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Virus That Kills Cancer Cells Shows Promise
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Doctors have enlisted a live virus in the war on cancer, and it appears to be moderately effective in killing cancer cells but not healthy ones, doctors report in preliminary research out Monday.

The therapeutic germ is a genetically altered strain of adenovirus, a family of cold viruses. The virus is chemically weakened but not killed, so that it can be given in low doses. The virus then multiplies, filling infected cancer cells with offspring until the cells burst open and die.

In the new study, researchers tested the virus, called ONYX-015, in 35 patients with colon cancers that had spread to their livers. They infused the virus directly into the artery that nourishes the liver. The treatment seemed to slow tumor growth safely in 28 patients given high doses.

The high-dose patients survived an average of one year, six months longer than expected. "No one was cured," says the study's lead researcher, T.R. Reid of the Palo Alto Veterans Administration Medical Center. "But we saw some things that indicated we weren't harming the liver and, in some patients, we saw tumors regress."

What makes the approach promising is that the virus selectively infects cells lacking a certain tumor-fighting gene, Reid says. This gene, p53, alerts the cell to genetic abnormalities, especially those that prompt uncontrolled cell replication.

When p53 identifies a potentially cancerous cell, it prompts the cell to fix itself or commit suicide. Up to two-thirds of cancer cells have abnormal p53 function. That means the virus, made by Onyx Pharmaceuticals of Richmond, Calif., may affect a range of cancers.

"This could be a new form of chemotherapy that kills cancer cells without killing normal ones," says another study author, Daniel Sze of Stanford University School of Medicine. Sze reports the results Monday at an annual meeting of the Society of Cardiovascular and Interventional Radiology in Baltimore.

Most chemotherapy agents kill rapidly dividing cells, whether they're cancerous or not. That's why chemotherapy makes people sick and causes their hair to fall out. Mindful of chemotherapy's discomfort - and failure rates - doctors have spent decades searching for drugs that will kill only cancer cells. Newer drugs, including Rituxin, Herceptin and Gleevac, target specific features of certain types of cancer cells, but not a broad range of cancers.

ONYX-015 also has been tested in head and neck tumors but wasn't potent enough as a stand-alone therapy. Chemotherapy was administered as well, says Dawn Willis, chief scientific officer of the American Cancer Society.

Nevertheless, she calls the new results promising.

"These were very sick patients," Willis says. "Extending their lives from six months to a year, and with good quality, is not a bad thing. It's clearly not a cure at this stage."
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