XB-ART-58873
PLoS Biol
2022 May 04;205:e3001616. doi: 10.1371/journal.pbio.3001616.
Show Gene links
Show Anatomy links
Mechanistic basis for multidrug resistance and collateral drug sensitivity conferred to the malaria parasite by polymorphisms in PfMDR1 and PfCRT.
Shafik SH
,
Richards SN
,
Corry B
,
Martin RE
.
???displayArticle.abstract???
Polymorphisms in the Plasmodium falciparum multidrug resistance protein 1 (pfmdr1) gene and the Plasmodium falciparum chloroquine resistance transporter (pfcrt) gene alter the malaria parasite's susceptibility to most of the current antimalarial drugs. However, the precise mechanisms by which PfMDR1 contributes to multidrug resistance have not yet been fully elucidated, nor is it understood why polymorphisms in pfmdr1 and pfcrt that cause chloroquine resistance simultaneously increase the parasite's susceptibility to lumefantrine and mefloquine-a phenomenon known as collateral drug sensitivity. Here, we present a robust expression system for PfMDR1 in Xenopus oocytes that enables direct and high-resolution biochemical characterizations of the protein. We show that wild-type PfMDR1 transports diverse pharmacons, including lumefantrine, mefloquine, dihydroartemisinin, piperaquine, amodiaquine, methylene blue, and chloroquine (but not the antiviral drug amantadine). Field-derived mutant isoforms of PfMDR1 differ from the wild-type protein, and each other, in their capacities to transport these drugs, indicating that PfMDR1-induced changes in the distribution of drugs between the parasite's digestive vacuole (DV) and the cytosol are a key driver of both antimalarial resistance and the variability between multidrug resistance phenotypes. Of note, the PfMDR1 isoforms prevalent in chloroquine-resistant isolates exhibit reduced capacities for chloroquine, lumefantrine, and mefloquine transport. We observe the opposite relationship between chloroquine resistance-conferring mutations in PfCRT and drug transport activity. Using our established assays for characterizing PfCRT in the Xenopus oocyte system and in live parasite assays, we demonstrate that these PfCRT isoforms transport all 3 drugs, whereas wild-type PfCRT does not. We present a mechanistic model for collateral drug sensitivity in which mutant isoforms of PfMDR1 and PfCRT cause chloroquine, lumefantrine, and mefloquine to remain in the cytosol instead of sequestering within the DV. This change in drug distribution increases the access of lumefantrine and mefloquine to their primary targets (thought to be located outside of the DV), while simultaneously decreasing chloroquine's access to its target within the DV. The mechanistic insights presented here provide a basis for developing approaches that extend the useful life span of antimalarials by exploiting the opposing selection forces they exert upon PfCRT and PfMDR1.
???displayArticle.pubmedLink??? 35507548
???displayArticle.link??? PLoS Biol
Species referenced: Xenopus laevis
Genes referenced: akr1c2
???attribute.lit??? ???displayArticles.show???
Fig 1. Heterologous expression of functional human P-gp and PfMDR1 in Xenopus oocytes. (a) Schematic showing the transport of a [3H]drug via human P-gp or PfMDR1 in the Xenopus oocyte system. (b) The relationship between the quantity of human P-gp cRNA injected into the oocyte and the level of human P-gp–mediated [3H]vinblastine transport measured. (c) The transport of [3H]vinblastine via human P-gp was approximately linear with time for at least 2 hours. (d) The human P-gp–mediated efflux of [3H]vinblastine from oocytes was reduced by known inhibitors of the transporter (nicardipine, PSC8333, vanadate, and verapamil) and was unaffected by amantadine (a drug that does not interact with human P-gp). (e) The field isoforms of PfMDR1 characterized in this study. Residues that differ from the wild-type amino acid sequence are shaded gray. (f) Immunofluorescence microscopy images confirmed that PfMDR1 localized to the oocyte plasma membrane. The expression of 3xHA-tagged PfMDR1NYSND resulted in a fluorescent band external to the pigment layer, indicating that the protein was expressed at the oocyte surface. The band was not present in ne. The length of the scale bar is 50 μm. Images showing the presence of the other