An approach for conjugation of (177)Lu- DOTA-SCN- Rituximab (BioSim) & its evaluation for radioimmunotherapy of relapsed & refractory B-cell non Hodgkins lymphoma patients

BACKGROUND & OBJECTIVES: The prerequisite of radioimmunotherapy is stable binding of a radionuclide to monoclonal antibodies, which are specific to the tumour-associated antigen. Most B-cell lymphomas express CD20 antigen on the surface of the tumour cells, making it a suitable target for therapeutic radioactive monoclonal antibodies. In the present study, the immunoconjugate of biosimilar Rituximab (Reditux™) and macrocyclic chelator, p-SCN-Bz-DOTA, was prepared and radiolabelled with Lutetium-177 followed by quality control procedures. METHODS: Rituximab(BioSim) was desalted with sodium bicarbonate (0.1M, pH 9.0) and incubated with DOTA-SCN (1:50). The effectiveness of the conjugation was evaluated by determining the number of chelators per antibody molecule. This conjugate was radiolabelled with Lutetium-177 and purified using PD10 column. The quality control parameters like pH, clarity, radiochemical purity, in vitro stability and sterility were studied. Immunoreactivity of (177)Lu-DOTA-Rituximab (BioSim) was assessed using RAMOS cells. The radioimmunoconjugate (RIC) after stringent quality assurance was injected in three patients and the biodistribution profile was analysed. RESULTS: An average of 4.25 ± 1.04 p-SCN-Bz-DOTA molecules could be randomly conjugated to a single molecule of Rituximab (BioSim). The radiochemical purity of the labelled antibody was > 95 per cent with preserved affinity for CD20 antigen. The final preparation was stable up to about 120 h when tested under different conditions. A favourable biodistribution profile was observed with liver showing the maximum uptake of the RIC. INTERPRETATION & CONCLUSIONS: A favourable radiochemical purity, stability and biodistribution of the radiolabelled immunoconjugate indicate that clinical trials for evaluation of toxicity and efficacy of (177)Lu-DOTA-antiCD20 antibody-Rituximab (BioSim) in patients of relapsed and refractory non Hodgkin's lymphoma can be considered.