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Updated: Jun 25, 2026

Simple and Fast Rolling Circle Amplification-Based Detection of Topoisomerase 1 Activity in Crude Biological Samples
Published on: December 2, 2022
Calothrixins, a new class of human DNA topoisomerase I poisons
Qasim A Khan1, Jun Lu, Sidney M Hecht
1Center for BioEnergetics, Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA.
Abstract:
Calothrixins A (1) and B (2) were converted to their O- and N-methylated derivatives, respectively. All four compounds were found to act as poisons of DNA topoisomerase I and to do so reversibly. Three of the calothrixins (1-3) were tested for their cytotoxicity toward cultured (p53 proficient) CEM leukemia cells and found to exhibit IC(50) values ranging from 0.20 to 5.13 muM. The cell cycle effects of calothrixins 1-3 were also studied. Calothrixin B (2) produced G(1) arrest at 0.1 muM concentration, while higher concentrations of calothrixins 1 and 3 resulted in cell accumulation in both the S and G(2)/M phases of the cell cycle. The cell cycle effects produced by the calothrixins were more readily reversible upon removal of the compounds than those produced by camptothecin.
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