Cytotoxicity and spectrum of BQR antiviral activity. (A) Structure of BQR. (B) CFI assay. A549 cells were infected with DENV-2 (MOI, 0.3) in the presence of 2-fold serial dilutions of BQR. After incubation at 37°C for 48 h, the expression of viral envelope protein was quantified by an immunodetection method (see Materials and Methods). Average results from three experiments are shown. (C) Spectrum of BQR antiviral activity. Vero cells were infected with the indicated viruses at an MOI of 0.1; the infected cells were immediately treated with BQR. For DENV-2, WNV, YFV, PWV, and WEEV, culture media were collected at 42 h p.i. and viral titers were measured using plaque assays. For VSV, culture medium was collected at 16 h p.i. and the viral titer was measured. Average results and standard deviations (n = 3) are presented. (D) Cytotoxicity of BQR in Vero and A549 cells. Cytotoxicity was examined by incubation of Vero and A549 cells with the indicated concentrations of BQR. Cell viability was measured by an MTS assay and is presented as a percentage of the colorimetric absorbance derived from the compound-treated cells compared with that derived from the mock-treated (0.9% DMSO) cells. Average results from three experiments are shown.