Analysis of mefloquine resistance and amplification of pfmdr1 in multidrug-resistant Plasmodium falciparum isolates from Thailand.

Abstract

Abstract. Resistance to quinoline-containing compound has been associated with the Plasmodium falciparum multidrug resistance 1 (pfmdr1) gene. We analyzed wild P. falciparum isolates with high levels of chloroquine and mefloquine resistance for their macrorestriction maps of chromosome 5 and sequence of pfmdr1. Two types of chromosome 5 amplification were found. Eleven of 62 resistant isolates displayed Bgl I fragments larger than 100 kb. Twenty-nine isolates possessed multiple copies of the fragments. We failed to detect any amplification of this region on chromosome 5 in 22 mefloquine-resistant isolates, suggesting that other mechanisms can mediate the mefloquine-resistant phenotype. There was no direct association between pfmdr1 mutations and chloroquine sensitivity. Resistant lines could have Asn-86 and Tyr-184 or Phe-184, the predicted sequence of those chloroquine-sensitive isolates. No mutation at Asn-1042 and Asp-1246 was detected among these chloroquine-resistant isolates. Therefore, a few base substitutions in the pfmdr1 gene may not be sufficient to account for all chloroquine-resistant phenotypes.In Thailand, malaria continues to be a major public health problem due to the emergence of multidrug-resistant organisms. Increasing levels and prevalence of Plasmodium falciparum resistance to choloroquine 1 and mefloquine 2-4 have been reported. This has made the treatment and prophylaxis of malaria increasingly complicated. Although new drugs and several drug combinations are being introduced, it is important to elucidate the molecular mechanism of aminoquinoline drug resistance to develop the appropriate strategies for malaria therapy.A P-glycoprotein homolog (Pgh 1) has been implicated in chloroquine-and mefloquine-resistant phenotypes of P. falciparum. [5][6][7][8] It is encoded by the P. falciparum multidrug resistance 1 (pfmdr1) gene and is localized on the membrane of the digestive vacuole of this parasite. 8,9 High levels of Pgh 1 expression have been shown in drug-resistant cell lines to confer a chloroquine-sensitive phenotype and in yeast to complement the ste 6 functions, 10 suggesting a role as a drug transporter. Controversy exists regarding the pfmdr 1 gene and chloroquine resistance from the work of Wellems and others 11 in that there is no linkage between pfmdr 1 and such resistance. In addition, in vitro selection of parasites for increased chloroquine resistance resulted in parasites with higher sensitivity to mefloquine. 12 Surprisingly, chromosome 5 of these parasite clones demonstrated deamplification and the expression of Pgh 1 was also decreased. 12 In subsequent drug selection studies, the higher levels of mefloquine resistance have been associated with amplification of pfmdr1. 8,13 Data from several field isolates with mefloquine resistance suggested that the amplification of pfmdr1 and an increase in mRNA expression is associated with natural resistance. Furthermore, cross-resistance to other related drugs such as halofantrine and quinine was also observed. [13][14][15] In this s...

Resistance to Antimalarials in Southeast Asia and Genetic Polymorphisms in pfmdr1

“…The lack of a polymorphism at position 1246 in this study supported previous reports from Asia, suggesting that this polymorphism may not be important for isolates from this region (4,13,17). Also, the coexistence of elevations in mefloquine, artemisinin, and artesunate IC 50 s for the same categories of isolates is also consistent with previous observations (1,7,16,21).…”

“…Also, some field studies have suggested that mutations or amplification of this gene is associated with chloroquine resistance, while others have suggested that mutations or gene amplification is associated with increased chloroquine sensitivity (1,6). On the other hand, there is more general agreement that mutations in pfmdr1 are associated with altered sensitivity to mefloquine and artemisinin derivatives in vitro, although the role of gene amplification is not clear (1,4,13,14). However, most previous studies were small (n Ͻ 20 isolates) or limited to single geographical areas where specific polymorphisms may have been absent.…”

In vivo-in vitro model for the assessment of clinically relevant antimalarial cross-resistance.

“…[11][12][13] Furthermore, the role of the pfmdr1 gene as a possible factor for the development of multidrug resistance, especially to mefloquine and artemisinin, has recently been proposed. 14,15 The findings from this study indicate a clinically relevant (in vivo) cross-sensitivity between artemisinin and mefloquine, similar to the one previously found in vitro. Such a relationship could have a significant impact on the future development of the artemisinin drug sensitivity of P. falciparum, especially if mefloquine is employed in highly malaria-endemic areas.…”

Genetics of Mefloquine Resistance in the Rodent Malaria Parasite Plasmodium chabaudi

“…However, in other studies no amplification was found in parasites selected for increased resistance (27,40,42). An association between amplification of pfmdr1 and mefloquine resistance has been claimed in some field investigations (34,35,51) but not in others (3,9).…”