Noninvasive optical imaging of firefly luciferase reporter gene expressionin skeletal muscles of living mice

The ability to monitor reporter gene expression noninvasively offers signif icant advantages over current techniques such as postmortem tissue staining or enzyme activity assays. Here we demonstrate a novel method of repetitiv ely tracking in vivo gene expression of firefly luciferase (FL) in skeletal muscles of mice using a cooled charged coupled device (CCD) camera. We fir st show that the cooled CCD camera provides consistent and reproducible res ults within +/- 8% standard deviation from mean values, and a detection sen sitivity (range tested: 1 X 10(4) - 1 X 10(9) plaque forming units (pfu)) o f 1 X 10(6) pfu of E1 -deleted adenovirus expressing FL driven by a cytomeg alovirus promoter (Ad-CMV-PL). The duration and magnitude of adenoviral med iated (1 X 10(9) pfu) FL gene expression were then followed over time. FL g ene expression in immunocompetent Swiss Webster mice peaks within the first 48 hours, falls by 98% after 20 days, and persists for > 150 days. In cont rast, FL activity in nude mice remains elevated for > 110 days. Finally, tr ansduced Swiss Webster and nude mice were sacrificed to show that the in vi vo CCD signals correlate well with in vitro luciferase enzyme assays (r(2) = 0.91 and 0.96, respectively). Our findings demonstrate the ability of the cooled CCD camera to sensitively and noninvasively track the location, mag nitude, and persistence of FL gene expression. Monitoring of gene therapy s tudies in small animals may be aided considerably with further extensions o f this technique.