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Updated: Jul 3, 2026

Simple and Fast Rolling Circle Amplification-Based Detection of Topoisomerase 1 Activity in Crude Biological Samples
Published on: December 2, 2022
Effect of phenazine compounds XR11576 and XR5944 on DNA topoisomerases
Andrew G Jobson1, Elaine Willmore, Michael J Tilby
1Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Newcastle Upon Tyne, NE2 4HH, UK.
Purpose:
Previous in vitro cleavage data showed that XR11576 and XR5944 stabilised topoisomerase I and topoisomerase II complexes on DNA in a dose-dependent fashion. However, some studies indicated a possible topoisomerase-independent mechanism of action for these drugs.
Methods:
Three methods, the TARDIS assay, immunoband depletion and the K(+)/SDS assay have been used to assess topoisomerase complex formation induced by XR11576 or XR5944 in human leukaemic K562 cells.
Results:
TARDIS and immunoband depletion assays demonstrated that XR11576 and XR5944 induced complex formation for both topoisomerase I and topoisomerase II (alpha and beta) in a dose- and time-dependent manner, following exposure times of 24 and 48 h at concentrations of 1 or 10 microM. The K(+)/SDS assay showed the formation of protein/DNA complexes after a 1 h exposure to 1 or 10 muM XR11576.
Conclusion:
Our data confirm that XR11576 or XR5944 can form topoisomerase complexes, after long periods of exposure.
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