LGG-15. CARBOPLATIN IS SYNERGISTIC WITH MAPK INHIBITORS TRAMETINIB AND EVEROLIMUS IN LOW GRADE GLIOMA MODELS

Abstract

AbstractPediatric lower grade glioma (LGG) can cause significant morbidity and mortality in patients. Tumors often initially respond to first line chemotherapies, such as carboplatin, but approximately 50% of the time tumors recur and require additional therapy. The discovery that aggressive LGG often have MAPK-ERK pathway, as well as mTOR activation, increases the number of treatment options available, such as trametinib, an ERK inhibitor, or everolimus, an mTORC1 inhibitor. Using preexisting and newly developed models for LGG, our lab sought to determine if there was synergy between carboplatin and the MAPK-ERK and mTOR inhibitors trametinib or everolimus. In the cell lines Res186 (derived from pilocytic astrocytoma grade I), and Res259 (derived from diffuse astrocytoma grade II), we found that the combination of carboplatin with either everolimus or trametinib decreased cellular proliferation in a dose-dependent manner (P<0.05). Both cell lines and drug combinations gave a combination index of <1, indicating synergy. Everolimus sensitized Res259 to carboplatin treatment, despite Res259 being resistant to everolimus treatment alone. Interestingly, the carboplatin and everolimus combination did not increase levels of apoptosis in cells, as measured by cleaved caspase 3 (CC3) staining and probing for cleaved PARP by western blot. We extended our findings to a human neural stem cell glioma model which has MAP kinase activation and confirmed that carboplatin and everolimus combined to suppress proliferation, as measured by BrdU incorporation, greater than either single agent (P<0.001 by ANOVA). Treatments again did not increase apoptosis as measured by CC3 immunofluroescence. Using BT40 patient derived xenografts, a low grade glioma-derived model that harbors a BRAF V600E mutation, preliminary data shows that the combining everolimus with carboplatin had superior growth suppression compared to either drug alone. In conclusion, the combination of carboplatin with everolimus demonstrates combinatorial efficacy in our in vivo and in vitro systems.