Biodistribution and excretion of radioactivity after the administration of Ho-chitosan complex (DW-166HC) into the prostate of rat

Purpose: The objective of this study was to determine the fate of the Ho-chitosan complex (DW-166HC) in rats by examining its absorption, distribution and excretion after administration into the prostate. Methods: About 100 Ci of DW-166HC [containing 0.1875 mg of Ho(NO3)3·5H2O and 0.25 mg of chitosan] was administered intraprostatically. The level of radioactivity in blood, urinary and faecal excretion, and radioactivity distributionwere examined. To determine the effect of chitosan in DW-166HC, Ho nitrate alone [0.1875 mg of Ho(NO3)3·5H2O] was administered into the prostate of male rats, and radioactivity distribution was examined using whole-body autoradiography. Results: After administration of DW-166HC into the prostate, cumulative urinary and faecal excretion over the period 0–72 h was 0.35% and 0.11%, respectively. The radioactivity at the administration site was extremely high at all time points up to 144 h (>98% of injected dose). The small amount of radioactivity which did transfer from the administration site distributed mainly to the liver, spleen, kidney cortex and bone. Compared with the DW-166HC group, the group that received Ho nitrate alone displayed threeto fourfold higher levels of radioactivity in the main tissues, including liver, spleen, kidney cortex and bone, at 24 h after administration (P<0.05). Conclusion:The results of this study show clearly that most of the administered DW-166HC remained at the administration site. It is concluded that the chitosan complex may be used to retain Ho within a limited area in cancer of the prostate.