Scorpion venom targets cancer

Researchers have discovered that toxin possesses an affinity for tumor cells

July 30, 2006|By MCCLATCHY-TRIBUNE

ST. LOUIS -- The search for cancer cures can at times produce some curious treatments, but the latest study just might stun you.

Neurosurgeons at St. Louis University are among the doctors injecting radioactive scorpion toxin directly into the brains of patients with a deadly brain cancer.

"It's not like people said, `Scorpion venom - this must be a good way to treat cancer,'" said Dr. Alison M. O'Neill, vice president for medical affairs for TransMolecular Inc. The company, based in Cambridge, Mass., is developing the toxin as a chemotherapy drug.

Results from an initial study show that the toxin delivers radioactive iodine to brain tumors but leaves healthy brain cells unharmed. The study involved 18 people with recurrent brain cancer at three sites, including two people treated at SLU. The report will appear in the August issue of the Journal of Clinical Oncology.

The toxin used in the study is not raw scorpion venom. It is a part of a toxin protein from the giant yellow Israeli scorpion.

Using the toxin to treat brain tumors wasn't an immediately obvious application. Scientists at the University of Alabama, Birmingham were exploring how the toxin targeted nerve cells in the scorpion's prey, O'Neill said. The researchers noticed that the toxin also had an affinity for tumor cells.

The toxin attaches to proteins found on primitive nerve cells, said Dr. Richard D. Bucholz, director of the division of neurosurgery at St. Louis University. Brain cancer cells, called glioblastoma cells, are also primitive nerve cells, unlike normal brain tissue.

About 18,000 cases of brain cancer are diagnosed yearly in the United States. About half are glioblastomas, said Dr. Gerry Linette, a neural oncologist at Siteman Cancer Center and Washington University. Only 3 percent of people diagnosed with the cancer are alive five years later.

Glioblastoma is a fast-growing type of tumor that destroys surrounding brain tissue, Bucholz said.

Even with the very best therapy, glioblastoma is "a disease that, at this point, is nearly uniformly fatal," O'Neill said.

Most patients with glioblastoma live about 12 to 14 months after surgery and radiation treatment, Linette said. A new chemotherapy buys most patients couple of more months and may help a third of patients survive for two years or more, he said. But when the tumor comes back, patients have few treatment options, he said. "This study is an excellent example of an innovative approach that fills that void," Linette said.

The study was designed to administer a single dose of the radioactive protein and show that it was safe, O'Neill said. Patients in the study had surgery to remove as much of the tumor as possible. They healed for two weeks and then got an injection of toxin protein through a small catheter in the tumor cavity.

The study did not examine whether the toxin protein was effective, but researchers saw "tantalizing suggestions" that the radioactive toxin could improve survival, Bucholz said. Two of the patients in the study, including a woman Bucholz treated, were in remission for more than 30 months.

"That's almost unheard of," Bucholz said.

The second phase of the study - already in progress - will compare the fate of patients who get three injections of the radioactive toxin to that of people who get six doses. Bucholz has treated five people in this phase of the study.

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