Improved renal clearance and tumor targeting of 99mTc-labeled anti-Tac monoclonal antibody Fab by chemical modifications

Nucl Med Biol. 2002 Feb;29(2):139-46. doi: 10.1016/s0969-8051(01)00296-7.

Abstract

This study was undertaken to improve the renal clearance and tumor targeting properties of 99mTc-labeled humanized anti-Tac (HuTac) monoclonal antibody Fab fragments using two chemical approaches: 1) labeling with a renal secretion agent 99mTc-mercaptoacetyltriglycine (MAG3) and 2) lowering its isoelectric point (pI) by acylation. HuTac Fab (3.3 mg/mL) was reacted with a trifluorophenyl ester (TFP) of 99mTc-MAG3 alone or was additionally reacted with TFP-glycolate to reduce the pI. In Balb/c mice, 99mTc-MAG3-Fab (pI > 9.3) rapidly accumulated in the kidneys (177% injected dose [ID]/g at 15 min) and then gradually cleared out of the kidneys. In contrast, the glycolation (pI 4.6 approximately 6.6) drastically reduced the renal uptake (31% ID/g) and also the whole-body retention (82% ID vs 101% for the nonglycolated) at 15 min, indicating that the glycolated 99mTc-MAG3-Fab (pI 4.6 approximately 6.6) was rapidly excreted. The glycolated remained in the blood longer than the nonglycolated (1.2% vs 0.3% ID/g at 360 min), but this effect was less drastic than the effect shown on the renal uptake. In nude mice bearing receptor-positive (ATAC4) tumors, the glycolated 99mTc-MAG3-Fab increased the peak tumor uptake to 14.8% ID/g from 8.3% ID/g for 99mTc-MAG3-Fab, whereas the glycolation resulted in a drastic reduction of the renal uptake at 15 min. We demonstrated that the renal clearance and the tumor targeting of Fab could be optimized by chemical modifications.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Antibodies, Monoclonal / pharmacokinetics*
  • Female
  • Glycolates / pharmacology
  • Hydrogen-Ion Concentration
  • Immunoglobulin Fab Fragments / metabolism*
  • Iodine Radioisotopes / blood
  • Iodine Radioisotopes / urine
  • Kidney / metabolism*
  • Lysine / pharmacology
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Neoplasms / diagnostic imaging
  • Neoplasms / metabolism*
  • Radionuclide Imaging
  • Radiopharmaceuticals / pharmacokinetics*
  • Technetium Tc 99m Mertiatide / pharmacokinetics*
  • Tissue Distribution

Substances

  • Antibodies, Monoclonal
  • Glycolates
  • Immunoglobulin Fab Fragments
  • Iodine Radioisotopes
  • Radiopharmaceuticals
  • Technetium Tc 99m Mertiatide
  • Lysine