Tissue distribution of copper-labeled 3-ethoxy-2-oxobutyraldehyde bis (thiosemicarbazone) (Cu-64 KTS) in mice and rats: concise communication

The antitumor activity of, 3-ethoxy-2-oxobutyraldehyde bis (thiosemicarbazone) (KTS), is related to the presence of copper(II) ion. We have studied the tissue distribution of Cu-64-labeled KTS in rats and mice carrying transplanted tumors to evaluate whether the uptake of the radioactivity in the tumor is adequate to warrant further investigation of the tracer as a tumor-seeking agent in patients. Four groups of three of four animals each were studied: (a) mice with fibrosarcoma; (b) mice with mammary adenocarcinoma; (c) rats with fibrosarcoma; and (d) rats with squamous cell carcinoma of the lung. The animals were killed at intervals of 0.25, 1, 4, 24, and 48 hr after i.v. injection of 1.6 X 10(-3) M Cu.KTS containing 3 to 18 muCi Cu-64. Blood, tumor, and six to ten additional tissues were counted for radioactivity. The mouse fibrosarcoma concentrated Cu-64, reaching 15% of the administered dose/g at 48 hr after injection. This suggests that for tumor scanning, the 61.7-hr Cu-67 might be more suitable as a label for KTS than the 12.7-hr Cu-64.