Verapamil-Sensitive Transport of Quinacrine and Methylene Blue via the Plasmodium falciparum Chloroquine Resistance Transporter Reduces the Parasite's Susceptibility to these Tricyclic Drugs.
BACKGROUND
It is becoming increasingly apparent that certain mutations in the Plasmodium falciparum chloroquine resistance transporter (PfCRT) alter the parasite's susceptibility to diverse compounds. Here we investigated the interaction of PfCRT with 3 tricyclic compounds that have been used to treat malaria (quinacrine [QC] and methylene blue [MB]) or to study P. falciparum (acridine orange [AO]).


METHODS
We measured the antiplasmodial activities of QC, MB, and AO against chloroquine-resistant and chloroquine-sensitive P. falciparum and determined whether QC and AO affect the accumulation and activity of chloroquine in these parasites. We also assessed the ability of mutant (PfCRT(Dd2)) and wild-type (PfCRT(D10)) variants of the protein to transport QC, MB, and AO when expressed at the surface of Xenopus laevis oocytes.


RESULTS
Chloroquine resistance-conferring isoforms of PfCRT reduced the susceptibility of the parasite to QC, MB, and AO. In chloroquine-resistant (but not chloroquine-sensitive) parasites, AO and QC increased the parasite's accumulation of, and susceptibility to, chloroquine. All 3 compounds were shown to bind to PfCRT(Dd2), and the transport of QC and MB via this protein was saturable and inhibited by the chloroquine resistance-reverser verapamil.


CONCLUSIONS
Our findings reveal that the PfCRT(Dd2)-mediated transport of tricyclic antimalarials reduces the parasite's susceptibility to these drugs.
Research School of Biology, Australian National University, Canberra, Australia.
Donelly A
DA
van Schalkwyk
Research School of Biology, Australian National University, Canberra, Australia.
Megan N
MN
Nash
Research School of Biology, Australian National University, Canberra, Australia.
Sarah H
SH
Shafik
Research School of Biology, Australian National University, Canberra, Australia.
Robert L
RL
Summers
Research School of Biology, Australian National University, Canberra, Australia.
Adele M
AM
Lehane
Division of Pharmacology, Department of Medicine, University of Cape Town, Rondebosch, South Africa.
Peter J
PJ
Smith
Research School of Biology, Australian National University, Canberra, Australia.
Rowena E
RE
Martin
D000818:Animals; D000962:Antimalarials / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D004351:Drug Resistance; D005786:Gene Expression Regulation / Q000502:physiology; D014644:Genetic Variation; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008751:Methylene Blue / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism*; D011796:Quinacrine / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology*; D014982:Xenopus laevis
D000962:Antimalarials; D026901:Membrane Transport Proteins; C416369:PfCRT protein, Plasmodium falciparum; D015800:Protozoan Proteins; D014700:Verapamil; D011796:Quinacrine; D008751:Methylene Blue
PfCRT; Plasmodium falciparum; Xenopus oocytes; drug resistance; fluorescence-based transport assay; methylene blue; tricyclic drug