Therapeutic efficacy and dose-limiting toxicity of auger-electron vs. beta emitters in radioimmunotherapy with internalizing antibodies: Evaluation of 125I- vs. 131I-labeled CO17-1A in a human colorectal cancer model

Thomas M. Behr, George Sgouros, Vassilios Vougioukas, Stavros Memtsoudis, Stefan Gratz, Heinz Schmidberger, Rosalyn D. Blumenthal, David M. Goldenberg, Wolfgang Becker

Research output: Contribution to journalArticle

Abstract

Recent clinical results suggest that higher anti-tumor efficacy may be achieved with internalizing monoclonal antibodies (MAbs) at lower toxicity when labeled with Auger-electron, as compared to conventional β-emitters. The aim of our study was to compare the toxicity and anti-tumor efficacy of the 125I-labeled internalizing MAb, CO17-1A, with its 131I-labeled form in a human colon cancer model in nude mice. Biodistribution studies were performed in nude mice bearing s.c. human colon cancer xenografts. For therapy, the mice were injected either with unlabeled 125I- or 131I- labeled CO17-1A at equitoxic doses. Control groups were left untreated, were given a radiolabeled isotype-matched irrelevant antibody or a tumor- specific, but noninternalizing antibody. The maximum tolerated activities (MTD) of 131I-and 125I-CO17-1A without artificial support were 300 μCi and 3 mCi, respectively. Myelotoxicity was dose-limiting; bone marrow transplantation allowed for an increase of the MTD to 400 μCi of 131I- 17-1A, whereas the MTD of 125I-17-1A with bone marrow support had not been reached at 5 mCi. Whereas no significant therapeutic effects were seen with unlabeled CO17-1A, tumor growth was retarded with 131I-CO17-1A. With the 125I-label, however, therapeutic results were clearly superior. In contrast, no significant difference was observed in the therapeutic efficacy of the 131I- vs. 125I-labeled, noninternalizing antibodies. Our data indicate a superiority of Auger-electron emitters, such as 125I, as compared to therapy with conventional β-emitters with internalizing antibodies. The lower toxicity of Auger emitters may be due to the short path length of their low-energy electrons, which can reach the nuclear DNA only if the antibody is internalized (as is the case in antigen-expressing tumor tissue, but not in the stem cells of the red marrow).

Original languageEnglish (US)
Pages (from-to)738-748
Number of pages11
JournalInternational Journal of Cancer
Volume76
Issue number5
DOIs
Publication statusPublished - 1998
Externally publishedYes

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ASJC Scopus subject areas

  • Cancer Research
  • Oncology

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