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

Abstract 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) × (compound-stimulated ATPase activity) −1 vs. (compound concentration); the K m of epimagnolin and verapamil was 42.9 ± 7.53  μM and 12.3 ± 4.79  μM, respectively, and the corresponding V max values were 156 ± 15.0  μM and 109 ± 3.18  μM. 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  μM epimagnolin A. Conclusion These results strongly suggest that epimagnolin A affects the transport activity of ABCB1 as a substrate.