Study on Tumor Affinity of ^99mTc-labeled Radiopharmaceuticals

—^99mTc-Sn-Urokinase, ^99mTc-Sn-Mannitol—

Abstract

Biologic distribution of ^99mTc-labeled fibrinolytic agent, urokinase, and ^99mTc-labeled mannitol, which was obtained as a side-product in the preparation of ^99mTc (Sn) -urokinase, have been studied in Ehrlich's tumor-bearing mice to get a promising indicator for the positive delineation of malignant tumor. The preparation of ^99mTc-labeled radiophar-maceuticals, ^99mTc-UK and ^99mTc-Man, was made by the reduction with stannous chloride and labeling efficiency was examined by Sephadex G-25M gel chromatography and by silica gel plate thin layer chromatography. Labeling yield of ^99mTc-UK by Sephadex G-25M in 0.9% NaCl eluant was 13% and that of ^99mTc-Man by TLC in 85% methanol solvent was over 95%. A higher uptake to the implanted solid tumor tissue in mice was found in ^99mTc-Man than in ^99mTc-UK, of which the excellent tumor accumulation was expected from the positive delineation of malignant tumor with ¹³¹I-fibrinogen, ¹³¹I-fibrinogen antibody and ¹²⁵I-plasmin. The poor result in ^99mTc-UK, however, may be attributed to the poor fibrinolytie activity of Ehrlich's tumor. In biologic distribution of ^99mTc-UK was found high concentration for liver, kidney and stomach. In the other hand, a higher tumor tissue uptake, a fast blood disappearance and a low concentration for different organs were found in biologic distribution of ^99mTc-Man. Therefore, ^99mTc-Man may be assumed as a more preferable ^99mTc-labeled tumor localizing radiopharmaceuticals, to which it would be needed as absolute biologic characteristics that ^99mTc-labeled compounds possess a high tumor uptake as well as a fast blood disappearance with a low uptake for different organs. However, the possible delineation with ^99mTc-labeled fibrinolytic agents, including urokinase and streptokinase, may be promised for malignant tumors in human-subject, which generally have a higher activity in fibrinogenesis than in febrinolysis.