Inhibition of mucin-type O -glycosylation impairs melanogenesis, melanoma growth, and metastatic capacity

Tumor-associated glycans are critical regulators of immune evasion in melanoma. Despite the success of immune checkpoint blockade, resistance and relapse remain a challenge, highlighting the need to therapeutically target additional immunosuppressive axes. One such axis involves Siglec-sialoglycan interactions that facilitate tumor immune evasion. The melanoma-associated antigen Pmel17/gp100 is a melanosomal glycoprotein overexpressed in tumor cells and essential for melanosomal architecture. Pmel17/gp100 forms amyloid fibrils within melanosomes, and its extensive O- glycosylation contributes to melanin biosynthesis and melanoma progression. We show that pharmacological inhibition of O- glycosylation using peracetyl N- thioglycolyl-D-galactosamine (Ac 5 GalNTGc, 1a ) decreases Pmel17/gp100 glycosylation and melanin synthesis in B16F10 melanoma cells, induces tumor surface hyposialylation, diminishes Siglec-E engagement, and disrupts the Siglec-sialoglycan immune checkpoint. In C57BL/6J mice, 1a significantly delayed tumor growth, prolonged survival, and reduced lung metastases relative to controls. These findings identify O- glycosylation as a dual-mode therapeutic vulnerability, linking melanosome dysfunction to attenuation of Siglec-mediated immune evasion in melanoma. Summary Mucin-type O- glycans on melanoma cell surfaces and the melanosomal protein, Pmel17/gp100, regulate melanogenesis and melanoma metastasis. The O- glycosylation inhibitor, peracetyl N- thioglycolyl-D-galactosamine (Ac 5 GalNTGc, 1a ), suppressed melanin synthesis and induced hyposialylation, thereby disrupting Siglec-mediated immune evasion and retarding tumor growth and metastasis.