Conservation of a novel vacuolar transporter in Plasmodium
species and its central role in chloroquine resistance of
P. falciparum
Jane MR Carlton*, David A Fidock†, Abdoulaye Djimd釧¶,
Christopher V Plowe§ and Thomas E Wellems#
Chloroquine resistance in Plasmodium falciparum has recently 75–90 million cases of non-fatal malaria annually [2•], has been shown to result from mutations in the novel vacuolar recently become an area of increasing concern. transporter PfCRT. Field studies have demonstrated theimportance of these mutations in clinical resistance. Although Here, we review recent progress in deciphering CQ resis- a pfcrt homolog has been identified in Plasmodium vivax, there tance in malaria parasites. These developments include is no association between in vivo chloroquine resistance and the identification of mutations in a vacuolar transporter as codon mutations in the P. vivax gene. [AU:OK?] This is
the basis for CQ resistance in P. falciparum and the finding consistent with lines of evidence that suggest alternative of absolute selection of these mutations in clinical cases of mechanisms of chloroquine resistance among various malaria CQ treatment failure. These results are generating new hypotheses on the molecular mechanism of CQ resistance.
Investigations into CQ resistance in other malaria parasites Addresses
also provide evidence that mechanisms of resistance differ *National Center for Biotechnology Research, National Library of Medicine, National Institutes of Health, Building 45, 45 Center Drive,Bethesda, MD 20892-6510, USA Three distinct evolutionary clades of malaria
†Department of Microbiology and Immunology, Albert Einstein Collegeof Medicine of Yeshiva University, 1300 Morris Park Avenue, parasites
Malaria parasites are classified in the phylum ‡Malaria Research and Training Center, Faculty of Medicine, Apicomplexa, a large protist group consisting of almost Pharmacy and Dentistry, University of Mali, PO Box 1805, Bamako, Mali 5000 species. All apicomplexans are parasites and contain §Malaria Section, Center for Vaccine Development, University ofMaryland School of Medicine, 685 West Baltimore Street, HSF 480, an organellar structure, the apical complex, involved in host cell invasion. Within the phylum, the genus #Malaria Genetics Section, Laboratory of Parasitic Diseases, National Plasmodium includes ~200 known malaria species that par- Institute of Allergy and Infectious Diseases, National Institutes of asitize birds, reptiles, and mammals. The genus divides Health, Building 4, 4 Center Drive, MSC 0425, Bethesda, into three distinct and highly divergent evolutionary clades MD 20892-0425, USA; email: [email protected] [3,4]: the first includes P. falciparum and a closely related Current Opinion in Microbiology 2001, 4:XXX–XXX
parasite of apes, P. reichenowi; the second clade consists of P. vivax and monkey malaria species including P. knowlesi; 2001 Elsevier Science Ltd. All rights reserved.
and finally, the third clade includes rodent malaria speciessuch as P. berghei and P. chabaudi. [AU:OK?] Major differ- Abbreviations

ences in host specificity and disease manifestation occur P. falciparum chloroquine resistance transporter among species of these clades, as do wide variations ingenome composition and codon usage [5,6]. Because of the Introduction
difficulties of working with P. falciparum in the laboratory, [AUQ1: I have shortened the title slightly to make it more there has been support for the use of many of these relat- concise. I understand you want to emphasis the fact that ed species as models, for example, in studies of host cell the transporter plays a role in CQ resistance in P. falci- invasion [7], malaria vaccine development [8], and anti- parum and not P. vivax but I think this is covered in the malarial drug resistance (reviewed in [9•]).
abstract and it’s better THIS IS A PROOF The mechanism of chloroquine action
In human erythrocytes, P. falciparum supports its growth by
Malaria parasite resistance to the drug chloroquine (CQ) taking up host cell cytoplasm in an acidic digestive food poses a severe and increasing public health threat. This vacuole [10]. Toxic heme, in its hematin (µ-oxodimer) inexpensive and widely consumed drug has been the main [AU:OK?] form, is released in the vacuole by hemoglobin line of attack against the parasite, and its increasing failure digestion and crystallized into innocuous hemozoin, or accompanies a return of malaria-related morbidity and malaria pigment. CQ is proposed to interfere with this mortality levels not seen for decades [1•]. The problem is process by complexing with hematin [11,12], thereby cre- most acute in Plasmodium falciparum malaria, the species ating toxic complexes that cause parasite death. The actual responsible for the most severe form of the disease. The mechanism of toxicity [AUQ2: Is this toxicity of hematin or emergence of CQ-resistant P. vivax, a species that causes the CQ—hematin complex? Or both?] is still subject to Host–microbe interactions: parasites
debate, but hematin can increase membrane permeability [AU: New paragraph OK?] Of the 15 CQ-sensitive lines leading to cell lysis [13] and is known to inhibit parasite tested, [AU: What strains are being referred to here? Are enzymes [14]. Recent studies on the crystal structure of β- they from the original genetic cross (ref 25, 26) or are they hematin, a synthetic analog of malaria pigment, indicate clinical strains from around the world (ref 29)?] all but one that CQ is ‘chemiabsorbed’ onto hemozoin, capping crys- carried the pfcrt sequence of the CQ-sensitive HB3 parent.
