Antimalarial pantothenamide metabolites target acetyl-coenzyme A biosynthesis in Plasmodium falciparum

Malaria eradication is critically dependent on new therapeutics that target resistant Plasmodium parasites and block transmission of the disease. Here, we report that pantothenamide bioisosteres were active against blood-stage Plasmodium falciparum parasites and also blocked transmission of sexual stages to the mosquito vector. These compounds were resistant to degradation by serum pantetheinases, showed favorable pharmacokinetic properties, and cleared parasites in a humanized mouse model of P. falciparum infection. Metabolomics revealed that coenzyme A biosynthetic enzymes converted pantothenamides into coenzyme A analogs that interfered with parasite acetyl-coenzyme A anabolism. Resistant parasites generated in vitro showed mutations in acetyl-coenzyme A synthetase and acyl-coenzyme A synthetase 11. Introduction and reversion of these mutations in P. falciparum using CRISPR-Cas9 gene editing confirmed the roles of these enzymes in the sensitivity of the malaria parasites to pantothenamides. These pantothenamide compounds with a new mode of action may have potential as drugs against malaria parasites.

Safety of Single-Dose Primaquine in G6PD-Deficient and G6PD-Normal Males in Mali Without Malaria: An Open-Label, Phase 1, Dose-Adjustment Trial

Background

The World Health Organization recommendation on the use of a single low dose of primaquine (SLD-PQ) to reduce Plasmodium falciparum malaria transmission requires more safety data.

Methods

We conducted an open-label, nonrandomized, dose-adjustment trial of the safety of 3 single doses of primaquine in glucose-6-phosphate dehydrogenase (G6PD)-deficient adult males in Mali, followed by an assessment of safety in G6PD-deficient boys aged 11–17 years and those aged 5–10 years, including G6PD-normal control groups. The primary outcome was the greatest within-person percentage drop in hemoglobin concentration within 10 days after treatment.

Results

Fifty-one participants were included in analysis. G6PD-deficient adult males received 0.40, 0.45, or 0.50 mg/kg of SLD-PQ. G6PD-deficient boys received 0.40 mg/kg of SLD-PQ. There was no evidence of symptomatic hemolysis, and adverse events considered related to study drug (n = 4) were mild. The mean largest within-person percentage change in hemoglobin level between days 0 and 10 was −9.7% (95% confidence interval [CI], −13.5% to −5.90%) in G6PD-deficient adults receiving 0.50 mg/kg of SLD-PQ, −11.5% (95% CI, −16.1% to −6.96%) in G6PD-deficient boys aged 11–17 years, and −9.61% (95% CI, −7.59% to −13.9%) in G6PD-deficient boys aged 5–10 years. The lowest hemoglobin concentration at any point during the study was 92 g/L.

Conclusion

SLD-PQ doses between 0.40 and 0.50 mg/kg were well tolerated in G6PD-deficient males in Mali.

Clinical Trials Registration

NCT02535767.

Completed suicides of citalopram users-the role of CYP genotypes and adverse drug interactions

Depression is known to be a risk factor for suicide. Currently, the most used antidepressants are selective serotonin reuptake inhibitors (SSRIs). Not all users, however, benefit from them. In such cases, treatment failure can be explained in part by genetic differences. In this study, we investigated the role of pharmacogenetic factors in citalopram-positive completed suicides (n = 349). Since citalopram is metabolized by CYP2C19 and CYP2D6 enzymes, the study population was genotyped for clinically relevant CYP2C19 and CYP2D6 polymorphisms and CYP2D6 copy number variation. To assess genetic differences between suicide cases and Finns in general, Finnish population samples (n = 855) were used as controls. Also, the role of drug interactions among suicide cases was evaluated. We found enrichment of a combined group of genetically predicted poor and ultrarapid metabolizer phenotypes (gMPs) of CYP2C19 among suicide victims compared to controls 0.356 [0.31-0.41] vs. 0.265 [0.24-0.30] (p = 0.0065). In CYP2D6 gMPs, there was no difference between cases and controls when the study population was analyzed as a whole. However, there were significantly more poor metabolizers among females who committed suicide by poisoning compared to female controls. In 8% of all drug poisoning deaths, lifetime drug-drug interaction was evaluated having a contribution to the fatal outcome. From clinical perspective, pharmacogenetic testing prior to initiation of SSRI drug could be beneficial. It may also be useful in medico-legal settings as it may elucidate obscure poisoning cases. Also, the possibility of unintentional drug interactions should be taken into account in drug poisoning deaths.

Comparison of molecular quantification of Plasmodium falciparum gametocytes by Pfs25 qRT-PCR and QT-NASBA in relation to mosquito infectivity

Background

Quantifying gametocyte densities in natural malaria infections is important to estimate malaria transmission potential. Two molecular methods (Pfs25 mRNA quantitative reverse transcriptase PCR (qRT-PCR) and Pfs25 mRNA quantitative nucleic acid sequence based amplification (QT-NASBA)) are commonly used to determine gametocyte densities in clinical and epidemiological studies and allow gametocyte detection at densities below the microscopic threshold for detection. Here, reproducibility of these measurements and the association between estimated gametocyte densities and mosquito infection rates were compared.

