A synthetic form of protein from the venom of Giant Yellow Israeli scorpions attacked cancer cells without harming the healthy cells of brain cancer patients who participated in the study.

The protein, TM-601, carried radioactive iodine directly to cancer cells left over following surgery to remove malignant gliomas, a lethal kind of brain tumor. In addition to its unusual transport ability, the protein appeared to have anticancer activity of its own, according to Dr. Adam N. Mamelak, lead author of the report.

No Evidence of Tumor in Two Patients

Dr. Mamelak, a neurosurgeon at Cedars-Sinai Medical Center in Los Angeles, explained that TM-601 is able to pass through the blood-brain barrier, an obstacle to most chemicals. It then binds to glioma cells, which are vulnerable to the radioactive iodine it carries. He speculated that it might also be synergistic, with the ability to increase the effect of other therapies.

About 17,000 Americans are diagnosed with gliomas each year. The tumors are extremely aggressive and deadly; life expectancy is typically a matter of months, with only 8 percent of patients surviving two years, and 3 percent surviving five years from diagnosis.

Median length of survival for the 18 participants in the latest study was 27 weeks. However, two patients, women in their early 40s, had a "complete radiographic response," meaning there was no evidence of residual tumor, according to magnetic resonance imaging scans. They were still alive beyond 33 and 35 months after surgery, despite the low doses of TM-601 they received, and radiation levels that were below expected therapeutic levels.

The treatment was essentially nontoxic. Analyses showed that most of the radioactivity delivered by the drug left the region within 24 hours of administration.

That which lingered was "tightly localized to the tumor cavity and surrounding regions, suggesting discrete binding to the tumor," according to the report. The drug was eliminated primarily through the urine, with radiation doses to the thyroid and other vital organs remaining extremely low and harmless.

Prevents Cancer Cell Invasion

Neurobiologist Harold Sontheimer of the University of Alabama at Birmingham developed TM-601. The venom blocks chloride channels in cells -- an action that allows the Giant Yellow Israeli scorpion to paralyze the cockroaches it preys on, Sontheimer explained. That process prevents cancer cells from invading surrounding tissue in humans.

Boston-based Transmolecular Industries, Inc., has been licensed to develop the synthetic scorpion venom protein, and it provided financial support for the study.

"Despite advances in surgical technology, radiation therapy and cancer-killing drugs, length of survival has remained virtually unchanged for patients with gliomas," said Keith L. Black, MD, interim chair of Cedars-Sinai's Department of Neurosurgery. "Only in the recent past have we begun to discover some of the molecular, genetic and immunologic mechanisms that enable these deadly cancer cells to evade or defy our treatments, and we are developing innovative approaches, such as this one, that capitalize on these revelations."

Trials are planned to see if the protein can also be effective against other types of tumors.

Synthetic scorpion venom is just one of several medicines recently derived from animal toxins. Experiments with snake venom as an anti-bleeding agent, sea snail venom as a painkiller, and Gila monster venom as a treatment for diabetes are ongoing.