Regulation of Geldanamycin Biosynthesis by Cluster-Situated Transcription Factors and the Master Regulator PhoP.

Geldanamycin and the closely related herbimycins A, B, and C are benzoquinone-type ansamycins with antitumoral activity. They are produced by Streptomyces hygroscopicus var. geldanus, Streptomyces lydicus and Streptomyces autolyticus among other Streptomyces strains. Geldanamycins interact with the Hsp-90 chaperone, a protein that has a key role in tumorigenesis of human cells. Geldanamycin is a polyketide antibiotic and the polyketide synthase contain seven modules organized in three geldanamycin synthases genes named gdmAI, gdmAII, and gdmAIII. The loading domain of GdmI activates AHBA, and also related hydroxybenzoic acid derivatives, forming geldanamycin analogues. Three regulatory genes, gdmRI, gdmRII, and gdmRIII were found associated with the geldanamycin gene cluster in S. hygroscopicus strains. GdmRI and GdmRII are LAL-type (large ATP binding regulators of the LuxR family) transcriptional regulators, while GdmRIII belongs to the TetR-family. All three are positive regulators of geldanamycin biosynthesis and are strictly required for expression of the geldanamycin polyketide synthases. In S. autolyticus the gdmRIII regulates geldanamycin biosynthesis and also expression of genes in the elaiophylin gene cluster, an unrelated macrodiolide antibiotic. The biosynthesis of geldanamycin is very sensitive to the inorganic phosphate concentration in the medium. This regulation is exerted through the two components system PhoR-PhoP. The phoRP genes of S. hygroscopicus are linked to phoU encoding a transcriptional modulator. The phoP gene was deleted in S. hygroscopicus var geldanus and the mutant was unable to grow in SPG medium unless supplemented with 5 mM phosphate. Also, the S. hygroscopicus pstS gene involved in the high affinity phosphate transport was cloned, and PhoP binding sequences (PHO boxes), were found upstream of phoU, phoRP, and pstS; the phoRP-phoU sequences were confirmed by EMSA and nuclease footprinting protection assays. The PhoP binding sequence consists of 11 nucleotide direct repeat units that are similar to those found in S. coelicolor Streptomyces avermitilis and other Streptomyces species. The available genetic information provides interesting tools for modification of the biosynthetic and regulatory mechanisms in order to increase geldanamycin production and to obtain new geldanamycin analogues with better antitumor properties.

Combined molecular modelling and 3D-QSAR study for understanding the inhibition of NQO1 by heterocyclic quinone derivatives.

A combination of three-dimensional quantitative structure-activity relationship (3D-QSAR), and molecular modelling methods were used to understand the potent inhibitory NAD(P)H:quinone oxidoreductase 1 (NQO1) activity of a set of 52 heterocyclic quinones. Molecular docking results indicated that some favourable interactions of key amino acid residues at the binding site of NQO1 with these quinones would be responsible for an improvement of the NQO1 activity of these compounds. The main interactions involved are hydrogen bond of the amino group of residue Tyr128, π-stacking interactions with Phe106 and Phe178, and electrostatic interactions with flavin adenine dinucleotide (FADH) cofactor. Three models were prepared by 3D-QSAR analysis. The models derived from Model I and Model III, shown leave-one-out cross-validation correlation coefficients (q2LOO ) of .75 and .73 as well as conventional correlation coefficients (R2 ) of .93 and .95, respectively. In addition, the external predictive abilities of these models were evaluated using a test set, producing the predicted correlation coefficients (r2pred ) of .76 and .74, respectively. The good concordance between the docking results and 3D-QSAR contour maps provides helpful information about a rational modification of new molecules based in quinone scaffold, in order to design more potent NQO1 inhibitors, which would exhibit highly potent antitumor activity.

Potencialidad terapéutica de los flavonoides prenilados: flavonoides prenilados como potenciales componentes de medicamentos / Therapeutic potential of prenilated flavonoids: prenilated flavonoids as potential components of drugs

Los flavonoides representan un destacado grupo dentro de los compuestos naturales y tienen amplia distribución en el reino vegetal. A ningún otro grupo de compuestos de origen natural se le han atribuido tan numerosas, variadas e importantesactividades en el crecimiento y desarrollo de las plantas. En general, no son tóxicos y presentan múltiples actividades biológicas; algunos de ellos han sido aprobados como principios activos de medicamentos en la Argentina y otros países. En este trabajo se resumen los efectos farmacológicos más relevantes de los flavonoides prenilados, un subgrupo con estructurasde escasa distribución en la naturaleza. Han sido poco estudiados desde el punto de vista químico y farmacológico. Sinembargo, los avances realizados en los últimos años permiten estimar interesantes aplicaciones terapéuticas. Así, por ejemplo, se han reportado sus actividades antimicrobiana, antitumoral, antiinflamatoria y antioxidante. Se dan ejemplos de información científica relacionada primordialmente con flavonoides prenilados extraídos de especies vegetales autóctonas de laArgentina.

Flavonoids are natural compounds synthesized by plants, in which are vital metabolites involved in diverse and important functions such as growth and development. In general, they are innocuous and present many biological activities. In the paper we review the most relevant pharmacological effects of prenylated flavonoids, a subgroup of low distribution in nature that has not been much studied from the chemical and pharmacological points of view. Nevertheless, the advances achieved in the last years allow to estimate interesting therapeutical applications for them. Thus, the antimicrobial, antitumoral, anti-inflammatory and antioxidant activities have been described. Examples of information related to compounds extracted from indigenous plants from Argentina were selected.

A glimpse on biological activities of tellurium compounds

Tellurium is a rare element which has been regarded as a toxic, non-essential trace element and its biological role is not clearly established to date. Besides of that, the biological effects of elemental tellurium and some of its inorganic and organic derivatives have been studied, leading to a set of interesting and promising applications. As an example, it can be highlighted the uses of alkali-metal tellurites and tellurates in microbiology, the antioxidant effects of organotellurides and diorganoditellurides and the immunomodulatory effects of the non-toxic inorganic tellurane, named AS-101, and the plethora of its uses. Inasmuch, the nascent applications of organic telluranes (organotelluranes) as protease inhibitors and its applications in disease models are the most recent contribution to the scenario of the biological effects and applications of tellurium and its compounds discussed in this manuscript.

O telúrio é um elemento não-essencial raro que vem sendo considerado tóxico, e o seu papel biológico é ainda pouco esclarecido. Apesar disso, os efeitos biológicos do telúrio elementar e de alguns derivados inorgânicos e orgânicos que têm sido estudados revelam um conjunto de aplicações diversificadas interessantes e promissoras. Como exemplo, pode-se destacar os usos de teluritos e teluratos de metais alcalinos em microbiologia, o efeito antioxidante de teluretos e diteluretos orgânicos, os efeitos imunomodulatórios e a diversidade de usos correlacionados a este efeito de uma telurana inorgânica denominada AS-101. Ademais, as aplicações de teluranas orgânicas (organoteluranas) como inibidoras de proteases e as aplicações em modelos de doenças compõem a mais recente contribuição ao cenário dos efeitos e aplicações biológicas do telúrio e seus compostos discutidas neste manuscrito.