Arno Therapeutics, Inc. and Leica Biosystems have entered into a co-development agreement for the development of a companion diagnostic, or CDx, for Arno's lead compound and personalized therapy, onapristone. This CDx test will help to identify patients who are APR positive and therefore most likely to respond to treatment with onapristone. This also has potential application in castration-resistant prostate cancer (CRPC).

In preclinical work sponsored by Arno, IHC testing on archived specimens has shown that approximately 40% of archived endometrioid cancer specimens and approximately 25% of archived breast cancer specimens were APR positive. Initial findings by Arno indicate that progesterone receptor (PR) was present in CRPC specimens and potentially active in a subset of tumors. Under the terms of the co-development agreement, Arno will sponsor and conduct clinical trials for onapristone.

Leica will develop and validate the CDx for APR with responsibility for ensuring the investigational CDx kit is ready, available and meets FDA and other health authority standards for a planned Phase II trial of onapristone in endometrioid cancer. The co-development program aims to achieve simultaneous approval and launch of onapristone and the CDx IVD for APR.