Methods

To quantify intra- and inter-assay variation of QT-NASBA and qRT-PCR, a series of experiments was performed using culture-derived mature Plasmodium falciparum gametocytes from three different parasite isolates (NF54, NF135, NF166). Pfs25 mRNA levels were also determined in samples from clinical trials in Mali and Burkina Faso using both methods. Agreement between the two methods and association with mosquito infection rates in membrane feeding assays were assessed.

Results

Intra- and inter-assay variability was larger in QT-NASBA compared to qRT-PCR, particularly at low gametocyte densities (< 1 gametocyte per μL). Logistic models, including log-transformed gametocytaemia estimated by QT-NASBA, explained variability in mosquito feeding experiment results as well as log-transformed gametocytaemia by qRT-PCR (marginal R² 0.28 and 0.22, respectively). Densities determined by both methods strongly correlated with mosquito infection rates [Spearman’s rank correlation coefficient, 0.59 for qRT-PCR and 0.64 for QT-NASBA (P < 0.001 for both)]. Gametocyte densities estimated by qRT-PCR were higher than levels estimated by QT-NASBA or light microscopy at high densities (>100 gametocyte per μL). Samples collected in one of the two transmission studies had extremely low gametocyte densities by both molecular methods, which is suggestive of RNA degradation due to an unknown number of freeze–thaw cycles and illustrates the reliance of molecular gametocyte diagnostics on a reliable cold-chain.

Conclusions

The experiments indicate that both qRT-PCR and QT-NASBA are of value for quantifying mature gametocytes in samples collected in field studies. For both assays, estimated gametocyte densities correlated well with mosquito infection rates. QT-NASBA is less reproducible than qRT-PCR, particularly for low gametocyte densities.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1584-z) contains supplementary material, which is available to authorized users.

Primaquine to reduce transmission of Plasmodium falciparum malaria in Mali: a single-blind, dose-ranging, adaptive randomised phase 2 trial

BACKGROUND

Single low doses of primaquine, when added to artemisinin-based combination therapy, might prevent transmission of Plasmodium falciparum malaria to mosquitoes. We aimed to establish the activity and safety of four low doses of primaquine combined with dihydroartemisinin-piperaquine in male patients in Mali.

METHODS

In this phase 2, single-blind, dose-ranging, adaptive randomised trial, we enrolled boys and men with uncomplicated P falciparum malaria at the Malaria Research and Training Centre (MRTC) field site in Ouelessebougou, Mali. All participants were confirmed positive carriers of gametocytes through microscopy and had normal function of glucose-6-phosphate dehydrogenase (G6PD) on colorimetric quantification. In the first phase, participants were randomly assigned (1:1:1) to one of three primaquine doses: 0 mg/kg (control), 0·125 mg/kg, and 0·5 mg/kg. Randomisation was done with a computer-generated randomisation list (in block sizes of six) and concealed with sealed, opaque envelopes. In the second phase, different participants were sequentially assigned (1:1) to 0·25 mg/kg primaquine or 0·0625 mg/kg primaquine. Primaquine tablets were dissolved into a solution and administered orally in a single dose. Participants were also given a 3 day course of dihydroartemisinin-piperaquine, administered by weight (320 mg dihydroartemisinin and 40 mg piperaquine per tablet). Outcome assessors were masked to treatment allocation, but participants were permitted to find out group assignment. Infectivity was assessed through membrane-feeding assays, which were optimised through the beginning part of phase one. The primary efficacy endpoint was the mean within-person percentage change in mosquito infectivity 2 days after primaquine treatment in participants who completed the study after optimisation of the infectivity assay, had both a pre-treatment infectivity measurement and at least one follow-up infectivity measurement, and who were given the correct primaquine dose. The safety endpoint was the mean within-person change in haemoglobin concentration during 28 days of study follow-up in participants with at least one follow-up visit. This study is registered with ClinicalTrials.gov, number NCT01743820.

FINDINGS

Between Jan 2, 2013, and Nov 27, 2014, we enrolled 81 participants. In the primary analysis sample (n=71), participants in the 0·25 mg/kg primaquine dose group (n=15) and 0·5 mg/kg primaquine dose group (n=14) had significantly lower mean within-person reductions in infectivity at day 2-92·6% (95% CI 78·3-100; p=0·0014) for the 0·25 mg/kg group; and 75·0% (45·7-100; p=0·014) for the 0·5 mg/kg primaquine group-compared with those in the control group (n=14; 11·3% [-27·4 to 50·0]). Reductions were not significantly different from control for participants assigned to the 0·0625 mg/kg dose group (n=16; 41·9% [1·4-82·5]; p=0·16) and the 0·125 mg/kg dose group (n=12; 54·9% [13·4-96·3]; p=0·096). No clinically meaningful or statistically significant drops in haemoglobin were recorded in any individual in the haemoglobin analysis (n=70) during follow-up. No serious adverse events were reported and adverse events did not differ between treatment groups.

