Chitosan Oligosaccharide Suppresses Fibronectin- and Osteopontin-Associated Malignant Phenotypes in A2058 Melanoma Cells

Background: While chitosan oligosaccharide (COS) has been reported to exert anti-tumor and immunomodulatory effects, its functional impact on malignant melanoma remains poorly defined. Herein, we investigated the biological actions of COS in A2058 human melanoma cells, focusing on malignant behavior.Methods: COS was prepared from highly deacetylated, low-viscosity chitosan and applied to A2058 cells under conventional monolayer culture and spheroid formation cultures in fetal bovine serum (FBS)- or growth factor (GF)–supplemented conditions. Cell viability, migration, spheroid formation, Western blotting for epithelial-mesenchymal transition and aggressiveness were assessed. Immunohistochemistry was used to evaluate osteopontin expression in human skin cancer tissue microarrays.Results: Although COS exhibited limited direct cytotoxicity in A2058 melanoma cells, it suppressed spheroid formation. Fibronectin, upregulated during spheroid formation, was reversed by COS in a concentration-dependent manner, whereas other epithelial-mesenchymal markers were less consistently affected. COS significantly downregulated osteopontin in monolayer and spheroids in GF-supplemented conditions. While exogenous recombinant osteopontin enhanced migration in a dose-dependent manner, low-dose COS (50 µg/mL) abolished this pro-migratory effect. In tissue microarrays, osteopontin immunostaining was higher in normal skin than in melanoma and tended to decrease with stage advancement. While COS did not alter the secretory fraction of osteopontin, it reduced exogenous osteopontin levels.Conclusions: COS selectively suppresses malignant phenotype by reducing fibronectin, and attenuates osteopontin expression and its functional contribution to migration in melanoma. This suggests that COS may serve as an adjuvant or preventive strategy to restrain melanoma progression and metastatic dissemination.