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

Background Colorectal cancer (CRC) is considered the third most common type of cancer worldwide. Tumor-associated macrophages (TAMs) have been shown to promote drug resistance. Adenosine-to-inosine RNA-editing, as regulated by adenosine deaminase acting on RNA (ADAR), is a process that induces the posttranscriptional modification of critical oncogenes. The aim of this study is to determine whether the signals from cancer cells would induce RNA-editing in macrophages.
Methods The effects of RNA-editing on phenotypes in macrophages were analyzed using clinical samples and in vitro and in vivo models.
Results The intensity of the RNA-editing enzyme ADAR1 (Adenosine deaminase acting on RNA 1) in cancer and mononuclear cells indicated a strong positive correlation between the nucleus and cytoplasm. The ADAR1-positive mononuclear cells were positive for CD68 and CD163, a marker for M2 macrophages. Cancer cells transport pro-inflammatory cytokines or ADAR1 protein directly to macrophages via the exosomes, promoting RNA-editing in AZIN1 (Antizyme Inhibitor 1) and GLI1 (Glioma-Associated Oncogene Homolog 1) and resulting in M2 macrophage polarization. GLI1 RNA-editing in the macrophages induced by cancer cells promotes the secretion of SPP1, which is supplied to the cancer cells. This activates the NF kappa B pathway in cancer cells, promoting oxaliplatin resistance. When the JAK inhibitors were administered, oncogenic RNA-editing in the macrophages was suppressed. This altered the macrophage polarization from M2 to M1 and decreased oxaliplatin resistance in cancer cells.
Conclusions This study revealed that ADAR1-high TAMs are crucial in regulating drug resistance in CRC and that targeting ADAR1 in TAMs could be a promising treatment approach for overcoming drug resistance in CRC.