Exposing Anopheles mosquitoes to antimalarials blocks Plasmodium parasite transmission.

Bites of Anopheles mosquitoes transmit Plasmodium falciparum parasites that cause malaria, which kills hundreds of thousands of people every year. Since the turn of this century, efforts to prevent the transmission of these parasites via the mass distribution of insecticide-treated bed nets have been extremely successful, and have led to an unprecedented reduction in deaths from malaria1. However, resistance to insecticides has become widespread in Anopheles populations2-4, which has led to the threat of a global resurgence of malaria and makes the generation of effective tools for controlling this disease an urgent public health priority. Here we show that the development of P. falciparum can be rapidly and completely blocked when female Anopheles gambiae mosquitoes take up low concentrations of specific antimalarials from treated surfaces-conditions that simulate contact with a bed net. Mosquito exposure to atovaquone before, or shortly after, P. falciparum infection causes full parasite arrest in the midgut, and prevents transmission of infection. Similar transmission-blocking effects are achieved using other cytochrome b inhibitors, which demonstrates that parasite mitochondrial function is a suitable target for killing parasites. Incorporating these effects into a model of malaria transmission dynamics predicts that impregnating mosquito nets with Plasmodium inhibitors would substantially mitigate the global health effects of insecticide resistance. This study identifies a powerful strategy for blocking Plasmodium transmission by female Anopheles mosquitoes, which has promising implications for efforts to eradicate malaria.

Tafenoquine-Atovaquone Combination Achieves Radical Cure and Confers Sterile Immunity in Experimental Models of Human Babesiosis.

Human babesiosis is a potentially fatal tick-borne disease caused by intraerythrocytic Babesia parasites. The emergence of resistance to recommended therapies highlights the need for new and more effective treatments. Here we demonstrate that the 8-aminoquinoline antimalarial drug tafenoquine inhibits the growth of different Babesia species in vitro, is highly effective against Babesia microti and Babesia duncani in mice and protects animals from lethal infection caused by atovaquone-sensitive and -resistant B. duncani strains. We further show that a combination of tafenoquine and atovaquone achieves cure with no recrudescence in both models of human babesiosis. Interestingly, elimination of B. duncani infection in animals following drug treatment also confers immunity to subsequent challenge. Altogether, the data demonstrate superior efficacy of tafenoquine plus atovaquone combination over current therapies for the treatment of human babesiosis and highlight its potential in providing protective immunity against Babesia following parasite clearance.

Atovaquone enhances antitumor efficacy of TCR-T therapy by augmentation of ROS-induced ferroptosis in hepatocellular carcinoma.

T-cell receptor (TCR) engineered T-cell therapy has recently emerged as a promising adoptive immunotherapy approach for tumor treatment, yet hindered by tumor immune evasion resulting in poor therapeutic efficacy. The introduction of ferroptosis-targeted inducers offers a potential solution, as they empower T cells to induce ferroptosis and exert influence over the tumor microenvironment. Atovaquone (ATO) stands as a prospective pharmaceutical candidate with the potential to target ferroptosis, effectively provoking an excessive generation and accumulation of reactive oxygen species (ROS). In this study, we evaluated the effectiveness of a combination therapy comprising ATO and TCR-T cells against hepatocellular carcinoma (HCC), both in vitro and in vivo. The results of lactate dehydrogenase and cytokine assays demonstrated that ATO enhanced cytotoxicity mediated by AFP-specific TCR-T cells and promoted the release of IFN-γ in vitro. Additionally, in an established HCC xenograft mouse model, the combined therapy with low-dose ATO and TCR-T cells exhibited heightened efficacy in suppressing tumor growth, with no apparent adverse effects, comparable to the results achieved through monotherapy. The RNA-seq data unveiled a significant activation of the ferroptosis-related pathway in the combination therapy group in comparison to the TCR-T cells group. Mechanistically, the synergy between ATO and TCR-T cells augmented the release of IFN-γ by TCR-T cells, while concurrently elevating the intracellular and mitochondrial levels of ROS, expanding the labile iron pool, and impairing the integrity of the mitochondrial membrane in HepG2 cells. This multifaceted interaction culminated in the potentiation of ferroptosis within the tumor, primarily induced by an excess of ROS. In summary, the co-administration of ATO and TCR-T cells in HCC exhibited heightened vulnerability to ferroptosis. This heightened susceptibility led to the inhibition of tumor growth and the stimulation of an anti-tumor immune response. These findings suggest that repurposing atovaquone for adoptive cell therapy combination therapy holds the potential to enhance treatment outcomes in HCC.

