Development of a Potent DOTA-conjugated Bombesin Antagonist for Targeting GRPr-positive Tumours

Eur J Nucl Med Mol Imaging. 2011 Jan;38(1):97-107. doi: 10.1007/s00259-010-1596-9. Epub 2010 Aug 18.

Abstract

Purpose: Radiolabelled somatostatin-based antagonists show a higher uptake in tumour-bearing mouse models than agonists of similar or even distinctly higher receptor affinity. Very similar results were obtained with another family of G protein-coupled receptor ligands, the bombesin family. We describe a new conjugate, RM2, with the chelator DOTA coupled to D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH(2) via the cationic spacer 4-amino-1-carboxymethyl-piperidine for labelling with radiometals such as (111)In and (68)Ga.

Methods: RM2 was synthesized on a solid support and evaluated in vitro in PC-3 cells. IC(50) and K(d) values were determined. The antagonist potency was evaluated by immunofluorescence-based internalization and Ca(2+) mobilization assays. Biodistribution studies were performed in PC-3 and LNCaP tumour-bearing mice with (111)In-RM2 and (68)Ga-RM2, respectively. PET/CT studies were performed on PC-3 and LNCaP tumour-bearing nude mice with (68)Ga-RM2.

Results: RM2 and (111)In-RM2 are high-affinity and selective ligands for the GRP receptor (7.7 ± 3.3 nmol/l for RM2; 9.3 ± 3.3 nmol/l for (nat)In-RM2). The potent antagonistic properties were confirmed by an immunofluorescence-based internalization and Ca(2+) mobilization assays. (68)Ga- and (111)In-RM2 showed high and specific uptake in both the tumour and the pancreas. Uptake in the tumour remained high (15.2 ± 4.8%IA/g at 1 h; 11.7 ± 2.4%IA/g at 4 h), whereas a relatively fast washout from the pancreas and the other abdominal organs was observed. Uptake in the pancreas decreased rapidly from 22.6 ± 4.7%IA/g at 1 h to 1.5 ± 0.5%IA/g at 4 h.

Conclusion: RM2 was shown to be a potent GRPr antagonist. Pharmacokinetics and imaging studies indicate that (111)In-RM2 and (68)Ga-RM2 are ideal candidates for clinical SPECT and PET studies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bombesin / antagonists & inhibitors*
  • Cell Line, Tumor
  • Drug Discovery*
  • Female
  • HEK293 Cells
  • Heterocyclic Compounds, 1-Ring / chemistry*
  • Humans
  • Male
  • Mice
  • Oligopeptides / chemistry
  • Oligopeptides / metabolism*
  • Oligopeptides / pharmacokinetics
  • Oligopeptides / pharmacology*
  • Prostatic Neoplasms / metabolism*
  • Prostatic Neoplasms / pathology
  • Protein Transport
  • Receptors, Bombesin / metabolism*
  • Xenograft Model Antitumor Assays

Substances

  • Heterocyclic Compounds, 1-Ring
  • Oligopeptides
  • Receptors, Bombesin
  • 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid
  • Bombesin