Abstract
Brain tumors represent a diverse group of neoplasms with distinct genetic, molecular, and cellular characteristics that drive their pathogenesis and therapeutic resistance. Glioblastoma (GBM) is the most common and most deadly primary malignant brain tumor. GBM is associated with a dismal prognosis and an average life expectancy of ~15 months despite optimal therapy consisting of surgery, chemotherapy and radiation. Medulloblastoma (MB) is the most common pediatric brain tumor. Medulloblastoma is a CNS tumor that arises from the cerebellum, primarily in pediatric patients. The 5-year survival rate for pediatric MB patients is ~ 70%. However, patients treated with radiation therapy frequently experience permanent neurological deficits such as reduced motor and cognitive functions. T-type calcium channels are low-voltage-activated calcium channels with established roles in neuronal excitability, neuronal plasticity, proliferation, and differentiation.
In Chapter 2 we elucidate the role of microenvironmental and intrinsic T-type calcium channels in glioblastoma (GBM) progression. We demonstrate that Cav3.2 deletion in the tumor microenvironment significantly reduces tumor growth and prolongs survival. Using syngeneic GBM models in the Cav3.2 knockout (KO) mice and single-cell RNA sequencing (scRNA-seq), we show that microenvironmental Cav3.2 modulates neuronal and glial processes, downregulating genes critical for maintaining the oligodendrocyte progenitor cell (OPC) state, including SOX10 and Olig2. Additionally, neuronal Cav3.2 enhances neuron-GBM stem cell (GSC) synaptic interactions, promoting GSC proliferation. Pharmacological inhibition of Cav3 with mibefradil suppresses neuronal gene expression in GSCs and synergizes with temozolomide (TMZ) and radiation to further reduce tumor burden and improve survival. These findings underscore the significance of Cav3.2 in both the tumor and microenvironment, supporting mibefradil as a potential therapeutic adjunct to standard GBM treatments.
In Chapter 3 we investigate the role of T-type calcium channels in medulloblastoma. We analyzed publicly available bulk and single-cell RNA-seq datasets showing that T-type calcium channels are upregulated in over 30% of medulloblastomas, with high expression correlating with poor prognosis. Expression levels vary across molecular subgroups, highlighting their heterogeneous role in tumor biology. Functional assays demonstrate that pharmacological inhibition with mibefradil or siRNA-mediated silencing reduces tumor cell proliferation, viability, and invasion. We performed. Proteomic screenings (RPPA) and single-cell co-expression analyses to identify key cancer signaling pathways modulated by T-type calcium channel inhibition. In vivo, oral administration of mibefradil suppresses tumor growth and extends survival in orthotopic xenograft models. This study provides the first comprehensive multi-omic characterization of T-type calcium channels in medulloblastoma and supports repurposing mibefradil as a potential therapeutic strategy for these aggressive pediatric brain tumors.
This dissertation establishes T-type calcium channels as critical regulators of brain tumor progression, influencing both tumor-intrinsic and microenvironmental processes. In glioblastoma, Cav3.2 in the tumor microenvironment promotes neuronal and glial signaling, facilitating tumor growth. In medulloblastoma, T-type calcium channels drive tumor proliferation, invasion, and survival. Pharmacological inhibition with mibefradil effectively disrupts these oncogenic processes, demonstrating therapeutic potential in both tumor types. These findings underscore the translational relevance of targeting T-type calcium channels and support further investigation into mibefradil as a viable therapeutic strategy for aggressive brain tumors.
