Biotheryx Advances BTX-9341 CDK4/6 Degrader into Dose Expansion Phase for HR+/HER2- Breast Cancer
核心洞察
Biotheryx (搜索) has dosed the first patient in the dose expansion phase of its BTX-9341 clinical trial, a first-in-class CDK4/6 (搜索) degrader for HR+/HER2- breast cancer (搜索) patients who previously received CDK4/6 inhibitor therapy.
The randomized dose expansion study will enroll approximately 80 patients across two treatment arms to evaluate BTX-9341 in combination with fulvestrant, with Overall Response Rate as the primary endpoint.
BTX-9341 demonstrated superiority to CDK4/6 (搜索) inhibitors in preclinical models through targeted protein degradation and the ability to overcome key resistance mechanisms that limit current inhibitor approaches.
Biotheryx (搜索) has initiated the dose expansion phase of its clinical trial evaluating BTX-9341, a first-in-class CDK4/6 (搜索) protein degrader, marking a significant milestone in the development of a potentially transformative treatment for hormone receptor-positive, HER2-negative (HR+/HER2-) breast cancer patients who have progressed on CDK4/6 inhibitor therapy.
The company announced that the first patient has been dosed in the randomized dose expansion study, which is designed to evaluate the efficacy and safety of BTX-9341 in combination with fulvestrant. The trial is being conducted at multiple sites in the United States and is expected to enroll approximately 80 patients across two treatment arms based on the recommended dose identified in the earlier dose escalation phase.
Clinical Trial Design and Endpoints
The dose expansion study builds on the recently completed dose escalation phase that evaluated the safety, tolerability, pharmacokinetics and pharmacodynamic activity of BTX-9341. The primary endpoint of this study is the Overall Response Rate (ORR), with key secondary endpoints including the measurement of investigator-assessed Clinical Benefit Rate (CBR) and Progression Free Survival (PFS).
"We are pleased to have dosed the first patient in the dose expansion portion of our clinical trial evaluating BTX-9341 in combination with fulvestrant," said Dr. Leah Fung, Chief Executive Officer of Biotheryx (搜索). "The encouraging safety, pharmacokinetics, and preliminary activity observed in the earlier dose escalation portion of the study support advancing BTX-9341 into this next stage of clinical evaluation."
Differentiated Mechanism of Action
BTX-9341 represents a novel approach to targeting CDK4/6 (搜索), important targets for a range of cancers and clinically validated in HR+/HER2- breast cancer (搜索). Unlike traditional CDK4/6 inhibitors, BTX-9341 operates through targeted protein degradation, demonstrating superiority in preclinical breast cancer models through potent and highly selective catalytic degradation of CDK4 and CDK6, robust inhibition of CDK2 (搜索) and Cyclin E (搜索) transcription, cell cycle arrest, and ultimately superior in vivo efficacy in breast cancer xenografts.
The drug is differentiated from CDK4/6 (搜索) inhibitor approaches through its ability to overcome key resistance mechanisms that limit the impact of inhibitors in second line HR+/HER2- metastatic breast cancer. "We believe the differentiated mechanism of targeted CDK4/6 degradation has the potential to address resistance seen with currently available CDK4/6 inhibitors," Dr. Fung noted.
Upcoming Data Presentation
Biotheryx (搜索) will present results from its Phase 1A dose escalation study at the 2026 European Society for Medical Oncology (ESMO) Breast Cancer Annual Congress, taking place May 6-8 in Berlin, Germany. The presentation, titled "Dose optimization of BTX-9341, a first-in-class CDK4/6 (搜索) bifunctional degrader, in CDK4/6 inhibitor-pretreated HR+/HER2− advanced/metastatic breast cancer," will be delivered by Dr. Matthew Goetz, MD, from Mayo Clinic, Rochester, USA, during the Rapid Oral Session 2 on Friday, May 8, 2026.
Company Background
Biotheryx (搜索) 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 the founding and scientific teams previously developed the first U.S. Food and Drug Administration (FDA) approved modulators of Cereblon (搜索), the most widely validated E3 ligase involved in protein degradation. The company has applied this expertise to build its proprietary PRODEGY platform and pipeline of protein degraders for oncology and inflammatory diseases.