Topline data readout from Phase 1a clinical trial expected in Q1 2026
SAN DIEGO, CA, November 17, 2025 – Biotheryx, Inc., a biopharmaceutical company focused on the discovery and development of first-in-class protein degraders for cancer and inflammatory diseases, today announced the completion of enrollment in the ongoing Phase 1a clinical trial of BTX-9341, a potent and selective CDK4/6 degrader, for the treatment of advanced and/or metastatic HR+/HER2- breast cancer in patients who have previously received CDK4/6 inhibitor therapy either in the adjuvant or metastatic setting.
The Phase 1a clinical trial began with dose escalation of BTX-9341 as a monotherapy, followed by a combination with fulvestrant. The primary objective of the Phase 1a trial is to assess safety, tolerability, pharmacokinetic and pharmacodynamic activity of BTX-9341 as a monotherapy and in combination with fulvestrant. Based on the recommended dose from Phase 1a, there will be a formal evaluation of efficacy in the dose expansion phase of the trial.
“Completing enrollment in the Phase 1a trial for BTX-9341 marks a significant step forward in advancing a very promising first-in-class treatment option for patients with HR+/HER2- breast cancer who have received prior CDK4/6 inhibitor therapy.” said Dr. Leah Fung, Chief Executive Officer of Biotheryx. “We are deeply grateful to the patients, investigators, and our team who made this possible as we continue to work together towards the common goal of improving patient lives.”
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 molecular glues and bifunctional degraders. Members of our founding and scientific teams previously developed the first U.S. Food and Drug Administration (FDA) approved modulators of Cereblon, the most widely validated E3 ligase involved in protein degradation. We have applied our expertise in Cereblon modulation to build our proprietary PRODEGY platform and pipeline of protein degraders for oncology and inflammatory diseases. Our approach deploys molecular glues to target undruggable proteins and bifunctional degraders to target validated proteins that conventional strategies, like protein inhibition, have insufficiently addressed. The Biotheryx pipeline includes BTX-9341, a first-in-class, oral, CDK4/6 bifunctional degrader that inhibits the transcription of CDK2 and Cyclin E, in FIH Phase 1a clinical studies in HR+/HER2- breast cancer patients who have progressed on CDK4/6 inhibitor therapy. Our pre-clinical pipeline advances undisclosed bifunctional degraders and molecular glues, including degraders as payloads for antibody drug conjugation. For more information, please visit www.biotheryx.com and engage with us on LinkedIn.
Contacts:
Biotheryx Investors/Media
David Pieters
[email protected]