T-type Calcium Channel Inhibitors Induce Apoptosis in Medulloblastoma Cells Associated With Altered Metabolic Activity

Abstract

Medulloblastoma (MB) is the most common malignant paediatric brain tumour. In our previous studies, we developed a novel 3D assay for MB cells and screened of plasma membrane calcium channel modulators. These studies identified T-type (CaV3) channel inhibitors, mibefradil and NNC-55-0396 (NNC) as selective inhibitors of MB cell growth. Mibefradil was originally approved for 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. In this study, we aimed to characterise the effect of mibefradil and NNC on MB cells and elucidate 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 a synergistic 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. 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.