Stephanie G. Valderramos

pfmdr1 mutations contribute to quinine resistance and enhance mefloquine and artemisinin sensitivity in Plasmodium falciparum

The emergence and spread of multidrug resistant Plasmodium falciparum has severely limited the therapeutic options for the treatment of malaria. With ever‐increasing failure rates associated with chloroquine or sulphadoxine‐pyrimethamine treatment, attention has turned to the few alternatives, which include quinine and mefloquine. Here, we have investigated the role of pfmdr1 3′ coding region point mutations in antimalarial drug susceptibility by allelic exchange in the GC03 and 3BA6 parasite lines. Results with pfmdr1‐recombinant clones indicate a significant role for the N1042D mutation in contributing to resistance to quinine and its diastereomer quinidine. The triple mutations S1034C/N1042D/D1246Y, highly prevalent in South America, were also found to enhance parasite susceptibility to mefloquine, halofantrine and artemisinin. pfmdr1 3′ mutations showed minimal effect on P. falciparum resistance to chloroquine or its metabolite mono‐desethylchloroquine in these parasite lines, in contrast to previously published results obtained with 7G8 parasites. This study supports the hypothesis that pfmdr1 3′ point mutations can significantly affect parasite susceptibility to a wide range of antimalarials in a strain‐specific manner that depends on the parasite genetic background.

Decreasing pfmdr1 Copy Number in Plasmodium falciparum Malaria Heightens Susceptibility to Mefloquine, Lumefantrine, Halofantrine, Quinine, and Artemisinin

The global dissemination of drug-resistant Plasmodium falciparum is spurring intense efforts to implement artemisinin (ART)-based combination therapies for malaria, including mefloquine (MFQ)-artesunate and lumefantrine (LUM)-artemether. Clinical studies have identified an association between an increased risk of MFQ, MFQ-artesunate, and LUM-artemether treatment failures and pfmdr1 gene amplification. To directly address the contribution that pfmdr1 copy number makes to drug resistance, we genetically disrupted 1 of the 2 pfmdr1 copies in the drug-resistant FCB line, which resulted in reduced pfmdr1 mRNA and protein expression. These knockdown clones manifested a 3-fold decrease in MFQ IC(50) values, compared with that for the FCB line, verifying the role played by pfmdr1 expression levels in mediating resistance to MFQ. These clones also showed increased susceptibility to LUM, halofantrine, quinine, and ART. No change was observed for chloroquine. These results highlight the importance of pfmdr1 copy number in determining P. falciparum susceptibility to multiple agents currently being used to combat malaria caused by multidrug-resistant parasites.

Gene encoding a deubiquitinating enzyme is mutated in artesunate- and chloroquine-resistant rodent malaria parasites

Artemisinin‐ and artesunate‐resistant Plasmodium chabaudi mutants, AS‐ART and AS‐ATN, were previously selected from chloroquine‐resistant clones AS‐30CQ and AS‐15CQ respectively. Now, a genetic cross between AS‐ART and the artemisinin‐sensitive clone AJ has been analysed by Linkage Group Selection. A genetic linkage group on chromosome 2 was selected under artemisinin treatment. Within this locus, we identified two different mutations in a gene encoding a deubiquitinating enzyme. A distinct mutation occurred in each of the clones AS‐30CQ and AS‐ATN, relative to their respective progenitors in the AS lineage. The mutations occurred independently in different clones under drug selection with chloroquine (high concentration) or artesunate. Each mutation maps to a critical residue in a homologous human deubiquitinating protein structure. Although one mutation could theoretically account for the resistance of AS‐ATN to artemisinin derivates, the other cannot account solely for the resistance of AS‐ART, relative to the responses of its sensitive progenitor AS‐30CQ. Two lines of Plasmodium falciparum with decreased susceptibility to artemisinin were also selected. Their drug‐response phenotype was not genetically stable. No mutations in the UBP‐1 gene encoding the P. falciparum orthologue of the deubiquitinating enzyme were observed. The possible significance of these mutations in parasite responses to chloroquine or artemisinin is discussed.

From Mosquitos to Humans: Genetic Evolution of Zika Virus

Initially isolated in 1947, Zika virus (ZIKV) has recently emerged as a significant public health concern. Sequence analysis of all 41 known ZIKV RNA open reading frames to date indicates that ZIKV has undergone significant changes in both protein and nucleotide sequences during the past half century.

