A simple and convenient method to estimate therapeutic radiopharmaceuticals for transcatheter arterial embolization

1299 Objectives: Co-administration of a therapeutic radiopharmaceutical with lipiodol enhances therapeutic efficacies of hepatomas by transcatheter arterial embolization (TAE). Efforts are being made to develop lipophilic radiopharmaceuticals of high residence time in lipiodol. Preclinical evaluation is made by injecting a candidate to hepatoma-bearing animals through the hepatic artery. Since the method is not suitable to narrow many compounds down to a few candidates, a hypodermal injection of a candidate in lipiodol to mice was estimated. Methods: 186Re-TDD (2,2,9,9-tetramethyl-4,7-diaza-1,10-decanedithiol) and 186Re-HDD (4-hexadecyl-2,2,9,9-tetramethyl-4,7-diaza-1,10-decanedithiol) were selected as model compounds. The partition coefficients of the two 186Re compounds between lipiodol and a buffered-solution (pH 7.4) were determined. Each compound in lipiodol was injected hypodermically to the left thigh of normal mice to pursue biodistribution. Results: Both 186Re compounds showed high radioactivity counts in lipiodol fractions after incubation with the buffer (95% for 186Re-TDD and 99% for 186Re-HDD). When injected to mice, 186Re-TDD showed rapid elimination rates from the injection sites. At 24 h postinjection, 1.1%ID of 186Re-TDD remained at the injection sites with over 70%ID excreted from the body. 186Re-HDD exhibited much higher radioactivity levels at the injection sites with over 60%ID present after 24 h. These results were well correlated with prior studies of the two 186Re compounds. Conclusions: The hypodermic injection of candidate compounds would constitute a useful procedure for screening of therapeutic radiopharmaceuticals for TAE.