title: Investigating the role of tumour cell derived iNOS on tumour growth and vasculature in vivo using a tetracycline regulated expression system.
abstract: Nitric oxide (NO) is a free radical signalling molecule involved in various physiological and pathological processes, including cancer. Both tumouricidal and tumour promoting effects have been attributed to NO, making its role in cancer biology controversial and unclear. To investigate the specific role of tumour-derived NO in vascular development, C6 glioma cells were genetically modified to include a doxycycline regulated gene expression system that controls the expression of an antisense RNA to inducible nitric oxide synthase (iNOS) to manipulate endogenous iNOS expression. Xenografts of these cells were propagated in the presence or absence of doxycycline. Susceptibility magnetic resonance imaging (MRI), initially with a carbogen (95% O2/5% CO2) breathing challenge and subsequently an intravascular blood pool contrast agent, was used to assess haemodynamic vasculature (ΔR2*) and fractional blood volume (fBV), and correlated with histopathological assessment of tumour vascular density, maturation and function. Inhibition of NO production in C6 gliomas led to significant growth delay and inhibition of vessel maturation. Parametric fBV maps were used to identify vascularised regions from which the carbogen-induced ΔR2* was measured and found to be positively correlated with vessel maturation, quantified ex vivo using fluorescence microscopy for endothelial and perivascular cell staining. These data suggest that tumour-derived iNOS is an important mediator of tumour growth and vessel maturation, hence a promising target for anti-vascular cancer therapies. The combination of ΔR2* response to carbogen and fBV MRI can provide a marker of tumour vessel maturation that could be applied to non-invasively monitor treatment response to iNOS inhibitors.
authors.affiliation: Cardiovascular and Cell Sciences Research Institute, St. George's, University of London, Cranmer Terrace, London, SW17 0RE, United Kingdom.
authors.forename: Efthymia
authors.initials: E
authors.lastname: Papaevangelou
authors.affiliation: Cardiovascular and Cell Sciences Research Institute, St. George's, University of London, Cranmer Terrace, London, SW17 0RE, United Kingdom.
authors.forename: Guy S
authors.initials: GS
authors.lastname: Whitley
authors.affiliation: Cardiovascular and Cell Sciences Research Institute, St. George's, University of London, Cranmer Terrace, London, SW17 0RE, United Kingdom.
authors.forename: Alan P
authors.initials: AP
authors.lastname: Johnstone
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, Belmont, Sutton, Surrey, SM2 5NG, United Kingdom.
authors.forename: Simon P
authors.initials: SP
authors.lastname: Robinson
authors.affiliation: Cardiovascular and Cell Sciences Research Institute, St. George's, University of London, Cranmer Terrace, London, SW17 0RE, United Kingdom.
authors.forename: Franklyn A
authors.initials: FA
authors.lastname: Howe
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003287:Contrast Media / Q000737:chemistry; D005609:Free Radicals; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005910:Glioma / Q000235:genetics* / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D051379:Mice; D009389:Neovascularization, Pathologic / Q000235:genetics*; D009569:Nitric Oxide / Q000096:biosynthesis / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis / Q000235:genetics*; D013752:Tetracycline / Q000008:administration & dosage; D023041:Xenograft Model Antitumor Assays
chemical_list: D003287:Contrast Media; D005609:Free Radicals; D009569:Nitric Oxide; C496319:NOS2 protein, human; D052247:Nitric Oxide Synthase Type II; D013752:Tetracycline
keywords: MRI; inducible expression; nitric oxide; nitric oxide synthase; tumour vessel maturation