Identification of a Mutant PfCRT-Mediated Chloroquine Tolerance Phenotype in Plasmodium falciparum

Mutant forms of the Plasmodium falciparum transporter PfCRT constitute the key determinant of parasite resistance to chloroquine (CQ), the former first-line antimalarial, and are ubiquitous to infections that fail CQ treatment. However, treatment can often be successful in individuals harboring mutant pfcrt alleles, raising questions about the role of host immunity or pharmacokinetics vs. the parasite genetic background in contributing to treatment outcomes. To examine whether the parasite genetic background dictates the degree of mutant pfcrt-mediated CQ resistance, we replaced the wild type pfcrt allele in three CQ-sensitive strains with mutant pfcrt of the 7G8 allelic type prevalent in South America, the Oceanic region and India. Recombinant clones exhibited strain-dependent CQ responses that ranged from high-level resistance to an incremental shift that did not meet CQ resistance criteria. Nonetheless, even in the most susceptible clones, 7G8 mutant pfcrt enabled parasites to tolerate CQ pressure and recrudesce in vitro after treatment with high concentrations of CQ. 7G8 mutant pfcrt was found to significantly impact parasite responses to other antimalarials used in artemisinin-based combination therapies, in a strain-dependent manner. We also report clinical isolates from French Guiana that harbor mutant pfcrt, identical or related to the 7G8 haplotype, and manifest a CQ tolerance phenotype. One isolate, H209, harbored a novel PfCRT C350R mutation and demonstrated reduced quinine and artemisinin susceptibility. Our data: 1) suggest that high-level CQR is a complex biological process dependent on the presence of mutant pfcrt; 2) implicate a role for variant pfcrt alleles in modulating parasite susceptibility to other clinically important antimalarials; and 3) uncover the existence of a phenotype of CQ tolerance in some strains harboring mutant pfcrt.

X-ray structural analysis of Plasmodium falciparum enoyl acyl carrier protein reductase as a pathway toward the optimization of triclosan antimalarial efficacy.

The x-ray crystal structures of five triclosan analogs, in addition to that of the isoniazid-NAD adduct, are described in relation to their integral role in the design of potent inhibitors of the malarial enzyme Plasmodium falciparum enoyl acyl carrier protein reductase (PfENR). Many of the novel 5-substituted analogs exhibit low micromolar potency against in vitro cultures of drug-resistant and drug-sensitive strains of the P. falciparum parasite and inhibit purified PfENR enzyme with IC50 values of <200 nm. This study has significantly expanded the knowledge base with regard to the structure-activity relationship of triclosan while affording gains against cultured parasites and purified PfENR enzyme. In contrast to a recent report in the literature, these results demonstrate the ability to improve the in vitro potency of triclosan significantly by replacing the suboptimal 5-chloro group with larger hydrophobic moieties. The biological and x-ray crystallographic data thus demonstrate the flexibility of the active site and point to future rounds of optimization to improve compound potency against purified enzyme and intracellular Plasmodium parasites.

Investigations into the Role of the Plasmodium falciparum SERCA (PfATP6) L263E Mutation in Artemisinin Action and Resistance

ABSTRACT Artemisinin-based combination therapies (ACTs) are highly effective for the treatment of Plasmodium falciparum malaria, yet their sustained efficacy is threatened by the potential spread of parasite resistance. Recent studies have provided evidence that artemisinins can inhibit the function of PfATP6, the P. falciparum ortholog of the ER calcium pump SERCA, when expressed in Xenopus laevis oocytes. Inhibition was significantly reduced in an L263E variant, which introduced the mammalian residue into a putative drug-binding pocket. To test the hypothesis that this single mutation could decrease P. falciparum susceptibility to artemisinins, we implemented an allelic-exchange strategy to replace the wild-type pfatp6 allele by a variant allele encoding L263E. Transfected P. falciparum clones were screened by PCR analysis for disruption of the endogenous locus and introduction of the mutant L263E allele under the transcriptional control of a calmodulin promoter. Expression of the mutant allele was demonstrated by reverse transcriptase (RT) PCR and verified by sequence analysis. Parasite clones expressing wild-type or L263E variant PfATP6 showed no significant difference in 50% inhibitory concentrations (IC50s) for artemisinin or its derivatives dihydroartemisinin and artesunate. Nonetheless, hierarchical clustering analysis revealed a trend toward reduced susceptibility that neared significance (artemisinin, P ≈ 0.1; dihydroartemisinin, P = 0.053 and P = 0.085; and artesunate, P = 0.082 and P = 0.162 for the D10 and 7G8 lines, respectively). Notable differences in the distribution of normalized IC50s provided evidence of decreased responsiveness to artemisinin and dihydroartemisinin (P = 0.02 for the D10 and 7G8 lines), but not to artesunate in parasites expressing mutant PfATP6.

