In vivo comparison of macrocyclic and acyclic ligands for radiolabeling of monoclonal antibodies with 177Lu for radioimmunotherapeutic applications

The studies reported herein present the first in vitro and in vivo comparison of radioimmunoconjugates (RIC) radiolabeled with Lu-177 using the acyclic CHX-A-DTPA ligand and the macrocyclic ligands, C-DOTA and PA-DOTA. The in vivo studies include pharmacokinetics and biodistribution of the formed Lu-177-labeled immunoconjugates in a tumor bearing murine model with engineered monoclonal antibody HuCC49DeltaCH2. The in vitro analysis indicated that the CHX-A RIC was superior with respect to immunoreactiviry, radiolabeling with Lu-177, and specific activity. The in vivo pharmacokinetic data by itself indicated that the Lu(III)-PA-DOTA complex may not be as stable as Lu(III) complexes with CHX-A or C-DOTA. All three RICs demonstrated tumor targeting of human colon carcinoma xenografts in athymic mice. In these biodistribution studies, there appears to be no overall pattern or trend of one RIC over the other two. Based on these in vitro and in vivo studies, the CHX-A DTPA ligand should be considered a suitable bifunctional chelate for the radiolabeling of monoclonal antibodies with Lu-177 for radioimmunotherapy applications. Published by Elsevier Science Inc.