Abstract
Strategies for non-invasive and quantitative imaging of gene expression in vivo have been developed over the past decade. Non-invasive assessment of the dynamics of gene regulation is of interest for the detection of endogenous disease-specific biological alterations (e.g., signal transduction) and for monitoring the induction and regulation of therapeutic genes (e.g., gene therapy). To demonstrate that non-invasive imaging of regulated expression of any type of gene after in vivo transduction by versatile vectors is feasible, we generated regulatable herpes simplex virus type 1 (HSV-1) amplicon vectors carrying hormone (mifepristone) or antibiotic (tetracycline) regulated promoters driving the proportional co-expression of two marker genes. Regulated gene expression was monitored by fluorescence microscopy in culture and by positron emission tomography (PET) or bioluminescence (BLI) in vivo. The induction levels evaluated in glioma models varied depending on the dose of inductor. With fluorescence microscopy and BLI being the tools for assessing gene expression in culture and animal models, and with PET being the technology for possible application in humans, the generated vectors may serve to non-invasively monitor the dynamics of any gene of interest which is proportionally co-expressed with the respective imaging marker gene in research applications aiming towards translation into clinical application.
Highlights
Molecular imaging has become an important technology to noninvasively assess and monitor disease-specific biological processes in vivo
Induction of gene expression can be detected in cell culture by fluorescence microscopy via RFP or eGFP expression and in vivo by positron emission tomography (PET) via TK expression
This study demonstrates for the first time a detailed quantitative analysis of inducible and regulated gene expression mediated by universal herpes simplex virus type 1 (HSV-1) amplicon vectors after in vivo transduction in experimental gliomas using imaging-guided vector administration
Summary
Molecular imaging has become an important technology to noninvasively assess and monitor disease-specific biological processes in vivo. It is based on nuclear, magnetic resonance and optical imaging. In recent years reporter systems for these imaging techniques have been developed allowing the analysis of dynamic processes of endogenous and exogenous gene expression in living animals [1,2,3,4]. To non-invasively assess exogenous gene expression, e.g., imaging expression of a therapeutic transgene, strategies have been developed to couple and proportionally co-express a reporter gene with a transgene of interest [7,8,9,10]. Saito [11] and Tjuvajev et al [12] first described the HSV-1-tk as a suitable reporter gene to follow herpes virus infection and to image the expression of gene transduction in vivo
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