tal growth that is required for hematin sequestration [15••].
The one exception, 106/1, was found to encode all of the [AUQ3: Please clarify: according to this model, CQ doesn’t PfCRT mutations associated with CQ resistance except form a complex with hematin but with hemozoin, thereby the amino acid mutation at position 76, supporting a cen- preventing binding/crystallization of hematin to hemo- tral role for this residue in CQ resistance. Episomal transformation of 106/1 and two additional CQ-sensitivestrains with constructs expressing pfcrt from CQ-resistant The physiologic basis of chloroquine resistance
parasites resulted in transformed lines that grew at CQ A consistent characteristic of CQ-resistant P. falciparum concentrations tolerated only by naturally CQ-resistant parasites in vitro is their reduced accumulation of CQ in strains. Stepwise CQ pressure on the transformed 106/1 the digestive vacuole relative to accumulation of the drug parasites ultimately resulted in loss of the transfected in CQ-sensitive parasites [16–18]. Another characteristic of DNA and selection of a highly CQ-resistant line that had CQ-resistant parasites is their chemosensitization to CQ by undergone a single K76→I point mutation, providing addi- structurally diverse agents that include verapamil, a Ca2+ tional evidence for the central role of position 76 in CQ channel blocker [19]. [AUQ4: Does this mean that they became sensitive to CQ after exposure to verapamil?]Proposals to explain these features of resistant parasites The K76→T mutation has not been observed in the have included alterations in the intraerythrocytic parasite absence of mutations at other positions in PfCRT, that affect CQ uptake or efflux at the cytoplasmic mem- although the reverse situation has been documented (i.e.
brane, or change H+ or CQ concentration in the digestive mutations at other positions can occur without the pres- ence of K76→T, as in the 106/1 line). It is plausible thatmutations at other positions are required to maintain criti- Identification of the genetic determinant of
cal functional properties of the molecule in the presence of chloroquine resistance in P. falciparum
the K76→T change. The mutation A220→S may fulfill a To investigate the genetic basis of P. falciparum CQ resis- particular requirement in this regard, since this mutation tance, Wellems et al. [25] established a genetic cross has consistently been found to accompany K76→T in CQ- between a CQ-sensitive clone, HB3 from Honduras, and a resistant parasites from the different New World and Old CQ-resistant clone, Dd2 from Indochina. Linkage analysis World foci. The suggestion that K76→T cannot occur in of 16 independent progeny showed that the verapamil- the absence of other PfCRT point mutations may also reversible CQ-resistant phenotype segregated as a single explain the slow genesis of CQ resistance in the field as Mendelian trait that mapped to chromosome 7 [26].
well as the difficulties that have been experienced with Examination of further progeny localized this CQ resis- attempts to select CQ resistance in the laboratory. Indeed, tance determinant to a 36 kb segment on the chromosome the CQ-resistant line containing the K76→I point muta- [27]. A gene (cg2) initially identified as a probable CQ tion reported by Fidock et al. [29••] was obtained from the resistance candidate was ruled out by allelic-exchange CQ-sensitive 106/1 line that already contained six PfCRT mutations at other positions seen [AU:OK?] in SoutheastAsian and African parasites. Recently, Fidock et al. [29••] identified the pfcrt (P. falci-parum chloroquine resistance transporter) gene near cg2 in Characterization of the protein product of pfcrt
the 36 kb segment. In the CQ-resistant Dd2 parent, eight The protein product of pfcrt, PfCRT, belongs to a previ- point mutations (M74→I, N75→E, K76→T, A220→S, ously uncharacterized family of putative transporters, with Q271→E, N326→S, I356→T, and R371→I) were found in 10 transmembrane segments (Figure 1) but few other rec- ognizable features [31••]. Localization studies place it at pfcrt gene. Seven of these eight mutations were detected the membrane of the parasite’s digestive vacuole [29••].
