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

IntroductionWith 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 18F-labeled Lactosome as a novel contrast agent for the tumor PET imaging technique carried out.Methods18F-labeled Lactosomes were prepared by a film hydration method under sonication in water at 50 °C from a mixture of 4-[18F]fluoro-benzoyl poly-L-lactic acid (18F-BzPLLA30) 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 18F-labeled Lactosome and NIRF-labeled Lactosome.Results18F-labeled Lactosomes were prepared at good yields (222–420 MBq) and more than 99% of 18F-BzPLLA30 was incorporated into 18F-labeled Lactosome. The radioactivity of 18F-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 18F-labeled Lactosome was as capable as tumor NIRF imaging with NIRF-labeled Lactosome.ConclusionTumor PET imaging using Lactosome as a nanocarrier may be therefore a potential candidate for a facile and general solid tumor imaging technique.