Cytotoxicity and topoisomerase I/II inhibition activity of novel 4-aryl/alkyl-1-(piperidin-4-yl)-carbonylthiosemicarbazides and 4-benzoylthiosemicarbazides

Abstract

A series of eight thiosemicarbazide derivatives was examined for cytotoxicity in breast cancer cell cultures. Among them, 4-benzoylthiosemicarbazides proved to be only slightly less potent than chlorambucil in both MDA-MB-231 and MCF-7 lines. In contrast, 4-aryl/alkylthiosemicarbazides revealed significantly lower cytotoxicity effect. Subsequently, all titled compounds were tested as potential human topoisomerase I and II (topo I and topo II) inhibitors. Mechanistic studies revealed that tested thiosemicarbazides act as both topoisomerase I and topoisomerase II inhibitors. Among them, the best inhibitory activity was found for 4-benzoylthiosemicarbazides (1 and 2) with IC₅₀ at 50?µM against topo II.     

Exploring Left-Hand-Side substitutions in the benzoxazinone series of 4-amino-piperidine bacterial type IIa topoisomerase inhibitors

An SAR survey at the C-6 benzoxazinone position of a novel scaffold which inhibits bacterial type IIa topoisomerase demonstrates that a range of small electron donating groups (EDG) and electron withdrawing groups (EWG) are tolerated for antibacterial activity. Cyano was identified as a preferred substituent that affords good antibacterial potency while minimizing hERG cardiac channel activity.     

How unfinished business from S‐phase affects mitosis and beyond

The eukaryotic cell cycle is conventionally viewed as comprising several discrete steps, each of which must be completed before the next one is initiated. However, emerging evidence suggests that incompletely replicated, or unresolved, chromosomes from S‐phase can persist into mitosis, where they present a potential threat to the faithful segregation of sister chromatids. In this review, we provide an overview of the different classes of loci where this ‘unfinished S‐phase business’ can lead to a variety of cytogenetically distinct DNA structures throughout the various steps of mitosis. Furthermore, we discuss the potential ways in which cells might not only tolerate this inevitable aspect of chromosome biology, but also exploit it to assist in the maintenance of genome stability.     

Selective leishmanicidal effect of 1,3,4-thiadiazole derivatives and possible mechanism of action against Leishmania species

With the aim of determining selectivity and the possible target(s) of nitroheteroaryl-1,3,4-thiadiazoles considered as possible leads for the development of anti-leishmanial agents, we studied 5-nitroimidazole, 5-nitrofuran and 5-nitrothiophene analogs of N-substituted-piperazinyl-1,3,4-thiadiazoles. We investigated 21 representative compounds 1-3(a-g) for the following properties: selectivity and efficiency against different Leishmania wild type species and intracellular parasite, toxicity against host cells and inhibition of topoisomerases I and II. Our results indicate that the nitroimidazole analogs 1a and 1f, and nitrofuran derivatives 2a, 2b, 2c, 2f, and 2g exhibited low toxicity against the host cells (IC₅₀ ? 80 μM), but high selectivity against intracellular amastigotes (selectivity index > 12). Leishmania topoisomerases revealed impressive sensitivity to the agents (%inhibition >50 at IC₅₀ doses of compounds against Leishmania). Our findings showed that at least part of leishmaniacidal effect of the compounds could be attributed to disruption DNA-relaxed activities of topoisomerases I and II, and cleavable-complex formation.     

Tea flavanols inhibit cell growth and DNA topoisomerase II activity and induce endoreduplication in cultured Chinese hamster cells

Tea polyphenols are promising chemopreventive anticancer agents, the properties of which have been studied both in vitro and in vivo, providing evidence that – within this group of compounds – the tea flavanols are able to inhibit carcinogenesis, an effect that in some cases could be correlated with increased cell apoptosis and decreased cell proliferation. Of four main tea flavanols, namely (−)-epigallocatechin-3-gallate (EGCG), (−)-epigallocatechin (EGC), (+)-catechin (CA) and (−)-epicatechin (EC), it was found that EGCG was the most potent to inhibit dose dependently the topoisomerase II (TOPO II) catalytic activity isolated from hamster ovary AA8 cells. In the range of concentrations that caused TOPO II inhibition, a high level of endoreduplication, a rare phenomenon that consists in two successive rounds of DNA replication without intervening mitosis, was observed, while neither micronuclei nor DNA strand breaks (Comet assay) were detected at the same doses. We propose that the anticarcinogenic effect of tea flavanols can be partly explained by their potency and effectiveness to induce endoreduplication. Concerning such an induction, maximum effect seems to require a pyrogallol structure at the B-ring. Additional substitution with a galloylic residue at the C3 hydroxyl group leads to further augmentation of the effect. Thus, we suggest that the chemopreventive properties of tea flavanols can be at least partly due to their ability to interfere with the cell cycle and block cell proliferation at early stages of mitosis.     

Variety of molecular conformation of plasmid pUC18 DNA and solenoidally supercoiled DNA

The plasmid pUC18 DNA isolated from Escherichia coli HB101 were analyzed by two-dimensional agarose gel electrophoresis and hybridization. The results show that the DNA sample can be separated into six groups of different structural components. The plectonemically and solenoidally supercoiled pUC18 DNA coexist in it. These two different conformations of supercoiled DNA are interchangeable with the circumstances (ionic strength and type, etc.). The amount of solenoidally supercoiled pUC18 DNA in the samples can be changed by treatment of DNA topoisome rases. Under an electron microscope, the solenoidal supercoiling DNA has a round shape with an average diameter of 45 nm. The facts suggest that solenoidaUy supercoiled DNA be a structural entity independent of histones. The polymorphism of DNA structure may be important to packing of DNA in vivo.     

Inhibitory effect of conjugated eicosapentaenoic acid on human DNA topoisomerases I and II

DNA topoisomerases (topos) and DNA polymerases (pols) are involved in many aspects of DNA metabolism such as replication reactions. We reported previously that long chain unsaturated fatty acids such as polyunsaturated fatty acids (PUFA) (i.e., eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA)) inhibited the activities of eukaryotic pols in vitro. In the present study, we found that PUFA also inhibited human topos I and II activities, and the inhibitory effect of conjugated fatty acids converted from EPA and DHA (cEPA and cDHA) on pols and topos was stronger than that of normal EPA and DHA. cEPA and cDHA inhibited the activities of mammalian pols and human topos, but did not affect the activities of plant and prokaryotic pols or other DNA metabolic enzymes tested. cEPA was a stronger inhibitor than cDHA with IC(50) values for mammalian pols and human topos of 11.0-31.8 and 0.5-2.5 microM, respectively. Therefore, the inhibitory effect of cEPA on topos was stronger than that on pols. Preincubation analysis suggested that cEPA directly bound both topos I and II, but did not bind or interact with substrate DNA. This is the first report that conjugated PUFA such as cEPA act as inhibitors of pols and topos. The results support the therapeutic potential of cEPA as a leading anti-cancer compound that poisons pols and topos.