Texas-sized molecule battles cancer.

Fancifully named after the Lone Star State, a light-sensitive drug called texaphyrin has shown success in treating metastatic brain cancer. Given intravenously to a patient, texaphyrin boosts the effectiveness of X-ray therapy and makes small clusters of cancer cells easier to see on magnetic resonance images.

Researchers at Pharmacyclics in Sunnyvale, Calif., are conducting preliminary tests of the drug on 17 people with metastatic brain cancer. The patients' median survival time after radiation treatments increased from 4 months to 1 year. "These early stage data are exciting and inspire us to keep going," says Jonathan L. Sessler of the University of Texas at Austin, who first synthesized texaphyrin 2 decades ago.

To treat brain cancer, the researchers use texaphyrin bound to gadolinium ions. Sessler says they are "still sorting out" how the drug works, but it may mop up free electrons, preventing them from neutralizing tumor-attacking hydroxyl radicals.

The group is also testing texaphyrin's value as part of a cancer treatment called photodynamic therapy, or PDT (SN: 1/14/89, p. 26). In PDT, a doctor gives the patient a light-sensitive drug that collects in tumors. Shining light on the tumors activates the drug and kills the cancer cells.

The drug most often used for PDT is Photofrin, which is activated by red light. Other PDT drugs being developed absorb infrared light, which has a longer wavelength and penetrates tissues more easily. Although texaphyrin is one of a dozen such drugs, says Thomas Dougherty of the Roswell Park Cancer Institute in Buffalo, N.Y., it absorbs the longest wavelengths of the group. "It's rather unique in that sense."