Kasugamycin Inhibits Melanoma Lung Metastasis and CHI3L1-Driven M2-Like Tumor-Associated Macrophage Differentiation.

PURPOSE: Chitinase-3-like-1 (CHI3L1) is a potent immune modulator implicated in tumor progression and immune suppression, including melanoma lung metastasis. Kasugamycin (KSM) has been reported as a pan-chitinase inhibitor with antifibrotic activity, but its effects on CHI3L1-driven immune regulation remain poorly defined. This study aimed to determine whether KSM suppresses CHI3L1-mediated tumor progression by modulating tumor-associated macrophage (TAM) differentiation and to elucidate the underlying molecular mechanisms. METHODS: The anti-tumor effects of KSM were evaluated using a B16/F10 melanoma lung metastasis model. CHI3L1 gain-of-function approaches were used to assess specificity. Lung immune populations were analyzed by flow cytometry. Human THP-1 monocytes were used to examine CHI3L1-induced macrophage differentiation in vitro. Bulk RNA sequencing was performed on differentiated macrophages to identify downstream signaling pathways. Pharmacologic inhibition studies were conducted using the epidermal growth factor receptor (EGFR) inhibitor gefitinib to validate mechanistic links. RESULTS: KSM treatment significantly reduced melanoma lung metastasis in a dose-dependent manner. CHI3L1 overexpression enhanced melanoma lung colony formation, which was effectively abrogated by KSM, indicating CHI3L1-specific anti-tumor activity. In melanoma-challenged lungs, KSM markedly decreased M2-like macrophages expressing CD206, CD163, and PD-L1. In vitro, CHI3L1 promoted M2 macrophage differentiation in THP-1 cells, which was strongly suppressed by KSM. Transcriptomic analysis revealed that EGFR expression was robustly induced by CHI3L1 and counter-regulated by KSM. Inhibition of EGFR signaling with gefitinib significantly attenuated CHI3L1-driven STAT3 activation and M2 macrophage polarization. CONCLUSION: These findings identify a previously unrecognized anti-tumor mechanism of KSM through inhibition of CHI3L1-EGFR-STAT3 signaling and suppression of M2-like TAM differentiation. KSM may therefore represent a promising immunomodulatory strategy for treating melanoma lung metastasis and other CHI3L1-driven malignancies.