Radiolabeling antibodies with holmium-166.

We report the preliminary results from radiolabeling of a chelate-conjugated antibody with 166Ho produced from the beta(-)-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 alpha-HIBA at pH = 4.3 as eluent. Evaporation to dryness of 166Ho fraction (up to 25 mL) and thermal decomposition of alpha-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 166 Ho was readily achieved with approximately 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 any Fe3+ ions present in alpha-HIBA as an impurity interfere with the labeling.