The development and in-vivo behavior of tin containing radiopharmaceuticals--II. Autoradiographic and scintigraphic studies in normal animals and in animal models of bone disease.

Various 117mSn (2+ and 4+) compounds in well defined oxidation states were studied in normal mice using whole body autoradiography (WBARG), tissue distribution and scintigraphy in animal models of vitamin A induced bone disease, fracture, infected fracture and ischemic muscle lesions. The 117mSn4+-DTPA showed high affinity to normal bone with low soft tissue concentration. Increased deposition of this compound in fractures and ischemic lesions in muscle was also demonstrated. In hypervitaminosis A, reduced bone uptake of 117mSn4+-DTPA was shown to occur. Nude mice bearing osteogenic sarcoma of human origin showed uptake in spiculated pattern. The similar distribution of 117mSn4+-DTPA which does not contain phosphate or phosphonate groups, and the 99mTc(Sn) skeletal imaging compounds may indicate that tin is important in binding to bone. 117mSn4+-DTPA may not be ideal for routine imaging except when long term follow up is required. It should however be considered for therapy of bone tumors because of the long physical half-life of 117mSn (t1/2 = 14.03 days), abundance of short-range conversion and Auger electrons and its preferential deposition in cortical bone as indicated by our results.