Liposome-encapsulated anticancer drugs: still waiting for the magic bullet?

Anticancer drugs are essential agents in the global strategy developed to fight cancer. Still, narrow therapeutic indices, erratic pharmacokinetics profiles and lack of selectivity towards malignant tissues often hamper their efficacy at the bedside, when they not cause severe toxicities. In this respect, developing innovative drug delivery strategies that would selectively target malignant tissues is still an ongoing story, both in experimental and in clinical oncology. Delivery systems such as liposomes are usually required when an existing formulation is not satisfactory, because encapsulation is expected to provide higher therapeutic efficacy and safety. Such significant improvement in therapeutic efficacy and/or therapeutic indices has already been achieved in patients with some liposome-encapsulated drugs such as anthracyclines. It is now possible to develop a wide range of vectors varying in size, composition, and surface morphology suitable for a variety of therapeutic applications, including for targeting tumor tissues. Reformulation of anticancer drugs in liposomes remains a challenging opportunity to stretch the therapeutic indices of many cytotoxic drugs, through the optimization of their distribution in the body. Despite these promising and exciting perspectives in oncology, to date only few drugs (e.g., anthracyclines) have actually made their way as liposomes from the bench to the bedside. However, as target therapies have brought a new hope in the cancer war in the 2000's, developing now targeted delivery systems is more and more seen as the next step to further improve clinical outcome in cancer patients. This review covers the achievements, limits, and new expectancies of anticancer drugs as candidates for liposomal encapsulation.