Radiotoxicity of systemically administered 211At-labeled human/mouse chimeric monoclonal antibody: a long-term survival study with histologic analysis.

PURPOSE

The antitenascin human/mouse chimeric monoclonal antibody labeled with the alpha-particle-emitting radionuclide 211At is of interest as an endoradiotherapeutic agent for the treatment of brain tumors. To facilitate the investigation of 211At-labeled chimeric 81C6 in patients, the long-term radiotoxicity of this radiopharmaceutical has been evaluated.

METHODS AND MATERIALS

Antibody labeling was performed using N-succinimidyl 3-[211At]astato-benzoate. After an initial dose-finding experiment, a second toxicity study was carried out at 4 dose levels in groups of 30 nonthyroid blocked B6C3F1 mice per group (15 males, 15 females). Male mice received either saline or 15-81 kBq/g and females received either saline or 16-83 kBq/g of 211At-labeled antibody. Ten animals (5 males, 5 females) were followed for 6 months and the remainder for 1 year.

RESULTS

The lethal dose in 10% of animals (LD10) for 211At-labeled chimeric 81C6 was 46 kBq/g in females and 102 kBq/g in males. Toxic effects--perivascular fibrosis of the intraventricular septum of the heart, bone marrow suppression, splenic white pulp atrophy, and spermatic maturational delay--generally were confined to a few animals receiving the highest doses of labeled antibody.

CONCLUSIONS

The LD10 of 211At-labeled chimeric 81C6 in this mouse strain was about half that of [211At]astatide. These results establish the preclinical maximum tolerated dose of 211At-labeled chimeric 81C6 and define in the mouse the target organs for toxicity. These studies will be useful for determining starting doses for clinical studies with 211At-labeled chimeric 81C6.