A relatively new strategy to longitudinally monitor
tumor load in intact animals and the effects of
therapy is noninvasive bioluminescence imaging (BLI). The validity of BLIf or quantitative assessment of
tumor load in small animals is critically evaluated in the present review.
Cancer cells are grafted in mice or rats after transfection with a
luciferase gene--usually that of a firefly. To determine
tumor load, animals receive the substrate agent
luciferin intraperitoneally, which
luciferase converts into
oxyluciferin in an
ATP-dependent manner Light emitted by
oxyluciferin in viable
cancer cells is captured noninvasively with a highly sensitive charge-coupled device (CCD) camera. Validation studies indicate that BLI is useful to determine
tumor load in the course of time, with each animal serving as its own reference. BLI is rapid, easy to perform, and sensitive. It can detect
tumor load shortly after inoculation, even when relatively few
cancer cells (2500-10,000) are used. BLI is less suited for the determination of absolute
tumor mass in an animal because of quenching of bioluminescence by tissue components and the exact location of
tumors because its spatial resolution is limited. Nevertheless, BLI is a powerful tool for high-throughput longitudinal monitoring of
tumor load in small animals and allows the implementation of more advanced orthotopic
tumor models in
therapy intervention studies with almost the same simplicity as when measuring traditional ectopic subcutaneous models in combination with calipers.