Assessment of the Activity of Decoquinate and Its Quinoline-O-Carbamate Derivatives against Toxoplasma gondii In Vitro and in Pregnant Mice Infected with T. gondii Oocysts

In vitro and in vivo activities of a trithiolato-diRuthenium complex conjugated with sulfadoxine against the apicomplexan parasite Toxoplasma gondii

Organometallic compounds, including Ruthenium complexes, have been widely developed as anti-cancer chemotherapeutics, but have also attracted much interest as potential anti-parasitic drugs. Recently hybrid drugs composed of organometallic Ruthenium moieties that were complexed to different antimicrobial agents were synthesized. One of these compounds, a trithiolato-diRuthenium complex (RU) conjugated to sulfadoxine (SDX), inhibited proliferation of Toxoplasma gondii tachyzoites grown in human foreskin fibroblast (HFF) monolayers with an IC50 < 150 nM, while SDX and the non-modified RU complex applied either individually or as an equimolar mixture were much less potent. In addition, conjugation of SDX to RU lead to decreased HFF cytotoxicity. RU-SDX did not impair the in vitro proliferation of murine splenocytes at concentrations ranging from 0.1 to 0.5 μM but had an impact at 2 μM, and induced zebrafish embryotoxicity at 20 μM, but not at 2 or 0.2 μM. RU-SDX acted parasitostatic but not parasiticidal, and induced transient ultrastructural changes in the mitochondrial matrix of tachyzoites early during treatment. While other compounds that target the mitochondrion such as the uncouplers FCCP and CCCP and another trithiolato-Ruthenium complex conjugated to adenine affected the mitochondrial membrane potential, no such effect was detected for RU-SDX. Evaluation of the in vivo efficacy of RU-SDX in a murine T. gondii oocyst infection model comprised of non-pregnant outbred CD1 mice showed no effects on the cerebral parasite burden, but reduced parasite load in the eyes and in heart tissue.

In vitro screening technologies for the discovery and development of novel drugs against Toxoplasma gondii

INTRODUCTION

Toxoplasmosis constitutes a challenge for public health, animal production and welfare. Since more than 60 years, only a limited panel of drugs has been in use for clinical applications.

AREAS COVERED

Herein, the authors describe the methodology and the results of library screening approaches to identify inhibitors of Toxoplasma gondii and related strains. The authors then provide the reader with their expert perspectives for the future.

EXPERT OPINION

Various library screening projects, in particular those using reporter strains, have led to the identification of numerous compounds with good efficacy and specificity in vitro. However, only few compounds are effective in suitable animal models such as rodents. Whereas no novel compound has cleared the hurdle to applications in humans, the few compounds with known indication and application profiles in human patients are of interest for further investigations. Taken together, drug repurposing as well as high-throughput screening of novel compound libraries may shorten the way to novel drugs against toxoplasmosis.

Synthesis, Photophysical Properties and Biological Evaluation of New Conjugates BODIPY: Dinuclear Trithiolato-Bridged Ruthenium(II)-Arene Complexes

The synthesis, photophysical properties and antiparasitic efficacy against Toxoplasma gondii β-gal (RH strain tachyzoites expressing β-galactosidase) grown in human foreskin fibroblast monolayers (HFF) of a series of 15 new conjugates BODIPY-trithiolato-bridged dinuclear ruthenium(II)-arene complexes are reported (BODIPY=4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, derivatives used as fluorescent markers). The influence of the bond type (amide vs. ester), as well as that of the length and nature (alkyl vs. aryl) of the spacer between the dye and the diruthenium(II) complex moiety, on fluorescence and biological activity were evaluated. The assessed photophysical properties revealed that despite an important fluorescence quenching effect observed after conjugating the BODIPY to the diruthenium unit, the hybrids could nevertheless be used as fluorescent tracers. Although the antiparasitic activity of this series of conjugates appears limited, the compounds demonstrate potential as fluorescent probes for investigating the intracellular trafficking of trithiolato-bridged dinuclear Ru(II)-arene complexes in vitro.

Structure-activity relationships of Toxoplasma gondii cytochrome bc1 inhibitors

INTRODUCTION

Toxoplasma gondii is a prolific apicomplexan parasite that infects human and nonhuman animals worldwide and can cause severe brain and eye disease. Safer, more effective therapies for toxoplasmosis are needed. Cytochrome bc1 inhibitors are remarkably effective against toxoplasmosis and other apicomplexan-caused diseases.

AREAS COVERED

This work reviews T. gondii cytochrome bc1 inhibitors. Emphasis is placed on the structure-activity relationships of these inhibitors with regard to efficacy, pharmacokinetics, selectivity of T. gondii cytochrome bc1 over host, safety, and potential therapeutic strategies.

EXPERT OPINION

Cytochrome bc1 inhibitors are highly promising compounds for toxoplasmosis that have been effective in clinical and preclinical studies. Clinical experience with atovaquone previously validated cytochrome bc1 as a tractable drug target and, over the past decade, optimization of cytochrome bc1 inhibitors has resulted in improved bioavailability, metabolic stability, potency, blood-brain barrier penetration, and selectivity for the T. gondii cytochrome bc1 over the mammalian bc1. Recent studies have demonstrated preclinical safety, identified novel therapeutic strategies for toxoplasmosis using synergistic combinations or long-acting administration and provided insight into their role in chronic infection. This research has identified drug candidates that are more effective than clinically used drugs in preclinical measures of efficacy.

Preparation of protamine-hyaluronic acid coated core-shell nanoparticles for enhanced solubility, permeability, and oral bioavailability of decoquinate

Decoquinate (DQ) has low oral bioavailability owing to its poor water solubility. In this study, a DQ solid dispersion (DQ-SD) was fabricated using mechanochemical technology to encapsulate DQ and improve its oral bioavailability. DQ-SD is easily generated via self-assembly in the aqueous phase to form micelles consisting of disodium glycyrrhizinate (Na₂GA) nanoparticles with a protamine (PRM) and anionic hyaluronic acid (HA) layers. The spherical DQ nanoparticles with an average diameter of 114.95 nm were obtained in an aqueous phase with a critical micelle concentration of 0.157 mg/mL, zeta potential of -38.38 mV, polydispersity index of 0.200, and drug loading of 5.66 %. The dissolution rate and cumulative release of DQ-SD were higher than those of pure DQ. Furthermore, the bioavailability of DQ-SD was approximately 6.3 times higher than that of pure DQ. Pharmacokinetic and biodistribution studies indicated that DQ-SD possessed a significantly higher concentration in the blood and preferential liver tissue accumulation, than that of pure DQ. The developed DQ-SD exhibited considerable potential for developing old DQ for a new application as a hematogenous parasite drug and provides a reference for developing more efficient delivery systems for hydrophobic bioactive agents.