Radiosynthesis and initial evaluation of 18F labeled nanocarrier composed of poly(L-lactic acid)-block-poly(sarcosine) amphiphilic polydepsipeptide

Introduction: With the aim of developing radiotracers for in vivo positron emission tomography (PET) imaging of solid tumors based on the enhanced permeability and retention effect of nanocarriers, we have developed a polymer micelle named Lactosome, which is composed of the amphiphilic polydepsipeptide, poly(L-lactic acid)-block-poly(sarcosine). This paper describes and evaluates the initial evaluation of the F-18-labeled Lactosome as a novel contrast agent for the tumor PET imaging technique carried out. Methods: F-18-labeled Lactosomes were prepared by a film hydration method under sonication in water at 50 degrees C from a mixture of 4-[F-18]fluoro-benzoyl poly-L-lactic acid (F-18-BzPLLA(30)) and the amphiphilic polydepsipeptide. For biodistribution studies, BALB/cA Jcl-nu/nu mice bearing HeLa cells in the femur region were used. We took both PET and near-infrared fluorescence (NIRF) images of tumor bearing mice after co-injection of F-18-labeled Lactosome and NIRF-labeled Lactosome. Results: F-18-labeled Lactosomes were prepared at good yields (222-420 MBq) and more than 99% of F-18-BzPLLA(30) was incorporated into F-18-labeled Lactosome. The radioactivity of F-18-labeled Lactosome was found to be stable and maintained at high level for up to 6 h after injection into the blood stream. Tumor uptake increased gradually after the injection. The uptake ratio of tumor/muscle was 2.7 at 6 h from the time of injection. Tumor PET imaging with F-18-labeled Lactosome was as capable as tumor NIRF imaging with NIRF-labeled Lactosome. Conclusion: Tumor PET imaging using Lactosome as a nanocarrier may be therefore a potential candidate for a facile and general solid tumor imaging technique. (C) 2013 Elsevier Inc. All rights reserved.