Abstract
^153^Sm/^166^Ho‐chitosan complexes have been considered promising agents for internal radiation therapy. By direct administration, complexes solution converts into a gel, at physiological pH, allowing its retention for a long time. Herein, we report on the synthesis of ^153^Sm/^166^Ho complexes with the novel amino acid–chitosan polymers, N‐(γ‐propanoyl‐valin)–chitosan (CHICO‐val) and N‐(γ‐propanoyl‐aspartic acid)–chitosan (CHICO‐asp). The main goal of this study was to obtain data on the radiochemical and biological behaviour of these complexes and information regarding their therapeutic potential when compared to ^153^Sm/^166^Ho‐chitosan. Radiolabelling yield of ^153^Sm/^166^Ho‐amino acid–chitosan complexes was dependent on polymer concentration but less dependent on pH. Radiochemical stability was shown to be higher for amino acid–chitosans than for chitosan, with ^153^Sm/^166^Ho‐CHICO‐val being stable up to 3 h, while ^153^Sm/^166^Ho‐CHICO‐asp is stable up to 24 h. In the presence of ascorbic acid radiochemical stability of ^153^Sm/^166^Ho‐CHICO‐val and ^153^Sm/^166^Ho‐CHICO was improved, decreasing for ^153^Sm/^166^Ho‐CHICO‐asp. In vivo behaviour of ^153^Sm complexes was studied in mice. The radioactive amino acid–chitosans can be directly injected into blood stream without significant retention on injection site, being trapped by liver. Biodistribution studies suggest that the radioactive amino acid–chitosans, due to its water solubility and stability may be considered potential candidates to be further explored for liver targeted nuclear therapy. Copyright © 2008 John Wiley & Sons, Ltd.