Mechanistic basis for multidrug resistance and collateral drug sensitivity conferred to the malaria parasite by polymorphisms in PfMDR1 and PfCRT

PLoS Biol. 2022 May 4;20(5):e3001616. doi: 10.1371/journal.pbio.3001616. eCollection 2022 May.


Polymorphisms in the Plasmodium falciparum multidrug resistance protein 1 (pfmdr1) gene and the Plasmodium falciparum chloroquine resistance transporter (pfcrt) gene alter the malaria parasite's susceptibility to most of the current antimalarial drugs. However, the precise mechanisms by which PfMDR1 contributes to multidrug resistance have not yet been fully elucidated, nor is it understood why polymorphisms in pfmdr1 and pfcrt that cause chloroquine resistance simultaneously increase the parasite's susceptibility to lumefantrine and mefloquine-a phenomenon known as collateral drug sensitivity. Here, we present a robust expression system for PfMDR1 in Xenopus oocytes that enables direct and high-resolution biochemical characterizations of the protein. We show that wild-type PfMDR1 transports diverse pharmacons, including lumefantrine, mefloquine, dihydroartemisinin, piperaquine, amodiaquine, methylene blue, and chloroquine (but not the antiviral drug amantadine). Field-derived mutant isoforms of PfMDR1 differ from the wild-type protein, and each other, in their capacities to transport these drugs, indicating that PfMDR1-induced changes in the distribution of drugs between the parasite's digestive vacuole (DV) and the cytosol are a key driver of both antimalarial resistance and the variability between multidrug resistance phenotypes. Of note, the PfMDR1 isoforms prevalent in chloroquine-resistant isolates exhibit reduced capacities for chloroquine, lumefantrine, and mefloquine transport. We observe the opposite relationship between chloroquine resistance-conferring mutations in PfCRT and drug transport activity. Using our established assays for characterizing PfCRT in the Xenopus oocyte system and in live parasite assays, we demonstrate that these PfCRT isoforms transport all 3 drugs, whereas wild-type PfCRT does not. We present a mechanistic model for collateral drug sensitivity in which mutant isoforms of PfMDR1 and PfCRT cause chloroquine, lumefantrine, and mefloquine to remain in the cytosol instead of sequestering within the DV. This change in drug distribution increases the access of lumefantrine and mefloquine to their primary targets (thought to be located outside of the DV), while simultaneously decreasing chloroquine's access to its target within the DV. The mechanistic insights presented here provide a basis for developing approaches that extend the useful life span of antimalarials by exploiting the opposing selection forces they exert upon PfCRT and PfMDR1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antimalarials* / pharmacology
  • Antimalarials* / therapeutic use
  • Chloroquine / metabolism
  • Chloroquine / pharmacology
  • Chloroquine / therapeutic use
  • Drug Resistance / genetics
  • Drug Resistance, Multiple
  • Lumefantrine / pharmacology
  • Lumefantrine / therapeutic use
  • Malaria, Falciparum* / parasitology
  • Mefloquine / metabolism
  • Mefloquine / pharmacology
  • Mefloquine / therapeutic use
  • Multidrug Resistance-Associated Proteins / genetics
  • Multidrug Resistance-Associated Proteins / metabolism
  • Multidrug Resistance-Associated Proteins / therapeutic use
  • Parasites* / metabolism
  • Plasmodium falciparum / genetics
  • Plasmodium falciparum / metabolism
  • Protein Isoforms / metabolism
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism


  • Antimalarials
  • Multidrug Resistance-Associated Proteins
  • Protein Isoforms
  • Protozoan Proteins
  • Chloroquine
  • Lumefantrine
  • Mefloquine

Grant support

This work was supported by the Australian Research Council (fellowship FT160100226 to R.E.M.), the National Health and Medical Research Council (project grant 1127338 to R.E.M. and fellowship 1053082 to R.E.M.), and the Australian Department of Education (Australian Postgraduate Awards to S.H.S. and S.N.R.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.