title: The effect of antibody valency and lysosomotropic amines on the synergy between ricin A chain- and ricin B chain-containing immunotoxins.
abstract: The cytotoxicity of A chain immunotoxins containing IgG or Fab fragments specific for the surface immunoglobulin of the Daudi cell line was assessed in the presence of B chain immunotoxins (IgG or Fab) or lysosomotropic amines, or both. The concentration required for 50% inhibition of protein synthesis (IC50) in Daudi cells was 1.3 X 10(-8) M for IgG-A and 5 X 10(-8) M for Fab-A. The toxicity of both A chain immunotoxins was enhanced twofold by ammonium chloride. In the presence of A chain immunotoxins and ammonium chloride, a maximum of 99 and 90% reduction of clonal precursors was obtained with IgG and Fab-A chain immunotoxins respectively. Immunotoxins containing ricin B chain and IgG or Fab fragments specific for the antibody portion of A chain immunotoxins were used as secondary "piggyback" immunotoxins to treat cells that were pretreated with A chain immunotoxins. Both B chain immunotoxins were nontoxic at 1 X 10(-6) M. When added to target cells pretreated with specific A chain immunotoxins, the IC50 of the A chain immunotoxins was decreased up to 16-fold in the absence of ammonium chloride. In contrast to the results obtained with A chain immunotoxins alone, ammonium chloride significantly increased the toxicity of the complete piggyback system, resulting in the killing of 99.999% or five logs of target cells in the clonal assay. This decreased the IC50 of A chain immunotoxins up to 116-fold when compared with A chain immunotoxin alone. This enhanced toxicity was independent of the valency of either immunotoxin.
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D000918:Antibody Specificity; D000970:Antineoplastic Agents / Q000633:toxicity*; D001666:Binding Sites, Antibody; D002051:Burkitt Lymphoma / Q000276:immunology; D002460:Cell Line; D002999:Clone Cells / Q000187:drug effects; D003602:Cytotoxicity, Immunologic; D004357:Drug Synergism; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism* / Q000502:physiology; D007074:Immunoglobulin G / Q000378:metabolism* / Q000502:physiology; D008247:Lysosomes / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D012276:Ricin / Q000276:immunology / Q000633:toxicity*
chemical_list: D000276:Adjuvants, Immunologic; D000970:Antineoplastic Agents; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D000643:Ammonium Chloride; D012276:Ricin