Artesunate demonstrates in vitro synergism with several antiviral agents against human cytomegalovirus

Background: Human cytomegalovirus (HCMV) infections remain a major problem in immunocompromised patients. Three antiviral agents, ganciclovir (GCV), foscarnet (FOS) and cidofovir (CDV), are currently approved for the treatment of HCMV infections. They all target the viral DNA polymerase and are associated with significant side effects. Combinations of novel antiviral compounds acting on different targets such as artesunate (ART) with currently approved drugs or eventually letermovir or maribavir (MBV) may result in synergistic effects. Here, we evaluated the in vitro activity of a series of two-drug combinations against a wild-type recombinant HCMV strain by the Gaussia luciferase (GLuc) reporter assay. Methods: The in vitro activity of each drug was first tested individually against HCMV by using the GLuc reporter assay. The activity of two-drug combinations consisting of ART and currently approved drugs, as well as letermovir or MBV, was then analysed by the Chou-Talalay method. Results: The concentrations of GCV, FOS, CDV and ART that reduced the GLuc activity by 50% (EC50 values) were 3.92 +/- 1.64 mu M, 62.45 +/- 8.39 mu M, 0.68 +/- 0.19 mu M and 3.86 +/- 1.25 mu M, respectively, whereas those of MBV and letermovir were 64 +/- 22 nM and 2.50 +/- 0.83 nM, respectively. The combination of ART with GCV, CDV or MBV was associated with synergism, whereas combination of ART with FOS or letermovir resulted in moderate synergism. As expected, the combination of MBV with GCV was antagonistic. Conclusions: These results suggest that the combination of ART with the antiviral agents tested in this study could be an interesting strategy for the treatment of HCMV infections to reduce toxicity and drug-resistance development.