|Pancreatic cancer is a devastating disease with a current overall 5-year survival rate of only 10%, making it the deadliest cancer. The dismal treatment outcome of pancreatic cancer is largely attributed to its highly metastatic and chemo-resistant nature. Cancer cell epithelial to mesenchymal transition (EMT) contributes importantly to cell invasion, metastasis, and drug resistance in pancreatic cancer. In addition, pancreatic cancer cells exhibit an elevated basal level of unfolded protein response (UPR) signaling for survival, due to increased cellular endoplasmic reticulum (ER) stress under hypoxia. Inhibiting EMT and aggravating ER stress both pose as promising approaches to improve pancreatic cancer treatment. However, the relationship between ER stress and cancer cell EMT has not yet been fully understood. We previously reported a high throughput screening (HTS) study aiming to find small molecule inhibitors for EMT in pancreatic cancer cells. This dissertation documents our investigation on the top hit compound (namely C150) for its activities and mechanisms in inhibiting pancreatic cancer cell EMT, suppressing cell invasion, inducing ER stress, and reducing tumor growth in mice. These studies also discovered a mechanistic link between ER stress and pancreatic cancer cell EMT. We investigated the activities of C150 in inhibiting pancreatic cancer cell invasion and the mechanism of EMT inhibition (Chapter 4). C150 exhibited well-separated cytotoxicity between pancreatic cancer cells and non-cancerous cells. The IC50 values were 1~2.5 mM in multiple pancreatic cancer cell lines and 12.5 mM in non-cancerous pancreatic epithelial cells. C150 significantly inhibited pancreatic cancer cell migration and invasion in both 3-dimensional (3D) cell invasion assays and 2-dimensional (2D) wound scratching assays and Boyden chamber trans-well migration-invasion assays. Moreover, C150 treatment decreased matrix metallopeptidase-2 (MMP-2) and matrix metallopeptidase-9 (MMP-9) gene expressions in pancreatic cancer cells and reduced MMP-2 activity. In an orthotopic mouse model of pancreatic cancer, C150 significantly reduced tumor growth at the dose regimen of 15 mg/kg by intraperitoneal (IP) injection 3x weekly for 6 weeks. Mechanistically, C150 enhanced proteasome-mediated degradation of Snail protein, an important EMT-promoting transcription factor, and decreased the mesenchymal marker N-cadherin, while it increased the epithelial markers ZO-1 and Claudin-1. Findings from this first part of the study suggested that C150 is a novel EMT inhibitor with the potential of inhibiting pancreatic cancer growth and metastasis. The enhanced proteasome-mediated degradation of Snail by C150 intrigued our investigation into the mechanisms by which this occurred (Chapter 5). Further studies found that b-catenin, Sox-2, and TP53 protein levels were also decreased by C150 treatment. Data revealed that C150 increased proteasome activity by inducing ER stress and triggering UPR. The increased proteasome activity was due to enhanced proteasome assembly but not upregulation of subunits’ expressions. The increased proteasome assembly enhanced the degradation of transcription factors involved in EMT, as shown in Chapter 4. Moreover, as a cellular response to the ER stress, C150 treatment resulted in cell autophagy and decreased general translation in pancreatic cancer cells. The C150-induced ER stress eventually resulted in G2/M cell cycle arrest and cellular senescence. These stresses on pancreatic cancer cells greatly synergized with gemcitabine in inducing cytotoxicity in pancreatic cancer cells. In an orthotopic syngeneic mouse model, C150 treatment significantly reduced tumor growth and ascites occurrence, and improved survival of tumor-bearing mice. The elevated ER stress and senescence were confirmed in tumor tissues of C150-treated mice.Taken together, studies in this dissertation introduced a potential drug candidate for pancreatic cancer treatment (summarized and discussed in Chapter 6). C150 induced ER stress in pancreatic cancer cells, causing cell cycle arrest and senescence. It significantly suppressed tumor growth and improved survival in mouse xenograft models. Furthermore, as a response to C150-induced ER stress, pancreatic cancer cells increased proteasome activity, which enhanced the protein degradation of Snail, along with other EMT or stem cell-related transcription factors, leading to EMT inhibition and reduced cell invasion. An additional consequence is that C150 greatly sensitized PANC-1 cells to gemcitabine treatment, implying the compound’s value to overcome drug resistance in pancreatic cancer treatment. As C150 is the first of its class, work from this dissertation provides a preclinical basis to further explore C150 and its analogs as potential therapeutic agents for pancreatic cancer. Future studies are warranted in target identification, pharmacokinetics/pharmacodynamics, and more thorough in vivo mechanism examinations to eventually uncover the therapeutic value of C150 and shed more light on our understandings on inhibiting cancer cell EMT and enhancing ER stress to comprehensively inhibit pancreatic cancer.