Abstract 7519: Elucidation of the mechanism of acquisition of immune checkpoint inhibitor resistance by chronic inflammation
Authors: Yumoto Shinsei , Horiguchi Haruki , Baba Hideo , Oike Yuichi 
Published: March 2024

Abstract
Introduction: Eight molecules that are structurally similar to angiopoietin but do not bind to angiopoietin's specific receptor Tie2 were identified and named angiopoietin-like factors (ANGPTL). ANGPTL2, particularly abundantly expressed in adipose tissue, promotes damage repair through tissue remodeling, and contributes to tissue homeostasis; however, in severe obesity, ANGPTL2 is overexpressed, resulting in irreversible tissue remodeling, which induces chronic inflammation and is involved in systemic insulin resistance and diabetes development. On the other hand, it is unclear how systemic chronic inflammation controlled by ANGPTL2 is involved in cancer progression and acquisition of immune checkpoint inhibitor (ICI) resistance. Therefore, we aimed to elucidate the mechanisms in the acquisition of ICI resistance by systemic chronic inflammation from the perspective of ANGPTL2.
Materials and Methods: 1. To induce chronic inflammation in adipose tissue, BALB/c mice were fed high-fat-diet (HFD) for 6 weeks. CT26 cells, a mouse colon cancer cell line, were subcutaneously implanted in normal diet (ND) and HFD mice and anti PD-1/PD-L1 antibody was administered intraperitoneally. Immune cell fractions in tumor tissue and bone marrow were analyzed by flow cytometry. 2. CT26 was subcutaneously implanted in WT and systemic ANGPTL2-deficient (Angptl2−/−) mice, and anti PD-1/PD-L1 antibody was administered intraperitoneally. Tumor size and survival time were analyzed. Bone marrow cells were isolated and the immune cell fractions were analyzed by flow cytometry, and the expression of inflammatory cytokines in adipose tissue were also analyzed. 3. Bone marrow cells were isolated from BALB/c mice, and myeloid-derived suppressor cells (MDSCs) were established in vitro by GM-CSF and IL-6. Recombinant ANGPTL2 protein was added, and MDSC differentiation and function were evaluated by flow cytometry and qRT-PCR.
Results: 1. HFD mice had larger tumor size and poorer response to ICI treatment compared to ND mice. In tumor microenvironment, MDSCs were increased in HFD mice. HFD mice had significantly increased MDSCs, especially polymorphonuclear MDSCs (PMN-MDSCs) in bone marrow. 2. ICI-treated Angptl2−/− mice showed higher treatment efficacy and prolonged survival compared to WT mice. In bone marrow, MDSCs were reduced in Angptl2−/− mice under ICI treatment. In adipose tissue, the expression of chronic inflammatory markers was increased. 3. In vitro, addition of recombinant ANGPTL2 protein to MDSCs induced differentiation from mouse bone marrow cells did not significantly increase the cell ratio of MDSCs. No changes in the expression of MDSCs markers were observed in qRT-PCR.
Conclusions: Chronic inflammation induced by ANGPTL2 promotes MDSCs differentiation and maturation in the bone marrow, which may suppress anti-tumor immunity and contribute to ICI resistance.
Citation Format: Shinsei Yumoto, Haruki Horiguchi, Hideo Baba, Yuichi Oike. Elucidation of the mechanism of acquisition of immune checkpoint inhibitor resistance by chronic inflammation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7519.