Targeting the Viral Polymerase of Diarrhea-Causing Viruses as a Strategy to Develop a Single Broad-Spectrum Antiviral Therapy

Viral gastroenteritis is an important cause of morbidity and mortality worldwide, being particularly severe for children under the age of five. The most common viral agents of gastroenteritis are noroviruses, rotaviruses, sapoviruses, astroviruses and adenoviruses, however, no specific antiviral treatment exists today against any of these pathogens. We here discuss the feasibility of developing a broad-spectrum antiviral treatment against these diarrhea-causing viruses. This review focuses on the viral polymerase as an antiviral target, as this is the most conserved viral protein among the diverse viral families to which these viruses belong to. We describe the functional and structural similarities of the different viral polymerases, the antiviral effect of reported polymerase inhibitors and highlight common features that might be exploited in an attempt of designing such pan-polymerase inhibitor.

Characterisation of three alpha-helical antimicrobial peptides from the venom of Scorpio maurus palmatus

Scorpion venoms provide a rich source of anti-microbial peptides. Here we characterise three from the venom of Scorpion maurus palmatus. Smp13 is biologically inactive, despite sharing homology with other antimicrobial peptides, probably because it lacks a typically charged structure. Both Smp-24 and Smp-43 have broad spectrum antimicrobial activity, disrupting bacterial membranes. In addition, there is evidence that Smp24 may inhibit DNA synthesis in Bacillus subtilis. Smp24 haemolysed red blood cells but in contrast, Smp43 was non-haemolytic. The introduction of a flexible Gly-Val-Gly hinge into the middle of Smp24 did not alter the haemolytic activity of Smp24 (as might have been predicted from earlier studies with Pandinin2 (Pin2), although C-terminal truncation of Smp-24 reduced its haemolytic activity, in agreement with earlier Pin 2 studies. Smp24 and its derivatives, as well as Smp-43, were all cytotoxic (ATP release assay) toward mammalian HepG2 liver cells. Our results highlight the beneficial effect of helical-hinge-helical conformation on promoting prokaryotic selectivity of long chain scorpion AMPs, as well as the importance of examining a wide range of mammalian cell types in cytotoxicity testing.

Isolation, structure, and antibacterial activity of phaeosphenone from a Phaeosphaeria sp. discovered by antisense strategy

Ribosomal protein S4 (RPSD), a part of the ribosomal small subunit, is one of the proteins that is a part of the ribosomal machinery and is a potential new target for the discovery of antibacterial agents. Continued screening of microbial extracts using antisense-sensitized rpsD Staphylococcus aureus strain led to the isolation of a new dimeric compound, phaeosphenone (2). Compound 2 showed broad-spectrum antibacterial activity against Gram-positive bacteria, exhibiting MIC values ranging from 8 to 64 microg/mL. Phaeosphenone showed the highest sensitivity for Streptococcus pneumoniae (8 microg/mL) and inhibited the growth of Candida albicans with an MIC of 8 microg/mL. Phaeosphenone showed a modest selectivity for the inhibition of RNA synthesis over DNA and protein synthesis in S. aureus.

Taxol derivatives are selective inhibitors of DNA polymerase alpha

During screening for mammalian DNA polymerase inhibitors, we found and succeeded in isolating a potent inhibitor from a higher plant, Taxus cuspidate. The compound was unexpectedly determined to be taxinine, an intermediate of paclitaxel (taxol) metabolism. Taxinine was found to selectively inhibit DNA polymerase alpha (pol.alpha) and beta (pol.beta). We therefore, tested taxol and other derivatives and found that taxol itself had no such inhibitory effect, and only taxinine could inhibit both pol.alpha and beta. The other compounds used, one derivative, cephalomannine, and five intermediates synthesized chemically inhibited only the pol.alpha activity in vitro. None of the compounds, including taxinine, influenced the activities of the other DNA polymerases, which are reportedly targeted by many pol.beta inhibitors. With both pol.alpha and beta, all of the compounds tested noncompetitively inhibited with respect to both the DNA template-primer and the dNTP substrate.

Iridoids as allelochemicals and DNA polymerase inhibitors

Growth inhibitory activities and nutritional indices of catalpol (1), 8-O-acetylharpagide (2), and harpagide (3) were determinated in larvae and adults of Tribolium castaneum, respectively. Compound 1 produced a series of allelochemical effects probably related with the DNA synthesis. This iridoid possessed the highest inhibitory activity against DNA polymerase. Molecular orbital calculations suggest that a pi-pi charge transfer recognition model could explain the action of iridioids toward nucleic acid synthesis.

Apoptosis of HL-60 leukemia cells induced by the bisindole alkaloids sungucine and isosungucine from Strychnos icaja

Sungucine and isosungucine are two bisindole alkaloids isolated from the roots of the African plant Strychnos icaja Baillon. They both exhibit antiplasmodial activities but also show cytotoxic effects against human cancer cell lines. In order to elucidate their mechanism of action, we have investigated the interaction of the alkaloids with DNA and their capacity to inhibit nucleic acids and protein synthesis in the human HL-60 promyelocytic leukemia cell line. Cell treatment with both sungucine and isosungucine leads to the appearance of a hypo-diploid DNA content peak. Western blotting analysis reveals that the two alkaloids induce cleavage of the poly(ADP-ribose) polymerase (PARP) and promote the cleavage of a caspase-3 DEVD peptide substrate. The activation of the caspase cascade is accompanied with a fragmentation of DNA in cells, as revealed by the TUNEL assay. Altogether, the results shed light on the mechanism of action of these two plant alkaloids and identify signaling factors involved in (iso)sungucine-induced apoptosis in HL-60 cells.

Cytochalasin D from Hypocrella bambusae

Cytochalasin D which shows marked cytotoxic effects on multi-tumor cells was newly isolated at high content(5.28 mg/g, dry weight) from Fungus Hypocrella bambusae(B.et Br.) Sacc. Its structure was elucidated by spectroscopic methods. Two-dimensional NMR techniques were applied to make complete assignment for the 1H- and 13C-NMR chemical shifts of this compound.

Inhibition of DNA synthesis and tube morphogenesis of cultured vascular endothelial cells by chondromodulin-I

Cartilage is an avascular tissue, and exhibits anti-angiogenic properties. Cartilage extracts have been shown to contain an inhibitor for DNA synthesis in vascular endothelial cells in vitro. Here we purified the inhibitory activity in the 10-50 kDa fraction of guanidine extracts from fetal bovine epiphyseal cartilage, and found that the inhibitor was identical with chondromodulin-I (ChM-I). Purified ChM-I inhibited tube morphogenesis of cultured vascular endothelial cells, as well as DNA synthesis. These results indicate that cartilage-specific glycoprotein ChM-I may participate in the maintenance of avascularity and anti-angiogenic properties of cartilage.