A First-in-Class, Oral Progesterone Receptor Antagonist
ABOUT HORMONE DRIVEN CANCERS
Over 75,000 patients with metastatic breast, ovarian, or uterine (endometrial) cancers die per year in the United States. For many of these patients, continuous progesterone and estrogen signaling drives disease progression. Currently, only medicines that block estrogen are approved, meaning that progesterone signaling continues in those patients receiving anti-estrogen therapy.
Apristor (onapristone extended release) is an investigational medicine that prevents progesterone signaling by blocking the interaction between progesterone and its binding partner, progesterone receptor. Apristor is the only known full PR antagonist.
ROLE OF PR IN CANCER
Under normal conditions, progesterone is primarily responsible for the development of sex organs and for regulating the menstrual cycle. Cancer cells hijack progesterone to stimulate cancer cell proliferation, metastases, regeneration, and immune evasion - thus, leading to worse outcomes.
Monotherapy activity in a variety of patient populations with PR+ cancer, including first line metastatic breast cancer (56% ORR, 17.5 month DoR, 14 month mPFS), tamoxifen resistant breast cancer (25% ORR, 50% CBR), and heavily-pretreated Phase 1 population (17% CBR).
Early clinical studies employing an immediate release formulation of onapristone have shown that onapristone is well-tolerated except for transient, low grade enzyme elevations that may be attributed to plasma concentration fluctuations. Apristor (onapristone extended release) was developed to provide a more tightly controlled release of onapristone.