Selective cytotoxic activity of immunotoxins composed of a monoclonal anti-Thy 1.1 antibody and the ribosome-inactivating proteins bryodin and momordin

Abstract

Summary The ribosome-inactivating proteins, bryodin, from Bryonia dioica, and momordin, from Momordica charantia, were coupled by a disulphide bond to a monoclonal anti-Thy 1.1 antibody (OX7). Both immunotoxins were specifically cytotoxic to the Thy 1.1-expressing mouse lymphoma cell* line AKR-A in vitro. The OX7-bryodin immunotoxins were the more powerfully toxic and reduced protein synthesis in AKR-A cells by 50% at a concentration of 1-4 x 10 -I M as compared with 1 x 0 -9M for the OX7-momordin immunotoxins. Neither of the immunotoxins was toxic to mouse lymphoma EL4 cells, which lack the Thy 1.1 antigen, at concentrations up to 3 x 10-8M. Further, bryodin and momordin immunotoxins made from an antibody (RIO) of irrelevant specificity were without effect on AKR-A cells.An alternative to using toxin A-chains to form antibodytoxin conjugates (immunotoxins) is to link single-chain ribosome-inactivating proteins (RIPs) to the antibody. The RIPs are plant proteins that are evolutionarily related to the toxin A-chains and catalytically inactivate eukaryotic ribosomes by the same mechanism as the toxin A-chains Stirpe et al., 1988). They offer the advantages over the toxin A-chains for immunotoxin production that they are safer to handle in quantity and do not need the same extensive purification to exclude traces of B-chain which causes non-specific toxicity. Further, the RIPs often do not cross-react immunologically so that the sequential use of immunotoxins prepared with different RIPs could avoid the problem of immunological neutralization in vivo.To date, RIP immunotoxins have been prepared with gelonin, from Gelonium multiflorum (Thorpe et al., 1981;Colombatti et al., 1983;Wiels et al., 1984;Lambert et al., 1985; Scott et al., 1987a,b;Sivam et al., 1987), pokeweed antiviral protein (PAP) from Phytolacca americana (Masuho et al., 1982;Ramakrishnan & Houston, 1984a,b, 1985Uckun et al., 1985;Lambert et al., 1985) and saporin from Saponaria officinalis (Thorpe et al., 1985;Letvin et al., 1986;Glennie et al., 1987 (Amersham, UK). lodo-gen was from Pierce Ltd., (Chester, UK). N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) was from Pharmacia Ltd., (London, UK). Reagents for measuring cell-free protein synthesis and cell culture media were obtained from the same sources as used previously (Thorpe et al., 1981).Purification of RIPs Bryodin was purified by the procedure described previously ) and appeared as a single protein band (apparent Mr, 30,000) when analysed by SDS-PAGE. Momordin was purified as previously (Barbieri et al., 1980) except that the method was adapted to allow the processing of 500 g of seeds at a time. When examined by SDS-PAGE, it appeared as a single protein band (apparent Mr, 31,000) with traces of a contaminant protein with lower Mr. The purified proteins were dialyzed extensively against water and were freeze-dried and stored at -20°C. Preparation of immunotoxinsThe RIPs were dissolved in 50mM borate buffer titrated to pH 9.0 with NaOH and the solution centrifuged to remove any undissol...

Tat-mediated delivery of heterologous proteins into cells.

“…However, by analogy to ricin A chain (25), it is not clear whether this molecule is nontoxic when added to cells simply because it lacks binding activity and whether it may retain a translocation function. This idea is supported by the cytotoxicity of momordin immunotoxins (26). In contrast, the structure/function of PE has been studied in great detail (27,28), and the translocation activity of the native toxin has been localized to domain II.…”

Characterization of Ribosome-Inactivating Proteins Isolated from Bryonia dioica and Their Utility as Carcinoma-Reactive Immunoconjugates

“…The linkage of toxic proteins including ribosome-inactivating proteins isolated from plants and bacterial toxins with antibody molecules results in antigen-specific cytotoxic agents referred to as immunotoxins (19). Immunotoxins have been prepared using a variety of RIPs, including BD (7,(20)(21)(22), ricin (23,24), saporin (25), and pokeweed antiviral protein (26). Type I RIPs offer advantages over Type II RIPs or bacterial toxins such as diphtheria toxin or Pseudomonas exotoxin A in that removal of the toxin-binding domain is not required to gain target selectivity (27).…”

Hyperuricaemia, Xanthine Oxidoreductase and Ribosome‐Inactivating Proteins from Plants: The Contributions of Fiorenzo Stirpe to Frontline Research

“…Thus, the first IT with a type 1 RIP was achieved, contributing to the implementation of immunotherapy with anticancer purposes. A few years later, ITs made of the same antibody conjugated with saporin [ 96 ], bryodin or momordin [ 97 ] were prepared. The saporin-containing IT showed a higher power in comparison to the ricin-containing IT against T-lymphoma cells and significantly delayed the neoplastic growth in nude mice, hence prolonging the life of tumour-bearing animals.…”