Absence of association between pyronaridine in vitro responses and polymorphisms in genes involved in quinoline resistance in Plasmodium falciparum

BACKGROUND: The aim of the present work was to assess the in vitro cross-resistance of pyronaridine with other quinoline drugs, artesunate and several other commonly used anti-malarials and to evaluate whether decreased susceptibility to pyronaridine could be associated with genetic polymorphisms in genes involved in reduced quinoline susceptibility, such as pfcrt, pfmdr1, pfmrp and pfnhe. METHODS: The in vitro chemosusceptibility profiles of 23 strains of Plasmodium falciparum were analysed by the standard 42-hour (3)H-hypoxanthine uptake inhibition method for pyronaridine, artesunate, chloroquine, monodesethylamodiaquine, quinine, mefloquine, lumefantrine, atovaquone, pyrimethamine and doxycycline. Genotypes were assessed for pfcrt, pfmdr1, pfnhe-1 and pfmrp genes. RESULTS: The IC(50 )values for pyronaridine ranged from 15 to 49 nM (geometric mean = 23.1 nM). A significant positive correlation was found between responses to pyronaridine and responses to artesunate (r(2 )= 0.20; P = 0.0317) but too low to suggest cross-resistance. No significant correlation was found between pyronaridine IC(50 )and responses to other anti-malarials. Significant associations were not found between pyronaridine IC(50 )and polymorphisms in pfcrt, pfmdr1, pfmrp or pfnhe-1. CONCLUSION: There was an absence of cross-resistance between pyronaridine and quinolines, and the IC(50 )values for pyronaridine were found to be unrelated to mutations in the transport protein genes pfcrt, pfmdr1, pfmrp or pfnhe-1, known to be involved in quinoline resistance. These results confirm the interest and the efficacy of the use of a combination of pyronaridine and artesunate in areas in which parasites are resistant to quinolines.