Development of radiolabeled 111In-albumin liposomes for long-term imaging of tumors

Abstract Background: The current study aims to develop a clinically applicable radiopharmaceutical agent for long-term imaging in the diagnosis and management of oncologic patients in the field of nuclear medicine. Liposomes, as pharmaceutical nanocarriers, have been extensively studied in pharmaceutical industry and depending on their structural characteristics could be disposed in various pathological sites in the body. PEGylated liposomes have smaller volume of distribution and decreased clearance, consequently, due to their more prolonged presence in the bloodstream and their stability during this time, could be used for tumor imaging. In this work, liposomal formulations encapsulating albumin were synthesized by solvent evaporation method and extrusion and were labeled by 111In-oxine similar to leukocytes labeling method. Their biodistribution in C26-colon carcinoma tumor-bearing mice by injection dose/gram and gamma scintigraphy were studied. Results: The result of our study displayed that 111In -radiolabeled liposomes having a size of about 130 nanometers, were capable of accumulating in tumor sites based on enhanced penetration and retention (EPR) phenomenon. These liposomes also have high stability for maintaining encapsulated albumin for a long time up to 96 hours and probably so on. In the study of biodistribution of our formulation in tumor-bearing mice, they accumulated more in the kidney, liver, spleen and tumor sites, so that even after clearance of formulation in the bloodstream, they existed in significantly high levels in the mentioned organs and furthermore tumor site up to 96 hours. In gamma scintigraphy, organs with high activity accumulation from early time from administration to 96 hours, were visible in the form of hot spots demonstrating stability in the tumor. Conclusions: Our in vitro and in vivo studies demonstrated that this PEGylated radiolabeled liposomal formulation have considerable stability and efficiency for long-term tumor imaging which merit further studies for its transformation into clinical application.