The contribution of plukenetione A to the anti-tumoral activity of Cuban propolis.

Increasing efforts are directed toward finding applications for natural products and their derivatives in the treatment of human diseases. Among such products, propolis, a resinous substance produced by honey bees from various plant sources, has been found to be a promising source of potential therapeutics. In the present work, we aimed at studying the perspective of Cuban propolis as a source of possible anti-cancer agents. We found an anti-metastatic effect in mice and considerable cytotoxicity without cross-resistance in both wild-type and chemoresistant human tumor cell lines. Plukenetione A--identified for the first time in Cuban propolis--induced G0/G1 arrest and DNA fragmentation in colon carcinoma cells. Furthermore, the activities of both topoisomerase I and DNA polymerase were inhibited, while the expression of topoisomerase II-beta, EGF receptor, and multidrug resistance-related protein genes was found repressed. We assume that plukenetione A contributes to the anti-tumoral effect of Cuban propolis mainly by targeting topoisomerase I as well as DNA polymerase.

La ADN topoisomerasa tipo I de protozoos patógenos como Diana terapéutica de fármacos antitumorales / Type I DNA topoisomerase from protozoan pathogens as a potential target for anti-tumoral drugs

La utilización intensiva de fármacos antiparasitarios es la causa principal de la aparición de microorganismos parásitos multirresistentes en las regiones del planeta donde son precisamente endémicos. Los agentes etiológicos de las denominadas enfermedades tropicales -malaria, criptosporiodiosis, enfermedad del sueño, enfermedad de Chagas o los distintos tipos de leishmaniosis- son protozoos unicelulares sobre los que no se ha desarrollado en la actualidad ninguna vacuna eficaz y cuyo tratamiento se basa en medidas sanitarias preventivas y en el uso de medicamentos. La quimioterapia antiparasitaria actual es cara, no está ausente de efectos adversos y no supone beneficios a las empresas que la comercializan, por lo que la inversión en I & D es marginal comparada con la llevada a cabo para otros procesos patológicos de menor relevancia médica. La identificación de las ADN topoisomerasas como dianas farmacológicas se basa en los excelentes resultados obtenidos en los ensayos clínicos llevados a cabo con los derivados de la camptotecina en la terapia antitumoral. Las importantes diferencias estructurales entre las ADN topoisomerasas de tipo I de tripanosomas y leishmanias con respecto a sus homólogas de mamífero ha abierto un nuevo campo de investigación que combina las técnicas de biología molecular con la cristalización de proteínas para poder diseñar nuevos fármacos dirigidos específicamente a su inhibición. Revisamos aquí las características de estas nuevas dianas farmacológicas, así como los compuestos que en el momento están siendo utilizados para su inhibición en los agentes parasitarios que causan las principales enfermedades tropicales.

The intensive use of antiparasitic drugs is the main cause of the emergence of multiresistant parasite strains on those regions where these parasites are endemic. The aetiological agents of the so-called tropical diseases viz. malaria, cryptosporidiosis, sleeping sickness, Chagas disease or leishmaniasis, among others, are unicellular protozoan parasites with no immune-prophylactic treatment and where the chemotherapeutical treatment is still under controversy. At present, the chemotherapeutic approach to these diseases is expensive, has side or toxic effects and it does not provide economic profits to the Pharmaceuticals which then have no or scarce enthusiasm in R & D investments in this field. The identification of type I DNAtopoisomerases as promising drug targets is based on the excellent results obtained with camptothecin derivatives in anticancer therapy. The recent finding of significant structural differences between human type I DNAtopoisomerase and their counterparts in trypanosomatids has open a new field in drug discovery, the aim is to find structural insights to be targeted by new drugs. This review is an update of DNA-topoisomerases as potential chemotherapeutic targets against the most important protozoan agents of medical interest.

[Type I DNA topoisomerase from protozoan pathogens as a potential target for anti-tumoral drugs]. / La ADN topoisomerasa tipo I de protozoos patógenos como diana terapéutica de fármacos antitumorales.

The intensive use of antiparasitic drugs is the main cause of the emergence of multiresistant parasite strains on those regions where these parasites are endemic. The aetiological agents of the so-called tropical diseases viz. malaria, cryptosporidiosis, sleeping sickness, Chagas disease or leishmaniasis, among others, are unicellular protozoan parasites with no immune-prophylactic treatment and where the chemotherapeutical treatment is still under controversy. At present, the chemotherapeutic approach to these diseases is expensive, has side or toxic effects and it does not provide economic profits to the Pharmaceuticals which then have no or scarce enthusiasm in R & D investments in this field. The identification of type I DNA-topoisomerases as promising drug targets is based on the excellent results obtained with camptothecin derivatives in anticancer therapy. The recent finding of significant structural differences between human type I DNA-topoisomerase and their counterparts in trypanosomatids has open a new field in drug discovery, the aim is to find structural insights to be targeted by new drugs. This review is an update of DNA-topoisomerases as potential chemotherapeutic targets against the most important protozoan agents of medical interest.

