In vitro activity of anti-malarial ozonides against an artemisinin-resistant isolate

Fabian Baumgärtner, Joëlle Jourdan, Christian Scheurer, Benjamin Blasco, Brice Campo, Pascal Mäser, Sergio Wittlin

Recently published data suggest that artemisinin derivatives and synthetic peroxides, such as the ozonides OZ277 and OZ439, have a similar mode of action. Here the cross-resistance of OZ277 and OZ439 and four additional next-generation ozonides was probed against the artemisinin-resistant clinical isolate Plasmodium falciparum Cam3.I, which carries the K13-propeller mutation R539T (Cam3.I(R539T)). The previously described in vitro ring-stage survival assay (RSA0-3h) was employed and a simplified variation of the original protocol was developed. At the pharmacologically relevant concentration of 700 nM, all six ozonides were highly effective against the dihydroartemisinin-resistant P. falciparum Cam3.I(R539T) parasites, showing a per cent survival ranging from <0.01 to 1.83%. A simplified version of the original RSA0-3h method was developed and gave similar results, thus providing a practical drug discovery tool for further optimization of next-generation anti-malarial peroxides. The absence of in vitro cross-resistance against the artemisinin-resistant clinical isolate Cam3.I(R539T) suggests that ozonides could be effective against artemisinin-resistant P. falciparum. How this will translate to the human situation in clinical settings remains to be investigated.