Abstract
Genetic heterogeneity and signaling alterations diminish the effectiveness of single-agent therapies in glioblastoma multiforme (GBM). HSP90 is a molecular chaperone for several signaling proteins that are deregulated in glioma cells. Thus, HSP90 inhibition may offer an approach to coordinately correct multiple signaling pathways as a strategy for GBM therapy. In this study, we evaluated the effects of a novel HSP90 inhibitor, NVP-HSP990, in glioma tumor-initiating cell (GIC) populations, which are strongly implicated in the root pathobiology of GBM. In GIC cultures, NVP-HSP990 elicited a dose-dependent growth inhibition with IC50 values in the low nanomolar range. Two GIC subgroups with different responses were observed with an Olig2-expressing subset relatively more sensitive to treatment. We also showed that Olig2 is a functional marker associated with cell proliferation and response to NVP-HSP990, as NVP-HSP990 attenuated cell proliferation in Olig2-high GIC lines. In addition, NVP-HSP990 disrupted cell-cycle control mechanism by decreasing CDK2 and CDK4 and elevating apoptosis-related molecules. Mechanistic investigations revealed molecular interactions between CDK2/CDK4 and Olig2. Inhibition of CDK2/CDK4 activity disrupted Olig2-CDK2/CDK4 interactions and attenuated Olig2 protein stability. In vivo evaluation showed a relative prolongation of median survival in an intracranial model of GIC growth. Our results suggest that GBM characterized by high-expressing Olig2 GIC may exhibit greater sensitivity to NVP-HSP990 treatment, establishing a foundation for further investigation of the role of HSP90 signaling in GBM.