We isolated a coumarin compound decursin (C19H20O5; molecular wt. 328) from Korean angelica (Angelica gigas) root by silica gel column and thin layer chromatography, and characterized it by IR, NMR and MS. Here, for the first time we observed that decursin (25, 50 and 100 μM) treatment for 24-96 h strongly inhibits growth (22-90%; P<0.01-0.001) and induces death (15-45% versus 11-12% in controls; P<0.01-0.001) of advanced human prostate carcinoma DU145 cells. Further, we observed that decursinol [in which (CH3)2-C=CH-COO- side chain in decursin is substituted with -OH group] has much lower growth inhibitory effect as compared to decursin, suggesting a possible structure-activity relationship of these compounds in which decursin side chain could be attributed for its anticancer efficacy. Further, in mechanistic investigation, decursin-induced cell growth inhibition was associated with a strong increase in G1 arrest in cell cycle progression, which started at 12 h and persisted through 72 h of the treatment with optimum effects at 24 h. After 24 h of (25-100 μM) decursin treatment, 50-78% cells (P<0.001) were accumulated in G1 phase in a dose-dependent manner as compared to 45% cells in control. The increase in G1 cell population was mainly at the expense of S phase cell population (6-29% decrease, P<0.01) and to a lesser extent a decrease in G2-M phase cell population. Consistent with these results, decursin strongly increased the protein expression of cyclin-dependent kinase (cdk) inhibitors Cip1/p21 and Kip1/p27 with a slight decrease in cdk2, 4 and 6 and cyclin D1 levels. As expected, decursin also decreased kinase activities associated with cdk 2 and 4, and cyclin D1 and E. Annexin V-staining showed that decursin-caused cell death is associated with an increase in apoptosis (9-38% at 50-100 μM doses of decursin for 24-48 h versus 6-8% in controls; P<0.01-0.001). Further, we observed that caspase cascade is the major pathway activated by decursin. Western blot analysis showed a strong increase in cleaved levels of caspase-9 and -3 as well as poly (ADP-ribose) polymerase by decursin. Next, we observed that pre-treatment with all caspase inhibitor (z-VAD-fmk) completely reversed the decursin-induced apoptosis. These findings suggest a novel anticancer efficacy of decursin mediated via induction of G1 arrest and apoptosis against hormone refractory human prostate carcinoma DU145 cells, and warrant further in vivo investigation.
[Proc Amer Assoc Cancer Res, Volume 45, 2004]