HA-tagged PfMDR1 isoforms at the oocyte surface are shown in S4 Fig. (g) Semiquantification of PfMDR1 protein levels in the membranes of oocytes expressing different 3xHA-PfMDR1 isoforms indicated that the 7 isoforms were expressed at similar levels. (h) The transport of [3H]vinblastine via PfMDR1. (i) The efflux of [3H]lumefantrine from oocytes expressing PfMDR1NYSND was reduced by nicardipine, PSC8333, vanadate, and verapamil and was unaffected by amantadine. (j) The relationship between the quantity of PfMDR1NYSND cRNA microinjected into the oocyte and the level of PfMDR1NYSND-mediated [3H]lumefantrine transport measured. (k) The transport of [3H]lumefantrine via PfMDR1NYSND was approximately linear with time for at least 2 hours. (l) Microinjection of additional ATP into the oocyte greatly stimulated [3H]lumefantrine transport via PfMDR1NFCDY. The data are the mean of n = 4 to 9 independent experiments, each yielding similar results and overlaid as individual data points in panels d, g, h, and i, and the error is the SEM. Where not visible, the error bars fall within the symbols. The asterisks denote a significant difference from human P-gp (panel d), 3xHA-PfMDR1NYSND (panel g), or PfMDR1NYSND (panels h and i); ***P < 0.001, ns, not significant (1-way ANOVA). The data underlying this figure is supplied in S3 Data. ne, nonexpressing oocytes; PfMDR1, Plasmodium falciparum multidrug resistance protein 1; P-gp, P-glycoprotein. https://doi.org/10.1371/journal.pbio.3001616.g001 | |
Fig 2. Field isoforms of PfMDR1 differ significantly in their capacities for antimalarial drug transport. (a–i) Field isoforms of PfMDR1 transported the antimalarial drugs [3H]lumefantrine (a), [3H]mefloquine (b), [3H]chloroquine (c), [3H]quinidine (d), [3H]amodiaquine (e), [3H]piperaquine (f), [3H]dihydroartemisinin (g), methylene blue (h), and quinacrine (i). (j–l) All of the field isoforms of PfMDR1 also transported the human P-gp substrates rhodamine B (j) and [3H]vinblastine (k), but none transported [3H]amantadine (l). The transport of methylene blue, quinacrine, and rhodamine B was detected using the intrinsic fluorescence of these compounds and a fluorescence-based transport assay (see S2 Text). The data are the mean of n = 4 independent experiments (each yielding similar results and overlaid as individual data points), and the error is the SEM. The asterisks denote a significant difference from PfMDR1NYSND; *P < 0.05, **P < 0.01, ***P < 0.001, ns, not significant (1-way ANOVA). The data underlying this figure is supplied in S3 Data. ne, nonexpressing oocytes; PfMDR1, Plasmodium falciparum multidrug resistance protein 1. https://doi.org/10.1371/journal.pbio.3001616.g002 | |
Fig 3. Characterization of lumefantrine, mefloquine, and chloroquine transport via PfMDR1. (a–c) There were significant differences in the apparent kinetic parameters of lumefantrine (a), mefloquine (b), and chloroquine (c) transport between field isoforms of PfMDR1. The concentration dependence of PfMDR1-mediated drug transport was calculated by subtracting the leakage from ne from that of oocytes expressing a PfMDR1 isoform at each drug concentration. (d–f) The transport of [3H]vinblastine via PfMDR1 was inhibited by lumefantrine (d), [3H]mefloquine (e), and [3H]chloroquine (f). The data are the mean of n = 4 independent experiments (each yielding similar results), and the error is the SEM. The asterisks denote a significant difference from PfMDR1NYSND; *P < 0.05, **P < 0.01, ***P < 0.001, ns nonsignificant (1-way ANOVA). The data underlying this figure is supplied in S3 Data. ne, nonexpressing oocytes; PfMDR1, Plasmodium falciparum multidrug resistance protein 1. https://doi.org/10.1371/journal.pbio.3001616.g003 | |
