Abstract B63: Synergistic combination between resveratrol and tanshinone I for effective prevention of pancreatic cancer

Pancreatic cancer is the fourth most common cause of cancer-related mortality in the United States. Pancreatic cancer is often dubbed the silent killer because it seldom causes symptoms until advanced. As a result, few pancreatic cancers are operable at diagnosis. Furthermore, pancreatic cancer is often resistant to conventional radiotherapy or chemotherapy, and the morbidity rate almost equals the mortality rate. Therefore, search for effective regimens with moderate side effects for pancreatic cancer therapy and prevention is an urgent necessity. Chinese herbal medicines have been used for centuries with demonstrated safety profiles, thus their bioactive ingredients may be effective candidates for the prevention and/or treatment of pancreatic cancer. Danshen (Salvia miltiorrhiza) has been widely adopted in the traditional Chinese medicinal preparations for treatment of cardiovascular disease with minimal side effects. In the present study, we evaluated the effect of several major Danshen components, tanshinone IIA (T2A), tanshinone I (T1) and cryptotanshinone (CT) on pancreatic cancer cells. We found that CT, T2A and T1 all showed inhibitory effects on the growth of human pancreatic cancer cell lines MIA PaCa-2 and ASPC-1 with IC50 around 30μM, 3–8μM and 3–5μM, respectively. The drug-resistant human pancreatic cancer cell line PANC-1 showed less sensitivity to CT and T2A treatment but was very sensitive to T1 treatment with IC50 around 3.5μM. The potent T1 activity against pancreatic cancer cells was associated with downregulation of several protein markers related to cell cycle (cyclin D and cyclin B) and anti-apoptosis (Bcl2 and survivin), c-myc and Aurora A and B kinases in both MIA PaCa-2 and PANC-1 cells. To further identify more potent synergistic combination effect of natural bioactive compounds against pancreatic cancer, we determined the anti-growth activity of the combination between T1 and resveratrol, a natural compound found in the skin of red grape and other fruits. T1 and resveratrol combinations consistently showed synergistic effect on inhibiting the growth of MIA PaCa-2, ASPC-1 and PANC-1 cells. Protein assays showed that the synergistic combination effect of T1 and resveratrol was associated with combined downregulation of c-myc and Aurora A protein levels, suggesting that T1 and resveratrol may inhibit the growth of pancreatic cancer cells in part via combined inhibition on the functions of c-myc and Aurora A. Aurora A is the kinase that plays a critical role in controlling mitosis and cell growth. We further confirmed if Aurora A was a functional target for the synergistic combination effect of T1 and resveratrol. Knockdown of Aurora A dramatically inhibited PANC-1 cell growth and decreased the T1 and resveratrol combination activity, suggesting that Aurora A could be one of the targets by the T1 and resveratrol combination effect. Aurora A gene promoter contains the c-myc binding site, suggesting that Aurora A may be regulated by c-myc and the inhibition of c-myc expression may be one of the causes of reduced Aurora A expression following T1 treatment. To confirm this, we treated PANC-1 cells with a c-myc inhibitor and found decreased Aurora A gene expression in a time-dependent manner, indicating the regulation of c-myc on Aurora A gene expression. Our results suggest that the T1 and resveratrol combination may serve as a novel chemopreventive regimen for effective prevention of pancreatic cancer. Supported in part by DOD (PC073988) and NCI/NIH (R21CA127794) Citation Information: Cancer Prev Res 2011;4(10 Suppl):B63.