Apigenin enhances gemcitabine-induced pancreatic cancer cell apoptosis

Abstract

Body. Pancreatic adenocarcinoma is only marginally responsive to its first-line chemotherapeutic agent, gemcitabine. Apigenin, a naturally occurring flavanoid, has been shown to inhibit growth in some cancer cell lines but has not been studied in pancreatic cancer. We hypothesized that apigenin would inhibit growth and enhance gemcitabine’s effect on pancreatic cancer cells. Methods. Four human pancreatic cancer cell lines (AsPC-1, CD18, MiaPaCa2, and S2013) were treated with varying concentrations (6.25–100 μM) of apigenin alone and in combination with gemcitabine (100 μM). Cells were analyzed at different time points (24–96 h). Proliferation was measured by 3H-thymidine incorporation and cell counting. Cell-cycle analysis and apoptosis was determined by flow cytometry with propidium iodide DNA staining and annexin-V binding. Cell-cycle-associated proteins were investigated by Western blotting. Analysis of variance was used to determine if there were significant differences among the means. Results. Apigenin caused both time- and concentration-dependent inhibition of DNA synthesis (55% decrease in 24 h, P < 0.001) and cell proliferation (81.4% decrease in 72 h, P < 0.001) of all four pancreatic cancer cell lines. Apigenin induced G2/M phase cell-cycle arrest (control 12.88% versus treated 21.54%, P < 0.002). Apigenin reduced levels of cyclin A, B, cdc2 phosphatase, and cdc25 (proteins required for G2/M transition). With gemcitabine, apigenin increased the number of apoptotic cells more than either agent alone (combination 32.5% versus control 5.0%, P < 0.001; versus apigenin 11.7%, P < 0.01; versus gemcitabine 15.3%, P < 0.05). Conclusions. Apigenin inhibits growth of pancreatic cancer cells through suppression of cyclin B-associated cdc2 activity and G2/M arrest. Even greater effect was seen in combination with gemcitabine. Apigenin enhances gemcitabine-induced apoptosis in pancreatic cancer cells and appears promising in combination as a chemotherapeutic agent.