Gold Nanoparticle Inhibits the Tumor‐Associated Macrophage M2 Polarization by Inhibiting m6A Methylation‐Dependent ATG5/Autophagy in Prostate Cancer

Background: This study aims to study how gold nanoparticles (AuNPs) function in the recruitment and polarization of tumor‐associated macrophages (TAMs) in hormone‐sensitive prostate cancer (HSPC) and castration‐resistant prostate cancer (CRPC). Methods: Phorbol ester (PMA)‐treated THP‐1 cells were cocultured with LNCaP or PC3 cells to simulate TAMs. Macrophage M2 polarization levels were detected using flow cytometry and M2 marker determination. ATG5 expression was detected by western blotting. Luciferase reporter assay was used to analyze the N6‐methyladenosine (m 6 A) site activity of ATG5 3′ untranslated regions (3′‐UTRs). Methylated RNA immune precipitation (MeRIP)–quantitative polymerase chain reaction (qPCR) was performed to determine the m 6 A levels at ATG5 3′‐UTR. Xenograft mouse models were used to determine the function of AuNPs in vivo. Results: Macrophages exhibited reduced M2 polarization in both HSPC and CRPC cells after AuNP treatment which was prevented by induction of autophagy. AuNP treatment decreased the m 6 A levels in the 3′‐UTR of ATG5. Mutational analysis of potential m 6 A sites within ATG5 3′‐UTR revealed that these sites were required for AuNP regulation, indicating that AuNPs inhibited ATG5 levels in an m 6 A‐dependent manner. The mouse model revealed that AuNPs significantly reduced the M2 polarization of TAMs in an autophagy‐dependent manner in vivo. This suggests that AuNPs inhibit tumor growth in vivo partially through targeting M2 TAM. Conclusion: The ATG5/autophagy pathway is inhibited by AuNP treatment in an METTL3/m 6 A‐dependent manner. AuNPs inhibit the TAM M2 polarization in HSPC and CRPC by inhibiting ATG5/autophagy.