Targetable T-type calcium channels drive glioblastoma

Glioblastoma stem-like cells (GSC) promote tumor initiation, progression and therapeutic resistance. Here we show how GSC can be targeted by the FDA approved drug mibefradil which inhibits the T-type calcium channel Cav3.2. This calcium channel was highly expressed in human GBM specimens and enriched in GSC. Analyses of the TCGA and REMBRANDT databases confirmed upregulation of Cav3.2 in a subset of tumors and showed that overexpression associated with worse prognosis. Mibefradil treatment or RNAi-mediated attenuation of Cav3.2 was sufficient to inhibit the growth, survival and stemness of GSC, and also sensitized them to temozolomide (TMZ) chemotherapy. Proteomic and transcriptomic analyses revealed that Cav3.2 inhibition altered cancer signaling pathways and gene transcription. Cav3.2 inhibition suppressed GSC growth in part by inhibiting pro-survival AKT/mTOR pathways and stimulating pro-apoptotic survivin and BAX pathways. Further, Cav3.2 inhibition decreased expression of oncogenes (PDGFA, PDGFB, and TGFB1) and increased expression of tumor suppressor genes (TNFRSF14 and HSD17B14). Oral administration of mibefradil inhibited growth of GSC-derived GBM murine xenografts, prolonged host survival and sensitized tumors to TMZ treatment. Our results offer a comprehensive characterization of Cav3.2 in GBM tumors and GSC, and provide a preclinical proof of concept for repurposing mibefradil as a mechanism-based treatment strategy for GBM.

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