in 15 CQ-resistant parasite strains collected from diverse Moreover, PfCRT mutations are associated with a decrease regions of Asia and Africa (the remaining mutation (acidification) in the pH of the digestive vacuole of CQ- I356→T was detected in some strains). CQ-resistant resistant parasites by some 0.3–0.5 units compared with strains from South America were found to harbor distinct the pH of the digestive vacuole of CQ-sensitive parasites sets of PfCRT mutations but shared the K76→T and [29••]. This result might appear paradoxical given that vac- A220→S mutations in common with the Asian and African uolar acidification predicts increased CQ accumulation in strains. These findings suggested that PfCRT mutations the digestive vacuole on the basis of Henderson- arose separately in association with CQ resistance in South Hasselbach equilibrium [18,32], whereas CQ-resistant America and Asia/Africa, a result consistent with the inde- parasites are known to exhibit reduced CQ accumulation.
pendent genesis of CQ resistance in these regions [30]. CQ accumulation in the digestive vacuole, however, is dri- A novel vacuolar transporter in Plasmodium species Carlton et al.
The schematic structure of the proteinproduct of the pfcrt gene, PfCRT, showing theten predicted transmembrane domains. Thepositions of the mutations identified from theanalysis of over forty geographically diverse isolates are indicated by filled circles.
[AUQ17: In the text it says there are eight
point mutations but there are ten shown
here. Please clarify.]
The K (lysine) to T
(threonine) change at position 76 (indicated
by the arrow) is critical to CQ resistance in
P. falciparum.
ven to a large extent by binding of CQ to hematin [AUQ5: mutation in vivo by CQ treatment. [AUQ10: I don’t under- See AUQ3] [17,22], and recent data have shown a steep stand why this demonstrates a selection for the K76→T pH-dependence in the conversion of soluble hematin- mutation by CQ treatment. 41% of the infections had the receptor [AUQ6: What is this receptor?] to hemozoin K76→T mutation (i.e. CQ resistant) yet only 14% of the [12,23••]. These results have suggested a model whereby infections were not successfully treated with CQ. Is the alterations in PfCRT could cause increased acidification of take home message the fact that 100% of these failed treat- the digestive vacuole, resulting in reduced levels of acces- ments had the mutation?] The presence of K76→T at the sible hematin with a consequent reduction in time of treatment was strongly associated with subsequent CQ—hematin complexes [AUQ7: See AUQ3] and toxicity. failure of CQ treatment [37••]. Moreover, the ability ofindividuals [AU:OK?] to clear infections carrying the The above theory is, however, difficult to reconcile with K76→T mutation in this highly endemic area was strongly the reported effectiveness of CQ analogs with substituted associated with increasing age. These data suggest that or shortened side chains against CQ-resistant parasites immunity against P. falciparum acquired with age con- [33–36]. Such findings support a second theory: that tributed to successful treatment outcomes of some PfCRT mutations alter CQ flux across the digestive vac- individuals harboring parasites with the K76→T mutation uole membrane. The predicted structure of PfCRT places amino acid substitutions K76→T and K76→I within atransmembrane region that may be involved in transport of [AUQ11: New paragraph OK?] Although it is possible that diprotic [AUQ8: What does “diprotic” mean?] CQ or parasite genetic factors other than pfcrt may modulate another charged substance. Both of these changes involve in vitro or in vivo levels of CQ resistance and that host fac- loss of a positive charge at position 76 in the molecule.
tors other than acquired immunity may affect the clearanceof CQ-resistant parasites, such factors have yet to be clear- PfCRT mutations and their association with
ly demonstrated and understood in the context of failure of chloroquine treatment
treatment failures. The identification of PfCRT K76→T mutation as a key molecular marker of CQ resistance offers evidence that mutations in PfCRT were critical for CQ new opportunities for diagnosis and public health surveil- resistance in vivo [37••]. In this trial, CQ treatment lance of P. falciparum infections.
responses were followed in 469 cases of uncomplicated fal-ciparum malaria. CQ failed to treat 14% of these cases.
