Drug delivery using liposomes

The concept of liposomal drug delivery has revolutionised the pharmaceutical field and came into praxis some 20 years ago when the first liposomal formulation of the anti-cancer drug doxorubicin was approved for clinical use. Liposomes, <200 nm phospholipid vesicles, are longer retained in blood circulation and accumulate at pathological sites (tumours or inflamed tissues), leading to higher efficacy and lower systemic toxicity compared to the free drugs they encapsulate. To target liposomes to certain tissues or cells, such as tumour cells, a specific binder of a unique protein (an antigen) on the targeted cell, known as a monoclonal antibody, must be linked to the liposome surface. This coupling is called the functionalization of the liposome and done chemically, often at the final stages of liposome production and can potentially damage the liposome or targeting antibody.

The new study by Anna Ohradanova-Repic and colleagues from the Institute for Hygiene and Applied Immunology, Center for Pathophysiology, Infectiology and Immunology of the Medical University of Vienna in collaboration with the University of Minho, Braga, Portugal, shows not only a smart but also easy way for liposome functionalization: They linked the small specific fragment of the antibody, called Fab, by gene technology with a hydrophobic anchor. Via this hydrophobic anchor, the Fab fragment got naturally inserted into the hydrophobic liposomal membrane part during liposomal preparation. "It was quite fascinating to see how easy the liposome functionalization was. We tested two different Fab fragments and they both worked very well. We observed specific targeting not only to the antigen-positive cells in the lab dish but also in mice, where our liposomes precisely recognized human tumours that we had implanted.," says Anna Ohradanova-Repic, the leading researcher behind the study.

Hannes Stockinger, the senior author of the study, adds: "If we coupled this delivery method with screening of patient's tumours for the presence of a unique surface protein, which we can target with the Fab fragment-functionalized liposomes, we might be able to treat tumours more efficiently and decrease the side effects of the delivered anti-cancer drugs substantially. I foresee this as a personalized medicine of the future. Yet, a lot of work is ahead of us to implement this treatment strategy in clinical practice."