Cholecystokinin Receptor Antagonist Improves Efficacy of Chemotherapy in Murine Models of Pancreatic Cancer by Altering the Tumor Microenvironment

SIMPLE SUMMARY: Our research team has identified the cholecystokinin-B receptor (or CCK-BR) as a novel target for treatment of pancreatic cancer. CCK-BRs are over-expressed in pancreatic cancer and activation stimulates growth in cell culture and in animal models. CCK-BRs are also expressed on pancreatic stellate cells—or the fibroblasts that are responsible for the dense fibrosis in the tumor microenvironment that impedes the penetration of chemotherapy. We show strong evidence that treatment with a CCK receptor antagonist, proglumide, decreases fibrosis in the pancreatic tumor microenvironment and increases the influx of T-cells rendering chemotherapy-resistant cancer, sensitive to gemcitabine. Mice treated with the combination therapy had fewer metastases and greater survival. Tumors from these mice had higher gemcitabine levels and novel differentially expressed genes by RNA-Seq. Proglumide is an older drug that was developed many years ago for peptic ulcer disease but is no longer in use. Repurposing this older drug may improve survival from this recalcitrant malignancy. ABSTRACT: Pancreatic cancer is resistant to chemotherapy in part due to the dense desmoplastic fibrosis surrounding the tumor, the immunosuppressive cells in the tumor microenvironment (TME), and the early rate of metastases. In this study, we examined the effects of a CCK receptor antagonist, proglumide, alone and in combination with gemcitabine in murine models of pancreatic cancer. Tumor growth rate, metastases, and survival were assessed in mice bearing syngeneic murine or human pancreatic tumors treated with PBS (control), gemcitabine, proglumide, or the combination of gemcitabine and proglumide. Excised tumors were evaluated histologically for fibrosis, immune cells, molecular markers, and uptake of chemotherapy by mass spectroscopy. Peripheral blood was analyzed with a microRNAs biomarker panel associated with fibrosis and oncogenesis. Differentially expressed genes between tumors of mice treated with gemcitabine monotherapy and combination therapy were compared by RNAseq. When given in combination the two compounds exhibited inhibitory effects by decreasing tumor growth rate by 70%, metastases, and prolonging survival. Proglumide monotherapy altered the TME by decreasing fibrosis, increasing intratumoral CD8(+) T-cells, and decreasing arginase-positive cells, thus rendering the tumor sensitive to chemotherapy. Proglumide altered the expression of genes involved in fibrosis, epithelial–mesenchymal transition, and invasion. CCK-receptor antagonism with proglumide renders pancreatic cancer susceptible to chemotherapy.