Importance of the Antigen-Binding Valency and the Nature of the Cross-Linking Bond in Ricin A-Chain Conjugates with Antibody

Publisher Website
Google Scholar
Abstract
As a continuation of our work on toxin A-chain conjugates with antitumor antibodies for selective delivery of the toxin to the target cells, four ricin A-chain conjugates were prepared by linking A-chain to Fab′ or F(ab′)2 of rabbit IgG against L1210 with or without employing a cross-linking agent, N,N′-o-phenylenedimaleimide (PDM), N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) or N-succinimidyl m-(N-maleimido)benzoate (SMB), and the effects of antigen-binding valency and of the nature of the cross-linking bond on their in vitro cytotoxicity were studied. The relative potencies of the conjugates in terms of IC94'S were as follows: F(ab′)2-SPDP-A-chain, 100; Fab′-S-S-A-chain, 21; F(ab′)2-SMB-A-chain, 1.3; Fab′-PDM-A-chain 0.38. Among the four conjugates, F(ab′2-SPDP-A-chain and Fab′-S-S-A-chain can be cleaved into the homing and the cytotoxic components with 2 mM 2-mercaptoethanol. These results suggest that divalency in antigen-binding and susceptibility of the cross-linking bond to cleavage by mercapto reagent are desirable for high potency. Protein synthesis in a cell-free system of rabbit reticu-locyte lysate was inhibited by Fab′-S-S-A-chain and by Fab′-PDM-A-chain as effectively as by free A-chain, indicating that the liberation of A-chain is not important, at least on ribosomes, but it is important for the A-chain to reach a ribo-some after binding of the conjugates to the cell-surface.

This publication has 0 references indexed in Scilit: