Prostate cancer chemoprevention by penta-galloyl-glucose

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The overall goal of this research project is to develop Oriental herbal compound 1,2,3,4,6-penta-O-galloyl- beta-D-glucose (PGG) for the chemoprevention of prostate cancer (PCa), the number 2 cause of cancer death in US men. Our preliminary data show that PGG induced G1 and S-phase arrests in human LNCaP (p53 wild type, androgen dependent) and DU145 (mutant p53, androgen independent) PCa cells as well as caspase- mediated apoptosis involving reactive oxygen species (ROS). We data suggest novel targets/pathways of PGG for chemoprevention include a rapid inhibition of DNA replicative synthesis, and an activation of the p53 tumor suppressor and inactivating the Stat3 oncogenic signaling, associated with cyclin D1 (cell cycle) and Bcl-xL/Mcl-1 (cell survival) down regulation. Furthermore, PGG significantly inhibited the in vivo growth of human DU145 PCa xenografts in nude mice without adverse effect on body weight. In work accomplished by our collaborator Sung-Hoon Kim, PGG possesses potent anti-angiogenic activities and exerts a strong anti- tumor effect in a mouse lung cancer model. We hypothesize that PGG prevents PCa by inhibiting cancer cell proliferation through distinct G1 and S arrest mechanisms, inducing p53-dependent and -independent apoptosis and by inhibiting angiogenesis. We propose to accomplish 5 specific aims to test these hypotheses. Aim 1. To determine how PGG inhibits DNA replicative synthesis and the role in S-arrest and apoptosis with an emphasis on DNA damage/replicative stress-checkpoint pathways (e.g., ATM/ATR, p53). Aim 2. To investigate the role of cyclin D1 and Stat3 as targets for PGG to inhibit G1 progression and validate G1- and S- arrest mechanisms in mitogen-activated vascular endothelial cells as one mechanism of anti-angiogenesis action of PGG. Aim 3. To test the role and the subcellular origin of ROS in cell cycle arrests and apoptosis signaling and evaluate the contribution of the intrinsic and the extrinsic caspase cascades. In the above cell culture models, biochemical, pharmacological and genetic approaches will be used to establish cause-effects. Aim 4. To establish the chemopreventive efficacy of PGG against the autochthonous transgenic adenocarcinoma mouse prostate (TRAMP) model of primary prostate carcinogenesis. Aim 5. To characterize in vivo biomarkers of chemopreventive efficacy including cell proliferation, apoptosis, angiogenesis and molecular targets of PGG (e.g., cyclin D1, p-Stat3, Bcl-2 family, VEGF) using suitable tissues from Aim 4. The cell culture studies (Aims 1-3) will provide a comprehensive understanding of the novel mechanisms, targets and pathways of chemopreventive action of PGG through distinct cell cycle G1 and S-arrests and caspase-mediated apoptosis in PCa cells and in vascular endothelial cells. The animal studies (Aim 4) will test the merit of PGG to inhibit primary prostate carcinogenesis and in particular the prevention or delay of genesis of androgen-independent PCa. The biomarker analyses in Aim 5 will help to identify and validate in vivo relevant molecular targets and pathways for the chemopreventive efficacy of PGG. The overall goal of this research project is to develop Oriental herbal compound 1,2,3,4,6-penta-O-galloyl-beta- D-glucose (PGG) for the chemoprevention of prostate cancer (PCa), the number 2 cause of cancer death in US men. Chemoprevention has become recognized as a plausible and cost-effective alternative approach to reduce the morbidity and mortality of PCa. Our proposal is supported by exciting preliminary data that suggest novel mechanisms/targets for PGG to inhibit prostate cancer cell proliferation through not only G1 arrest but also S arrest and induces caspase-mediated apoptosis. In particular, our preliminary data support a potent and rapid inhibition of DNA replicative synthesis by PGG in PCa cells of diverse androgen-dependence and p53 status as a primary anti-proliferative mechanism. This, to our knowledge, has not been described for cancer chemopreventive agents so far studied. The proposed elucidation of the mechanisms could lead to the establishment of a new paradigm for a novel class of chemopreventive agents for not only prostate cancer, but also cancers of other organ sites. These multiple targeting activities plus published work supporting anti- angiogenesis activity provide strong rationale for testing the efficacy of PGG for prostate cancer chemoprevention.