Dual Phosphoinositide 3-Kinase/Mammalian Target of Rapamycin Blockade Is an Effective Radiosensitizing Strategy for the Treatment of Non-Small Cell Lung Cancer Harboring K-RAS Mutations

Non-small cell lung cancer (NSCLC) is a leading cause of cancer-related death worldwide. NSCLC often harbors oncogenic K-RAS mutations that lead to the aberrant activation of several intracellular networks including the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway. Oncogenic K-RAS predicts poor prognosis and resistance to treatment with ionizing radiation (111). Oncogenic K-Ras expression in the respiratory epithelium is sufficient to initiate NSCLC tumorigenesis, which requires the catalytic subunit of PI3K. Thus, effective inhibition of the PI3K signaling should lead to significant antitumor effects. However, therapy with rapamycin analogues has yielded disappointing results due in part to compensatory up-regulation of AKT. We hypothesized that dual PI3K/mTOR blockade would overcome these limitations. We tested this hypothesis with BEZ235, a novel dual PI3K/mTOR inhibitor that has recently entered clinical development. We found that BEZ235 induces a striking antiproliferative effect both in transgenic mice with oncogenic K-RAS-induced NSCLC and in NSCLC cell lines expressing oncogenic K-RAS. We determined that treatment with BEZ235 was not sufficient to induce apoptosis. However, we found that dual PI3K/mTOR blockade effectively sensitizes NSCLC expressing oncogenic K-RAS to the proapoptotic effects of IR both in vitro and in vivo. We conclude that dual PI3K/mTOR blockade in combination with IR may benefit patients with NSCLC expressing oncogenic K-RAS. These findings may have general applicability in cancer therapy, because aberrant activation of PI3K occurs frequently in human cancer. [Cancer Res 2009;69(19):7644-52]