MBRS-18. TUMOR SUPPRESSOR p53 DEFINES THE THERAPEUTIC RESPONSES IN TREATMENT OF MEDULLOBLASTOMA

Medulloblastoma (MB) is the most common primary pediatric malignant brain tumor. Current molecular analysis classifies MB into 4 groups, classic (WNT), sonic hedgehog (Shh), group 3, and group 4. Furthermore, atypical p53 signaling is associated with disease progression and confers poor prognosis. This study investigated the correlation of mutational status of p53 and iSO17q with disease progression and metastatic potential. In addition, we used small molecule inhibitors of PI3K (Buparlisib; BKM120) and HDAC (LBH-589) on a p53-mutant MB cell line to find novel therapeutic targets. Efficacy of these drugs were assessed using functional assays (cell proliferation, migration, cell cycle and drug resistance). MB tumors (n=53) were evaluated for GLI-1, GAB-1, NPR, KV1, YAP expression and mutant p53 via immunohistochemistry and correlated to patient outcomes. Results demonstrated that: 1) high expression of GAB-1 and YAP were found in the Shh group, while KV1 expression was present in all subtypes; 2) mutant p53 expression was present in various subsets of MB with no apparent correlation with metastasis or disease progression; 3) patients displaying iSO17q (determined by fluorescence in situ hybridization (FISH) technique) exhibited metastatic disease; 4) LBH-589 and BKM120 caused both time and dose-dependent inhibition of MB cell proliferation and migration; 5) combined treatment of BKM120 and LBH-589 had a synergistic effect; 6) MB cells demonstrated drug-resistance to BKM120. In conclusion, these findings underscore use of Buparlisib and LBH-589 in treatment of MB. Further, the role of mutant p53 in disease progression remains elusive, whereas presence of iSO17q defines metastatic potential.