INTERPRETATION

A single dose of 0·25 mg/kg primaquine, given alongside dihydroartemisinin-piperaquine, was safe and efficacious for the prevention of P falciparum malaria transmission in boys and men who are not deficient in G6PD. Future studies should assess the safety of single-dose primaquine in G6PD-deficient individuals to define the therapeutic range of primaquine to enable the safe roll-out of community interventions with primaquine.

FUNDING

Bill & Melinda Gates Foundation.

Single low dose primaquine to reduce gametocyte carriage and Plasmodium falciparum transmission after artemether-lumefantrine in children with asymptomatic infection: a randomised, double-blind, placebo-controlled trial

BACKGROUND

A single low dose (0.25 mg/kg) of primaquine is recommended as a gametocytocide in combination with artemisinin-based combination therapies for Plasmodium falciparum but its effect on post-treatment gametocyte circulation and infectiousness to mosquitoes has not been quantified.

METHODS

In this randomised, double-blind, placebo-controlled trial, 360 asymptomatic parasitaemic children aged 2-15 years were enrolled and assigned to receive: artemether-lumefantrine (AL) and a dose of placebo; AL and a 0.25 mg/kg primaquine dose; or AL and a 0.40 mg/kg primaquine dose. On days 0, 2, 3, 7, 10 and 14, gametocytes were detected and quantified by microscopy, Pfs25 mRNA quantitative nucleic acid sequence based amplification (QT-NASBA), and quantitative reverse-transcriptase PCR (qRT-PCR). For a subset of participants, pre- and post-treatment infectiousness was assessed by mosquito feeding assays on days -1, 3, 7, 10 and 14.

RESULTS

Both primaquine arms had lower gametocyte prevalences after day 3 compared to the placebo arm, regardless of gametocyte detection method. The mean (95% confidence interval) number of days to gametocyte clearance in children with patent gametocytes on day 0 (N = 150) was 19.7 (14.6 - 24.8), 7.7 (6.3 - 9.1) and 8.2 (6.7 - 9.6) for the AL-placebo, the 0.25 mg/kg primaquine dose and the 0.40 mg/kg primaquine dose arms, respectively. While 38.0% (30/79) of selected gametocytaemic individuals were infectious before treatment, only 1/251 participant, from the AL-placebo group, infected mosquitoes after treatment.

CONCLUSIONS

We observed similar gametocyte clearance rates after 0.25 and 0.40 mg/kg primaquine doses. Infectivity to mosquitoes after AL was very low and absent in primaquine arms. CLINICALTRIALS.

GOV REGISTRATION

NCT01935882.

Submicroscopic carriage of Plasmodium falciparum and Plasmodium vivax in a low endemic area in Ethiopia where no parasitaemia was detected by microscopy or rapid diagnostic test

BACKGROUND

Motivated by the success in malaria control that was documented over the last decade Ethiopia is aiming at malaria elimination by 2020 in selected districts. It is currently unknown if asymptomatic, submicroscopic malaria parasite carriage may form a hurdle to achieve elimination. The elimination effort may further be complicated by possible glucose-6 phosphate dehydrogenase (G6PD) deficiency which would hinder the use of 8-aminoquinolines in the elimination efforts.

METHOD

In February 2014 a community-based cross-sectional survey was conducted in Malo, southwest Ethiopia. Finger-prick blood samples (n = 555) were tested for presence of Plasmodium falciparum and Plasmodium vivax with microscopy, rapid diagnostic test (RDT), and nested polymerase chain reaction (nPCR). Multiplicity of P. falciparum infections was determined based on genotyping the polymorphic merozoite surface protein-2 (MSP-2) gene. Individuals were also genotyped for mutations in the gene that produces G6PD.

RESULTS

All study participants were malaria infection negative by microscopy and RDT. Nested PCR revealed P. falciparum mono-infection in 5.2% (29/555), P. vivax mono-infection in 4.3% (24/555) and mixed infection in 0.2% (1/555) of individuals. All parasitemic individuals were afebrile (axillary temperature <37.5°C). None of the study participants carried mutations for the G6PD African A-(202GA) and Mediterranean (563CT) variants. All infections, except one, were single-clone infection by MSP-2 genotyping.

CONCLUSION

The detection of a substantial number of subpatent malaria infections in an apparently asymptomatic population without evidence for malaria transmission by conventional diagnostics raises questions about the path to malaria elimination. It is currently unknown how important these infections are for sustaining malaria transmission in the study sites. The absence of G6PD deficiency indicates that 8-aminoquinolines may be safely deployed to accelerate elimination initiatives.