isoangustone-a and Prostatic-Neoplasms

Licorice extract which is used as a natural sweetener has been shown to possess inhibitory effects against prostate cancer, but the mechanisms responsible are poorly understood. Here, we report a compound, isoangustone A (IAA) in licorice that potently suppresses the growth of aggressive prostate cancer and sought to clarify its mechanism of action. We analyzed its inhibitory effects on the growth of PTEN-deleted human prostate cancer cells, in vitro and in vivo. Administration of IAA significantly attenuated the growth of prostate cancer cell cultures and xenograft tumors. These effects were found to be attributable to inhibition of the G1/S phase cell cycle transition and the accumulation of p27(kip1). The elevated p27(kip1) expression levels were concurrent with the decrease of its phosphorylation at threonine 187 through suppression of CDK2 kinase activity and the reduced phosphorylation of Akt at Serine 473 by diminishing the kinase activity of the mammalian target of rapamycin (mTOR). Further analysis using recombinant proteins and immunoprecipitated cell lysates determined that IAA exerts suppressive effects against CDK2 and mTOR kinase activity by direct binding with both proteins. These findings suggested that the licorice compound IAA is a potent molecular inhibitor of CDK2 and mTOR, with strong implications for the treatment of prostate cancer. Thus, licorice-derived extracts with high IAA content warrant further clinical investigation for nutritional sources for prostate cancer patients.

Topics: Animals; Antineoplastic Agents, Phytogenic; Blotting, Western; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase Inhibitor p27; Enzyme Activation; Fluorescent Antibody Technique; Glycyrrhizic Acid; Humans; Immunohistochemistry; Immunoprecipitation; Indicators and Reagents; Isoflavones; Male; Mice; Mice, Inbred BALB C; Phosphorylation; Prostatic Neoplasms; TOR Serine-Threonine Kinases; Xenograft Model Antitumor Assays

Although licorice is known to exert anticarcinogenic effects, it contains large quantities of glycyrrhizin (GL), which causes severe hypertension. We have previously demonstrated that the hexane/ethanol extract of Glycyrrhiza uralensis (HEGU) contains no detectable GL and suppresses doxorubicin-induced apoptosis in H9c2 rat cardiac myoblasts. The principal objective of this study was to determine whether and by what mechanism HEGU and its active component, isoangustone A, inhibit cell-cycle progression in DU145 human prostate and 4T1 mouse breast cancer cells. HEGU and isoangustone A dose-dependently decreased DNA synthesis and induced G1 phase arrest in both DU145 and 4T1 cells. HEGU and isoangustone A reduced the levels of CDK2 and CDK4 as well as cyclin A and cyclin D1 proteins, and also induced a decrease in CDK2 activity. The addition of HEGU to drinking water significantly suppressed the orthotopic growth of 4T1 allografts and the expression of the proliferating nuclear cell antigen, CDK2 and CDK4 proteins in the tumor tissues. These results demonstrate the potential of HEGU containing isoangustone A as an antitumor agent.

Topics: Animals; Antineoplastic Agents, Phytogenic; Apoptosis; Cell Line, Tumor; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinases; Cyclins; Female; G1 Phase; Glycyrrhiza uralensis; Humans; Isoflavones; Male; Mammary Neoplasms, Experimental; Mice; Mice, Inbred BALB C; Plant Extracts; Prostatic Neoplasms; Xenograft Model Antitumor Assays

Glycyrrhiza uralensis (licorice) is one of the most frequently prescribed ingredients in Oriental medicine, and licorice extract has been shown to exert anti-carcinogenic effects. However, its use as a cancer chemopreventive agent is rather limited, due to the fact that its principal component, glycyrrhizin, is known to induce hypertension. This study determined the effects of a hexane/ethanol extract of G. uralensis (HEGU), which contains undetectable amounts of glycyrrhizin, on the apoptosis of androgen-insensitive DU145 cells. HEGU induced apoptosis and increased the levels of cleaved caspase-9, caspase-7, caspase-3 and poly (ADP-ribose) polymerase (PARP). HEGU also induced mitochondrial membrane depolarization and cytochrome c release to the cytosol. HEGU increased the levels of Fas, death receptor 4 (DR4), cleaved caspase-8, Mcl-1S, and truncated Bid proteins. A caspase-8 inhibitor suppressed HEGU-induced apoptosis. An active fraction of HEGU was separated via column chromatography and the structure of the active compound isoangustone A was identified via 1H-NMR and 13C-NMR. Isoangustone A increased apoptotic cells, the cleavage of PARP and caspases, and the levels of DR4 and Mcl-1S. Transfection with DR4 small interfering RNA attenuated HEGU- and isoangustone A-induced apoptosis. These results demonstrate that the activation of DR4 contributes to HEGU- and isoangustone A-induced apoptosis of DU145 cells.

Topics: Antineoplastic Agents, Phytogenic; Apoptosis; Caspase Inhibitors; Caspases; Cell Line, Tumor; Cell Survival; Glycyrrhiza uralensis; Humans; Isoflavones; Male; Membrane Potential, Mitochondrial; Mitochondria; Molecular Structure; Myeloid Cell Leukemia Sequence 1 Protein; Permeability; Plant Extracts; Poly(ADP-ribose) Polymerases; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; Receptors, TNF-Related Apoptosis-Inducing Ligand; RNA, Small Interfering; Signal Transduction