Eating undercooked chicken contaminated with Salmonella bacteria can make a body mighty sick. But Salmonella also have been shown to be cancer fighters, and according to new research, when a genetically modified form of the bacteria is delivered along with radiation into mice bearing human skin cancers, the two therapies appear to work together to produce a potent antitumor effect.

A scientific paper on the research, written by John M. Pawelek, PhD, and colleagues, appears in the current issue of in the European Journal of Cancer.

"We were surprised at how effective the combination was," says Pawelek, senior research scientist in dermatology at Yale University School of Medicine, in a written statement. "With either X-rays alone or Salmonella alone, we could get another two or three weeks of suppression of the tumor growth in mice. But when we combined the two together, we got more than double the effects of the individual treatments."

The combination of high-dose X-rays and Salmonella delayed the formation of new tumors by up to six times over that seen in untreated animals, five times that seen in mice treated with Salmonella alone, and by about 50% longer than that of animals treated with X-rays alone, report Pawelek and colleagues at Yale and Vion Pharmaceuticals, both in New Haven, Conn.

Pawelek and colleagues previously had shown that Salmonella appear to be good at finding their way into tumors, a property that could make the bacteria effective as both a cancer-drug delivery system and as lethal weapons in their own right. In an earlier experiment, Pawelek reported that when naturally occurring Salmonella were introduced into mice that carried human melanoma tumors, the most serious and occasionally fatal form of skin cancer, the bacteria were found to congregate within the tumor at a level high enough to kill the mice.

Yet, the bacteria alone weren't sufficient to stop tumor growth altogether, Pawelek says in an interview with WebMD. "We found out that the Salmonella itself holds back the tumor, but it never wins. The Salmonella gives dramatic effects, but sooner or later, the tumor starts to come back, so we've got to do better than just the Salmonella alone."

Pawelek say he's not sure why the combined X-ray and Salmonella therapy seems to be so effective at slowing tumor growth in mice.

It's possible that the bacteria could interfere with the ability of tumor cells to repair themselves after they have been exposed to X-rays, or that X-rays themselves could "soften" up the cells, allowing Salmonella to come in for the "kill." A third possibility is that the presence of Salmonella might put the immune system on guard that the body has been invaded, and that X-rays might make tumor cells more vulnerable to immune attack, the authors speculate.

But a researcher who has collaborated with Pawelek on other projects cautions that the combined therapy may prove to be more useful for treating other forms of cancer.

"The work that John has done is very interesting, but you need to put it into context," says Mario Sznoll, MD, vice president for clinical affairs of Vion Pharmaceuticals, in an interview with WebMD. "Radiotherapy is not a standard treatment for melanoma, which is usually metastatic, so it's just representative of what one could do in other settings where radiotherapy is a useful modality."

Sznoll says his company has investigated the bacteria in combination with standard chemotherapy drugs in mice and found it to be just as effective as the radiation-Salmonella combination. Vion currently is working on a second generation of the bacteria modified to carry an enzyme that will convert a harmless drug into a cancer-killer when the drug is injected into the body.

The first generation of the modified bacteria currently is being investigated for safety in human clinical trials. If it proves to be safe, it can then be studied as a possible treatment for melanomas and perhaps other forms of cancer, Sznoll says.

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