On July 17, 2024 Biotheryx, Inc., a biopharmaceutical company discovering and developing a portfolio of first-in-class protein degraders with a focus on validated targets in cancer and inflammatory diseases, reported that the first patient has been dosed in its Phase 1 clinical trial evaluating BTX-9341, an investigational oral and bifunctional degrader of cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6), 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 (Press release, BioTheryX, JUL 17, 2024, View Source;breast-cancer-302198738.html [SID1234644940]).

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"BTX-9341 is a potent and selective CDK4/6 degrader that has shown significant anti-tumor activity in both CDK4/6 inhibitor naïve and resistant preclinical models. We are optimistic that it will meet a critical unmet medical need for patients with HR+/HER2- breast cancer who have received prior CDK4/6 inhibitor therapy," said Leah Fung, Ph.D., CEO of Biotheryx. "Dosing the first patient in this trial represents a significant milestone for Biotheryx, the patients we aim to serve and the scientists who have made this possible."

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.

"We are thrilled to have dosed the first patient with BTX-9341 at The START Center for Cancer Research," stated START Co-Founder and Co-Director of Clinical Research, Dr. Amita Patnaik, MD, FRCPC. "BTX-9341 is a highly novel, first-in-class, potent and selective degrader of CDK4/6, representing an innovative therapeutic approach. It has the potential to transform the care of patients with advanced and/or metastatic HR+/HER2- breast cancer, particularly those who have received prior CDK4/6 inhibitor therapies. This milestone is perfectly aligned with START’s mission to accelerate drug development and provide early access to cutting-edge anticancer therapies, bringing hope to patients and their families."

In preclinical studies, orally administered BTX-9341 demonstrated in vivo CDK4/6 degradation and improved anti-tumor activity as a monotherapy compared to current standard of care treatment regimens. BTX-9341 also demonstrated synergies with selective estrogen receptor degraders including fulvestrant, elacestrant and camizestrant in CDK4/6 naïve and resistant models.

About BTX-9341

BTX-9341 is a first-in-class, oral degrader of CDK4/6, important targets for a range of cancers and clinically validated in HR+/HER2- breast cancer. In preclinical breast cancer models, BTX-9341 demonstrated superiority to CDK4/6 inhibitors through potent and highly selective catalytic degradation of CDK4 and CDK6, robust inhibition of Cyclin E and CDK2 transcription, cell cycle arrest and ultimately superior in vivo efficacy in breast cancer xenografts. Beyond this increased efficacy potential, BTX-9341 is differentiated from CDK4/6 inhibitor approaches through the ability to overcome key resistance mechanisms that limit the impact of inhibitors in second line HR+/HER2- breast cancer.