ABSTRACT
7-Chloro-1,3-dihydroxyacridone (1) reversibly inhibited growth of KB and vero cell lines with IC50's of 35 and 40 microM, respectively, and a topoisomerase II-mediated multidrug resistant KB sub-clone was found to be about three-fold more susceptible to 1. In contrast, two cell lines of lymphoid origin were killed following treatments with 60 microM and at higher concentrations of 1. KB cell growth inhibition correlated with a rapid, reversible suppression of thymidine incorporation. Uridine but not leucine incorporation was also rapidly suppressed. The in vitro activities of DNA topoisomerase II and novel protein kinase C-subtype delta were inhibited at effective concentrations in tissue-culture, but 1 did not stimulate intracellular protein-associated DNA breaks nor interfere initially with topoisomerase II-mediated DNA cleavage in KB cells. In addition to antiproliferative effects against cells, the compound was weakly virustatic for herpes simplex virus type I with an IC50 of 8 microM. Limited studies comparing three 1-congeners and citpressine-I, an acridone alkaloid with reported antiherpes activity, demonstrated that 7-substituted 1,3-dihydroxyacridones are novel antiproliferative agents which share similar biological and biochemical properties.
Subject(s)
Acridines/pharmacology , Cell Division/drug effects , Enzyme Inhibitors/pharmacology , Protein Kinase C/antagonists & inhibitors , Topoisomerase II Inhibitors , Acridines/chemical synthesis , Animals , Antiviral Agents/chemistry , Antiviral Agents/pharmacology , Cell Survival/drug effects , Chlorocebus aethiops , DNA/biosynthesis , DNA/metabolism , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/chemistry , Humans , Isoenzymes/antagonists & inhibitors , KB Cells , Molecular Structure , Simplexvirus/drug effects , Vero CellsABSTRACT
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)
