TY - JOUR T1 - Inhibition of Autophagy as a Strategy to Augument Radiosensitization by the Dual PI3K/mTOR Inhibitor NVP-BEZ235 JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.112.080408 SP - mol.112.080408 AU - George J Cerniglia AU - Jayashree Karar AU - Sonia Tyagi AU - Melpo Christofidou-Solomidou AU - Ramesh Rengan AU - Constantinos Koumenis AU - Amit Maity Y1 - 2012/01/01 UR - http://molpharm.aspetjournals.org/content/early/2012/09/18/mol.112.080408.abstract N2 - We investigated the effect of NVP-BEZ235 (Novartis), a dual PI3K/mTOR inhibitor currently being tested in phase I clinical trials, in radiosensitization. BEZ235 radiosensitized a variety of cancer cell lines including SQ20B head and neck carcinoma cells and U251 glioblastoma cells. BEZ235 also increased in vivo radiation response in SQ20B xenografts. Knockdown of Akt1, p110α, or mTOR resulted in radiosensitization, but not to the same degree as with BEZ235. BEZ235 interfered with DNA damage repair following radiation as measured by the Comet assay and resolution of γH2AX foci. BEZ235 abrogated the radiation-induced phosphorylation of both DNA-PKcs and ATM. Knockdown of either p110α or mTOR failed to decrease phosphorylation of DNA-PKcs, suggesting that the effect of the drug was direct rather than mediated via p110α or mTOR. Treatment of cells with BEZ235 also promoted autophagy. To assess the importance of this process in radiosensitization, we used the autophagy inhibitors 3-methyladenine and chloroquine and found that either drug increased cell killing after BEZ235 treatment and radiation. Knocking down the essential autophagy proteins ATG5 and Beclin1 increased BEZ235-mediated radiosensitization. Furthermore, BEZ235 radiosensitized autophagy deficient ATG5-/- fibroblasts to a greater extent than ATG5+/+ cells. We conclude that BEZ235 radiosensitizes cell and induces autophagy, by apparently distinct mechanisms. Inhibiting autophagy via pharmacologic or genetic means increases radiation killing following BEZ235 treatment; hence, autophagy appears to be cytoprotective in this situation. Our data offer a rationale for combining BEZ235 along with an autophagy inhibitor (i.e. chloroquine) and radiation in future clinical trials. ER -