Using an antimalarial in mosquitoes overcomes Anopheles and Plasmodium resistance to malaria control strategies.

The spread of insecticide resistance in Anopheles mosquitoes and drug resistance in Plasmodium parasites is contributing to a global resurgence of malaria, making the generation of control tools that can overcome these roadblocks an urgent public health priority. We recently showed that the transmission of Plasmodium falciparum parasites can be efficiently blocked when exposing Anopheles gambiae females to antimalarials deposited on a treated surface, with no negative consequences on major components of mosquito fitness. Here, we demonstrate this approach can overcome the hurdles of insecticide resistance in mosquitoes and drug resistant in parasites. We show that the transmission-blocking efficacy of mosquito-targeted antimalarials is maintained when field-derived, insecticide resistant Anopheles are exposed to the potent cytochrome b inhibitor atovaquone, demonstrating that this drug escapes insecticide resistance mechanisms that could potentially interfere with its function. Moreover, this approach prevents transmission of field-derived, artemisinin resistant P. falciparum parasites (Kelch13 C580Y mutant), proving that this strategy could be used to prevent the spread of parasite mutations that induce resistance to front-line antimalarials. Atovaquone is also highly effective at limiting parasite development when ingested by mosquitoes in sugar solutions, including in ongoing infections. These data support the use of mosquito-targeted antimalarials as a promising tool to complement and extend the efficacy of current malaria control interventions.

Inhibition of Wnt Signaling by Atovaquone Inhibits Gastric Cancer and Enhances Chemotherapy Effectiveness Through Activation of Casein Kinase 1α.

Abnormal activation of the Wnt/ß-catenin signaling pathway is a driving force behind the progression of gastric cancer. Atovaquone, known as an antimalarial drug, has emerged as a potential candidate for anti-cancer therapy. This study investigated atovaquone's effects on gastric cancer and its underlying mechanisms. Using gastric cancer cell lines, we found that atovaquone, at concentrations relevant to clinical use, significantly reduced their viability. Notably, atovaquone exhibited a lower effectiveness in reducing the viability of normal gastric cells compared to gastric cancer cells. We further demonstrated that atovaquone inhibited gastric cancer growth and colony formation. Mechanism studies revealed that atovaquone inhibited mitochondrial respiration and induced oxidative stress. Experiments using ρ0 cells, deficient in mitochondrial respiration, indicated a slightly weaker effect of atovaquone on inducing apoptosis compared to wildtype cells. Atovaquone increased phosphorylated ß-catenin at Ser45 and Ser33/37/Thr41, elevated Axin, and reduced ß-catenin. The inhibitory effects of atovaquone on ß-catenin were reversed upon depletion of CK1α. Furthermore, the combination of atovaquone with paclitaxel suppressed gastric cancer growth and improved overall survival in mice. Given that atovaquone is already approved for clinical use, these findings suggest its potential as a valuable addition to the drug arsenal available for treating gastric cancer.

Inhibition of mitochondrial function by approved drugs overcomes nasopharyngeal carcinoma chemoresistance.

The development of chemo-resistance in nasopharyngeal carcinoma (NPC) presents a significant therapeutic challenge, and its underlying mechanisms remain poorly understood. In our previous studies, we highlighted the association between isoprenylcysteine carboxylmethyltransferase (ICMT) and chemoresistance in NPC. In this current research, we revealed that both 5-FU and cisplatin-resistant NPC cells exhibited elevated mitochondrial function and increased expression of mitochondrial genes, independent of ICMT. Our investigations further showed that classic mitochondrial inhibitors, such as oligomycin, antimycin, and rotenone, were notably more effective in reducing viability in chemo-resistant NPC cells compared to parental cells. Moreover, we identified two antimicrobial drugs, tigecycline and atovaquone, recognized as mitochondrial inhibitors, as potent agents for decreasing chemo-resistant NPC cells by targeting mitochondrial respiration. Remarkably, tigecycline and atovaquone, administered at tolerable doses, inhibited chemo-resistant NPC growth in mouse models and extended overall survival rates. This work unveils the efficacy of mitochondrial inhibition as a promising strategy to overcome chemo-resistance in NPC. Additionally, our findings highlight the potential repurposing of clinically available drugs like tigecycline and atovaquone for treating NPC patients who develop chemoresistance.

