Abstract 3394: A gamma secretase inhibitor reduces large neurosphere formation in glioma cell lines which correlates with decreased tumorigenicity

Notch signaling regulates many aspects of development, cell fate and tissue renewal. Recent work has implicated the pathway in regulating and maintaining tumor initiating cells. Phase 1 clinical trial results have recently shown responses in patients with brain tumors. The objective of the current study is to evaluate the effect of a potent and specific gamma-secretase inhibitor (GSI, MRK-003) on the growth of a neurosphere stem cell-like population from glioblastoma cell lines. Our studies demonstrate glioma cell lines grown in serum-free neurosphere culture conditions have 10-40 fold higher expression of Notch pathway direct target genes Hes5, Hey1 and Hey 2, as compared to their expression in standard 2D serum-cultured cells. Using a novel imaging based readout with the Isocyte platform, we have collected multiple neurosphere colony parameters, such as colony size, colony number, colony shape, frequency and fluorescence intensity, before and after drug treatment. In vitro GSI treatment of U251 neurospheres as compared to DMSO and inactive enantiomer controls yields a 5 fold reduction in the number of large colonies with a correlated increase in the number of small colonies, suggesting a cytostatic effect. This effect translates into a 40 day delay in tumor formation and a 5 fold decrease in tumor volume after subcutaneous injection of 5-day GSI pre-treated neurospheres (p-value Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3394. doi:10.1158/1538-7445.AM2011-3394