Balancing drug resistance and growth rates via compensatory mutations in the Plasmodium falciparum chloroquine resistance transporter

Abstract

Summary The widespread use of chloroquine to treat Plasmodium falciparum infections has resulted in the selection and dissemination of variant haplotypes of the primary resistance determinant PfCRT. These haplotypes have encountered drug pressure and within-host competition with wild-type drug-sensitive parasites. To examine these selective forces in vitro, we genetically engineered P. falciparum to express geographically diverse PfCRT haplotypes. Variant alleles from the Philippines (PH1 and PH2, which differ solely by the C72S mutation) both conferred a moderate gain of chloroquine resistance and a reduction in growth rates in vitro. Of the two, PH2 showed higher IC50 values, contrasting with reduced growth. Furthermore, a highly mutated pfcrt allele from Cambodia (Cam734) conferred moderate chloroquine resistance and enhanced growth rates, when tested against wild-type pfcrt in co-culture competition assays. These three alleles mediated cross-resistance to amodiaquine, an antimalarial drug widely used in Africa. Each allele, along with the globally prevalent Dd2 and 7G8 alleles, rendered parasites more susceptible to lumefantrine, the partner drug used in the leading first-line artemisinin-based combination therapy. These data reveal ongoing region-specific evolution of PfCRT that impacts drug susceptibility and relative fitness in settings of mixed infections, and raise important considerations about optimal agents to treat chloroquine-resistant malaria.

Intermittent Preventive Treatment with Dihydroartemisinin-Piperaquine in Ugandan Schoolchildren Selects for Plasmodium falciparum Transporter Polymorphisms That Modify Drug Sensitivity

“…Polymorphisms in addition to those commonly described in African isolates have been identified in other regions, in some cases with biochemical and clinical consequences (49,50). Sequencing of pfcrt in a subset of samples either under or not under the selective pressure of DP identified a few previously unidentified pfcrt mutations, but it did not suggest that additional polymorphisms were selected by DP.…”

Antimalarial drug resistance: linking Plasmodium falciparum parasite biology to the clinic

“…Structurally, PPQ comprises two CQ-like 4-aminoquinoline moieties with a central linker. This drug is generally effective against parasites that evolved resistance to CQ through specific sets of point mutations in the P. falciparum CQ resistance transporter (PfCRT), which is also present on the digestive vacuole membrane 34,35 (Fig. 2 and Box 1).…”

“…Most mutant pfcrt alleles come with a fitness cost, indicated in the field by a decrease in their allelic prevalence in the absence of CQ pressure 177 , and in vitro as reduced growth rates when compared to recombinant isogenic parasites expressing the wild-type allele 35,169,178 . Reduced fitness might involve less efficient Hb catabolism and peptide transport in PfCRT mutants, as well as other digestive-vacuole-related physiological processes 178,179 .…”

“…Reduced fitness might involve less efficient Hb catabolism and peptide transport in PfCRT mutants, as well as other digestive-vacuole-related physiological processes 178,179 . Interestingly, parasites from Cambodia harbor a uniquely polymorphic pfcrt allele (Cam734, with nine point mutations) that mediates moderate CQ resistance without compromising parasite fitness 35,179 .…”

Adaptive evolution of malaria parasites in French Guiana: Reversal of chloroquine resistance by acquisition of a mutation in pfcrt

“…Such a difference between South America and other endemic regions in response to CQ withdrawal is generally attributed to other amino acid changes in PfCRT and PfMDR1 (both present on the parasite digestive vacuole membrane), which accompany the PfCRT K76T substitution. Specifically, the SVMNT haplotype of South American parasites at PfCRT amino acids 72-76 has been found to be less deleterious than the CVIET haplotype present elsewhere (14,15). Another explanation for the virtual fixation of CQR alleles in South American parasites is that CQ continues to be used to treat P. vivax infections and therefore, may exert a residual pressure.…”