title: Toxicity of ligand and antibody-directed ricin A-chain conjugates recognizing the epidermal growth factor receptor.
abstract: Approximately equal amounts of 125I-mAb 225 (a monoclonal antibody recognizing the human epidermal growth factor receptor) and 125I-labeled epidermal growth factor (125I-EGF) were bound by HeLa cells. However, these two EGF receptor binding moieties had different fates after binding. Sixty percent of cell-associated 125I-EGF was internalized. The majority of internalized 125I was released from the cell within 2 hr. In contrast, whereas only 30% of bound 125I-mAb 225 was internalized by HeLa cells, the internalized radioactivity remained cell-associated. EGF and mAb 225 were used to construct ricin A-chain (RTA) conjugates. The two chimeric molecules, EGF-RTA and mAb 225-RTA, were equally toxic to human HeLa cells. EGF-RTA was also toxic to murine 3T3 cells. In contrast, mAb 225-RTA was not toxic to 3T3 cells, consistent with the human EGF-receptor specificity of mAb 225. Neither conjugate was cytotoxic to EGF receptor-deficient 3T3-NR6 cells. Rapidity and potency of protein synthesis inhibition of HeLa cells were equivalent for the two chimeric conjugates, as was the degree to which colony-forming ability was reduced. However, ammonium chloride enhanced the toxicity of EGF-RTA but not mAb 225-RTA, suggesting that the two toxic chimeric toxins--like the unconjugated receptor-binding moieties--are processed differently by HeLa cells.
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000378:metabolism; D000918:Antibody Specificity; D001682:Biological Availability; D002451:Cell Compartmentation; D004357:Drug Synergism; D004815:Epidermal Growth Factor / Q000008:administration & dosage / Q000378:metabolism*; D066246:ErbB Receptors / Q000276:immunology / Q000378:metabolism*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D000922:Immunotoxins / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D011485:Protein Binding; D014176:Protein Biosynthesis; D012276:Ricin / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D014410:Tumor Stem Cell Assay
chemical_list: D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D000643:Ammonium Chloride; D004815:Epidermal Growth Factor; D012276:Ricin; D066246:ErbB Receptors