P2.01-086 Luteolin is a Novel Target of Axl Receptor Tyrosine Kinase to Inhibit Cell Proliferation and Circumvent Chemoresistance in Lung Cancer Cells

Abstract

Axl receptor tyrosine kinase (RTK) plays a critical role in cell growth, proliferation, and anti-apoptosis. In this study, we demonstrated the effect of luteolin, a non-toxic flavonoid widely found in various plants, on expression and activation of Axl RTK in NSCLC, H460, and its cisplatin-resistant cell, H460/CisR. 1. Cell viability measurement & Clonogenic assay. 2. Western blot analysis. 3. Promoter activity test. 4. Ectopic expression of Axl. 5. siRNA trasnfection for Axl knockdown. Luteolin treatment of H460 and H460/CisR cells was found to cause a dose-dependent decline of Axl protein as well as mRNA levels. Axl promoter activity was also reduced by luteolin, suggesting the transcriptional down-regulation of Axl expression by luteolin. Axl phosphorylation upon its ligand, Gas6, was inhibited by luteolin, indicating that luteolin also abrogates Gas6-induced Axl phosphorylation. Next, it was found that treatment of both H460 and H460/CisR cells with luteolin decreased the cell viability and clonogenic ability in dose-dependent manner. We further observed the synergistic anti-proliferative effect of luteolin in cells transfected with Axl specific siRNA, while the reduction of its cytotoxic effect in Axl RTK overexpressing cells, confirming that luteolin exerts its anticancer potential via interference of Axl expression. In addition, luteolin was found to result in the increase of p21, a cyclin-dependent kinase inhibitor, in H460 and H460/CisR cells. In summary, our data demonstrate that luteolin inhibits Axl expression and the activation which are associated with its anti-proliferative activity in both parental and cisplatin-resistant NSCLC cells. Thus, Axl seems to be a potent therapeutic target of luteolin to inhibit cell proliferation and to overcome chemoresistance of NSCLC cells.