Coordination-Mediated Synthesis of Purification-Free Bivalent 99mTc-Labeled Probes for in Vivo Imaging of Saturable System

Bioconjug Chem. 2018 Feb 21;29(2):459-466. doi: 10.1021/acs.bioconjchem.7b00788. Epub 2018 Jan 31.

Abstract

In the synthesis of technetium-99m (99mTc) labeled target-specific ligands, the presence of a large excess of unlabeled ligands over 99mTc in the injectate hinders target accumulation of 99mTc-labeled ligands by competing for target molecules. To circumvent the problem, we recently developed a concept of the metal coordination-mediated multivalency, and proved the concept with a 99mTc-labeled trivalent compound [99mTc(CO)3(CN-RGD)3]+. In this study, D-penicillamine (Pen) was selected as a chelating molecule and a cyclic RGDfK peptide was conjugated to Pen via a hexanoic linkage (Pen-Ahx-c(RGDfK)). 99mTc complexation reaction, and the stability, integrin αvβ3 binding affinity, and biodistribution of the 99mTc-labeled probe were investigated to evaluate the applicability of the concept to bivalent probes. 99mTc-[Pen-Ahx-c(RGDfK)]2 was obtained over 95% radiochemical yields under low Pen-Ahx-c(RGDfK) concentration (50 μM). 99mTc-[Pen-Ahx-c(RGDfK)]2 showed approximately 10-times higher integrin αvβ3 binding affinity than the monovalent compounds, Pen-Ahx-c(RGDfK) and c(RGDyV). In biodistribution studies, the tumor accumulation of 99mTc-[Pen-Ahx-c(RGDfK)]2 was decreased to 77% and 43% of HPLC-purified (Pen-Ahx-c(RGDfK)-free) 99mTc-[Pen-Ahx-c(RGDfK)]2 by the presence of 5 nmol of unlabeled Pen-Ahx-c(RGDfK) and Re-[Pen-Ahx-c(RGDfK)]2, respectively. 99mTc-[Pen-Ahx-c(RGDfK)]2 provided tumor image without removing unlabeled ligand, while a 99mTc-labeled monovalent probe prepared from a monovalent ligand could not. These findings indicate the availability of the design concept to prepare 99mTc-labeled bivalent probes with a variety of 99mTc core and other metallic radionuclides of clinical relevance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Chelating Agents / chemistry*
  • Chelating Agents / metabolism
  • Chelating Agents / pharmacokinetics
  • Humans
  • Integrin alphaVbeta3 / analysis
  • Integrin alphaVbeta3 / metabolism
  • Male
  • Mice, Inbred BALB C
  • Mice, Nude
  • Neoplasms / diagnostic imaging*
  • Neoplasms / metabolism
  • Organotechnetium Compounds / chemistry*
  • Organotechnetium Compounds / metabolism
  • Organotechnetium Compounds / pharmacokinetics
  • Penicillamine / chemistry*
  • Penicillamine / metabolism
  • Penicillamine / pharmacokinetics
  • Peptides, Cyclic / chemistry*
  • Peptides, Cyclic / metabolism
  • Peptides, Cyclic / pharmacokinetics
  • Technetium / chemistry*
  • Technetium / metabolism
  • Technetium / pharmacokinetics
  • Tissue Distribution
  • Tomography, Emission-Computed, Single-Photon / methods*

Substances

  • Chelating Agents
  • Integrin alphaVbeta3
  • Organotechnetium Compounds
  • Peptides, Cyclic
  • cyclic (arginyl-glycyl-aspartyl-phenylalanyl-lysyl)
  • Technetium
  • Penicillamine