ET-10THE SYNERGISTIC EFFECT OF INHIBITOR OF INHIBITOR OF APOPTOSIS PROTEINS- LCL161 AND STANDARD ANTI-CANCER AGENTS ON MEDULLOBLASTOMA CELLS

Medulloblastoma is the most common malignant pediatric brain tumor, comprising 15-20% of intracranial tumor in children. Most metastatic and recurrent medulloblastoma cells are resistant to current therapeutic approaches including radiation and high-dose chemotherapy. In addition, some studies indicate that subsets of medulloblastomas exhibit loss of caspase-8 expression and therefore they can resist TRAIL-induced apoptosis.A chemo-drug, LCL161, has a mimic structure of Smac/DIABLO, which can inhibit XIAP and cIAP, and then enhance caspse-3, caspase-7 and caspase-9 activation. Our study purpose is to determine whether LCL161 induce cell apoptosis and activate caspases cascade through inhibition of IAPs in medulloblastoma cells(DAOY and d283) and to examine whether LCL161 can sensitize standard anti-cancer agents(vincrstine, or cisplatin) induced apoptosis. Based on prior data, DAOY cells had higher, and d283 cells had lower caspase-8 expressions respectively. LCL161 alone did not inhibit tumor growth for both medulloblastoma cells. Our data showed synergistic effect of LCL161-combined vincrstine, or cisplatin can be observed in DAOY cells. For d283 med cells, synergistic effect still exist but was not as significant as that of DAOY cells. LCL161-combined vincristine decreased around 40% and 20% cell viability in DAOY cells and d283 med cells compared to vincrisitne alone. LCL-combined cisplatin inhibited 20% growth rate in DAOY cells. Nevertheless, synergistic effect did not work in d283 cells. DNA flow and Annexin V/PI assay were indicated LCL 161 alone increased 16% of apoptotic cells. In addition, LCL161 enhanced 18% of apoptotic cells treated with vincristine, and the combined treatment approached to IC50 for medulloblastoma cells. LCL161-combined cisplatin increased 18% of apoptotic cells compared to cisplatin alone. Overall, the synergistic effect of LCL161 and standard anti-cancer agents was more significant on DAOY cells, which express higher caspase-8. The finding indicated that loss of caspase 8 play an important role in this therapeutic strategy.