Biodistribution and kinetics of holmium-166-chitosan complex (DW-166HC) in rats and mice

The fate of 166Ho-chitosan complex, a radiopharmaceutical drug for cancer therapy, was determined by studying its absorption, distribution and excretion in rats and mice. METHODS: Holmium-166-chitosan complex [0.75 mg of Ho(NO3)3 x 5H2O and 1 mg chitosan/ head] was administered intrahepatically to male rats. Radioactive concentrations in blood, urinary and fecal excretion and radioactive distribution in tissues were examined. To determine the effects of chitosan in 166Ho-chitosan complex, 166Ho alone [0.75 mg of Ho(NO3)3 x 5H2O/head] was intrahepatically administered to male rats, and radioactive concentrations in blood, urinary and fecal excretion and radioactive distribution were examined. In B16 melanoma-transplanted nude mice, radioactive distribution after intratumoral administration of 166Ho-chitosan complex [0.075 mg of Ho(NO3)3 x 5H2O and 0.10 mg chitosan/head] was investigated also. RESULTS: After administration of 166Ho-chitosan complex, the radioactive concentrations in blood were low, and cumulative urinary and fecal excretions over a period of 0-72 hr were 0.53% and 0.54%, respectively. The radioactive concentrations in tissues and the whole-body autoradiography images showed that most of the administered radioactivity was localized at the administration site, and only slight radioactivity was detected from the liver, spleen, lungs and bones. On the other hand, results of intrahepatic administration of 166Ho alone showed high radioactive concentrations in the blood, and the whole-body autoradiographs showed that the administered radioactivity was distributed in many organs and tissues. These results strongly suggest that 166Ho is retained at the administration site only when it forms a chelate complex with chitosan. Autoradiographs after intratumoral administration of 166Ho-chitosan complex showed that radioactivity was localized at the site of administration without distribution to the other organs and tissues. CONCLUSION: Administered 166Ho-chitosan complex is retained at the administration site after either intrahepatic or intratumoral administration to rats or tumor-transplanted nude mice.