Comparative evaluation of radionuclide therapy using Y and Lu.

Objective: Both Y and Lu are attractive β-emitters for radionuclide therapy and have been used in clinical practice. Nevertheless, comparative evaluation between Y- and Lu-labeled molecules has not been fully conducted. Thus, in this study, the features of Y and Lu for radionuclide therapy were assessed in tumor-bearing mice.

Methods: Two tumor cell lines with different growth rates were used. Biodistribution studies of Lu-labeled antibodies (Lu-Abs) were conducted in each tumor-bearing mouse model. Subsequently, the therapeutic effect of Y- and Lu-Ab were assessed in tumor-bearing mice. The absorbed radiation dose for the tumor was estimated using the Monte Carlo simulation.

Results: Lu-Abs demonstrated high tumor accumulation in both tumor-xerograph. In the fast-growing tumor model, Y-Ab showed a better therapeutic effect than Lu-Ab, reflecting a higher absorbed radiation dose of Y-Ab than that of Lu-Ab. In the slow-growing tumor model, both Y- and Lu-Ab showed an excellent therapeutic effect; however, Lu-Ab had a longer efficacy period than Y-Ab, which could be attributed to the longer half-life and better dose uniformity of Lu than those of Y.

Conclusions: To accomplish a maximum therapeutic effect, selecting Y or Lu, to depend on the growth rate of individual cancer, would be helpful.