ABSTRACT
Two new tricyclic ß-aminoacrylate derivatives (2e and 3e) have been found to be inhibitors of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) with Ki 0.037 and 0.15µM respectively. 1H and 13C NMR spectroscopic data show that these compounds undergo ready cis-trans isomerisation at room temperature in polar solvents. In silico docking studies indicate that for both molecules there is neither conformation nor double bond configuration which bind preferentially to PfDHODH. This flexibility is favourable for inhibitors of this channel that require extensive positioning to reach their binding site.
Subject(s)
Acrylates/pharmacology , Oxidoreductases Acting on CH-CH Group Donors/antagonists & inhibitors , Plasmodium falciparum/enzymology , Acrylates/chemical synthesis , Acrylates/chemistry , Dihydroorotate Dehydrogenase , Dose-Response Relationship, Drug , Molecular Docking Simulation , Molecular Structure , Oxidoreductases Acting on CH-CH Group Donors/genetics , Oxidoreductases Acting on CH-CH Group Donors/metabolism , Structure-Activity RelationshipABSTRACT
A high-throughput screen (HTS) was undertaken against the respiratory chain dehydrogenase component, NADH:menaquinone oxidoreductase (Ndh) of Mycobacterium tuberculosis (Mtb). The 11000 compounds were selected for the HTS based on the known phenothiazine Ndh inhibitors, trifluoperazine and thioridazine. Combined HTS (11000 compounds) and in-house screening of a limited number of quinolones (50 compounds) identified â¼100 hits and four distinct chemotypes, the most promising of which contained the quinolone core. Subsequent Mtb screening of the complete in-house quinolone library (350 compounds) identified a further â¼90 hits across three quinolone subtemplates. Quinolones containing the amine-based side chain were selected as the pharmacophore for further modification, resulting in metabolically stable quinolones effective against multi drug resistant (MDR) Mtb. The lead compound, 42a (MTC420), displays acceptable antituberculosis activity (Mtb IC50 = 525 nM, Mtb Wayne IC50 = 76 nM, and MDR Mtb patient isolates IC50 = 140 nM) and favorable pharmacokinetic and toxicological profiles.
Subject(s)
Mycobacterium tuberculosis/drug effects , Quinolones/chemical synthesis , Quinolones/pharmacology , Animals , Caco-2 Cells , Carbon-13 Magnetic Resonance Spectroscopy , Drug Design , Electron Transport/drug effects , Hep G2 Cells , High-Throughput Screening Assays , Humans , Microbial Sensitivity Tests , Mycobacterium tuberculosis/metabolism , Proton Magnetic Resonance Spectroscopy , Quinolones/chemistry , Quinolones/pharmacokinetics , Rats , Spectrometry, Mass, Electrospray Ionization , Structure-Activity Relationship , Toxicity TestsABSTRACT
The de novo pyrimidine biosynthesis enzyme dihydroorotate dehydrogenase is an emerging drug target for the treatment of malaria. In this context a key property of Plasmodium falciparum DHODH (PfDHODH) is that it can be selectively inhibited over its human homologue (HsDHODH). However, HsDHODH is also a validated drug target for autoimmune diseases such as arthritis. Here a series of novel inhibitors is described that includes compounds that switch specificity between the two enzymes as a result of small alterations in chemical structure. Structure-activity relationship (SAR), crystallography, docking, and mutagenesis studies are used to examine the binding modes of the compounds within the two enzymes and to reveal structural changes induced by inhibitor binding. Within this series, compounds with therapeutically relevant HsDHODH activity are described and their binding modes characterized using X-ray crystallography, which reveals a novel conformational shift within the inhibitor binding site.