Toxicity of ligand and antibody-directed ricin A-chain conjugates recognizing the epidermal growth factor receptor

✍ Scribed by Angelika M. Vollmar; Deborah E. Banker; John Mendelsohn; Harvey R. Herschman

• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 868 KB
• Volume: 131
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041310314

✦ Synopsis

Approximately equal amounts of Iz51-mAb 225 (a monoclonal antibody recognizing the human e idermal growth factor receptor) and 1251-labeled epidermal growth factor (P251-EGF) were bound by HeLa cells. However, these two EGF receptor bindin moieties had different fates after binding. Sixty percent of cell-associated "8-EGF was internalized. The majority of internalized lZ1 was released from the cell within 2 hr. In contrast, whereas only 30% of bound lZ51-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.