Evolution of Bombesin Conjugates for Targeted PET Imaging of Tumors

Hanwen Zhang, Keelara Abiraj, Daniel L J Thorek, Beatrice Waser, Peter M. Smith-Jones, Michael Honer, Jean Claude Reubi, Helmut R. Maecke

Research output: Contribution to journalArticle

Abstract

Bombesin receptors are under intense investigation as molecular targets since they are overexpressed in several prevalent solid tumors. We rationally designed and synthesized a series of modified bombesin (BN) peptide analogs to study the influence of charge and spacers at the N-terminus, as well as amino acid substitutions, on both receptor binding affinity and pharmacokinetics. This enabled development of a novel 64/67Cu-labeled BN peptide for PET imaging and targeted radiotherapy of BN receptor-positive tumors. Our results show that N-terminally positively charged peptide ligands had significantly higher affinity to human gastrin releasing peptide receptor (GRPr) than negatively charged or uncharged ligands (IC50: 3.2±0.5 vs 26.3±3.5 vs 41.5±2.5 nM). The replacement of Nle14 by Met, and deletion of D-Tyr6, further resulted in 8-fold higher affinity. Contrary to significant changes to human GRPr binding, modifications at the N-terminal and at the 6th, 11th, and 14th position of BN induced only slight influences on affinity to mouse GRPr. [CuII]-CPTA-[βAla11] BN(7-14) ([CuII]-BZH7) showed the highest internalization rate into PC-3 cells with relatively slow efflux because of its subnanomolar affinity to GRPr. Interestingly, [64/67Cu]-BZH7 also displayed similar affinities to the other 2 human BN receptor subtypes. In vivo studies showed that [64/67Cu]-BZH7 had a high accumulation in PC-3 xenografts and allowed for clear-cut visualization of the tumor in PET imaging. In addition, a CPTA-glycine derivative, forming a hippurane-type spacer, enhanced kidney clearance of the radiotracer. These data indicate that the species variation of BN receptor plays an important role in screening radiolabeled BN. As well, the positive charge from the metallated complex at the N-terminal significantly increases affinity to human GRPr. Application of these observations enabled the novel ligand [64/67Cu]-BZH7 to clearly visualize PC-3 tumors in vivo. This study provides a strong starting point for optimizing radiopeptides for targeting carcinomas that express any of the BN receptor subtypes.

Original languageEnglish (US)
Article numbere44046
JournalPLoS One
Volume7
Issue number9
DOIs
StatePublished - Sep 14 2012
Externally publishedYes

Fingerprint

bombesin
Bombesin Receptors
positron-emission tomography
Bombesin
Tumors
Imaging techniques
neoplasms
Neoplasms
peptides
Ligands
Peptides
bombesin receptors
Pharmacokinetics
Radiotherapy
amino acid substitution
radiotherapy
Amino Acid Substitution
in vivo studies
glycine (amino acid)
Heterografts

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

Zhang, H., Abiraj, K., Thorek, D. L. J., Waser, B., Smith-Jones, P. M., Honer, M., ... Maecke, H. R. (2012). Evolution of Bombesin Conjugates for Targeted PET Imaging of Tumors. PLoS One, 7(9), [e44046]. https://doi.org/10.1371/journal.pone.0044046

Evolution of Bombesin Conjugates for Targeted PET Imaging of Tumors. / Zhang, Hanwen; Abiraj, Keelara; Thorek, Daniel L J; Waser, Beatrice; Smith-Jones, Peter M.; Honer, Michael; Reubi, Jean Claude; Maecke, Helmut R.

In: PLoS One, Vol. 7, No. 9, e44046, 14.09.2012.

Research output: Contribution to journalArticle

Zhang, H, Abiraj, K, Thorek, DLJ, Waser, B, Smith-Jones, PM, Honer, M, Reubi, JC & Maecke, HR 2012, 'Evolution of Bombesin Conjugates for Targeted PET Imaging of Tumors', PLoS One, vol. 7, no. 9, e44046. https://doi.org/10.1371/journal.pone.0044046
Zhang H, Abiraj K, Thorek DLJ, Waser B, Smith-Jones PM, Honer M et al. Evolution of Bombesin Conjugates for Targeted PET Imaging of Tumors. PLoS One. 2012 Sep 14;7(9). e44046. https://doi.org/10.1371/journal.pone.0044046
Zhang, Hanwen ; Abiraj, Keelara ; Thorek, Daniel L J ; Waser, Beatrice ; Smith-Jones, Peter M. ; Honer, Michael ; Reubi, Jean Claude ; Maecke, Helmut R. / Evolution of Bombesin Conjugates for Targeted PET Imaging of Tumors. In: PLoS One. 2012 ; Vol. 7, No. 9.
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