Direct correlation between positron emission tomographic images of two reporter genes delivered by two distinct adenoviral vectors

Biodistribution, magnitude and duration of a therapeutic transgene's expres sion may be assessed by linking it to the expression of a positron emission tomography (PET) reporter gene (PRG) and then imaging the PRG's expression by a PET reporter probe (PRP) in living animals. We validate the simple ap proach of co-administering two distinct but otherwise identical adenoviruse s, one expressing a therapeutic transgene and the other expressing the PPG, to track the therapeutic gene's expression. Two PET reporter genes, a muta nt herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) and dopamine- 2 receptor (D2R), each regulated by the same cytomegalovirus (CMV) promoter , have been inserted into separate adenoviral vectors (Ad). We demonstrate that cells co-infected with equivalent titers of Ad-CMV-HSV1-sr39tk and Ad- CMV-D2R express both reporter genes with good correlation (r(2) = 0.93). Si milarly, a high correlation (r(2) = 0.97) was observed between the expressi on of both PRGs in the livers of mice co-infected via tail-vein injection w ith equivalent titers of these two adeno viruses. Finally, microPET imaging of HSV1-sr39tk and D2R expression with 9-(4-[F-18]fluoro-3-hydroxymethylbu tyl) guanine ([F-18]FHBG) and 3-(2-[F-18]fluoroethyl)spiperone ([F-18]FESP) , utilizing several adenovirus-mediated delivery routes, illustrates the fe asibility of evaluating relative levels of transgene expression in living a nimals, using this approach.