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

Treatment of malignant and metastatic melanoma remains a clinical challenge, despite the success of immune checkpoint blockade and kinase inhibitors, highlighting the need to target complementary pathways. Cancerous cells display a dense glycocalyx, containing tumor-associated carbohydrate antigens, which serves as a shield against immune recognition, confers a survival advantage to the tumor, and reduces intracellular drug entry. On the one hand, interactions between sialoglycans expressed on tumor cell surfaces and sialic acid-binding immunoglobulin-type lectins (Siglecs) on immune cells facilitate immune suppression. On the other hand, hyperactive melanosome and higher melanin content correlate with a poor prognosis in melanoma. The O-glycosylation of PMEL17/gp100, overexpressed in melanoma, is indispensable for melanosome architecture, melanin biosynthesis, and melanoma aggressiveness. We show that pharmacological inhibition of O-glycosylation in B16F10 (mouse melanoma) cells using peracetyl N-thioglycolyl-D-galactosamine (Ac5GalNTGc, 1a,) decreased both PMEL/17gp100 glycosylation and melanin content, and diminished the Siglec-E engagement to disrupt the sialoglycan-siglec immune-checkpoint through hyposialylation of the cell surface. In C57BL/6J mice, administration of 1a, but not controls, significantly delayed B16F10 tumor growth, prolonged the survival of mice, and significantly reduced the lung metastases. These findings identify O-glycosylation as a dual-mode therapeutic vulnerability, combining melanosome dysfunction and abrogation of siglec-mediated immune evasion in melanoma.