Abstract B044: Bromodomain and Extra-Terminal Protein inhibition decreases pancreatic cancer proliferation via MYC-independent pathways

Abstract

Abstract Introduction: The bromodomain and extra-terminal (BET) protein family contains proteins which have evolutionarily conserved bromodomains (BRDs) that specifically recognize acetylated lysine residues on the histone tails of chromatin and regulate gene transcription. Deregulation of these BRD-containing proteins has been seen in carcinogenesis as they are also known to play role in the regulation of the cell-cycle and MYC oncogenes. BMS-986158 is an oral BET inhibitor which has been used in the clinical trials for both hematologic and advanced solid tumor cancers. We hypothesized that BET inhibition (BETi) decreases pancreatic ductal adenocarcinoma (PDA) proliferation. Methods: Pancreatic cancer cell lines and patient-derived cell-lines (PDCLs) were treated with 2.5 to 100nM BMS-986158 for 72 hours to study dose-response effect with Incucyte. We performed RNA-seq, qPCR, protein analysis, and flow cytometry to evaluate comprehensive changes and underlying mechanisms/pathways including epithelial to mesenchymal transition (EMT) and the cancer stem cell (CSC) phenotype. Various doses of BMS-986158 were used in PDCL and PDA patient-derived organoids (PDO) in combination with chemotherapy drug to evaluate combinational effects. Results: We found that BETi induced dose-dependent decrease in growth of PDA and PDCLs and induced cancer cell death. BETi demonstrated PDO growth inhibition which was enhanced when combined with gemcitabine and paclitaxel chemotherapy. Next, we found that BETi did not affect MYC expression but decreased expression of the SNAI1 (a mesenchymal marker) protein and increased E-cadherin protein expression in PDA cell line and PDO consistent with decreased activation of an EMT program. BETi also decreased expression of CD133, a marker of CSCs in PDO. BETi also induced G1/S Phase cell cycle arrest in PDA PDCLs. Furthermore, RNA-seq studies revealed that BETi treatment inhibits KRAS pathway and upregulates pathways involved in metabolism of lipids and lysosomal degradation. RNA-seq and qPCR demonstrated that GPX3 (glutathione peroxidase 3, a key protein in reactive oxygen species response) gene expression is upregulated in BETi treated samples. Conclusions: Thus, our data demonstrate that BETi through BMS-986158 is an additional therapy for inhibiting PDA growth through mechanisms that are independent of MYC pathway, inhibition of abnormal lipid metabolism and scavenging of reactive oxygen species. Citation Format: Manjul Rana, Rita G. Kansal, Jie Fang, Benjamin T. Allen, Jun Yang, Evan S. Glazer. Bromodomain and Extra-Terminal Protein inhibition decreases pancreatic cancer proliferation via MYC-independent pathways [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B044.