Fig 4. Quinine transport via PfMDR1. (a) Field isoforms of PfMDR1 transported [3H]quinine, with PfMDR1NFSDD exhibiting the highest level of quinine transport activity. (b) There were significant differences in the apparent kinetic parameters for quinine transport via field isoforms of PfMDR1. The concentration dependence of PfMDR1-mediated quinine transport was calculated by subtracting the leakage from ne from that of oocytes expressing a PfMDR1 isoform at each drug concentration. The data are the mean of n = 4 independent experiments (each yielding similar results and overlaid as individual data points in panel a), and the error is the SEM. The asterisks denote a significant difference from PfMDR1NYSND; **P < 0.01 and ***P < 0.001 (1-way ANOVA). The data underlying panels a and b of this figure is supplied in S3 Data. (c) Inward-open homology model of PfMDR1 based on the C. elegans P-gp crystal structure (PDB 4F4C) showing the location of the mutations found in the 5 field PfMDR1 isoforms characterized in this study (orange). A putative binding pose of quinine in the central cavity is shown (pink). (d) A comparison of the inward-open model and outward-open models (based on the crystal structure of human P-gp; PDB 6C0V) as viewed from the side of the protein facing into the DV lumen. The N86Y mutation is part of a cluster of 3 residues forming the extracellular gate of the transporter (the participating residues are shown). These 3 residues are in close proximity in the inward-open state but move apart in the outward-open conformation. (e) Putative quinine binding site in PfMDR1NFSDD. Amino acids interacting with quinine are indicated (apart from L71, I1071, and F1072 that are removed to clearly view the binding pose). Atoms are shaded as follows: carbon in quinine, pink; carbon in the 1042D residue, orange; nitrogen, blue; oxygen, red; hydrogen, white. ne, nonexpressing oocytes; PfMDR1, Plasmodium falciparum multidrug resistance protein 1; P-gp, P-glycoprotein. https://doi.org/10.1371/journal.pbio.3001616.g004 | |
Fig 5. Correlations between rates of drug transport via PfMDR1 in Xenopus oocytes and in vitro parasite drug resistance indices. The rates of PfMDR1-mediated transport of lumefantrine, mefloquine, chloroquine, and quinine (Figs 2 and 4, and S1 Data) were plotted against the in vitro resistance index for the relevant drug and parasite strain (S3 Table). Where not shown, error bars fall within the symbols. (a) A positive correlation was observed between the rate of lumefantrine transport via PfMDR1 and the in vitro lumefantrine response (Pearson correlation coefficient = 0.76, r2 = 0.58, P = 0.078). (b) A positive correlation was observed between the rate of mefloquine transport via PfMDR1 and the in vitro mefloquine response (Pearson correlation coefficient = 0.75, r2 = 0.56, P = 0.008). The data point for Dd2 is an outlier and its removal significantly improved the correlation (Pearson correlation coefficient = 0.97, r2 = 0.94, P = 0.006). Dd2 parasites typically harbor 2 to 4 copies of PfMDR1 and have been reported to express greater levels of PfMDR1 than the other parasite strains included in the analysis [85,87]. Given that pfmdr1 amplification has been associated with mefloquine resistance [30–32,88,89], it is possible that the overexpression of PfMDR1 in Dd2 parasites imparts a higher level of resistance to this strain (see S3 Text for an extended analysis). (c) An inverse correlation was observed between the rate of chloroquine transport via PfMDR1 and the in vitro chloroquine response. The removal of the 7G8 data point (see S3 Text for an extended analysis) resulted in a stronger correlation between the rate of chloroquine transport via PfMDR1 and the parasite’s chloroquine response in vitro (Pearson correlation coefficient = −0.86, r2 = 0.74, P = 0.054). (d) There was no correlation between the rate of quinine transport via PfMDR1 and the in vitro quinine response (see S4 Text for an extended analysis). The data for the in vitro resistance indices are the mean of n = 2 to 18 published studies, and the data for the PfMDR1-mediated drug transport rates are the mean of n = 4 independent experiments. The error is the SEM except for the in vitro resistance indices that were calculated from 2 studies, in which case the error is the range/2. The data underlying this figure is supplied in S3 Data. PfMDR1, Plasmodium falciparum multidrug resistance protein 1. https://doi.org/10.1371/journal.pbio.3001616.g005 | |
