About Us

Dr. Zhang was named chief executive officer in July 2021, having previously served as chief scientific officer and senior vice president of research. He joined Plexxikon in 2001, leading the company’s efforts in both computational chemistry and computational biology. Dr. Zhang assumed additional responsibilities in 2008 when the structural biology and informatics teams were merged to strengthen the company’s core expertise in structure-guided drug design. Dr. Zhang helped build the scaffold-based drug discovery platform at Plexxikon, and has been a leader and key contributor to the company’s wealth of discovery efforts, including the discovery of Plexxikon’s FDA-approved drugs, Turalio^® and Zelboraf^®. Prior to Plexxikon, Dr. Zhang was a scientist at Incyte Genomics where he developed an integrated genomics information system for mining disease-related genes and novel drug targets. Dr. Zhang earned his PhD in biomedical engineering from Boston University, and was a postdoctoral fellow at the University of California at Berkeley.

Dr. Spevak was named senior vice president of research in July 2021, having previously served as vice president of chemistry since August 2018. He joined Plexxikon in 2004 as a senior scientist and has led the chemistry group since 2009. Dr. Spevak is an inventor on 45 issued U.S. patents, and was a contributing member of drug discovery teams leading to 11 novel molecules entering human clinical trials, including Turalio^® and Zelboraf^®, Plexxikon’s FDA-approved drugs. Prior to Plexxikon, he was director of chemistry at Thios Pharmaceuticals. He began his industry career at Telik, holding a series of positions with increasing responsibility. Dr. Spevak earned his undergraduate degree from Northwestern University, and his PhD degree in chemistry from the University of California, Berkeley. He was a postdoctoral fellow at the Lawrence Berkeley National Laboratory.

Gideon E. Bollag, PhD

Chief Biologist

Dr. Bollag transitioned to a part-time role as chief biologist in July 2021, having served as chief executive officer since 2013. Previously, he had served as senior vice president of research and vice president of discovery biology. Dr. Bollag joined Plexxikon in 2002, and was instrumental in the discovery and development of both Turalio^® and Zelboraf^®, Plexxikon’s FDA-approved drugs. Prior to Plexxikon, he helped build drug discovery capabilities at Syrrx, Inc., where he was the director of cellular pharmacology. Before Syrrx, he held escalating positions at Onyx Pharmaceuticals, initially as one of the founding scientists and eventually senior director of small molecule therapeutics. While there, Dr. Bollag was involved in the Onyx collaboration with Bayer to discover BAY 43-9006 (Nexavar), now an approved cancer treatment. Prior to Onyx, Dr. Bollag held various scientific positions at Cetus, Inc. Dr. Bollag earned his PhD in biochemistry from the University of California, Berkeley.

Jackie Walling MBChB PhD is an experienced biotech pharma executive with expertise in global clinical development and strategy. She has more than 30 years’ experience in developing new medicines for cancer patients and has contributed in various leadership roles to the approvals of widely used agents such as gemcitabine, pemetrexed and talazoparib.

Dr. Jason Halladay has served as Vice President of Nonclinical Development since April 2020. His department integrates DMPK, preclinical and clinical pharmacology, toxicology, and pharmaceuticals and is responsible for the design and execution of translational strategy to bridge preclinical research and clinical studies. Dr. Halladay joined Plexxikon in 2017 to lead the DMPK and early formulation functions and strengthen the company’s core competencies in small molecule drug discovery and development. Prior to Plexxikon, he was Director of DMPK at Anacor Pharmaceuticals. Dr. Halladay began his industry career at Theravance and Genentech, holding a series of positions with increasing responsibility for 13 years. He has a strong interest in drug metabolism, transporters, pharmacokinetics, and hypothesis-driven research to identify molecules with drug-like properties and progress them to the clinic. He is an author on 45 publications and was a contributing member of drug discovery teams leading to several NCEs entering human clinical trials. Dr. Halladay earned his undergraduate degree from Southern Utah University, and his PhD degree in Pharmacology and Toxicology from the University of Arizona.

Michael Sterba was named vice president of clinical operations in April 2021, having previously served as director and senior director of clinical operations since joining Plexxikon in 2017. He and his clinical operations colleagues are responsible for management of clinical trial vendors and sites, pharmacovigilance, biometrics, medical writing, and trial master files. A key priority for Michael and his team has been support of the NDA for Plexxikon’s FDA-approved drug Turalio^®. Prior to joining Plexxikon, Michael was Executive Director of Clinical Operations at Rigel Pharmaceuticals, Inc. At Rigel from 2001 to 2017, he initially supported project management and toxicology before focusing for 15 years on various aspects of clinical trial execution for 10 small molecule NCEs, including the FDA-approved drug Tavalisse^®. He began his career at Sugen, Inc. from 1999 to 2001, where he contributed to preclinical evaluation of the FDA-approved drug Sutent^®. Michael earned his BS in pharmacology at the University of California, Santa Barbara.