2.7. Thymidine incorporation assay
The DP and HaCaT cells were plated in six-well plates and grown for 12—24 h in DMEM supplemented with 10% FBS. After washing twice with PBS, the cells were placed in FBS-free DMEM, together with 1 mCi of [3H]thymidine and the indicated concentrations of A. radix extract. Following incubation for 48 h, the cells were washed twice with PBS, and once with 5% cold TCA. The cells were then lysed with 0.1N NaOH, 1% SDS and the levels of radioactivity were measured by liquid scintillation counter (Beckman).