Bioluminescence and near-infrared fluorescence imaging for detection of metastatic bone tumors.

Bioluminescence imaging is being increasingly utilized in biological research. However, since the most commonly used firefly luciferase generates relatively weak bioluminescent signals, detection of low numbers of luciferase-expressing cells in vivo is challenging. The weak signal makes it difficult to detect cells located in deep tissues, which is problematic for preclinical research in tumor metastasis. In this study, three different types of fluorophores such as D-luciferin, AkaLumine-HCl, and P800SO3 were compared to evaluate the progression of bone metastasis induced by MDA-MB-231 breast cancer cells in vivo. The fluorescent signals for D-luciferin, AkaLumine-HCl, and P800SO3 were differently detected in the chest and knee joint. In particular, the fluorescence signal of P800SO3 was clearly observed in a section of the ribs, where it pointed out fractured bone fragments by tumor mass. Moreover, the P800SO3 signal from the left knee joint also showed a small bone fragment in the distal femur and was highlighted in the proximal tibia. Using targeted NIR fluorophores, metastatic bone tumors were monitored under the NIR fluorescence imaging system in real time, which enabled the in vivo diagnosis of bone metastasis by providing the location of the metastatic bone tumors.