Repurposing Auranofin and Evaluation of a New Gold(I) Compound for the Search of Treatment of Human and Cattle Parasitic Diseases: From Protozoa to Helminth Infections.

Neglected parasitic diseases remain a major public health issue worldwide, especially in tropical and subtropical areas. Human parasite diversity is very large, ranging from protozoa to worms. In most cases, more effective and new drugs are urgently needed. Previous studies indicated that the gold(I) drug auranofin (Ridaura®) is effective against several parasites. Among new gold(I) complexes, the phosphole-containing gold(I) complex {1-phenyl-2,5-di(2-pyridyl)phosphole}AuCl (abbreviated as GoPI) is an irreversible inhibitor of both purified human glutathione and thioredoxin reductases. GoPI-sugar is a novel 1-thio-ß-d-glucopyranose 2,3,4,6-tetraacetato-S-derivative that is a chimera of the structures of GoPI and auranofin, designed to improve stability and bioavailability of GoPI. These metal-ligand complexes are of particular interest because of their combined abilities to irreversibly target the essential dithiol/selenol catalytic pair of selenium-dependent thioredoxin reductase activity, and to kill cells from breast and brain tumors. In this work, screening of various parasites-protozoans, trematodes, and nematodes-was undertaken to determine the in vitro killing activity of GoPI-sugar compared to auranofin. GoPI-sugar was found to efficiently kill intramacrophagic Leishmania donovani amastigotes and adult filarial and trematode worms.

Torin 2 Derivative, NCATS-SM3710, Has Potent Multistage Antimalarial Activity through Inhibition of P. falciparum Phosphatidylinositol 4-Kinase (Pf PI4KIIIß).

Drug resistance is a constant threat to malaria control efforts making it important to maintain a good pipeline of new drug candidates. Of particular need are compounds that also block transmission by targeting sexual stage parasites. Mature sexual stages are relatively resistant to all currently used antimalarials except the 8-aminoquinolines that are not commonly used due to potential side effects. Here, we synthesized a new Torin 2 derivative, NCATS-SM3710 with increased aqueous solubility and specificity for Plasmodium and demonstrate potent in vivo activity against all P. berghei life cycle stages. NCATS-SM3710 also has low nanomolar EC50s against in vitro cultured asexual P. falciparum parasites (0.38 ± 0.04 nM) and late stage gametocytes (5.77 ± 1 nM). Two independent NCATS-SM3710/Torin 2 resistant P. falciparum parasite lines produced by growth in sublethal Torin 2 concentrations both had genetic changes in PF3D7_0509800, annotated as a phosphatidylinositol 4 kinase (Pf PI4KIIIß). One line had a point mutation in the putative active site (V1357G), and the other line had a duplication of a locus containing Pf PI4KIIIß. Both lines were also resistant to other Pf PI4K inhibitors. In addition NCATS-SM3710 inhibited purified Pf PI4KIIIß with an IC50 of 2.0 ± 0.30 nM. Together the results demonstrate that Pf PI4KIIIß is the target of Torin 2 and NCATS-SM3710 and provide new options for potent multistage drug development.

MEPicides: potent antimalarial prodrugs targeting isoprenoid biosynthesis.

The emergence of Plasmodium falciparum resistant to frontline therapeutics has prompted efforts to identify and validate agents with novel mechanisms of action. MEPicides represent a new class of antimalarials that inhibit enzymes of the methylerythritol phosphate (MEP) pathway of isoprenoid biosynthesis, including the clinically validated target, deoxyxylulose phosphate reductoisomerase (Dxr). Here we describe RCB-185, a lipophilic prodrug with nanomolar activity against asexual parasites. Growth of P. falciparum treated with RCB-185 was rescued by isoprenoid precursor supplementation, and treatment substantially reduced metabolite levels downstream of the Dxr enzyme. In addition, parasites that produced higher levels of the Dxr substrate were resistant to RCB-185. Notably, environmental isolates resistant to current therapies remained sensitive to RCB-185, the compound effectively treated sexually-committed parasites, and was both safe and efficacious in malaria-infected mice. Collectively, our data demonstrate that RCB-185 potently and selectively inhibits Dxr in P. falciparum, and represents a promising lead compound for further drug development.

The Schistosoma mansoni Cytochrome P450 (CYP3050A1) Is Essential for Worm Survival and Egg Development.

