ATPS-22RITANSERIN AND TEMOZOLOMIDE SYNERGIZE AGAINST HUMAN GLIOBLASTOMA IN VITRO AND IN ESTABLISHED TUMORS IN VIVO

Abstract

BACKGROUND: Diacylglycerol Kinase Alpha (DGKα) inhibition with the known inhibitor {type:entrez-nucleotide,attrs:{text:R59022,term_id:829717,term_text:R59022}}R59022 results in strong cytotoxicity against glioblastoma cells in vitro. The use of {type:entrez-nucleotide,attrs:{text:R59022,term_id:829717,term_text:R59022}}R59022 in vivo against orthotopic xenografts was less successful due to limited solubility, short serum half-life, and possible low penetration of the blood-brain barrier. In addition, the known pro-immune effect of {type:entrez-nucleotide,attrs:{text:R59022,term_id:829717,term_text:R59022}}R59022 on DGKα in T-cells is unlikely to occur in immunocompromised mice. We show combined oral treatment with the related compound ritanserin and temozolomide results in markedly prolonged survival in orthotopic GBM xenograft-bearing mice. METHODS: In vitro studies of synergism between temozolomide (25 µM to 150 µM), and ritanserin (2.5 µM to 20 µM), were carried out using alamarBlue assay at 72 hours after treatment. U251 and several glioblastoma stem cell (GSC) lines were used. In GSCs, Perkin Elmer Operetta Digital Phase-Contrast was used to analyze cell numbers. CompuSyn was used generate Chou-Talalay Combination Index (CI) values. 200,000 U251 cells were implanted into the right parenchyma of 36 nude female mice. 6 days per week (dpw) oral gavage 30 mg/kg temozolomide in H2O and/or 50mg/kg ritanserin in corn oil, or vehicle began 7 days post tumor. A Kaplan-Meier survival curve was generated upon humane endpoints. RESULTS: U251 cells showed synergistic response at 25 µM to 50 µM temozolomide and 2.5 µM ritanserin. For GSC lines, synergy was also observed in cell counts. Median survival for vehicle-treated and ritanserin-treated U251-bearing mice was 29 days, and for temozolomide-treated mice was 32 days. At this time, 66% of ritanserin- and temozolomide-treated mice have survived 75 days. CONCLUSIONS: Our preliminary results with U251 and GSCs indicate strong synergy between ritanserin and temozolomide in tissue culture, and this was recapitulated in vivo.