Loss of aryl hydrocarbon receptor reduces pancreatic tumor growth by increasing immune cell infiltration

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease which remains poorly understood. Increasing evidence suggests that the aryl hydrocarbon receptor (AHR) plays a role in the pathogenesis of several cancers; however, its role in PDAC is unclear because AHR exhibits both pro- and anti-tumor activities. Here we evaluated the role of AHR in CR705 and K8484 murine PDAC cells in vitro and CR705 cells in vivo. Loss of Ahr did not affect cell proliferation compared with Cas9 control cells and no differences in tumor development between CR705^Cas9 and CR705^AhrKO cells were observed in immunocompromised mice. Conversely, tumors from CR705^AhrKO cells grew more slowly than tumors from CR705^Cas9 cells in immune competent mice. RNA sequencing identified 1279 genes upregulated and 586 genes downregulated in CR705^AhrKO tumors compared with CR705^Cas9 tumors. Pathway analysis identified immunoregulatory interactions, interferon signaling, and chemokine signaling among the top upregulated pathways. Increased infiltration of CD45⁺ cells and higher numbers of CD8⁺ T cells and F4/80⁺ cells were observed in CR705^AhrKO tumors. Ahr deficiency in macrophages (LysMCre) or lymphocytes (RorcCre) did not alter tumor development of CR705^Cas9 cells compared with Ahr^fl/fl mice. CR705^AhrKO tumors in RorcCre mice, but not in LysMCre mice had significantly lower tumor weights normalized to body weights compared with CR705^AhrKO tumors in WT mice. These findings show that Ahr loss in CR705 pancreatic cancer cells is sufficient to induce proinflammatory gene responses that contribute to increased immune cell infiltration and reduced tumor growth.