Rhein inhibits angiogenesis and the viability of hormone-dependent and -independent cancer cells under normoxic or hypoxic conditions in vitro.

Hypoxia is a hallmark of solid tumors, including breast cancer, and the extent of tumor hypoxia is associated with treatment resistance and poor prognosis. Considering the limited treatment of hypoxic tumor cells and hence a poor prognosis of breast cancer, the investigation of natural products as potential chemopreventive anti-angiogenic agents is of paramount interest. Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid), the primary anthraquinone in the roots of Cassia alata L., is a naturally occurring quinone which exhibits a variety of biologic activities including anti-cancer activity. However, the effect of rhein on endothelial or cancer cells under hypoxic conditions has never been delineated. Therefore, the aim of this study was to investigate whether rhein inhibits angiogenesis and the viability of hormone-dependent (MCF-7) or -independent (MDA-MB-435s) breast cancer cells in vitro under normoxic or hypoxic conditions. Rhein inhibited vascular endothelial growth factor (VEGF(165))-stimulated human umbilical vein endothelial cell (HUVEC) tube formation, proliferation and migration under normoxic and hypoxic conditions. In addition, rhein inhibited in vitro angiogenesis by suppressing the activation of phosphatidylinositol 3-kinase (PI3K), phosphorylated-AKT (p-AKT) and phosphorylated extracellular signal-regulated kinase (p-ERK) but showed no inhibitory effects on total AKT or ERK. Rhein dose-dependently inhibited the viability of MCF-7 and MDA-MB-435s breast cancer cells under normoxic or hypoxic conditions, and inhibited cell cycle in both cell lines. Furthermore, Western blotting demonstrated that rhein inhibited heat shock protein 90alpha (Hsp90α) activity to induce degradation of Hsp90 client proteins including nuclear factor-kappa B (NF-κB), COX-2, and HER-2. Rhein also inhibited the expression of hypoxia-inducible factor-1 alpha (HIF-1α), vascular endothelial growth factor (VEGF(165)), epidermal growth factor (EGF), and the phosphorylation of inhibitor of NF-κB (I-κB) under normoxic or hypoxic conditions. Taken together, these data indicate that rhein is a promising anti-angiogenic compound for breast cancer cell viability and growth. Therefore, further studies including in vivo and pre-clinical need to be performed.

trans-resveratrol inhibits hyperglycemia-induced inflammation and connexin downregulation in retinal pigment epithelial cells.

The purpose of this study was to determine the inhibitory activity of trans-resveratrol against hyperglycemia-induced inflammation and degradation of gap junction intercellular communication in retinal pigment epithelial cells. Retinal (ARPE-19) cells were incubated with 5.5 mM glucose, 5.5 mM glucose and 10 microM resveratrol, 33 mM glucose, or 33 mM glucose and 0-10 microM trans-resveratrol at 37 degrees C and 5% CO(2) for 9 days. Cell viability was determined by the crystal violet assay. The levels of low-grade inflammation biomarkers interleukin-6 and interleukin-8 (IL-6 and IL-8), angiogenic factors, and vascular endothelial growth factor (VEGF) were determined by the enzyme-linked immunosorbent assay (ELISA). Gap junction intercellular communication (GJIC) was determined by the scrape-load/dye transfer method. The expression levels of protein kinase Cbeta (PKCbeta), connexin 43 (Cx43), transforming growth factor-beta1 (TGF-beta1), and cyclooxygenase-2 (COX-2) were determined by Western blot. Incubation of retinal cells with 10 microM trans-resveratrol in the presence of 5.5 mM glucose did not affect any of the biomarkers investigated. Incubation of ARPE-19 cells with 33 mM glucose for 9 days significantly induced the accumulation of VEGF, IL-6, IL-8, TGF-beta, and COX-2, activation of PKCbeta, and reduction of Cx43 and GJIC. Incubation of ARPE-19 cells with 33 mM glucose in the presence of 0-10 microM trans-resveratrol dose-dependently inhibited VEGF, TGF-beta1, COX-2, IL-6, and IL-8 accumulation, PKCbeta activation, and Cx43 degradation and enhanced GJIC. These data suggest that trans-resveratrol can protect the retinal pigment epithelial cells against hyperglycemia-induced low-grade inflammation and GJIC degradation.