Radioactive venom from an Israeli scorpion species might not be the first thing one would think of to treat a form of brain cancer called glioma. A company called TransMolecular that's pushing the idea, though, announced "favorable safety results" from a second-phase trial of such a substance (click for PDF).
The substance, called 131I-TM-601, is actually a synthetic version of a chemical in the scorpion venom. It's coupled with a radioactive isotope of iodine with an atomic weight of 131. The 131I-TM-601 binds with receptors in the cancer cells but leaves healthy cells alone, TransMolecular said. Then the radioactive decay of the iodine in close proximity to the tumor cells kills them.
The approach is similar to a treatment for thyroid cancer; the thyroid gland has an affinity for iodine, so injections of radioactive iodine-131 are concentrated at the cancer site. The Food and Drug Administration approved investigations of 131I-TM-601 in 2002.