GLV-1h68 imaging in vivo shows selective and prolonged virus-mediated luciferase activity in tumors. A. Established MSKQLL2 flank tumors were injected with GLV-1h68 (5 × 106 pfu) and luciferase activity imaged following retro-orbital coelenterazine injections over a 10 day period. The late reduction of luciferase activity correlated with tumor size regression. B. Quantification of luciferase activity over a 10 day time course using software assessment of emitted photons was performed (n = 3 animals). C & D. MSKQLL2 flank tumors were excised 3 days after GLV-1h68 injection and stained for β-galactosidase expression (C) or examined under a GFP filter after tumors were exposed surgically (D) for photomicroscopy (100×).