Abstract
Noninvasive bioluminescence imaging (BLI) of luciferase-expressing tumor cells has advanced pre-clinical evaluation of cancer therapies. Yet despite its successes, BLI is limited by poor spatial resolution and signal penetration, making it unusable for deep tissue or large animal imaging and preventing precise anatomical localization or signal quantification. To refine pre-clinical BLI methods and circumvent these limitations, we compared and ultimately combined BLI with tomographic, quantitative imaging of the sodium iodide symporter (NIS). To this end, we generated tumor cell lines expressing luciferase, NIS, or both reporters, and established tumor models in mice. BLI provided sensitive early detection of tumors and relatively easy monitoring of disease progression. However, spatial resolution was poor, and as the tumors grew, deep thoracic tumor signals were massked by overwhelming surface signals from superficial tumors. In contrast, NIS-expressing tumors were readily distinguished and precisely localized at all tissue depths by positron emission tomography (PET) or single photon emission computed tomography (SPECT) imaging. Furthermore, radiotracer uptake for each tumor could be quantitated noninvasively. Ultimately, combining BLI and NIS imaging represented a significant enhancement over traditional BLI, providing more information about tumor size and location. This combined imaging approach should facilitate comprehensive evaluation of tumor responses to given therapies.