Synthesis and Preclinical Evaluation of (177)Lu-CHX-A"-DTPA-Rituximab as a Radioimmunotherapeutic Agent for Non-Hodgkin's Lymphoma

Radioimmunotherapy is a feasible treatment modality for B-cell lymphomas expressing CD20 antigen. Tagging of anti-CD20 monoclonal antibody with a β(-) emitter will deliver radiation to the tumor preferentially, thereby causing its destruction. This work explores the utility of (177)Lu-CHX-A"-DTPA-Rituximab as a radioimmunotherapeutic agent for non-Hodgkin's lymphoma (NHL). Rituximab was conjugated with p-NCS-Bn-CHX-A"-DTPA and radiolabeled with (177)Lu. (177)Lu-CHX-A"-DTPA-Rituximab was characterized by SE-HPLC. In vitro cell binding and inhibition studies were carried out in Raji cells which express CD20 antigen. Biodistribution studies were performed in SCID mice bearing lymphoma at various time intervals. The CHX-A"-DTPA-Rituximab conjugate prepared had three molecules of DTPA per Rituximab molecule. Radiochemical purity of (177)Lu-CHX-A"-DTPA-Rituximab was >95%. In the HPLC system, (177)Lu-CHX-A"-DTPA-Rituximab showed a single peak (Rt ∼15.5 minutes). In vitro cell binding studies showed 38.9%±1.1% binding of (177)Lu-CHX-A"-DTPA-Rituximab (∼6.7 nM of radioimmunoconjugate) with Raji cells which reduced to 17.7%±0.5% with the addition of 67 nM of cold antibody. Biodistribution studies showed good tumor uptake at all the time points studied. In vitro and in vivo studies showed good specificity of (177)Lu-CHX-A"-DTPA-Rituximab toward CD20 antigen. It can be concluded that (177)Lu-CHX-A"-DTPA-Rituximab could be a promising agent in the treatment of NHL.