Kasugamycin inhibits melanoma lung metastasis and regulates CHI3L1-driven M2-like tumor-associated macrophage differentiation.

CHI3L1, a chitinase-like protein, is a potent immune modulator involved in various diseases, including lung cancer. While recent studies have demonstrated that kasugamycin (KSM) is a pan-chitinase inhibitor with strong anti-fibrotic activity, its effects on specific chitinase-like proteins remain undefined. This study shows that KSM effectively abrogates CHI3L1-stimulated cellular signaling and bioactivities. In a B16/F10 melanoma lung metastasis model, where CHI3L1 plays a critical role, KSM treatment significantly reduced melanoma lung metastasis dose-dependently. The anti-tumor effect of KSM was found to be CHI3L1-specific, as CHI3L1 overexpression enhanced melanoma lung colony formation, which was effectively blocked by KSM. In melanoma-challenged lungs, KSM treatment significantly reduced the elevation of M2 macrophages expressing CD206, CD163, and PD-L1. In studies using human monocytic THP-1 cells, CHI3L1 promoted M2 macrophage differentiation, which KSM significantly suppressed. Bulk RNA sequencing of differentiated macrophages revealed that CHI3L1 highly induced the expression of epidermal growth factor receptor (EGFR), and this induction was counter-regulated by KSM, and CHI3L1-driven M2 macrophage activation was reduced with EGFR blocker treatment. These findings reveal a novel anti-tumor mechanism of KSM, which inhibits M2-like tumor-associated macrophage differentiation, potentially through the CHI3L1-EGFR axis.