GPx3 supports ovarian cancer progression by manipulating the extracellular redox environment.

Ovarian cancer remains the most lethal gynecologic malignancy, and is primarily diagnosed at late stage when considerable metastasis has occurred in the peritoneal cavity. At late stage abdominal cavity ascites accumulation provides a tumor-supporting medium in which cancer cells gain access to growth factors and cytokines that promote survival and metastasis. However, little is known about the redox status of ascites, or whether antioxidant enzymes are required to support ovarian cancer survival during transcoelomic metastasis in this medium. Gene expression cluster analysis of antioxidant enzymes identified two distinct populations of high-grade serous adenocarcinomas (HGSA), the most common ovarian cancer subtype, which specifically separated into clusters based on glutathione peroxidase 3 (GPx3) expression. High GPx3 expression was associated with poorer overall patient survival and increased tumor stage. GPx3 is an extracellular glutathione peroxidase with reported dichotomous roles in cancer. To further examine a potential pro-tumorigenic role of GPx3 in HGSA, stable OVCAR3 GPx3 knock-down cell lines were generated using lentiviral shRNA constructs. Decreased GPx3 expression inhibited clonogenicity and anchorage-independent cell survival. Moreover, GPx3 was necessary for protecting cells from exogenous oxidant insult, as demonstrated by treatment with high dose ascorbate. This cytoprotective effect was shown to be due to GPx3-dependent removal of extracellular H2O2. Importantly, GPx3 was necessary for clonogenic survival when cells were cultured in patient-derived ascites fluid. While oxidation reduction potential (ORP) of malignant ascites was heterogeneous in our patient cohort, and correlated positively with ascites iron content, GPx3 was required for optimal survival regardless of ORP or iron content. Collectively, our data suggest that HGSA ovarian cancers cluster into distinct groups of high and low GPx3 expression. GPx3 is necessary for HGSA ovarian cancer cellular survival in the ascites tumor environment and protects against extracellular sources of oxidative stress, implicating GPx3 as an important adaptation for transcoelomic metastasis.

Angiostatic actions of capsicodendrin through selective inhibition of VEGFR2-mediated AKT signaling and disregulated autophagy.

Angiogenesis is the formation of new blood vessels from existing vasculature critical for embryonic development and vascular remodeling. Its dysregulation underlies numerous pathologic states ranging from ischemia to tumor growth and as such identifying new targeted- therapies is of significant interest for angiogenesis-based medicine. Here we evaluated the potential angiostatic properties of capsicodendrin (CPCD), a natural compound isolated from Cinnamosma macrocarpa, a plant belonging to the Malagasy Cinnamosma. CPCD potently inhibits endothelial proliferation, migration and capillary tube formation at nanomolar to low micromolar concentrations without inducing cytotoxic effects. We show that CPCD directly inactivates VEGFR2 and downstream AKT signaling, thereby strongly inducing autophagy as determined by increased expression of beclin1, autophagy-related gene (Atg) 3, Atg5 and LC3 cleavage. Ectopic AKT overexpression counteracts the inhibitory effects of CPCD on proliferation and capillary tubule formation. Importantly, CPCD treatment in vivo inhibits sprouting angiogenesis as evidenced by strongly reduced intersegmental vessel (ISV) sprouting and subintestinal vessel (SIV) formation during zebrafish embryonic development, and correlates with increased presence of LC3II along the ISVs despite overall reduced vasculature. These findings demonstrate CPCD as a potent inhibitor of the VEGFR2/AKT pathway at nanomolar concentrations and inducer of autophagy-related angiostatic effects.