Phase 2 study of Capesaris (GTx-758) for the treatment of advanced prostate cancer

GTx Incorporated announced top line results of its Phase 2 trial evaluating Capesaris (GTx-758) for the treatment of advanced prostate cancer. In the trial, 60 healthy male volunteers (ages 18-40) were randomized to one of three Capesaris treatment arms, 600mg, 1000mg, or 1500mg. Subject compliance was determined by statistical comparison of trough Capesaris plasma concentrations. Subjects received oral Capesaris for 56 days or until they demonstrated castrate levels of testosterone (<50ng/dL) on two consecutive measures. The primary endpoint was serum total testosterone level. Key secondary endpoints included levels of serum free testosterone, the form of testosterone which prostate cancer cells utilize for growth, and sex hormone binding globulin (SHBG), a protein produced by the liver which strongly binds with testosterone and reduces serum free testosterone.

Men receiving 1000mg and 1500mg of Capesaris achieved medical castration with a median time to castration of 17 days. In the 1500mg cohort, 91% of treatment compliant subjects (10 of 11) met the endpoint of castration with a total serum testosterone <50ng/dL.  In the 1000mg dose group, 10 of 14 subjects (71%) who were deemed to be compliant and completed the study achieved castration. Castration was not achieved in men treated with 600mg of Capesaris.

The mean serum free testosterone level in compliant subjects was 0.34 pg/mL (range 0.15–0.96 pg/mL). The mean levels of serum free testosterone range from 2.1 – 2.3 pg/mL in castration studies evaluating luteinizing hormone releasing hormone (LHRH) agonist treatment in young males and in men with prostate cancer. Treatment with Capesaris resulted in significant increases in SHBG, with a mean change from baseline of 446% and 596% for men in the 1000mg and 1500mg cohorts, respectively.

Capesaris is a novel oral selective estrogen receptor alpha agonist being developed for the first line treatment of advanced prostate cancer.

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