Abstract1, 2, 3, 4, 6-penta-O-galloyl-β-D-glucose (PGG) is a polyphenolic compound highly enriched in a number of medicinal herbals. Several in vitro and a handful of in vivo studies have shown that PGG exhibits multiple biological activities which implicate a great potential for PGG in the therapy and prevention of several major diseases including cancer and diabetes. Chemically and functionally, PGG appears to be distinct from its constituent gallic acid or tea polyphenols. For anti-cancer activity, three published in vivo preclinical cancer model studies with PGG support promising efficacy to selectively inhibit malignancy without host toxicity. Potential mechanisms include antiangiogenesis, anti-proliferative actions through inhibition of DNA replicative synthesis and S-phase arrest and also G 1 arrest, induction of apoptosis, anti-inflammation and anti-oxidation. Putative molecular targets include p53, Stat3, Cox-2, VEGFR1, AP-1, SP-1, Nrf-2 and MMP-9. For antidiabetic activity, PGG and analogues appear to improve glucose uptake. However, very little is known about the absorption, pharmacokinetics and metabolism of PGG, nor its toxicity profile. The lack of large quantity of highly pure PGG has been a bottleneck limiting in vivo validation of cancer preventive and therapeutic efficacies in clinically relevant models.

Summary Accumulating evidence suggests that co-deletion of tumor suppressor genes Pten and p53 plays a crucial role in the development of castration-resistant prostate cancer in vivo. However, the molecular mechanism underlying Pten/p53-deficiency driven prostate tumorigenesis remains incompletely understood. Building upon insights gained from our studies with Pten/p53-deficient mouse embryonic fibroblasts (MEFs), we report here that hexokinase 2 (HK2) is selectively upregulated by the combined loss of Pten and p53 in prostate cancer cells. Mechanistically, Pten deletion increases HK2 mRNA translation through activation of the AKT-mTORC1-4EBP1 axis and p53 loss enhances HK2 mRNA stability through inhibition of miR143 biogenesis. Genetic studies demonstrate that HK2-mediated aerobic glycolysis, known as the Warburg effect, is required for Pten/p53-deficiency driven tumor growth in xenograft mouse models of prostate cancer. Our findings suggest that HK2 might be a therapeutic target for prostate cancer patients carrying Pten and p53 mutations.

Methylselenol has been implicated as an active anticancer selenium (Se) metabolite. However, its in vivo efficacy against prostate cancer (PCa) has yet to be established. Here, we evaluated the growth inhibitory effects of two presumed methylselenol precursors methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) in comparison with selenomethionine (SeMet) and selenite in DU145 and PC-3 human PCa xenografts in athymic nude mice. Each Se was given by a daily single oral dose regimen starting the day after the subcutaneous inoculation of cancer cells. We analyzed serum, liver and tumor Se content to confirm supplementation status and apoptosis indices and tumor microvessel density for association with antitumor efficacy. Furthermore, we analyzed lymphocyte DNA integrity to detect genotoxic effect of Se treatments. The data show that MSeA and MSeC exerted a dose-dependent inhibition of DU145 xenograft growth and both were more potent than SeMet and selenite, in spite of less tumor Se retention than in the SeMet-treated mice. Selenite treatment increased DNA single-strand breaks in peripheral lymphocytes, whereas the other Se forms did not. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) and cleaved caspase-3 indices (apoptosis) from MSeC-treated tumors were higher than tumors from control mice or MSeA-treated mice, whereas the microvessel density index was lower in tumors from MSeA-treated mice. In the PC-3 xenograft model, only MSeA was growth inhibitory at a dose of 3 mg/kg body wt. In summary, our data demonstrated superior in vivo growth inhibitory efficacy of MSeA over SeMet and selenite, against two human PCa xenograft models without the genotoxic property of selenite.