Biological comparison of 149Pm-, 166Ho-, and 177Lu-DOTA-biotin pretargeted by CC49 scFv-streptavidin fusion protein in xenograft-bearing nude mice.

The radiolanthanides (149)Pm, (166)Ho, and (177)Lu possess a range of half-lives and alpha(-) beta(-) energies for targeted radiotherapy of cancer. (149)Pm-, (166)Ho-, and (177)Lu-DOTA-biotin were pretargeted to LS174T colorectal tumors in nude mice with CC49 scFvSA antibody-streptavidin fusion protein. Tumor uptakes of (149)Pm (22.9% ID/g), (166)Ho (30.2% ID/g), and (177)Lu (35.4% ID/g) peaked at 1-4 h. Rapid blood disappearance was accompanied by urinary excretion of 59-66% ID within 1 h. Biodistributions of these agents show promise for pretargeted radioimmunotherapy of cancer.