Screening and In Vitro Evaluation of Potential Plasmodium falciparum Leucyl Aminopeptidase Inhibitors

Abstract

Background: Plasmodium falciparum leucyl aminopeptidase (PfA-M17) regulates the intracellular pool of amino acids required for the growth and development of parasites. Thus, PfA-M17 is a promising target for anti-malarial drug development.

Method: In the present study, structure-based drug design was used to identify novel PfA-M17 inhibitors, which were subsequently validated by in vitro PfA-M17 and human LAP3 enzyme inhibition assay. A library of 3,147,882 compounds was screened using receptor-based virtual screening against the active site of PfA-M17, and three levels of accuracy were used: high-throughput virtual screening, gridbased ligand docking with energetics (Glide standard precision) and Glide extra precision.

Results: Seventeen screened compounds were selected and tested in the rPfA-M17 enzyme inhibition assay. Of these nine compounds were found to be effective inhibitors. To test the target activity, all nine PfA-M17 inhibitors were tested against rhLAP3, the human homolog of PfA-M17. One compound (compound 2) was found to be moderately effective against PfA-M17 (Ki = 287 μM) with limited inhibitory activity against hLAP3 (Ki of 4,464 μM). Subsequently, induced fit docking and pharmacophore modelling were used to further understand more precise ligand-protein interactions in the protein-inhibitor complexes.

Conclusion: Among the 9 effective PfA-M17 inhibitors, 5 compounds were found effective in the P. falciparum schizont maturation inhibition (SMI) assay. A good correlation (r =0.83) was observed between the rPfA-M17 enzyme inhibition concentration and SMI assay.