Butein inhibits the tyrosine-specific protein kinase activities of the EGF receptor and p60^c-src with an IC50 of 65 μM in vitro, as well as the epidermal growth factor (EGF)-stimulated auto-phosphotyrosine level of the EGF receptor in HepG2 cells. For the EGF receptor tyrosine kinase, the inhibition is non-competitive to the poly (Glu, Ala, Tyr) 6:3:1 phosphate acceptor and competitive to ATP. However, the actions of serine- and threonine-specific protein kinases, like PKC or PKA, are non-significantly inhibited by butein. [1] NF-κB and Nuclear Factor (NF)-κB-regulated gene expression are inhibited by butein by directly inhibiting IκBα Kinase β on Cysteine 179 Residue.[2] In LPS-stimulated RAW 264.7 cells, butein (10 μM) inhibits over 90% of the expression of iNOS and COX-2, as well as the production of nitrite and TNF-α. Butein (10 μM) increases binding of the osteopontin a vb3 integrin receptor and inhibits the 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.[3] When bladder cancer cells BLS(M) are treated with butein (20 μM), their morphologic changes from elongated to rounded epithelial-like cells are observed. Additionally, vimentin is downregulated and E-cadherin is gained in comparison to untreated control cells, suggesting that the mesenchymal-like phenotype is reversed. Through the ERK1/2 and NF-κB signaling pathways, butein (20 μM) reverses the EMT-like phenotype that TNF-α induced in BLS(M) cells and inhibits their ability to invade and move. In [4] With a dose-dependent effect that reaches a maximum at 50 μM, butein prevents the constitutive activation of STAT3 in HepG2 cells by blocking the activation of upstream kinases c-Src and Janus-activated kinase2. Additionally, IL-6-induced STAT3 phosphorylation in SNU-387 cells could be totally inhibited by butein (50 μM). Butein suppresses the expression of STAT3 activation markers, such as cyclin D1, Bcl-2, Bcl-xL, survivin, and VEGF. The apoptotic effects of doxorubicin (18% to 55%) and paclitaxel (15%) are significantly increased by butein (50 μM). [5] Butein is an effective antioxidant that prevents LDL and lipid peroxidation. With an IC50 of 3.3 μM, butein prevents lipid peroxidation caused by iron in rat brain homogenate. With an IC0.2 of 9.2 μM, butein is just as effective as α-tocopherol in scavenging the stable free radical diphenyl-2-picrylhydrazyl (DPPH). Moreover, butein has an IC50 of 5.9 μM against xanthine oxidase activity. In the aqueous phase, butein scavenges the peroxyl radical produced by 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH). Moreover, butein inhibits human low-density lipoprotein (LDL) oxidation caused by copper in a concentration-dependent manner. Butein functions as a chelator for copper and ferrous ions.[6]