Abstract 3197: Blockade of regulatory signaling pathways reduces immunosuppression in the PDAC tumor microenvironment
Authors: Greenlees Lydia , Cheng Li , Omar Bilal , Lazdun Yelena , Wang Jixin , Pilataxi Fernanda , Kuziora Michael , Cooper Zachary , Vence Luis , Streicher Katie 
Published: June 2022

Abstract
Pancreatic cancer (PDAC) has the highest mortality rate of all major cancers, with few treatment options that provide long-term benefit to patients. Cancer associated fibroblasts (CAFs), the primary cellular component of the pancreatic tumor stroma, play a key role in the formation of an immunosuppressive tumor microenvironment (TME). A better understanding of the disease biology and cellular pathways that could be targeted for treatment of PDAC are needed.
To investigate mechanisms driving immune suppression and pathways that might be targetable for treatment in PDAC, we used models where cross-talk between stromal and tumor cells could be evaluated. Three PDAC tumor cell lines were co-cultured (CC) with primary CAFs from multiple donors for 3 days, and secretion of numerous immunosuppressive cytokines, including IL6, IL8, IL10, CXCL12, was found to be upregulated in CC vs single culture (SC). IL6 and IL8 were shown to increase 2-38-fold in CC vs SC CAFs, and 1.5-20,000-fold vs SC PANCs, dependent upon cell line. By whole genome array, an upregulation of genes involved in NFkB, IL6, IL8, and AKT signaling was also observed (-log(p-value)&gt;4) in CAF cells following CC.
Multiple pathways have been implicated in regulating the immunosuppressive PDAC TME, including: CD73, a critical mediator of adenosine formation which is known to alter immune activity; and IL1, which is secreted by PDAC tumor cells, known to increase inflammation in the TME, and promote PDAC progression. The effects of CD73 inhibition and IL1R inhibition were evaluated to better characterize the downstream effects of these pathways on regulating tumor immunosuppression. Inhibition of CD73 in the CC reduced production of the immunosuppressive cytokines IL6, IL8, MCP1 CXCL12, IL1a, IL1b, IL10 (16-59%). Preliminary genomic studies indicated that inhibition of CD73 decreased genes involved in invasion, migration, metastasis, EMT and angiogenesis, as well as increasing genes involved in type 1 IFN activation, including OAS1, DDX60, IFIT1 and IRF7 (FC 1.5-2). Similarly, blockade of IL1R (which is highly expressed on PDAC CAFs and is the receptor for both IL1a and IL1b) reduced immune suppressive cytokine production from PDAC tumor conditioned media-stimulated CAFs, e.g. lowering secretion of IL6 and IL8 (4-20-fold) in a dose-dependent manner. Blocking IL1R in a PDAC dissociated tumor cell (DTC) model resulted in decreased secretion of CXCL1 and IL6 (60-75% over 3-6 days in culture), and an upregulation of IFNg (2-10-fold) in this culture by d3.
These results suggest that a blockade of regulatory signaling pathways may be useful to reduce immune suppression and return the PDAC TME to a phenotype more amenable to immune checkpoint inhibition. Further characterization of these pathways may lead to new therapeutic combination approaches for pancreatic cancer.
Citation Format: Lydia Greenlees, Li Cheng, Bilal Omar, Yelena Lazdun, Jixin Wang, Fernanda Pilataxi, Michael Kuziora, Zachary Cooper, Luis Vence, Katie Streicher. Blockade of regulatory signaling pathways reduces immunosuppression in the PDAC tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3197.