The Role of Nitric Oxide Synthase Uncoupling in Tumor Progression.

Christopher S Rabender, Asim Alam, Gobalakrishnan Sundaresan, Robert J Cardnell, Vasily A Yakovlev, Nitai D Mukhopadhyay, Paul Graves, Jamal Zweit, Ross B Mikkelsen

Index: Mol. Cancer Res. 13 , 1034-43, (2015)

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Abstract

Here, evidence suggests that nitric oxide synthases (NOS) of tumor cells, in contrast with normal tissues, synthesize predominantly superoxide and peroxynitrite. Based on high-performance liquid chromatography analysis, the underlying mechanism for this uncoupling is a reduced tetrahydrobiopterin:dihydrobiopterin ratio (BH4:BH2) found in breast, colorectal, epidermoid, and head and neck tumors compared with normal tissues. Increasing BH4:BH2 and reconstitution of coupled NOS activity in breast cancer cells with the BH4 salvage pathway precursor, sepiapterin, causes significant shifts in downstream signaling, including increased cGMP-dependent protein kinase (PKG) activity, decreased β-catenin expression, and TCF4 promoter activity, and reduced NF-κB promoter activity. Sepiapterin inhibited breast tumor cell growth in vitro and in vivo as measured by a clonogenic assay, Ki67 staining, and 2[18F]fluoro-2-deoxy-D-glucose-deoxyglucose positron emission tomography (FDG-PET). In summary, using diverse tumor types, it is demonstrated that the BH4:BH2 ratio is lower in tumor tissues and, as a consequence, NOS activity generates more peroxynitrite and superoxide anion than nitric oxide, resulting in important tumor growth-promoting and antiapoptotic signaling properties.The synthetic BH4, Kuvan, is used to elevate BH4:BH2 in some phenylketonuria patients and to treat diseases associated with endothelial dysfunction, suggesting a novel, testable approach for correcting an abnormality of tumor metabolism to control tumor growth.©2015 American Association for Cancer Research.