Elucidation of antiviral mechanisms of natural therapeutic molecules Herbacetin and Caffeic acid phenethyl ester against chikungunya and dengue virus

Arthropod-borne viruses of the alphavirus and flavivirus genera are human pathogens of significant concern, and currently, no specific antiviral treatment is available for these viruses. This study has elucidated the antiviral mechanisms of natural small molecules against the dengue (DENV) and chikungunya virus (CHIKV). Herbacetin (HC) and Caffeic acid phenethyl ester (CAPE) depleted polyamine levels in Vero cells, which has been demonstrated by thin-layer chromatography (TLC). As polyamines play an essential role in the replication and transcription of RNA viruses, the depletion of polyamines by HC and CAPE was anticipated to inhibit the virus replication. To test this hypothesis, HC and CAPE were evaluated for antiviral activities using a cell-based virus yield assay by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), plaque reduction assay, and immunofluorescence assay (IFA). HC and CAPE displayed potent inhibition with EC₅₀of 463 nM and 0.417 nM for CHIKV and 8.5 µM and 1.15 µM for DENV, respectively. However, the addition of exogenous polyamines did not ultimately rescue the virus titer in both CHIKV and DENV-infected cells. This finding suggested additional antiviral mechanisms for HC and CAPE. Further,in silicoanalysis revealed that HC and CAPE may directly target the viral methyltransferases (MTase) of CHIKV and DENV. The inhibition of virus-specific MTases by HC and CAPE was confirmed using purified viral MTase of CHIKV and DENV. Altogether, the dual targeting of the host pathway and the viral MTase using potent natural antiviral molecules is expected to facilitate the development of effective biological therapies.