Carnosol, a Dietary Diterpene, Displays Growth Inhibitory Effects in Human Prostate Cancer PC3 Cells Leading to G sub(2)-Phase Cell Cycle Arrest and Targets the 5'-AMP-Activated Protein Kinase (AMPK) Pathway

Purpose: This study examines the anti-cancer effect of carnosol in human prostate cancer PC3 cells and its role in modulating multiple signaling pathways associated with carcinogenesis. Methods: PC3 cells were treated with carnosol and were evaluated using a flow cytometry, a protein array and Western blot analysis to identify signaling pathways targeted by carnosol. Results: Using an MTT assay we found that carnosol (10-70 mu M) decreases cell viability in a time and dose-dependent manner. Further analysis using flow cytometry as well as biochemical analysis identified G sub(2)-phase cell cycle arrest. To establish a more precise mechanism, we performed a protein array that evaluated 638 proteins involved in cell signaling pathways. The protein array identified 5'-AMP-activated protein kinase (AMPK), a serine/threonine protein kinase involved in the regulation of cellular energy balance as a potential target. Further downstream effects consistent with cancer inhibition included the modulation of the mTOR/HSP70S6k/4E-BP1 pathway. Additionally, we found that carnosol targeted the PI3K/Akt pathway in a dose dependent manner. Conclusions: These results suggest that carnosol targets multiple signaling pathways that include the AMPK pathway. The ability of carnosol to inhibit prostate cancer in vitro suggests carnosol may be a novel agent for the management of PCa.