Development of resistance to BET bromodomain inhibitor JQ1 and demonstration of epithelial-mesenchymal transition in pancreatic cancer cells.

Abstract

e15263 Background: Pancreatic ductal adenocarcinoma (PDAC) continues to be the leading cause of cancer related death in part due to limited efficacy of conventional chemotherapy. As such, there is increasing interest in developing inhibitors targeting epigenetic changes, including targeting BET proteins that bind acetylated histones to regulate gene transcription. We have found that the BET-inhibitor JQ1 is effective against pancreatic cancer cells. Since cancer cells can develop resistance to targeted therapies, we examined whether it was possible for PDAC cells to develop resistance to JQ1. Methods: The PDAC cell line CD18 cells (CD18-P) were treated with increasing concentration of JQ1 over a prolonged period of time to develop JQ1-resistent cells (CD18-JQ1r). We also generated CD18 cells resistant to 5-fluorouracil (CD18-CR) by treating CD18-P cells with increasing concentration of 5-fluorouracil. Results: Unlike CD18-P, CD18-JQ1r cells were resistant to the effects of JQ1 in 3D collagen. Moreover, JQ1 target genes c-MYC, FOSL1, and HMGA2, which are repressed in CD18-P cells treated with acute JQ1 treatment, were not repressed in CD18-JQ1R cells. When compared to the chemoresistant cells (CD18-CR) CD18-JQ1r showed less evidence of mesenchymal phenotype with lack of fibroblastic phenotype, repression of E-cadherin without expression of vimentin, repression of miR200 family of microRNA and upregulation of ZEB1. Additionally, CD18-JQ1r showed decreased cell matrix adhesion, lower levels of a2 and b1-integrin expression, and reduced FAK signaling. Transfection with ZEB1 siRNA restored cell-cell and cell-matrix adhesion defects seen in CD18-JQ1r cells. Moreover, ZEB1 siRNA partially repressed c-MYC, FOSL1 and HMGA2 in CD18-JQ1r cells. Conclusions: Pancreatic cancer cells can develop resistance to BET inhibitors. These resistant cells demonstrate defect in cell-cell and cell-matrix adhesion driven by ZEB1. Knockdown of ZEB1 can restore epithelial phenotype and enhance cell-cell and cell-matrix adhesion, and partly repress JQ1-target genes c-MYC, FOSL1 and HMGA2.