Sensitivity of cancer cell lines to the novel non-toxic type 2 ribosome-inactivating protein nigrin b

The cytotoxicity of the type 2 ribosome-inactivating proteins (RIPs) ricin and nigrin b was determined in a variety of cancer cells. Nigrin b. conside red to be a novel non-toxic type 2 RIP as compared with ricin, was approxim ately 10(4)-10(5) times less toxic than ricin in all cancer cells studied, with the exception of melanoma cells. Cancer cells displayed considerable h eterogeneity in their sensitivity to ricin, melanoma cells being the least sensitive. Rabbit polyclonal anti-nigrin b antibodies did not cross-react w ith ricin as analyzed by enzyme-linked immunosorbent assays. The low non-sp ecific toxicity of nigrin b as compared with that of ricin and the lack of immunological cross-reaction between anti-nigrin b antibodies and ricin sup ports the use of nigrin b in the construction of cytotoxic conjugates as an alternative to ricin when anti-ricin antibodies are produced during cancer therapy. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.