Stability and antiviral activity against human cytomegalovirus of artemisinin derivatives

Objectives: Artesunate, a derivative of dihydroartemisinin, itself a product of artemisinin, inhibits the replication of cytomegalovirus in vitro. In vivo, artesunate undergoes rapid conversion into the active metabolite dihydroartemisinin. The in vitro stability of the compounds and the antiviral activity of dihydroartemisinin are of great concern for the interpretation of in vitro testing. The aim of the study was to measure artesunate conversion into dihydroartemisinin in culture medium and to evaluate the stability and antiviral activity of artemisinin derivatives, according to culture conditions. Methods: Conversion of artesunate into dihydroartemisinin was measured in culture medium with or without fetal calf serum, in the presence or absence of fibroblast monolayers, at different times. The stability of artemisinin derivatives was determined in serum-enriched medium. Concentrations of each compound inhibiting viral DNA synthesis by 50% were determined in fibroblasts cultured in serum-free or serum-enriched medium, after addition of compound as a single dose or fractional doses. Results: Conversion of artesunate into dihydroartemisinin in serum-free or serum-enriched medium was non-equimolar. The half-lives of artesunate, dihydroartemisinin and artemisinin were 10.3 +/- 0.9, 5.2 +/- 0.5 and 11.2 +/- 1.2 h, respectively. Activity of dihydroartemisinin and artesunate was markedly reduced in serum-starved cells. Unexpectedly, dihydroartemisinin displayed a lower activity than artesunate. Addition of both compounds as fractional doses increased their activity. Artemisinin had no anticytomegaloviral activity. Conclusions: Artemisinin derivatives were shown to be unstable in vitro and their addition as fractional doses could partly compensate for this instability. Importantly, the cellular physiological condition was a determinant of their antiviral activity.