Experimental drug seems safe, effective against prostate cancer

A recent clinical trial concluded that the targeted therapy MDV3100 is both safe and effective for patients with castration-resistant prostate cancer—disease that no longer responds to hormone therapy. (Castration-resistant prostate cancer may also be called androgen independent or hormone refractory prostate cancer.)

In the trial, 140 men with castration-resistant prostate cancer received doses of MDV3100 ranging from 30 to 600 milligrams (mg) daily. Researchers used bone scans, PET imaging, and blood tests to assess the drug’s antitumor effects. Overall, more than half of the patients experienced a decline in prostate-specific antigen (PSA) levels of at least 50%, while 22% saw their tumors shrink. Over two-thirds of patients had partial remission or learned that disease that had spread to bone or soft tissue was no longer progressing.

Circulating tumor cells, cells that break away from the tumor and travel in the bloodstream, also decreased in 49% of patients, and more than 90% of patients who started therapy with favorable cell counts retained their counts throughout treatment. This is an important finding, given that post-treatment changes in tumor cell counts are often more predictive of survival than changes in PSA.

MDV3100 works by blocking testosterone from binding to the androgen receptor, which, in turn, prevents the receptor from entering a cell, binding to its DNA, turning on specific genes, and allowing the cell to grow. Ultimately, this process leads to cancer cell death, research shows.

Investigators established 240 mg as the maximum daily dose. Fatigue was the most common side effect, though some patients experienced nausea, constipation, diarrhea, and anorexia.

An international phase III clinical trial now under way will compare MDV3100 with a placebo in prostate cancer patients previously treated with chemotherapy. For more information about the trial and a list of participating medical centers, log on to www.clinicaltrials.gov and search for MDV3100.

Editor’s note: Several of the authors of this study are employed by, have stock in, or have received funding from Medivation, the maker of MDV3100.

Source: Scher HI, Beer TM, Higano CS, et al. Antitumour Activity of MDV3100 in Castration-Resistant Prostate Cancer: A Phase 1-2 Study. Lancet 2010;375:1437–46. PMID: 20398925.

Originally published September 2010; last reviewed March 31, 2011.