GTx initiates Phase IIb trial of Capesaris for advanced prostate cancer

GTx, Inc. has announced the initiation of  a randomized Phase IIb trial of their selective estrogen receptor α agonist Capsesaris™ (previously known as GTx-758) versus leuprolide acetate (Lupron Depot®) as first-line androgen deprivation therapy for progressive and advanced forms of prostate cancer.

The study is designed to establish the dose of Capesaris required to maintain an effective level of medical castration. According to the media release issued by GTx on Monday this week, the trial will enroll 156 men with advanced prostate cancer. The patients will be randomized to receive one of two doses of Capesaris (either 1,000 or 2,000 mg orally each day) or an injection of Lupron Depot every 3 months. The primary endpoint of the study is the percentage of the patients that achieve castration by day 60. Secondary trial endpoints include maintenance of castration beyond 60 days, levels of free testosterone, sex hormone binding globulin (SHBG), luteinizing hormone, and prostate specific antigen (PSA), as well as the relative safety of Capesaris compared to leuprolide, including such factors as hot flashes, changes in libido, lipid profile, body composition, bone turnover markers, and bone mineral density.

The key question is whether a selective estrogen receptor α agonist like Capsesaris — which can be given as an oral tablet — can work as effectively and perhaps with fewer side effects than an injectable LHRH agonist like leuprolide acetate.

GTx also states in this media release that the company intends to initiate two additional Phase II studies in advanced prostate cancer patients:

  • The first additional study (to be initiated in the second half of 2011) will be designed to determine the loading dose of Capesaris required to achieve medical castration in > 90 percent of patients within 28 days.
  • The second study will investigate the activity of Capesaris as second-line therapy for patients with castration-resistant prostate cancer who are no longer responding to primary androgen deprivation therapy with an LHRH agonist.

Additional information about the current trial is available on the web site. It will be enrolling patients at 40 different centers, all in the USA.

Should this Phase IIb trial show that Capesaris has equivalent efficacy to Lupron Depot (and at least an equivalent safety profile), The “New” Prostate Cancer InfoLink would expect GTx to initiate one or more randomized, multi-center Phase III clinical trials to support an application for marketing approval of the drug.

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