Chemical modification to reduce renal uptake of disulfide-bonded variable region fragment of anti-Tac monoclonal antibody labeled with 99mTc

Bioconjug Chem. 1999 May-Jun;10(3):447-53. doi: 10.1021/bc980129m.


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.

MeSH terms

  • Animals
  • Antibodies, Monoclonal / chemistry*
  • Antibodies, Monoclonal / metabolism
  • Disulfides
  • Female
  • Immunoglobulin Variable Region / chemistry*
  • Immunoglobulin Variable Region / metabolism
  • Isoelectric Focusing
  • Kidney / metabolism*
  • Mice
  • Mice, Nude
  • Neoplasm Transplantation
  • Receptors, Interleukin-2 / immunology*
  • Technetium
  • Tissue Distribution
  • Transplantation, Heterologous


  • Antibodies, Monoclonal
  • Disulfides
  • Immunoglobulin Variable Region
  • Receptors, Interleukin-2
  • Technetium