Chlorogenic acid promotes macrophage phagocytosis through the METTL3-SIRPA axis in an m6A-dependent manner for colon cancer therapy.

Epigenetic modifications, particularly N6-methyladenosine (m6A) modifications, alter the phenotype of macrophages. Among the m6A-related proteins, methyltransferase 3 (METTL3), as the catalytic core methyltransferase subunit, plays an essential role in regulating the function of macrophages. This study aimed to explore novel m6A inhibitors from natural products that target METTL3 to modulate the phagocytic function of macrophages in the treatment of colon cancer. In this work, first, a high-throughput screening of biological m6A by colorimetric assay was conducted to rapidly identify candidate inhibitors from a natural product library. Second, bioinformatics analysis and molecular biological methods revealed the underlying mechanisms through which METTL3 regulates macrophage-mediated phagocytosis. Subsequently, Mettl3f/fLyz2-Cre mice were generated to further elucidate the mechanism through which METTL3 inhibition promotes the phagocytic function of macrophages by modulating the mRNA stability of SIRPA, a key phagocytic-related protein, in vivo. We determined that chlorogenic acid (CHA) is a potential therapeutic METTL3 inhibitor because of its influence on METTL3 enzymatic activity and expression. METTL3 inhibition promoted the phagocytic function of macrophages. METTL3 increases the mRNA stability of the intrinsic immune checkpoint SIRPA by activating IGF2BP2 in an m6A-dependent manner, which subsequently increases its protein expression and suppresses the phagocytosis of macrophages both in vivo and in vitro. In conclusion, CHA is a candidate inhibitor compound that targets the METTL3-SIRPA axis through enhancing the phagocytic function of macrophages and is thus a promising therapy for treating colon cancer.