Know your enemy: understanding the role of PfCRT in drug resistance could lead to new antimalarial tactics

Summers, Robert L.; Nash, Megan N.; Martin, R. L.

doi:10.1007/s00018-011-0906-0

Cited by 65 publications

(101 citation statements)

References 225 publications

(379 reference statements)

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“…The activity of the 1,2,4-oxadiazole series mirrored that of chloroquine rather than that of the DHFR inhibitors pyrimethamine and cycloguanil, with a 60-fold or greater increase in activity against pfcrt wild-type strain HL1212 than pfcrt mutant HL1210 (Table 3). These results suggest that mutated PfCRT might play a direct role in P. falciparum resistance to the 1,2,4-oxadiazole series and, by extension, that the mode of action of these compounds could reside in the digestive vacuole, from which mutant forms of the PfCRT transmembrane transporter are postulated to exclude chloroquine in resistant parasites (32,33).…”

Section: Genotypic Validation Of Selected P Falciparum Strainsmentioning

confidence: 91%

Identification and Deconvolution of Cross-Resistance Signals from Antimalarial Compounds Using Multidrug-Resistant Plasmodium falciparum Strains

Chugh

Scheurer

Sax

et al. 2015

Antimicrob Agents Chemother

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h Plasmodium falciparum, the most deadly agent of malaria, displays a wide variety of resistance mechanisms in the field. The ability of antimalarial compounds in development to overcome these must therefore be carefully evaluated to ensure uncompromised activity against real-life parasites. We report here on the selection and phenotypic as well as genotypic characterization of a panel of sensitive and multidrug-resistant P. falciparum strains that can be used to optimally identify and deconvolute the cross-resistance signals from an extended panel of investigational antimalarials. As a case study, the effectiveness of the selected panel of strains was demonstrated using the 1,2,4-oxadiazole series, a newly identified antimalarial series of compounds with in vitro activity against P. falciparum at nanomolar concentrations. This series of compounds was to be found inactive against several multidrug-resistant strains, and the deconvolution of this signal implicated pfcrt, the genetic determinant of chloroquine resistance. Targeted mode-of-action studies further suggested that this new chemical series might act as falcipain 2 inhibitors, substantiating the suggestion that these compounds have a site of action similar to that of chloroquine but a distinct mode of action. New antimalarials must overcome existing resistance and, ideally, prevent its de novo appearance. The panel of strains reported here, which includes recently collected as well as standard laboratory-adapted field isolates, is able to efficiently detect and precisely characterize cross-resistance and, as such, can contribute to the faster development of new, effective antimalarial drugs.

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Section: Genotypic Validation Of Selected P Falciparum Strainsmentioning

confidence: 91%

Identification and Deconvolution of Cross-Resistance Signals from Antimalarial Compounds Using Multidrug-Resistant Plasmodium falciparum Strains

Chugh

Scheurer

Sax

et al. 2015

Antimicrob Agents Chemother

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“…Resistance to CQ is attributed primarily to mutations in the Plasmodium falciparum chloroquine resistance transporter (PfCRT), an integral membrane protein localized to the DV, and is associated with a significant reduction in CQ accumulation within the DV (9)(10)(11)(12). Mutations in PfCRT can also modulate the parasite's susceptibility to other current antimalarial drugs (13,14). We recently established a robust system for the functional characterization of PfCRT in Xenopus laevis oocytes (15).…”

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confidence: 99%

“…1A) have distinct PfCRT haplotypes. These haplotypes all contain a mutation at position 76-the replacement of the positively-charged lysine (K) with an uncharged residue, usually threonine (T)-but are otherwise diverse, containing at least 4 and up to 10 mutations (13). Here, we used the Xenopus oocyte system to determine whether these PfCRT proteins also mediate the saturable transport of CQ and, if so, to ascertain the number of mutations (and the order of addition) required to confer CQ transport activity upon PfCRT.…”

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confidence: 99%

Diverse mutational pathways converge on saturable chloroquine transport via the malaria parasite’s chloroquine resistance transporter

Summers

Dave

Dolstra

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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123

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Mutations in the chloroquine resistance transporter (PfCRT) are the primary determinant of chloroquine (CQ) resistance in the malaria parasite Plasmodium falciparum. A number of distinct PfCRT haplotypes, containing between 4 and 10 mutations, have given rise to CQ resistance in different parts of the world. Here we present a detailed molecular analysis of the number of mutations (and the order of addition) required to confer CQ transport activity upon the PfCRT as well as a kinetic characterization of diverse forms of PfCRT. We measured the ability of more than 100 variants of PfCRT to transport CQ when expressed at the surface of Xenopus laevis oocytes. Multiple mutational pathways led to saturable CQ transport via PfCRT, but these could be separated into two main lineages. Moreover, the attainment of full activity followed a rigid process in which mutations had to be added in a specific order to avoid reductions in CQ transport activity. A minimum of two mutations sufficed for (low) CQ transport activity, and as few as four conferred full activity. The finding that diverse PfCRT variants are all limited in their capacity to transport CQ suggests that resistance could be overcome by reoptimizing the CQ dosage.drug resistance | evolutionary biochemistry | Xenopus oocytes

