title: Comparison of the binding and internalization properties of 12 DOTA-coupled and ¹¹¹In-labelled CCK2/gastrin receptor binding peptides: a collaborative project under COST Action BM0607.
abstract: OBJECTIVE
  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 for inoperable 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 cell line 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 4°C for different times up to 120 min. Surface-bound peptide was then stripped either by acid wash or subsequent incubation with 1 μM unlabelled peptide at 4°C.
  
  
  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 37°C.
  
  
  CONCLUSIONS
  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.
authors.affiliation: AF Medicina Nucleare, Istituto Nazionale Tumori, Fondazione G. Pascale, Via M. Semmola, 80131 Naples, Italy. l.aloj@istitutotumori.na.it
authors.forename: Luigi
authors.initials: L
authors.lastname: Aloj
authors.forename: Michela
authors.initials: M
authors.lastname: Aurilio
authors.forename: Valentina
authors.initials: V
authors.lastname: Rinaldi
authors.forename: Laura
authors.initials: L
authors.lastname: D'ambrosio
authors.forename: Diego
authors.initials: D
authors.lastname: Tesauro
authors.forename: Petra Kolenc
authors.initials: PK
authors.lastname: Peitl
authors.forename: Theodosia
authors.initials: T
authors.lastname: Maina
authors.forename: Rosalba
authors.initials: R
authors.lastname: Mansi
authors.forename: Elisabeth
authors.initials: E
authors.lastname: von Guggenberg
authors.forename: Lieke
authors.initials: L
authors.lastname: Joosten
authors.forename: Jane K
authors.initials: JK
authors.lastname: Sosabowski
authors.forename: Wouter A P
authors.initials: WA
authors.lastname: Breeman
authors.forename: Erik
authors.initials: E
authors.lastname: De Blois
authors.forename: Stuart
authors.initials: S
authors.lastname: Koelewijn
authors.forename: Marleen
authors.initials: M
authors.lastname: Melis
authors.forename: Beatrice
authors.initials: B
authors.lastname: Waser
authors.forename: Karin
authors.initials: K
authors.lastname: Beetschen
authors.forename: Jean Claude
authors.initials: JC
authors.lastname: Reubi
authors.forename: Marion
authors.initials: M
authors.lastname: de Jong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D003299:Cooperative Behavior; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry*; D020128:Inhibitory Concentration 50; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D043887:Receptor, Cholecystokinin B / Q000378:metabolism*
chemical_list: D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D010455:Peptides; D043887:Receptor, Cholecystokinin B; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid