# Nassim Usman

> Nassim Usman is an organic chemist turned biotech operator who runs Totus Medicines, an Emeryville, California company using a DNA-encoded covalent library platform (OmniDEL) paired with machine learning to build small-molecule drugs against targets long considered undruggable. He took the CEO chair in December 2023 alongside a $66 million Series B, and its lead drug, TOS-358, is the first covalent PI3K-alpha inhibitor in the clinic. Over three decades he has moved from bench chemistry on RNA and ribozymes to the top jobs at Sirna Therapeutics, Catalyst Biosciences, and Principia Biopharma, plus a stint as a venture investor at Morgenthaler Ventures.

- **Role:** President & CEO at Totus Medicines
- **Organizations:** Totus Medicines, Gyre Therapeutics (Board), Catalyst Biosciences (former), Sirna Therapeutics (former), Principia Biopharma (former), Morgenthaler Ventures (former)
- **Education:** B.Sc. in Organic Chemistry, McGill University, Ph.D. in Organic Chemistry, McGill University, Post-doctoral fellowship, Massachusetts Institute of Technology (MIT)
- **Known for:** Named President & CEO of Totus Medicines and closed a $66M Series B (December 2023), Advanced TOS-358, the first and only covalent PI3K-alpha inhibitor, into clinical development, Led Catalyst Biosciences as President, CEO and Board member

## Career timeline

- **1990s** — Bench chemist and researcher working on RNA, ribozymes, and nucleic acid therapeutics
- **2000s** — Executive roles (CSO, COO) at Sirna Therapeutics, later acquired by Merck
- **2000s** — Venture capital investing at Morgenthaler Ventures
- **2010s** — President, CEO and Board member at Catalyst Biosciences (NASDAQ: CBIO)
- **2010s** — Involvement with Principia Biopharma, later acquired by Sanofi
- **2023-12** — Appointed President & CEO of Totus Medicines alongside a $66M Series B
- **2025-01** — Totus completes Phase 1 dose-escalation of TOS-358 and starts expansion trial
- **2026-03** — Totus presents Phase 1a TOS-358 data at ESMO TAT 2026
- **2026-05** — Totus reports 100% disease control rate for TOS-358 + fulvestrant in HR+/HER2- breast cancer at ESMO Breast

## Achievements

- Named President & CEO of Totus Medicines and closed a $66M Series B (December 2023)
- Advanced TOS-358, the first and only covalent PI3K-alpha inhibitor, into clinical development
- Led Catalyst Biosciences as President, CEO and Board member
- Held C-suite roles (CSO, COO, CEO, Principal Financial Officer) across multiple public and private biotechs
- Involved with Sirna Therapeutics (acquired by Merck) and Principia Biopharma (acquired by Sanofi)
- Published research on ribozyme and RNA chemistry
- Advanced multiple drugs into clinical development and executed multiple licensing deals across his career

## Latest updates

- **2026-05** — Totus Medicines reported early Phase 1b data showing a 100% disease control rate and class-leading safety for TOS-358 plus fulvestrant in HR+/HER2- breast cancer at ESMO Breast Cancer Congress 2026.
- **2026-03** — Totus presented Phase 1a clinical data for TOS-358, a covalent PI3K-alpha inhibitor, at ESMO TAT 2026.
- **2025-01** — Totus completed a Phase 1 dose-escalation study of TOS-358 and initiated an expansion trial; appointed Zelanna Goldberg as CMO.

## Links

- Website: https://totusmedicines.com
- LinkedIn: http://www.linkedin.com/in/nassim-usman-69750274
- Twitter/X: https://twitter.com/Totus_Medicines

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Profile page: https://yespress.io/nassim-usman
Published by YesPress — https://yespress.io
Last updated: 2026-07-01