A Molecular Screening Approach to Identify and Characterize Inhibitors of Glioblastoma Stem Cells

Glioblastoma multiforme (GBM) is amongst the most lethal of all cancers. GBM consist of a heterogeneous population of tumor cells amongst which a tumor initiating and treatment-resistant subpopulation, here termed GBM stem cells (GSC), have been identified as primary therapeutic targets. Here, we describe a high-throughput small molecule screening approach that enables the identification and characterization of chemical compounds that are effective against GSC. The paradigm uses a tissue culture model to enrich for GSC derived from human GBM resections and combines a phenotype-based screen with gene target-specific screens for compound identification. We used 31,624 small molecules from seven chemical libraries that we characterized and ranked based on their effect on a panel of GSC-enriched cultures as well as their effect on the expression of a module of genes whose expression negatively correlates with clinical outcome: MELK, ASPM, TOP2A and FOXM1b. Of the 11 compounds meeting criteria for exerting differential effects across cell types used, 4 compounds demonstrated selectivity by inhibiting multiple GSC-enriched cultures compared to non-enriched cultures: Emetine, N-Arachidonoyldopamine (NADA), N-Oleoyldopamine (OLDA), and N-Palmitoyldopamine (PALDA). ChemBridge compounds #5560509 and #5256360 inhibited the expression of the 4 mitotic module genes. OLDA, Emetine, and compounds #5560509 and #5256360 were chosen for more detailed study and inhibited GSC in self-renewal assays in vitro and in a xenograft model in vivo. These studies demonstrate that our screening strategy provides potential candidates as well as a blueprint for lead compound identification in larger scale screens or screens involving other cancer types.