[Antimalarial drug resistance]

Abstract

Drug resistant malaria is mostly due to Plasmodium falciparum, the highly prevalent species in tropical Africa, Amazon, and Southeast Asia. P. falciparum is responsible for severe involvement of fever or anemia causing more than a million deaths per year. Rationale for treatment is becoming weak as multiple drug resistance against well-tolerated drugs develops. P. falciparum drug resistant malaria originates from chromosomal mutations. Analyses using molecular, genetic and biochemical approaches showed that: 1) impaired uptake of chloroquine by the parasite vacuole is a common characteristic of resistant strains, this phenotype correlates with pfmdr1 and pfcrt gene mutations; 2) one S108N to four (N51I, C59R, I164L) point mutations of dihydrofolate reductase, the enzyme target of antifolinics (pyrimethamine and proguanil), give moderate to high level of resistance to these drugs; 3) resistance to sulfonamides and sulfones involves mutations of dihydropteroate synthase (A437G, K540E), their enzyme target, impairing their capacity to potentiate antifolinic drugs; 4) resistance to atovaquone plus proguanil involves one single mutation on atovaquone target, cytochrome b (Y268S, C or N); 5) resistance to mefloquine is thought to be linked to the over expression of pfmdr1, a pump expelling toxic waste from eukaryotic cells. P. falciparum resistance levels may differ according to places and time, depending on malaria transmission and drug pressure. Coupling in vivo to in vitro tests, and using molecular tests is essential for the surveillance of replacement drugs. Low cost biochemical tools are urgently needed for a prospective monitoring of resistance.