Potential Anti-Mpox Virus Activity of Atovaquone, Mefloquine, and Molnupiravir, and Their Potential Use as Treatments.

BACKGROUND: Mpox virus (MPXV) is a zoonotic orthopoxvirus and caused an outbreak in 2022. Although tecovirimat and brincidofovir are approved as anti-smallpox drugs, their effects in mpox patients have not been well documented. In this study, by a drug repurposing approach, we identified potential drug candidates for treating mpox and predicted their clinical impacts by mathematical modeling. METHODS: We screened 132 approved drugs using an MPXV infection cell system. We quantified antiviral activities of potential drug candidates by measuring intracellular viral DNA and analyzed the modes of action by time-of-addition assay and electron microscopic analysis. We further predicted the efficacy of drugs under clinical concentrations by mathematical simulation and examined combination treatment. RESULTS: Atovaquone, mefloquine, and molnupiravir exhibited anti-MPXV activity, with 50% inhibitory concentrations of 0.51-5.2 µM, which was more potent than cidofovir. Whereas mefloquine was suggested to inhibit viral entry, atovaquone and molnupiravir targeted postentry processes. Atovaquone was suggested to exert its activity through inhibiting dihydroorotate dehydrogenase. Combining atovaquone with tecovirimat enhanced the anti-MPXV effect of tecovirimat. Quantitative mathematical simulations predicted that atovaquone can promote viral clearance in patients by 7 days at clinically relevant drug concentrations. CONCLUSIONS: These data suggest that atovaquone would be a potential candidate for treating mpox.

Amplicon Deep Sequencing Reveals Multiple Genetic Events Lead to Treatment Failure with Atovaquone-Proguanil in Plasmodium falciparum.

Atovaquone-proguanil (AP) is used as treatment for uncomplicated malaria, and as a chemoprophylactic agent against Plasmodium falciparum. Imported malaria remains one of the top causes of fever in Canadian returning travelers. Twelve sequential whole-blood samples before and after AP treatment failure were obtained from a patient diagnosed with P. falciparum malaria upon their return from Uganda and Sudan. Ultradeep sequencing was performed on the cytb, dhfr, and dhps markers of treatment resistance before and during the episode of recrudescence. Haplotyping profiles were generated using three different approaches: msp2-3D7 agarose and capillary electrophoresis, and cpmp using amplicon deep sequencing (ADS). A complexity of infection (COI) analysis was conducted. De novo cytb Y268C mutants strains were observed during an episode of recrudescence 17 days and 16 h after the initial malaria diagnosis and AP treatment initiation. No Y268C mutant reads were observed in any of the samples prior to the recrudescence. SNPs in the dhfr and dhps genes were observed upon initial presentation. The haplotyping profiles suggest multiple clones mutating under AP selection pressure (COI > 3). Significant differences in COI were observed by capillary electrophoresis and ADS compared to the agarose gel results. ADS using cpmp revealed the lowest haplotype variation across the longitudinal analysis. Our findings highlight the value of ultra-deep sequencing methods in the understanding of P. falciparum haplotype infection dynamics. Longitudinal samples should be analyzed in genotyping studies to increase the analytical sensitivity.

A High-Throughput Amenable Dual Luciferase System for Measuring Toxoplasma gondii Bradyzoite Viability after Drug Treatment.

It is estimated that more than 2 billion people are chronically infected with the intracellular protozoan parasite Toxoplasma gondii (T. gondii). Despite this, there is currently no vaccine to prevent infection in humans, and there is no recognized curative treatment to clear tissue cysts. A major hurdle for identifying effective drug candidates against chronic-stage cysts has been the low throughput of existing in vitro assays for testing the survival of bradyzoites. We have developed a luciferase-based platform for specifically determining bradyzoite survival within in vitro cysts in a 96-well plate format. We engineered a cystogenic type II T. gondii PruΔku80Δhxgpr strain for stage-specific expression of firefly luciferase in the cytosol of bradyzoites and nanoluciferase for secretion into the lumen of the cyst (DuaLuc strain). Using this DuaLuc strain, we found that the ratio of firefly luciferase to nanoluciferase decreased upon treatment with atovaquone or LHVS, two compounds that are known to compromise bradyzoite viability. The 96-well format allowed us to test several additional compounds and generate dose-response curves for calculation of EC50 values indicating relative effectiveness of a compound. Accordingly, this DuaLuc system should be suitable for screening libraries of diverse compounds and defining the potency of hits or other compounds with a putative antibradyzoite activity.

