Author/Editor		Aloj, Luigi; Aurilio, Michela; Rinaldi, Valentina; D'Ambrosio, Laura; Tesauro, Diego; Kolenc-Peitl, Petra; Maina, Theodosia; Mansi, Rosalba; Guggenberg von, Elisabeth; Joosten, Lieke; Sosabowski, Jane K.; Breeman, Wouter A.P.; De Blois, Erik; Koelewijn, Stuart; Melis, Marleen; Waser, Beatrice; Beetschen, Karin; Reubi, Jean Claude; De Jong, Marion
Title		Comparison of the binding and internalization properties of 12 DOTA-coupled and (111)In-labelled CCK2/gastrin receptor binding peptides: a collaborative project under COST Action BM0607
Type		članek
Vol. and No.		Letnik 38, št. 8
Publication year		2011
Volume		str. 1417-1425
ISSN		1619-7070 - European journal of nuclear medicine and molecular imaging
Language		eng
Abstract		PURPOSE: Specific overexpression of cholecystokinin 2 (CCK2)/gastrin receptors has been demonstrated in several tumours of neuroendocrine origin. In some of these cancer types, such as medullary thyroid cancer (MTC), a sensitive diagnostic modality is still unavailable and therapeutic options forinoperable lesions are needed. Peptide receptor radionuclide therapy (PRRT)may be a viable therapeutic strategy in the management of these patients. Several CCK2R-targeted radiopharmaceuticals have been described in recent years. As part of the European Union COST Action BM0607 we studied the in vitro and in vivo characteristics of 12 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated CCK2R binding peptides. In the present study, we analysed binding and internalization characteristics. Stability, biodistribution and imaging studies have been performed in parallel by other centres involved in the project. METHODS: Determination of IC(50) values was performed using autoradiography, with DOTA-peptides displacing (125)I-CCK from receptors on tissue sections from human tumours. Saturation binding and internalization experiments were performed using (111)In-labelled peptides. The rat AR42J cellline and the human A431-CCK2R transfected cell line were utilized for in vitro experiments; dissociation constants (K(d)) and apparent number of binding sites (B(max)) were determined. Internalization was determined in receptor-expressing cells by incubating with tracer amounts of peptide at 37 and 4⁰C for different times up to 120 min. Surface-bound peptide was then stripped either by acid wash or subsequent incubation with 1 ?M unlabelled peptide at 4⁰C. RESULTS: All peptides showed high receptor affinity with IC(50) values ranging from 0.2 to 3.4 nM. Saturation experiments also showed high affinity with K(d) values in the 10(-9)-10(-8) M range. B(max) values estimated in A431-CCK2R cells ranged from 0.6 to 2.2 * 10(6) per cell. All peptides showed high levels of internalization when incubated at 37⁰C. CONCLUSION: All DOTA-conjugated peptides showed high receptor binding and internalization properties and appear suitable for further characterization, as described in other articles of this issue.
Keywords		DOTA gastrin tumor holecistokinin