Abstract 2539: Macrophage derived WNTs regulate immune checkpoint expression and inflammation induced colon cancer
Authors: Saha Subhrajit , Gupta Pooja , Chugh Rishi Man , Olea Ximena Diaz , Arora Tanu , Bhanja Payel 
Published: June 2022

Abstract
Colorectal cancer is the third most common cancer in the world. Patients with inflammatory bowel disease are at an elevated risk for developing colon cancer. Macrophages are important members of tumor microenvironment (TME) and promote inhibition of anti-tumor immunity by activation of immune checkpoints and other neo-antigens expressions. However, paracrine signals regulating these checkpoint expressions in macrophages need to be determined. Macrophage-derived WNT ligands play important role in tissue homeostasis in multiple organs. In the present study we have demonstrated that inhibition of macrophage-derived WNT promotes inflammation-induced colon cancer. In both the mice model and human in vitro model we have shown that the absence of macrophage-derived WNT promotes immunosuppressive microenvironment with upregulation of immune checkpoint expressions in tumor-associated macrophages and T cells. Release of WNT ligands expressed in macrophages was inhibited by using Csf1r.iCre; Porcn fl/fl mice where gene expressing PORCUPINE involved in post translational modification and release of WNT ligands was deleted in macrophages using Cre recombinase expressed under Csf1r promoter. In these mice and wild type littermates, Inflammation-induced colon cancer was developed using AOM-DSS treatment. Mice were treated with a single dose of 16mg/kg of body weight Azoxymethane (AOM) (i.p.) and subsequent three cycles of 3.5% of Dextran sodium sulfate (DSS) (supplementation in drinking water). Development of colon cancer was monitored using small animal colonoscopy. After 3 cycles of DSS Csf1r.iCre; Porcn fl/fl mice demonstrated a significantly higher number of colon tumors compared to wild type littermate (Macro size: p&lt;0.0005, Micro size: p&lt;0.013). Moreover, flow cytometric analysis of tumor tissue demonstrated that in Csf1r.iCre; Porcn fl/fl mice both PD1 and PDL1 expression was high in tumor-associated macrophages compared to wild type mice. PDL1 expression was also high in colon tumor tissue, myeloid-derived suppressor cells (MDSCs) and helper T cells in Csf1r.iCre; Porcn fl/fl mice. Similar observation was made in ex-vivo co-culture model using human pan T cells, HTB-38 human colon cancer cells and human peripheral blood mononuclear cell (PBMC) derived macrophages pre-treated with PORCUPINE inhibitor C59. Therefore, our present study demonstrated for the first time that macrophage-derived WNT is required to modulate the immunosuppressive role of macrophages in inflammation-induced colon cancer. Inhibition of WNT release specific from macrophages promotes PDL1 expression in colon cancer cells and other cell types in TME including MDSCs, and T helper cells. Further studies are ongoing to determine the mechanism of autocrine action of WNT ligands in tumor-associated macrophages to maintain anti-tumor immunity.
Citation Format: Subhrajit Saha, Pooja Gupta, Rishi Man Chugh, Ximena Diaz Olea, Tanu Arora, Payel Bhanja. Macrophage derived WNTs regulate immune checkpoint expression and inflammation induced colon cancer [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 2539.