The cancer microenvironment allows tumor cells to evade immune surveillance through a variety of mechanisms. While interferon-γ (IFNγ) is central to effective antitumor immunity, its effects on the microenvironment are not as clear and have in some cancers been shown to induce immune checkpoint ligands. The heterogeneity of these responses to IFNγ remains poorly characterized in desmoplastic malignancies with minimal inflammatory cell infiltration, such as pancreatic cancer (PC). Thus, the IFNγ response within and on key cells of the PC micro-environment was evaluated. IFNγ induced expression of human leukocyte antigen (HLA) class I and II on PC cell lines, primary pancreatic cancer epithelial cells (PPCE) and patient-derived tumor-associated stroma, concomitant with an upregulation of PDL1 in the absence of CD80 and CD86 expression. As expected, IFNγ also induced high levels of CXCL10 from all cell types. In addition, significantly higher levels of CXCL10 were observed in PC specimens compared to those from chronic pancreatitis, whereby intratumoral CXCL10 concentration was an independent predictor of poor survival. Immunohistochemical analysis revealed a subset of CXCR3-positive cancer cells in over 90 % of PC specimens, as well as on a subset of cultured PC cell lines and PPCE, whereby exposure to CXCL10 induced resistance to the chemotherapeutic gemcitabine. These findings suggest that IFNγ has multiple effects on many cell types within the PC microenvironment that may lead to immune evasion, chemoresistance and shortened survival.

Background: The systemic treatment of pancreatic cancer (PC) is hindered by the rapid development of chemoresistance to current cytotoxic therapies. Mechanisms governing the development of chemoresistance remain poorly characterized, particularly with respect to contributions from the tumor microenvironment. Thus, the goal of this study was to identify novel mechanisms acting within the tumor microenvironment which lead to PC chemoresistance. Methods: Intratumoral soluble mediator concentrations from resected PC specimens (n = 26) as well as supernatants from co-cultures of primary tumor-associated pancreatic stellate cells (PSCs) and PC cells (n = 12) were evaluated using a panel of 41 growth factors, chemokines and cytokines. The effect of CXCL10, a highly expressed soluble mediator during co-culture, on viability, proliferation, and apoptosis of PC cells was evaluated with and without gemcitabine treatment. In addition, the contribution of CXCL10 on migration patterns of peripheral blood mononuclear cells (PBMCs) was assessed. Results: Co-culture of tumor-associated PSCs with PC cells revealed increased CXCL10 levels compared to either cell type cultured alone. In addition, high intratumoral CXCL10 concentrations correlated with reduced overall survival (HR 6.9; P = .006). While CXCL10 treatment had a small effect on the viability of PC cells, it led to significantly increased PC cell viability in the presence of gemcitabine. Further, gemcitabine treatment induced the expression of the CXCL10 receptor, CXCR3, and this induction of CXCR3 was associated with the absence of apoptotic markers in PC cells. Finally, constitutive expression of CXCL10 by PC cells preferentially led to the migration of regulatory immune cell subsets. Conclusion: Paracrine CXCL10 signaling between stromal, PC and immune cells may be responsible not only for chemoresistance to gemcitabine, but also the recruitment and potential polarization of regulatory immune cell subsets in the pancreatic cancer microenvironment. Citation Format: Daniel Delitto, Chelsey Perez, Brian S. Black, Heather L. Sorenson, Andrea E. Knowlton, Song Han, Dongyu Zhang, George A. Sarosi, Lyle L. Moldawer, Kevin E. Behrns, Chen Liu, Thomas J. George, Ryan M. Thomas, Jose G. Trevino, Shannon M. Wallet, Steven J. Hughes. CXCL10 within the tumor microenvironment induces gemcitabine resistance in pancreatic cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5028. doi:10.1158/1538-7445.AM2015-5028