Paramagnetic liposomes as innovative contrast agents for magnetic resonance (MR) molecular imaging applications

This article illustrates some innovative applications of liposomes loaded with paramagnetic lanthanide-based complexes in MR molecular imaging field. When a relatively high amount of a Gd^III chelate is encapsulated in the vesicle, the nanosystem can simultaneously affect both the longitudinal (R₁) and the transverse (R₂) relaxation rate of the bulkH₂O H-atoms, and this finding can be exploited to design improved thermosensitive liposomes whose MRI response is not longer dependent on the concentration of the probe. The observation that the liposome compartmentalization of a paramagnetic Ln^III complex induce a significant R₂ enhancement, primarily caused by magnetic susceptibility effects, prompted us to test the potential of such agents in cell-targeting MR experiments. The results obtained indicated that these nanoprobes may have a great potential for the MR visualization of cellular targets (like the glutamine membrane transporters) overexpressing in tumor cells. Liposomes loaded with paramagnetic complexes acting as NMR shift reagents have been recently proposed as highly sensitive CEST MRI agents. The main peculiarity of CEST probes is to allow the MR visualization of different agents present in the same region of interest, and this article provides an illustrative example of the in vivo potential of liposome-based CEST agents.