A Method to Rapidly and Accurately Compare the Relative Efficacies of Non-invasive Imaging Reporter Genes in a Mouse Model and its Application to Luciferase Reporters

Our goal is to develop a simple, quantitative, robust method to compare the efficacy of imaging reporter genes in culture and in vivo. We describe an adenoviral vector-liver transduction procedure and compare the luciferase reporter efficacies. Alternative reporter genes are expressed in a common adenoviral vector. Vector amounts used in vivo are based on cell culture titrations, ensuring that the same transduction efficacy is used for each vector. After imaging, in vivo and in vitro values are normalized to hepatic vector transduction using quantitative real-time PCR. We assayed standard firefly luciferase (FLuc), enhanced firefly luciferase (EFLuc), luciferase 2 (Luc2), humanized Renilla luciferase (hRLuc), Renilla luciferase 8.6-535 (RLuc8.6), and a membrane-bound Gaussia luciferase variant (extGLuc) in cell culture and in vivo. We observed greater than 100-fold increase in bioluminescent signal for both EFLuc and Luc2 when compared to FLuc and greater than 10(6)-fold increase for RLuc8.6 when compared to hRLuc. ExtGLuc was not detectable in liver. Our findings contrast, in some cases, with conclusions drawn in prior comparisons of these reporter genes and demonstrate the need for a standardized method to evaluate alternative reporter genes in vivo. Our procedure can be adapted for reporter genes that utilize alternative imaging modalities (fluorescence, bioluminescence, MRI, SPECT, PET).