QS301. Apigenin Potentiates Gemcitabine-Induced Growth Arrest of Pancreatic Cancer Cells Through Blocking of Gemcitabine-Induced Upregulation of Cell Cycle Proteins

Introduction: Despite attempts of curative resection and adjuvant therapy, patients diagnosed with pancreatic cancer continue to have a poor prognosis. Novel therapeutics are currently under investigation. The flavonoid apigenin exhibits growth inhibition in several cancer cell lines. We have previously shown that apigenin inhibits pancreatic cancer cell proliferation through the induction of G2/M cell cycle arrest. In the present study we evaluated the effects of combination therapy with apigenin and gemcitabine on cell proliferation, the cell cycle and the pro-survival factor pAkt. Further, we evaluate the effect of Apiginen in Gemcitabine-resistant pancreatic cancer cells. Methods: Cell counting and thymidine incorporation were utilized to assess the combination effects of apigenin and gemcitabine on AsPC-1 and CD18 human pancreatic cancer cell proliferation. Flow cytometry was used to evaluate the effects of apigenin and gemcitabine treatment on the cell cycle. Western blot analysis was used to evaluate pAkt, cyclin A, cyclin B, cyclin E and CDK2 expression as a function of apigenin alone, gemcitabine alone or in combination in CD 18, AsPC-1 and AsPC-1 Gemcitabine-resistant cells. Results: Combination treatment with apigenin (25 μM) and gemcitabine (10 μM) significantly inhibited cell number and cell proliferation compared to controls and gemcitabine alone in both CD18 and AsPC-1 human pancreatic cancer cells (P<0.05). Apigenin down-regulated pAkt expression and prevented gemcitabine mediated pAkt induction in both CD18 and AsPC-1 cell lines. As determined by flow cytometry, combination treatment induced cells to accumulate in the S phase. Gemcitabine induced the expression of cyclin A, cyclin B, cyclin E and CDK2. In the combination treatment, apigenin blocked gemcitabine-induced upregulation of the aforementioned cell cycle proteins. Furthermore, apigenin treatment (0-100 μM) inhibited cell proliferation of AsPC-1 cells resistant to gemcitabine (P<0.01). Conclusions: Combination treatment with apigenin and gemcitabine inhibited cell growth in human pancreatic cells, causing cell cycle arrest in the S phase. Apigenin blocked gemcitabine’s induction of cell cycle regulatory proteins as well as pro-survival factor p-Akt. These results indicate combination therapy may prove useful for the treatment of pancreatic cancer.