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Miltirone Is a Dual Inhibitor of P-Glycoprotein and Cell Growth in Doxorubicin-Resistant HepG2 Cells

Zhou, Xuelin, Wang, Yan, Lee, Wayne Y. W., Or, Penelope M. Y., Wan, David C. C., Kwan, Yiu Wa, Yeung, John H. K.
Journal of natural products 2015 v.78 no.9 pp. 2266-2275
P-glycoproteins, Salvia miltiorrhiza, active sites, antineoplastic activity, apoptosis, binding capacity, cell growth, cytotoxicity, diterpenoids, doxorubicin, drug resistance, flow cytometry, growth retardation, hepatoma, human cell lines, humans, median effective concentration, mitogen-activated protein kinase, molecular models, neoplasm cells, signal transduction, synergism
Miltirone (1), an abietane-type diterpene quinone isolated from Salvia miltiorrhiza, possesses anticancer activity in p-glycoprotein (P-gp)-overexpressing human cancer cells. Results of the current study suggest a dual effect of miltirone on P-gp inhibition and apoptotic induction in a human hepatoma HepG2 cell line and its P-gp-overexpressing doxorubicin-resistant counterpart (R-HepG2). Miltirone (1) elicited a concentration-dependent cytotoxicity, with a similar potency (EC₅₀ ≈ 7–12 μM), in HepG2 and R-HepG2 cells. Miltirone (1) (1.56–6.25 μM) produced synergistic effects on doxorubicin (DOX)-induced growth inhibition of R-HepG2 (synergism: 0.3 < combination index < 0.5). Molecular docking studies illustrated that miltirone (1) interacted with the active site of P-gp with a higher binding affinity than DOX, suggesting that it was a P-gp inhibitor. Flow cytometric analysis confirmed miltirone (1) as a competitive inhibitor of P-gp. At non-necrotic concentrations (1.56–25 μM), miltirone (1) activated caspase-dependent apoptotic pathways and triggered the generation of reactive oxygen species (ROS) and ROS-mediated mitogen-activated protein kinase (MAPK) signaling pathways (e.g., p38 MAPK, stress-activated protein kinase/c-Jun N-terminal kinase, and extracellular regulated kinase 1/2) in both HepG2 and R-HepG2 cells. Thus, we conclude that miltirone (1) is a dual inhibitor of P-gp and cell growth in human drug-resistant hepatoma cells.