pfmdr1 amplification is related to increased Plasmodium falciparum in vitro sensitivity to the bisquinoline piperaquine

The Shoklo Malaria Research Unit is part of the Mahidol Oxford University Tropical Medicine Research Unit, supported by the Wellcome Trust of Great Britain.The 4-aminoquinoline bisquinoline piperaquine is an important partner drug in one of the presently recommended artemisinin combination therapies. Recent clinical trials have confirmed its high efficacy in combination with dihydroartemisinin. Resistance to piperaquine alone has, however, been documented. Amplification in copy number of the Plasmodium falciparum multidrug resistance locus on chromosome 5, containing the pfmdr1 gene, has been shown to confer resistance to structurally unrelated antimalarials. Through the determination of the 50% inhibitory concentrations (IC(50)s) and IC(90)s for piperaquine and chloroquine in a set of 46 adapted P. falciparum cultures originating from the Thai-Burmese border, we have characterized the regions around the pfmdr1 gene and identified a significant association between the presence of pfmdr1 duplications and enhanced sensitivity to piperaquine (P = 0.005 for IC(50) and P = 0.002 for IC(90)) and chloroquine, reaching statistical significance at IC(90)s (P = 0.026). These results substantiate the potential importance of pfmdr1 copy number amplifications in the efficacy of the combination therapy piperaquine-dihydroartemisinin. It supports the rational use of 4-aminoquinolines and artemisinin-based compounds, as they independently select for mutually incompatible combinations of mutations.This work was supported by project grants from Swedish Development Cooperation Agency-Department for Research Cooperation (SWE 2005-0017, SWE 2005-4596, SWE-2007-174, and SWE-2005-4027). M.I.V. was supported by a postdoctoral grant from Fundação para a Ciência e Tecnologia (FCT)/Ministerio da Ciência e Ensino Superior, Portugal MCES (SFRH/BPD/76614/2011)