Assessment of tissue levels of miR-146a and proinflammatory cytokines in experimental cerebral toxoplasmosis following atovaquone and clindamycin treatment: An in vivo study.

BACKGROUND: Despite recent advances for treating cerebral toxoplasmosis (CT), monitoring the parasite burden and treatment response is still challenging. miRNAs are small non-coding RNAs with regulatory functions that can be used in diagnosis and treatment monitoring. We investigated the changes in miR-146a, BAG-1 gene, IL-6, and IL-10 tissue levels in the brain of BALB/c mice with chronic CT caused by the PRU strain of T. gondii following anti-parasitic and antibiotic treatment. METHOD: Fifty-three 6-to 8-week-old BALB/c mice were infected using intraperitoneal inoculation of cerebral cysts of T. gondii PRU strain and then divided into five groups as follows: group 1 included mice treated with 100 mg/kg/d Atovaquone (AT), group 2 included mice treated with 400 mg/kg/d clindamycin (CL), group 3 included mice treated with combination therapy (AT + CL), group 4 included infected untreated mice as a positive control (PC), and; group 5 included uninfected untreated mice as negative control (NC). After the completion of the treatment course, tissue level of mir-146a, miR-155, BAG-1 gene, IL-6, and IL-10 was investigated with real-time polymerase chain reaction. The IL-6/IL-10 ratio was calculated as an indicator of immune response. Moreover, brain cyst numbers were counted on autopsy samples. RESULTS: miR-146a, IL-6, IL-10, and BAG-1 genes were expressed in PC, but not in the NC group; miR-146a, IL-6, IL-10, and BAG-1 gene expression were significantly lower in AT, CL, and AT + CL compared with PC. MiR-146a and BAG-1 levels in AT and CL were not different statistically, however, they both had lower levels compared to AT + CL (P < 0.01). There was no difference in the expression of IL-6 and IL-10 between treatment groups. BAG-1 expression was significantly lower in AT, than in CL and AT + CL (P < 0.0089 and < 0.002, respectively). The PC group showed a higher ratio of IL-6/IL-10, although this increase was not statistically significant. It is noteworthy that the treatment with AT reduced this ratio; in the inter-group comparison, this ratio showed a decrease in the AT and AT + CL compared to the PC. The number of brain tissue cysts was significantly lower in AT, CL, and AT + CL, than in PC (p < 0.0001). AT had significantly lower brain cysts than CL and AT + CL (P < 0.0001). CONCLUSION: It seems that the factors studied in the current research (microRNA and cytokines) are a suitable index for evaluating the response to antiparasitic and antibiotic treatment. However, more studies should be conducted in the future to confirm our findings.

Oxidative phosphorylation inhibitors inhibit proliferation of endometriosis cells.

In brief: Developing novel therapies to cure and manage endometriosis is a major unmet need that will benefit over 180 million women worldwide. Results from the current study suggest that inhibitors of oxidative phosphorylation may serve as novel agents for the treatment of endometriosis. Abstract: Current therapeutic strategies for endometriosis focus on symptom management and are not curative. Here, we provide evidence supporting the inhibition of oxidative phosphorylation (OXPHOS) as a novel treatment strategy for endometriosis. Additionally, we report an organotypic organ-on-a-chip luminal model for endometriosis. The OXPHOS inhibitors, curcumin, plumbagin, and the FDA-approved anti-malarial agent, atovaquone, were tested against the endometriosis cell line, 12Z, in conventional as well as the new organotypic model. The results suggest that all three compounds inhibit proliferation and cause cell death of the endometriotic cells by inhibiting OXPHOS and causing an increase in intracellular oxygen radicals. The oxidative stress mediated by curcumin, plumbagin, and atovaquone causes DNA double-strand breaks as indicated by the elevation of phospho-γH2Ax. Mitochondrial energetics shows a significant decrease in oxygen consumption in 12Z cells. These experiments also highlight differences in the mechanism of action as curcumin and plumbagin inhibit complex I whereas atovaquone blocks complexes I, II, and III. Real-time assessment of cells in the lumen model showed inhibition of migration in response to the test compounds. Additionally, using two-photon lifetime imaging, we demonstrate that the 12Z cells in the lumen show decreased redox ratio (NAD(P)H/FAD) and lower fluorescence lifetime of NAD(P)H in the treated cells confirming major metabolic changes in response to inhibition of mitochondrial electron transport. The robust chemotoxic responses observed with atovaquone suggest that this anti-malarial agent may be repurposed for the effective treatment of endometriosis.

