The ubiquinone synthesis pathway is a promising drug target for Chagas disease.

Chagas disease is caused by infection with the protozoan parasite Trypanosoma cruzi (T. cruzi). It was originally a Latin American endemic health problem, but now is expanding worldwide as a result of increasing migration. The currently available drugs for Chagas disease, benznidazole and nifurtimox, provoke severe adverse effects, and thus the development of new drugs is urgently required. Ubiquinone (UQ) is essential for respiratory chain and redox balance in trypanosomatid protozoans, therefore we aimed to provide evidence that inhibitors of the UQ biosynthesis have trypanocidal activities. In this study, inhibitors of the human COQ7, a key enzyme of the UQ synthesis, were tested for their trypanocidal activities because they were expected to cross-react and inhibit trypanosomal COQ7 due to their genetic homology. We show the trypanocidal activity of a newly found human COQ7 inhibitor, an oxazinoquinoline derivative. The structurally similar compounds were selected from the commercially available compounds by 2D and 3D ligand-based similarity searches. Among 38 compounds selected, 12 compounds with the oxazinoquinoline structure inhibited significantly the growth of epimastigotes of T. cruzi. The most effective 3 compounds also showed the significant antitrypanosomal activity against the mammalian stage of T. cruzi at lower concentrations than benznidazole, a commonly used drug today. We found that epimastigotes treated with the inhibitor contained reduced levels of UQ9. Further, the growth of epimastigotes treated with the inhibitors was partially rescued by UQ10 supplementation to the culture medium. These results suggest that the antitrypanosomal mechanism of the oxazinoquinoline derivatives results from inhibition of the trypanosomal UQ synthesis leading to a shortage of the UQ pool. Our data indicate that the UQ synthesis pathway of T. cruzi is a promising drug target for Chagas disease.

Identification of small molecule inhibitors of human COQ7.

Given that the associated clinical manifestations of ubiquinone (UQ, or coenzyme Q) deficiency diseases are highly heterogeneous and complicated, effective new research tools for UQ homeostasis studies are awaited. We set out to develop human COQ7 inhibitors that interfere with UQ synthesis. Systematic structure-activity relationship development starting from a screening hit compound led to the identification of highly potent COQ7 inhibitors that did not disturb physiological cell growth of human normal culture cells. These new COQ7 inhibitors may serve as useful tools for studying the balance between UQ supplementation pathways: de novo UQ synthesis and extracellular UQ uptake.

A novel Pim-1 kinase inhibitor targeting residues that bind the substrate peptide.

A new screening method using fluorescent correlation spectroscopy was developed to select kinase inhibitors that competitively inhibit the binding of a fluorescently labeled substrate peptide. Using the method, among approximately 700 candidate compounds selected by virtual screening, we identified a novel Pim-1 kinase inhibitor targeting its peptide binding residues. X-ray crystal analysis of the complex structure of Pim-1 with the inhibitor indicated that the inhibitor actually binds to the ATP-binding site and also forms direct interactions with residues (Asp128 and Glu171) that bind the substrate peptide. These interactions, which cause small side-chain movements, seem to affect the binding ability of the fluorescently labeled substrate. The compound inhibited Pim-1 kinase in vitro, with an IC(50) value of 150 nM. Treatment of cultured leukemia cells with the compound reduced the amount of p21 and increased the amount of p27, due to Pim-1 inhibition, and then triggered apoptosis after cell-cycle arrest at the G(1)/S phase. This screening method may be widely applicable for the identification of various new Pim-1 kinase inhibitors targeting the residues that bind the substrate peptide.