Background: Macrophage polarization to M2 type plays a key role in promoting the progression of oral squamous cell carcinoma (OSCC). Curcumin, as a natural active ingredient, has been proven to have anti-tumor activity, but its regulatory mechanism on macrophage polarization in OSCC remains unclear. This study aims to explore whether curcumin affects the M2 polarization of macrophages by regulating the axis inhibition protein 2 (AXIN2)/β-catenin pathway, and to clarify its effects and molecular mechanisms on the growth and invasion of OSCC cells.

Methods: RAW264.7 cells were selected to be treated with different concentrations (0, 5, 10, 20 μM) of curcumin, and the expression of M2 markers was detected by Real-time fluorescence quantitative PCR (qRT-PCR) and flow cytometry. The expression of AXIN2/β-catenin pathway molecules and downstream genes was detected using Western blotting. The localization and expression intensity of arginase-1 (ARG1) and β-catenin were observed using immunofluorescence staining. The secretion levels of cytokines were detected by enzyme-linked immunosorbent assay (ELISA). The conditioned medium of curcumin-pre-treated macrophages was collected and used to treat OSCC cell lines (HSC3, CAL33). Cell viability, proliferation, apoptosis and invasion ability were evaluated. The role of AXIN2 in curcumin-regulated macrophage polarization and OSCC cell behavior was verified by knockdown of AXIN2 in macrophages.

Results: Curcumin inhibited the polarization of M2 type macrophages in a concentration-dependent manner (p < 0.01). Mechanistically, curcumin upregulated AXIN2 expression in macrophages and inhibited the nuclear translocation of β-catenin and the expression of its downstream target genes (p < 0.01). The conditioned medium from curcumin-pre-treated macrophages significantly inhibited the viability, colony formation ability, and invasion ability of OSCC cells, and promoted cell apoptosis (p < 0.01). Knockdown of AXIN2 partially reversed the inhibitory effect of curcumin on M2 polarization of macrophages and weakened the inhibitory effect of the conditioned medium on the growth and invasion of OSCC cells (p < 0.01).

Conclusions: Curcumin inhibits the activation of the β-catenin pathway by up-regulating AXIN2 expression, thereby blocking the polarization of macrophages to the M2 type, reducing the secretion of pro-cancer cytokines, and ultimately suppressing the growth and invasion of OSCC cells. This study reveals a new mechanism by which curcumin regulates the polarization of macrophages in the tumor microenvironment, providing experimental evidence for targeted therapy of OSCC.