Biodistribution of 18F- and 125I-labeled anti-Tac disulfide-stabilized Fv fragments in nude mice with interleukin 2 alpha receptor-positive tumor xenografts.
We evaluated the biodistribution, pharmacokinetics, and generation of catabolites of an 18F- and 125I-labeled anti-Tac disulfide-stabilized Fv fragment (dsFv) in tumor-bearing nude mice. This dsFv is genetically engineered from a murine monoclonal antibody that recognizes the alpha subunit of the interleukin 2 (IL-2 alpha) receptor. Labeling was performed with 18F using N-succinimidyl 4-([18F]fluoromethyl)benzoate or with 125I using the Iodo-Gen method. The immunoreactivities of the radiolabeled anti-Tac dsFv were > 82%. The biodistribution was evaluated (at 15, 45, and 90 min and 6 h) in athymic nude mice (approximately five/group) bearing s.c. tumor xenografts. Cell line A431 served as the IL-2 receptor-negative control tumor, whereas the ATAC4 cell line served as our IL-2 receptor-positive tumor. Animals received injections of 18F-labeled anti-Tac dsFv (0.7-1.4 megabecquerels/1.5-3 micrograms) and 125I-labeled anti-Tac dsFv (0.1-0.4 megabecquerels/0.9-1 microgram). Blood clearance for both preparations was rapid, with < 10% retained in the blood by 15 min. Maximum accumulation in ATAC4 tumors occurred between 45 and 90 min and peaked at a mean of 4.2% injected dose/g (18F) and 5.6% of injected dose/g (125I). At 6 h, the ATAC4 tumors contained 11 times more 18F and 3 times more 125I than did the A431 tumors. The ATAC4 tumor:blood ratios for the 18F and 125I were > 12:1 and > 1.4:1 at 6 h, respectively, whereas the ratios for the antigen-negative A431 tumor were less than 1. The kidneys were the major route of elimination. Catabolites appeared quickly and were identified as [125I]iodide and predominantly N-epsilon-[18F]4-fluoromethylbenzoyl(alpha-N-acetyl) lysine. This is the first study to evaluate the biodistribution of an 18F-labeled Fv fragment in vitro and in vivo. In vivo, the dsFv was taken up rapidly by the kidneys, producing lysine-containing catabolites for 18F-labeled dsFv and [125I]iodide for 125I-labeled dsFv.
Choi
C W
CW
Department of Nuclear Medicine, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892-1180, USA.
Lang
L
L
Lee
J T
JT
Webber
K O
KO
Yoo
T M
TM
Chang
H K
HK
Le
N
N
Jagoda
E
E
Paik
C H
CH
Pastan
I
I
D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics*; D005260:Female; D005462:Fluorine Radioisotopes; D006801:Humans; D007128:Immunoglobulin Fragments / Q000378:metabolism*; D007457:Iodine Radioisotopes; D051379:Mice; D008819:Mice, Nude; D011786:Quality Control; D016719:Radioimmunodetection; D015375:Receptors, Interleukin-2 / Q000032:analysis / Q000276:immunology*; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D005462:Fluorine Radioisotopes; D007128:Immunoglobulin Fragments; D007457:Iodine Radioisotopes; D015375:Receptors, Interleukin-2; C055966:immunoglobulin Fv