Abstract 1583: Plumbagin, a medicinal plant-derived naphthoquinone with both chemopreventive and therapeutic properties, selectively inhibits expression of Protein Kinase Cε, a predictive biomarker of prostate cancer progression
Authors: Ajit K. Verma, Moammir H. Aziz, Bharat B. Aggarwal
Journal: Cancer Research (2010)

Abstract PKC is a major intracellular receptor for the mouse skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). PKC represents a large family of phosphatidylserine-dependent serine/threonine kinases. Protein kinase Cε (PKCε) is a member of the novel PKC sub-family. PKCε is a transforming oncogene and a predictive biomarker of various human cancers, including prostate cancer (PCa). We have shown that PKCε expression level correlates with human PCa aggressiveness. PKCε overexpression is sufficient to transform androgen-dependent LNCaP cells into an androgen-independent variant, which rapidly initiates growth in vivo in both intact and castrated male nude mice. PKCε silencing using specific siRNA in DU145 cells inhibits Stat3-regulated gene expression (COX-2) and cell invasion. Also, PKCε deletion (even one allele) in TRAMP mice prevents development of PCa. Taken together, the evidence indicates an association of PKCε to PCa development and aggressiveness. Thus, PKCε may be a potential molecular target for prevention and treatment of PCa. To screen for PKCε inhibitors, we evaluated by Western Blot analyses 19 plant-derived chemopreventive agents and found plumbagin (PL) to be a selective inhibitor of PKCε expression. In this experiment, human prostate DU145 cells at 70% to 80% confluency were serum starved for 24 hr. Cells were treated with various natural agents: curcurmin (50μM), capsaicin (50μM), silibinin (200μM), epigallocatechin gallate (25μM), resveratrol (50μM), diallyl sulfide (50μM), lycopene (10μM), apigenin (10μM), docosahexacnoic acid (10μM), caffeic acid (25μM), genistein (10μM), tocopherol (10μM), β-carotene (10%), guggul (50μM), PL (50μM), ursodeoxycholic acid (50μM) in DMSO (final concentration, 0.1%) for 6 hr. Whole-cell lysates were prepared and used for Western blot analysis of PKC isoforms (α, βI, βII, δ, ε, γ, η, μ. ζ). Proteins, normalized to β-actin, were quantitated and only PL inhibited PKCε expression. In a more detailed dose-response study (5-20μM) with PL determined 10μM as IC50 for PKCε. Treatment of PCa cells (DU145 and CW22Rv1) with PL inhibits activation of transcription factors (AP-1, Stat3 and NF-kB), cell invasion and PCa cell xenografts in nude mice (J Biol Chem 2006, 281:17023; Cancer Res. 2008, 68:9024). PL (5-hydroxy-2-methyl-1,4-napthoquinone), a medicinal plant-derived naphthoquinone, was isolated from the roots of the Plumbago zeylanica L. (also known as Chitrak;). The roots of Plumbago zeylanica have been used in Indian medicine for more than 2,500 years for treatments of various ailments. PL is also present in black walnut and other various medicinal plants. We conclude that PL may be explored as a naturally occurring agent in the prevention and treatment of prostate cancer (Support: NIH grant CA35368). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1583.