Fig 6. Transport of lumefantrine and mefloquine via PfCRT in Xenopus oocytes and in situ. (a, d) The transport of [3H]lumefantrine (a) and [3H]mefloquine (d) via PfCRTDd2 and PfCRT7G8 was reduced by verapamil (VP; 100 μM). The asterisks denote a significant difference from the ne (gray asterisks), the PfCRT7G8 control (orange asterisks), or the PfCRTDd2 control (red asterisks). (b, e) The transport of lumefantrine (b) and mefloquine (e) via PfCRTDd2 and PfCRT7G8 was saturable. The asterisks denote a significant difference from PfCRTDd2 (red asterisks). (c, f) The effects of unlabeled lumefantrine (c) and unlabeled mefloquine (f) on [3H]VDPVNF transport via PfCRT3D7, PfCRTDd2, and PfCRT7G8. The asterisks denote a significant difference from PfCRT3D7 (blue asterisks). (g) Lumefantrine and mefloquine (2.5 μM) increased the rate of DV alkalinization in the chloroquine-resistant C67G8 and C4Dd2 parasite lines but not in the chloroquine-sensitive C2GC03 line. Unless labeled ns, P < 0.05 relative to the absence of a test solute. (h) The increase in the rate of DV alkalinization caused by lumefantrine and mefloquine was inhibited by VP (50 μM). The asterisks denote a significant difference from the relevant C2GC03 (blue asterisks), C67G8 (orange asterisks), or C4Dd2 (red asterisks) treatments in the absence of verapamil. (i, j) Lumefantrine (i) and mefloquine (j) increased the rate of DV alkalinization in a concentration-dependent manner. The data are the mean of n = 4 independent experiments, each yielding similar results and overlaid as individual data points in panels a, d, g, and h, and the error is the SEM. Where not visible, the error bars fall within the symbols. **P < 0.01, ***P < 0.001, ns, not significant (1-way ANOVA). The data underlying this figure is supplied in S3 Data. ne, nonexpressing oocytes; PfCRT, Plasmodium falciparum chloroquine resistance transporter. https://doi.org/10.1371/journal.pbio.3001616.g006 | |
Fig 7. Roles of PfMDR1 and PfCRT in the parasite’s susceptibility to lumefantrine, mefloquine, and chloroquine. Mechanistic explanations for how polymorphisms in pfmdr1 and pfcrt alter the parasite’s response to lumefantrine and mefloquine (a) and chloroquine (b). Lumefantrine, mefloquine, and chloroquine are weak bases that enter the DV via 2 main routes: (1) simple diffusion of the neutral species across the membrane and subsequent protonation within the acidic DV lumen; and (2) ATP-driven import via PfMDR1. Wild-type PfMDR1 has a high capacity for drug transport and this activity, together with the inability of wild-type PfCRT to efflux lumefantrine, mefloquine, or chloroquine from the DV, causes these drugs to sequester within the DV. Overexpression of PfMDR1 results in a further increase in the rate of drug transport from the cytosol into the DV and thus greater accumulation of lumefantrine, mefloquine, and chloroquine in the DV (as well as concomitant reductions in their cytosolic concentrations). In parasites carrying a mutant PfMDR1 isoform (and/or only one pfmdr1 copy) as well as a mutant isoform of PfCRT, there is a marked reduction in the DV accumulation of lumefantrine, mefloquine, and chloroquine as a result of (1) a decrease in the rate of drug import via PfMDR1; and (2) the PfCRT-mediated efflux of drugs from the DV back into the cytosol. The reduction in the concentration of chloroquine at its primary site of action allows the parasite to evade its killing effects, thereby causing chloroquine resistance. On the other hand, the concomitant increases in the cytosolic drug concentrations render these parasites more sensitive to lumefantrine and mefloquine, indicating that the primary targets of both drugs are located outside of the DV. CQ, chloroquine; DV, digestive vacuole; LM, lumefantrine; MQ, mefloquine; PfCRT, Plasmodium falciparum chloroquine resistance transporter; PfMDR1, Plasmodium falciparum multidrug resistance protein 1. https://doi.org/10.1371/journal.pbio.3001616.g007 |
References [+] :
Allen,
Plasmodium falciparum culture: the benefits of shaking.
2010, Pubmed
Allen, Plasmodium falciparum culture: the benefits of shaking. 2010, Pubmed
Amoah, Heterologous expression and ATPase activity of mutant versus wild type PfMDR1 protein. 2007, Pubmed
Baniecki, High-throughput Plasmodium falciparum growth assay for malaria drug discovery. 2007, Pubmed
Baro, Analysis of chloroquine resistance transporter (CRT) isoforms and orthologues in S. cerevisiae yeast. 2011, Pubmed
Beck, Effects of indole alkaloids on multidrug resistance and labeling of P-glycoprotein by a photoaffinity analog of vinblastine. 1988, Pubmed
