Meet our Team

David J. Earp, J.D., Ph.D. - President & CEO

David J. Earp, J.D., Ph.D., has served as the President & CEO of Circle since October 2013. Previously, David held various roles at Geron Corporation (GERN), including chief patent counsel, chief legal officer and senior vice president of corporate transactions, building a broad IP portfolio and playing an integral role in numerous partnering, licensing and collaboration deals. He led the spin-out of Geron’s nuclear transfer technology into StART Licensing, Inc., and its subsequent acquisition by Viagen Corp. (Austin, Texas). He served on the boards of StART and Viagen, including as executive chairman of Viagen and led the sale of the company to TransOva Genetics (subsequently acquired by Intrexon). David was also a member of the board of directors of TA Therapeutics Ltd. (Hong Kong, PRC). He was previously a partner in the intellectual property law firm of Klarquist Sparkman, LLP (Portland, Oregon). He currently also serves as a board member of Sienna Cancer Diagnostics (Melbourne, Australia).
David received his B.Sc. (with first class honours) in microbiology from the University of Leeds, his Ph.D. in biochemistry and molecular biology from the University of Cambridge, and his J.D. (magna cum laude) from the Northwestern School of Law of Lewis and Clark College. He was a postdoctoral research fellow at the University of California, Berkeley / USDA PGEC.

Rajinder Singh, Ph.D.

Chief Scientific Officer

Rajinder Singh, Ph.D. - Chief Scientific Officer

Rajinder Singh, Ph.D., has served as our Chief Scientific Officer since July 2020. From 2016 to 2020, Dr. Singh held the position of Senior Vice President of Research & Pharmaceutics at ChemoCentryx – where he worked on the complement system (C5aR inhibition with avacopan), diverse chemokine receptors (such as CCR1, CCR2, CCR6, CXCR2, CXCR7) and immune-oncology with small molecules targeting PD-1/PD-L1. From 1998 to 2016, Dr. Singh held various management positions including Vice President, Chemistry at Rigel Pharmaceuticals, Inc., where he oversaw the advancement of numerous drug candidates from discovery to clinical development, which included the filing of numerous Investigational New Drug applications leading to the approval of Tavalisse (fostamatinib) a Syk kinase inhibitor in the areas of immunology and oncology. Prior to joining Rigel, Dr. Singh was a lead chemist at Chiron Corporation from 1994 to 1998. From 1992 to 1994, Dr. Singh was a Postdoctoral Fellow at Eli Lilly & Company. Dr. Singh received his Ph.D. degree in Organic Chemistry from the University of Oxford and B.Sc in Chemistry from University of Cardiff.

Jim Aggen, Ph.D.

VP, Medicinal Chemistry

Jim Aggen, Ph.D. - VP, Medicinal Chemistry

Dr. Aggen has over 20 years of experience in medicinal chemistry. He most recently served as the Senior Director of Medicinal Chemistry at Revolution Medicines and earlier in his career held various positions at Oligiasis, Achaogen, Chemocentryx, Gilead Sciences and Theravance, as well as Associate Professor of Medicinal and Natural Products Chemistry at Northeastern University. Dr. Aggen has successfully led teams engaged in targeted drug discovery against multiple oncology targets including mTORC1 and KRAS, and has experience in the medicinal chemistry of larger molecules, including as an inventor of the aminoglycoside antibiotic plazomicin, now marketed as Zemdri. He also served in the US Marine Corps Reserves. Dr. Aggen was awarded a doctorate in synthetic organic chemistry from the University of California, Irvine, where he studied under Prof. Richard Chamberlin.

Constantine Kreatsoulas, Ph.D.

VP, Research Informatics and Computational Chemistry

Constantine Kreatsoulas, Ph.D. - VP, Research Informatics and Computational Chemistry

Constantine Kreatsoulas, Ph.D., has served as our VP of Research Informatics and Computational Chemistry since February, 2021. Dr. Kreatsoulas joined Circle from GlaxoSmithKline (GSK) where he was the Head of US Molecular Design and Interim Head of Computational Toxicology. His responsibilities at GSK included leading structure-based drug design (SBDD) teams as well as the development of informatics tools for quantitative experimental data analytics and drug hazard identification. Previous to his time at GSK, Dr. Kreatsoulas was a Research Fellow at Merck & Co., Inc., where he focused on SBDD, molecular modeling, machine learning, and small molecule safety assessment. While a Postdoctoral Fellow at Bristol-Meyers Squibb, Dr. Kreatsoulas focused on machine learning in predictive toxicology. Dr. Kreatsoulas was awarded a doctorate in Chemistry from Princeton University, holds a Master’s degree in Regulatory Affairs and Quality Assurance from Temple University, and earned his Bachelor’s degree in Mathematics and Chemistry from New York University.