Screening Criteria for Ophthalmic Manifestations of Congenital Zika Virus Infection

Importance Current guidelines recommend screening eye examinations for infants with microcephaly or laboratory-confirmed Zika virus infection but not for all infants potentially exposed to Zika virus in utero. Objective To evaluate eye findings in a cohort of infants whose mothers had polymerase chain reaction–confirmed Zika virus infection during pregnancy. Design, Setting, and Participants In this descriptive case series performed from January 2 through October 30, 2016, infants were examined from birth to 1 year of age by a multidisciplinary medical team, including a pediatric ophthalmologist, from Fernandes Figueira Institute, a Ministry of Health referral center for high-risk pregnancies and infectious diseases in children in Rio de Janeiro, Brazil. Participants Mother-infant pairs from Rio de Janeiro, Brazil, who presented with suspected Zika virus infection during pregnancy were referred to our institution and had serum, urine, amniotic fluid, or placenta samples tested by real-time polymerase chain reaction for Zika virus. Main Outcomes and Measures Description of eye findings, presence of microcephaly or other central nervous system abnormalities, and timing of infection in infants with confirmed Zika virus during pregnancy. Eye abnormalities were correlated with central nervous system findings, microcephaly, and the timing of maternal infection. Results Of the 112 with polymerase chain reaction–confirmed Zika virus infection in maternal specimens, 24 infants (21.4%) examined had eye abnormalities (median age at first eye examination, 31 days; range, 0-305 days). Ten infants (41.7%) with eye abnormalities did not have microcephaly, and 8 (33.3%) did not have any central nervous system findings. Fourteen infants with eye abnormalities (58.3%) were born to women infected in the first trimester, 8 (33.3%) in the second trimester, and 2 (8.3%) in the third trimester. Optic nerve and retinal abnormalities were the most frequent findings. Eye abnormalities were statistically associated with microcephaly (odds ratio [OR], 19.1; 95% CI, 6.0-61.0), other central nervous system abnormalities (OR, 4.3; 95% CI, 1.6-11.2), arthrogryposis (OR, 29.0; 95% CI, 3.3-255.8), and maternal trimester of infection (first trimester OR, 5.1; 95% CI, 1.9-13.2; second trimester OR, 0.5; 95% CI, 0.2-1.2; and third trimester OR, 0.3; 95% CI, 0.1-1.2). Conclusions and Relevance Eye abnormalities may be the only initial finding in congenital Zika virus infection. All infants with potential maternal Zika virus exposure at any time during pregnancy should undergo screening eye examinations regardless of the presence or absence of central nervous system abnormalities.

Differential Drug Efflux or Accumulation Does Not Explain Variation in the Chloroquine Response of Plasmodium falciparum Strains Expressing the Same Isoform of Mutant PfCRT

ABSTRACT Mutant forms of the Plasmodium falciparum chloroquine resistance transporter (PfCRT) mediate chloroquine resistance by effluxing the drug from the parasites digestive vacuole, the acidic organelle in which chloroquine exerts its parasiticidal effect. However, different parasites bearing the same mutant form of PfCRT can vary substantially in their chloroquine susceptibility. Here, we have investigated the biochemical basis for the difference in chloroquine response among transfectant parasite lines having different genetic backgrounds but bearing the same mutant form of PfCRT. Despite showing significant differences in their chloroquine susceptibility, all lines with the mutant PfCRT showed a similar chloroquine-induced H+ leak from the digestive vacuole, indicative of similar rates of PfCRT-mediated chloroquine efflux. Furthermore, all lines showed similarly reduced levels of drug accumulation. Factors other than chloroquine efflux and accumulation therefore influence the susceptibility to this drug in parasites expressing mutant PfCRT. Furthermore, in some but not all strains bearing mutant PfCRT, the 50% inhibitory concentration (IC50) for chloroquine and the degree of resistance compared to that of recombinant control parasites varied with the length of the parasite growth assays. In these parasites, the 50% inhibitory concentration for chloroquine measured in 72- or 96-h assays was significantly lower than that measured in 48-h assays. This highlights the importance of considering the first- and second-cycle activities of chloroquine in future studies of parasite susceptibility to this drug.

The value of the first trimester ultrasound in the era of cell free DNA screening

To describe the clinically relevant findings detected by the first trimester ultrasound (FTU) and to determine the additional value of the FTU compared to cell free DNA (cfDNA) alone.