Therefore, to overcome this problem, targeted drug delivery systems such as thermo-, pH-, ultrasound-, and optical-sensitive liposomes have been studied. However, utilization of liposomes as drug-carrying vehicles for intracellular delivery of anticancer drugs loaded in the liposomes is limited due to the lack of specific interaction between liposomal carriers and the target cells. Many studies have reported that modification of the surface of liposomes with a hydrophilic moiety such as polyethylene glycol (PEG) can increase the circulation time of the liposomes in the bloodstream due to reduced uptake of the liposomes by the reticuloendothelial system (RES). In the field of targeted drug delivery, liposomes have been extensively studied in an attempt to enhance the therapeutic efficacy of various drugs. Liposomes are spherical vesicles composed of phospholipid bilayer membranes. The results of our study suggest that the paramagnetic and sonosensitive liposomes, GdSL, may provide a versatile platform for molecular imaging and targeted drug delivery. Intracellular uptake of DOX for ultrasound-triggered GdSL was higher than that for non-ultrasound-triggered GdSL. Intracellular uptake properties of GdSL were evaluated according to the intensity of ultrasound. The relaxivities ( r 1) of GdSL were 6.6 to 7.8 mM −1 s −1, which were higher than that of MR-bester®. Sonosensitivity of GdSL to 20-kHz ultrasound induced 33% to 40% of DOX release. The GdSL was prepared using synthesized Gd(III)-DOTA-1,2-distearoyl- sn-glycero-3-phosphoethanolamine lipid. The objective of this study was to prepare Gd(III)-DOTA-modified sonosensitive liposomes (GdSL), which could deliver a model drug, doxorubicin (DOX), to a specific site and, at the same time, be capable of magnetic resonance (MR) imaging. Liposomal contrast agents having Gd(III) are known as a nano-contrast agent system for the efficient and selective delivery of contrast agents into pathological sites.

Ultrasound-sensitive (sonosensitive) liposomes for tumor targeting have been studied in order to increase the antitumor efficacy of drugs and decrease the associated severe side effects.

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