In follow-up experiments, the researchers showed that Fbxw7 binds to and degrades a protein called Myc, which fuels leukemic stem cells, and has long been associated with many other cancers and the recurrence of cancer after treatment. When Fbxw7 is mutated, Myc is left unchecked, they found, and the population of cancer stem cells swells. This insight also helps explain why healthy blood stem cells seem to "ignore" mutated Fbxw7. Unlike leukemic stem cells, healthy blood stem cells typically lie dormant until the body requires an emergency supply of blood and they rarely express Myc. "Normal blood stem cells express very little Myc because they are not cycling. A mutation does not affect the substrate because the substrate does not exist," says Dr. Aifantis. "Leukemia stem cells, however, do express Myc and Fbxw7 mutations increase its abundance."
The researchers then wondered if eliminating Myc could potentially block leukemia. Indeed, deleting the Myc gene in mice with leukemia depleted leukemic stem cells and stopped the growth of tumors. They achieved the same results in mice and human cell and bone marrow samples of T-ALL using a new class of cancer drug called a BET inhibitor that blocks Myc. "We found that the BET inhibitor could actually kill leukemia stem cells. And without stem cells, the leukemia simply cannot grow," says Dr. Aifantis.
The researchers believe they can use the BET inhibitor to target pediatric and adult T-ALL leukemia. This work was supported by a grant from the National Cancer Institute.
|Contact: Christopher Rucas|
NYU Langone Medical Center / New York University School of Medicine