Optical bioluminescence and positron emission tomography imaging of a novel fusion reporter gene in tumor xenografts of living mice

Noninvasive imaging of reporter gene expression using various imaging modalities is playing an increasingly important role in defining molecular events in the field of cancer biology, cell biology, and gene therapy. In this study, a novel reporter vector was constructed encoding a fusion protein comprised of a mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) (tk), a positron emission tomography (PET) reporter gene, and renilla luciferase (H), a bioluminescence optical reporter gene joined by a 20 amino acid long spacer sequence. We validated the activity of the two enzymes encoded by the fusion protein (tk(20)rl) in cell culture. Then, tumors stably expressing the tk(20)rl fusion gene were imaged both by microPET and optically using a cooled charge coupled device camera in xenograft-bearing living mice. Using a single fusion reporter (PET/optical) gene should accelerate the validation of reporter gene approaches developed in cell culture for translation into preclinical and clinical models.