Selection for high-level chloroquine resistance results in deamplification of the pfmdr1 gene and increased sensitivity to mefloquine in Plasmodium falciparum.

Abstract

A chloroquine resistant cloned isolate of Plasmodium falciparum, FAC8, which carries an amplification in the pfmdrl gene was selected for high-level chloroquine resistance, resulting in a cell line resistant to a 10-fold higher concentration of chloroquine. These cells were found to have lost the amplification in pfmdrl and to no longer over-produce the protein product termed Pglycoprotein homologue 1 (Pghl). The pfmdrl gene from this highly resistant cell line was not found to encode any amino acid changes that would account for increased resistance. Verapamil, which reverses chloroquine resistance in FAC8, also reversed high-level chloroquine resistance. Furthermore, verapamil caused a biphasic reversal of chloroquine resistance as the high-level resistance was very sensitive to low amounts of verapamil. These data suggest that over-expression of the Pglycoprotein homologue is incompatible with high levels of chloroquine resistance. In order to show that these results were applicable to other chloroquine selected lines, two additional mutants were selected for resistance to high levels of chloroquine. In both cases they were found to deamplify pfmdrl. Interestingly, while the level of chloroquine resistance of these mutants increased, they became more sensitive to mefloquine. This suggests a linkage between the copy number of the pfimdrl gene and the level of chloroquine and mefloquine resistance.

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

“…Thus, no inverse relationship involving pfmdr1 between mefloquine and chloroquine was shown in mefloquine-selected FAC8 lines as previously reported. [12][13][14] Several investigators have also suggested that resistance to mefloquine, halofantrine, and quinine are linked. 13,14 We found that the IC 50 of field isolates for halofantrine usually increased as the parasites become more resistant to mefloquine.…”

“…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.…”

“…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.…”

Molecular epidemiology of malaria in Cameroon. X. Evaluation of PFMDR1 mutations as genetic markers for resistance to amino alcohols and artemisinin derivatives.

“…The results of several studies, mostly involving laboratory-adapted P. falciparum strains that were subjected to in vitro drug pressure, have suggested that amplification of pfmdr1 may be associated with resistance to chloroquine and/or amino alcohol drugs. [7][8][9][10][11][12] In some studies, however, the copy number of the pfmdr1 gene and in vitro drug resistance were not associated. 13,14 In addition to gene amplification, the pfmdr1 gene is known to undergo mutations leading to the substitution of amino acids at five distinct positions: 86, 184, 1034, 1042, and 1246.…”

Expresión del gen asociado con la resistencia múltiple a medicamentos (pfmdrl) en cepas colombianas de Plasmodium falciparum

“…En 1990, se presentaron serias evidencias que dejaban en entredicho la relación entre el gen pfmdrl y la resistencia a medicamentos; se encontró que el fenotipo resistente no segregaba con el gen pfmdrl en un cruce genético (8) y que se presentaba un aumento en la resistencia a cloroquina acompañada de una disminución en la expresión del gen y en el número de copias del mismo (9). En 1994, al expresar el tipo silvestre del gen pfmdrl en células CHO (células de ovario de hámster chino), se observó un aumento en la sensibilidad a cloroquina, ocasionada por un aumento en la acumulación del medicamento, a partir de lo cual se postuló que la P-glicoproteína producto del gen podría estar mediando la acumulación de cloroquina y no su eflujo (10).…”