Atovaquone inhibits colorectal cancer metastasis by regulating PDGFRß/NF-κB signaling pathway.

BACKGROUND: Colorectal cancer is a common malignant tumour. Invasive growth and distant metastasis are the main characteristics of its malignant biological behaviour, and they are also the primary factors leading to death in colon cancer patients. Atovaquone is an antimalarial drug, and its anticancer effect has recently been demonstrated in several cancer models in vitro and in vivo, but it has not been examined in the treatment of colorectal cancer. METHODS: To elucidate the effect of atovaquone on colorectal cancer. We used RNA transcriptome sequencing, RT‒PCR and Western blot experiments to examine the expression of NF-κB (p-P65), EMT-related proteins and related inflammatory factors (IL1B, IL6, CCL20, CCL2, CXCL8, CXCL6, IL6ST, FAS, IL10 and IL1A). The effect of atovaquone on colorectal cancer metastasis was validated using an animal model of lung metastases. We further used transcriptome sequencing, the GCBI bioinformatics database and the STRING database to predict relevant target proteins. Furthermore, pathological sections were collected from relevant cases for immunohistochemical verification. RESULTS: This study showed that atovaquone could inhibit colorectal cancer metastasis and invasion in vivo and in vitro, inhibit the expression of E-cadherin protein, and promote the protein expression of N-cadherin, vimentin, ZEB1, Snail and Slug. Atovaquone could inhibit EMT by inhibiting NF-κB (p-P65) and related inflammatory factors. Further bioinformatics analysis and verification showed that PDGFRß was one of the targets of atovaquone. CONCLUSION: In summary, atovaquone can inhibit the expression of NF-κB (p-P65) and related inflammatory factors by inhibiting the protein expression of p-PDGFRß, thereby inhibiting colorectal cancer metastasis. Atovaquone may be a promising drug for the treatment of colorectal cancer metastasis.

Exploiting the tumor immune microenvironment and immunometabolism using mitochondria-targeted drugs: Challenges and opportunities in racial disparity and cancer outcome research.

Black and Hispanic cancer patients have a higher incidence of cancer mortality. Many factors (e.g., socioeconomic differences, insufficient access to healthcare) contribute to racial disparity. Emerging research implicates biological disparity in cancer outcomes. Studies show distinct differences in the tumor immune microenvironment (TIME) in Black cancer patients. Studies also have linked altered mitochondrial metabolism to changes in immune cell activation in TIME. Recent publications revealed a novel immunomodulatory role for triphenylphosphonium-based mitochondrial-targeted drugs (MTDs). These are synthetically modified, naturally occurring molecules (e.g., honokiol, magnolol, metformin) or FDA-approved small molecule drugs (e.g., atovaquone, hydroxyurea). Modifications involve conjugating the parent molecule via an alkyl linker chain to a triphenylphosphonium moiety. These modified molecules (e.g., Mito-honokiol, Mito-magnolol, Mito-metformin, Mito-atovaquone, Mito-hydroxyurea) accumulate in tumor cell mitochondria more effectively than in normal cells and inhibit mitochondrial respiration, induce reactive oxygen species, activate AMPK and redox transcription factors, and inhibit cancer cell proliferation. Besides these intrinsic effects of MTDs in redox signaling and proliferation in tumors, MTDs induced extrinsic effects in the TIME of mouse xenografts. MTD treatment inhibited tumor-suppressive immune cells, myeloid-derived suppressor cells, and regulatory T cells, and activated T cells and antitumor immune effects. One key biological disparity in Black cancer patients was related to altered mitochondrial oxidative metabolism; MTDs targeting vulnerabilities in tumor cells and the TIME may help us understand this biological disparity. Clinical trials should include an appropriate number of Black and Hispanic cancer patients and should validate the intratumoral, antihypoxic effects of MTDs with imaging.