Effects of pfmdr1 and other secondary genes
[AU:OK?] In every case of treatment failure, the K76→T on chloroquine resistance levels
mutation, in concert with other PfCRT mutations, was Although the association of pfcrt alleles with CQ resistance exclusively present in the post-treatment infection. This in vitro and in vivo is evident, the roles of other genes, such compared with a baseline prevalence of 41% of infections as the multidrug resistance gene pfmdr1 [38,39], are less carrying the K76→T mutation in a random sample of 116 clear. Impetus for the isolation of pfmdr1 came from the patients, [AUQ9: Were these patients from the CQ effica- finding that verapamil, which inhibits P-glycoprotein cy trail?] demonstrating absolute selection for this mediated multidrug resistance in mammalian tumor cells, Host–microbe interactions: parasites
Evidence for another chloroquine resistance
mechanism in P. vivax
Since its introduction, CQ has been the drug of choice for
eliminating not only P. falciparum blood-stage parasites but also infections caused by the three other human parasites P. ovale, P. malariae and P. vivax. To date, no reports of CQ- resistant P. ovale and P. malariae have been confirmed [46].
CQ-resistant P. vivax, however, was first reported from Papua New Guinea in 1989 [47] and since then has been an increasing problem in other countries.
To investigate whether similar mechanisms of CQ resis- Depiction of the factors that contribute to the failure of chloroquinetreatment (clinical resistance) in uncomplicated P. falciparum malaria.
tance exist in P. falciparum and P. vivax, pfcrt homologs Mutations in pfcrt confer the CQ resistance (CQR) phenotype to were identified in P. vivax, as well as in other Plasmodium P. falciparum malaria parasites. In the presence of these mutations, species, and assessed for possible relationship with CQ immune status is a critical factor in therapeutic outcome.
resistance. Results from this study showed that pfcrt hashighly conserved homologs in all of the Plasmodium clades also chemosensitized CQ-resistant P. falciparum strains [31••]. Homologs of pfcrt from P. vivax, P. knowlesi and [19]. The pfmdr1gene encodes an ATP-dependent trans- P. berghei were sequenced, revealing the gene family to be membrane protein, Pgh-1, that has also been localized to highly conserved in composition and structure across all the parasite’s digestive vacuole [40]. Evidence from differ- three lineages. Regions of the orthologous P. vivax gene, ent studies has sometimes shown associations between CQ pvcg10, were sequenced from 20 geographically distinct resistance and pfmdr1 copy number [38] or mutations [41], laboratory lines and field isolates of P. vivax. No association most notably at position 86 in the protein where mutation between codon mutations in pvcg10 and in vivo CQ of an asparagine residue to tyrosine has frequently been response could be demonstrated, indicating that the mole- documented (N86→Y; ‘K1 allele’); however, many excep- cular events underlying CQ resistance in P. vivax differ tions to these associations have been established both from from those in P. falciparum [31••].
a genetic cross [25] and from field surveys (reviewed in[42•]). In this light, it is useful to consider laboratory models ofmalaria and ask what information they may provide of rel- Concomitant with mutant pfcrt selection in clinical cases of evance to the mechanisms of CQ resistance in human malaria, Djimdé et al. [37••] found an increase of the Pgh-1 malaria species. Although little can be said with regard to N86→Y mutation from a baseline prevalence of 50% to a P. vivax at this point, available data suggest that mecha- prevalence of 86% in cases of CQ treatment failure. A total nisms of CQ resistance in the rodent malaria parasites, of 30% of infections from the treatment failure group car- P. chabaudi and P. berghei [AU:OK?], have notable differ- ried the wild-type Pgh-1 N86 (16% as mixed parasite ences from the mechanism in P. falciparum. CQ-resistant populations with the N86 and Y86 codons). Furthermore, lines of P. chabaudi have been selected with relative ease in the presence of parasites with the mutant N86→Y in addi- the laboratory [48], in contrast to the difficulties in obtain- tion to the PfCRT K76→T mutation did not increase the ing CQ-resistant P. falciparum lines [49]. Quantitative trait relative risk of treatment failure when compared with mapping of progeny from crosses between CQ-resistant infections carrying only the PfCRT K76→T mutation and CQ-sensitive P. chabaudi clones produced evidence for before treatment. Prediction of CQ susceptibility in clini- a combined role of several genes on different chromo- cal cases of malaria was therefore not possible through somes in conferring CQ resistance [50], unlike the major monitoring of pfmdr1 genetic alterations. genetic locus identified in P. falciparum [26,27]. An unsta-ble form of CQ resistance in P. berghei has been associated [AUQ12: New paragraph OK?] Interestingly, recent allelic- with reduced malaria pigment formation [51], whereas showed that, although pfmdr1 mutations there are no obvious differences in the quantity of hemo- could not confer resistance to CQ-sensitive parasites, zoin in CQ-resistant and CQ-sensitive P. falciparum [52].
