3-[123I]Iodo-L-alpha-methyl tyrosine transport into human fibroblasts and comparison with Ewing's sarcoma cells

Characterization of 123I-iodo-α-methyltyrosine transport in rat lymphoma cells

(123)I-Iodo-alpha-methyltyrosine (IMT) transport into lymphomas has not been fully characterized. In rat Nb2-11C and Nb2-Sp lymphoma cell lines, linear uptake of (123)I-IMT occurred rapidly within 5-10 min. Eadie-Hoftee plots of (123)I-IMT uptake gave apparent Km's of 8.34+/-1.17 and 9.64+/-1.05 microM for Nb2-11C and Nb2-Sp cells, respectively, and involved the L and B(0,+) systems. In lymphoma-bearing rats, injected (123)I-IMT accumulated rapidly in the primary tumors but gave a low tumor-to-background ratio of 2:1. (123)I-IMT was transported rapidly into lymphoma cells both in vitro and in vivo, but low target-to-nontarget ratio may not make (123)I-IMT practical for scanning in vivo.

Characterization of uptake of 3-[131I]iodo-α-methyl-L-tyrosine in human monocyte-macrophages

The radiopharmaceutical 3-[(123)I]iodo-alpha-methyl-L-tyrosine ([(123)I]IMT) can be used to study amino acid transport by single-photon emission tomography (SPET). In order to evaluate the potential contribution of [(123)I]IMT accumulation in macrophages to overall uptake values measured in neoplastic lesions in vivo, we studied the mechanisms governing the uptake of this tracer by human monocyte-macrophages (HMMs). HMMs were isolated from healthy human donors by density gradient centrifugation using Ficoll methods. The human glioblastoma cell line U-138 MG (GLIOs) was obtained from American Type Culture Collection. Using multiwell dishes, cells were incubated in phosphate buffered saline or an equivalent sodium-free buffer with 50 kBq [(131)I]IMT per well. [(131)I]IMT uptake was quantified as % injected dose per mass of protein within each culture well. Several natural and artificial amino acids were used as potential transport inhibitors both in sodium-containing and sodium-free medium. [(131)I]IMT uptake was significantly lower in HMMs than in GLIOs (34 +/- 2 %/mg (40 min) vs. 507 +/- 50 %/mg at 30 minutes of incubation, respectively; p < 0.01). Endotoxin (LPS) significantly increased [(131)I]IMT uptake in HMMs by a factor of approximately 2. Transport into non-stimulated HMMs was exclusively sodium-independent and inhibitable by BCH, but not by MeAIB. Under LPS stimulation exclusively, there was in addition also a sodium-dependent inhibition of [(131)I]IMT uptake by L-arginine and MeAIB, albeit to a minor extent. [(131)I]IMT accumulation in HMMs is mainly mediated via an L-like amino acid transport system and increases on HMM activation by LPS. LPS may induce an additional Na(+)-dependent transport system in HMMs. The considerably lower [(131)I]IMT uptake in HMMs than in GLIOs suggests that overall uptake values of this tracer measured by SPET in tumors are not significantly affected by [(123)I]IMT accumulation in macrophages within the neoplastic lesion.