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Side Effects May Sideline New Osteoporosis Drugs

Estrens did build bone, but might also raise cancer risks, study finds

FRIDAY, Sept. 1, 2006 (HealthDay News) -- Experimental osteoporosis drugs called estrens do not perform as well as researchers had hoped, new animal studies suggest.

The drugs did build bone, but they also had adverse effects on reproductive organs and on human breast cancer cells, say researchers from Yale University School of Medicine and a French company called ProStrakan Pharmaceuticals.

The researchers "were not able to replicate many of the findings that were found in the original study reported in Science in 2002," said Ushma S. Neill, executive editor of the Journal of Clinical Investigation, which published the findings in its September issue.

According to Neill, who also wrote an editorial on the findings, the authors' conclusion is that estren drugs "should not be taken into human trials."

The study was partially funded by ProStrakan, a specialty pharmaceutical company that focuses on treatments for bone disease and other areas. Several of the co-authors work or have worked for the company.

The results of the current study are at odds with prior research.

"Estrens were touted in several [scientific] papers as the answer to osteoporosis in both men and women based on studies in mice," said lead researcher Roland Baron, professor of orthopaedics and cell biology at Yale University. One study, published four years ago, found that the compounds increased bone mass and bone strength in animals and had no adverse effect on reproductive organs.

The hope was that the estrens might replace the synthetic estrogens used in hormone replacement therapy (HRT). Millions of American women used long-term HRT to help protect bones and ease menopausal symptoms. But that all changed in 2002, when a major study found the therapy boosted risks for cardiovascular events and breast cancer.

In this new study, Baron and colleagues directly compared the new compounds with drugs called SERMs (selective estrogen receptor modulators). SERMs, a newer alternative to estrogens, are thought to display selectivity in the tissues they target, minimizing side effects to reproductive organs.

Every drug can have a downside, however. Chronic administration of tamoxifen, one of the most widely used SERMs, has been suggested to be associated with an increased risk for uterine cancer. That makes the search for a safe alternative more imperative, the researchers said.

In their study, Baron's team compared the effects in mice of several doses of SERMs vs. two estrens.

The results: Estrens prevented bone loss but caused enlargement of reproductive organs in both male and female mice. They also enhanced the proliferation of human breast cancer cells.

"It may be that, administered differently, one would find beneficial effects and no bad effects on the reproductive tract," Baron added. But for now, he said, his team has concluded that estrens provide "moderate protection" against bone loss, "but also strong negative effects on the uterus, breast and prostate, suggesting increased risk of cancer if transposed to humans."

Osteoporosis is considered a major public health threat for about 44 million Americans, or 55 percent of people age 50 and above, according to the National Osteoporosis Foundation. About 10 million Americans have osteoporosis and are at high risk for disabling fractures. Another 34 million are at risk for getting it because they have low bone mass.

More information

To learn more about osteoporosis, visit the National Osteoporosis Foundation.

SOURCES: Ushma Neill, Ph.D., executive editor, Journal of Clinical Investigation; : Roland Baron, D.D.S., Ph.D., professor, orthopedics and cell biology, Yale University, New Haven, Conn; September 2006 Journal of Clinical Investigation
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