removal of three pfmdr1 mutations S1034→C, N1042→D,and D1246→Y from a CQ-resistant parasite modified the The fact that mechanisms of CQ resistance among differ- in vitro measures of resistance [43••]. Mutations in pfmdr1, ent Plasmodium species can vary has several implications.
and in other as yet undefined modulator genes, may thus Clearly, results from one species and studies that utilize represent secondary adaptations that enhance parasite fit- laboratory models of malaria should be extrapolated with ness in the presence of pfcrt mutations. Such adaptations care. In particular, similarity between Plasmodium species would be analogous to the compensatory alterations pro- in terms of conserved molecular mechanisms of drug duced in response to acquisition of central resistance response and resistance may depend on the class of anti- determinants shown in other microbial systems [44,45•].
malarial. For example, in contrast to CQ resistance, themolecular basis for pyrimethamine resistance, where a sin- A novel vacuolar transporter in Plasmodium species Carlton et al.
gle point mutation in the drug target dihydrofolate-reduc- McCutchan TF, Dame JB, Miller LH, Barnwell J: Evolutionary
relatedness of Plasmodium
species as determined by the
tase (dhfr) can render the parasite resistant, appears to be structure of DNA. Science 1984, 225:808-811.
a common mechanism in many malaria species ([9•,53] and Menard R, Sultan AA, Cortes C, Altszuler R, van Dijk MR, Janse CJ, references therein). Development of similar or divergent Waters AP, Nussenzweig RS, Nussenzweig V: Circumsporozoite
mechanisms of drug resistance among species may be protein is required for development of malaria sporozoites in
Nature 1997, 385:336-340.
influenced by the nature of the drug target, for example a Doolan DL, Hedstrom RC, Gardner MJ, Sedegah M, Wang H, readily mutable target such as dhfr as opposed to an Gramzinski RA, Margalith M, Hobart P, Hoffman SL: DNA vaccination
as an approach to malaria control: current status and strategies.
Curr Top Microbiol Immunol 1998, 226:37-56.
Conclusions and prospects for antimalarial
Carlton JMR, Hayton K, Cravo PVL, Walliker D: Of mice and malaria
mutants: unravelling the genetics of drug resistance using rodent
drug design
malaria models. Trends Parasitol 2001, in press. [AUQ14: Do you
How will understanding the molecular mechanism of CQ further details for this reference?]
A concise summary of the studies undertaken to determine the genetics of resistance help in the design of future effective antimalar- antimalarial drug resistance using rodent models of malaria. Such studies ial drugs? The CQ-resistance mechanism mediated by may be useful in understanding mechanisms of drug resistance among
[AU:OK?] malaria parasite species.
PfCRT appears to have a significant component of struc-tural specificity because it is less effective against CQ 10. Francis SE, Sullivan DJ, Goldberg DE: Hemoglobin metabolism in
the malaria parasite Plasmodium falciparum. Annu Rev Microbiol
analogs and other classes of molecules that act on malaria 1997, 51:97-123.
parasites through hematin-related toxicity. Structurally 11. Chou AC, Fitch CD: Ferriprotoporphyrin IX fulfills the criteria for
related 4-aminoquinolines and other hematin-targeting identification as the chloroquine receptor of malaria parasites.
drugs may therefore provide promising avenues for the Biochemistry 1980, 19:1543-1549.
development of new antimalarials active against CQ-resis- 12. Dorn A, Vippagunta SR, Matile H, Jaquet C, Vennerstrom JL, Ridley RG: An assessment of drug-haematin binding as a
mechanism for inhibition of haematin polymerisation by quinoline
Biochem Pharmacol 1998, 55:727-736.
And what of CQ action and resistance in P. vivax malaria? 13. Chou AC, Fitch CD: Mechanism of hemolysis induced by
The action of CQ on hematin is likely to be similar in ferriprotoporphyrin IX. J Clin Invest 1981, 68:672-677.
P. vivax, P. falciparum, and other species of malaria.
14. Vander Jagt DL, Hunsaker LA, Campos NM: Characterization of a
hemoglobin-degrading, low molecular weight protease from
Mechanisms of resistance, however, need not be geneti- Plasmodium falciparum. Mol Biochem Parasitol 1986, 18:389-400.
cally similar. In evolutionary terms, it may be hypothesized 15. Pagola S, Stephens PW, Bohle DS, Kosar AD, Madsen SK: The
that P. vivax and P. falciparum began with different sets of structure of malaria pigment β-haematin. Nature 2000,
genetic polymorphisms and produced alternative solutions 404:307-310.
