In vitro cytotoxicity of carcinoma cells with 111In-labeled antibodies to HER-2

• Published in: Molecular cancer therapeutics Vol. 4; no. 6; pp. 927 - 937
• Main Authors: Michel, Rosana B, Andrews, Philip M, Castillo, Mary Ellen, Mattes, M Jules
• Format: Journal Article
• Language: English
• Published: United States American Association for Cancer Research 01.06.2005
• Subjects: Antibodies - chemistry; Antibodies - immunology; Antibodies - toxicity; antibody therapy; Auger electron emitters; Carcinoma - immunology; Carcinoma - metabolism; Carcinoma - pathology; Cell Line, Tumor; Cell Survival - drug effects; Cell Survival - radiation effects; Humans; Indium Radioisotopes; Radioimmunotherapy; radiolabeled antibodies; Receptor, ErbB-2 - immunology; Receptor, ErbB-2 - metabolism
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-04-0340

Antibodies conjugated to radionuclides emitting low-energy electrons, which include Auger electrons and some conversion electrons, were recently shown to efficiently kill cells bearing a high density of the antigen recognized. The primary purpose of this study was to determine if such killing could be obtained with anti–HER-2 antibodies conjugated to 111 In, using the chelator benzyl-diethylenetriaminepentaacetic acid, or 125 I. Target cells were the breast carcinoma SK-BR-3 and the ovarian carcinoma SK-OV-3.ip1. In preliminary experiments, antibody accumulation and catabolism during a 2- to 3-day incubation with antibody was investigated. The level of antibody uptake, in terms of molecules per cell, was high enough such that killing seemed feasible. With an 125 I label, but not an 111 In label, increasing the antibody concentration past a certain point caused a decrease in total antibody accumulation, which might be attributed to effects of antibody binding. To test for cytotoxicity, cells were incubated for 2 days with the labeled antibody, then assayed for colony-forming units with a limiting dilution assay. SK-BR-3 cells were strongly killed (∼3 logs) by antibody 21.1, and 100% kill was obtained by combining two noncompeting antibodies to HER-2 (21.1 and 4D5). SK-OV-3.ip.1 cells were more resistant to killing, but use of the two-antibody mixture produced a surviving fraction of ∼0.002. 111 In-labeled antibodies to other high-density antigens, epithelial glycoprotein-1 and epithelial glycoprotein-2, also killed these target cells. In contrast, unlabeled antibodies or a nonreactive-labeled antibody produced much less cytotoxicity. The same experiment with an 131 I label (a β-particle emitter) resulted in much greater levels of nonspecific cytotoxicity and essentially no specific cytotoxicity. This approach may be effective for therapy of micrometastases.