title: Complement killing of human neuroblastoma cells: a cytotoxic monoclonal antibody and its F(ab')2-cobra venom factor conjugate are equally cytotoxic.
abstract: Only a few monoclonal antibodies mediate complement lysis of tumor cells, but for several antibodies it has been demonstrated that a complement-activating function can be introduced by covalent coupling of cobra venom factor (CVF), a non-toxic glycoprotein which is a structural and functional homologue of human complement component C3. In this study we compared the efficacy of complement killing of human neuroblastoma cells by the complement-activating monoclonal antibody 3F8 directed against the GD2 ganglioside antigen with that of its F(ab')2-CVF conjugate. At equal numbers bound per cell the 3F8 antibody and the 3F8 F(ab')2-CVF conjugate were found to be equally cytotoxic in the presence of complement from several species including human. Maximal killing reached up to 98%. The kinetics of killing and the bivalent metal requirement confirmed that the cytotoxic activity of the 3F8 antibody is mediated via the classical pathway and that of the 3F8 F(ab')2-CVF conjugate via the alternative pathway. To achieve a comparable degree of killing, an approximately eight-fold higher concentration of the 3F8 F(ab')2-CVF conjugate was required which appears to be a consequence of the approximately eight-fold lower binding activity of the 3F8 F(ab')2-CVF conjugate compared to the intact 3F8 antibody. Our data suggest that the coupling of CVF to non-cytotoxic antibodies allows the generation of conjugates with a cytotoxic activity similar to that of inherently cytotoxic antibodies.
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgetown University, Washington, DC 20007.
authors.forename: H
authors.initials: H
authors.lastname: Juhl
authors.forename: E C
authors.initials: EC
authors.lastname: Petrella
authors.forename: N K
authors.initials: NK
authors.lastname: Cheung
authors.forename: R
authors.initials: R
authors.lastname: Bredehorst
authors.forename: C W
authors.initials: CW
authors.lastname: Vogel
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D003167:Complement Activation; D003165:Complement System Proteins / Q000502:physiology; D003602:Cytotoxicity, Immunologic; D004546:Elapid Venoms / Q000627:therapeutic use*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000627:therapeutic use; D000922:Immunotoxins / Q000138:chemical synthesis / Q000627:therapeutic use*; D009447:Neuroblastoma / Q000628:therapy*; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D004546:Elapid Venoms; D007140:Immunoglobulin Fab Fragments; D000922:Immunotoxins; C016310:cobra venom factor; D003165:Complement System Proteins