Chemotherapy is widely used for cancer treatment; however, it causes unwanted side
effects in patients. To avoid these adverse effects, nanocarriers have been developed, which can be
loaded with the chemotherapeutic agents, directed to the cancer site and, once there, are exposed to
stimuli that will trigger the drug release.
Liposomes can be chemically modified to increase their circulation time, their stability, and their
sensitivity to specific stimulus. Additionally, ligands can be conjugated to their surface, allowing for their specific binding
to receptors overexpressed on the surface of cancer cells and the subsequent internalization via endocytosis. Using a
triggering mechanism, including temperature, ultrasound, enzymes or a change in pH, the release of the drug is controlled
and induced inside the cells, hence avoiding drug release in systemic circulation, which in turn reduces the undesired side
effects of conventional chemotherapy. Ultrasound has been widely studied as a drug release trigger from liposomes, due
to its well-known physics and previous uses in medicine.
This review focuses on liposome-based drug delivery systems, using different trigger mechanisms, with a focus on
ultrasound. The physical mechanisms of ultrasound release are also investigated and the results of in vitro and in vivo
studies are summarized.