Abstract C059: Targeting tumor intrinsic p38 MAPK signaling to block IL-1α-mediated inflammatory tumor-stromal crosstalk in pancreatic cancer
Authors: Singh Samara P. , Dosch Austin R. , Mehra Siddharth , Silva Iago de Castro , Bianchi Anna , Tonin-Garrido Vanessa , Deshpande Nilesh U. , Zhou Zhiqun , Nagathihalli Nagaraj , Datta Jashodeep , Merchant Nipun B. 
Published: November 2022

Abstract
Introduction: Pancreatic cancer (PDAC) remains a major therapeutic challenge due to its innate and acquired chemoresistance. Activating KRAS mutations, a hallmark of PDAC, mediate autocrine effects and crosstalk within the tumor microenvironment (TME), by inducing cytokines and chemokines that promote a pro-inflammatory and immunosuppressive stroma. We have identified KRAS-driven interleukin-1α (IL-1α) as a critical mediator of the inflammatory response due to its pleiotropic effects on cancer-associated fibroblast (CAF) activation and immune evasion, however the mechanisms that regulate IL-1α production remain poorly understood. In our efforts to identify targetable kinase pathways downstream of KRAS that are involved in IL-1α expression, we identified p38 stress-associated MAPK α (p38α MAPK) as a key regulatory pathway involved in IL-1α production in PDAC tumor cells. Methods: KRAS-mutant tumor cells were treated with pharmacologic inhibitors to pathways downstream KRAS and IL1A levels determined in response by qPCR. Mutant KRAS G12D plasmid was overexpressed in mouse embryonic fibroblasts, and IL-1α levels were determined in response by qPCR and ELISA with and without p38 inhibition. Inhibition of phosphorylated p38 MAPK was achieved pharmacologically with ARRY-614 and genetically with an shRNA lentiviral system in human and murine PDAC cell lines. ChIP-qPCR was performed on a human PDAC cell line with and without p38 MAPK inhibition. Tumor cells pre-treated with ARRY-614 were cocultured with human pancreatic stellate cells, and inflammatory CAF genes were measured by qPCR. Ptf1aCre/+;LSL-KrasG12D/+; Tgfbr2flox/flox (PKT) mice, a highly aggressive PDAC genetically engineered mouse model (GEMM), were treated daily with ARRY-614, chemotherapy, or combination therapy for downstream analysis. Results: Both pharmacologic and genetic inhibition of p38 MAPK significantly reduces IL1A transcription and protein levels in multiple human and murine PDAC tumor cell lines. Furthermore, p38 MAPK inhibition reduces binding of NF-kB to the IL1A promoter and prevents IL-1α-mediated activation of CAFs, characterized by a reduction in pro-inflammatory genes. Lastly, ARRY-614 in combination with chemotherapy significantly reduces overall tumor burden and favorably remodels the tumor microenvironment in a PDAC GEMM. Conclusions: These findings provide a compelling rationale to explore p38 MAPK inhibition in tumor cells as a novel treatment strategy to suppress IL-1α-mediated stromal activation and to combine p38 MAPK inhibition with chemotherapy to overcome therapeutic resistance through modulation of the stromal and immune microenvironment in PDAC.
Citation Format: Samara P. Singh, Austin R. Dosch, Siddharth Mehra, Iago de Castro Silva, Anna Bianchi, Vanessa Tonin-Garrido, Nilesh U. Deshpande, Zhiqun Zhou, Nagaraj Nagathihalli, Jashodeep Datta, Nipun B. Merchant. Targeting tumor intrinsic p38 MAPK signaling to block IL-1α-mediated inflammatory tumor-stromal crosstalk in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C059.