Abstract 2336: AD1 promotes astroglial differentiation and depletes glioblastoma stem cells

Abstract

Abstract Glioblastoma are among the least curable cancers in man, at least in part because of stem-like cellular subpopulations (herein referred to as glioma stem cells, GSC) refractory to current therapies. The cancer stem cell hypothesis suggests that tumor cells are organized in a pyramidal unidirectional differentiation cascade with GSC at the top and functionally defined by the ability to self-renew and initiate tumors identical to the original tumors from which they are derived. GSCs are maintained by both cell intrinsic and micro-environmental factors and conditions. In this study we focused on identifying small molecules which target tumor heterogeneity by promoting differentiation of GSC into less aggressive, more differentiated subpopulations. To this end, we have developed reporter models for astroglial and neuronal differentiation in HSR-GBM1, HSR040622 and HSR040821 tumor-derived, GSC-enriched, neurospheres lines, using lineage-specific reporter constructs. We employed these reporter lines to screen a library of over 700 bioactive small molecules for potential inducers of GSC differentiation. We identified several molecules which significantly induce astroglial differentiation in multiple GSC-enriched lines. In this report, we focus on one of these agents, (AD1 = (Astroglial Differentiation-1), which induces astroglial differentiation by up to 30-fold as compared with DMSO control. Interestingly, the effects of AD-1 appear to be primarily cytostatic rather than cytotoxic. As differentiation should result in reduced self-renewal capacity, we next determined the effect of AD1 on clonogenicity in vitro using the extreme limited dilution assay (ELDA). We found that 48h treatment with AD1 significantly reduced clonogenic capacity of HSR-GBM1, HSR-040622 and HSR-040821 reporter lines by over 90%. To test this in vivo we examined the effect of AD1 on tumor initiation in an intracranial transplantation model. We found that ex vivo treatment with AD1 resulted in a significant increase in the survival of animals as 6 (of 6) animals transplanted with DMSO-treated cells exhibited massively infiltrating tumors while 2 (of 6) of the animals implanted with AD1 treated cells developed tumors, and those began to appear several weeks later. Importantly, the effects of AD1 are likely to be irreversible as cells extracted from tumors maintained reporter expression even after six passages in vitro. Taken together, our results support the therapeutic value of a drug-induced differentiation and define how differentiation affects the GSC compartment in glioma. Citation Format: Raffaella Spina, Dillon M. Voss, Andrew Sloan, Eli E. Bar. AD1 promotes astroglial differentiation and depletes glioblastoma stem cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2336. doi:10.1158/1538-7445.AM2015-2336