Preclinical evaluation of NETA-based bifunctional ligand for radioimmunotherapy applications using 212Bi and 213Bi: Radiolabeling, serum stability, and biodistribution and tumor uptake studies

IntroductionDespite the great potential of targeted α-radioimmunotherapy (RIT) as demonstrated by pre-clinical and clinical trials, limited progress has been made on the improvement of chelation chemistry for 212Bi and 213Bi. A new bifunctional ligand 3p-C-NETA was evaluated for targeted α RIT using 212Bi and 213Bi.MethodsRadiolabeling of 3p-C-NETA with 205/6Bi, a surrogate of 212Bi and 213Bi, was evaluated at pH 5.5 and room temperature. In vitro stability of the 205/6Bi-3p-C-NETA-trastuzumab conjugate was evaluated using human serum (pH 7, 37 °C). Immunoreactivity and specific activity of the 205/6Bi-3p-C-NETA-trastuzumab conjugate were measured. An in vivo biodistribution study was performed to evaluate the in vivo stability and tumor targeting properties of the 205/6Bi-3p-C-NETA-trastuzumab conjugate in athymic mice bearing subcutaneous LS174T tumor xenografts.ResultThe 3p-C-NETA-trastuzumab conjugate was extremely rapid in complexing with 205/6Bi, and the corresponding 205/6Bi-3p-C-NETA-trastuzumab was stable in human serum. 205/6Bi-3p-C-NETA-trastuzumab was prepared with a high specific activity and retained immunoreactivity. 205/6Bi-3p-C-NETA-trastuzumab conjugate displayed excellent in vivo stability and targeting as evidenced by low normal organ and high tumor uptake.ConclusionThe results of the in vitro and in vivo studies indicate that 3p-C-NETA is a promising chelator for RIT applications using 212Bi and 213Bi. Further detailed in vivo evaluations of 3p-C-NETA for targeted α RIT are warranted.