Targeting a marker of the tumour neovasculature using a novel anti-human CD105-immunotoxin containing the non-toxic type 2 ribosome-inactivating protein nigrin b

Targeting tumour neovasculature using antibodies to the endothelial receptor CD105 (endoglin), is a potentially useful approach for anti-tumour therapy. We report on the preparation and the cytotoxicity of a novel immunotoxin consisting in the non-toxic type 2 ribosome-inactivating protein (RIP) nigrin b linked to the monoclonal anti-human CD105 (hCD105) antibody 44G4. The immunotoxin kills specifically mouse fibroblasts expressing the biomarker CD105 (L929-hCD105+ cells) with an IC50 value of 6 × 10−10 M while nigrin b does it at 2.4 × 10−7 M. Immunofluorescence analysis indicated that the immunotoxin accumulates in a perinuclear region. In contrast, 44G4 showed a specific localization on the cell surface.