A report describing the crystal structure of β-hematin, a synthetic analog of to CQ toxicity. Characterization and comparison of the dif- hemozoin. The molecules are shown to be present as dimers, which form ferent determinants of CQ resistance in P. falciparum and chains connected by hydrogen bonds. This structure agrees with a mecha-nism of chloroquine action whereby the drug is ‘chemiabsorbed’ onto crys- P. vivax will provide valuable information for the future 16. Bray PG, Howells RE, Ritchie GY, Ward SA: Rapid chloroquine
efflux phenotype in both chloroquine sensitive and chloroquine
References and recommended reading
resistant Plasmodium falciparum. A correlation of chloroquine
sensitivity with energy dependent drug accumulation.
Papers of particular interest, published within the annual period of review, Pharmacol 1992, 44:1317-1324.
Fitch CD: Plasmodium falciparum in owl monkeys: drug
resistance and chloroquine binding capacity. Science 1970,
Baird JK: Resurgent malaria at the millennium: control strategies
18. Yayon A, Cabantchik ZI, Ginsburg H: Identification of the acidic
in crisis. Drugs 2000, 59:719-743.
compartment of Plasmodium falciparum-infected human
A review documenting the factors that have contributed to the global resur- erythrocytes as the target of the antimalarial drug chloroquine.
gence of malaria. Resistance to chloroquine is identified as probably the sin- EMBO J 1984, 3:2695-2700.
19. Martin SK, Oduola AM, Milhous WK: Reversal of chloroquine
Mendis K, Sina B, Carter R: The neglected burden of Plasmodium
resistance in Plasmodium falciparum by verapamil. Science 1987,
vivax malaria. Am J Trop Med Hyg 2001, in press. [AUQ13: Do you
have further details for this review?]
A discussion of the nature of the current burden of P. vivax malaria across 20. Krogstad DJ, Gluzman IY, Kyle DE, Oduola AM, Martin SK, the world. The authors suggest that, as control measures eventually become Milhous WK, Schlesinger PH: Efflux of chloroquine from
more effective, the residual malaria burden is likely to become that of Plasmodium falciparum: mechanism of chloroquine resistance.
Science 1987, 238:1283-1285.
Waters AP, Higgins DG, McCutchan TF: Plasmodium falciparum
21. Geary TG, Divo AD, Jensen JB, Zangwill M, Ginsburg H: Kinetic
appears to have arisen as a result of lateral transfer between
modeling of the response of Plasmodium falciparum to
avian and human hosts. Proc Natl Acad Sci USA 1991,
chloroquine and its experimental testing in vitro. Implications for
mechanism of action of and resistance to the drug. Biochem
1990, 40:685-691.
Escalante AA, Ayala FJ: Phylogeny of the malarial genus
, derived from rRNA gene sequences. Proc Natl Acad
22. Bray PG, Mungthin M, Ridley RG, Ward SA: Access to hematin: the
Sci USA 1994, 91:11373-11377.
basis of chloroquine resistance. Mol Pharmacol 1998, 54:170-179.
Garnham PCC: Malaria Parasites And Other Haemosporidia. Oxford,UK: Blackwell Scientific Press; 1966.
Host–microbe interactions: parasites
23. Dzekunov SM, Ursos LM, Roepe PD: Digestive vacuolar pH of intact
38. Foote SJ, Thompson JK, Cowman AF, Kemp DJ: Amplification of the
intraerythrocytic P. falciparum either sensitive or resistant to
multi-drug resistance gene in some chloroquine-resistant isolates
chloroquine. Mol Biochem Parasitol 2000, 110:107-124.
of P. falciparum. Cell 1989, 57:921-930.
The first single-cell analysis of digestive vacuolar pH in chloroquine-resistantand chloroquine-sensitive strains.
39. Wilson CM, Serrano AE, Wasley A, Bogenschutz MP, Shankar AH, Wirth DF: Amplification of a gene related to mammalian mdr
24. Sanchez CP, Wunsch S, Lanzer M: Identification of a chloroquine
genes in drug-resistant Plasmodium falciparum. Science 1989,
importer in Plasmodium falciparum. Differences in import kinetics
are genetically linked with the chloroquine-resistant phenotype.
