Please refer to usage guidelines at http://researchonline.lshtm.ac.uk/policies.html or alternatively contact researchonline@lshtm.ac.uk. Available under license: Copyright the publishersT h e ne w e ngl a nd jou r na l o f m e dic i ne n engl j med 361;5 nejm

BACKGROUND-KAE609 (cipargamin; formerly NITD609, Novartis Institute for Tropical Diseases) is a new synthetic antimalarial spiroindolone analogue with potent, dose-dependent antimalarial activity against asexual and sexual stages of Plasmodium falciparum.

The reduced in vivo sensitivity of Plasmodium falciparum has recently been confirmed in western Cambodia. Identifying molecular markers for artemisinin resistance is essential for monitoring the spread of the resistant phenotype and identifying the mechanisms of resistance. Four candidate genes, including the P. falciparum mdr1 (pfmdr1) gene, the P. falciparum ATPase6 (pfATPase6) gene, the 6-kb mitochondrial genome, and ubp-1, encoding a deubiquitinating enzyme, of artemisinin-resistant P. falciparum strains from western Cambodia were examined and compared to those of sensitive strains from northwestern Thailand, where the artemisinins are still very effective. The artemisinin-resistant phenotype did not correlate with pfmdr1 amplification or mutations (full-length sequencing), mutations in pfATPase6 (full-length sequencing) or the 6-kb mitochondrial genome (full-length sequencing), or ubp-1 mutations at positions 739 and 770. The P. falciparum CRT K76T mutation was present in all isolates from both study sites. The pfmdr1 copy numbers in western Cambodia were significantly lower in parasite samples obtained in 2007 than in those obtained in 2005, coinciding with a local change in drug policy replacing artesunate-mefloquine with dihydroartemisinin-piperaquine. Artemisinin resistance in western Cambodia is not linked to candidate genes, as was suggested by earlier studies.Antimalarial drug resistance is the single most important threat to global malaria control. Over the past 40 years, as firstline treatments (chloroquine and sulfadoxine-pyrimethamine) failed, the malaria-attributable mortality rate rose, contributing to a resurgence of malaria in tropical countries (11). In the last decade, artemisinins, deployed as artemisinin combination therapies (ACTs), have become the cornerstone of the treatment of uncomplicated falciparum malaria (20) and, in conjunction with other control measures, have contributed to a remarkable decrease in malaria morbidity and mortality in many African and Asian countries (4). The recent confirmation of the reduced artemisinin sensitivity of Plasmodium falciparum parasites in western Cambodia has therefore alarmed the malaria community (6). A large containment effort has been launched by the World Health Organization, in collaboration with the national malaria control programs of Cambodia and neighboring Thailand. The resistant phenotype has not been well characterized and is not well reflected by the results of conventional in vitro drug susceptibility assays. No molecular marker has been identified, which impedes surveillance studies to monitor the spread of the resistant phenotype. Identification of molecular markers would give insight into the mechanisms underlying artemisinin resistance and the mechanism of antimalarial action of the artemisinins.Mutations in several candidate genes have been postulated to confer artemisinin resistance. (i) P. falciparum mdr1 (pfmdr1) encodes the P-glycoprotein homologue 1 (Pgh1), which belongs to the ATP-binding cassette transporter superfamily...