Figure 1. Esketamine synergizes with 5-FU to inhibit colon cancer cell viability. (A) DLD1 and HCT15 cells were treated with the indicated concentrations of esketamine for 24 h or 48 h. (B) Cells were treated with the indicated concentrations of 5-FU alone or in combination with esketamine for 48 h. Cell viability was measured by Cell counting Kit-8 (CCK-8) assay. Data are normalized to the vehicle control (DMSO) group and presented as the mean ± SD (n = 3 independent experiments). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 vs. control group (unless otherwise specified). (C) CI values were calculated using the Chou-Talalay method via CompuSyn software after 48 h of combination treatment. CI < 1 indicates synergy. 5-FU, 5-fluorouracil. CI, combination index.