Epimagnolin A, a tetrahydrofurofuranoid lignan from Magnolia fargesii, reverses ABCB1-mediated drug resistance

Background: Epimagnolin A is an ingredient of the Chinese crude drug Shin-i, derived from the dried flower buds of Magnolia fargesii and Magnolia flos, which has been traditionally used for the treatment of allergic rhinitis and nasal congestion, empyema, and sinusitis. The pharmacokinetic activity of epimagnolin A remains to be evaluated. Purpose: In this study, we examined the possible interactions of epimagnolin A with human ATP-binding cassette (ABC) transporter ABCB1, a membrane protein vital in regulating the pharmacokinetics of drugs and xenobiotics. Study design/methods: The interaction of epimagnolin A with ABCB1 was evaluated in calcein, ATPase, and MTT assays by using Flp-In-293/ABCB1 cells and purified ABCB1 and simulated in molecular docking studies. Results: Epimagnolin A inhibited calcein export by Flp-In-293/ABCB1 cells in a concentration-dependent manner in a calcein assay. ATPase assay revealed a concentration-dependent stimulation of the ATPase activity of ABCB1 by epimagnolin A. Epimagnolin A also showed saturation kinetics in the relationship between the compound-stimulated ATPase activity and the compound concentration, suggesting Michaelis-Menten kinetics similar to those of the control drug, verapamil. K-m and V-max values were calculated from Hanes-Woolf plots of (compound concentration) x (compound-stimulated ATPase activity)(-1) vs. (compound concentration); the K-m of epimagnolin and verapamil was 42.9 +/- 7.53 mu M and 12.3 +/- 4.79 mu M, respectively, and the corresponding V-max values were 156 +/- 15.0 mu M and 109 +/- 3.18 mu M. Molecular docking studies on human ABCB1 showed that epimagnolin A docked to the same binding pocket as verapamil, and 3-(4,5-dimethyl-2-thiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays showed that the sensitivities of Flp-In-293/ABCB1 cells against anti-cancer drugs were enhanced upon exposure to 10 mu M epimagnolin A. Conclusion: These results strongly suggest that epimagnolin A affects the transport activity of ABCB1 as a substrate.