Abstract 4105: ADAR1-high tumor-associated macrophages induce drug resistance and are therapeutic targets in colorectal cancer

Abstract Background: Colorectal cancer (CRC) is one of the most prevalent cancers. In case of CRC with distant metastasis, it is initially treated by chemotherapy, and oxaliplatin is often used in first-line regimen. However, chemoresistance often becomes an issue and it remains unclear. We previously reported that RNA editing enzyme ADAR1 causes stemness (JCI Insight, 2018) and induces the poor prognosis in the liver metastasis of CRC (Scientific Reports, 2023). In this study, we cleared the role of RNA editing in chemoresistance of CRC. Methods: We performed immunohistochemistry (IHC) of ADAR1 in 151 cases of CRC with distant metastasis. In vitro, we analyzed ADAR1 expression and RNA editing levels in both cancer cells and macrophages with the CRC cell lines and differentiated THP-1(dTHP-1). RNA-sequence was performed to compare wild type and ADAR1 knockdown dTHP-1 co-cultured with CRC cells respectively. In vivo, xenograft mouse models were made by mixing CRC cells and macrophages, and treatment experiment was conducted using oxaliplatin. Results: IHC scoring showed that high expression of ADAR1 in CRC cancer cells relates the poor prognosis (p<0.01). Moreover, high expression of ADAR1 in the stromal mononuclear cells relates the poor prognosis (p=0.032) and resistance to oxaliplatin (p<0.01). Additionally, there was a positive correlation between the expression levels of ADAR1 in macrophages in tumor tissue and cancer cells (ρ=0.74, p < 0.001). In vitro, macrophages increased the intensity of ADAR1 expression when indirectly co-cultured with CRC cells (p<0.01). These results suggested that ADAR1 might be supplied from CRC cells to macrophages through some liquid factors. We focused on extracellular vesicles (EVs). Western blotting revealed that EVs from CRC cells contained ADAR1. When these EVs were added to macrophages, ADAR1 expression increased in the macrophages. ADAR1 increased RNA editing levels in macrophages, including AZIN1 and GLI1. Next, RNA-sequence analysis showed an enrichment of pathways associated with distant tumor metastasis in macrophages with high ADAR1 expression (p<0.05). Additionally, an increase in SPP1 gene expression, which is involved in tumor immune suppression, was observed. In vivo, xenograft mouse models were made, knockdown of ADAR1 in macrophages enhanced the effect of oxaliplatin to inhibit tumor growth (p<0.01). Treatment model mouse was made using oxaliplatin in combination with filgotinib, JAK inhibitor that reduces ADAR1 expression. The results showed a significant inhibition of tumor growth in the oxaliplatin plus JAK inhibitor group (p=0.0197). Conclusions: We showed that ADAR1-high macrophages are induced by stimulation from CRC cells via EVs and it may cause chemoresistance. Cancer cells and macrophages dual-targeted RNA editing suppression therapy was considered a promising treatment option. Citation Format: Kazuya Moriwake, Kunitoshi Shigeyasu, Hibiki Umeda, Toshiaki Takahashi, Masashi Kayano, Kaori Nitta, Shunsuke Nakamura, Masafumi Takahashi, Yuya Sakurai, Yuki Matsumi, Yoshitaka Kondo, Fuminori Teraishi, Hiroshi Tazawa, Toshiyoshi Fujiwara. ADAR1-high tumor-associated macrophages induce drug resistance and are therapeutic targets in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4105.