The Aspergillus nidulans npkA gene encodes a Cdc2-related kinase that genetically interacts with the UvsBATR kinase.

The DNA damage response is a protective mechanism that ensures the maintenance of genomic integrity. We have used Aspergillus nidulans as a model system to characterize the DNA damage response caused by the antitopoisomerase I drug, camptothecin. We report the molecular characterization of a p34Cdc2-related gene, npkA, from A. nidulans. The npkA gene is transcriptionally induced by camptothecin and other DNA-damaging agents, and its induction in the presence of camptothecin is dependent on the uvsBATR gene. There were no growth defects, changes in developmental patterns, increased sensitivity to DNA-damaging agents, or effects on septation or growth rate in the A. nidulans npkA deletion strain. However, the DeltanpkA mutation can partially suppress HU sensitivity caused by the DeltauvsBATR and uvsD153ATRIP checkpoint mutations. We demonstrated that the A. nidulans uvsBATR gene is involved in DNA replication and the intra-S-phase checkpoints and that the DeltanpkA mutation can suppress its intra-S-phase checkpoint deficiency. There is a defect in both the intra-S-phase and DNA replication checkpoints due to the npkA inactivation when DNA replication is slowed at 6 mm HU. Our results suggest that the npkA gene plays a role in cell cycle progression during S-phase as well as in a DNA damage signal transduction pathway in A. nidulans.

Identification of a topoisomerase I mutant, scsA1, as an extragenic suppressor of a mutation in scaA(NBS1), the apparent homolog of human nibrin in Aspergillus nidulans.

The Mre11-Rad50-Nbs1 protein complex has emerged as a central player in the human cellular DNA damage response, and recent observations suggest that these proteins are at least partially responsible for the linking of DNA damage detection to DNA repair and cell cycle checkpoint functions. Mutations in scaA(NBS1), which encodes the apparent homolog of human nibrin in Aspergillus nidulans, inhibit growth in the presence of the antitopoisomerase I drug camptothecin. This article describes the selection and characterization of extragenic suppressors of the scaA1 mutation, with the aim of identifying other proteins that interfere with the pathway or complex in which the ScaA would normally be involved. Fifteen extragenic suppressors of the scaA1 mutation were isolated. The topoisomerase I gene can complement one of these suppressors. Synergistic interaction between the scaA(NBS1) and scsA(TOP1) genes in the presence of DNA-damaging agents was observed. Overexpression of topoisomerase I in the scaA1 mutant causes increased sensitivity to DNA-damaging agents. The scsA(TOP1) and the scaA(NBS1) gene products could functionally interact in pathways that either monitor or repair DNA double-strand breaks.

[DNA supercoiling and topoisomerases in Escherichia coli]. / Superenrollamiento del DNA y topoisomerasas de Escherichia coli.

The chromosomal DNA of all cells is under helical tension or supercoiling. There are two classes of DNA supercoiling: plectonemic and toroidal. Plectonemic supercoiling is generated by the action of DNA topoisomerases, while toroidal supercoiling is generated by DNA-protein interactions and by topoisomerase activitities. DNA supercoiling plays an important role in replication, repair, recombination, transposition and transcription. DNA topoisomerases type I are ATP-independent enzymes that cut one DNA strand and relax supercoiled molecules. DNA topoisomerases type II requiere ATP, cut both DNA strands and supercoil relaxed molecules. All organisms have more than one topoisomerase of each, type I and type II. Escherichia coli has two topoisomerases type I: topoisomerase I and topoisomerase III and two topoisomerases type II: topoisomerase II or gyrase and topoisomerase IV. In this review we discuss the concept of DNA supercoiling and present current knowledge on E. coli DNA topoisomerases.

[The bacterial nucleoid]. / El nucleoide bacteriano.

The bacterial genome is present in the cell within a complex structure, the nucleoid. The nucleoid contains the genomic DNA, and molecules of RNA and proteins. The main proteins of the nucleoid are: RNA polymerase, topoisomerases and the histone-like proteins: HU, H-NS (H1), H, HLP1, IHF and FIS. The DNA molecule in the nucleoid is under helical tension or supercoiling and is organized into 43 +/- 10 topodomains. DNA supercoiling is generated by the activity of the topoisomerases and by DNA-protein interactions. In this review, we analize current knowledge in Escherichia coli about genome organization and proteins of the nucleoid.