Evolution of a unique Plasmodium falciparum chloroquine-resistance phenotype in association with pfcrt polymorphism in Papua New Guinea and South America

The mechanistic basis for chloroquine resistance (CQR) in Plasmodium falcip arum recently has been linked to the polymorphic gene pfcrt. Alleles associ ated with CQR in natural parasite isolates harbor threonine (T), as opposed to lysine (K) at amino acid 76. A falciparum CQR strains of African and So utheast Asian origin carry pfcrt alleles encoding an amino acid haplotype o f CVIET (residues 72-76), whereas most South American CQR strains studied c arry an allele encoding an SVMNT haplotype, chloroquine-sensitive strains f rom malarious regions around the world carry a CVMNK haplotype. Upon invest igating the origin of pfcrt alleles in Papua New Guinean (PNG) A falciparum we found either the chloroquine-sensitive-associated CVMNK or CQR-associat ed SVMNT haplotypes previously seen in Brazilian isolates. Remarkably we di d not find the CVIET haplotype observed in CQR strains from Southeast Asian regions more proximal to PNG. Further we found a previously undescribed CQ R phenotype to be associated with the SVMNT haplotype from PNG and South Am erica. This CQR phenotype is significantly less responsive to verapamil che mosensitization compared with the effect associated with the CVIET haplotyp e. Consistent with this, we observed that verapamil treatment of A falcipar um isolates carrying pfcrt SVMNT is associated with an attenuated increase in digestive vacuole pH relative to CVIET pfcrt-carrying isolates. These da ta suggest a key role for pH-dependent changes in hematin receptor concentr ation in the A falciparum CQR mechanism. Our findings also suggest that A f alciparum CQR has arisen through multiple evolutionary pathways associated with pfcrt K76T.