Expression, characterization and inhibition of Toxoplasma gondii 1-deoxy-D-xylulose-5-phosphate reductoisomerase

1-Deoxy-d-xylulose 5-phosphate reductoisomerase as target for anti Toxoplasma gondii agents: crystal structure, biochemical characterization and biological evaluation of inhibitors

Toxoplasma gondii is a widely distributed apicomplexan parasite causing toxoplasmosis, a critical health issue for immunocompromised individuals and for congenitally infected foetuses. Current treatment options are limited in number and associated with severe side effects. Thus, novel anti-toxoplasma agents need to be identified and developed. 1-Deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) is considered the rate-limiting enzyme in the non-mevalonate pathway for the biosynthesis of the isoprenoid precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate in the parasite, and has been previously investigated for its key role as a novel drug target in some species, encompassing Plasmodia, Mycobacteria and Escherichia coli. In this study, we present the first crystal structure of T. gondii DXR (TgDXR) in a tertiary complex with the inhibitor fosmidomycin and the cofactor NADPH in dimeric conformation at 2.5 Å resolution revealing the inhibitor binding mode. In addition, we biologically characterize reverse α-phenyl-β-thia and β-oxa fosmidomycin analogues and show that some derivatives are strong inhibitors of TgDXR which also, in contrast with fosmidomycin, inhibit the growth of T. gondii in vitro. Here, ((3,4-dichlorophenyl)((2-(hydroxy(methyl)amino)-2-oxoethyl)thio)methyl)phosphonic acid was identified as the most potent anti T. gondii compound. These findings will enable the future design and development of more potent anti-toxoplasma DXR inhibitors.

Over 40 Years of Fosmidomycin Drug Research: A Comprehensive Review and Future Opportunities

To address the continued rise of multi-drug-resistant microorganisms, the development of novel drugs with new modes of action is urgently required. While humans biosynthesize the essential isoprenoid precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via the established mevalonate pathway, pathogenic protozoa and certain pathogenic eubacteria use the less well-known methylerythritol phosphate pathway for this purpose. Important pathogens using the MEP pathway are, for example, Plasmodium falciparum, Mycobacterium tuberculosis, Pseudomonas aeruginosa and Escherichia coli. The enzymes of that pathway are targets for antiinfective drugs that are exempt from target-related toxicity. 2C-Methyl-D-erythritol 4-phosphate (MEP), the second enzyme of the non-mevalonate pathway, has been established as the molecular target of fosmidomycin, an antibiotic that has so far failed to be approved as an anti-infective drug. This review describes the development and anti-infective properties of a wide range of fosmidomycin derivatives synthesized over the last four decades. Here we discuss the DXR inhibitor pharmacophore, which comprises a metal-binding group, a phosphate or phosphonate moiety and a connecting linker. Furthermore, non-fosmidomycin-based DXRi, bisubstrate inhibitors and several prodrug concepts are described. A comprehensive structure-activity relationship (SAR) of nearly all inhibitor types is presented and some novel opportunities for further drug development of DXR inhibitors are discussed.

Structural characterization of 1-deoxy-D-xylulose 5-phosphate Reductoisomerase from Vibrio vulnificus

Vibrio vulnificus, a gram-negative bacterium, is the leading cause of seafood-borne illnesses and mortality in the United States. Previous studies have identified metabolites 2-C-methylerythritol 4-phosphate (MEP) as being essential for V. vulnificus growth and function. It was shown that 1-deoxy-D-xylulose-5-phosphate reductoisomerase (Dxr) is a critical enzyme in the viability of V. vulnificus, and many other bacteria, as it catalyzes the rearrangement of 1-deoxy-D-xylulose-5-phosphate (Dxp) to 2-C-methylerythritol 4-phosphate (MEP) within the MEP pathway, found in plants and bacteria. The MEP pathway produces the isoprenoids, isopentenyl diphosphate and dimethylallyl pyrophosphate. In this study, we produced and structurally characterized V. vulnificus Dxr. The enzyme forms a dimeric assembly and contains a metal ion in the active site. Protein produced in Escherichia coli co-purifies with Mg²⁺ ions, however the Mg²⁺ cations may be substituted with Mn²⁺, as both of these metals may be utilized by Dxrs. These findings will provide a basis for the design of Dxr inhibitors that may find application as antimicrobial compounds.

Isoprenoid metabolism in apicomplexan parasites

Apicomplexan parasites include some of the most prevalent and deadly human pathogens. Novel antiparasitic drugs are urgently needed. Synthesis and metabolism of isoprenoids may present multiple targets for therapeutic intervention. The apicoplast-localized methylerythritol phosphate (MEP) pathway for isoprenoid precursor biosynthesis is distinct from the mevalonate (MVA) pathway used by the mammalian host, and this pathway is apparently essential in most Apicomplexa. In this review, we discuss the current field of research on production and metabolic fates of isoprenoids in apicomplexan parasites, including the acquisition of host isoprenoid precursors and downstream products. We describe recent work identifying the first MEP pathway regulator in apicomplexan parasites, and introduce several promising areas for ongoing research into this well-validated antiparasitic target.

Triazole-based compound as a candidate to develop novel medicines to treat toxoplasmosis

This article reports anti-Toxoplasma gondii activity of 3-(thiophen-2-yl)-1,2,4-triazole-5-thione. The compound displayed significant and reproducible antiparasitic effects at nontoxic concentrations for the host cells, with an experimentally determined 50% inhibitory concentration (IC50) at least 30 times better than that of the known chemotherapeutic agent sulfadiazine. Purine nucleoside phosphorylase was defined as the probable target for anti-Toxoplasma activity of the tested compound. These results provide the foundation for future work to develop a new class of medicines to better treat toxoplasmosis.

1,4-Disubstituted thiosemicarbazide derivatives are potent inhibitors of Toxoplasma gondii proliferation

A series of 4-arylthiosemicarbazides substituted at the N1 position with a 5-membered heteroaryl ring was synthesized and evaluated in vitro for T. gondii inhibition proliferation and host cell cytotoxicity. At non-toxic concentrations for the host cells all studied compounds displayed excellent anti-parasitic effects when compared to sulfadiazine, indicating a high selectivity of their anti-T. gondii activity. The differences in bioactivity investigated by DFT calculations suggest that the inhibitory activity of 4-aryl-thiosemicarbazides towards T. gondii proliferation is connected with the electronic structure of the molecule. Further, these compounds were tested as potential antibacterial agents. No growth-inhibiting effect on any of the test microorganisms was observed for all the compounds, even at high concentrations.