Synthesis and biological evaluation of EC20: a new folate-derived, (99m)Tc-based radiopharmaceutical

Bioconjug Chem. 2002 Nov-Dec;13(6):1200-10. doi: 10.1021/bc0200430.


A new peptide derivative of folic acid was designed to efficiently coordinate (99m)Tc. This new chelate, referred to as EC20, was found to bind cultured folate receptor (FR)-positive tumor cells in both a time- and concentration-dependent manner with very high affinity (K(D) approximately 3 nM). Using an in vitro relative affinity assay, EC20 was also found to effectively compete with (3)H-folic acid for cell binding when presented either alone or as a formulated metal chelate. Following intravenous injection into Balb/c mice, (99m)Tc-EC20 was rapidly removed from circulation (plasma t(1/2) approximately 4 min) and excreted into the urine in a nonmetabolized form. Data from gamma scintigraphic and quantitative biodistribution studies performed in M109 tumor-bearing Balb/c mice confirmed that (99m)Tc-EC20 predominantly accumulates in FR-positive tumor and kidney tissues. These results suggest that (99m)Tc-EC20 may be clinically useful as a noninvasive radiodiagnostic imaging agent for the detection of FR-positive human cancers.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport
  • Carrier Proteins / metabolism*
  • Drug Delivery Systems
  • Folate Receptors, GPI-Anchored
  • Folic Acid / analogs & derivatives*
  • Folic Acid / chemical synthesis
  • Folic Acid / metabolism*
  • Folic Acid / pharmacokinetics
  • Humans
  • KB Cells
  • Mice
  • Mice, Inbred BALB C
  • Molecular Structure
  • Neoplasm Transplantation
  • Oligopeptides / chemical synthesis
  • Oligopeptides / metabolism*
  • Oligopeptides / pharmacokinetics
  • Radiopharmaceuticals / chemical synthesis*
  • Radiopharmaceuticals / chemistry
  • Radiopharmaceuticals / metabolism*
  • Radiopharmaceuticals / pharmacokinetics
  • Receptors, Cell Surface*
  • Technetium*
  • Tissue Distribution


  • Carrier Proteins
  • EC20 folate peptide
  • Folate Receptors, GPI-Anchored
  • Oligopeptides
  • Radiopharmaceuticals
  • Receptors, Cell Surface
  • Technetium
  • Folic Acid