Biological activity of analogs of guanine and guanosine against American Trypanosoma and Leishmania spp

In Silico and In Vitro Screening of Antipathogenic Properties of Melianthus comosus (Vahl) against Pseudomonas aeruginosa

Bacterial quorum sensing (QS) system regulates pathogenesis, virulence, and biofilm formation, and together they contribute to nosocomial infections. Opportunistic pathogens, such as Pseudomonas aeruginosa, rely on QS for regulating virulence factors. Therefore, blocking the QS system may aid management of various infectious diseases caused by human pathogens. Plant secondary metabolites can thwart bacterial colonization and virulence. As such, this study was undertaken to evaluate three extracts from the medicinal plant, Melianthus comosus, from which phytochemical compounds were identified with potential to inhibit QS-dependent virulence factors in P. aeruginosa. Chemical profiling of the three extracts identified 1,2-benzene dicarboxylic acid, diethyl ester, neophytadiene and hexadecanoic acid as the common compounds. Validation of antibacterial activity confirmed the same MIC values of 0.78 mg/mL for aqueous, methanol and dichloromethane extracts while selected guanosine showed MIC 0.031 mg/mL. Molecular docking analysis showed anti-quorum sensing (AQS) potential of guanosine binding to CviR’ and 2UV0 proteins with varying docking scores of −5.969 and −8.376 kcal/mol, respectively. Guanosine inhibited biofilm cell attachment and biofilm development at 78.88% and 34.85%, respectively. Significant swimming and swarming motility restriction of P. aeruginosa were observed at the highest concentration of plant extracts and guanosine. Overall, guanosine revealed the best swarming motility restrictions. M. comosus extracts and guanosine have shown clear antibacterial effects and subsequent reduction of QS-dependent virulence activities against P.aeruginosa. Therefore, they could be ideal candidates in the search for antipathogenic drugs to combat P.aeruginosa infections.

6-Methyl-7-Aryl-7-Deazapurine Nucleosides as Anti-Trypanosoma cruzi Agents: Structure-Activity Relationship and in vivo Efficacy

Chagas disease is a tropical infectious disease resulting in progressive organ-damage and currently lacks efficient treatment and vaccine options. The causative pathogen, Trypanosoma cruzi, requires uptake and processing of preformed purines from the host because it cannot synthesize these de novo, instigating the evaluation of modified purine nucleosides as potential trypanocides. By modifying the pyrimidine part of a previously identified 7-aryl-7-deazapurine nucleoside, we found that substitution of a 6-methyl for a 6-amino group allows retaining T. cruzi amastigote growth inhibitory activity but confers improved selectivity towards mammalian cells. By keeping the 6-methyl group unaltered, and introducing different 7-aryl groups, we identified several analogues with sub-micromolar antitrypanosomal activity. The 7-(4-chlorophenyl) analogue 14, which was stable in microsomes, was evaluated in an acute mouse model. Oral administration of 25 mg/kg b.i.d. suppressed peak parasitemia and protected mice from infection-related mortality, gave similar reductions as the reference drug of blood parasite loads determined by qPCR, but as benznidazole failed to induce sterile cure in the short time period of drug exposure (5 days).

New ligand-based approach for the discovery of antitrypanosomal compounds

The antitrypanosomal activity of 10 already synthesized compounds was in silico predicted as well as in vitro and in vivo explored against Trypanosoma cruzi. For the computational study, an approach based on non-stochastic linear fingerprints to the identification of potential antichagasic compounds is introduced. Molecular structures of 66 organic compounds, 28 with antitrypanosomal activity and 38 having other clinical uses, were parameterized by means of the TOMOCOMD-CARDD software. A linear classification function was derived allowing the discrimination between active and inactive compounds with a confidence of 95%. As predicted, seven compounds showed antitrypanosomal activity (%AE>70) against epimastigotic forms of T. cruzi at a concentration of 100mug/mL. After an unspecific cytotoxic assay, three compounds were evaluated against amastigote forms of the parasite. An in vivo test was carried out for one of the studied compounds.

A novel non-stochastic quadratic fingerprints-based approach for the 'in silico' discovery of new antitrypanosomal compounds

A non-stochastic quadratic fingerprints-based approach is introduced to classify and design, in a rational way, new antitrypanosomal compounds. A data set of 153 organic chemicals, 62 with antitrypanosomal activity and 91 having other clinical uses, was processed by a k-means cluster analysis to design training and predicting data sets. Afterwards, a linear classification function was derived allowing the discrimination between active and inactive compounds. The model classifies correctly more than 93% of chemicals in both training and external prediction groups. The predictability of this discriminant function was also assessed by a leave-group-out experiment, in which 10% of the compounds were removed at random at each time and their activity predicted a posteriori. In addition, a comparison with models generated using four well-known families of 2D molecular descriptors was carried out. As an experiment of virtual lead generation, the present TOMOCOMD approach was finally satisfactorily applied on the virtual evaluation of 10 already synthesized compounds. The in vitro antitrypanosomal activity of this series against epimastigotes forms of Trypanosomal cruzi was assayed. The model was able to predict correctly the behaviour of these compounds in 90% of the cases.

Purine and pyrimidine transport in pathogenic protozoa: From biology to therapy

Purine salvage is an essential function for all obligate parasitic protozoa studied to date and most are also capable of efficient uptake of preformed pyrimidines. Much progress has been made in the identification and characterisation of protozoan purine and pyrimidine transporters. While the genes encoding protozoan or metazoan pyrimidine transporters have yet to be identified, numerous purine transporters have now been cloned. All protozoan purine transporter-encoding genes characterised to date have been of the Equilibrative Nucleoside Transporter family conserved in a great variety of eukaryote organisms. However, these protozoan transporters have been shown to be sufficiently different from mammalian transporters to mediate selective uptake of therapeutic agents. Recent studies are increasingly addressing the structure and substrate recognition mechanisms of these vital transport proteins.