In vivo near-infrared fluorescence imaging of osteoblastic activity.

In vertebrates, the development and integrity of the skeleton requires hydroxyapatite (HA) deposition by osteoblasts. HA deposition is also a marker of, or a participant in, processes as diverse as cancer and atherosclerosis. At present, sites of osteoblastic activity can only be imaged in vivo using gamma-emitting radioisotopes. The scan times required are long, and the resultant radioscintigraphic images suffer from relatively low resolution. We have synthesized a near-infrared (NIR) fluorescent bisphosphonate derivative that exhibits rapid and specific binding to HA in vitro and in vivo. We demonstrate NIR light-based detection of osteoblastic activity in the living animal, and discuss how this technology can be used to study skeletal development, osteoblastic metastasis, coronary atherosclerosis, and other human diseases.