Siegall C B, Gawlak S L, Chace D, Wolff E A, Mixan B, Marquardt H
Molecular Immunology Department, Bristol-Myers Squibb, Pharmaceutical Research Institute, Seattle, Washington 98121.
Bioconjug Chem. 1994 Sep-Oct;5(5):423-9. doi: 10.1021/bc00029a008.
Two ribosome-inactivating proteins (RIPs) were isolated and characterized from the roots of Bryonia dioica. One of these was a novel 27-kDa protein termed bryodin 2 (BD2), while the second was a previously reported RIP, referred to here as bryodin 1 (BD1). The amino-terminal sequence obtained for BD2 was similar, but distinct from BD1, ricin A chain, trichosanthin, and momorcharin. BD2-specific monoclonal antibodies were generated and found not to react with BD1 or ricin A chain. Purified BD1 and BD2 RIP inhibited protein synthesis in a cell-free in vitro translation assay at EC50 values of 7 and 9 pM, respectively. Intravenous administration of BD1 was less toxic to mice than BD2, with LD50 values of > 40 for BD1 and 10-12 mg/kg for BD2. Primary human endothelial cells were 5-8-fold less sensitive to BD1 and BD2 than compared to ricin A chain. BD1 and BD2 were constructed as immunoconjugates with the chimeric form of BR96 (chiBR96), a carcinoma-reactive, internalizing antibody. ChiBR96-BD1 and chiBR96-BD2 were found to bind to and kill BR96 antigen-positive carcinoma cells while not killing antigen-negative carcinoma cells. Bryodins represent RIPs that may be useful in constructing immunotoxin conjugates with reduced toxicity and vascular sensitivity, as compared to ricin A chain immunotoxins.
