On December 23, Regor Therapeutics, a clinical-stage biotech company, announced authorization from the US Food and Drug Administration (FDA) to proceed with Regor's Phase 1 clinical development plans for RGT-419B.

RGT-419B is a new generation CDK2/4/6, small molecule inhibitor with an optimized kinase activity spectrum. It is expected to improve the safety of and combat the resistance to currently approved CDK4/6 inhibitors that are given in combination with endocrine-based therapy for treatment of pre/perimenopausal or postmenopausal women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced or metastatic breast cancer.

In cell model experiments, RGT-419B has demonstrated single agent activity with greater suppression of ER+ tumor cell growth when compared to abemaciclib and palbociclib. In ER+ breast cancer cells with acquired resistance to currently approved CDK4/6 inhibitors, RGT-419B has demonstrated full suppression of cancer cell proliferation. In these experiments, RGT-419B's tumor cell suppression was further augmented when combined with a selective estrogen receptor degrader or a PI3K signaling pathway inhibitor.

As a single agent and in combination with other approved therapies, RGT-419B will initially be developed for the treatment of patients with HER2-, ER+ breast cancer who have primary or acquired resistance to currently approved CDK4/6 inhibitors. As CDK4/6 inhibitors are widely adopted in clinical practice, refractory and relapsed patients previously treated by CDK4/6 inhibitors are becoming a greater and clinically significant unmet medical need. RGT-419B's clinical development programs will address this resistance to CDK4/6 and other hormone receptor modulation therapy, providing a new opportunity to improve the survival and quality of life in breast cancer patients with advanced disease.

RGT-419B is the first of many innovative oncology drugs being developed by Regor. Dr. Xiayang Qiu, Founder and CEO of Regor Therapeutics, said, "This milestone marks Regor's success in entering into the area of oncology therapeutics. Achieving an optimal selectivity profile against several CDKs by leveraging Regor's proprietary CARD platform, this innovative drug is entering clinical stage development in the U.S. We are excited by this opportunity to bring new and differentiated treatment options to the many patients suffering from breast cancer worldwide.