The use of ²¹²Pb-labeled monoclonal antibody in the treatment of murine erythroleukemia

Abstract

$\text{Purpose}$: The goals of this study were to learn whether the DOTA chelator was useful for targeting lead radionuclides (^203,212Pb) to cells and tissues invaded by the Rauscher leukemia virus (RVB3) and to investigate the therapeutic efficacy of targeted ²¹²Pb in treating the murine leukemia.

$\text{Methods and Materials}$: Five to 6-week-old BALB/c mice were inoculated i.v. with RVB3. This virus causes marked splenomegaly and death by day 13 and day 70 postinfection, respectively. Biodistribution, tumor targeting, and toxicity studies were performed using varying doses of ²¹²Pb-DOTA-103A. A heavy metal chelator, DMPS, was administered orally and parenterally in two phases of the toxicity study.

$\text{Results}$: Biodistribution studies showed marked tumor targeting (58% ID/g spleen) in mice treated with ²⁰³Pb-103A as compared to mice treated with control antibody B3 (4.6% ID/g spleen). Histologic cure was achieved in all leukemic mice treated with 20 μCi ²¹²Pb-103A; however, all of the mice died with leukopenia and secondary bacterial infections due to severe bone marrow toxicity. Nonleukemic mice and mice treated with 20 μCi ²¹²Pb-B3 experienced less marrow toxicity and longer survival. Coadministration of the heavy metal chelator did not diminish the bone marrow toxicity.

$\text{Conclusion}$: An effective, nonlethal dose could not be established to treat this tumor. The severe bone marrow toxicity associated with this radionuclide may limit its usefulness in systemic radioimmunotherapy.