title: Chemical modification to reduce renal uptake of disulfide-bonded variable region fragment of anti-Tac monoclonal antibody labeled with 99mTc.
abstract: The anti-Tac disulfide-bonded variable region fragment (dsFv) is a genetically engineered, 25 kDa, murine monoclonal antibody fragment that recognizes the alpha subunit of the interleukin-2 receptor (IL-2Ralpha). The dsFv radiolabeled with the tetrafluorophenyl ester (TFP) of [99mTc]mercaptoacetyltriglycine ([99mTc]MAG3-TFP) showed rapid tumor uptake and fast blood clearance in mice, resulting in high tumor-to-nontumor background ratios. However, its high renal uptake was a problem. In this study, we tested the effect of lowering the isoelectric point (pI) of dsFv to <9.3 on renal and tumor uptake. To lower the pI, dsFv was acylated simultaneously with both [99mTc]MAG3-TFP and TFP-glycolate. The acylation of dsFv decreased its pI and its immunoreactivity inversely proportional to the molar ratio of TFP-glycolate to dsFv, whereas the conjugation of [99mTc]MAG3-TFP alone did not. When biodistribution studies were performed in nude mice, the effect of the lowered pI was reflected primarily in decreased kidney uptake and whole-body retention, with its highest effect seen at the earliest time point (15 min) after injection. In tumor-bearing nude mice, glycolated [99mTc]MAG3-dsFv with a pI range of 4.9 to 6.5 accumulated selectively into IL-2 receptor-positive SP2/Tac tumor similar to that of the control [125I]dsFv labeled by the Iodo-Gen method, whereas its renal uptake was 25% of [125I]dsFv at 15 min. At 90 min, the ratios of tumor to receptor-negative SP2/0 tumor, liver, kidney, stomach, and blood had peaked at 10.9, 8.5, 0.3, 5.0, and 6.2, respectively, for the glycolated [99mTc]MAG3-dsFv. The corresponding ratios for [125I]dsFv were 3.7, 5.0, 0.1, 1.5, and 2.1, respectively.
authors.affiliation: Nuclear Medicine Department, Warren G. Magnuson Clinical Center, Building 21, Room 136, and Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: I S
authors.initials: IS
authors.lastname: Kim
authors.forename: T M
authors.initials: TM
authors.lastname: Yoo
authors.forename: H
authors.initials: H
authors.lastname: Kobayashi
authors.forename: M K
authors.initials: MK
authors.lastname: Kim
authors.forename: N
authors.initials: N
authors.lastname: Le
authors.forename: Q C
authors.initials: QC
authors.lastname: Wang
authors.forename: I
authors.initials: I
authors.lastname: Pastan
authors.forename: J A
authors.initials: JA
authors.lastname: Carrasquillo
authors.forename: C H
authors.initials: CH
authors.lastname: Paik
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000378:metabolism; D004220:Disulfides; D005260:Female; D007135:Immunoglobulin Variable Region / Q000737:chemistry* / Q000378:metabolism; D007525:Isoelectric Focusing; D007668:Kidney / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D013667:Technetium; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D000911:Antibodies, Monoclonal; D004220:Disulfides; D007135:Immunoglobulin Variable Region; D015375:Receptors, Interleukin-2; D013667:Technetium