The effects of triptolide resistance on pancreatic cancer cell lines
Pancreatic cancer is currently the third leading cause of cancer-related deaths in the United States with a five-year survival rate of <7%. Therefore, the need to find more effective treatments for this disease is more urgent than ever. The objective of this study was to study the effects an anticancer agent called triptolide has on super-enhancer networks and gene expression using previously generated drug resistant lines containing different copies of c-MYC gene. Triptolide, derived from Tripterygium wilfordii, is currently in phase II clinical trials for treating patients with advanced pancreatic cancer and is known to target multiple pathways including those that relate to super-enhancer activity. The multifaceted oncogene c-MYC is, also, a super-enhancer regulated gene. Triptolide resistant pancreatic cancer cells were previously generated from PANC-1 and PSN-1 cells which have relatively lower and higher copies of c-MYC, respectively. To measure the extent of triptolide resistance compared to parental cells lines, an SRB assay was performed, which concluded that PANC-1 cells had an 11-fold resistance and PSN-1 cells had a 13-fold resistance to triptolide. Following this, we carried out RNA sequencing to assess the gene expression profiles in sensitive versus resistant cells. The data from transcriptome analysis showed that in comparing sensitive parental and drug resistant lines 549 genes up regulated and 789 down regulated in PANC-1 background, with the large groups of the genes being nucleic acid binding (e.g. BARX1 and IGF2BP1), and hydrolase (e.g. SSC5D and DMBT1). In comparison, 84 genes up regulated and 128 down regulated in PSN-1 with the most noticeable protein classes being signaling molecules (e.g. BMP4 and S100A2) and enzyme modulators (e.g. INFPSF10D and IL7R). Among these, 97 genes were commonly deregulated between both cell line backgrounds and a prominent number of genes were classified to be signaling molecules (e.g. CXCL1 and IL1B). Western blotting analysis of the cell lysates showed a possible down regulation of Brd4 and XPB in the triptolide resistant cells regardless of the levels of c-MYC in each cell. A cell mitochondrial metabolic stress assay was also conducted to evaluate the oxygen consumption using 3-dimensional spheroids in response to treatment with triptolide (targeting XPB) and THZ1 (targeting CDK7), two potential super-enhancer targeting compounds. Spheroids used in this study were derived by co-culturing Patu8902 pancreatic cancer cells and PS1 fibroblasts. The test concluded that spheroids exposed to triptolide were dramatically compromised for mitochondrial function, as were those treated with THZ1, although at a lower level. Our results suggest that triptolide affects super-enhancer mediated signaling, regardless of the c-MYC levels and that receptors, enzyme modulators, hydrolases, and nucleic acid binding genes are deregulated in a c-MYC-dependent manner. Furthermore, triptolide perturbs mitochondrial respiration to kill pancreatic cancer cells. Triptolide holds promise in the development of novel therapies for pancreatic cancer.