The medicine used to wean addicts from heroin kills leukemia cells, a new study shows. Researchers found that methadone, the therapy used in drug rehabilitation, knocks out cancer cells that previously resisted chemotherapy and does so without affecting healthy cells. But critics question whether this laboratory study can translate to effective therapy in cancer patients.
Methadone works by attaching to opioid receptors in the brain. It then blocks other opioids, such as heroin, from reaching the receptors and producing the high craved by addicts. The idea that methadone might act against cancer surfaced in 1999, when researchers found that methadone killed lung cancer cells in lab tests.
Claudia Friesen, a molecular biologist at the University of Ulm in Germany, has now discovered that it also acts on leukemia cells, triggering their death. She and her team treated flasks of leukemia cells and normal human blood cells with 30, 20, 15, and 10 micromoles per liter of methadone. After 48 hours, the highest concentration of methadone killed almost all of the cancer cells but virtually none of the healthy blood cells, which don't have the specific receptor to which methadone binds. In another experiment, they found that methadone killed leukemia cells known to resist other anticancer drugs. The researchers report their findings in the 1 August issue of Cancer Research.
Friesen says the next step is to test methadone in animal models to see if it works against other forms of cancer and to better understand its side effects. But Scott Kaufmann, a cellular pharmacologist at the Mayo Clinic in Rochester, Minnesota, is skeptical that methadone could become a treatment. The dose that killed the leukemia cells, 30 micromoles per liter, would be toxic to humans, he says. So unless they can overcome the side effects, "it's a tantalizing idea, just like in lung cancer, but I don't think it has practical significance." Friesen says that unpublished experiments have shown that methadone kills tumors with smaller doses given daily.
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