The companies are expected to investigate the effects of the drug without a background of medical or surgical castration.
Astellas and Medivation intend to recruit around 60 patients in Europe to investigate MDV3100 at a dose of 160mg taken orally once daily for 24 weeks.
The primary endpoint of the trial is prostate-specific antigen (PSA) response.
Astellas Pharma Global Development president Steven Ryder said this is the second of two Phase 2 trials that they and their partner Medivation have initiated this year to evaluate the potential benefit of MDV3100 in both advanced and earlier stage prostate cancer patients.
"Investigating MDV3100 monotherapy is the next important step to potentially providing a new option for prostate cancer patients with earlier stage disease," Ryder said.
Medivation and Astellas agreed to jointly develop and commercialize MDV3100 in October 2009.
Subject to receipt of regulatory approval, the companies will jointly commercialize MDV3100 in the US and Astellas will have responsibility for commercializing MDV3100 outside the US.
Medivation received a $110m up-front payment upon entering into the collaboration agreement.
It is also eligible to receive up to $335m in development milestone payments, up to $320m in commercial milestone payments, 50% of profits on sales in the US, and tiered, double-digit royalties on sales outside the US.