Schistosomiasis affects millions of people in developing countries and is responsible for more than 200,000 deaths annually. Because of toxicity and limited spectrum of activity of alternatives, there is effectively only one drug, praziquantel, available for its treatment. Recent data suggest that drug resistance could soon be a problem. There is therefore the need to identify new drug targets and develop drugs for the treatment of schistosomiasis. Analysis of the Schistosoma mansoni genome sequence for proteins involved in detoxification processes found that it encodes a single cytochrome P450 (CYP450) gene. Here we report that the 1452 bp open reading frame has a characteristic heme-binding region in its catalytic domain with a conserved heme ligating cysteine, a hydrophobic leader sequence present as the membrane interacting region, and overall structural conservation. The highest sequence identity to human CYP450s is 22%. Double stranded RNA (dsRNA) silencing of S. mansoni (Sm)CYP450 in schistosomula results in worm death. Treating larval or adult worms with antifungal azole CYP450 inhibitors results in worm death at low micromolar concentrations. In addition, combinations of SmCYP450-specific dsRNA and miconazole show additive schistosomicidal effects supporting the hypothesis that SmCYP450 is the target of miconazole. Treatment of developing S. mansoni eggs with miconazole results in a dose dependent arrest in embryonic development. Our results indicate that SmCYP450 is essential for worm survival and egg development and validates it as a novel drug target. Preliminary structure-activity relationship suggests that the 1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethan-1-ol moiety of miconazole is necessary for activity and that miconazole activity and selectivity could be improved by rational drug design.

High-throughput screening against thioredoxin glutathione reductase identifies novel inhibitors with potential therapeutic value for schistosomiasis.

BACKGROUND: Schistosomiasis, a parasitic disease also known as bilharzia and snail fever, is caused by different species of flatworms, such as Schistosoma mansoni (S. mansoni). Thioredoxin glutathione reductase (TGR) from S. mansoni (SmTGR) is a well-characterized drug target for schistosomiasis, yet no anti-SmTGR compounds have reached clinical trials, suggesting that therapeutic development against schistosomiasis might benefit from additional scaffolds targeting this enzyme. METHODS: A high-throughput screening (HTS) assay in vitro against SmTGR was developed and applied to a diverse compound library. SmTGR activity was quantified with ThioGlo®, a reagent that fluoresces upon binding to the free sulfhydryl groups of the reaction product GSH (reduced glutathione). RESULTS: We implemented an HTS effort against 59,360 synthetic compounds. In the primary screening, initial hits (928 or 1.56 %) showing greater than 90 % inhibition on SmTGR activity at a final concentration of 10 µM for each compound were identified. Further tests were carried out to confirm the effects of these hits and to explore the concentration-dependent response characteristics. As a result, 74 of them (0.12 %) representing 17 chemical scaffolds were confirmed and showed a great concentration-dependent inhibitory trend against SmTGR, including structures previously shown to be lethal to schistosomal growth. Of these, two scaffolds displayed a limited structure-activity relationship. When tested in cultured larvae, 39 compounds had cidal activity in 48 h, and five of them killed larvae completely at 3.125 µM. Of these, three compounds also killed adult worms ex vivo at concentrations between 5 µM and 10 µM. CONCLUSION: These confirmed hits may serve as starting points for the development of novel therapeutics to combat schistosomiasis.

Characterization of potential drug targets farnesyl diphosphate synthase and geranylgeranyl diphosphate synthase in Schistosoma mansoni.

Schistosomiasis affects over 200 million people worldwide, with over 200,000 deaths annually. Currently, praziquantel is the only drug available against schistosomiasis. We report here that Schistosoma mansoni farnesyl diphosphate synthase (SmFPPS) and geranylgeranyl diphosphate synthase (SmGGPPS) are potential drug targets for the treatment of schistosomiasis. We expressed active, recombinant SmFPPS and SmGGPPS for subsequent kinetic characterization and testing against a variety of bisphosphonate inhibitors. Recombinant SmFPPS was found to be a soluble 44.2-kDa protein, while SmGGPPS was a soluble 38.3-kDa protein. Characterization of the substrate utilization of the two enzymes indicates that they have overlapping substrate specificities. Against SmFPPS, several bisphosphonates had 50% inhibitory concentrations (IC50s) in the low micromolar to nanomolar range; these inhibitors had significantly less activity against SmGGPPS. Several lipophilic bisphosphonates were active against ex vivo adult worms, with worm death occurring over 4 to 6 days. These results indicate that FPPS and GGPPS could be of interest in the context of the emerging resistance to praziquantel in schistosomiasis therapy.

Multiplicity of Plasmodium falciparum infection following intermittent preventive treatment in infants.

