Biodistribution of ⁹⁵Nb and ¹⁸²Ta in Tumor-bearing Animals and Mechanisms for Accumulation in Tumor and Liver

Abstract

The biodistribution and binding substances of ⁹⁵Nb and ¹⁸²Ta were investigated and compared with other nuclides using tumor-bearing rats and mice. Retention values of ⁹⁵Nb in tumor tissue were greater than those for ⁶⁷Ga-citrate, while those for ¹⁸²Ta were similar to those for ⁶⁷Ga. The values for these nuclides in the liver and spleen were much smaller than those for ⁶⁷Ga. However, the values for blood and some soft tissues were much greater than those for ⁶⁷Ga. The concentrations of ⁹⁵Nb and ¹⁸²Ta were more dominant in the connective tissue (especially inflammatory tissue) than in the other categories of tumor tissue. These nuclides accumulated rapidly into the mitochondrial fraction (containing lysosome) of the liver, reaching about 50% after 48 hours, but these nuclides existed relatively uniformly in the tumor cells. The main binding substance of these nuclides in the above tissues was the acid mucopolysaccharide whose molecular mass exceeded 40, 000 daltons. Radioactive niobium can be a potential tumor imaging agent. Among radioactive niobiums, ^95mNb has physical characteristics (half-life 90 hours, IT decay, 234-keV energy of 100% abundance) suitable for clinical imaging study.