David C. Spellmeyer, Ph.D.

Advisor, Informatics and Computational Chemistry

David C. Spellmeyer, Ph.D. - Advisor, Informatics and Computational Chemistry

David Spellmeyer brings over 25 years of scientific leadership experience to Circle, having served in senior positions at several drug development and life science services companies. These roles include CTO & CIO at Nodality, CSO at Signature BioScience, and vice president of computational sciences at CombiChem(acquired by DuPont). David was involved in the development of peptoids as therapeutics at Chiron. He serves as an Executive-in-Residence at ShangPharma Innovation, which is an investor in Circle. He heads Interlaken Associates, a life sciences advisory company, and is Adjunct Associate Professor in the Department of Pharmaceutical Chemistry at U.C. San Francisco, where he completed his postdoctoral studies. David received his PhD in theoretical organic chemistry at U.C. Los Angeles and a BS in computer science and chemistry from Purdue University.

Pablo D. Garcia, Ph.D.

Sr. Director, Biology Research

Pablo D. Garcia, Ph.D. - Sr. Director, Biology Research

Pablo D. Garcia, Ph.D., is a cellular and molecular biologist with extensive experience in oncology drug discovery and preclinical development. With over 17 years of experience at Chiron Corporation and the Novartis Institutes for Biomedical Research in Emeryville, he made significant contributions to the areas of target identification and validation, the implementation of diverse discovery platforms and the management of a cancer biology discovery group. Pablo has led several drug discovery projects, including the PIM kinase inhibitor project at Chiron/Novartis. As the project leader, he oversaw all stages of preclinical development, from the initial validation of relevance to human disease to delivery of a drug candidate to clinical development. Pablo has a B.A. in Biology, a Masters in Genetics from Universidad Católica de Valparaíso (Chile) and a Ph.D. in Biochemistry from the University of California, San Francisco (UCSF).

Amy Cowgill

Director, Business Operations and Administration

Amy Cowgill - Director, Business Operations and Administration

Amy Cowgill brings a wealth of business and technology leadership experience to Circle, having successfully built solutions and organizational capacity in multiple industries for a range of organizations. Prior to joining Circle, Amy worked at Genentech in leadership roles within the Personalized Healthcare business unit and the Bioinformatics department. Prior to Genentech, Amy spent time at Tech and Financial Services organizations where she led initiatives as well as groups that delivered impactful solutions using both data and technology to enable company objectives. Amy holds a Master’s degree in International Development and a Bachelor’s degree in Mathematics.

Siegfried S.F. Leung, Ph.D.

Sr. Scientist, Computational Chemistry

Siegfried S.F. Leung, Ph.D. - Sr. Scientist, Computational Chemistry

Siegfried Leung, Ph.D., specializes in computational drug design and has over a decade of experience in macrocycle design and modeling. He joined Circle after undertaking postdoctoral research in the laboratory of Circle founder Matt Jacobson at UC San Francisco. His work there focused on the development of physics-based predictive models for passive membrane permeability and the application of these methods in designing cell permeable cyclic peptides. He was a key member of the Pfizer / Jacobson laboratory collaboration investigating the engineering of permeability into macrocyclic peptides, developing computational protocols for target-based design of permeable macrocycles. Siegfried received a B.S. (cum laude) from University of San Francisco and his Ph.D. in chemistry from Yale University under the mentorship of Prof. William Jorgensen.

Andrew T. Bockus, Ph.D.

Sr. Scientist, Chemistry

Andrew T. Bockus, Ph.D. - Sr. Scientist, Chemistry

Andrew T. Bockus, Ph.D., leads Circle’s chemistry team. Andrew is a chemist with over a decade of experience in the field of passively-permeable peptidic macrocycles. Prior to joining Circle Pharma, Andrew worked in the lab of Prof. Scott Lokey, a co-founder of Circle, where he synthesized natural product-like cyclic peptides and identified drivers of structure-permeability relationships in diverse peptidic scaffolds. He then developed applications for synthetic receptors and taught undergraduate courses in organic chemistry as a postdoc for Prof. Adam Urbach at Trinity University. Andrew holds a B.A. in Chemistry and Biochemistry from Skidmore College and a Ph.D. in Chemistry from the University of California, Santa Cruz.

