# Tyr1497 in the BRG1 Bromodomain of the SWI/SNF Complex is Critical for the Binding and Function of a Selective BRG1 Inhibitor

## TL;DR

A specific amino acid in the BRG1 protein is essential for a drug's ability to enhance glioblastoma treatment effectiveness.

## Contribution

Identified Tyr1497 as critical for the function of a selective BRG1 inhibitor in sensitizing glioblastoma cells to treatment.

## Key findings

- Tyr1497 is crucial for IV-255's effect on TMZ-induced GBM cell death.
- IV-255 increases γH2AX staining, indicating impaired DNA repair in GBM cells.
- IV-255 sensitizes GBM cells to TMZ-induced apoptosis via Tyr1497.

## Abstract

BRG1 and BRM are subunits of the SWI/SNF chromatin remodelling complex, which has DNA‐stimulated ATPase activity and can destabilise histone–DNA interactions. Targeting SWI/SNF is beneficial for treating various tumours, including glioblastoma (GBM). Our research focussed on BRG1 due to its overexpression in GBM. We developed IV‐255, a selective bromodomain (BRD) inhibitor that binds to BRG1 but not BRM. IV‐255 sensitised GBM cells to temozolomide (TMZ), the standard GBM treatment. We identified the binding site of IV‐255 within the BRG1 BRD and found that the Tyr1497 residue is crucial for IV‐255's effect on TMZ‐induced GBM cell death, while Asn1540 is not. Structural analyses confirmed that Tyr1497 is involved in the IV‐255 binding pocket. Mechanistically, IV‐255 increases γH2AX staining in GBM cell nuclei in response to TMZ, indicating an impaired DNA double‐strand break response dependent on Tyr1497. IV‐255 also sensitised GBM cells to TMZ‐induced apoptosis, as shown by PARP and caspase‐3 cleavage, which also requires Tyr1497. In conclusion, Tyr1497 within the BRD of BRG1 is critical for its interaction with IV‐255 and for sensitising GBM cells to TMZ‐induced DNA double‐strand breaks and apoptotic cell death.