LK-A inhibits cell viability and colony formation of the human NPC cells CNE1 and CNE2. (A) The chemical structural of LK-A and oridonin. (B, C) A comparison of the cytotoxic effects of LK-A and oridonin on NPC cells. CNE1 and CNE2 (0, 0.78, 1.56, 3.12, 6.25, 12.5 and 25 μΜ) of LK-A or oridonin for 24, 48 and 72 hrs. Cell viability was determined by MTT assays. The IC50 values 48 hrs after treatment were 1.26 ± 0.17 μM, 1.52 ± 0.22 μM, 3.66 ± 0.37 μM and 5.93 ± 0.48 μM for B and C , respectively. Data are shown as the mean ± SD of three independent experiments. *p < 0.05 vs. control group (untreated cells). (D) The colony forming ability of NPC cells was inhibited by LK-A treatment. Bar chart showing the decreased proportion of the cloned ratio after treatment with LK-A. Data are shown as the mean ± SD of two independent experiments. *p < 0.05 vs. control group (untreated cells).