Biotheryx, Inc., a California-based biopharmaceutical company discovering and developing a portfolio of protein degraders with a focus on validated targets in cancer and inflammatory diseases, announced on Wednesday that the first patient has been dosed in its Phase 1 clinical trial evaluating BTX-9341.

BTX-9341, an investigational oral and bifunctional degrader of cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6), is being evaluated in the trial as a monotherapy and in combination with fulvestrant, for patients with advanced and/or metastatic hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer who have previously received CDK4/6 inhibitor therapy either in the adjuvant or metastatic setting.

The Phase 1 clinical trial will begin with dose escalation of BTX-9341 as a monotherapy, followed by a combination with fulvestrant and will conclude with dose expansion of BTX-9341 in combination with fulvestrant. The trial will assess safety, tolerability, pharmacokinetic and pharmacodynamic activity of BTX-9341 as a monotherapy and in combination with fulvestrant. Once the recommended Phase 2 dose of the combination has been determined, there will be a formal evaluation of efficacy in an expansion cohort.