Bellanca, Multiple drugs compete for transport via the Plasmodium falciparum chloroquine resistance transporter at distinct but interdependent sites. 2014, Pubmed , Xenbase
Bergeron, Frog oocytes to unveil the structure and supramolecular organization of human transport proteins. 2011, Pubmed , Xenbase
Best, Optimization of the additive CHARMM all-atom protein force field targeting improved sampling of the backbone φ, ψ and side-chain χ(1) and χ(2) dihedral angles. 2012, Pubmed
Boesch, In vivo circumvention of P-glycoprotein-mediated multidrug resistance of tumor cells with SDZ PSC 833. 1991, Pubmed
Bohórquez, Quinine localizes to a non-acidic compartment within the food vacuole of the malaria parasite Plasmodium falciparum. 2012, Pubmed
Bröer, Comparison of lactate transport in astroglial cells and monocarboxylate transporter 1 (MCT 1) expressing Xenopus laevis oocytes. Expression of two different monocarboxylate transporters in astroglial cells and neurons. 1997, Pubmed , Xenbase
Callaghan, Plasmodium falciparum chloroquine resistance transporter (PfCRT) isoforms PH1 and PH2 perturb vacuolar physiology. 2016, Pubmed
Callaghan, Functional Comparison of 45 Naturally Occurring Isoforms of the Plasmodium falciparum Chloroquine Resistance Transporter (PfCRT). 2015, Pubmed
Calçada, Expansion of a Specific Plasmodium falciparum PfMDR1 Haplotype in Southeast Asia with Increased Substrate Transport. 2020, Pubmed
Carter, Isolation and functional characterization of the PfNT1 nucleoside transporter gene from Plasmodium falciparum. 2000, Pubmed , Xenbase
Chugh, Identification and deconvolution of cross-resistance signals from antimalarial compounds using multidrug-resistant Plasmodium falciparum strains. 2015, Pubmed
Cowell, Mapping the malaria parasite druggable genome by using in vitro evolution and chemogenomics. 2018, Pubmed
Cowman, Selection for mefloquine resistance in Plasmodium falciparum is linked to amplification of the pfmdr1 gene and cross-resistance to halofantrine and quinine. 1994, Pubmed
Cowman, A P-glycoprotein homologue of Plasmodium falciparum is localized on the digestive vacuole. 1991, Pubmed
Deane, Chlorpheniramine Analogues Reverse Chloroquine Resistance in Plasmodium falciparum by Inhibiting PfCRT. 2014, Pubmed , Xenbase
Drexler, Mycoplasma contamination of cell cultures: Incidence, sources, effects, detection, elimination, prevention. 2002, Pubmed
Duraisingh, The tyrosine-86 allele of the pfmdr1 gene of Plasmodium falciparum is associated with increased sensitivity to the anti-malarials mefloquine and artemisinin. 2000, Pubmed
Duraisingh, Increased sensitivity to the antimalarials mefloquine and artemisinin is conferred by mutations in the pfmdr1 gene of Plasmodium falciparum. 2000, Pubmed
Eastman, PfCRT and PfMDR1 modulate interactions of artemisinin derivatives and ion channel blockers. 2016, Pubmed
Eyase, The role of Pfmdr1 and Pfcrt in changing chloroquine, amodiaquine, mefloquine and lumefantrine susceptibility in western-Kenya P. falciparum samples during 2008-2011. 2013, Pubmed
Eytan, Efficiency of P-glycoprotein-mediated exclusion of rhodamine dyes from multidrug-resistant cells is determined by their passive transmembrane movement rate. 1997, Pubmed
Ferreira, PfMDR1: mechanisms of transport modulation by functional polymorphisms. 2011, Pubmed
Fidock, Mutations in the P. falciparum digestive vacuole transmembrane protein PfCRT and evidence for their role in chloroquine resistance. 2000, Pubmed
Fitch, Lysis of Plasmodium falciparum by ferriprotoporphyrin IX and a chloroquine-ferriprotoporphyrin IX complex. 1982, Pubmed
Foley, Quinoline antimalarials: mechanisms of action and resistance and prospects for new agents. 1998, Pubmed
Foote, Several alleles of the multidrug-resistance gene are closely linked to chloroquine resistance in Plasmodium falciparum. 1990, Pubmed
Friedrich, Assessment of Plasmodium falciparum PfMDR1 transport rates using Fluo-4. 2014, Pubmed
Godfrey, Effect of water hardness on oocyte quality and embryo development in the African clawed frog (Xenopus laevis). 2004, Pubmed , Xenbase
Gribble, A novel method for measurement of submembrane ATP concentration. 2000, Pubmed , Xenbase
