Inhibition of DNA topoisomerases by sanguiin H-6, a cytotoxic dimeric ellagitannin from Sanguisorba officinalis.
Many tannins were previously identified as candidate topoisomerase poisons. Here we report further studies on sanguiin H-6, a dimeric ellagitannin isolated from Sanguisorba officinalis as an inhibitor of DNA topoisomerases. Catalytic strand-passing activities of topoisomerases I and II were inhibited in vitro with IC50 values of 1 microM and 0.01 microM, respectively. This inhibition was not associated with stabilization of covalent enzyme-DNA complexes but rather by a mechanism preventing formation of such covalent intermediates, as measured by interference with drug-induced cleavage in vitro. The IC50 values for topoisomerase I-DNA complexes induced by camptothecin and with topoisomerase II-DNA complexes induced by VP-16 were 0.02 microM and 0.16 microM, respectively. Pre-incubation studies followed by drug-dilution revealed that the in vitro inhibitory effects of sanguiin H-6 were irreversible, and for topoisomerase I, the test compound prevented enzyme-DNA interaction as seen by shifts in mobility on agarose gels. By measuring interference with drug-induced protein-linked DNA breaks in isolated HeLa nuclei, inhibition of topoisomerases I and II on a natural chromatin template was demonstrated with IC50 values of 5 microM and > 10 microM, respectively. Sanguiin H-6 inhibited HeLa cell growth with an ED50 of 12 microM and also interfered in a dose-dependent fashion with intracellular topoisomerase activities but with lower potencies than those observed using subcellular assay systems. Based on these studies, sanguiin H-6 could be broadly classified as a type of poison which does not stimulate the formation of cleavable-complexes, with intracellular activity but without any marked selectivity.(ABSTRACT TRUNCATED AT 250 WORDS)
Division of Medicinal Chemistry, University of North Carolina, Chapel Hill 27599.
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Bastow
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Bori
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Fukushima
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Kashiwada
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Tanaka
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Nonaka
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Nishioka
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Lee
D002384:Catalysis; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects; D004247:DNA / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047348:Hydrolyzable Tannins; D015394:Molecular Structure; D010944:Plants / Q000737:chemistry*; D013634:Tannins / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured
D047348:Hydrolyzable Tannins; D013634:Tannins; D059004:Topoisomerase I Inhibitors; C013515:ellagitannin; C081844:sanguiin H 6; D004247:DNA; D004264:DNA Topoisomerases, Type I