TY - JOUR T1 - 5-[<sup>123</sup>I/<sup>125</sup>I]Iodo-2′-Deoxyuridine in Metastatic Lung Cancer: Radiopharmaceutical Formulation Affects Targeting JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 800 LP - 806 VL - 46 IS - 5 AU - Elham Safaie Semnani AU - Ketai Wang AU - S. James Adelstein AU - Amin I. Kassis Y1 - 2005/05/01 UR - http://jnm.snmjournals.org/content/46/5/800.abstract N2 - This study assesses targeting of lung metastases in mice with the radioiodinated thymidine analog 5-[123I/125I]iodo-2′-deoxyuridine (123I-IUdR/125I-IUdR), formulated with varying amounts of tributyltin precursor and injected intravenously. Methods: Six- to 8-wk-old C57BL/6 mice were injected intravenously with B16F10 melanoma cells. Two weeks later, when lung tumors were established, the animals were injected intravenously with 125I-IUdR synthesized using 1, 35, 100, 150, 200, or 250 μg 5-tributylstannyl-2′-deoxyuridine (SnUdR) in the presence of an oxidant. Nontumor-bearing mice were also injected with these formulations and served as control animals. Twenty-four hours later, the animals were killed, and the radioactivity associated with the lungs and other tissues was measured in a γ-counter. The percentage injected dose per gram tissue (%ID/g) and tumor-to-nontumor ratios (T/NT ratios) were calculated. Phosphor imaging was done on lungs from tumor-bearing and nontumor-bearing mice injected with 125I-IUdR formulated with each tin precursor concentration. Scintigraphy was also performed 3 and 24 h after intravenous injection of 123I-IUdR. Results: The %ID/g 125I-IUdR was higher in lungs of tumor-bearing animals than in lungs of control animals. Although the increase in SnUdR present led to a small but statistically significant decrease in the radioactive content of normal lungs, a 3-fold increase was observed in the lungs of tumor-bearing animals with radiopharmaceutical formulated with 100 μg SnUdR (5 μg per mouse). This enhancement in radioactive uptake by the lungs led to approximately 14-fold increases in T/NT ratios. Phosphor imaging (125I-IUdR) of lungs as well as scintigraphy (123I-IUdR) of whole animals substantiated these findings. Conclusion: The formulation for the synthesis of radio-IUdR that leads to the highest %ID/g in tumor and the best T/NT ratio has been identified. Further studies are required to determine the factors responsible for specific enhancement in IUdR tumor uptake. ER -