Growth of
pancreatic cancer is stimulated by
gastrin in both a paracrine and an autocrine fashion. Traditional
therapies have not significantly improved survival, and recently
pancreatic cancer has been deemed a "cold"
tumor due to its poor response to
immunotherapy. Strategies to improve survival of
pancreatic cancer are desperately needed. In the current investigation, we studied the effects of an anti-
gastrin cancer vaccine, polyclonal antibody stimulator (PAS; formerly called G17DT and
Gastrimmune), used alone or in combination with a programmed cell death receptor (PD)-1 immune checkpoint antibody on
pancreatic cancer growth,
metastases, and the tumor microenvironment (TME). Immune-competent female C57BL/6 mice bearing syngeneic orthotopic murine
pancreatic cancer treated with PAS had significantly smaller
tumors and fewer
metastases. Examination of the TME demonstrated decreased
fibrosis with fewer M2 and more M1 tumor-associated macrophages. Expression of the
E-cadherin gene was significantly increased and expression of the TGFβR2 gene was decreased compared with controls. Mice treated with PAS or the combination of PAS and PD-1 antibody exhibited significantly less
tumor expression of phospho-
paxillin, the focal adhesion
protein β-
catenin, and
matrix metalloproteinase-7. This study suggests that inhibition of the
cancer-promoting effects of
gastrin in
pancreatic cancer can decrease
metastases by altering the TME and decreasing pathways that activate the epithelial mesenchymal transition. The PAS
vaccine appears to change the TME, making it more susceptible to
therapy with an immune checkpoint antibody. This novel combination of two
immunotherapies may improve survival of
pancreatic cancer by decreasing both
tumor growth and
metastasis formation.NEW & NOTEWORTHY Survival from advanced
pancreatic cancer is poor, in part due to dense
fibrosis of the tumor microenvironment, increased number of M2-polarized macrophages that promote angiogenesis and invasion, and lack of "target-specific"
therapy. Herein, we report that a
tumor vaccine that selectively targets
gastrin decreases
pancreatic cancer growth and
metastases. Furthermore, the
gastrin vaccine polyclonal antibody stimulator alters the tumor microenvironment rendering it more responsive to
immunotherapy with a programmed cell death receptor-1 immune checkpoint antibody.