Griffin, Mutation in the Plasmodium falciparum CRT protein determines the stereospecific activity of antimalarial cinchona alkaloids. 2012, Pubmed
Hayward, The pH of the digestive vacuole of Plasmodium falciparum is not associated with chloroquine resistance. 2006, Pubmed
Hrycyna, Quinine dimers are potent inhibitors of the Plasmodium falciparum chloroquine resistance transporter and are active against quinoline-resistant P. falciparum. 2014, Pubmed , Xenbase
Humphrey, VMD: visual molecular dynamics. 1996, Pubmed
Jin, Crystal structure of the multidrug transporter P-glycoprotein from Caenorhabditis elegans. 2012, Pubmed
Johnson, Evidence for a central role for PfCRT in conferring Plasmodium falciparum resistance to diverse antimalarial agents. 2004, Pubmed
Karcz, Nucleotide binding properties of a P-glycoprotein homologue from Plasmodium falciparum. 1993, Pubmed
Kim, Structure and drug resistance of the Plasmodium falciparum transporter PfCRT. 2019, Pubmed
Kim, Molecular structure of human P-glycoprotein in the ATP-bound, outward-facing conformation. 2018, Pubmed
Klonis, Evaluation of pH during cytostomal endocytosis and vacuolar catabolism of haemoglobin in Plasmodium falciparum. 2007, Pubmed
Kuhn, Trafficking of the phosphoprotein PfCRT to the digestive vacuolar membrane in Plasmodium falciparum. 2010, Pubmed
Lakshmanan, A critical role for PfCRT K76T in Plasmodium falciparum verapamil-reversible chloroquine resistance. 2005, Pubmed
Lehane, A verapamil-sensitive chloroquine-associated H+ leak from the digestive vacuole in chloroquine-resistant malaria parasites. 2008, Pubmed
Lehane, Chloroquine resistance-conferring mutations in pfcrt give rise to a chloroquine-associated H+ leak from the malaria parasite's digestive vacuole. 2008, Pubmed
Lehane, Efflux of a range of antimalarial drugs and 'chloroquine resistance reversers' from the digestive vacuole in malaria parasites with mutant PfCRT. 2010, Pubmed
Loo, Attachment of a 'molecular spring' restores drug-stimulated ATPase activity to P-glycoprotein lacking both Q loop glutamines. 2017, Pubmed
Mahar Doan, Passive permeability and P-glycoprotein-mediated efflux differentiate central nervous system (CNS) and non-CNS marketed drugs. 2002, Pubmed
Martin, The transportome of the malaria parasite. 2020, Pubmed , Xenbase
Martin, Chloroquine transport via the malaria parasite's chloroquine resistance transporter. 2009, Pubmed , Xenbase
Martin, Saquinavir inhibits the malaria parasite's chloroquine resistance transporter. 2012, Pubmed , Xenbase
Martin, Mechanisms of resistance to the partner drugs of artemisinin in the malaria parasite. 2018, Pubmed
Mehlotra, Evolution of a unique Plasmodium falciparum chloroquine-resistance phenotype in association with pfcrt polymorphism in Papua New Guinea and South America. 2001, Pubmed
Mu, Multiple transporters associated with malaria parasite responses to chloroquine and quinine. 2003, Pubmed
Mu, Plasmodium falciparum genome-wide scans for positive selection, recombination hot spots and resistance to antimalarial drugs. 2010, Pubmed
Mwai, Genome wide adaptations of Plasmodium falciparum in response to lumefantrine selective drug pressure. 2012, Pubmed
Newmeyer, Assembly in vitro of nuclei active in nuclear protein transport: ATP is required for nucleoplasmin accumulation. 1986, Pubmed , Xenbase
Nsobya, In vitro sensitivities of Plasmodium falciparum to different antimalarial drugs in Uganda. 2010, Pubmed
Otienoburu, Selection of Plasmodium falciparum pfcrt and pfmdr1 polymorphisms after treatment with artesunate-amodiaquine fixed dose combination or artemether-lumefantrine in Liberia. 2016, Pubmed
Papakrivos, Functional characterization of the Plasmodium falciparum chloroquine-resistance transporter (PfCRT) in transformed Dictyostelium discoideum vesicles. 2012, Pubmed
Parker, Identification of a nucleoside/nucleobase transporter from Plasmodium falciparum, a novel target for anti-malarial chemotherapy. 2000, Pubmed , Xenbase
Patel, A Computational Approach towards the Understanding of Plasmodium falciparum Multidrug Resistance Protein 1. 2013, Pubmed
Peel, A strong association between mefloquine and halofantrine resistance and amplification, overexpression, and mutation in the P-glycoprotein gene homolog (pfmdr) of Plasmodium falciparum in vitro. 1994, Pubmed
