Abstract
An aqueous ethanol extract from the marine tunicate species Ecteinascidia turbinata was studied to determine its effect on semiconservative DNA synthesis in human skin fibroblast cultures as measured by [ 3H] thymidine uptake in acid-insoluble cell fractions. In addition, the effect of this extract on DNA excision repair in ultraviolet light (254 nm) irradiated fibroblasts was measured by the bromodeoxyuridine photolysis assay, thymine dimer chromatography, and DNA single-strand break analysis on alkaline sucrose gradients. An extract concentration of 0.5 mg/ml resulted in 91 and 98% reductions in cell growth and DNA synthesis, respectively, after 20 hr. An extract concentration of 3.0 mg/ml resulted in a 44% reduction in excision repair in ultraviolet-irradiated cells over a 6 hr repair period; this was reduced to 26% after 24 hr of repair, and to 15% after 48 hr. Repair inhibition was accompanied by an accumulation of single-strand DNA breaks which was enhanced by the addition of 2 mM hydroxyurea. These results are discussed with respect to a mechanism of action of the marine tunicate extract at the level of DNA polymerases and are contrasted with previously studied inhibitory mechanisms of arabinofuranosyl nucleosides.
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