acacetin and Skin-Neoplasms

The identification of primary molecular targets of cancer-preventive phytochemicals is essential for a comprehensive understanding of their mechanism of action. In the present study, we investigated the chemopreventive effects and molecular targets of acacetin, a flavonoid found in Robinia p seudoacacia, also known as black locust. Acacetin treatment significantly suppressed epidermal growth factor (EGF)-induced cell transformation. Immunoblot analysis revealed that acacetin attenuated EGF-induced phosphorylation of Akt and p70(S6K), which are downstream effectors of phosphatidylinositol 3-kinase (PI3-K). An immunoprecipitation kinase assay of PI3-K and pull-down assay results demonstrated that acacetin substantially inhibits PI3-K activity by direct physical binding. Acacetin exhibited stronger inhibitory effects against anchorage-dependent and -independent cell growth in cells expressing higher PI3-K activity compared with those exhibiting relatively low PI3-K activity. Binding assay data combined with computational modeling suggest that acacetin binds in an adenosine triphosphate (ATP)-competitive manner with the p110α subunit of PI3-K and interacts with Val828, Glu826, Asp911, Trp760, Ile777, Ile825, Tyr813, Ile910 and Met900 residues. Acacetin was also found to significantly reduce SK-MEL-28 tumor growth and Akt phosphorylation in vivo. Taken together, these results indicate that acacetin is an ATP-competitive PI3-K inhibitor and a promising agent for melanoma chemoprevention.

Topics: Adenosine Triphosphate; Animals; Antineoplastic Agents, Phytogenic; Cell Proliferation; Cell Transformation, Neoplastic; Class Ia Phosphatidylinositol 3-Kinase; Enzyme Inhibitors; Epidermal Growth Factor; Flavones; Mice; Mice, Nude; Molecular Docking Simulation; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proto-Oncogene Proteins c-akt; Skin Neoplasms; Tumor Cells, Cultured; Xenograft Model Antitumor Assays

Acacetin (5,7-dihydroxy-4'-methoxyflavone), a flavonoid compound, has anti-peroxidative and anti-inflammatory effects. In this study, we investigated the inhibitory effects of acacetin and a related compound, wogonin, on the induction of NO synthase (NOS) and COX-2 in RAW 264.7 cells activated with lipopolysaccharide (LPS). Acacetin markedly and actively inhibited the transcriptional activation of iNOS and COX-2. Western blotting, reverse transcription-polymerase chain reaction (PCR), and real-time PCR analyses demonstrated that acacetin significantly blocked protein and mRNA expression of iNOS and COX-2 in LPS-inducted macrophages. Treatment with acacetin reduced translocation of nuclear factor-kappa B (NF kappa B) subunit and the dependent transcriptional activity of NF kappa B. The activation of NF kappa B was inhibited by prevention of the degradation of inhibitor kappa B (I kappa B). Furthermore, acacetin inhibited LPS-induced phosphorylation as well as degradation of I kappa B alpha. We further investigated the roles of tyrosine kinase, phosphatidylinositiol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK) in LPS-induced macrophages. We found that acacetin also inhibited LPS-induced activation of PI3K/Akt and p44/42, but not p38 MAPK. After initiation of 7,12-dimethlybene[a]anthracene (DMBA), applying acacentin topically before each 12-O-tetradecanoylphorbol 13-acetat (TPA) treatment was found to reduce the number of papillomas at 20 weeks. Taken together, these results show that acacetin down regulates inflammatory iNOS and COX-2 gene expression in macrophages by inhibiting the activation of NF kappa B by interfering with the activation PI3K/Akt/IKK and MAPK, suggesting that acacetin is a functionally novel agent capable of preventing inflammation-associated tumorigenesis.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Anti-Inflammatory Agents, Non-Steroidal; Anticarcinogenic Agents; Cell Line; Cocarcinogenesis; Cyclooxygenase 2; Female; Flavones; Lipopolysaccharides; Macrophages; Mice; Mice, Inbred ICR; Nitric Oxide Synthase Type II; Papilloma; Skin Neoplasms; Tetradecanoylphorbol Acetate; Up-Regulation