Non-invasive imaging of cardiac transgene expression with PET: comparison of the human sodium/iodide symporter gene and HSV1-tk as the reporter gene
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Genes encoding for intracellular enzymes or transmembrane proteins are suitable as reporters, but may differ in terms of applicability for cardiac imaging. The aim of this study was to compare the human sodium iodide symporter gene (hNIS) with the herpes simplex virus type 1 thymidine kinase gene (HSV1-tk) as the reporter gene in non-invasive imaging of cardiac transgene expression with positron emission tomography (PET).
Equal doses of adenoviral vectors encoding for hNIS, wild-type HSV1-tk, mutant HSV1-sr39tk or LacZ as the control gene were directly injected into the myocardium of 34 animals. Two days later, dynamic PET was performed with a clinical scanner, using reporter probes specific for the respective reporter gene. Imaging with 13N-ammonia was also performed to identify cardiac regions of interest.
Kinetics differed significantly: 124I as the probe for hNIS showed rapid early uptake, remaining stable over time. Maximal myocardial concentration was 3.61±1.15%. The nucleoside 18F-FHBG, as the specific probe for HSV1-sr39tk, showed increasing uptake over time, but maximal accumulation was significantly lower (1.45±0.54%, P=0.0009). 124I-FIAU, as the specific probe for wild-type HSV1-tk, showed early uptake with subsequent washout. Maximal accumulation was lowest (0.63±0.23%, P<0.0001). Post-mortem analysis by autoradiography and gamma counting confirmed the in vivo data.
Reporter genes encoding for transporter proteins such as hNIS are an attractive alternative to overexpression of intracellular enzymes for cardiac gene product imaging. hNIS yielded higher signal intensity and imaging contrast for PET than did HSV1-tk and HSV1-sr39tk. Therefore, this approach may be preferable for the future monitoring of cardiac gene- or cell-based therapy.
KeywordsGene therapy Myocardium Sodium iodide symporter HSV1-tk Adenovirus
This study was supported by research grants from the Deutsche Forschungsgemeinschaft (Be 2217/4-1). We thank the PET center, cyclotron unit and animal care unit of the Technische Universität München for assistance in the conduct of experiments. Dr. Sam Gambhir, Stanford University, California, USA, and Dr. Christine Spitzweg, Ludwig-Maximilians-University, Munich, Germany, are acknowledged for providing adenoviral vector constructs. We are grateful to Prof. Wolfgang Brandau, Nuklearmedizinische Klinik der Universität Essen, Germany, for providing 124I, and to Dr. Bernhanrd Noll, Forschungszentrum Rossendorf, Germany, for providing precursor for FHBG synthesis.
- 15.Bengel FM, Anton M, Avril N, Brill T, Nguyen N, Haubner R, et al. Uptake of radiolabeled 2′-fluoro-2′-deoxy-5-iodo-1-β-d-arabinofuranosyluracil in cardiac cells after adenoviral transfer of the herpesvirus thymidine kinase gene: the cellular basis for cardiac gene imaging. Circulation 2000;102:948–50PubMedGoogle Scholar
- 16.Gambhir SS, Bauer E, Black ME, Liang Q, Kokoris MS, Barrio JR, et al. A mutant herpes simplex virus type 1 thymidine kinase reporter gene shows improved sensitivity for imaging reporter gene expression with positron emission tomography. Proc Natl Acad Sci U S A 2000;97:2785–90Google Scholar
- 17.Hitt M, Bett AJ, Addison CL, Prevec L, Graham FL. Techniques for human adenovirus vector construction and characterization. In: Adolph KW, editor. Viral gene techniques. San Diego: Academic, 1995. p. 13–30Google Scholar
- 18.Brust P, Haubner R, Friedrich A, Scheunemann M, Anton M, Koufaki ON, et al. Comparison of [18F]FHPG and [124/125I]FIAU for imaging herpes simplex virus type 1 thymidine kinase gene expression. Eur J Nucl Med 2001;28:721–9Google Scholar