Abstract
The integration of nuclear imaging with nanomedicine is a powerful tool for efficient development and clinical translation of liposomal drug delivery systems. Furthermore, it may allow highly efficient imaging-guided personalised treatments. In this article, we critically review methods available for radiolabelling liposomes. We discuss the influence that the radiolabelling methods can have on their biodistribution and highlight the often-overlooked possibility of misinterpretation of results due to decomposition in vivo. We stress the need for knowing the biodistribution/pharmacokinetics of both the radiolabelled liposomal components and free radionuclides in order to confidently evaluate the images, as they often share excretion pathways with intact liposomes (e.g. phospholipids, metallic radionuclides) and even show significant tumour uptake by themselves (e.g. some radionuclides). Finally, we describe preclinical and clinical studies using radiolabelled liposomes and discuss their impact in supporting liposomal drug development and clinical translation in several diseases, including personalised nanomedicine approaches.
Highlights
Nanomedicine-based drug delivery aims to improve disease treatment by increasing the targeted accumulation of small-molecule drugs into diseased tissue while minimising systemic toxicity
Once synthesised, preformed liposomes could be radiolabelled using a solid phase transition method wherein the positron emission tomography (PET) probe was transferred to a glass vial, and the solvent removed, the liposomes were added with agitation allowing the long alkyl chain to intercalate with the lipid bilayer on the liposome surface
52Mn-labelled Doxil® was shown to be stable in the blood pool for up to 24 h, imaging 72 h after administration and ex vivo biodistribution showed a profile similar to that of non-chelated 52Mn with high uptake in the pancreas, salivary glands and kidneys observed (Fig. 7D) [144]. These results suggest that following uptake in the reticulo-endothelial system (RES), the subsequent destruction of the liposomes led to the release of the drug cargo and the radionuclide
Summary
Nanomedicine-based drug delivery aims to improve disease treatment by increasing the targeted accumulation of small-molecule drugs into diseased tissue while minimising systemic toxicity. Besides its clear role in the development of liposomal therapies, another factor where imaging drug delivery systems could play an important role in the future is the individualised prediction of therapeutic efficacy This is critical when we consider that the most common mechanism by which liposomal nanomedicines accumulate at target tissues (i.e. the enhanced permeation and retention effect or EPR), is a phenomenon that is highly heterogeneous in humans [5,6]. Labelling liposomal nanomedicines with optical labels such as fluorophores, allows imaging using techniques such as fluorescence molecular tomography (FMT) [13] This technique allows high sensitivity and quantifiable in vivo biodistribution studies in animal models, but with limited applications in the clinical setting due to its low tissue penetration. We will draw some conclusions and outline future perspectives of this exciting area of radionuclide imaging and nanomedicine
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