By changing its genetic code, scientists are turning the destructive energies of the herpes simplex virus on an even more formidable foe -- cancer.
Researchers say a treatment based on the altered virus can slow the spread of human stomach cancers in mice, with no noticeable side effects.
"I suspect that this therapy is going to be effective in a lot of cancers, not just gastric cancers," said study lead researcher Dr. Yuman Fong, of Cornell University and Memorial Sloan-Kettering Cancer Center, New York. His colleague, Dr. Joseph Bennett, presented the findings at the Experimental Biology 2000 conference held here this week.
Speaking with Reuters Health, Fong explained that scientists have long sought to harness the powers of the herpes virus, which enters and then destroys cells from the inside. But he said "the challenge to all researchers is -- what can we do to make these viruses more toxic toward cancer cells and less toxic to normal cells?"
Searching for a suitable viral candidate, Fong and Bennett's team examined a number of genetically-altered versions of the herpes virus until they settled on one in particular, called NV1020. According to Fong, NV1020 appears to be "dependent on cells that are replicating (and) making DNA very quickly" -- a characteristic of most cancer cells.
The researchers tested the virus' anti-cancer activity in mice injected with human stomach cancer cells. Fong explained that they chose stomach cancer because it is especially hard to treat once it has spread beyond the stomach wall.
The result? The virus "killed cancer cells very effectively," according to Fong. After three weeks, mice that had the modified virus injected into their abdomen developed half as many tumors as mice that did not get the virus. Furthermore, the therapy showed "no side effects that we could see."
Fong cautioned that the therapy is still new, and he stressed that humans may be more vulnerable to side effects from the therapy than mice since "rodents are slightly more resistant to the effects of herpes than man."
Nevertheless, human trials using modified herpes viruses to treat brain cancers are already underway, and Fong expects that trials involving patients with other forms of cancer will begin soon. Preliminary results on the effectiveness and safety of the treatment should be available within the next few years.
In the meantime, modified herpes viruses have already proven effective weapons against many types of tumor cells under laboratory conditions -- including colon, prostate, and pancreas cancer cells. "In the Petri dish," Fong said, "these agents will kill almost all types of human cancers."
