Drug prevents bone loss in prostate cancer: Amgen

By Deena Beasley

LOS ANGELES (Reuters) - In a study, Amgen Inc's experimental drug denosumab reduced the risk of osteoporosis and fracture in men being treated with prostate cancer medicines that can cause bone loss, the company said on Monday.

But investors remain focused on upcoming data that will show whether the drug is effective in the larger market of osteoporosis patients, and Amgen shares were little changed in afternoon trading.

"We believe that denosumab has further demonstrated activity in cancer patients. However, we await this agent's pivotal FREEDOM study (in women with post-menopausal osteoporosis) later this year to answer questions regarding the agent's utility in that important setting," Robert W. Baird & Co analyst Christopher Raymond said in a research note.

Denosumab -- a bioengineered antibody that targets a protein involved with bone-destroying cells called osteoclasts -- is seen as key to Amgen's future now that growth of its flagship anemia drug franchise has waned due to safety concerns.

A three-year study of more than 1,400 men with non-metastatic prostate cancer undergoing androgen deprivation therapy showed denosumab produced greater increases in bone mineral density at the lumbar spine and non-vertebral sites than a placebo.

Men receiving denosumab also experienced less than half the incidence of new vertebral fractures than those receiving the placebo, Amgen said.

Both findings were statistically significant, it said. There were also fewer non-vertebral fractures in the denosumab patients, but the difference was not statistically significant.

"We're excited by the evidence of clinical activity -- which is reduction of vertebral fractures," said Roger Dansey, director of Amgen's denosumab oncology program. He said the study also confirmed previous trial results showing that denosumab increases bone mineral density.

In the study, about 6 percent of men treated with denosumab developed serious infections, compared with 5 percent of patients given a placebo.

Some earlier trials have shown an even higher risk of infection with denosumab, leading to questions about whether the drug's safety profile will be adequate for regulatory approval, particularly in the broad market of osteoporosis patients.

In an analysis published on Monday, Sanford Bernstein analyst Geoffrey Porges estimated that the denosumab Phase III trial in women with post-menopausal osteoporosis is likely to show that the drug reduces the risk of fracture by 45 percent to 55 percent compared with placebo.

"This improvement, while statistically significant, may not result in substantial market share when generic alendronate (Fosamax) is widely available," he said in research note.

Merck & Co's Fosamax, used for osteoporosis and other bone diseases, is an oral drug taken weekly.

Denosumab is given twice yearly by injection.

Amgen shares were off 2 cents at $51.00 on Nasdaq.

(Additional reporting by Susan Kelly in Chicago; editing by John Wallace)