J Biol Chem
1997, 272:2652-2658.
40. Cowman AF, Karcz S, Galatis D, Culvenor JG: A P-glycoprotein
homologue of Plasmodium falciparum is localised on the
25. Wellems TE, Panton LJ, Gluzman IY, Rosario VE, Gwadz RW, digestive vacuole. J Cell Biol 1991, 113:1033-1042.
Walker-Jonah A, Krogstad DJ: Chloroquine-resistance not linked to
mdr-like genes in a Plasmodium falciparum
cross. Nature 1990,
41. Foote SJ, Kyle DE, Martin RK, Oduola AM, Forsyth K, Kemp DJ, 345:253-255.
Cowman AF: Several alleles of the multidrug-resistance gene are
closely linked to chloroquine resistance in Plasmodium

26. Wellems TE, Walker-Jonah A, Panton LJ: Genetic mapping of the
falciparum. Nature 1990, 345:255-258.
chloroquine-resistance locus on Plasmodium falciparum
chromosome 7. Proc Natl Acad Sci USA 1991, 88:3382-3386.
42. Dorsey G, Fidock DA, Wellems TE, Rosenthal PJ: Mechanisms of
quinoline resistance. In Antimicrobial Chemotherapy: Mechanisms
Su XZ, Kirkman LA, Fujioka H, Wellems TE: Complex
of Action, Resistance, and New Directions in Drug Discovery. 2001, polymorphisms in an ~330kD protein are linked to chloroquine-
in press. [AUQ16: Do you have further details for this book — i.e.
resistant P. falciparum in south-east Asia and Africa. Cell 1997,
editors, publishers and place of publication.]
An extensive review of the current understanding and controversies regard-ing the mechanisms of resistance to the quinoline antimalarials in P. falci- 28. Fidock DA, Nomura T, Cooper RA, Su XZ, Talley AK, Wellems TE: Allelic modifications of the cg2 and cg1 genes do not alter the
chloroquine response of drug-resistant Plasmodium falciparum
43. Reed MB, Saliba KJ, Caruana SR, Kirk K, Cowman AF: Pgh1
Mol Biochem Parasitol 2000, 110:1-10.
modulates sensitivity and resistance to multiple antimalarials in
This paper reports the allelic-exchange studies that ruled out a principal role Plasmodium falciparum. Nature 2000, 403:906-909.
for the candidate gene cg2 in P. falciparum chloroquine resistance. A paper describing the role of 7G8-type mutations in Pgh-1 in resistance tomefloquine, quinine, and halofantrine. The same mutations are shown to 29. Fidock DA, Nomura T, Talley AK, Cooper RA, Dzekunov SM, modulate parasite resistance toward chloroquine and artemisinin.
Ferdig MT, Ursos LMB, Sidhu ABS, Naudé B, Deitsch KW et al.:
Mutations in the P. falciparum digestive vacuole transmembrane
44. Wilson M, DeRisi J, Kristensen HH, Imboden P, Rane S, Brown PO, protein PfCRT and evidence for their role in chloroquine
Schoolnik GK: Exploring drug-induced alterations in gene
resistance. Mol Cell 2000, 6:861-871.
expression in Mycobacterium tuberculosis by microarray
This paper presents the identification and characterization of the P. falci- hybridization. Proc Natl Acad Sci USA 1999, 96:12833-12838.
parum chloroquine resistance gene pfcrt and description of the mutant pfcrtalleles found in various geographically diverse isolates. Genetic transforma- 45. Levin BR, Perrot V, Walker N: Compensatory mutations, antibiotic
tions, association of the mutant PfCRT protein with changes in the pH of the resistance and the population genetics of adaptive evolution in
digestive vacuole, and the implications for a mechanism of resistance are bacteria. Genetics 2000, 154:985-997.
A report showing that drug-resistant microorganisms can reduce the physi-ological cost of resistance associated with resistance-conferring mutations 30. Payne D: Spread of chloroquine resistance in Plasmodium
falciparum. Parasitol Today 1987, 3:241-246.
46. Peters W: Drug resistance in malaria parasites of animals and
31. Nomura T, Carlton JMR, Baird JK, Del Portillo HA, Fryauff DJ, man. Adv Parasitol 1998, 41:1-62.
Rathore D, Fidock DA, Su XZ, Collins WE, McCutchan TF et :
Evidence for different mechanisms of chloroquine resistance in
Rieckmann KH, Davies DR, Hutton DC: Plasmodium vivax
two Plasmodium species that cause human malaria. J Infect Dis
resistance to chloroquine. Lancet 1989, ii:1183-1184.
