u-0126 and alpha-naphthoflavone

To investigate mechanisms of discrepancy in response to a MEK/ERK inhibitor, U0126, in KRAS- and BRAF-mutant colorectal cancer cells.. Multiparametric flow cytometry was performed on two colon cancer cell lines, HCT116 and HT29. Cells were treated with U0126, and phospho-specific antibodies were used to monitor ERK signaling.. HCT116 and HT29 cells were treated with increasing amounts of U0126. The western blot analysis revealed that by increasing the amount of U0126 resulted in inhibition of phospho-ERK, in HCT116 and to a lesser degree in HT29 cells. Microarray profiling identified CYP1A1 and 1A2 overexpression in HT29 cells and that inhibition of CYP1A1 with α-naphthoflavone and furanfylline restored sensitivity to U0126 in HT29 cells.. Combination of a CYP inhibitor with MEK/ERK inhibitor enhances the inhibitory effect on ERK in BRAF-mutant colon cancer cells.

Topics: Benzoflavones; Butadienes; Cell Line, Tumor; Cell Proliferation; Colonic Neoplasms; Cytochrome P-450 CYP1A1; Cytochrome P-450 CYP1A2; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Humans; MAP Kinase Signaling System; Nitriles; Proto-Oncogene Proteins B-raf

It was originally shown by Woerner and Schrenk [Woerner, W., Schrenk, D., 1998. 2,3,7,8-Tetrachlorodibenzo-p-dioxin suppresses apoptosis and leads to hyperphosphorylation of p53 in rat hepatocytes. Environ. Toxicol. Pharmacol. 6, 239-247] that TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) acts as an antagonist against the action of UV-irradiation to induce apoptosis in rat primary hepatocytes. Since prevention of apoptosis has been shown to promote carcinogenesis, we have decided to investigate this phenomenon in a human mammary gland epithelial cell line, MCF10A. We found that, in this cell line, TCDD can antagonize apoptosis that was induced by a variety of treatments, such as UV- and gamma-irradiation, growth factor starvation and trypsinization, or by the addition of H(2)O(2), TGFbeta, and staurosporine. Furthermore, other agents that are known to elicit defensive cellular responses, such as LPS, Fe(3+), nitric oxide and hypoxia could also antagonize UV induced apoptosis just as in the case of TCDD. In addition, we found that, in this cell line, such anti-apoptotic action of TCDD resembles that of exogenously added EGF or TGF alpha. To study the basic mechanism of such an action of TCDD, we tested a variety of diagnostic agents to reverse the effect of TCDD. Antagonists of TCDD which were found to be effective in this way were (a) inhibitors of c-Src kinase, such as PP-2 and CGP77675, (b) those known to block the action of TGF alpha, such as anti-TGF alpha antibody, and alpha(1)-antitrypsin, (c) PD98059, a specific inhibitor of ERK activation, but not SB202190 (an inhibitor of p38 MAPK activation) or SP600125 (a JNK inhibitor) and (d) Ah receptor antagonists, alpha-naphthoflavone and 1, 10-phenanthroline. These results support the notion that TCDD acts as an anti-apoptotic agent by mimicking the action of EGF through activation of the c-Src/ERK signaling pathway.

Topics: Adaptation, Physiological; alpha 1-Antitrypsin; Apoptosis; bcl-2-Associated X Protein; Benzoflavones; Butadienes; Cell Line; DNA Fragmentation; Epidermal Growth Factor; Epithelial Cells; Female; Ferric Compounds; Flavonoids; Glutathione; Humans; Hydrogen Peroxide; Lipopolysaccharides; Mitogen-Activated Protein Kinases; Nitriles; Nitro Compounds; Phenanthrolines; Polychlorinated Dibenzodioxins; Pyrimidines; Pyrroles; Quaternary Ammonium Compounds; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors; Transforming Growth Factor alpha; Ultraviolet Rays