Abstract 4110: Attenuation of colon cancer cell adaptation to hypoxia by cGMP-dependent protein kinase

There is growing evidence for the antitumor effects of cGMP-dependent protein kinase (PKG) in colon cancer cells. We reported recently that ectopically expressed PKG resulted in defective angiogenesis in xenografts, and was associated with reduced levels of vascular-endothelial growth factor (VEGF). In order to better understand the therapeutic potential of this enzyme, the present work has examined the mechanism of VEGF regulation by PKG. In contrast to the SW620 xenografts, PKG had no effect on VEGF expression in SW620 cells grown under standard tissue culture conditions in vitro. However, the increase in VEGF expression observed when the cells were subjected to hypoxic stress was significantly attenuated by PKG at both the mRNA and protein levels. Using luciferase reporter assays, PKG was shown to inhibit hypoxia inducible factor (HIF) transcriptional activity in several colon cancer cell lines, including SW620, HCT116, and HT29. The attenuation of HIF by PKG reflected a more fundamental inhibition of the hypoxic response, which was supported by the ability of PKG expression to block the hypoxia-induced activation of glycolytic genes including enolase and hexokinase 2. The reduced levels of glycolytic enzymes in PKG-expressing cells relative to control cells was associated with reduced glycolysis, mitochondrial activity, and cellular ATP levels under hypoxic conditions. While the inhibition of SW620 cell proliferation occurred independently of PKG expression in a 1% O2 environment, PKG reduced cell viability and increased necrosis under these conditions. These findings demonstrate for the first time that PKG can block the adaptation of colon cancer cells to hypoxia, and highlights this enzyme for further evaluation as a potential target for colon cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4110.