Biotheryx Announces First Patient Dosed in Phase 1 Clinical Trial of BTX-9341, a First-in-Class, Dual Bifunctional Degrader of CDK4/6, as a Monotherapy and in Combination with Fulvestrant for HR+/HER2- Breast Cancer

SAN DIEGO, July 17, 2024 /PRNewswire/ -- 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, today announced 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. 

"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.

About Biotheryx, Inc.

Biotheryx is a clinical-stage biopharmaceutical company discovering and developing a portfolio of first-in-class protein degraders, including bifunctional degraders and molecular glues. Our focus is on deploying the differentiated potential of degraders towards validated targets in cancer and inflammatory disease. Members of our founding and scientific teams previously developed the IMiDs, the first U.S. Food and Drug Administration (FDA) approved modulators of Cereblon, the most widely validated E3 ligase involved in protein degradation, and we have applied our expertise in Cereblon binding to build our proprietary PRODEGY platform. Biotheryx's clinical program, BTX-9341, a bifunctional degrader of CDK4 and CDK6, began a Phase 1 clinical trial in the third quarter of 2024. Biotheryx's pipeline also includes BTX-10908, a first-in-class degrader of SOS1 for pan-KRAS mutant cancers and PDE4 degraders for inflammatory diseases. For more information, please visit biotheryx.com and engage with us on LinkedIn.

SOURCE Biotheryx, Inc.