TR-07: LB100, A NOVEL PROTEIN PHOSPHATASE 2A INHIBITOR, ENHANCES CISPLATIN AND RADIATION MEDIATED CYTOTOXICITY AND OVERCOME CISPLATIN RESISTANCE IN-VITRO

INTRODUCTION: Medulloblastoma is the most common malignant brain tumors. Current therapeutic strategies combining surgery, chemotherapy and radiation offer high survival rate but confer significant treatment-related comorbidity. LB100, a novel small molecule Protein Phosphatase 2A (PP2A) inhibitor, has demonstrated efficacy in a number of non-intracranial tumors. The objective of this study is to assess LB100 effectiveness for treatment of medulloblastoma. METHODS: Experiments were performed using DAOY and D341-MED cell lines: XTT assay was performed to assess for cell viability, immunohistochemistry was performed to assess for DNA double-strand breaks and mitotic catastrophe using gamma H2X and alpha tubulin staining respectively. Flow cytometry was performed for cell cycle analysis. A cisplatin - resistant D341 cell line was developed by constant exposure to escalating concentration of cisplatin (up to 4 uM) resulting in a stably resistant cell line with 8-fold increases in IC50. RESULTS: LB100 enhances cisplatin-mediated cytotoxicity. XTT assay showed the IC50 of cisplatin decreased from ∼7uM to < 2uM and from ∼3uM to <0.5 uM with 5uM LB100 in DAOY and D341 respectively after 48 hours of drug exposure. In DAOY, LB100 enhances radiation induced DNA double-strand breaks with ∼5 fold increase in gamma H2X foci and ∼4 fold increase in proportion of cells undergoing mitotic catastrophe on immunohistochemistry with 5uM LB100. In D341, cell cycle analysis demonstrates ∼ 2 fold increase in percentage of cells in G2/M with 10uM LB100 consistent with increased mitotic catastrophe. There is no difference in sensitivity to increasing concentration of LB100 between wide-type D341 and cisplatin resistant D341 on cell viability suggesting that LB100 has equal potency against wild type and cisplatin resistant cell line. CONCLUSIONS: LB100 treatment is an effective radiation and chemotherapy sensitizing agent in-vitro. Further in-vivo study will provide the preclinical data needed to consider LB100 as an adjuvant agent for treatment of medulloblastoma.