title: A novel method to purify immunotoxins from free antibodies using modified recombinant toxins.
abstract: Monoclonal antibodies linked to toxin polypeptides (immunotoxins) are developed for clinical application against cancer and graft rejection. Immunotoxins prepared by many conventional methods often contain a trace amount of free antibody. Present studies describe a method to purify immunotoxins from free antibody in conjugation mixtures. Recombinant ricin A chain and a truncated form of diphtheria toxin (385 residues) containing ten consecutive histidine residues at the amino terminus were prepared. The modified toxin polypeptides retaining full biological activity were chemically linked to monoclonal antibodies (317G5 and 454C11) reactive to breast cancer cells. The high affinity of consecutive histidine residues for nickel-based resin (Ni-NTA) was exploited to purify immunotoxins from unreacted free antibodies. SDS-PAGE analysis of conjugates eluted from nickel column contained trace amounts of detectable free antibody whereas conjugates purified by other conventional methods using phenyl Sepharose or Cibacron blue Sepharose chromatography contained significant amounts of unconjugated antibody. Furthermore, the immunotoxin fraction containing predominantly two toxin molecules linked to one antibody can be separated from stoichiometric conjugates by Ni-NTA column. Cytotoxicity experiments showed that the complex of two toxin molecules linked to an antibody was more cytotoxic to tumor cells in vitro than the fraction enriched with immunotoxin containing equimolar stoichiometry.
authors.affiliation: Department of Pharmacology, University of Minnesota, Minneapolis 55455, USA.
authors.forename: M
authors.initials: M
authors.lastname: Dhanabal
authors.forename: D K
authors.initials: DK
authors.lastname: Fryxell
authors.forename: S
authors.initials: S
authors.lastname: Ramakrishnan
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000302:isolation & purification; D000918:Antibody Specificity; D000951:Antigens, Neoplasm; D001483:Base Sequence; D001943:Breast Neoplasms / Q000276:immunology; D002846:Chromatography, Affinity / Q000379:methods; D002847:Chromatography, Agarose / Q000379:methods; D017931:DNA Primers / Q000235:genetics; D004167:Diphtheria Toxin / Q000235:genetics / Q000302:isolation & purification*; D005260:Female; D006801:Humans; D007158:Immunologic Techniques; D000922:Immunotoxins / Q000302:isolation & purification*; D051379:Mice; D008969:Molecular Sequence Data; D010051:Ovarian Neoplasms / Q000276:immunology; D010446:Peptide Fragments / Q000235:genetics / Q000302:isolation & purification*; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification; D012276:Ricin / Q000235:genetics / Q000302:isolation & purification*; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D017931:DNA Primers; D004167:Diphtheria Toxin; D000922:Immunotoxins; D010446:Peptide Fragments; D011994:Recombinant Proteins; C029795:diphtheria toxin fragment A; D012276:Ricin