Physicochemical Evaluation of Lyophilized Formulation of p-SCN-Bn-DOTA- and p-SCN-Bn-DTPA-rituximab for NHL Radio Immunotherapy

Radioimmunotherapy (RIT) of Non-Hodgkin's lymphoma (NHL) is said to be more advantageous compared to unlabelled therapeutic antibodies. To this date, radiolabelled murine anti-CD20 mAbs, Zevalin® and Bexxar® have been approved for imaging and therapy. A preparation containing rituximab, chimeric mAb radio immunoconjugate suitable for Lu-177 labeling, could provide better imaging and therapeutic profile at the same time. This study was conducted to evaluate prepared lyophilized formulations of two rituximab immune conjugates, intended for immediate Lu-177 labeling, for imaging and therapy. The characterization of the conjugates and demonstration of the integrity of the protein and purity after conjugation and lyophilization was performed by SDS-PAGE, FT-IR and MALDI-TOF-MS. The results showed preserved antibody structure and average of 6.1 p-SCN-Bn-DOTA and 8.8 p-SCN-Bn-DTPA groups per antibody molecule which is suitable for successful labeling. These results support the possibility of developing a "ready-to-label" rituximab immune conjugates for NHL imaging/therapy.