In vivo evaluation of a lead-labeled monoclonal antibody using the DOTA ligand.

The aim of this study was to assess the utility of a radioimmunoconjugate containing a lead radionuclide for therapy and scintigraphy applications. The radioimmunoconjugate evaluated consisted of a bifunctional DOTA ligand and monoclonal antibody (MAb) B72.3 using athymic mice bearing LS-174T tumors, human colon carcinoma xenografts. In the studies reported here, the lead-203-DOTA complex itself was first demonstrated to have in vivo stability. MAb B72.3 was then conjugated with the DOTA ligand and labeled with [sup 203] Pb, and the immunoreactivity of B72.3 was maintained. The localization of the radioimmunoconjugate to tumor tissue and other select organs paralleled that of DOTA-[sup 125] I-B72.3, suggesting a similar metabolic pattern of the two radioimmunoconjugates. Thus, the DOTA-metal complex does not alter the behavior of the radioimmunoconjugate. Tumor localization of the [sup 203] Pb-DOTA-B72.3 conjugate was demonstrated with biodistribution studies as well as immunoscintigraphy studies. Such data highlight the stability of a lead radionuclide in the DOTA ligand. The suitability of this chelation chemistry for labeling radioimmunoconjugates with a lead radionuclide now makes its application in nuclear medicine a feasible proposition. [ABSTRACT FROM AUTHOR]