Novel Toxoplasma gondii inhibitor chemotypes

Antimalarial Dibenzannulated Medium-Ring Keto Lactams

We discovered dibenzannulated medium-ring keto lactams (11,12-dihydro-5H-dibenzo[b,g]azonine-6,13-diones) as a new antimalarial chemotype. Most of these had chromatographic LogD7.4 values ranging from <0 to 3 and good kinetic solubilities (12.5 to >100 μg/mL at pH 6.5). The more polar compounds in the series (LogD7.4 values of <2) had the best metabolic stability (CLint values of <50 μL/min/mg protein in human liver microsomes). Most of the compounds had relatively low cytotoxicity, with IC50 values >30 μM, and there was no correlation between antiplasmodial activity and cytotoxicity. The four most potent compounds had Plasmodium falciparum IC50 values of 4.2 to 9.4 nM and in vitro selectivity indices of 670 to >12,000. They were more than 4 orders-of-magnitude less potent against three other protozoal pathogens (Trypanosoma brucei rhodesiense, Trypanosoma cruzi, and Leishmania donovani) but did have relatively high potency against Toxoplasma gondii, with IC50 values ranging from 80 to 200 nM. These keto lactams are converted into their poorly soluble 4(1H)-quinolone transannular condensation products in vitro in culture medium and in vivo in mouse blood. The similar antiplasmodial potencies of three keto lactam-quinolone pairs suggest that the quinolones likely contribute to the antimalarial activity of the lactams.

Quercetin inhibits Toxoplasma gondii tachyzoite proliferation and acts synergically with azithromycin

Quercetin (QUE) is a natural polyphenol known to have numerous pharmacological properties against infectious and non-infectious diseases. Azithromycin (AZ) is an antibiotic that belongs to the azalide class of antimicrobials and an antiparasitic that is known to be effective in combination with clindamycin against pyrimethamine/sulfadiazine-resistant Toxoplasma gondii tachyzoites in clinical settings. Both compounds are known to target protein synthesis and have anti-inflammatory properties. However, little is known about QUE and AZ synergistic interaction against T. gondii growth. Here, we report for the first time the effects of the combination of QUE and AZ on T. gondii growth. The 50% inhibitory concentration (IC50) for QUE at 72 h of interaction was determined to be 0.50 µM, whereas AZ gave an IC50 value of 0.66 µM at 72 h of interaction with parasites. Combination testing of QUE and AZ in a ratio of 2:1 (QUE:AZ) showed an IC50 value of 0.081 µM. Interestingly, a fractional inhibitory index value of 0.28 was observed, indicating a strong synergy. QUE was also found to upregulate the generation of reactive oxygen species and cause dysfunction of the mitochondria membrane of both intracellular and extracellular T. gondii tachyzoites. Overall, the results indicate that QUE is a novel lead capable of synergizing with AZ for inhibiting T. gondii growth and may merit future investigation in vivo for possible combination drug development.

Anti-Toxoplasma gondii activity of Trametes versicolor (Turkey tail) mushroom extract

Toxoplasma gondii (T. gondii) infection continues to rise globally in humans and animals with high socioeconomic and public health challenges. Current medications used against T. gondii infection are limited in efficacy, safety, and affordability. This research was conducted to assess the higher fungi extract effect on T. gondii tachyzoites growth in vitro and possibly decipher its mechanism of action. Furthermore, we evaluated the extract's effect on human foreskin fibroblast viability. The methanol extracts of Turkey tail (TT) mushroom was tested against T. gondii tachyzoites growth using an RH-RFP type I strain that expresses red fluorescent protein throughout culture in a dose-dependent manner using a fluorescent plate reader. Similarly, we tested the effect of the extract on host cell viability. We observed that TT extract inhibited tachyzoites growth with a 50% minimum inhibitory concentration (IC_50s), IC₅₀ = 5.98 ± 1.22 µg/mL, and 50% cytotoxic concentration (CC_50s), CC₅₀ ≥ 100 µg/mL. It was discovered that TT extract induced strong mitochondria superoxide and  reactive oxygen species production and disrupted mitochondria membrane potential in T. gondii tachyzoites. Additionally, scanning electron microscopy depicted that TT extract and pyrimethamine (PY) caused a morphological deformation of tachyzoites in vitro. In conclusion, TT methanol extract made up of phytosterols, bioactive sphingolipids, peptides, phenolic acids, and lactones could be a promising source of new compounds for the future development of anti-Toxoplasma gondii drugs. Extracts were non-cytotoxic, even at higher concentrations.

