A heterodimeric [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] αvβ3/GRPr-targeting antagonist radiotracer for PET imaging of prostate tumors

Nucl Med Biol. 2014 Feb;41(2):133-9. doi: 10.1016/j.nucmedbio.2013.11.006. Epub 2013 Nov 28.

Abstract

Introduction: In the present study, we describe a (64)Cu-radiolabeled heterodimeric peptide conjugate for dual αvβ3/GRPr (αvβ3 integrin/gastrin releasing peptide receptor) targeting of the form [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] (RGD: the amino acid sequence [Arg-Gly-Asp], a nonregulatory peptide used for αvβ3 integrin receptor targeting; Glu: glutamic acid; NO2A: 1,4,7-triazacyclononane-1,4-diacetic acid; 6-Ahx: 6-amino hexanoic acid; and RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2), an antagonist analogue of bombesin (BBN) peptide used for GRPr targeting).

Methods: RGD-Glu-6Ahx-RM2] was conjugated to a NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) complexing agent to produce [RGD-Glu-[NO2A]-6-Ahx-RM2], which was purified by reversed-phase high-performance liquid chromatography (RP-HPLC) and characterized by electrospray ionization-mass spectrometry (ESI-MS). Radiolabeling of the conjugate with (64)Cu produced [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2 in high radiochemical yield (≥95%). In vivo behavior of the radiolabeled peptide conjugate was investigated in normal CF-1 mice and in the PC-3 human prostate cancer experimental model.

Results: A competitive displacement receptor binding assay in human prostate PC-3 cells using (125)I-[Tyr(4)]BBN as the radioligand showed high binding affinity of [RGD-Glu-[(nat)Cu-NO2A]-6-Ahx-RM2] conjugate for the GRPr (3.09±0.34 nM). A similar assay in human, glioblastoma U87-MG cells using (125)I-Echistatin as the radioligand indicated a moderate receptor-binding affinity for the αvβ3 integrin (518±37.5 nM). In vivo studies of [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] showed high accumulation (4.86±1.01 %ID/g, 1h post-intravenous injection (p.i.)) and prolonged retention (4.26±1.23 %ID/g, 24h p.i.) of tracer in PC-3 tumor-bearing mice. Micro-positron emission tomography (microPET) molecular imaging studies produced high-quality, high contrast images in PC-3 tumor-bearing mice at 4h p.i.

Conclusions: The favorable pharmacokinetics and enhanced tumor uptake of (64)Cu-NOTA-RGD-Glu-6Ahx-RM2 warrant further investigations for dual integrin and GRPr-positive tumor imaging and possible radiotherapy.

Keywords: Bombesin; Copper-64; Gastrin-releasing peptide; Prostate cancer; Prostate-specific membrane antigen.

Publication types

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

MeSH terms

  • Aminocaproic Acid
  • Animals
  • Cell Line, Tumor
  • Cell Transformation, Neoplastic
  • Copper Radioisotopes*
  • Dimerization*
  • Female
  • Heterocyclic Compounds / chemistry
  • Heterocyclic Compounds, 1-Ring
  • Humans
  • Integrin alphaVbeta3 / metabolism*
  • Male
  • Mice
  • Oligopeptides* / chemistry
  • Oligopeptides* / metabolism
  • Oligopeptides* / pharmacokinetics
  • Positron-Emission Tomography / methods*
  • Prostatic Neoplasms / diagnostic imaging
  • Prostatic Neoplasms / pathology*
  • Radioactive Tracers
  • Receptors, Bombesin / antagonists & inhibitors*
  • Receptors, Bombesin / metabolism

Substances

  • Copper Radioisotopes
  • Heterocyclic Compounds
  • Heterocyclic Compounds, 1-Ring
  • Integrin alphaVbeta3
  • Oligopeptides
  • Radioactive Tracers
  • Receptors, Bombesin
  • 1,4,7-triazacyclononane-N,N',N''-triacetic acid
  • arginyl-glycyl-aspartic acid
  • Aminocaproic Acid