Arno Therapeutics, Inc. has enrolled the first patient in a Phase I dose escalation study evaluating onapristone in post-menopausal women with progesterone receptor (PR) positive tumors, including breast, endometrial and other solid tumors. The Phase I trial is designed to identify the recommended Phase II dose and determine the overall safety profile of onapristone. Onapristone has the potential to be the first approved anti-progestin for oncology indications and provide chemotherapy-sparing treatment to cancer patients who express a specific biomarker, as detected by a companion diagnostic under development.

Onapristone is an oral, anti-progestin hormone blocker that has been shown in previous Phase II clinical trials to have anti-tumor activity in patients with breast cancer. In extensive pre-clinical testing, onapristone has demonstrated the ability to block the activation of the progesterone receptor. This mechanism is believed to inhibit the growth of breast, endometrial and other tumors.

The activated form of the progesterone receptor (APR) has the potential to function as a biomarker of anti-progestin activity. The Phase I study will evaluate onapristone in sustained release and immediate release formulations in up to six dose levels (10-50 mg BID and 100 mg QD) to identify the recommended Phase II dose. In addition, the study will gather data showing antitumor activity.

This multi-site trial is taking place in France and expected to enroll a total of 60 patients. The first patient has been enrolled by investigator Andrea Varga, MD at Gustave Roussy Institute of Oncology, Villejuif, France.