BACKGROUND: Intermittent preventive treatment in infants with sulphadoxine-pyrimethamine (IPTi-SP) reduces malaria morbidity by 20% to 33%. Potentially, however, this intervention may compromise the acquisition of immunity, including the tolerance towards multiple infections with Plasmodium falciparum. METHODS: Plasmodium falciparum isolates were obtained from children participating in two Ghanaian IPTi-SP trials (Tamale, Afigya Sekyere) at 15 months of age, i.e., six months after they had received the second dose of IPTi-SP or placebo. By typing the polymorphic merozoite surface protein 1 (msp1) and msp2 genes, multiplicity of infection (MOI) was assessed in 389 isolates. A total of additional 133 samples were collected in Tamale at 3, 6, 9, and 12 months of age. Comparisons of MOI between groups were done by non-parametric statistical tests. RESULTS: The number of distinguishable P. falciparum clones (MOI) ranged between one and six. Mean MOI in Tamale was stable at 2.13 - 2.17 during the first year of life, and increased to 2.57 at age 15 months (P = 0.01). At no age did MOI differ between the IPTi-SP and placebo groups (each, P ≥ 0.5). At 15 months of age, i.e., six months after the second dose, MOI was very similar for children who had received IPTi or placebo (means, 2.25 vs. 2.33; P = 0.55) as was the proportion of polyclonal infections (69.6% vs. 69.7%; P = 0.99). Adjusting for study site, current and prior malaria, parasite density, and season did not change this finding. CONCLUSIONS: IPTi-SP appears to have no impact on the multiplicity of infection during infancy and thereafter. This suggests that tolerance of multiple infections, a component of protective immunity in highly endemic areas, is not affected by this intervention.

Influence of haemoglobins S and C on predominantly asymptomatic Plasmodium infections in northern Ghana.

The haemoglobin (Hb) variants HbS and HbC protect against severe malaria. Yet, the influence particularly of HbC on asymptomatic or mild Plasmodium infection is not well established. In a dry season cross-sectional survey among 2108 children aged 0.5-9 years in the Northern Region of Ghana, Plasmodium species and density, as well as Hb, were analysed with respect to Hb genotypes. HbAC occurred in 19.7% and HbAS in 7.4% (HbSC, 0.8%; HbCC, 0.8%; HbSS, 0.3%). Overall, 56% of the children had microscopically visible parasitaemia. By PCR, P. falciparum, P. malariae, and P. ovale were present in 74.5%, 9.7%, and 5.5%, respectively. Febrile parasitaemia was rare (2.8%) but anaemia (Hb<11g/dL) frequent (59.3%). Children with HbAA and HbAC showed virtually identical malariometric parameters. In contrast, children with HbAS had significantly less parasitaemia, lower parasite densities, and a higher proportion of submicroscopic P. falciparum infection. Remarkably, in children with HbCC, P. malariae infection occurred in 37.5% (adjusted odds ratio (aOR), 5.8; 95% CI, 1.8-18.8) and P. ovale in 18.8% (aOR, 3.61; 95% CI, 0.97-13.5). In this population with predominantly asymptomatic Plasmodium infection, HbAC shows no discernible effect on malaria-related parameters. Homozygous HbC, in contrast, confers an increased risk of P. malariae infection which conceivably may modulate falciparum malaria.

Reduced efficacy of intermittent preventive treatment of malaria in malnourished children.

Intermittent preventive treatment in infants with sulfadoxine-pyrimethamine (IPTi-SP) reduces malaria episodes by 20 to 59% across Africa. This protective efficacy, however, may be affected by the high frequency of malnutrition in African infants. We analyzed the impact of malnutrition as defined by anthropometry on the incidence of malaria and on the protective efficacy of IPTi in a cohort of 1,200 children in northern Ghana, where malaria is hyperendemic. These children received IPTi-SP or placebo at 3, 9, and 15 months of age and were monitored until 24 months of age. Malnutrition was present in 32, 40, and 50% of children at ages 3, 9, and 15 months, respectively. It was associated with increased risks of severe anemia and death but not an increased risk of malaria. Although malaria slightly contributed to chronic malnutrition, IPTi did not substantially improve child growth. Importantly, the protective efficacies of IPTi in malnourished children were roughly half or even less of those observed in nonmalnourished children. In the first year of life, IPTi reduced the incidence of malaria to a significantly lesser extent in infants who received both doses in a malnourished condition (25%; 95% confidence interval [CI], -7 to 48%) compared to that of nonmalnourished children (46%; 95% CI, 30 to 58%; P = 0.049). Moreover, in contrast to nutritionally advantaged children, the rate of severe malaria appeared to be increased in malnourished children who took IPTi. IPTi might exhibit reduced efficacy in regions of abundant malnutrition. Concomitant nutrition programs may be needed in these places to achieve the desired impact.

High rate of resistance to locally used antibiotics among enteric bacteria from children in Northern Ghana.

