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Abstract
DNA topoisomerases are essential enzymes that regulate the conformational changes in DNA topology by catalyzing the concerted breakage and rejoining of DNA strands during normal cellular growth. During the past few years, there has been considerable pharmacological interest in these enzymes because the inhibitors of DNA topoisomerases represent a major class of anticancer drugs. In this study, we investigated the effects of the extracts, prepared from a number of Helichrysum. taxa, on mammalian DNA topoisomerase I via in vitro. supercoil relaxation assays using plasmid substrate, pBR322. Cytotoxic alkaloid, camptothecin, an inhibitor of eukaryotic topoisomerase I, was used as reference compound throughout the assays. Quantitative comparisons of the supercoiled and relaxed DNA band intensities on agarose gels suggested that the extracts from H. pallasii. (Sprengel) Ledeb., H. armenium DC subsp.. araxinum. (Kirp.) Takht, and H. plicatum DC subsp.. plicatum. manifested a considerable inhibition on the enzyme in a dose-dependent manner. The inhibition of mammalian DNA topoisomerase I by Helichrysum. extracts is a significant result because they can be potential sources of anticancer drugs.