Four drugs used to treat HIV infection can inhibit a retrovirus recently linked to prostate cancer and chronic fatigue syndrome, researchers at Emory University/Atlanta Veterans Affairs Medical Center and the University of Utah said. The findings suggest that if XMRV (xenotropic murine leukemia virus-related virus) is proven to be a cause for prostate cancer or chronic fatigue syndrome, those illnesses may be treatable with drugs already approved for treating HIV. The results were published Thursday by the journal PLoS One. Discovered in 2006, XMRV has been detected in some prostate cancer patients' tumor biopsies by several investigators. However, its precise role in driving prostate cancer is unclear. A recent report detected XMRV in a majority of chronic fatigue syndrome patients, but these results have not been confirmed by other laboratories. 'Not all studies that have looked for XMRV have been able to detect it in prostate cancers or in samples from chronic fatigue syndrome,' says Ila Singh, associate professor of pathology at the University of Utah School of Medicine. 'We will need to see the results of clinical trials before these drugs can be used in a clinical setting.' Singh and Raymond Schinazi, professor of pediatrics and chemistry at Emory's Center for AIDS Research, and colleagues teamed up to test 45 anti-HIV compounds, some of these discovered by Emory researchers, and other antiviral compounds against XMRV in cell culture. The most potent drug against XMRV was raltegravir, produced by Merck and sold under the commercial name Isentress. The FDA initially approved raltegravir in 2007 only for persons whose HIV infection was resistant to other drugs, but in 2009 its approval was expanded to all HIV infected persons. Raltegravir represents a new class of antiretroviral drugs because it inhibits the integrase enzyme, preventing the virus from invading a cell's DNA. Besides raltegravir, three other compounds -- another integrase inhibitor and AZT and tenofovir DF, two reverse transcriptase inhibitors -- also inhibit XMRV replication. This suggests that these drugs could be used together in combination therapy, a particularly effective tactic against HIV that helps prevent the emergence of drug-resistant forms of the virus. 'Our study showed that these drugs inhibited XMRV at lower concentrations when two of them were used together, suggesting that highly potent 'cocktail' therapies might inhibit the virus from replicating and spreading,' Schinazi says. 'This combination of therapies might also have the added benefit of delaying or even preventing the virus from mutating into forms that are drug- resistant.' 