Codenamed MDV3100, the drug is designed to treat men with castration-resistant prostate cancer for whom chemotherapy has failed.

The U.S. Food and Drug Administration last month granted the drug a priority review, a designation given to expedite the review of treatments that aim to cure serious diseases and fill unmet medical needs.

Medivation and Astellas will equally share profit and costs of developing and marketing the drug in the United States under a 2009 marketing agreement.

Chemically called enzalutamide, Medivation's drug works in a fashion similar to Johnson & Johnson's Zytiga.

Zytiga belongs to a new class of prostate cancer drugs that aim to prolong the life of patients by specifically targeting certain mechanisms that help tumors proliferate.

The American Cancer Society estimates that about 241,740 new cases of prostate cancer will be diagnosed and about 28,170 men will die of the disease this year.

Medivation's shares rose less than a percent to $99.53 in after-market trade. They closed at $99.04 on Friday on the Nasdaq.

(Reporting by Zeba Siddiqui in Bangalore; Editing by Sriraj Kalluvila; )

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