Abstract
PURPOSE: Alteration of the BRAF/MEK/MAPK pathway is the hallmark of pediatric low-grade gliomas (PLGGs), and mTOR activation has been documented in the majority of these tumors. We investigated combinations of MEK1/2, BRAF(V600E) and mTOR inhibitors in gliomas carrying specific genetic alterations of the MAPK pathway. EXPERIMENTAL DESIGN: We used human glioma lines containing BRAF(V600E) (adult high-grade: AM-38, DBTRG, PLGG: BT40), or wild-type BRAF (pediatric high-grade: SF188, SF9427, SF8628) and isogenic systems of KIAA1549:BRAF-expressing NIH/3T3 cells and BRAF(V600E)-expressing murine brain cells. Signaling inhibitors included everolimus (mTOR), PLX4720 (BRAF(V600E)), and AZD6244 (MEK1/2). Proliferation was determined using ATP-based assays. In vivo inhibitor activities were assessed in the BT40 PLGG xenograft model. RESULTS: In BRAF(V600E) cells, the three possible doublet combinations of AZD6244, everolimus, and PLX4720 exhibited significantly greater effects on cell viability. In BRAF(WT) cells, everolimus + AZD6244 was superior compared with respective monotherapies. Similar results were found using isogenic murine cells. In KIAA1549:BRAF cells, MEK1/2 inhibition reduced cell viability and S-phase content, effects that were modestly augmented by mTOR inhibition. In vivo experiments in the BRAF(V600E) pediatric xenograft model BT40 showed the greatest survival advantage in mice treated with AZD6244 + PLX4720 (P < 0.01). CONCLUSIONS: In BRAF(V600E) tumors, combination of AZD6244 + PLX4720 is superior to monotherapy and to other combinatorial approaches. In BRAF(WT) pediatric gliomas, everolimus + AZD6244 is superior to either agent alone. KIAA1549:BRAF-expressing tumors display marked sensitivity to MEK1/2 inhibition. Application of these results to PLGG treatment must be exercised with caution because the dearth of PLGG models necessitated only a single patient-derived PLGG (BT40) in this study. Clin Cancer Res; 22(21); 5312-21. ©2016 AACR.