In vitro cytotoxicity assay. Luciferase-expressing TC-1 tumor cells were added to 24-well plates at a dose of 1 × 105/well. TC-1/luc tumor cells were (A & B) treated with solvent DMSO (0.1%) as a control or treated with different concentrations of apigenin (20, 40, 80 μM) or (C & D) treated with E7-specific cytotoxic T cells at different E:T ratios (1:1, 1:5) with or without treated 40 mM apigenin. Bioluminescence imaging was performed on D0, D1, D2 and D3. The degree of CTL-mediated killing of the tumor cells was indicated by the decrease of luminescence activity using the IVIS luminescence imaging system series 200. Bioluminescence signals were acquired for 10 seconds. (A & C) Representative luminescence images of 24-well plates showing lysis of the tumor cells by (A) different concentrations of apigenin or by (C) E7-specific T cells and apigenin. (B & D) Bar graph depicting the quantification of luminescence intensity in tumor cells treated with (B) different concentrations of apigenin or treated with (D) apigenin and/or E7-specific cytotoxic T cells (mean ± SD). P values less than 0.05 are considered to be statistically significant. Data shown are representative of two experiments performed.