Abstract
We have shown that decursin, a coumarin compound, induces cell cycle arrest and apoptosis in human prostate cancer cells (PCa); however, its molecular mechanisms are largely unexplored. We studied the mechanisms associated with its anticancer activity in advanced human prostate carcinoma cells. We found that decursin inhibited epidermal growth factor receptor (EGFR) signaling by inhibiting its activating phosphorylation at tyrosine 1068 residue in DU145 and 22Rv1 cells. This inhibition of EGFR was associated with the downregulation of ERK1/2 phosphorylation. Both EGFR and ERK1/2 are known to be deregulated/activated in many human malignancies. Consistent with our earlier study, decursin (25-100 µM) treatment for 24-72 h inhibited DU145 cell proliferation by 49%-87% (p < 0.001) which was associated with strong G1 phase arrest and cell death. It also decreased (p < 0.001) the number of surviving colonies. Decursin moderately increased the expression of Rb-related proteins p107 and p130 but decreased the levels of E2F family transcription factors including E2F-3, E2F-4 and E2F-5. Further, decursin strongly inhibited the growth of androgen-dependent prostate carcinoma 22Rv1 cells from 61% to 79% (p < 0.001) and arrested these cells at G1 phase via induction of cyclin-dependent kinase inhibitor p27/Kip1 and downregulation of CDK2 and CDK4 protein expression. Additionally, EGFR inhibitor erlotinib- and EGF ligand-modulated EGFR activation validated EGFR signaling as a target of decursin-mediated cell growth inhibition and cytotoxicity. Decursin decreased EGF ligand-induced phosphorylation of EGFR (Y-1068) as well as activation of its downstream mediator, ERK1/2. Furthermore, inhibitory targeting of EGFR-ERK1/2 axis by combinatorial treatment of decursin and erlotinib further sensitized DU145 cells for the decursin-induced growth inhibition and cell death. Overall, these findings strongly suggest that anticancer efficacy of decursin against human PCa involves inhibitory targeting of EGFR-ERK1/2 signaling axis, a pathway constitutively active in advanced PCa.