Inhibition of DNA Topoisomerases by Sanguiin H-6, a Cytotoxic Dimeric Ellagitannin from Sanguisorba officinalis1

K. F. Bastow; I. D. Bori; Y. Fukushima; Y. Kashiwada; T. Tanaka; G. Nonaka; I. Nishioka; K.-H. Lee

doi:10.1055/s-2006-959659

Planta Med 1993; 59(3): 240-245
DOI: 10.1055/s-2006-959659

Paper

Inhibition of DNA Topoisomerases by Sanguiin H-6, a Cytotoxic Dimeric Ellagitannin from Sanguisorba officinalis ¹

K. F. Bastow² , I. D. Bori² , Y. Fukushima² ^, ³ , Y. Kashiwada⁴ , T. Tanaka⁵ , G. Nonaka⁵ , I. Nishioka⁵ , K.-H. Lee⁴ ^, ⁶

²Division of Medicinal Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, U.S.A.
³Visiting Research Scholar -Present address: Nitto Denko Corp., 1-1-2, Shimohozumi, Ibaraki, Osaka 567, Japan
⁴Natural Products Laboratory, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, U.S.A.
⁵Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka 812, Japan
⁶Address for correspondence

1 Antitumor Agents 137. For paper 136 in this series, see Kashiwada, Y., Fujioka, T., Chang, J. J., Chen, I. S., Mihashi, K., Lee, K. H. (1992), J. Org. Chem. 57, 6946-6954

Abstract

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Abstract

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 µ and 0.01 µM, 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 µM and 0.16 µM, 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 agarosc 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 µM and > 10 µM, respectively. Sanguiin H-6 inhibited HeLa cell growth with an ED₅₀ of 12 µM and also interfered in a dose-dependent fashion with intracellular topoisomerase activities but with lower potencies than those observed using sub-cellular 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. The widespread presence of tannins in plant extracts may complicate drug-screening procedures designed to afford other types of novel topoisomerase poison from crude mixtures of phytochemicals.

Key words

Tannin - topoisomerase inhibitor - interference with cleavable-complexes - enzyme-DNA interaction - HeLa cells - cytotoxicity.

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Inhibition of DNA Topoisomerases by Sanguiin H-6, a Cytotoxic Dimeric Ellagitannin from Sanguisorba officinalis 1

Inhibition of DNA Topoisomerases by Sanguiin H-6, a Cytotoxic Dimeric Ellagitannin from Sanguisorba officinalis ¹