Abstract
Purpose :
Brg-1 is a catalytic subunit of the SWI/SNF chromatin-remodeling complex, which contains a bromodomain and helicase/ATPase activity. Although mutated in some cancers, Brg-1 is not mutated in uveal melanoma. Targeting Brg-1 in uveal melanoma (UM) could promote chromatin instability and sensitize it to alkylating agents. Herein, we examined the effects of the small molecule inhibitor PFI-3 which binds the bromodomain of Brg-1 in non-metastatic MEL270 and metastatic OMM2.5 UM cell lines. We previously showed that the STAT3 transcription factor was highly activated in metastatic UM cells versus non-metastatic UM cells. We also examined BRG1 and STAT3 expression in UM tissue in situ.
Methods :
Brg-1 protein expression was verified using immunoblot analysis. UM cells were plated into 96 well plates and exposed to varying concentrations and combinations of PF-I3 and temozolomide (10-100 mM), and cell death assays were performed by ELISA. RNA in-situ hybridization was performed on 5-μm FFPE sections of archived enucleated eyes.
Results :
Immunoblot analysis shows the Brg-1 protein is present in both UM cell lines. PFI3 alone had minimal effect on either UM cell line at 72 hours but increased sensitivity to TMZ-induced apoptosis. RNA-ISH showed co-localization of Brg-1 and STAT3 in vivo.
Conclusions :
Our study shows Brg-1 is present in UM cell lines. PFI3 sensitizes UM cell lines to temozolomide leading to increased cell death. Targeting the bromodomain in Brg-1 presents a possible novel therapeutic treatment for metastatic UM. Furthermore, BRG1 and STAT3 RNA is co-expressed in specific niches in UM tissue in situ.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.