Luteolin arrests cell cycling, induces apoptosis and inhibits the JAK/STAT3 pathway in human cholangiocarcinoma cells.

Cholangiocarcinoma (CCA) is one of the aggressive cancers with a very poor prognosis. Several efforts have been made to identify and develop new agents for prevention and treatment of this deadly disease. In the present study, we examined the anticancer effect of luteolin on human CCA, KKU-M156 cells. Sulforhodamine B assays showed that luteolin had potent cytotoxicity on CCA cells with IC50 values of 10.5±5.0 and 8.7±3.5 μM at 24 and 48 h, respectively. Treatment with luteolin also caused a concentration-dependent decline in colony forming ability. Consistent with growth inhibitory effects, luteolin arrested cell cycle progression at the G2/M phase in a dose-dependent manner as assessed by flow cytometry analysis. Protein expression of cyclin A and Cdc25A was down-regulated after luteolin treatment, supporting the arrest of cells at the G2/M boundary. Besides evident G2/M arrest, luteolin induced apoptosis of KKU-M156 cells, demonstrated by a distinct sub-G1 apoptotic peak and fluorescent dye staining. A decrease in the level of anti-apoptotic Bcl-2 protein was implicated in luteolin- induced apoptosis. We further investigated the effect of luteolin on JAK/STAT3, which is an important pathway involved in the development of CCA. The results showed that interleukin-6 (IL-6)-induced JAK/STAT3 activation in KKU-M156 cells was suppressed by treatment with luteolin. Treatment with a specific JAK inhibitor, AG490, and luteolin diminished IL-6-stimulated CCA cell migration as assessed by wound healing assay. These data revealed anticancer activity of luteolin against CCA so the agent might have potential for CCA prevention and therapy.