Effects of TORC1/2 inhibitor MLN0128 alone and in combination with MEK inhibition in BRAF mutated glioma cells.
INTRODUCTION: First generation allosteric inhibitors of mTORC1 have shown clinical benefit for the treatment of pediatric low-grade gliomas (PLGG). MEK inhibition has shown great promise in early phase clinical trials for PLGG with the hypothesis that tumors carrying the KIAA1549:BRAF are particularly sensitive to such treatment. MLN0128, a second-generation, ATP-competitive, pan-mTOR kinase inhibitor, acts on both mTORC1 and mTORC2. Herein we investigate the effects of MLN0128 monotherapy as well as in combination with MEK inhibition in models of PLGG. METHODS: We used human glioma cell lines containing BRAFV600E (AM38), wild-type BRAF (LN229, TN98, SF188) and isogenic systems of KIAA1549:BRAF-expressing NIH3T3 cells. Signaling inhibitors included MLN0128, everolimus, BRAFV600E specific inhibitor PLX4720 and MEK specific inhibitors AZD6244 and GSK1120212. Cell proliferation was determined using an ATP-based assay. Biochemical effects were assessed using western blot analysis. In vivo activity of these inhibitors are ongoing using the BT40 PLGG xenograft mouse model. RESULTS: MLN0128 monotherapy shows stronger anti-proliferative effects compared to everolimus across cell lines independent of BRAF status. As expected, treatment with MLN0128 leads to down-regulation of p-AKT and p-4EBP1, whereas treatment with everolimus only reduces expression of p-S6. MEK inhibition with AZD6244 effectively decreases p-ERK expression in all lines; however, the addition of MLN0128 to AZD6244 causes a rebound in p-ERK expression in BRAFWT gliomas but not in gliomas expression BRAFV600E or KIAA1549:BRAF alterations. In cells carrying either the BRAFV600Eor KIAA1549:BRAF alteration, combined treatment with MLN0128 and GSK1120212 or AZD6244 leads to synergistic anti-proliferative effects whereas such synergy is not present in BRAFWT gliomas. In vivo studies in the PLGG xenograft model BT40 are ongoing. CONCLUSION: MLN0128 has synergistic effects with MEK inhibition in gliomas bearing BRAFV600E or KIAA1549:BRAF. In BRAF wild-type cells such synergy is not present, perhaps due to rebound in p-ERK when MLN0128 is combined with AZD6244.