Synthetic scorpion venom helps to treat brain tumors

Venom used by a scorpion to paralyze its prey may be a potent weapon against malignant human brain tumors, according to a study released last week.

The study indicated that a synthetic version of a protein discovered in the venom of gigantic yellow Israeli scorpions, those live in the deserts of the Middle East and grow to about 4 inches long, targeted tumor cells but did not harm the healthy cells of brain cancer patients.

Dr. Adam Mamelak and colleagues at Cedars-Sinai Medical Center's Dunitz Neurosurgical Institute in Los Angeles had been testing the substance, designated TM-601, developed from a protein in the venom of the giant yellow Israeli scorpion.

"We're testing a new agent that has a lot of potential for patients who have had no meaningful treatments thus far," said Dr. Adam Mamelak, lead author of a report on the therapy in the August issue of the Journal of Clinical Oncology.

Other science experts discovered the venom protein has a unique affinity for malicious tumor cells and stays clear of normal tissue. Mamelak and fellow researchers thought it could be used like a guided missile to deliver radioactive iodine to the tumor cells.

For the experiment, the scientists recruited 18 patients with a recurrent glioblastoma multiforme, the most common and fatal brain tumor. The participants first had surgery to remove malignant gliomas, the lethal kind of brain tumor. After that doctors injected their brains with a solution of radioactive iodine and TM-601, the synthetic protein.

The solution bound almost exclusively to leftover tumor cells, suggesting that it could be combined with chemotherapy to fight cancer. Even with the low therapeutic dose of radioactive iodine, life was extended in eight of the 18 patients. In addition to this, two study patients were still alive nearly three years after the treatment.

This is the first time the therapy has been used in humans. "We are excited by these results," Mamelak, a neurosurgeon at Cedars-Sinai Medical Centre in Los Angeles, said. "If this can be effective, it might be the holy grail in treating these deadly brain tumors: It is safe and only targets malignant cells."

Because life expectancy for the 14,000 annual glioma patients in the United States is typically a matter of months, the results shore up animal research indicating that the venom protein may inhibit tumor growth even without a radioactive component, Mamelak said.

"Does that mean that the drug was miraculous? No," said Mamelak, "But we have shown that it is safe and that we should at least move forward."

The TM-601, which has an unusual ability to pass through the blood-brain barrier that keeps most chemicals from reaching brain tissue, was developed in the laboratory of Harold Sontheimer, a neurobiologist who heads the Civitan Research Center of the University of Alabama at Birmingham and was licensed to Transmolecular Industries, Inc., a Boston-based company which helped finance the study.

The TM-601 is one of numerous medicines recently derived from animal poisons.