CSIG-32. ABL1 AND 2 DRIVE MEDULLOBLASTOMA PROLIFERATION AND ADHESION IN LEPTOMENINGEAL DISSEMINATION

Abstract

Abstract INTRODUCTION The molecular mechanisms that drive leptomeningeal dissemination (LD) of medulloblastoma (MB) are largely unknown. The Abelson (ABL) family kinases, originally identified as oncogenes in leukemia, play an important role in lung cancer cell migration, invasion, cell adhesion, and chemotherapy resistance. The objective of this work was to elucidate the role of ABL kinases in MB LD. METHODS ABL1 and ABL2 mRNA expression of patient specimens was analyzed. shRNA knockdowns of ABL1/2 and pharmacologic inhibition of ABL1/2 were used for in vitro and in vivo analyses of MB LD. RESULTS ABL1 and ABL2 levels were significantly higher in MB patients with LD than without (p=2.6x10-10 and 7.2x10-7, respectively) and overall survival was significantly reduced in patients with high ABL1 and 2 expression (p=0.019 and 0.00027, respectively). In vitro pharmacologic inhibition and genetic knockdown of ABL1 and ABL2 in Group 3/4 MB resulted in statistically significant cell death, decreased adhesion to vitronectin (a key leptomeningeal extracellular matrix [ECM] protein), decreased migration through ECM extract, and decreased c-myc expression in multiple MB cell types. In mouse models of MB LD, ABL1/2 knockdown significantly decreased LD as determined by bioluminescence and improved overall survival (p=0.0044). Pharmacologic inhibition of ABL1/2 using nilotinib resulted in improved median overall survival (64 vs. 76.5 days). CONCLUSIONS ABL1 and ABL2 are preferentially expressed in patients with MB LD at diagnosis and are associated with poor survival. Both genetic inactivation and pharmacologic inhibition of ABL1 and 2 decreased MB LD in vitro and in vivo, likely via reduction of c-myc signaling. This preliminary work suggests a key role for ABL1/2 in driving MB LD.