of addiction researchers at Vanderbilt University. And thank you to Dr. Hong, for his career discussions and for being an aspirational example of a physician scientist. I would like to acknowledge my support for this work from the National Institute of Mental Health (5R21MH099363) and the National Institute of General Medical Sciences (T32GM007347) of the National Institutes of Health. This research was supported by funds from the Vanderbilt University Pharmacology Department and Vanderbilt Institute of Chemical Biology. Research funding was also provided through the PhRMA Foundation’s Paul Calabresi Medical Student Research Fellowship. I would like to thank D. Joseph Tracy, currently at North Carolina State University, for believing that college freshmen ought to pursue an independent research project. In his laboratory, I first learned how to think critically, problem solve, conduct experiments, present data, and write scientifically. Thank you also to his wife Dr. Lisa Tracy, who, together with Joe, helped me choose my career path as a physician scientist. I wholeheartedly thank all those who have taught and inspired me along my journey towards a greater understanding of our beautiful world. v TABLE OF CONTENTS Page DEDICATION ........................................................................................................................... ii ACKNOWLEDGMENTS ........................................................................................................ iii LIST OF TABLES ..................................................................................................................... ix LIST OF FIGURES .................................................................................................................... x ABBREVIATIONS ................................................................................................................. xii Chapter 1: INTRODUCTION..................................................................................................... 1 Overview ............................................................................................................................... 1 A Historical Perspective ....................................................................................................... 2 Ionic Gradients of Living Cells............................................................................................. 3 Ion Channels Diversity ......................................................................................................... 7 Ion Channel Gating ............................................................................................................... 8 Physiological Relevance of Ion Channels........................................................................... 10 The Membrane Potential ..................................................................................................... 10 The Action Potential ........................................................................................................... 14 An Introduction to G Protein-gated, Inwardly-rectifying, Potassium Ion Channels .......... 15 GIRK Channel Composition and Expression ..................................................................... 18 G Protein-Coupled Receptors and Phosphatidylinositol 4,5-bisphosphate Regulate GIRK Channels ................................................................................................................ 21 Additional Regulators of GIRK Channel Function ............................................................ 22 Natural and Synthetic Modulators of GIRK Channel Trafficking...................................... 23 Information Gleaned from the Crystal Structure of GIRK2 Channels ............................... 24 GIRK Channels in Normal and Pathological Physiology ................................................... 25 A Brief Overview of Opioid and Alcohol Drug Abuse in the United States of America ... 28 Non-GIRK1-containing GIRK Channel Involvement in Processes Underlying Addiction and Drug Abuse .............................................................................................. 31 The Utility of Selective GIRK Channel Modulators .......................................................... 32 Previous Discoveries and Reports of GIRK Channel Activators ....................................... 33 Previous Discoveries and Reports of GIRK Channel Inhibitors ........................................ 36 Previous Efforts Identifying Non-GIRK1-containing GIRK Channel Activators .............. 37 Chapter 2: DISCOVERY