*2.4. Zhankuic Acids A–C Inhibited P-gp E*ffl*ux Function*

Although four new compounds were isolated, they were in little amount. In order to better understand the main P-gp inhibitory effects of *T. camphoratus*, three of its major components, zhankuic acids (ZAs) A–C, were evaluated for their ability to inhibit P-gp using the calcein AM uptake assay. ZAs A, B, C inhibited P-gp efflux function in a concentration-dependent manner (Figure 6). Among the tested compounds, ZA-A demonstrated the most significant P-gp inhibitory effect.

**Figure 6.** The concentration-dependent inhibitory effects of zhankuic acids (ZAs) A, B, C on P-gp in *ABCB1*/Flp-InTM-293 cells. \* denotes *p* < 0.05 compared with the intracellular calcein fluorescence in control group.
