BOSTON ( TheStreet) -- An experimental drug from Germany's Bayer and the Norwegian biotech firm Algeta extended the lives of advanced prostate cancer patients by zapping tumors that invade bone with small doses of radiation, according to data from a late-stage study presented this weekend.

The Bayer/Algeta drug known as Alpharadin was hailed as a major advance in prostate cancer treatment by experts at a European cancer research meeting in Sweden because the drug is the first to improve bone symptoms and prolong survival.

Bayer plans to seek U.S. approval of Alpharadin in the middle of 2012. The emergence of Alpharadin complicates and may even block efforts by Amgen ( AMGN) and Exelixis ( EXEL) to advance their respective prostate cancer drugs.

Amgen's Xgeva is approved as a treatment for bone-related complications of cancer and the company is now seeking FDA approval to expand the drug's use to include a claim that it can delay the spread of prostate cancer to bone. Xgeva, however, does not help prostate cancer patients live longer.

Exelixis' experimental cancer drug cabozantinib, like Alpharadin, specifically targets prostate cancer that spreads to bone, but has not yet demonstrated that it can prolong survival. Exelixis is seeking FDA permission to conduct a registration study of cabozantinib that would rely on pain reduction and bone scan resolution as primary endpoints and the basis for the drug's approval.

FDA may balk at Exelixis' request without data showing that cabozantinib also helps patients live longer, especially now that Alpharadin has set a new standard for treatment.

"Alpharadin raises the bar for Exelixis. They have to produce overall survival data now," said Sally Church, a cancer drug consultant with Icarus Consultants who also co-writes the widely followed Biotech Strategy Blog.

"Alpharadin's overall survival data doesn't change our strategy," said Exelixis spokesman Charles Butler, in an email response to questions about the Bayer/Algeta drug.

Bayer/Algeta's Alpharadin, also known as Radium-233 is a new type of drug that delivers small, short-ranged doses of alpha radiation directly to prostate cancer that has spread to bones. The so-called "alpha pharmaceutical" specifically targets bone lesions with its radiation because it contains radium, which like calcium, sticks to bones. As a result, Alpharadin doesn't negatively affect surrounding, healthy tissue.

Advanced prostate cancer most commonly spreads or "metastasizes" to bone, interfering with bone strength and leading to pain, fractures, disability and death.

"This is really practice changing, and after regulatory approval, I think this is going to be a major player in advanced prostate cancer," Dr. Jean-Charles Soria of Institut Gustave Roussy in Villejuif, France, told MedPage Today.

The Alpharadin results were presented at the 2011 European Multidisciplinary Cancer Congress (EMCC) in Stockholm.

Bayer and Algeta conducted the phase III study enrolling 922 men with advanced prostate cancer. The men enrolled in the study had all either received docetaxel chemotherapy or were ineligible for the standard therapy. All the patients also had prostate cancer that had spread to bone. Patients were randomized to either injections of Alpharadin or a placebo.

The study was stopped early after an interim analysis concluded that Alpharadin decreased the risk of death by 30% compared to placebo. Median overall survival was 14 months for Alpharadin-treated patients compared to 11.2 months for patients in the placebo arm.

Alpharadin significantly delayed the time to first skeletal related events in patients by 5.2 months (13.6 months compared to 8.4 months) and also decreased reports of bone pain.

Commonly reported side effects of Alpharadin included nausea, diarrhea, constipation and vomiting -- all at rates similar to placebo. Rates of blood-related toxicity and infection were relatively low dueto the targeted nature of Alpharadin, researchers reported.

"It takes only a single alpha particle to kill a cell, and collateral damage is minimized because the particles have such a tiny range -- a few millionths of a meter," said Dr. Chris Parker of London's Royal Marsden Hospital during a media briefing at the EMCC conference, as reported by MedPage Today. "We can be sure that the damage is being done where it should be, to the metastasis, and very limited elsewhere."

Alpharadin's relatively few side effects may make it an ideal drug to be combined with other new prostate cancer therapies, including Johnson & Johnson's ( JNJ) Zytiga or Medivation's ( MDVN) still-experimental MDV-3100, researchers said.

Zytiga was recently approved as a treatment for advanced prostate cancer in patients who, like those in the Alpharadin study, were previously treated with chemotherapy. Medivation is expected to announce soon results from a phase III study in the same prostate cancer patient population.

Dendreon's ( DNDN) Provenge is used in patients with less advanced prostate cancer.

--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.

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