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Theseus Pharmaceuticals Emerges from Stealth Mode, Raises $100M in Series B Funding

NEW YORK – Theseus Pharmaceuticals on Tuesday emerged from stealth mode and closed a $100 million Series B financing round led by Foresite Capital.

Other new investors that participated in the Series B round include Adage Capital Management, Boxer Capital, Farallon Capital Management, Longitude Capital, Nextech Ventures, Omega Healthcare Investors, Pontifax Venture Capital, Rock Springs Capital, and T. Rowe Price. Theseus's Series A investor OrbiMed also participated.

Simultaneous with the funding announcement, Boston-based Theseus said Michael Rome, managing director of Foresite Capital, has joined its board of directors.

Theseus is developing pan-variant tyrosine kinase inhibitors. The firm presented preclinical data this week on its lead candidate THE-630, a pan-variant KIT inhibitor, in gastrointestinal stromal tumors. The drug showed activity in vitro in tumors with KIT-activating mutations and resistance mutations.

Theseus plans to file an investigational new drug application for THE-630 with the US Food and Drug Administration this year and expects to begin a Phase I trial in gastrointestinal stromal tumors in the second half of 2021.

The company's pipeline also includes an EGFR inhibitor, which Theseus is developing to overcome first- or later-line osimertinib (AstraZeneca's Tagrisso) resistance driven by EGFR C797S mutations in non-small cell lung cancer patients.

"For many driver-oncogene targets, current standard-of-care kinase inhibitors have insufficient activity to cover the broad array of variants that could lead to resistance, so they are limited by constantly mutating cancer," William Shakespeare, president of research and development at Theseus, said in a statement. "At Theseus, we take a pan-variant approach to targeting oncogenes with kinase inhibitors specifically designed to retain their effectiveness even as cancer mutates. Using sophisticated assays, we can predict how cancers will change, enabling new therapies to stay ahead of future mutations and overcome the demonstrated burden of treatment resistance."