2001, in press. [AUQ15: DO you have further details for this
48. Rosario VE: Genetics of chloroquine resistance in malaria
parasites. Nature 1976, 261:585-586.
This report describes the identification of pfcrt homologs from P. vivax,P. knowlesi and P. berghei. A survey of patient isolates and monkey-adapt- 49. Lim AS, Cowman AF: Plasmodium falciparum: chloroquine
ed lines of P. vivax showed no association between in vivo chloroquine resis- selection of a cloned line and DNA rearrangements. Exp Parasitol
tance and codon mutations in the P. vivax gene. 1996, 83:283-294.
32. Krogstad DJ, Schlesinger PH, Gluzman IY: Antimalarials increase
50. Carlton J, Mackinnon M, Walliker D: A chloroquine resistance locus
vesicle pH in Plasmodium falciparum. J Cell Biol 1985,
in the rodent malaria parasite Plasmodium chabaudi. Mol Biochem
Parasitol 1998, 93:57-72.
33. Ridley RG, Hofheinz W, Matile H, Jaquet C, Dorn A, Masciadri R, 51. Peters W: Morphological and physiological variations in
Jolidon S, Richter WF, Guenzi A, Girometta MA et al.: chloroquine-resistant Plasmodium berghei, Vincke and Lips, 1948.
4-aminoquinoline analogs of chloroquine with shortened side
Ann Soc Belg Med Trop 1965, 45:365-376.
chains retain activity against chloroquine-resistant Plasmodium
. Antimicrob Agents Chemother 1996, 40:1846-1854.
52. Krogstad D, De D: Chloroquine: modes of action and resistance
and the activity of chloroquine analogs. In Malaria: Parasite Biology,
34. Raynes K, Foley M, Tilley L, Deady LW: Novel bisquinoline
Pathogenesis and Protection, 1st edn. Edited by Sherman IW.
antimalarials. Synthesis, antimalarial activity, and inhibition of
Washington DC: American Society of Microbiology Press; haem polymerisation. THIS IS A PROOF
Biochem Pharmacol 1996, 52:551-559.
35. De D, Krogstad FM, Cogswell FB, Krogstad DJ: Aminoquinolines
53. de Pecoulas PE, Tahar R, Ouatas T, Mazabraud A, Basco LK: that circumvent resistance in Plasmodium falciparum in vitro. Am
Sequence variations in the Plasmodium vivax dihydrofolate
J Trop Med Hyg 1996, 55:579-583.
reductase-thymidylate synthase gene and their relationship with
pyrimethamine resistance.
Mol Biochem Parasitol 1998,
36. De D, Krogstad FM, Byers LD, Krogstad DJ: Structure-activity
relationships for antiplasmodial activity among 7- substituted
J Med Chem 1998, 41:4918-4926.
Djimdé A, Doumbo OK, Cortese JF, Kayentao K, Doumbo S, Diourte Y, Dicko A, Su XZ, Nomura T, Fidock DA et al.: A molecular
marker for chloroquine-resistant falciparum malaria.
New Engl J
2001, 344:257-263.
This study describes the association between the presence of the pfcrtK76→T mutation in P. falciparum and the development of chloroquine resis-tance during the treatment of malaria. The mutation can be used as a mole-cular marker for the surveillance of chloroquine-resistant falciparum malaria.


ALFRED HEALTH, Alfred Pathology Service Alfred Hospital, Caulfield Hospital, Sandringham Hospital THE COLLECTOR MUST LABEL AND SIGN or INITIAL EVERY SPECIMEN (TUBE) and MUST COMPLETE THE DECLARATION ON THE REQUEST FORM. Tube Guide for Common Tests HEPARIN PLASMA with GEL, 5.0 mL EDTA , 3 mL • Essential for — FBE, Hb, DCT, Retics Most urgent BI

Acupuncture Normalizes Dysfunction of Hypothalamic-Pituitary-Ovarian Axis Bo-Ying Chen M.D., Professor of Neurobiology Institute of Acupuncture and Department of Neurobiology Shanghai Medical University, Shanghai 200032, P.R. China (Received June 3, 1997; Accepted with revisions June 30,1997) ABSTRACT This article summarizes the studies of the mechanism of electroacupuncture (EA) in the r

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