Introduction: Expression of vascular adhesion protein‐1 (VAP‐1) is induced at the sites of inflammation where extravasation of leukocytes from blood to the peripheral tissue occurs. VAP‐1 is a potential target for anti‐inflammatory therapy and for in vivo imaging of inflammation. Purpose of this study was to preliminarily evaluate a novel VAP‐1‐targeting peptide as a potential PET imaging agent.
Methods: Cyclic 17‐amino‐acid peptide selected from phage display libraries was 1,4,7,10‐tetraazacyclododecane‐N,N′,N′′,N′′′‐tetraacetic acid (DOTA) conjugated via 8‐amino‐3,6‐diooxaoctanoyl linker (polyethylene glycol, PEG derivative) and labelled with 68Ga (68Ga‐DOTAVAP‐PEG‐P2). In vitro stability of 68Ga‐DOTAVAP‐PEG‐P2 was determined in saline, rat plasma and human plasma by radio‐HLPC. Lipophilicity was measured by calculating octanol‐water partition coefficient (logP). Whole‐body distribution kinetics and stability after intravenous injection in healthy rats was studied in vivo by PET imaging, ex vivo by measuring radioactivity of excised tissues, and by radio‐HPLC.
Results: In vitro the 68Ga‐DOTAVAP‐PEG‐P2 remained stable >4 h in saline and rat plasma, but degraded slowly in human plasma after 2 h of incubation. The logP value of 68Ga‐DOTAVAP‐PEG‐P2 was −1·3. In rats, 68Ga‐radioactivity cleared rapidly from blood circulation and excreted quickly in urine. At 120 min after injection the fraction of intact 68Ga‐DOTAVAP‐PEG‐P2 were 77 ± 6·0% and 99 ± 1·0% in rat plasma and urine, respectively.
Conclusions: These basic and essential in vitro and in vivo studies of the new VAP‐1 targeting peptide revealed promising properties for an imaging agent. Further investigations to clarify in vivo VAP‐1 targeting are warranted.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.