NEW YORK, May 15 (UPI) -- New York scientists have uncovered a natural cancer-fighting mechanism that could help make tumors more vulnerable to radiation therapy.
In the future, the scientists said, drugs could help boost the potency of anti-tumor radiation so cancer patients could receive lower doses of the dangerous rays and "toxicity to normal tissue may be reduced," researcher Richard Kolesnick, a molecular biologist at Memorial Sloan-Kettering Cancer Center, told United Press International
More than half of all people with cancer are treated with radiation. Unfortunately, "many tumors are very difficult to cure with radiation," radiation oncologist Ralph Weichselbaum at the University of Chicago told UPI.
Scientists already knew penetrating, high-energy doses of X-rays or particle beams could kill tumor cells directly by damaging their already haywire DNA. Still, for more than 40 years, researchers thought radiation therapies had little or no effect on healthy cells, such as the small, normal blood vessels that feed their diseased brethren.
However, in findings appearing in the May 16 issue of the journal Science, the medical investigators reveal the first genetic evidence that radiation therapy does damage these blood vessels. But in breaking them down, the radiation kick-starts a tumor-killing process.
"People assumed that damage to the DNA in the nuclei of tumor cells was the only way that radiation killed tumor cells. Our work shows that there is another radiation-induced pathway," Kolesnick said.
The researchers genetically deactivated a protein called "acid sphingomyelinase." Skin cancer growing in mice without this enzyme was resistant to radiation and did not shrink after they were blasted. The same tumors growing in mice that had the enzyme were aided by radiation as predicted, with the cells lining blood vessels developing a specialized form of programmed suicide.
"It's a very important finding," cancer researcher Amato Giaccia at Stanford University in California, who did not participate in this study, told UPI. He adds "it's a very provocative finding" since it suggests radiation zaps aimed specifically at these blood vessels could prove more effective than radiation at only the cancer. "It makes you rethink the dogma that's existed for many years."
"The potential clinical implications for radiotherapy are very important. The studies are elegant," Weichselbaum told UPI. "The blood vessels contribute to the curability of a tumor."
"Our results suggest possible new clinical approaches," radiation oncologist and co-researcher Zvi Fuks said. Methods to strip blood vessels of resistance to radiation "may provide new targets for tumor therapy," he explained.
The research team now plans to find ways to chemically enhance the effect of acid sphingomyelinase to sensitize tumors to the effect of radiation. Fuks said future experiments also need to tinker with radiation dose levels and timing of therapy.
Giaccia added that further testing is still needed on a wider range of tumors.
