Development of a potent DOTA-conjugated bombesin antagonist for targeting GRPr-positive tumours
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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-NH2 via the cationic spacer 4-amino-1-carboxymethyl-piperidine for labelling with radiometals such as 111In and 68Ga.
RM2 was synthesized on a solid support and evaluated in vitro in PC-3 cells. IC50 and Kd values were determined. The antagonist potency was evaluated by immunofluorescence-based internalization and Ca2+ mobilization assays. Biodistribution studies were performed in PC-3 and LNCaP tumour-bearing mice with 111In-RM2 and 68Ga-RM2, respectively. PET/CT studies were performed on PC-3 and LNCaP tumour-bearing nude mice with 68Ga-RM2.
RM2 and 111In-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 natIn-RM2). The potent antagonistic properties were confirmed by an immunofluorescence-based internalization and Ca2+ mobilization assays. 68Ga- and 111In-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.
RM2 was shown to be a potent GRPr antagonist. Pharmacokinetics and imaging studies indicate that 111In-RM2 and 68Ga-RM2 are ideal candidates for clinical SPECT and PET studies.
KeywordsProstate cancer Gastrin-releasing peptide receptor Bombesin Gallium-68 Indium-111
We thank Prof. Marion de Jong and Dr. Cristina Müller for support with the SPECT/CT measurements, Novartis Pharma for analytical assistance, M.L. Tamma and S. Tschumi for their expert technical help, and Bayer Schering Pharma for financial support.
Conflict of interest
Rosalba Mansi, Xuejuan Wang, Flavio Forrer, Beatrice Waser, Renzo Cescato, Jean Claude Reubi and Helmut R. Maecke declare that they have no conflict of interest.
- 3.Eisenwiener K-P, Prata MIM, Buschmann I, Zhang H-W, Santos AC, Wenger S, et al. NODAGATOC, a new chelator-coupled somatostatin analogue labeled with [67/68Ga] and [111In] for SPECT, PET, and targeted therapeutic applications of somatostatin receptor (hsst2) expressing tumors. Bioconjug Chem 2002;13:530–41.CrossRefPubMedGoogle Scholar
- 14.Zhang H, Chen J, Waldherr C, Hinni K, Waser B, Reubi JC, et al. Synthesis and evaluation of bombesin derivatives on the basis of pan-bombesin peptides labeled with indium-111, lutetium-177, and yttrium-90 for targeting bombesin receptor-expressing tumors. Cancer Res 2004;64:6707–15.CrossRefPubMedGoogle Scholar
- 22.Mansi R, Wang X, Forrer F, Kneifel S, Tamma ML, Waser B, et al. Evaluation of a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-conjugated bombesin-based radioantagonist for the labeling with single-photon emission computed tomography, positron emission tomography, and therapeutic radionuclides. Clin Cancer Res 2009;15:5240–9.CrossRefPubMedGoogle Scholar
- 26.Atherton E, Sheppard R. Fluorenylmethoxycarbonyl-polyamide solid phase peptide synthesis. General principles and development. Oxford: Oxford Information Press; 1989.Google Scholar