Population-specific variations in KCNH2 predispose patients to delayed ventricular repolarization upon dihydroartemisinin-piperaquine therapy.

Dihydroartemisinin-piperaquine is efficacious for the treatment of uncomplicated malaria and its use is increasing globally. Despite the positive results in fighting malaria, inhibition of the Kv11.1 channel (hERG; encoded by the KCNH2 gene) by piperaquine has raised concerns about cardiac safety. Whether genetic factors could modulate the risk of piperaquine-mediated QT prolongations remained unclear. Here, we first profiled the genetic landscape of KCNH2 variability using data from 141,614 individuals. Overall, we found 1,007 exonic variants distributed over the entire gene body, 555 of which were missense. By optimizing the gene-specific parametrization of 16 partly orthogonal computational algorithms, we developed a KCNH2-specific ensemble classifier that identified a total of 116 putatively deleterious missense variations. To evaluate the clinical relevance of KCNH2 variability, we then sequenced 293 Malian patients with uncomplicated malaria and identified 13 variations within the voltage sensing and pore domains of Kv11.1 that directly interact with channel blockers. Cross-referencing of genetic and electrocardiographic data before and after piperaquine exposure revealed that carriers of two common variants, rs1805121 and rs41314375, experienced significantly higher QT prolongations (ΔQTc of 41.8 ms and 61 ms, respectively, vs 14.4 ms in controls) with more than 50% of carriers having increases in QTc >30 ms. Furthermore, we identified three carriers of rare population-specific variations who experienced clinically relevant delayed ventricular repolarization. Combined, our results map population-scale genetic variability of KCNH2 and identify genetic biomarkers for piperaquine-induced QT prolongation that could help to flag at-risk patients and optimize efficacy and adherence to antimalarial therapy.

A Novel Ex Vivo Drug Assay for Assessing the Transmission-Blocking Activity of Compounds on Field-Isolated Plasmodium falciparum Gametocytes.

The discovery and development of transmission-blocking therapies challenge malaria elimination and necessitate standard and reproducible bioassays to measure the blocking properties of antimalarial drugs and candidate compounds. Most of the current bioassays evaluating the transmission-blocking activity of compounds rely on laboratory-adapted Plasmodium strains. Transmission-blocking data from clinical gametocyte isolates could help select novel transmission-blocking candidates for further development. Using freshly collected Plasmodium falciparum gametocytes from asymptomatic individuals, we first optimized ex vivo culture conditions to improve gametocyte viability and infectiousness by testing several culture parameters. We next pre-exposed ex vivo field-isolated gametocytes to chloroquine, dihydroartemisinin, primaquine, KDU691, GNF179, and oryzalin for 48 h prior to direct membrane feeding. We measured the activity of the drug on the ability of gametocytes to resume the sexual life cycle in Anopheles after drug exposure. Using 57 blood samples collected from Malian volunteers aged 6 to 15 years, we demonstrate that the infectivity of freshly collected field gametocytes can be preserved and improved ex vivo in a culture medium supplemented with 10% horse serum at 4% hematocrit for 48 h. Moreover, our optimized drug assay displays the weak transmission-blocking activity of chloroquine and dihydroartemisinin, while primaquine and oryzalin exhibited a transmission-blocking activity of ~50% at 1 µM. KDU691 and GNF179 both interrupted Plasmodium transmission at 1 µM and 5 nM, respectively. This new approach, if implemented, has the potential to accelerate the screening of compounds with transmission-blocking activity.

Reduced ex vivo susceptibility of Plasmodium falciparum after oral artemether-lumefantrine treatment in Mali.

BACKGROUND: Artemisinin-based combination therapy is the recommended first-line treatment for uncomplicated falciparum malaria worldwide. However, recent studies conducted in Mali showed an increased frequency of recurrent parasitaemia following artemether-lumefantrine (AL) treatment. METHODS: Study samples were collected during a large WANECAM study. Ex-vivo Plasmodium falciparum sensitivity to artemether and lumefantrine was assessed using the tritiated hypoxanthine-based assay. The prevalence of molecular markers of anti-malarial drug resistance (pfcrt K76T, pfmdr1 N86Y and K13-propeller) were measured by PCR and/or sequencing. RESULTS: Overall 61 samples were successfully analysed in ex vivo studies. Mean IC50s increased significantly between baseline and recurrent parasites for both artemether (1.6 nM vs 3.2 nM, p < 0.001) and lumefantrine (1.4 nM vs 3.4 nM, p = 0.004). Wild type Pfmdr1 N86 allele was selected after treatment (71 vs 91%, 112 of 158 vs 95 of 105, p < 0.001) but not the wild type pfcrt K76 variant (23.5 vs 24.8%, 40 of 170 vs 26 of 105, p = 0.9). Three non-synonymous K13-propeller SNPs (A522C, A578S, and G638R) were found with allele frequencies <2%. CONCLUSION: Malian post-AL P. falciparum isolates were less susceptible to artemether and lumefantrine than baseline isolates.

