title: The effect of mini-PEG-based spacer length on binding and pharmacokinetic properties of a 68Ga-labeled NOTA-conjugated antagonistic analog of bombesin.
abstract: The overexpression of gastrin-releasing peptide receptor (GRPR) in cancer can be used for peptide-receptor mediated radionuclide imaging and therapy. We have previously shown that an antagonist analog of bombesin RM26 conjugated to 1,4,7-triazacyclononane-N,N',N''-triacetic acid (NOTA) via a diethyleneglycol (PEG2) spacer (NOTA-PEG2-RM26) and labeled with 68Ga can be used for imaging of GRPR-expressing tumors. In this study, we evaluated if a variation of mini-PEG spacer length can be used for optimization of targeting properties of the NOTA-conjugated RM26. A series of analogs with different PEG-length (n = 2, 3, 4, 6) was synthesized, radiolabeled and evaluated in vitro and in vivo. The IC50 values of natGa-NOTA-PEGn-RM26 (n = 2, 3, 4, 6) were 3.1 ± 0.2, 3.9 ± 0.3, 5.4 ± 0.4 and 5.8 ± 0.3 nM, respectively. In normal mice all conjugates demonstrated similar biodistribution pattern, however 68Ga-NOTA-PEG3-RM26 showed lower liver uptake. Biodistribution of 68Ga-NOTA-PEG3-RM26 was evaluated in nude mice bearing PC-3 (prostate cancer) and BT-474 (breast cancer) xenografts. High uptake in tumors (4.6 ± 0.6%ID/g and 2.8 ± 0.4%ID/g for PC-3 and BT-474 xenografts, respectively) and high tumor-to-background ratios (tumor/blood of 44 ± 12 and 42 ± 5 for PC-3 and BT-474 xenografts, respectively) were found already at 2 h p.i. of 68Ga-NOTA-PEG3-RM26. Results of this study suggest that variation in the length of the PEG spacer can be used for optimization of targeting properties of peptide-chelator conjugates. However, the influence of the mini-PEG length on biodistribution is minor when di-, tri-, tetra- and hexaethylene glycol are compared.
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Varasteh
authors.affiliation: Organic Pharmaceutical Chemistry, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Ulrika
authors.initials: U
authors.lastname: Rosenström
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Irina
authors.initials: I
authors.lastname: Velikyan
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Bogdan
authors.initials: B
authors.lastname: Mitran
authors.affiliation: Biomedical Radiation Sciences, Department of Radiology, Oncology and Radiation Sciences, Faculty of Medicine, Uppsala University, Uppsala SE-751 85, Sweden.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Altai
authors.affiliation: Biomedical Radiation Sciences, Department of Radiology, Oncology and Radiation Sciences, Faculty of Medicine, Uppsala University, Uppsala SE-751 85, Sweden.
authors.forename: Hadis
authors.initials: H
authors.lastname: Honarvar
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Rosestedt
authors.affiliation: Organic Pharmaceutical Chemistry, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Lindeberg
authors.affiliation: Biomedical Radiation Sciences, Department of Radiology, Oncology and Radiation Sciences, Faculty of Medicine, Uppsala University, Uppsala SE-751 85, Sweden.
authors.forename: Jens
authors.initials: J
authors.lastname: Sörensen
authors.affiliation: Department of Medicinal Chemistry, Science for Life Laboratory, BMC, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Larhed
authors.affiliation: Biomedical Radiation Sciences, Department of Radiology, Oncology and Radiation Sciences, Faculty of Medicine, Uppsala University, Uppsala SE-751 85, Sweden. vladimir.tolmachev@bms.uu.se.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.affiliation: Preclinical PET Platform, Department of Medicinal Chemistry, Faculty of Pharmacy, Uppsala University, Uppsala SE-751 23, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
mesh_terms: D000818:Animals; D001839:Bombesin / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism* / Q000493:pharmacokinetics*; D005026:Ethylene Glycols / Q000737:chemistry; D005260:Female; D005710:Gallium Radioisotopes; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D007553:Isotope Labeling; D007700:Kinetics; D008024:Ligands; D051379:Mice; D057054:Molecular Imaging; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics; D011485:Protein Binding; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin / Q000737:chemistry / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D005026:Ethylene Glycols; D005710:Gallium Radioisotopes; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D008024:Ligands; D010455:Peptides; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin; C048993:1,4,7-triazacyclononane-N,N',N''-triacetic acid; C013484:diethylene glycol; D001839:Bombesin