Abstract
As part of a Phase II clinical trial of topotecan, DNA breakage in vivo was measured by detecting covalent topoisomerase/DNA intermediates in peripheral blood. The ICE (in vivo complex of enzyme) bioassay was used to assess topotecan activity in the peripheral blood of patients before, during, and after infusion therapy. The results can be summarized as: (a) ICE bioassay is a specific, antibody-based assay for topoisomerase I-mediated DNA damage. Topoisomerase I/DNA complex formation can be monitored unamibugously in the absence of topotecan to establish a basal level of endogenous enzyme action on DNA; (b) infusion of topotecan significantly stimulated formation of covalent enzyme/DNA complexes. Complexes were detected within 5 min postinfusion and increased over the course of a 30-min treatment; (c) after termination of infusion, complex formation decreased by 3–4-fold within 30 min, showing that cleavage complexes quickly reseal after drug withdrawal; and (d) formation of complexes varied widely between patients. The ICE bioassay can evaluate the effects of topoisomerase I inhibitors on target tissues; thus, it may valuable in predicting response to these drugs.
Footnotes
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↵1 Funds for this research were provided by NIH Grant RO1AI28362, Ohio State University Comprehensive Cancer Center Support (CORE Grant 2P30CA16058), NCI Grant UO1-CA63185 (Clinical Trials Consortium) and RO1 CA63653.
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↵2 To whom requests for reprints should be addressed, at Department of Molecular Genetics, 484 West 12th Avenue, Columbus, OH 43210.
- Received December 7, 1994.
- Accepted March 14, 1995.
- ©1995 American Association for Cancer Research.
Volume 55, Issue 10
