Demonstration of highly specific toxicity of the α-emitting radioimmunoconjugate 211At-rituximab against non-Hodgkin's lymphoma cells

The ability of an α-emitter conjugated to a chimaeric anti-CD20 monoclonal antibody to kill selectively human B-lymphoma cells in vitro is reported. Two B-lymphoma cell lines RAEL and K422, and normal haematopoietic progenitor cells from human bone marrow aspirates were incubated with211At-rituximab (Rituxan® or MabThera™) and plated in clonogenic assays for survival analyses. Following 1 h incubation with211At-rituximab, in concentrations which gave an initial activity of 50 kBq ml–1, a high tumour cell to normal bone marrow cell toxicity ratio was obtained; 4.1 to 1.0 log cell kill. Biodistribution studies of211At-rituximab in Balb/c mice showed similar stability as that of the iodinated analogue. The data indicate that testing of211At-rituximab in human patients is warranted. © 2000 Cancer Research Campaign