Pleeter, Purified Plasmodium falciparum multi-drug resistance protein (PfMDR 1) binds a high affinity chloroquine analogue. 2010, Pubmed
Polli, Rational use of in vitro P-glycoprotein assays in drug discovery. 2001, Pubmed
Preechapornkul, Plasmodium falciparum pfmdr1 amplification, mefloquine resistance, and parasite fitness. 2009, Pubmed
Price, Mefloquine resistance in Plasmodium falciparum and increased pfmdr1 gene copy number. , Pubmed
Reed, Pgh1 modulates sensitivity and resistance to multiple antimalarials in Plasmodium falciparum. 2000, Pubmed
Reiling, Monitoring PfMDR1 transport in Plasmodium falciparum. 2015, Pubmed
Richards, Molecular Mechanisms for Drug Hypersensitivity Induced by the Malaria Parasite's Chloroquine Resistance Transporter. 2016, Pubmed , Xenbase
Rohrbach, Genetic linkage of pfmdr1 with food vacuolar solute import in Plasmodium falciparum. 2006, Pubmed
Ross, Emerging Southeast Asian PfCRT mutations confer Plasmodium falciparum resistance to the first-line antimalarial piperaquine. 2018, Pubmed
Ruetz, The pfmdr1 gene of Plasmodium falciparum confers cellular resistance to antimalarial drugs in yeast cells. 1996, Pubmed
Safa, Photoaffinity labeling of the multidrug-resistance-related P-glycoprotein with photoactive analogs of verapamil. 1988, Pubmed
Sali, Comparative protein modelling by satisfaction of spatial restraints. 1993, Pubmed
Saliba, Sodium-dependent uptake of inorganic phosphate by the intracellular malaria parasite. 2006, Pubmed , Xenbase
Sanchez, Polymorphisms within PfMDR1 alter the substrate specificity for anti-malarial drugs in Plasmodium falciparum. 2008, Pubmed , Xenbase
Sanchez, Genetic linkage analyses redefine the roles of PfCRT and PfMDR1 in drug accumulation and susceptibility in Plasmodium falciparum. 2011, Pubmed
Schneider, NIH Image to ImageJ: 25 years of image analysis. 2012, Pubmed
Schultz, Housing and husbandry of Xenopus for oocyte production. 2003, Pubmed , Xenbase
Senarathna, The Interactions of P-Glycoprotein with Antimalarial Drugs, Including Substrate Affinity, Inhibition and Regulation. 2016, Pubmed
Shafik, The natural function of the malaria parasite's chloroquine resistance transporter. 2020, Pubmed , Xenbase
Shalinsky, Regulation of initial vinblastine influx by P-glycoprotein. 1993, Pubmed
Shen, Statistical potential for assessment and prediction of protein structures. 2006, Pubmed
Sidhu, Chloroquine resistance in Plasmodium falciparum malaria parasites conferred by pfcrt mutations. 2002, Pubmed
Sidhu, pfmdr1 mutations contribute to quinine resistance and enhance mefloquine and artemisinin sensitivity in Plasmodium falciparum. 2005, Pubmed
Sidhu, Decreasing pfmdr1 copy number in plasmodium falciparum malaria heightens susceptibility to mefloquine, lumefantrine, halofantrine, quinine, and artemisinin. 2006, Pubmed
Sisowath, In vivo selection of Plasmodium falciparum parasites carrying the chloroquine-susceptible pfcrt K76 allele after treatment with artemether-lumefantrine in Africa. 2009, Pubmed
Sisowath, In vivo selection of Plasmodium falciparum pfmdr1 86N coding alleles by artemether-lumefantrine (Coartem). 2005, Pubmed
Smilkstein, Simple and inexpensive fluorescence-based technique for high-throughput antimalarial drug screening. 2004, Pubmed
Solomonov, Crystal nucleation, growth, and morphology of the synthetic malaria pigment beta-hematin and the effect thereon by quinoline additives: the malaria pigment as a target of various antimalarial drugs. 2007, Pubmed
Sondo, Artesunate-Amodiaquine and Artemether-Lumefantrine Therapies and Selection of Pfcrt and Pfmdr1 Alleles in Nanoro, Burkina Faso. 2016, Pubmed
Spry, Pantothenamides are potent, on-target inhibitors of Plasmodium falciparum growth when serum pantetheinase is inactivated. 2013, Pubmed
Sullivan, On the molecular mechanism of chloroquine's antimalarial action. 1996, Pubmed
Summers, Diverse mutational pathways converge on saturable chloroquine transport via the malaria parasite's chloroquine resistance transporter. 2014, Pubmed , Xenbase
Summers, Know your enemy: understanding the role of PfCRT in drug resistance could lead to new antimalarial tactics. 2012, Pubmed
Summers, Functional characteristics of the malaria parasite's "chloroquine resistance transporter": implications for chemotherapy. 2010, Pubmed , Xenbase
