Small Molecule Inhibitors Targeting Transgelin-2-Actin Interaction for Therapeutic Intervention in Glioblastoma

Abstract

<h3>Purpose/Objective(s)</h3> Glioblastoma (GBM) patients with wild-type <i>IDH1/2</i> experience worse response to the standard treatment due to their invasive phenotype leading to tumor recurrence compared with patients with mutant <i>IDH</i>1/2. In our clinical correlative studies, Transgelin-2 (<i>TAGLN2</i>) was identified as one of the top candidate genes associated with worse patient outcome. Previously, we have shown that <i>TAGLN2</i> is a candidate prognostic biomarker promoting tumorigenesis in human gliomas and a potential therapeutic target for gliomas. Transgelin-2 is known to induce actin polymerization, playing a critical role in cytoskeletal reorganization leading to cell proliferation, migration/invasion, and therapeutic resistance in GBM and other malignancies. However, there is no bonafide pharmacologic inhibitor that specifically blocks the Transgelin-2 functions in cancer. This study aims to target Transgelin-2 by small molecule inhibitors (SMIs) and explore the potential of these SMIs for therapeutic intervention in GBM. <h3>Materials/Methods</h3> Structure-based virtual screening using docking algorithms was used to identify SMIs of Transgelin-2 protein. These compounds were screened for their ability to permeate blood brain barrier (BBB), using SwissADME webtool and <i>in vitro</i> BBB model. A series of <i>in vitro</i> binding assays were performed to measure the binding affinity and kinetics of interaction of the compounds with Transgelin-2 and their potential to inhibit Transgelin-2-dependent actin polymerization. A series of functional assays; Cell proliferation, invasion, neurosphere and clonogenic assays were performed in GBM PDX cell lines to measure the potential of these SMIs to inhibit Transgelin-2-actin mediated functions and their ability to sensitize these cells to Temozolomide (TMZ) and/or radiation therapy (RT). <h3>Results</h3> <i>In silico</i> virtual screening identified 120 Transgelin-2 binding SMIs. Among which forty inhibitors were predicted to penetrate the BBB. Subsequent <i>in vitro</i> binding studies confirmed 12 compounds to bind and inhibit Transgelin-2-dependent actin polymerization. In a series of <i>in vitro</i> assays, these compounds significantly suppressed the growth and invasion of GBM 08-387 and 3359 PDX cell lines. These compounds also showed no significant toxicity to normal human cells. These SMIs also reduced the level of TAGLN2 protein in these cell lines in a dose- and time-dependent fashion. Subsequent <i>in vivo</i> xenograft mouse model experiments are underway to test the BBB permeability, efficacy and toxicity of these select SMIs. Further, the systemic toxicity of these compounds will also be tested in mice. <h3>Conclusion</h3> Our study identified a number of BBB permeable SMIs that specifically bind to TAGLN2 and inhibit its interaction with actin. Importantly, these SMIs suppress cell proliferation and invasion, and sensitize GBM cells to RT and/or TMZ treatment without significant toxicity to normal cells. Altogether, these SMIs of Transgelin-2 may serve as potential candidates for clinical trials.