Previously, it has been shown that
1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM), a natural compound isolated from leaf extracts of Melia azedarach L., inhibits the
vesicular stomatitis virus (VSV) multiplication cycle when added before or after
infection. Here, we have established that the lack of VSV
protein synthesis in CDM pre-treated Vero cells is ascribed to the inhibition of an initial step during virus multiplication, although indirect immunofluorescence (IFI) studies confirmed that the binding and uptake of [(35)S]
methionine-labelled VSV was not affected by CDM pre-treatment. Instead, our findings revealed that this compound impedes the uncoating of VSV nucleocapsids in pre-treated Vero cells, since the
antiviral action of CDM was partially reversed by inducing VSV direct fusion at the plasma membrane, and VSV M
protein fluorescence was confined to the endosomes, even 2 h post-internalization. Furthermore, CDM induced cytoplasmic alkalinization, as shown by
acridine orange staining, consistent with the inhibition of virus uncoating. Although VSV
proteins are synthesized when CDM is added after
infection, IFI studies revealed that
G protein was absent from the surface of infected cells and co-localized with a Golgi marker. Therefore, CDM inhibits the transport of
G protein to the plasma membrane. Taken together, these findings indicate that CDM exerts its
antiviral action on the endocytic and exocytic pathways of VSV by pre- or post-treatment, respectively.