Tunicamycin, an antibiotic, can potently inhibit the N-linked glycosylation (NLG) by competitively inhibiting UDP-GlcNAc-dolichol-phosphate N-acetylglucosamine-1 phosphate transferase (DPAGT1) activity and can target several types of tumors by reducing angiogenesis, inhibiting colony formation, and enhancing TRAIL-induced apoptosis.