Neurological and Neurobehavioral Disorders Associated with Toxoplasma gondii Infection in Humans

The intracellular parasite Toxoplasma gondii is estimated to infect up to 30% of the world population, leading to lifelong chronic infection of the brain and muscle tissue. Although most latent T. gondii infections in humans have traditionally been considered asymptomatic, studies in rodents suggest phenotypic neurological changes are possible. Consequently, several studies have examined the link between T. gondii infection and diseases such as schizophrenia, epilepsy, depression, bipolar disorder, dysphoria, Alzheimer's disease, Parkinson's disease, and obsessive-compulsive disorder (OCD). To date, there is varying evidence of the relationship of T. gondii to these human neurological or neurobehavioral disorders. A thorough review of T. gondii literature was conducted to highlight and summarize current findings. We found that schizophrenia was most frequently linked to T. gondii infection, while sleep disruption showed no linkage to T. gondii infection, and other conditions having mixed support for a link to T. gondii. However, infection as a cause of human neurobehavioral disease has yet to be firmly established.

Analogs of marinopyrrole A show enhancement to observed in vitro potency against acute Toxoplasma gondii infection

The apicomplexan parasite Toxoplasma gondii is the causative agent of toxoplasmosis, a globally distributed infection with severe clinical consequences for immunocompromised individuals and developing fetuses. There are few available treatments, and these are associated with potentially severe adverse effects. Marinopyrrole A, a compound discovered in a marine Streptomyces species, has previously been found to exhibit potent antimicrobial activity, prompting our interest in exploring efficacy against Toxoplasma gondii. We found that marinopyrrole A was a highly potent anti-Toxoplasma molecule, with an in vitro 50% maximal inhibitory concentration (IC₅₀) of 0.31 μM corresponding to a higher potency than that of the current standard of care (pyrimethamine); however, addition of 20% serum led to abrogation of potency, and toxicity to human cell lines was observed. Yet, application of marinopyrrole A to an in vivo lethal acute infection model facilitated significantly enhanced survival at doses of 5, 10, and 20 mg/kg. We then tested a series of marinopyrrole A analogs-RL002, RL003, and RL125-demonstrating significantly increased potency in vitro, with IC₅₀ values ranging from 0.09-0.17 μM (3.6-6.8X increase relative to pyrimethamine). No detectable cytotoxicity was observed up to 50 μM in human foreskin fibroblasts, with cytotoxicity in HepG2 cells ranging from ∼28-50 μM, corresponding to >200X selectivity for parasites over host cells. All analogs additionally showed reduced sensitivity to serum. Further, RL003 potently inhibited in vitro-generated bradyzoites at 0.245 μM. Taken together, these data support further development of marinopyrrole A analogs as promising anti-Toxoplasma molecules to further combat this prevalent infection.

Diaryl Ureas as an Antiprotozoal Chemotype

We now describe the physicochemical profiling, in vitro ADME, and antiparasitic activity of eight N,N'-diarylureas to assess their potential as a broad-spectrum antiprotozoal chemotype. Chromatographic LogD_7.4 values ranged from 2.5 to 4.5; kinetic aq. solubilities were ≤6.3 μg/mL, and plasma protein binding ranged from 95 to 99%. All of the compounds had low intrinsic clearance values in human, but not mouse, liver microsomes. Although no N,N'-diarylurea had submicromolar potency against Trypanosoma cruzi, two had submicromolar potencies against Toxoplasma gondii and Trypanosoma brucei rhodesiense, and five had submicromolar potencies against Leishmania donovani. Plasmodium falciparum appeared to be the most susceptible to growth inhibition by this compound series. Most of the N,N'-diarylureas had antiprotozoal selectivities ≥10. One N,N'-diarylurea had demonstrable activity in mouse models of malaria and toxoplasmosis.

In Vitro Selection Implicates ROP1 as a Resistance Gene for an Experimental Therapeutic Benzoquinone Acyl Hydrazone in Toxoplasma gondii

Toxoplasma gondii is a globally distributed apicomplexan parasite and the causative agent of toxoplasmosis in humans. While pharmaceuticals exist to combat acute infection, they can produce serious adverse reactions, demonstrating a need for enhanced therapies. KG8 is a benzoquinone acyl hydrazone chemotype identified from a previous chemical screen for which we previously showed in vitro and in vivo efficacy against T. gondii However, the genetic target and mechanism of action of KG8 remain unknown. To investigate potential targets, we generated resistant T. gondii lines by chemical mutagenesis followed by in vitro selection. Whole-genome sequencing of resistant clones revealed a P207S mutation in the gene encoding rhoptry organelle protein 1 (ROP1) in addition to two lesser resistance-conferring mutations in the genes for rhoptry organelle protein 8 (ROP8) and a putative ADP/ATP carrier protein (TGGT1_237700). Expressing ROP1^P207S in parental parasites was sufficient to confer significant (10.3-fold increased half-maximal effective concentration [EC₅₀]) KG8 resistance. After generating a library of mutants carrying hypermutated rop1 alleles followed by KG8 pressure, we sequenced the most resistant clonal isolate (>16.9-fold increased EC₅₀) and found independent recapitulation of the P207S mutation, along with three additional mutations in the same region. We also demonstrate that a rop1 knockout strain is insensitive to KG8. These data implicate ROP1 as a putative resistance gene of KG8. This work further identifies a compound that can be used in future studies to better understand ROP1 function and highlights this novel chemotype as a potential scaffold for the development of improved T. gondii therapeutics.

