Carnosol, a dietary diterpene, displays growth inhibitory effects leading to G1-phase cell cycle arrest and targets the 5'-AMP-activated protein kinase (AMPK) pathway in human prostate cancer PC3 cells.

3813

Prostate cancer (PCa) will be diagnosed in 218,890 males in the United States in 2007 and unfortunately, there are limited options for the successful management of this disease. Recently, there have been considerable activities directed toward the identification of dietary agents for both chemoprevention and the treatment of PCa. Carnosol, a dietary diterpene found in herbs that include basil, oregano, and sage, has been shown to display potent antioxidant properties. Additionally, traditional Chinese medicine uses rosemary extracts that contain high amounts of diterpenes and triterpenes to treat inflammatory conditions. Here, we evaluated carnosol for its potential anti-cancer properties in the human PCa PC3 cells. Using an MTT assay we found that carnosol (10 - 70 µM) decreases cell viability in a time and dose dependent manner. Next, we determined whether the decrease in cell viability was due to the induction of apoptosis and/or cell cycle arrest. We evaluated the effect of carnosol (20-60 uM) using flow cytometry and found that it induces G1-phase cell cycle arrest with limited proapoptotic effect. Cell cycle and apoptosis related proteins that were found to be modulated with carnosol included cyclins, cyclin dependent kinases, p21, Bax, and Bcl-2. To establish a more precise mechanism, we performed a protein array that evaluated 639 proteins involved in cell signaling pathways. A target of interest was identified as 5'-AMP-activated protein kinase (AMPK), a serine/threonine protein kinase involved in the regulation of energy balance of a cell. Significant upregulation of AMPK over a 48 hour period in PC3 cells treated with carnosol (40 µM) was observed. The role of AMPK has been studied in cardiovascular disease and metabolic disorders and shown to regulate fatty acid synthase and HMG-CoA reductase. It has been suggested that AMPK has an important role in carcinogenesis and should be considered as a novel target for anti-cancer drugs. We found that carnosol induces the upregulation of AMPK-β regulatory subunit having downstream effects consistent with cancer inhibition. As a result we are evaluating the role of carnosol in upregulating AMPK to modulate and interact with pathways directly or indirectly that include PTEN/PI3K/AKT and TSC2/mTOR/HSP70S6k1. Carnosol may be a novel dietary diterpene for the management of PCa.