Cascade Ligand- and Structure-Based Virtual Screening to Identify New Trypanocidal Compounds Inhibiting Putrescine Uptake.

Chagas disease is a neglected tropical disease endemic to Latin America, though migratory movements have recently spread it to other regions. Here, we have applied a cascade virtual screening campaign combining ligand- and structure-based methods. In order to find novel inhibitors of putrescine uptake in Trypanosoma cruzi, an ensemble of linear ligand-based classifiers obtained by has been applied as initial screening filter, followed by docking into a homology model of the putrescine permease TcPAT12. 1,000 individual linear classifiers were inferred from a balanced dataset. Subsequently, different schemes were tested to combine the individual classifiers: MIN operator, average ranking, average score, average voting, with MIN operator leading to the best performance. The homology model was based on the arginine/agmatine antiporter (AdiC) from Escherichia coli as template. It showed 64% coverage of the entire query sequence and it was selected based on the normalized Discrete Optimized Protein Energy parameter and the GA341 score. The modeled structure had 96% in the allowed area of Ramachandran's plot, and none of the residues located in non-allowed regions were involved in the active site of the transporter. Positivity Predictive Value surfaces were applied to optimize the score thresholds to be used in the ligand-based virtual screening step: for that purpose Positivity Predictive Value was charted as a function of putative yields of active in the range 0.001-0.010 and the Se/Sp ratio. With a focus on drug repositioning opportunities, DrugBank and Sweetlead databases were subjected to screening. Among 8 hits, cinnarizine, a drug frequently prescribed for motion sickness and balance disorder, was tested against T. cruzi epimastigotes and amastigotes, confirming its trypanocidal effects and its inhibitory effects on putrescine uptake. Furthermore, clofazimine, an antibiotic with already proven trypanocidal effects, also displayed inhibitory effects on putrescine uptake. Two other hits, meclizine and butoconazole, also displayed trypanocidal effects (in the case of meclizine, against both epimastigotes and amastigotes), without inhibiting putrescine uptake.

Studies on the interactions between the angiotensin converting enzyme inhibitor enalaprilat and calcium antagonists in rats.

OBJECTIVE: To investigate the hypotheses that the synergistic hypotensive interaction between angiotensin converting enzyme (ACE) inhibitors and calcium antagonists is mediated via alpha1-adrenoceptor blockade and that in the presence of ACE inhibitors the alpha1-adrenoceptor potency of clinically used calcium antagonists may be sufficiently enhanced to add to the hypotensive effect. METHODS: The interactions between the ACE inhibitor enalaprilat and the calcium antagonists diltiazem, cinnarizine, felodipine and verapamil were studied in anesthetized rats for effects on blood pressure and in isolated perfused rat tail arteries for effects at alpha1-adrenoceptors. RESULTS: It was found that in isolated tail arteries enalaprilat had no effect on the weak alpha1-adrenoceptor antagonist actions of diltiazem, cinnarizine and felodipine. Similarly, enalaprilat did not affect the hypotensive responses to these calcium antagonists. However, enalaprilat was found to potentiate the alpha1-adrenoceptor antagonist action of verapamil, both in vitro and in vivo, as well as the hypotensive action of verapamil. CONCLUSIONS: These results support the above hypothesis in the case of verapamil only; for calcium antagonists in general the hypothesis was not supported. The results are consistent with a growing body of evidence showing that the distinction between calcium antagonists and alpha1-adrenoceptor antagonists is becoming less sharply defined.