August 23, 2004

Bright idea could doom cancer and viruses, say Purdue scientists

WEST LAFAYETTE, Ind. – Cancer and viruses may someday find themselves blinded by the light of therapies based on recent Purdue University chemistry research.

A team of scientists including Harry Morrison has developed a group of rhodium-based compounds that, when exposed to light, can kill tumor cells and deactivate a virus closely related to the West Nile and yellow fever viruses. Unlike the ordinary substances used for chemotherapy, these chemicals are not harmful to the body in general – they only become lethal to DNA when activated by light of a specific frequency. While therapies based on the discovery are likely many years away, the compounds could have potential as anticancer agents and for blood sterilization.

"We have proven in principle that light and chemistry together can destroy tumor cells and the Sindbis virus, a member of a group of viruses that cause encephalitis, fever and arthritis," said Morrison, who is professor of chemistry and former dean of Purdue's School of Science. "This research offers hope that someday we may be able to replace standard chemotherapy drugs with others that are far less generally harmful to a patient's body and guarantee safe, sterile blood for transfusions."

The research, which appears in the current (Aug. 23) issue of Inorganic Chemistry, was conducted by lead author Elton L. Menon along with Rushika Perera, Richard J. Kuhn and Morrison, all of Purdue, and Maribel Navarro of the Instituto Venezolano de Investigaciones Cientificas, Venezuela.

Chemotherapy has long made use of platinum-based compounds to poison cancer cells. These compounds bind DNA in the cellular nucleus and render the cell unable to reproduce, effectively destroying it. The trouble is, such chemicals also kill many other healthy cells in the body in the process.

"That's the reason cancer patients often lose their hair," Morrison said. "Hair cells, like many others in the patient's body, are also destroyed by these platinum-based chemotherapy drugs. So for a long time, physicians have sought other substances they have more control over. If we had a drug we could activate when it reached a certain place in the body – and nowhere else – it would reduce the stress on the rest of a cancer patient's system."

Morrison's group experimented with several different chemical complexes that use rhodium, a rare metal, instead of platinum. Eventually they found one compound that was able to damage DNA in living cells in a manner similar to platinum chemotherapy drugs, but with one exception – it remains benign until irradiated with a light beam.

"Anticancer therapies could, in theory, be developed using such photo-activated rhodium complexes," Morrison said. "The interior of the body is dark, but it might be possible to thread a fiberoptic cable through the arteries and flood a tumor with light. Some lasers are also capable of shining through tissue without damaging it, and they might also be candidates for light delivery."

The compound – known as D