OBJECTIVES: Information on antimicrobial susceptibility of bacterial pathogens is scarce in resource-poor settings. We determined the susceptibility of bacterial enteric pathogens and faecal Escherichia coli isolates obtained from children in urban Tamale, Northern Ghana, to antibiotics widely used in the that area [ampicillin or amoxicillin, trimethoprim/sulfamethoxazole (SXT) and chloramphenicol] and to alternative drugs. METHODS: Five Shigella spp., 6 Salmonella spp. and 318 E. coli were isolated from stool specimens obtained from 367 children with or without acute diarrhoea. Isolates were differentiated using standard laboratory procedures and tested using a breakpoint microbroth dilution method for their susceptibility to 18 antimicrobials and by disc diffusion for their susceptibility to chloramphenicol. RESULTS: Although the salmonellae showed an acceptable resistance pattern, E. coli isolates and the closely related shigellae were highly resistant. About 91% and 81% of E. coli isolates from patients or controls, respectively, were resistant to ampicillin (MICs > or = 8 mg/L), 88% and 76% to trimethoprim/sulfamethoxazole (MICs > or = 80/4 mg/L) and 46% and 41% to chloramphenicol (inhibition zones < or = 12 mm). Resistance to beta-lactam antibiotics or chloramphenicol was observed more frequently among isolates obtained from infants when compared with older children (1-4 years of age). CONCLUSIONS: Enteric bacteria from children in urban Northern Ghana are highly resistant to antibiotics used in that area. Therefore, new antibiotics should be introduced for the treatment of infections caused by these bacteria. Additionally, the establishment of a surveillance of the prevalence of the main bacterial infectious agents and their antimicrobial resistance is desirable.

Acute childhood diarrhoea in northern Ghana: epidemiological, clinical and microbiological characteristics.

BACKGROUND: Acute diarrhoea is a major cause of childhood morbidity and mortality in sub-Saharan Africa. Its microbiological causes and clinico-epidemiological aspects were examined during the dry season 2005/6 in Tamale, urban northern Ghana. METHODS: Stool specimens of 243 children with acute diarrhoea and of 124 control children were collected. Patients were clinically examined, and malaria and anaemia were assessed. Rota-, astro-, noro- and adenoviruses were identified by (RT-) PCR assays. Intestinal parasites were diagnosed by microscopy, stool antigen assays and PCR, and bacteria by culturing methods. RESULTS: Watery stools, fever, weakness, and sunken eyes were the most common symptoms in patients (mean age, 10 months). Malaria occurred in 15% and anaemia in 91%; underweight (22%) and wasting (19%) were frequent. Intestinal micro-organisms were isolated from 77% of patients and 53% of controls (P < 0.0001). The most common pathogens in patients were rotavirus (55%), adenovirus (28%) and norovirus (10%); intestinal parasites (5%) and bacteria (5%) were rare. Rotavirus was the only pathogen found significantly more frequently in patients than in controls (odds ratio 7.7; 95%CI, 4.2-14.2), and was associated with young age, fever and watery stools. Patients without an identified cause of diarrhoea more frequently had symptomatic malaria (25%) than those with diagnosed intestinal pathogens (12%, P = 0.02). CONCLUSION: Rotavirus-infection is the predominant cause of acute childhood diarrhoea in urban northern Ghana. The abundance of putative enteropathogens among controls may indicate prolonged excretion or limited pathogenicity. In this population with a high burden of diarrhoeal and other diseases, sanitation, health education, and rotavirus-vaccination can be expected to have substantial impact on childhood morbidity.

Intermittent preventive treatment in infants as a means of malaria control: a randomized, double-blind, placebo-controlled trial in northern Ghana.

Morbidity and mortality from malaria remain unacceptably high among young children in sub-Saharan Africa. Intermittent preventive treatment in infancy (IPTi) involves the administration of antimalarials alongside routine vaccinations and might be an option in malaria control. In an area of intense, perennial malaria transmission in northern Ghana, 1,200 children received IPTi with sulfadoxine-pyrimethamine or placebo at approximately 3, 9, and 15 months of age. Children were followed up until 24 months of age to assess morbidity and adverse events. During the intervention period (3 to 18 months of age), IPTi reduced the incidences of malaria and severe anemia by 22.5% (95% confidence interval, 12 to 32%) and 23.6% (95% confidence interval, 4 to 39%), respectively, and reduced hospitalizations and episodes of asymptomatic parasitemia by one-third. Protection was pronounced in the first year of life and not discernible in the second. The malaria-protective effect was largely confined to a period of 1 month after sulfadoxine-pyrimethamine treatments. Following the intervention, protection against asymptomatic parasitemia persisted. In contrast, a significant rebound of severe malaria, predominantly severe malarial anemia, occurred among children having received IPTi. Although the treatment was generally well tolerated, one case of moderately severe skin reaction followed sulfadoxine-pyrimethamine treatment. IPTi reduces malaria and anemia in infants in northern Ghana. Extension of IPTi into the second year of life by administering a dose at 15 months of age provided no substantial benefit beyond a 1-month prophylactic effect. Although this simple intervention offers one of the few available malaria-preventive measures for regions where malaria is endemic, the observed rebound of severe malaria advises caution and requires further investigation.