Calcium Channels in Glioblastoma

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ABSTRACT Glioblastoma (GBM) is the most common and most deadly primary malignant brain tumor. Calcium signaling regulates a plethora of cancer-associated molecular and cellular processes including cell proliferation, apoptosis, motility, angiogenesis, differentiation, gene transcription as well as neurotransmission and synaptic plasticity. Calcium influx from the extracellular space to the cytosol is regulated by T-Type calcium channels (TTCC). Our preliminary data show that TTCC are upregulated in GBM cells, stem cells (GSC) and human tumors and that their blockage leads to inhibition of cancer-promoting parameters in tumor cell-intrinsic and microenvironment-dependent manners. Based on these data, we hypothesize that TTCC strongly regulate GBM molecular events and GBM-microenvironment interactions to drive tumor growth, and that targeting TTCC in combination with other modalities is a promising GBM therapy. To test this hypothesis, we propose to investigate the tumor cell-intrinsic and microenvironment-dependent functions, mechanisms of action, and therapeutic targeting of TTCC in GBM. In Aim 1, we will determine the GBM cell-intrinsic role and mechanisms of action of TTCC in new mouse models with intact microenvironment. We will develop new RCAS/Tva and transgenic immune competent TTCC mouse models and use them to study the role of TTCC in an intact GBM microenvironment. We will also use genomic and proteomic screenings and molecular and functional approaches to uncover the mechanisms of action of TTCC in these GBM tumors. In Aim 2, we will uncover the role of tumor microenvironment TTCC in mediating tumor-promoting neuron/GBM interactions. We hypothesize that neuronal TTCC and GBM TTCC cooperate to regulate the tumor-promoting interactions between GBM cells and neurons that were recently discovered. To test this hypothesis, we will use co-cultures and GBM animal models to investigate the role of TTCC in regulating neuron/GBM synaptic formation, calcium influx into tumor cells, and tumor growth and malignancy. In Aim 3, we will develop and test new strategies for the therapeutic targeting of TTCC in GBM. We have a repurposed FDA approved TTCC blocker, mibefradil, that was demonstrated to be safe and possibly effective in a phase I recurrent GBM trial. We will test the effects of mibefradil on the growth of GBM xenografts, syngeneic tumors and RCAS/Tva GBM mice using the standard clinical Stupp Regimen. We will also perform in vitro and in vivo synthetic lethal CRISPR screens to uncover druggable targets and drugs that synergize with mibefradil. We will then test combinations of mibefradil and the synthetic lethal drugs in GBM animal models. Altogether, the findings will generate new knowledge on the functions and mechanisms of action of TTCC in GBM and its microenvironment, develop new tools for the study of TTCC, uncover the role of TTCC in mediating tumor-promoting neuron/GBM interactions, and develop and test new efficacious GBM combination therapies that could be translated into clinical trials.