This is because the modification of C6 position at Ac3ManNAz using the protection molecules, such as cathepsin-B cleavable peptide of KGRR and prostate cancer antigen (PSA) protease-specific cleavable peptide of HSSKLY could interfere with the phosphorylation of C6-OH via ManNAc-6-kinase, a master regulator of sialic acid synthesis, during the sialic acid synthesis in the tumor cells7,8,28,29. The gene discussed is CTSB; the disease is neoplasm.