Calcium Channels in Glioblastoma

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.

Grant Number: 5R01NS122222-04
NIH Institute/Center: NIH
Principal Investigator: Roger Abounader