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Virus Shows Promise as Prostate Cancer Treatment

‘Retargeted’ viruses attack only cancer cells, leave normal cells unaffected (Feb. 25)

A recombinant Newcastle disease virus kills prostate cancer cells, including hormone-resistant cells, but leaves normal cells unaffected, according to an article published online in the Journal of Virology. A treatment for prostate cancer based on this virus would avoid the adverse side effects typically associated with hormonal treatment for prostate cancer, as well as those generally associated with cancer chemotherapies, says corresponding author Dr. Subbiah Elankumaran.

Newcastle disease virus kills chickens but does not harm humans. The oncolytic virus hones in on tumors and has shown promising results in human clinical trials for various forms of cancer. However, successful treatments have required multiple injections of large quantities of virus.

The researchers addressed this problem by modifying the virus’s fusion protein. Fusion proteins fuse the virus envelope to the cell membrane, thereby allowing the virus to enter the host cell. These proteins are activated by being cleaved by cellular proteases. The researchers modified fusion proteins so that they could be cleaved only by prostate-specific antigen (PSA), a protease. These “retargeted” viruses interact only with prostate cancer cells, thereby reducing the amount of virus needed for treatment.

Retargeted Newcastle disease virus has potential advantages over other cancer therapies, according to Elankumaran. First, its specificity for prostate cancer cells means it does not attack normal cells, thereby avoiding the adverse effects of conventional chemotherapies. In previous clinical trials, “only mild flu-like symptoms were seen in cancer patients,” even with large doses of naturally occurring strains, Elankumaran said. Second, the retargeted virus may provide a new treatment for hormone-refractory patients, without the side effects of testosterone suppression that result from hormonal treatments.

Sources: American Society for Microbiology; February 25, 2013; and Journal of Virology; January 23, 2013.

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