抄録
Chang hepatoma ascites (CHA) cells were previously used as an animal model for antibody-directed enzyme prodrug therapy (ADEPT) and internalization of surface lectin-binding sites in vivo and in vitro. A monoclonal antibody RH1 (Mab-RH1) that recognizes a CHA-specific antigen (CHAA) on the cell surface has been identified. Β -glucuronidase conjugated with Mab-RH1CHAA (Mab- β G-CHAA) inverts an antineoplastic prodrug, p-hydroxyaniline mustard glucuronide to toxic p-hydroxyaniline mustard and kills CHA cells. The possibility that CHAA may internalize into the tumor cells was hypothesized because the drug effect was reduced after long treatment. Nevertheless, the biological nature of CHAA and the mechanism of ADEPT remains unknown. In this study, various enzyme digestions characterize CHAA in situ. Furthermore, specific lectin-blocking methods determine the terminal monosaccharide that was recognized by Mab-RH1 on CHAA. The results indicate that the tumor-specific CHAA is a 32 kDa glycoprotein that is sensitive to protease treatment, but survives treatments of trypsin, chymotrypsin, lipase, neuraminidase, hyaluronidase, chondroitinase ABC and heparinase. Con A, WGA and RCA lectins block the recognition of Mab-RH1 and indicate that α-mannose, α-glucose, D-galactose and N-acetyl-D-glucosamine residues are essential for ADEPT. We conclude that internalization of Mab-βG-CHAA complexes causes the reduction of antineoplastic drug activity.
