Fig. 4. The effect of compound 1 and its enantiomers (Δ-1 and Λ-1) on the Ras/Raf/MEK/ERK signaling pathway. (a) Compound 1 and its enantiomers (Λ-1 and Δ-1) (5 μM) down-regulate the phosphorylation of MEK and ERK, but have no significant effect on total MEK and ERK content in A498 cells. (b) Racemic 1 and Δ-1 (5 μM) attenuate the transcriptional activity of AP-1 in a dose-dependent manner. Significantly different from control at *p < 0.05, **p < 0.005, ***p < 0.001, and ****p < 0.0001.