Csig-31. T-Type Calcium Channel Blockers Induce Metabolic Alterations and Apoptosis in Medulloblastoma Cells

Abstract

Medulloblastoma (MB) is the most common malignant paediatric brain tumour. In our previous studies, in a screen of a panel of calcium channel modulators in our novel high-throughput 3D assay, we identified T-type (CaV3) channel inhibitors, mibefradil and NNC-55-0396 (NNC) as selective inhibitors of MB cell growth. Mibefradil was originally approved for the treatment of hypertension and angina pectoris, and recently successfully completed a Phase-I trial for recurrent high-grade glioma. NNC is an analogue of mibefradil with multiple advantages compared to mibefradil that makes it attractive for potential future clinical trials. T-type channels have a unique low voltage-dependent activation/inactivation, and many studies suggest that they have a direct regulatory role in controlling Ca2+ signalling in non-excitable tissues, including cancers. In this study, we characterized the effect of mibefradil and NNC on MB cells and elucidated their mechanism of action. This study demonstrates that the induction of toxicity in MB cells is selective to T-type but not to L-type Ca2+ channel inhibitors. Addition of CaV3 inhibitors to vincristine sensitised MB cells to this MB chemotherapeutic agent, suggesting an additive effect. Furthermore, CaV3 inhibitors induced cell death in MB cells via apoptosis. Supported by proteomics data and cellular assays, apoptotic cell death was associated with reduced mitochondrial membrane potential and reduced ATP levels, which suggests that both compounds alter the metabolism of MB cells. We also identified that CACNA1H (encoding the CaV3.2 protein) is significantly upregulated in aggressive Groups 3 and 4 MB patient samples, and its higher expression is associated with higher metastasis and lower patient survival rates. This study offers new insights into the action of mibefradil and NNC and will pave the way to test these molecules or their analogues in pre-clinical MB models alone and in combination with vincristine to assess their suitability as a potential MB therapy.