Our Team


Michael Martin, Ph.D.

Chief Executive Officer

Dr. Martin is the President, Chief Executive Officer and a member of the Board of Directors.

Michael brings tremendous experience to Plexium as a scientific executive, global R&D leader, venture investor and corporate board member. Michael joined Plexium following his 12-year tenure at Takeda Pharmaceuticals, serving most recently as the Global Head of the Center for External Innovation where he was a key member of Takeda’s Leadership Team. While in this role, he was responsible for external research & development activities including Business Development, Search & Evaluation, Strategy & Operations, Academic Alliances, and Takeda Ventures, Inc. Prior to his most recent role at Takeda, Michael was President of Takeda Ventures, Inc., Takeda’s corporate venture capital company. He also previously held executive and scientific roles with Intellikine Inc. (acquired by Takeda), TargeGen, Inc. (acquired by Sanofi-Aventis), Arena Pharmaceuticals, Inc. (acquired by Pfizer) and Monsanto Corporation (acquired by Bayer).

Michael holds a Ph.D. in Medicinal Chemistry from University of Illinois, a M.S. in Analytical Chemistry and B.S. degrees in Chemistry and Mathematics. He has extensive experience as a corporate board member, for both private and publicly traded companies, and has acted as an advisor to several notable biotech investment funds in the United States, Europe, and Japan.

Stephen Mullennix

Chief Financial Officer
Stephen Mullennix

Stephen is the Chief Financial Officer at Plexium.

Stephen joined Plexium in 2022 to lead the Finance, Accounting and Investor Relations and other corporate functions at Plexium. He brings deep expertise in operational finance, capital markets and executive leadership roles.

Stephen joined Plexium from ProSciento, Inc., a leading Clinical Research Organization in the metabolic disease arena, where he served as CFO. Prior to ProSciento, Mr. Mullennix was CFO and COO of UroGen Pharma, Ltd (NYSE:URGN), a uro-oncology drug developer. During his tenure at UroGen, he led finance functions as the CFO, and then transitioned to COO as the company successfully launched JELMYTO, its first FDA-approved drug for urothelial cancer. Before UroGen, Mr. Mullennix was Chief Financial Officer and Senior Vice President of Operations at SolarReserve, LLC, and Managing Director at US Renewables Group, a private equity investment fund with more than $750 million of assets under management.He has been directly involved in $3.3 billion of public, private, equity, debt and M&A transactions.

Stephen earned his MBA from the Anderson School at University of California Los Angeles and BA in Economic Geography from Dartmouth College where he graduated Phi Beta Kappa and Summa Cum Laude.

Daniel Sipes

Senior Vice President, Head of Technology

Mr. Sipes leads Engineering and Operations.

Mr. Sipes leads the Engineering, Software, Informatics, and Compound Management groups at Plexium. Before joining Plexium, Daniel served as SVP, Strategy and Operations, Site Head San Diego at Strateos (formerly Transcriptic), where he was responsible for building and operating remotely controlled cloud labs for automated chemistry and biology. Before Strateos, he was Director, Advanced Automation Technologies at the Novartis Institutes for BioMedical Research (NIBR) San Diego location (formerly GNF). While at NIBR, Daniel developed and implemented new technologies for drug discovery, assay development, high throughput screening, automated cell culture, and protein production. Before that, he held positions focused on high throughput screening and compound management at Kalypsys, Inc. and Ligand Pharmaceuticals. Daniel started his career in the Hybridoma Laboratory at Genentech.

Dan received his BS in Molecular Biology from California State University, Sacramento, and an MS, in Immunology from the University of California, Davis.

Peggy Thompson, Ph.D.

Vice President, Biology

Peggy is the Vice President of Biology, leading the targeted protein degradation drug discovery efforts at Plexium.

Peggy joined Plexium in 2020 with more than 20 years of experience in drug discovery and development in the biotechnology industry. Prior to Plexium, she was a co-founder and Executive Director of Biology at eFFECTOR Therapeutics, where she established their technology platform for targeting dysregulated mRNA translation for supporting oncology drug development. She also led their eIF4A program (Zotatifin, Phase II) from concept to clinical development in solid tumor malignancies. Before that, Peggy served as the Director of Biology at Anadys Pharmaceuticals, Inc., where she held positions of increasing responsibility, including leading the drug discovery biology efforts and supporting the development of Setrobuvir until the acquisition by Roche Pharmaceuticals. Prior to Anadys, Peggy held positions at Biopraxis and the National Institutes of Health.

Peggy was an NIH postdoctoral fellow in Biophysics at the University of California, Berkeley, and completed her Ph.D. in Chemistry from the University of California, San Diego. She received her B.S. with Highest Distinction in Biochemistry from Washington State University.

Kevin Freeman-Cook, Ph.D.

 VP, Head of Medicinal and Computational Chemistry

Kevin is the Vice President of Chemistry, where he oversees Medicinal and Computational Chemistry as well as Library Chemistry, and leads the design and synthesis of targeted protein degraders at Plexium.

Kevin joined Plexium in 2022 with extensive pharmaceutical industry experience. Before joining Plexium, Kevin worked for twenty-two years at Pfizer, where he held positions of increasing responsibility, including Research Fellow. Kevin led numerous medicinal chemistry teams and drug discovery programs during this time. Kevin spent ten years in Groton, CT working in the therapeutic areas of allergy and respiratory disease, inflammation, antibacterials, oncology, and diabetes. In 2009, Kevin moved to Pfizer’s La Jolla, CA site, where he focused on medicinal chemistry design in oncology. Over these years, Kevin worked in and led teams that have nominated five compounds for clinical development across multiple therapeutic areas.

Dr. Freeman-Cook received his BA in chemistry from Carleton College in 1994 and a Ph.D. in organic chemistry from the University of Colorado Boulder in 1999.

Board of Directors

Mike Grey

Executive Chairman, Plexium

Cariad Chester

Partner, TCG X

Ian Peikon

Partner, Lux Capital

Rob Hopfner

Managing Partner, Pivotal Bioventure Partners

Gorjan Hrustanovic

Managing Director, BVF Partners L.P.

Eric Shiozaki

Partner DCVC

Brian Wong, M.D., Ph.D.

President and CEO, RAPT Therapeutics