In vitro activity: Butein inhibits the epidermal growth factor (EGF)-stimulated auto-phosphotyrosine level of EGF receptor in HepG2 cells, and also inhibits tyrosine-specific protein kinase activities of EGF receptor and p60c-src with IC50 of 65 μM in vitro. The inhibition is competitive to ATP and non-competitive to the phosphate acceptor, poly (Glu, Ala, Tyr) 6:3:1 for EGF receptor tyrosine kinase. In contrast, Butein non-significantly inhibits the activities of serine- and threonine-specific protein kinases such as PKC or PKA. Butein inhibits Nuclear Factor(NF)-κB and NF-κB-regulated gene expression through direct inhibition of IκBα Kinase β on Cysteine 179 Residue. Butein (10 μM) inhibits over 90% iNOS and COX-2 expression, as well as nitrite and TNF-α production in LPS-stimulated RAW 264.7 cells. Butein (10 μM) inhibits LPS-induced DNA binding activity of NF-κB, which is mediated through inhibition of the degradation of inhibitory factor-κB and phosphorylation of Erk1/2 MAP kinase, as well as increases binding of the osteopontin a vb3 integrin receptor. Butein (20 μM) treatment induces morphologic changes of bladder cancer cells BLS(M) from elongated morphology to rounded epithelial-like cells, accompanied by downregulation of vimentin, and gaining of E-cadherin compared to untreated control cells, indicating the reversal of mesenchymal-like phenotype. Butein (20 μM) suppresses motility and invasion capacity of BLS(M) cells, and reverts EMT-like phenotype induced by TNF-α, through the ERK1/2 and NF-κB signaling pathways. Butein inhibits the constitutive activation of STAT3 in HepG2 cells in a dose-dependent manner, with maximum inhibition occurring at 50 μM, mediated through the inhibition of activation of upstream kinases c-Src and Janus-activated kinase2. Butein (50 μM) also could completely inhibit IL-6-induced STAT3 phosphorylation in SNU-387 cells. Butein downregulates the expression of cyclin D1, Bcl-2, Bcl-xL, survivin, and VEGF, markers of STAT3 activation. Butein (50 μM) significantly enhance the apoptotic effects of doxorubicin from 18% to 55% and of paclitaxel from 15% to 42%. Butein is as a powerful antioxidant against lipid and LDL peroxidation. Butein inhibits iron-induced lipid peroxidation in rat brain homogenate with an IC50 of 3.3 μM. Butein is as potent α-tocopherol in reducing the stable free radical diphenyl-2-picrylhydrazyl (DPPH) with IC0.2 of 9.2 μM. Butein also inhibits the activity of xanthine oxidase with an IC50 of 5.9 μM. Butein scavenges the peroxyl radical derived from 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) in aqueous phase. Furthermore, Butein inhibits copper-catalyzed oxidation of human low-density lipoprotein (LDL) in a concentration-dependent manner. Butein is a chelator of ferrous and copper ions.

Kinase Assay: Butein inhibited the activation of AKT, extracellular signal-regulated kinase (ERKs) and p38 kinases in the presence of cisplatin.

Cell Assay: The cells (5× 103/mL, Human hepatoma cells HepG2) are incubated in triplicate in a 96-well plate in the presence or absence of indicated concentration of Butein in a final volume of 0.2 mL for different time intervals at 37 ℃. Thereafter, 20 μL MTT solution (5 mg/mL in PBS) is added to each well. After a 2-hour incubation at 37 ℃, 0.1 mL lysis buffer (20% SDS, 50% dimethylformamide) is added, incubation is continued overnight at 37 ℃, and then the optical density at 570 nm is measured by plate reader.

Biochem Biophys Res Commun. 1998 Apr 17;245(2):435-8; Clin Cancer Res. 2011 Mar 15;17(6):1425-39; Planta Med. 2003 Nov;69(11):990-4.