Repurposing Potential of Riluzole as an ITAF Inhibitor in mTOR Therapy Resistant Glioblastoma.

Alan Lichtenstein,Brent Holmes,Joseph Gera,Jacquelyn T Saunders,Robert N Nishimura,Angelica Benavides-Serrato

doi:10.3390/ijms21010344

Abstract

Internal ribosome entry site (IRES)-mediated protein synthesis has been demonstrated to play an important role in resistance to mechanistic target of rapamycin (mTOR) targeted therapies. Previously, we have demonstrated that the IRES trans-acting factor (ITAF), hnRNP A1 is required to promote IRES activity and small molecule inhibitors which bind specifically to this ITAF and curtail IRES activity, leading to mTOR inhibitor sensitivity. Here we report the identification of riluzole (Rilutek®), an FDA-approved drug for amyotrophic lateral sclerosis (ALS), via an in silico docking analysis of FDA-approved compounds, as an inhibitor of hnRNP A1. In a riluzole-bead coupled binding assay and in surface plasmon resonance imaging analyses, riluzole was found to directly bind to hnRNP A1 and inhibited IRES activity via effects on ITAF/RNA-binding. Riluzole also demonstrated synergistic anti-glioblastoma (GBM) affects with mTOR inhibitors in vitro and in GBM xenografts in mice. These data suggest that repurposing riluzole, used in conjunction with mTOR inhibitors, may serve as an effective therapeutic option in glioblastoma.

Highlights

Despite recent advances in cancer drug discovery, including high-throughput screening and structure-based drug design, significant increases in the number of new approved anticancer drugs which progress to the clinic is lacking [1]
We demonstrate that riluzole inhibits Internal ribosome entry site (IRES)-dependent translation and blocks hnRNP A1 binding to both the cyclin D1 and c-myc IRESs resulting in markedly reduced translational efficiencies of these transcripts
The docking results were ranked by the binding free energy and the top 10 candidates filtered as potential hnRNP A1 inhibitors

Summary

Introduction

Despite recent advances in cancer drug discovery, including high-throughput screening and structure-based drug design, significant increases in the number of new approved anticancer drugs which progress to the clinic is lacking [1]. GBM is a lethal tumor of the CNS which in part is due to the difficulty in complete surgical resection and the eventual development of resistance to drug therapies [3]. Hyperactivation of the PI3K pathway is observed in approximately 90% of all GBMs as a result of EGFR amplification or activating mutations and/or PTEN loss [5,6,7]. This leads to durable activation of the downstream effector, the mechanistic target of rapamycin (mTOR) kinases [8,9]. This leads to durable activation of the downstream effector, the mechanistic target of rapamycin (mTOR) kinases [8,9]. mTOR is present in cells as part of two distinct kinase complexes, mTORC1 and mTORC2 each with distinct substrate specificities [10]

Methods

Results

Conclusion