Remote loading of 64Cu2+ into liposomes without the use of ion transport enhancers

Research output: Contribution to journalJournal articleResearchpeer-review

Jonas Rosager Henriksen, Anncatrine Luisa Petersen, Anders Elias Hansen, Christian Grundahl Frankær, Pernille Harris, Dennis Ringkjøbing Elema, Annemarie Thuri Kristensen, Andreas Kjær, Thomas Lars Andresen

Due to low ion permeability of lipid bilayers, it has been and still is common practice to use transporter molecules such as ionophores or lipophilic chelators to increase transmembrane diffusion rates and loading efficiencies of radionuclides into liposomes. Here, we report a novel and very simple method for loading the positron emitter (64)Cu(2+) into liposomes, which is important for in vivo positron emission tomography (PET) imaging. By this approach, copper is added to liposomes entrapping a chelator, which causes spontaneous diffusion of copper across the lipid bilayer where it is trapped. Using this method, we achieve highly efficient (64)Cu(2+) loading (>95%), high radionuclide retention (>95%), and favorable loading kinetics, excluding the use of transporter molecule additives. Therefore, clinically relevant activities of 200-400 MBq/patient can be loaded fast (60-75 min) and efficiently into preformed stealth liposomes avoiding subsequent purification steps. We investigate the molecular coordination of entrapped copper using X-ray absorption spectroscopy and demonstrate high adaptability of the loading method to pegylated, nonpegylated, gel- or fluid-like, cholesterol rich or cholesterol depleted, cationic, anionic, and zwitterionic lipid compositions. We demonstrate high in vivo stability of (64)Cu-liposomes in a large canine model observing a blood circulation half-life of 24 h and show a tumor accumulation of 6% ID/g in FaDu xenograft mice using PET imaging. With this work, it is demonstrated that copper ions are capable of crossing a lipid membrane unassisted. This method is highly valuable for characterizing the in vivo performance of liposome-based nanomedicine with great potential in diagnostic imaging applications.

Original languageEnglish
JournalA C S Applied Materials and Interfaces
Volume7
Issue number41
Pages (from-to)22796-22806
Number of pages11
ISSN1944-8244
DOIs
Publication statusPublished - 1 Oct 2015

ID: 160835096