Identification of vanillic acid (Van) as a HIF-1 pathway inhibitor from a cell-based screening assay. (A) Chemical structure of vanillic acid (Van). (B) HCT116 cells were transiently co-transfected with a pGL3-HRE-Luciferase and pRL-CMV vectors. Following 24 h incubation, cells were treated with various concentrations of vanillic acid (Van) and then subjected to hypoxia, or remained in normoxia for 12 h. Data were shown as mean ± SD (n = 3). * p < 0.05, ** p < 0.01, *** p < 0.001, compared with hypoxia control. (C) Cells were incubated with different concentrations of vanillic acid (Van). After 24 h incubation, cell viability was determined by MTT assays.