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

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease which despite large research efforts remains poorly understood. Many studies provide evidence that the aryl hydrocarbon receptor (AHR) plays a critical role in the pathogenesis of several cancers and represents new anti-cancer therapeutic target. The role of AHR in PDAC is, however, unclear since AHR has been reported to exhibit both pro- and anti-tumor activities. In this study we evaluated the role of AHR in murine PDAC cells in vitro and in vivo. Loss of AHR did not affect cell proliferation compared with wildtype (WT). Consistent with these findings, no differences in tumor development between WT and AhrKO cells were observed in immunocompromised mice. However, tumors from AhrKO cells grew more slowly than tumors from WT cells in immune competent mice. RNA sequencing of the tumors resulted in 1009 genes upregulated and 477 genes downregulated in AhrKO tumors compared with WT tumors. Pathway analysis identified immunoregulatory interactions, interferon signaling, interleukin signaling and PD1 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 AhrKO tumors. Analysis of the F4/80+ cell populations revealed a lower percentage of anti-inflammatory (M2) macrophages in AhrKO tumors. Ahr deficiency in macrophages (LysMCre) or lymphocytes (RorcCre) did not alter tumor development of WT cells compared with WT C57BL/6 mice. AhrKO tumors in RorcCre mice, but not in LysMCre mice had significantly lower tumor weights normalized to body weights compared with AhrKO tumors in WT mice. These findings show that tumors derived from AhrKO pancreatic cancer cells exhibit a proinflammatory gene responses that contribute to increased immune cell infiltration and reduced tumor growth. They also suggesting that loss of AHR in lymphocytes together Ahr loss in cancer cells further reduces tumor growth.