Structure-Activity Relationship of Antischistosomal Ozonide Carboxylic Acids

Semisynthetic artemisinins and other bioactive peroxides are best known for their powerful antimalarial activities, and they also show substantial activity against schistosomes-another hemoglobin-degrading pathogen. Building on this discovery, we now describe the initial structure-activity relationship (SAR) of antischistosomal ozonide carboxylic acids OZ418 (2) and OZ165 (3). Irrespective of lipophilicity, these ozonide weak acids have relatively low aqueous solubilities and high protein binding values. Ozonides with para-substituted carboxymethoxy and N-benzylglycine substituents had high antischistosomal efficacies. It was possible to increase solubility, decrease protein binding, and maintain the high antischistosomal activity in mice infected with juvenile and adult Schistosoma mansoni by incorporating a weak base functional group in these compounds. In some cases, adding polar functional groups and heteroatoms to the spiroadamantane substructure increased the solubility and metabolic stability, but in all cases decreased the antischistosomal activity.

Activity of diphenyl ether benzyl amines against Human African Trypanosomiasis

Insect-borne parasite Trypanosoma brucei plagues humans and other animals, eliciting the disease Human African trypanosomiasis, also known as African sleeping sickness. This disease poses the biggest threat to the people in Sub-Saharan Africa. Given the high toxicity and difficulties with administration of currently available drugs, a novel treatment is needed. Building on known Human African trypanosomiasis structure-activity relationship (SAR), we now describe a number of functionally simple diphenyl ether analogs which give low micromolar activity (IC₅₀ = 0.16-0.96 μM) against T. b. rhodesiense. The best compound shows favorable selectivity against the L6 cell line (SI = 750) and even greater selectivity (SI = 1200) against four human cell lines. The data herein provides direction for the ongoing optimization of antitrypanosomal diphenyl ethers.

A new chemotype with promise against Trypanosoma cruzi

Pyridyl benzamide 2 is a potent inhibitor of Trypanosoma cruzi, but not other protozoan parasites, and had a selectivity-index of ≥10. The initial structure-activity relationship (SAR) indicates that benzamide and sulfonamide functional groups, and N-methylpiperazine and sterically unhindered 3-pyridyl substructures are required for high activity against T. cruzi. Compound 2 and its active analogs had low to moderate metabolic stabilities in human and mouse liver microsomes.

Recent progress on anti-Toxoplasma drugs discovery: Design, synthesis and screening

Toxoplasma gondii severely threaten the health of immunocompromised patients and pregnant women as this parasite can cause several disease, including brain and eye disease. Current treatment for toxoplasmosis commonly have high cytotoxic side effects on host and require long durations ranging from one week to more than one year. The regiments lack efficacy to eradicate T. gondii tissue cysts to cure chromic infection results in the needs for long treatment and relapsing disease. In addition, there has not been approved drugs for treating the pregnant women infected by T. gondii. Moreover, Toxoplasma vaccine researches face a wide variety of challenges. Developing high efficient and low toxic agents against T. gondii is urgent and important. Over the last decade, tremendous progress have been made in identifying and developing novel compounds for the treatment of toxoplasmosis. This review summarized and discussed recent advances between 2009 and 2019 in exploring effective agents against T. gondii from five aspects of drug discovery.

Derivatives of a benzoquinone acyl hydrazone with activity against Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite with global incidence. The acute infection, toxoplasmosis, is treatable but current regimens have poor host tolerance and no cure has been found for latent infections. This work builds upon a previous high throughput screen which identified benzoquinone acyl hydrazone (KG8) as the most promising compound; KG8 displayed potent in vitro activity against T. gondii but only marginal in vivo efficacy in a T. gondii animal model. To define the potential of this new lead compound, we now describe a baseline structure-activity relationship for this chemotype. Several derivatives displayed IC₅₀'s comparable to that of the control treatment pyrimethamine with little to no cytotoxicity. The best of these, KGW44 and KGW59, had higher metabolic stability than KG8. In an in vivo T. gondii murine model, KGW59 significantly increased survivorship. This work provides new insights for optimization of this novel chemotype.

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Derivatives from a previously described anti T. gondii compound were characterized.

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Top derivatives showed increased activity against T. gondii in vitro.

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Derivatives demonstrated low cytotoxicity in host cell lines.

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Derivative KGW59 showed efficacy in vivo with a strong therapeutic window.

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These early-leads are suitable for further development as toxoplasmosis therapies.