The Dual Androgen Receptor and Glucocorticoid Receptor Antagonist CB-03-10 as Potential Treatment for Tumors that have Acquired GR-mediated Resistance to AR Blockade.

CB-03-10 (cortexolone 17α-valerate-21-propionate) is a synthetic steroidal compound derived from cortexolone (11-deoxycortisone), an intermediate in cortisol biosynthesis. Characterization of the activity of CB-03-10 and its main related compound CB-03-05 (cortexolone 17α-valerate) included binding to the androgen and glucocorticoid receptors (AR and GR), antagonism of AR and GR transcriptional activities, and screening for antitumor activity across a selected panel of human prostate and in triple-negative breast cancer cell lines. CB-03-10 cytotoxic activity in these cancer cell lines was in the low micromolar range and was primarily associated with induction of the apoptotic cascade via activation of caspases. The compound's potential for antitumor activity was verified in a murine xenograft model utilizing the AR-positive LNCaP prostate cancer cell line as well as in an orthotopic model utilizing AR-negative/GR-positive MDA-MB-231 breast cancer cell line. Orally administered CB-03-10 inhibited prostate tumor growth and orthotopically implanted breast tumor growth in these mice and maintained body weight, as compared with vehicle-treated mice. On the basis of AR/GR binding affinities, antagonism of androgen and glucocorticoid-dependent transcriptional activities, and AR/GR mRNA and protein expression, the mechanism of tumor growth suppression is related to AR and GR antagonist activities. Importantly, these compounds lack biologically relevant AR/GR agonist activities. Overall, these preclinical findings support the selection of CB-03-10 for further development as an anticancer agent in cases where resistance to AR-targeted therapy or chemotherapy, via upregulation of GR activity, continues to limit the efficacy and duration of clinical benefit with these interventions.