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SAN FRANCISCO ( TheStreet) -- Medivation ( MDVN) is halting development of the Alzheimer's drug Dimebon and ending a partnership with Pfizer ( PFE - Get Report) after the failure of a second late-stage clinical trial.

Investors shrugged off Dimebon's demise, with Medivation shares falling less than 1% to $55.46 in early Tuesday trading. Dimebon was largely written off after the repurposed Russian allergy medicine failed to benefit Alzheimer's patients in an initial phase III study announced in March 2010.

Medivation's future now rests with the prostate cancer drug MDV3100. Positive, top-line results from a late-stage study of MDV3100 were announced in November, sending Medivation shares soaring once again.

A full presentation of these MDV3100 data is scheduled for Feb. 2 at a cancer meeting sponsored by the American Society of Clinical Oncology.

Dimebon is another reminder that effective treatments for Alzheimer's disease remain largely out of reach. Government officials are meeting this week to lay out plans for a national plan to fight the neurologically degenerative disease, which robs people of their memory, ability to think ability to perform even the most basic tasks.

About five million people in the U.S. have Alzheimer's -- a number that is expected to triple by 2050. U.S. health officials hope new research efforts will help find new, effective drugs by 2025.

Later this year, Johnson & Johnson ( JNJ - Get Report) is expected to announce results from a late-stage study of its experimental Alzheimer's bapineuzumab. Pfizer and Elan ( ELN) share economic rights to bapineuzumab. Similarly, Eli Lilly ( LLY - Get Report) is also scheduled to announce top-line results from a late-stage study of their own Alzheimers drug solinezumab.

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.