Catherine Gleason, Ph.D.

Sr. Scientist, Biology Research

Catherine Gleason, Ph.D. - Sr. Scientist, Biology Research

Catherine Gleason, Ph.D., received her B.S. in biochemistry from the University of Washington and earned her Ph.D. from the University of Pennsylvania under the mentorship of Prof. Morris Birnbaum. She trained as a postdoctoral research fellow with Prof. Philip Cohen at the Medical Research Council’s Protein Phosphorylation Unit at the University of Dundee, UK, where she studied the interplay of protein phosphorylation and ubiquitylation in Toll-like receptor signaling and the innate immune response. Before joining Circle Pharma, she was an Adjunct Assistant Professor at the University of California San Francisco, investigating the mTOR signaling pathway in regulation of renal metabolism and ion transport.

Luis Hernandez

Manager, Chemistry

Luis Hernandez - Manager, Chemistry

Luis Hernandez is a member of Circle’s chemistry team. Luis has applied his continuous improvement and management experience from his previous role in a manufacturing facility to streamline macrocycle production and information workflows for Circle. Luis previously held positions at Ingredion, Inc. and Formulation Technology, Inc. He holds a B.S. in Chemical Biology from the University of California, Berkeley.

Breena Fraga

Scientist, Chemistry

Breena Fraga - Scientist, Chemistry

Breena Walton earned a B.S. in Molecular Synthesis at the University of California, San Diego. After studying total synthesis at the University of Pennsylvania under Prof. Madeleine Joullie and earning an M.S., she went on to work at E.I Dupont de Nemours in the Crop Protection division where she was a co-inventor on several patent applications for bicyclic azoles and helped move a product towards market. She subsequently worked in medicinal chemistry at Theravance Biopharma, and now at Circle Pharma in the chemistry team where her work focuses on advanced chemical synthesis and design.

Meisam Nosrati, Ph.D.

Scientist, Biochemistry

Meisam Nosrati, Ph.D. - Scientist, Biochemistry

Meisam Nosrati, Ph.D., is an interdisciplinary scientist with track record accomplishments in the fields of biochemistry, structural biology and organic synthesis. Meisam is passionate about contributing to public health via translational research. His postdoc at Emory University was on bacterial aminoglycoside resistance through ribosome methylation under the supervision of Prof. Graeme L. Conn. His Ph.D work at Michigan State University was focused on protein engineering to make novel proteins and protein probes under the supervision of Prof. James H. Geiger. He holds a B.S. and M.S. from University of Tehran in Chemistry and Organic Chemistry, respectively.

Nathan Dupper, Ph.D.

Scientist, Organic Chemistry

Nathan Dupper, Ph.D. - Scientist, Organic Chemistry

Nathan Dupper, Ph.D., earned his doctorate at UCLA studying Synthetic Organic Chemistry under Professor Ohyun Kwon. After completing his graduate studies, he worked as a postdoc in the laboratory of Professor Charles McKenna at USC. Here, he helped develop antifungal agents targeting the bromodomain containing protein Bdf1. Before joining the Circle Pharma team, he worked as a Synthetic Chemist at AIM Biosciences (WuXi). His work is currently directed toward chemical synthesis and design.

Miles W. Membreno

Research Associate, Biology

Miles W. Membreno - Research Associate, Biology

Miles Membreno has worked in both the Biology and Chemistry teams at Circle and currently focuses on developing and running assays for hit identification and lead optimization. Miles previously worked at CS Bio, where he focused on peptide purification. He holds a B.S. in Pharmacology from the University of California, Santa Barbara.

Miguel P. Baldomero

Sr. Research Associate, Chemistry

Miguel P. Baldomero - Sr. Research Associate, Chemistry

Miguel Baldomero is a member of Circle’s chemistry team where he focuses on macrocycle synthesis. Miguel previously held positions at CS Bio and Bachem Americas. He holds a B.S. in Chemistry from the University of Wisconsin, Oshkosh.