Liposomes labeled with Indium-111 by a novel surface labeling method exhibits good biodistribution in vivo

Radioliposomes have potential applications as theranostic nanoparticles. Several techniques have been developed to label liposomes with radionuclides. Methods: In this study, a new In-111 surface labeling method for 1,4,7,10-tetraazacyclododecane-N, N´, N", N´"-tetraacetic acid (DOTA) derivative liposomes (DLs) is described. The in vitro stability and in vivo molecular imaging properties of the labeled liposomes were compared with those of conventional ¹¹¹In-liposomes (¹¹¹In-Ls) prepared by a remote loading method. In vitro stability tests were performed in normal saline, rat plasma, and human plasma at 37°C. Imaging characteristics of both radioliposomal preparations were determined in LS174T tumor-bearing mice. Results: The labeling efficiency of In-111-labeled DL (¹¹¹In-DLs) was greater than 95%; accordingly, no post-labeling purification was required, in contrast to the ¹¹¹In-Ls. The specificity of ¹¹¹In-DLs was higher (>10 ¹¹¹In per liposome) than that of ¹¹¹In-Ls (<;2 ¹¹¹In per liposome). The two radioliposomes showed similar in vitro stability. Non-invasive longitudinal monitoring by micro-single-photon emission computed tomography/computed tomography showed a similar in vivo tumor distribution for the two radioliposomes (48 h post-injection, P > 0.05). Conclusion: The new ¹¹¹In surface labeling method for liposomes was rapid, efficient, highly specific activity, and easy to perform. Although the two radioliposomes showed similar in vitro and in vivo characteristics, ¹¹¹In-DLs have benefits for clinical drug preparation, and this surface labeling method is a promising platform for radioliposomal theranostic nanoparticle preparation.