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 sec ond-generation polyamidoamine dendrimer (PAMAM) conjugated with 2-(p-isothi ocyanatobenzyl)-6-methyl-diethylenetri-aminepentaacetic acid (1B4M), a deri vative 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 In-111 at 37-48 MBq/mg (1.0-1.3 mCi/mg) or with Y-88 at 3. 7 - 4.8 MBq/mg (0.1 - 0.13 mCi/mg), and an aliquot of radiolabeled conjugat e was saturated with the corresponding stable yttrium or indium. Nontumor-b earing nude mice were injected intravenously with 55.5-66.6 kBq (1.5-1.8 mu Ci) of Y-88-labeled PAMAM-1B4M or with 185 kBq (5 mu Ci) of In-111-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 label ed 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 injectio n and in ATAC4 and A431 tumor-bearing mice 18 h after injection were evalua ted and compared with those of In-111-labeled 1B4M-HuTac. We noted signific antly higher accumulations (p < 0.05) of 111In-labeled and Y-88-labeled uns aturated PAMAM-1B4M than saturated preparations in the liver, kidney, splee n, and bone at most time points. The whole-body clearance times of unsatura ted preparations were significantly slower than those of saturated preparat ions at all time points, with the exception of 168 h for; 111In-labeled PAM AM-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 conjugate d HuTac in normal organs of tumor-bearing mice was similar to nontumor bear ing mice. Specific tumor (ATAC4) uptake was higher than that in nonspecific tumor (A431). In conclusion, we evaluated the biodistribution of radiolabe led PAMAM 1B4M. We noted high accumulation in the liver, kidney, and spleen , which significantly decreased when the chelates were saturated with the s table element. A similar phenomenon was observed between unsaturated and sa turated 111In-labeled HuTac-PAMAM-1B4M, indicating that the PAMAM dendrimer had a detrimental effect on biodistribiution.