Babesia duncani as a Model Organism to Study the Development, Virulence, and Drug Susceptibility of Intraerythrocytic Parasites In Vitro and In Vivo.

Human babesiosis is a malaria-like illness caused by tick-borne intraerythrocytic Babesia parasites of the Apicomplexa phylum. Whereas several species of Babesia can cause severe disease in humans, the ability to propagate Babesia duncani both in vitro in human erythrocytes and in mice makes it a unique pathogen to study Babesia biology and pathogenesis. Here we report an optimized B. duncani in culture-in mouse (ICIM) model that combines continuous in vitro culture of the parasite with a precise model of lethal infection in mice. We demonstrate that B. duncani-infected erythrocytes as well as free merozoites can cause lethal infection in C3H/HeJ mice. Highly reproducible parasitemia and survival outcomes could be established using specific parasite loads in different mouse genetic backgrounds. Using the ICIM model, we discovered 2 new endochin-like quinolone prodrugs (ELQ-331 and ELQ-468) that alone or in combination with atovaquone are highly efficacious against B. duncani and Babesia microti.

The effect of atovaquone on the mitochondrial membrane potential of Babesiagibsoni.

Atovaquone (ATV) has a growth inhibitory effect against Babesia gibsoni. The target site is considered mitochondria, as in the case of Plasmodium spp.; ATV would collapse the mitochondrial membrane potential. B. gibsoni has also reported that single nucleotide polymorphisms in cytochrome b of mitochondria are involved in ATV susceptibility. However, the details are still unknown. The study aim was to measure the mitochondrial membrane potential of B. gibsoni and evaluate the effect of ATV alone and combined with proguanil (PG) on the mitochondrial membrane potential. As a result of exposure of wild-type B. gibsoni to ATV alone, the number of cells with decreased mitochondrial membrane potential increased. When wild-type B. gibsoni was exposed to the ATV + PG combination, the peak value of mitochondrial membrane potential was larger than that when exposed to ATV alone. It was suggested that ATV alone affects the mitochondrial membrane potential of B. gibsoni, and the effect is enhanced by the combination of ATV and PG. The effect of ATV was weakened for B. gibsoni having reduced sensitivity to ATV (B. gibsoni with M121I), and the effect was not enhanced by the combination of ATV and PG. Although we still need to elucidate the mechanism of ATV and PG for B. gibsoni, these results strongly suggests that the target of ATV for B. gibsoni is also cytochrome b of mitochondria.

Exploring Ubiquinone Biosynthesis Inhibition as a Strategy for Improving Atovaquone Efficacy in Malaria.

Atovaquone (AV) acts on the malaria parasite by competing with ubiquinol (UQH2) for its union to the mitochondrial bc1 complex, preventing the ubiquinone-8 and ubiquinone-9 (UQ-8 and UQ-9) redox recycling, which is a necessary step in pyrimidine biosynthesis. This study focused on UQ biosynthesis in Plasmodium falciparum and adopted proof-of-concept research to better elucidate the mechanism of action of AV and improve its efficacy. Initially, UQ biosynthesis was evaluated using several radioactive precursors and chromatographic techniques. This methodology was suitable for studying the biosynthesis of both UQ homologs and its redox state. Additionally, the composition of UQ was investigated in parasites cultivated at different oxygen saturations or in the presence of AV. AV affected the redox states of both UQ-8 and UQ-9 homologs by increasing the levels of the respective reduced forms. Conversely, low-oxygen environments specifically inhibited UQ-9 biosynthesis and increased the antimalarial efficacy of AV. These findings encouraged us to investigate the biological importance and the potential of UQ biosynthesis as a drug target based on its inhibition by 4-nitrobenzoate (4-NB), a 4-hydroxybenzoate (4-HB) analog. 4-NB effectively inhibits UQ biosynthesis and enhances the effects of AV on parasitic growth and respiration rate. Although 4-NB itself exhibits poor antimalarial activity, its 50% inhibitory concentration (IC50) value increased significantly in the presence of a soluble UQ analog, p-aminobenzoic acid (pABA), or 4-HB. These results indicate the potential of AV combined with 4-NB as a novel therapy for malaria and other diseases caused by AV-sensitive pathogens.

Effective Therapy Targeting Cytochrome bc1 Prevents Babesia Erythrocytic Development and Protects from Lethal Infection.

