Evaluation of the in vivo biodistribution of indium-111 and yttrium-88 labeled dendrimer-1B4M-DTPA and its conjugation with anti-tac monoclonal antibody

We evaluated the in vivo biodistribution of indium- and yttrium-labeled second-generation polyamidoamine dendrimer (PAMAM) conjugated with 2-(p-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid (1B4M), a derivative of DTPA. In addition, we conjugated PAMAM-1B4M to humanized anti-Tac IgG (HuTac) and evaluated its in vitro and in vivo properties. PAMAM-1B4M was labeled with ¹¹¹In at 37-48 MBq/mg (1.0-1.3 mCi/mg) or with ⁸⁸Y at 3.7-4.8 MBq/mg (0.1-0.13 mCi/mg), and an aliquot of radiolabeled conjugate was saturated with the corresponding stable yttrium or indium. Nontumor-bearing nude mice were injected intravenously with 55.5-66.6 kBq (1.5-1.8 mCi) of ⁸⁸Y-labeled PAMAM-1B4M or with 185 kBq (5 μCi) of ¹¹¹In-labeled PAMAM-1B4M. The mice were then sacrificed at 15 min, 90 min, 1 day, and 4 days postinjection. Then the PAMAM-1B4M was conjugated with HuTac and labeled with ¹¹¹In at 111-259 MBq/mg (3-7 mCi/mg). Another preparation of ¹¹¹In-labeled HuTac-PAMAM-1B4M was saturated with stable indium. Immunoreactivity of both preparations and biodistribution in normal mice 1 h after injection and in ATAC4 and A431 tumorbearing mice 18 h after injection were evaluated and compared with those of ¹¹¹In-labeled 1B4MHuTac. We noted significantly higher accumulations (p < 0.05) of ¹¹¹In-labeled and ⁸⁸Y-labeled unsaturated PAMAM-1B4M than saturated preparations in the liver, kidney, spleen, and bone at most time points. The whole-body clearance times of unsaturated preparations were significantly slower than those of saturated preparations at all time points, with the exception of 168 h for ¹¹¹In-labeled PAMAM-1B4M. The saturated preparation of ¹¹¹In-labeled HuTac-PAMAM-1B4M showed lower hepatic uptake (27 ± 2%ID/g) than the unsaturated (32 ± 2%ID/g), but greater than the HuTac1B4M control (10 ± 0%ID/g). The splenic uptake showed 15 ± 1, 38 ± 5, and 8 ± 1%ID/g for the saturated, unsaturated, and control, respectively. The biodistribution of the dendrimer conjugated HuTac in normal organs of tumor-bearing mice was similar to nontumor-bearing mice. Specific tumor (ATAC4) uptake was higher than that in nonspecific tumor (A431). In conclusion, we evaluated the biodistribution of radiolabeled PAMAM-1B4M. We noted high accumulation in the liver, kidney, and spleen, which significantly decreased when the chelates were saturated with the stable element. A similar phenomenon was observed between unsaturated and saturated ¹¹¹In-labeled HuTac-PAMAM-1B4M, indicating that the PAMAM dendrimer had a detrimental effect on biodistribution.