Comparative biodistribution of indium- and yttrium-labeled B3 monoclonal antibody conjugated to either 2-(p-SCN-Bz)-6-methyl-DTPA (1 B4M-DTPA) or 2-(p-SCN-Bz)-1,4,7,10-tetraazacyclododecane tetraacetic acid (2B-DOTA)

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Abstract
The biodistribution of indium-111/yttrium-88-labeled B3 monoclonal antibody, a murine IgG1k, was evaluated in non-tumor-bearing mice. B3 was conjugated to either 2-(p-SCN-Bz)-6-methyl-DTPA (1B4M) or 2-(p-SCN-Bz)-1,4,7,10 tetraazacyclododecane tetra-acetic acid (2B-DOTA) and labeled with 111In at 1.4–2.4 mCi/mg and 88Y at 0.1–0.3 mCi/mg. Non-tumor-bearing nude mice were co-injected i.v. with 5–10 μCi/4–10 μg of 111In/88Y-labeled B3 conjugates and sacrificed at 6 h and daily up to 168 h post-injection. Mice injected with 111In/88Y (IB4M)-B3 showed a similar biodistribution of the two radiolabels in all tissues except the bones, where significantly higher accretion of 88Y than 111In was observed, with 2.8% ± 0.2% vs 1.3% ± 0.16% ID/g in the femur at 168 h, respectively (P111In/88Y-(DOTA)-B3 conjugate showed significantly higher accumulation of 111In than 88Y in most tissues, including the bones, with 2.0% ± 0.1% vs 1.2% ± 0.09% ID/g in the femur at 168 h, respectively (P111In/88Y-(IB4M)-B3 and 0.84, 1.23, 1.56, and 1.31 for 111In/88Y (DOTA)-B3, respectively, ratios ≈ 1 were observed between 111In-(IB4M)-B3 and 88Y-(DOTA)-B3. In summary, while neither IB4M nor DOTA was equally stable for 111In and 88Y, the fate of 88Y- (DOTA)-B3 could be closely traced by that of 111 In-(IB4M)-B3.

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