Medivation, Inc. (MDVN) has formally begun its phase III trial of the investigational drug MDV3100 with men who have advanced prostate cancer. The clinical trial known as AFFIRM will evaluate the novel androgen receptor antagonist, MDV3100, in men with castration-resistant prostate cancer who were previously treated with docetaxel-based chemotherapy.

AFFIRM is a randomized, placebo-controlled, double-blind, multi-national trial that is expected to enroll approximately 1,200 men at sites in the United States, Canada, Europe, South America, Australia and South Africa. The primary endpoint of the trial is overall survival (the FDA’s gold standard). The secondary endpoints include progression-free survival, safety and tolerability.

MDV3100 works as an anti-androgen drug like bicalutamide (casodex) and it has shown to have an approximately five fold higher binding affinity for the androgen receptor (AR) compared to the commonly used antiandrogen, bicalutamide (casodex).

[1] MDV3100 has been shown to be clinically active in men with metastatic castration-resistant prostate cancer in a phase II trial. The PSA level decreased more than 50 percent in 40/65 chemo-naive patients and 38/75 chemotherapy-treated patients.[2]

Referring to the phase I and II studies, the study’s principal investigator Howard Scher, MD, Chief of the Genitourinary Oncology Service and the D. Wayne Calloway Chair in Urologic Oncology at Memorial Sloan-Kettering Cancer Center said, “… the declines in PSA observed at these lowest doses are encouraging and provide proof of concept that castration resistant prostate cancers can still be sensitive to alternative hormone therapies like MDV3100.”

Yet we do not know if PSA reductions will correlate with an improvement in overall survival, the standard endpoint used in this pivotal Phase 3 studies for hormone-refractory prostate cancer. Only time will tell.

[1] Tran C, Ouk S, Clegg NJ, Chen Y, Watson PA, Arora V, Wongvipat J, Smith-Jones PM, Yoo D, Kwon A, Wasielewska T, Welsbie D, Chen CD, Higano CS, Beer TM, Hung DT, Scher HI, Jung ME, Sawyers CL (May 2009). “Development of a second-generation antiandrogen for treatment of advanced prostate cancer”. Science 324 (5928): 787–90. doi:10.1126/science.1168175. PMID 19359544.

[2]2 Scher HI, Beer TM, Higano CS, Taplin M, Efstathiou E, Anand A, Hung D, Hirmand M, Fleisher M (2009). “Antitumor activity of MDV3100 in a phase I/II study of castration-resistant prostate cancer (CRPC)”. J Clin Oncol 27 (15s): abstr 5011.

Joel T Nowak, MA, MSW