title: Positron emission tomography imaging of conditional gene activation in the heart.
abstract: The Cre-loxP system has been routinely used for conditional activation and deletion of gene expression. However, the spatiotemporal manner of these events in the heart has not yet been defined by in vivo imaging. Adenovirus (1 x 10(9 )pfu) carrying the silent positron emission tomography (PET) reporter gene, herpes simplex virus type 1 thymidine kinase (HSV1-tk), was injected into the left ventricular wall of male transgenic mice (n=15) or FVB controls (n=8). Transgenic mice expressed Cre recombinase driven by a cardiac-specific alpha-myosin heavy chain (alpha-MHC) promoter. Following injection of the 9-[4-fluoro-3-(hydroxymethyl)butyl]guanine ([18F]-FHBG; 137+/-25 microCi) reporter probe, microPET imaging was used to assess the expression of HSV1-tk reporter gene in the myocardium. Two days following adenoviral injection, cardiac HSV1-tk gene activation resulted in tracer uptake of 3.20+/-0.51% ID/g for alpha-MHC-Cre and 0.05+/-0.02%ID/g for control mice (P<0.01). The in vivo results were confirmed by RT-PCR and Western blot analysis. Similar transfections were evaluated in both cardiac-specific and non-cardiac-specific cell lines. Enzyme activity showed a robust correlation (r2=0.82) between in vivo molecular imaging technique and traditional in vitro enzyme assays. With further development and validation, PET imaging will likely play an important role in the noninvasive, repetitive, and quantitative measurement of conditional gene activation in the future.
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS) and Department of Radiology, Stanford University, Palo Alto, CA, USA.
authors.forename: Gwendolen Y
authors.initials: GY
authors.lastname: Chang
authors.forename: Feng
authors.initials: F
authors.lastname: Cao
authors.forename: Manickam
authors.initials: M
authors.lastname: Krishnan
authors.forename: Mei
authors.initials: M
authors.lastname: Huang
authors.forename: Zongjin
authors.initials: Z
authors.lastname: Li
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Xie
authors.forename: Ahmad Y
authors.initials: AY
authors.lastname: Sheikh
authors.forename: Grant
authors.initials: G
authors.lastname: Hoyt
authors.forename: Robert C
authors.initials: RC
authors.lastname: Robbins
authors.forename: Tzung
authors.initials: T
authors.lastname: Hsiai
authors.forename: Michael D
authors.initials: MD
authors.lastname: Schneider
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Wu
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D005786:Gene Expression Regulation; D006321:Heart / Q000000981:diagnostic imaging*; D019426:Integrases / Q000378:metabolism; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D011401:Promoter Regions, Genetic; D011859:Radiography; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D015533:Transcriptional Activation; D024723:Ventricular Myosins / Q000235:genetics / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; C045073:Cre recombinase; D019426:Integrases; D024723:Ventricular Myosins