Radiolabeling antibodies with holmium-166

We report the preliminary results from radiolabeling of a chelate-conjugated antibody with 166Ho produced from the β-decay of 166Dy. Ho-166 was separated from mg quantities of Dy target by reverse phase ion-exchange chromatography employing a cation exchange HPLC column and 0.085 M α-HIBA at pH = 4.3 eluent. Evaporation to dryness of 166Ho fraction (up to 25 mL) and thermal decomposition of α-HIBA yielded 166Ho in a dry state which was then solubilized in 0.5 mL of 0.1 M HCl. Subsequent radiolabeling of CHX-B-DTPA conjugated 135-14 monoclonal antibodies with purified 166Ho was readily achieved with ∼ 80% efficiency and with a specific activity of 3-4 mCi of 166Ho per mg of protein. 166Ho-antibody conjugates are stable with regards to transferrin challenge for a period of 50 h. Further, it was shown that an Fe3+ ions present in α-HIBA as an impurity interfere with the labelling. (author)