Suzuki, Possible involvement of cationic-drug sensitive transport systems in the blood-to-brain influx and brain-to-blood efflux of amantadine across the blood-brain barrier. 2015, Pubmed
Sá, Geographic patterns of Plasmodium falciparum drug resistance distinguished by differential responses to amodiaquine and chloroquine. 2009, Pubmed
Taylor, Accumulation of free amino acids in growing Xenopus laevis oocytes. 1987, Pubmed , Xenbase
Thompson, CLUSTAL W: improving the sensitivity of progressive multiple sequence alignment through sequence weighting, position-specific gap penalties and weight matrix choice. 1994, Pubmed
Twentyman, Resistance modification by PSC-833, a novel non-immunosuppressive cyclosporin [corrected]. 1991, Pubmed
Urbatsch, P-glycoprotein is stably inhibited by vanadate-induced trapping of nucleotide at a single catalytic site. 1995, Pubmed
Urbatsch, Mutations in either nucleotide-binding site of P-glycoprotein (Mdr3) prevent vanadate trapping of nucleotide at both sites. 1998, Pubmed
Urbatsch, Investigation of the role of glutamine-471 and glutamine-1114 in the two catalytic sites of P-glycoprotein. 2000, Pubmed
Valderramos, Identification of a mutant PfCRT-mediated chloroquine tolerance phenotype in Plasmodium falciparum. 2010, Pubmed
Van Tyne, Identification and functional validation of the novel antimalarial resistance locus PF10_0355 in Plasmodium falciparum. 2011, Pubmed
Vanommeslaeghe, CHARMM general force field: A force field for drug-like molecules compatible with the CHARMM all-atom additive biological force fields. 2010, Pubmed
Vanommeslaeghe, Automation of the CHARMM General Force Field (CGenFF) II: assignment of bonded parameters and partial atomic charges. 2012, Pubmed
Vanommeslaeghe, Automation of the CHARMM General Force Field (CGenFF) I: bond perception and atom typing. 2012, Pubmed
Veiga, Globally prevalent PfMDR1 mutations modulate Plasmodium falciparum susceptibility to artemisinin-based combination therapies. 2016, Pubmed
Vermaas, TopoGromacs: Automated Topology Conversion from CHARMM to GROMACS within VMD. 2016, Pubmed
Volkman, Functional complementation of the ste6 gene of Saccharomyces cerevisiae with the pfmdr1 gene of Plasmodium falciparum. 1995, Pubmed
Windle, Evidence for linkage of pfmdr1, pfcrt, and pfk13 polymorphisms to lumefantrine and mefloquine susceptibilities in a Plasmodium falciparum cross. 2020, Pubmed
Wong, Mefloquine targets the Plasmodium falciparum 80S ribosome to inhibit protein synthesis. 2017, Pubmed
Wurtz, Role of Pfmdr1 in in vitro Plasmodium falciparum susceptibility to chloroquine, quinine, monodesethylamodiaquine, mefloquine, lumefantrine, and dihydroartemisinin. 2014, Pubmed
Yeka, Artesunate/Amodiaquine Versus Artemether/Lumefantrine for the Treatment of Uncomplicated Malaria in Uganda: A Randomized Trial. 2016, Pubmed
Yuan, Chemical genomic profiling for antimalarial therapies, response signatures, and molecular targets. 2011, Pubmed
Zhang, Uncovering the essential genes of the human malaria parasite Plasmodium falciparum by saturation mutagenesis. 2018, Pubmed
Zhang, Lysis of malarial parasites and erythrocytes by ferriprotoporphyrin IX-chloroquine and the inhibition of this effect by proteins. 1987, Pubmed
Zhang, Characterization of a Dopamine Transporter and Its Splice Variant Reveals Novel Features of Dopaminergic Regulation in the Honey Bee. 2019, Pubmed , Xenbase
Zolnerciks, Evidence for a Sav1866-like architecture for the human multidrug transporter P-glycoprotein. 2007, Pubmed
Zolnerciks, The Q loops of the human multidrug resistance transporter ABCB1 are necessary to couple drug binding to the ATP catalytic cycle. 2014, Pubmed
van Es, Expression of the plasmodial pfmdr1 gene in mammalian cells is associated with increased susceptibility to chloroquine. 1994, Pubmed , Xenbase
van Schalkwyk, Verapamil-Sensitive Transport of Quinacrine and Methylene Blue via the Plasmodium falciparum Chloroquine Resistance Transporter Reduces the Parasite's Susceptibility to these Tricyclic Drugs. 2016, Pubmed , Xenbase
von Heijne, Control of topology and mode of assembly of a polytopic membrane protein by positively charged residues. 1989, Pubmed
von Heijne, Membrane-protein topology. 2006, Pubmed