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“…This finding is consistent with previous observations of resistance-reversers displaying modest but significant levels of intrinsic antiplasmodial activity against CQR strains 26 (while exerting little or no effect in CQS strains) and provides further support for the idea that PfCRT CQR could be viewed as a drug target. 8 None of the test compounds affected the IC 50 of CQ against CQS C2 GC03 parasites (Table 2; P > 0.2). However, VP, CP, and the four CP analogues each caused a significant decrease in the IC 50 of CQ against the CQR lines (Table 2; P < 0.01).…”

Section: 11mentioning

confidence: 92%

“…7 Whether these effects are due to PfCRT-mediated drug efflux and/or the inhibition of the transporter's normal function (which is essential for the survival of the parasite, but currently unknown) remains unclear. 8 A better understanding of the interactions between PfCRT CQR and its substrates and inhibitors could inform the development of new antimalarial chemotherapies and strategies.…”

mentioning

confidence: 99%

Chlorpheniramine Analogues Reverse Chloroquine Resistance inPlasmodium falciparumby Inhibiting PfCRT

Deane

Summers

Lehane

et al. 2014

ACS Med. Chem. Lett.

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ABSTRACT:The emergence and spread of malaria parasites that are resistant to chloroquine (CQ) has been a disaster for world health. The antihistamine chlorpheniramine (CP) partially resensitizes CQ-resistant (CQR) parasites to CQ but possesses little intrinsic antiplasmodial activity. Mutations in the parasite's CQ resistance transporter (PfCRT) confer resistance to CQ by enabling the protein to transport the drug away from its site of action, and it is thought that resistance-reversers such as CP exert their effect by blocking this CQ transport activity. Here, a series of new structural analogues and homologues of CP have been synthesized. We show that these compounds (along with other in vitro CQ resistance-reversers) inhibit the transport of CQ via a resistanceconferring form of PfCRT expressed in Xenopus laevis oocytes. Furthermore, the level of PfCRT-inhibition was found to correlate well with both the restoration of CQ accumulation and the level of CQ resensitization in CQR parasites.KEYWORDS: Malaria parasite, chloroquine resistance, chemosensitization, chlorpheniramine, PfCRT, Xenopus oocytes T he malaria parasite Plasmodium falciparum has proven largely refractory to the vaccine approaches trialled to date and reliance on chemotherapy is under serious threat with the recent emergence of parasites that are resistant to the current mainstay of malaria treatment (the artemisinin-based combination therapies).1 As a result, malaria remains a global health problem; there are around 225 million clinical cases and over 1.2 million deaths each year, 2 and the disease also imposes considerable socio-economic burdens upon afflicted countries. Chloroquine (CQ, Figure 1A) was a cheap, safe, and efficacious treatment for the disease until the eventual emergence and spread of resistant parasites. Resistance to CQ is caused primarily by mutations in the P. falciparum CQ resistance transporter, PfCRT.3 Within the P. falciparum-infected erythrocyte, PfCRT is found in the membrane of the parasite's digestive vacuole 4 (DV; pH 5−5.5); the organelle in which CQ accumulates and exerts its antimalarial effect. Mutations in PfCRT that confer CQ resistance result in a marked reduction in the accumulation of CQ within the DV. Using the Xenopus laevis oocyte expression system, a CQ resistance-conferring form of PfCRT (PfCRT CQR ) was shown to transport CQ, whereas the wild-type form found in CQ-sensitive (CQS) parasites (PfCRT CQS ) lacked this ability. 5Mutations in PfCRT have been associated with decreases or increases in the parasite's susceptibility to other antimalarials, 6 and the transporter has been shown to be one of the key determinants of the parasite's response to a diverse set of novel antiplasmodial compounds. 7 Whether these effects are due to PfCRT-mediated drug efflux and/or the inhibition of the transporter's normal function (which is essential for the survival of the parasite, but currently unknown) remains unclear.8 A better understanding of the interactions between PfCRT CQR and its substrates and inhibitors ...

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Know your enemy: understanding the role of PfCRT in drug resistance could lead to new antimalarial tactics

Cited by 65 publications

References 225 publications

Identification and Deconvolution of Cross-Resistance Signals from Antimalarial Compounds Using Multidrug-Resistant Plasmodium falciparum Strains

Identification and Deconvolution of Cross-Resistance Signals from Antimalarial Compounds Using Multidrug-Resistant Plasmodium falciparum Strains

Diverse mutational pathways converge on saturable chloroquine transport via the malaria parasite’s chloroquine resistance transporter

Chlorpheniramine Analogues Reverse Chloroquine Resistance inPlasmodium falciparumby Inhibiting PfCRT

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