An in silico-designed flavone derivative, 6-fluoro-4'-hydroxy-3',5'-dimetoxyflavone, has a greater anti-human cytomegalovirus effect than ganciclovir in infected cells

A novel type of antiviral agent for human cytomegalovirus (HCMV) is required, because the appearance of ganciclovir (GCV) resistant viruses has been reported. Tricin (4',5,7-trihydroxy-3',5'-dimethoxyflavone) has been shown to suppress significantly HCMV replication in human embryonic lung (HEL) fibroblast cells. Recently, we revealed that the action of tricin is different from that of GCV and cyclin-dependent kinase 9 (CDK9) is one of the target proteins of tricin. These results suggested that tricin is considered as a novel type of anti-HCMV agent. However, its anti-HCMV potency is not greater than that of GCV. This study tried to develop novel compounds with much greater anti-HCMV activity than GCV. We first made modifications to tricin by introducing fluorine atom, and then performed molecular docking simulations using the designed compounds and CDK9. The calculated binding energies showed that 6F-tricin (6-fluoro-4'-hydroxy-3',5'-dimetoxyflavone) binds to CDK9 much stronger than tricin. Based on these results, 6F-tricin was synthesized, and then its anti-HCMV effect was analyzed in HEL cell cultures. As a result, 6F-tricin strongly suppressed HCMV replication in a dose-dependent manner. The anti-HCMV activity with a 50% effective concentration (EC₅₀) was 0.126 nM, corresponding to about 1/200 and 1/400 of EC₅₀ of GCV (27.5 nM) and tricin (54.3 nM), respectively. Moreover, 6F-tricin had no cytotoxicity against HEL cells at concentrations up to 10 μM. We further performed detailed analysis on the amino acid contributions to the binding energies and found that the strong binding affinity for 6F-tricin to CDK9 is attributed to the specific binding orientation of 6F-tricin in the ATP-binding site. These results suggest that 6F-tricin is a promising candidate for anti-HCMV drug development.