Cancer associated fibroblasts (CAFs) comprise the majority of the tumor bulk of pancreatic adenocarcinomas (PDACs). Current efforts to eradicate these tumors focus predominantly on targeting the proliferation of rapidly growing cancer epithelial cells. We know that this is largely ineffective with resistance arising in most tumors following exposure to chemotherapy. Despite the long-standing recognition of the prominence of CAFs in PDAC, the effect of chemotherapy on CAFs and how they may contribute to drug resistance in neighboring cancer cells is not well characterized. Here we show that CAFs exposed to chemotherapy play an active role in regulating the survival and proliferation of cancer cells. We found that CAFs are intrinsically resistant to gemcitabine, the chemotherapeutic standard of care for PDAC. Further, CAFs exposed to gemcitabine significantly increase the release of extracellular vesicles called exosomes. These exosomes increased chemoresistance-inducing factor, Snail, in recipient epithelial cells and promote proliferation and drug resistance. Finally, treatment of gemcitabine-exposed CAFs with an inhibitor of exosome release, GW4869, significantly reduces survival in co-cultured epithelial cells, signifying an important role of CAF exosomes in chemotherapeutic drug resistance. Collectively, these findings show the potential for exosome inhibitors as treatment options alongside chemotherapy for overcoming PDAC chemoresistance.

The prognosis for patients with pancreatic ductal adenocarcinoma (PDAC) is dismal. Although gemcitabine (GEM) is the standard chemotherapeutic agent for adjuvant therapy of resectable PDAC, recurrent disease is observed in an alarming number of GEM-treated patients. Regardless of the adjuvant therapy, the vast majority of patients treated with chemotherapy after surgical resection show tumor recurrence. A better understanding of the molecular mechanisms that contribute to chemoresistance would aid the development of more effective treatment strategies. GRP78 is an endoplasmic reticulum (ER) chaperone protein that primarily resides in the lumen of the ER and is the master regulator of the unfolded protein response (UPR). Here, we report that expression of GRP78 is significantly higher in GEM-resistant PDAC compared to GEM-sensitive PDAC patient samples. We show that GRP78 induces chemoresistance in PDAC cells. Our results also show that knockdown of GRP78 reduces chemoresistance in PDAC. Finally, we found that IT-139, a ruthenium-based anticancer drug, can overcome GRP78-mediated chemoresistance. In vitro, IT-139 restores sensitivity to cytotoxic drugs in drug-resistant PDAC cells and induces twice as much cell death in combination treatment compared with GEM alone. In vivo, a single weekly IT-139 treatment in combination with GEM caused a 35% increase in median survival and a 25% increase in overall survival compared to GEM alone. Collectively, our data show that GRP78 expression promotes chemoresistance in PDAC and therapeutic strategies, blocking the activity of GRP78 increases the efficacy of currently available therapies.

Pancreatic ductal adenocarcinoma (PDAC) presents at metastatic stage in over 50% of patients. With a survival rate of just 2.7% for patients presenting with distant disease, it is imperative to uncover novel mechanisms capable of suppressing metastasis in PDAC. Previously, we reported that the loss of metastasis suppressor protein 1 (MTSS1) in PDAC cells results in significant increase in cellular migration and invasion. Conversely, we also found that overexpressing MTSS1 in metastatic PDAC cell lines corresponds with not only decreased metastatic phenotype, but also greater overall survival. While it is known that MTSS1 is downregulated in late-stage PDAC, the mechanism behind that loss has not yet been elucidated. Here, we build off our previous findings to present a novel regulatory mechanism for the stabilization of MTSS1 via the tumor suppressor protein phosphatase and tensin homolog (PTEN). We show that PTEN loss in PDAC cells results in a decrease in MTSS1 expression and increased metastatic potential. Additionally, we demonstrate that PTEN forms a complex with MTSS1 in order to stabilize and protect it from proteasomal degradation. Finally, we show that the inflammatory tumor microenvironment, which makes up over 90% of PDAC tumor bulk, is capable of downregulating PTEN expression through secretion of miRNA-23b, potentially uncovering a novel extrinsic mechanism of MTSS1 regulation. Collectively, these data offer new insight into the role and regulation of MTSS1in suppressing tumor cell invasion and migration and help shed light as to what molecular mechanisms could be leading to early cell dissemination in PDAC.

