Several clinical trials to test this concept in leukemia
patients are in progress. O126 Role of Tetrahydrobiopterin in Regulation of Tumor Angiogenesis Mediated by PI3K/Akt, eNOS and Ras Pathway Liye Chen1, Simon Briggs1, Eric O’Neill2, Jiliang Li3, Russell Leek3, David Kerr1, Adrian Harris3, Shijie Cai 1 1 Department of Clinical Pharmacology, University of learn more Oxford, Oxford, UK, 2 Gray Institute for Radiation Oncology and Biology, University of Oxford, Oxford, UK, 3 Cancer Research UK Medical Oncology Unit, University of Oxford, Oxford, UK Emerged evidence suggests endothelial nitric oxide synthase (eNOS)-derived NO is particularly important in tumour angiogenesis and hence a novel target TGF-beta cancer for cancer treatment. eNOS activation requires tetrahydrobiopterin
(BH4) as a cofactor for NO production. However, the role of BH4 in eNOS regulation, potentially involving phosphatidylinositol 3-kinase (PI-3K) signalling pathway, remains to be established. The effects of BH4 in tumour angiogenesis are not known. To investigate this pathway, we augmented BH4 levels in vascular endothelial cells by supplementing Captisol price cultures with sepiaterin, a BH4 precursor for the pterin salvage pathway synthesis. We also made a genetically modified murine fibroblast cell line over-expressing GTP cyclohydrolase I (GTPCH, the rate-limiting enzyme for the de novo BH4 synthesis) under doxycycline (Dox) control and analysed the effects in a mouse xenograft.
In cell cultures, sepiapterin increased Akt/eNOS phosphorylation in a dose dependent manner in COS-7 cells (no endogenous eNOS) transfected with human eNOS cDNA. This augmentation was abrogated by wortmannin or Ly294002, PI3K inhibitors. eNOS/Akt phosphorylation by sepiapterin in both HUVEC and bovine aortic endothelial cells (BAEC) was also significantly enhanced, Sodium butyrate in association with increases in NO production, cell proliferation and migration, and capillarity-like tube formation. Furthermore, sepiapterin greatly increased GTP-bound wild-type Ras protein. But this effect was diminished by L-NAME, an eNOS inhibitor. In mouse xenografts, GTPCH over-expression increased the expression of Ki67 and CD34 in tumour tissue. Conversely, switch off of GTPCH expression by Dox in drinking water or inhibition of its enzymatic activity by intraperitoneal injection of DAHP (GTPCH inhibitor) significantly decreased CD34 positive endothelial cells in mouse xenografts. This study demonstrates a critical role for BH4 in tumour angiogenesis, which is at least partially mediated by activating the pathway of PI3K/Akt/eNOS/wild-type Ras protein in vascular endothelial cells. Our findings suggest that BH4 synthesis may be a rational target for inhibiting tumour angiogenesis. O127 Angiotensin-(1–7) Inhibits Breast Tumor Growth in an Orthotopic Murine Model by Reducing Angiogenesis and Fibrosis Katherine Cook 1,2 , E. Ann Tallant1,2, Patricia E.