X-ray Structural Analysis of Plasmodium falciparum Enoyl Acyl Carrier Protein Reductase as a Pathway toward the Optimization of Triclosan Antimalarial Efficacy

Abstract

The x-ray crystal structures of five triclosan analogs, in addition to that of the isoniazid-NAD adduct, are described in relation to their integral role in the design of potent inhibitors of the malarial enzyme Plasmodium falciparum enoyl acyl carrier protein reductase (PfENR). Many of the novel 5-substituted analogs exhibit low micromolar potency against in vitro cultures of drug-resistant and drug-sensitive strains of the P. falciparum parasite and inhibit purified PfENR enzyme with IC 50 values of <200 nM. This study has significantly expanded the knowledge base with regard to the structure-activity relationship of triclosan while affording gains against cultured parasites and purified PfENR enzyme. In contrast to a recent report in the literature, these results demonstrate the ability to improve the in vitro potency of triclosan significantly by replacing the suboptimal 5-chloro group with larger hydrophobic moieties. The biological and x-ray crystallographic data thus demonstrate the flexibility of the active site and point to future rounds of optimization to improve compound potency against purified enzyme and intracellular Plasmodium parasites.

Advances in Antimalarial Drug Evaluation and New Targets for Antimalarials

“…These results stimulated efforts both to genetically validate these putative targets and to improve inhibitor discovery, by solving 3D structures and producing enzymes under recombinant active forms amenable to medium/high throughput screenings (Freundlich et al, 2007, Sato, 2011. In 2008, the genetic inactivation of FabI in P. falciparum and in P. berghei produced parasite blood stages that were growing normally and were still affected by triclosan (Yu et al, 2008).…”

SAR and pharmacophore models for the rhodanine inhibitors of Plasmodium falciparum enoyl‐acyl carrier protein reductase

“…Carrier solvent was acetonitrile-water (1:1 mixture). The flow rate of the solvent was maintained at 50 lL min 21 . The samples were dissolved in DMSO such that concentrations in micromolar range were achieved from which 5 lL of each sample was injected.…”

“…In yet another study, P. falciparum enzymes were expressed in vitro and reconstituted to mimick the in vivo machinery (17). We and others have shown diverse classes of compounds varying from triclosan analogs, polyphenols, green tea catechins to substituted pyrazoles to inhibit PfENR in the in vitro system (18)(19)(20)(21)(22)(23). Considering the suitability of ENR as a potent antimicrobial drug target, the available pool of inhibitor scaffolds discovered so far against it is very small.…”

Discovery of new targets for antimalarial chemotherapy

“…X-ray structural analysis of PfENR has expanded the knowledge of the structure-activity relationships of Triclosan. This leads to analogues active in low micromolar range in vitro on P. falciparum and displaying a higher affinity for PfENR (Freundlich et al, 2007).…”