Pancreatic ductal adenocarcinoma (PDAC) has a 5-year survival rate of 7%. This dismal prognosis is largely due to the inability to diagnose the disease before metastasis occurs. Tumor cell dissemination occurs early in PDAC. While it is known that inflammation facilitates this process, the underlying mechanisms responsible for this progression have not been fully characterized. Here, we functionally test the role of metastasis suppressor 1 (MTSS1) in PDAC. Despite evidence showing that MTSS1 could be important for regulating metastasis in many different cancers, its function in PDAC has not been studied. Here, we show that loss of MTSS1 leads to increased invasion and migration in PDAC cell lines. Moreover, PDAC cells treated with cancer-associated fibroblast-conditioned media also have increased metastatic potential, which is augmented by loss of MTSS1. Finally, overexpression of MTSS1 in PDAC cell lines leads to a loss of migratory potential in vitro and an increase in overall survival in vivo. Collectively, our data provide insight into an important role for MTSS1 in suppressing tumor cell invasion and migration driven by the tumor microenvironment and suggest that therapeutic strategies aimed at increasing MTSS1 levels may effectively slow the development of metastatic lesions, increasing survival of patients with PDAC.

No abstract

Purpose: We show that expression of GRP78, the master regulator of the endoplasmic reticulum (ER) stress response, leads to chemotherapy resistance in pancreatic ductal adenocarcinoma (PDAC) and utilize a small molecule inhibitor to block the activity of GRP78, increasing the efficacy of currently available therapies in vitro and in vivo. Background: Gemcitabine (GEM) is the standard chemotherapeutic agent for adjuvant therapy of PDAC and a commonly used agent in other treatment settings, including neoadjuvant treatment of borderline resectable PDAC and palliative treatment of metastatic PDAC. However, recurrent disease is observed in an alarming number of patients treated with GEM or GEM-based treatment regimens. A molecular-level understanding of the mechanisms that contribute to chemoresistance is essential for the development of more effective treatment strategies. ER chaperone proteins protect cells from apoptosis in response to cellular insults, including inflammation and pancreatitis. Elevated expression of chaperone proteins also causes the activation of many “pro-survival” pathways that promote cell survival and resistance to routinely utilized therapeutic regimens. We hypothesize that expression of ER chaperone protein GRP78, is responsible for innate and acquired resistant to GEM and that therapies targeting GRP78 by blocking its activity with the small molecule inhibitor, IT-139, could potentially improve patient response to GEM-based treatment regimens. Methods: We examined if GRP78 overexpression correlated with chemoresistance in PDAC through establishing a patient-derived orthotopic xenograft (PDX) model. Treating tumor-bearing mice with GEM continuously or releasing mice from GEM treatment after 3-4 weeks of exposure identified PDX lines that were either sensitive or resistant to GEM. Tumors from these cohorts were analyzed for GRP78 expression. To examine the role of GRP78 in chemoresistance in vitro, GRP78 expression was induced in GEM-sensitive cell lines prior to GEM treatment. Further, to investigate the effect of GRP78 loss on chemoresistance, siRNA knockdown of GRP78, followed by GEM treatment, was used in GEM-resistant cell lines. Finally, the efficacy of combination treatment with GEM and IT-139, a ruthenium-based anticancer drug and GRP78 inhibitor, was determined in vitro and in vivo. Results: Here, we report that PDX lines that result in GEM resistant PDAC have higher GRP78 expression than that of GEM sensitive PDX lines. In vitro, increased GRP78 induces chemoresistance in GEM-sensitive PDAC cell lines while knockdown of GRP78 reduces chemoresistance in GEM-resistant PDAC cell lines. Finally, we found that IT-139 can overcome GRP78 mediated chemoresistance. In vitro, IT-139 restores sensitivity to cytotoxic drugs in drug resistant PDAC cells and induces twice as much cell death in combination treatment compared with GEM alone. In vivo, a single weekly IT-139 treatment in combination with GEM caused a 35% increase in median survival and a 25% increase in overall survival compared to GEM alone. Conclusions: Collectively, our data show that GRP78 expression promotes chemoresistance in PDAC and therapeutic strategies blocking the activity of GRP78 increase the efficacy of currently available therapies. Citation Format: Jenifer B. Gifford, Wei Huang, Ann E. Zeleniak, Antreas Hindoyan, Hong Wu, Timothy R. Donahue, Reginald Hill.{Authors}. ER chaperone GRP78 increases chemoresistance in pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B08.