Theseus Debuts with $100 Million Series B to for Targeted Treatment-Resistant Cancer Mutations

Rare Daily Staff

Theseus Pharmaceuticals emerged from stealth with the close of a $100 million series B financing to develop drugs that target treatment-resistant cancer mutations. 

Forsite Capital led the financing with participation from 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, as well as OrbiMed, which incubated Theseus and funded its series A round in 2018. In conjunction with the financing, Michael Rome, managing director of Foresite Capital, has joined the Theseus Board of Directors, which also includes Carl Gordon, general partner at OrbiMed.

Theseus is developing a pipeline of pan-variant tyrosine kinase inhibitors (TKIs) that can anticipate and inhibit new cancer mutations. The company’s lead candidate, THE-630, is a next-generation pan-variant KIT inhibitor in development for the treatment of refractory gastrointestinal stromal tumors (GIST).

At the American Association for Cancer Research (AACR) 2021 annual meeting, Theseus presented preclinical data demonstrating that THE-630 has potent activity against all classes of activating and resistance mutations observed in KIT-mutated GIST. These data showed that THE-630 was highly efficacious in tumor models containing mutations that confer resistance to approved TKIs.  These data highlight the potential for a pan-variant inhibitor such as THE-630 to deliver meaningful clinical benefit for patients with refractory GIST.

Theseus expects to file an IND before the end of the year. Theseus’ pipeline also includes a selective EGFR inhibitor to overcome C797S-mediated resistance to first- or later-line osimertinib treatment for patients with non-small cell lung cancer, and a third kinase target candidate for an undisclosed indication.

“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,” said William Shakespeare, co-founder and president of research and development at Theseus. “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.”

Photo: William Shakespeare, co-founder and president of research and development at Theseus