An effective strategy to control blood-borne diseases and prevent outbreak recrudescence involves targeting conserved metabolic processes that are essential for pathogen viability. One such target for Plasmodium and Babesia, the infectious agents of malaria and babesiosis, respectively, is the mitochondrial cytochrome bc1 protein complex, which can be inhibited by endochin-like quinolones (ELQ) and atovaquone. We used the tick-transmitted and culturable blood-borne pathogen Babesia duncani to evaluate the structure-activity relationship, safety, efficacy, and mode of action of ELQs. We identified a potent and highly selective ELQ prodrug (ELQ-502), which, alone or in combination with atovaquone, eliminates B. microti and B. duncani infections in vitro and in mouse models of parasitemia and lethal infection. The strong efficacy at low dose, excellent safety, bioavailability, and long half-life of this experimental therapy make it an ideal clinical candidate for the treatment of human infections caused by Babesia and its closely related apicomplexan parasites.

Revisiting the mode of action of the antimalarial proguanil using the yeast model.

Proguanil in combination with its synergistic partner atovaquone has been used for malaria treatment and prophylaxis for decades. However its mode of action is not fully understood. Here we used yeast to investigate its activity. Proguanil inhibits yeast growth, causes cell death and acts in synergy with atovaquone. It was previously proposed that the drug would target the system that maintains the mitochondrial membrane potential when the respiratory chain is inhibited. However our data did not seem to validate that hypothesis. We proposed that proguanil would not have a specific target but accumulate in the mitochondrial to concentrations that impair multiple mitochondrial functions leading to cell death. Selection and study of proguanil resistant mutants pointed towards an unexpected resistance mechanism: the decrease of CoQ level, which possibly alters the mitochondrial membrane properties and lowers proguanil intramitochondrial level.

In vivo efficacy of combination therapy with albendazole and atovaquone against primary hydatid cysts in mice.

Alveolar echinococcosis (AE) is caused by the larval stage of Echinococcus multilocularis. Chemotherapy for AE involves albendazole (ABZ), which has shown insufficient efficacy. More effective chemotherapy for AE is needed. Previously, we have demonstrated that atovaquone (ATV), an antimalarial, inhibits mitochondrial complex III of E. multilocularis and restricts the development of larval cysts in in vivo experiments. Therefore, in this study, we evaluated the efficacy of ABZ and ATV combination therapy on E. multilocularis in culture and in vivo experiments. Protoscoleces were treated with 50 µM ABZ and/or ATV in the medium; the duration of parasite elimination was determined under aerobic and anaerobic culture. In the in vivo experiment, the effects of ABZ and ATV combination treatment in BALB/c mice infected orally with eggs from the feces of an adult-stage E. multilocularis-infected dog were compared with those of standard oral ABZ therapy. In the culture assay, the duration of elimination associated with ABZ and ATV combination treatment was shorter than that associated with ATV alone under aerobic conditions. Protoscolex viability progressively reduced owing to the combination treatment under anaerobic conditions; however, either drug used singly did not exhibit antiparasitic effects under hypoxia. Furthermore, compared with ABZ alone, the combination treatment significantly reduced the growth of the primary cyst in the liver of mice infected orally with parasite eggs (P = .011). ATV enhances the effect of ABZ in the treatment of AE in mice.

Novel molecule combinations and corresponding hybrids targeting artemisinin-resistant Plasmodium falciparum parasites.

Malaria is still considered as the major parasitic disease and the development of artemisinin resistance does not improve this alarming situation. Based on the recent identification of relevant malaria targets in the artemisinin resistance context, novel drug combinations were evaluated against artemisinin-sensitive and artemisinin-resistant Plasmodium falciparum parasites. Corresponding hybrid molecules were also synthesized and evaluated for comparison with combinations and individual pharmacophores (e.g. atovaquone, mefloquine or triclosan). Combinations and hybrids showed remarkable antimalarial activity (IC50 = 0.6 to 1.1 nM for the best compounds), strong selectivity, and didn't present any cross-resistance with artemisinin. Moreover, the combination triclosan + atovaquone showed high activity against artemisinin-resistant parasites at the quiescent stage but the corresponding hybrid lost this pharmacological property. This result is essential since only few molecules active against quiescent artemisinin-resistant parasites are reported. Our promising results highlight the potential of these combinations and paves the way for pharmacomodulation work on the best hybrids.