Affinity of 169Yb, 67Ga and 111In for malignant tumor, (2)

Comparisons of biological behavior of 169Yb-citrate and 111In-citrate and 67Ga-citrate in tumor tissue were performed by macro-autoradiography as well as by subcellular fractionation according to the method of Hogeboom and Schneider, using Yoshida sarcoma-bearing rats and Ehrlich tumor-bearing mice. The uptake of 169Yb, 67Ga and 111In into the tumor and various organs was assayed at 10, 30, 60 and 120 minutes after intravenous injection, using the rats subcutaneously transplanted with Yoshida sarcoma. Autoradiographical findings showed that the uptake of these nuclides was predominant in viable tumor tissue rather than in necrotic tumor tissue. Among subcellular fractions of Ehrlich tumor, most of the radioactivity was localized in the supernatant fraction and a small amount of radioactivity was found in the nuclear, mitochondria and microsome fractions. In Yoshida sarcoma, the results were almost similar in the three nuclides. And the specific activities of protein (cpm/mg) of these four fractions were not greatly different in the three nuclides. After intravenous injection of these nuclides, they were rapidly taken up into the tumor, and not excreted out of the tumor. It is a well-known fact that 169Yb, 67Ga and 111In are not sulfur coordinators, but weak nitrogen coordinators. Considering the above-described facts, it is presumed that the chemical bond of these elements is not a chelate ring, but an ionic bond. From an in vitro adsorption test of these nuclides with the hydroxy-apatite crystal and cation exchange resin, it is presumed that the reason for the strong affinity of 169Yb to the bone is attributed to the fact that 169Yb stays mostly in cation form in the blood. (auth.)