Relative therapeutic efficacy of 125I- and 131I-labeled monoclonal antibody A33 in a human colon cancer xenograft

E. C. Barendswaard, J. L. Humm, J. A. O'Donoghue, G. Sgouros, R. D. Finn, A. M. Scott, S. M. Larson, S. Welt

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


A33, a monoclonal antibody that targets colon carcinomas, was labeled with 125I or 131I and the relative therapeutic efficacy of the 2 radiolabeled species was compared in a human colon cancer xenograft system. Methods: Nude mice bearing human SW1222 colon carcinoma xenografts were administered escalating activities of 125I-A33 (9.25-148 MBq) or 131I-A33 (0.925-18.5 MBq), 125I- and 131I-labeled control antibodies, unlabeled antibody, or no antibody. The effects of treatment were assessed using the endpoints of tumor growth delay and cure. Results: Tumor growth delay increased with administered activity for all radiolabeled antibodies. Approximately 4.5 times more activity was required for 125I-A33 to produce therapeutic effects that were equivalent to those of 131I-A33. This ratio was approximately 7 for a nonspecific, noninternalizing isotype-matched, radiolabeled control antibody. Unlabeled A33 antibody had no effect on tumor growth. Approximately 10 times more activity of 125I-A33 produced toxicity similar to that of 131I-A33, and this ratio fell to approximately 6 for radiolabeled control antibody. Conclusion: Treatment with 125I-A33 resulted in a relative therapeutic gain of approximately 2 compared with 131I-A33 in this experimental system.

Original languageEnglish (US)
Pages (from-to)1251-1256
Number of pages6
JournalJournal of Nuclear Medicine
Issue number8
StatePublished - 2001
Externally publishedYes


  • Colon cancer xenograft
  • Radiolabeled mAb A33
  • Targeting
  • Therapeutic efficacy

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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