Complexity of Plasmodium falciparum infection and genetic variations associated with differences in parasite clearance time in two Malian villages.

Background: Effective approaches to fight against malaria include disease prevention, an early diagnosis of malaria cases, and rapid management of confirmed cases by treatment with effective antimalarials. Artemisinin-based combination therapies are first-line treatments for uncomplicated malaria in endemic areas. However, cases of resistance to artemisinin have already been described in South-East Asia resulting in prolonged parasite clearance time after treatment. In Mali, though mutations in the K13 gene associated with delayed clearance in Asia are absent, a significant difference in parasite clearance time following treatment with artesunate was observed between two malaria endemic sites, Bougoula-Hameau and Faladje. Hypothetically, differences in complexity of Plasmodium falciparum infections may be accounted for this difference. Hence, the aims of this study were to assess the complexity of infection (COI) and genetic diversity of P. falciparum parasites during malaria treatment in Bougoula-Hameau and Faladje in Mali. Methods: Thirty (30) patients per village were randomly selected from 221 patients enrolled in a prospective artesunate monotherapy study conducted in Faladje and Bougoula-Hameau in 2016. All parasitemic blood samples of patients from enrollment to last positive slide were retained to assess malaria parasite COI and polymorphisms. DNA were extracted with a Qiagen kit and Pfcsp and Pfama1 encoding gene were amplified by nested PCR and sequenced using the Illumina platform. The parasite clearance time (PCT) was determined using the parasite clearance estimator of Worldwide Antimarial Resistance Network (WWARN). Data were analyzed with R®. Results: The median number of genetically distinct parasite clones was similar at enrollment, 7 (IQR of 5-9) in Faladje and 6 (IQR of 4-10) in Bougoula-Hameau (p-value = 0.1). On the first day after treatment initiation, the COI was higher in Faladje (6; CI:4-8) than in Bougoula-Hameau (4; CI:4-6) with a p-value =0. 02. Overall, COI was high with higher PCT. Finally, there was a low genetic diversity between Faladje and Bougoula-Hameau. Conclusion: This study demonstrated that the difference in PCT observed between the two villages could be due to differences in the complexity of infection of these two villages.

Different Plasmodium falciparum clearance times in two Malian villages following artesunate monotherapy.

BACKGROUND: Artemisinin resistance described as increased parasite clearance time (PCT) is rare in Africa. More sensitive methods such as qPCR might better characterize the clearance phenotype in sub-Saharan Africa. METHODS: PCT is explored in Mali using light microscopy and qPCR after artesunate for uncomplicated malaria. In two villages, patients were followed for 28 days. Blood smears and spots were collected respectively for microscopy and qPCR. Parasitemia slope half-life was calculated after microscopy. Patient residual parasitemia were measured by qPCR. RESULTS: Uncorrected adequate clinical and parasitological responses (ACPR) observed in Faladje and Bougoula-Hameau were 78% and 92%, respectively (p=0.01). This reached 100% for both after molecular correction. Proportions of 24H microscopy positive patients in Faladje and Bougoula-Hameau were 97.2% and 72%, respectively (p<0.0001). Slope half-life was 2.8h in Faladje vs 2H in Bougoula-Hameau (p<0.001) and Proportions of 72H patients with residual parasitemia were 68.5% and 40% in Faladje and Bougoula-Hameau, respectively (p=0.003). The mean residual parasitemia was 2.9 in Faladje vs. 0.008 in Bougoula-Hameau (p=0.002). Although artesunate is efficacious in Mali, the longer parasite clearance time with submicroscopic parasitemia observed may represent early signs of developing P. falciparum resistance to artemisinins.