Unexpected Reactions by In Vivo Applications of PEGylated Liposomes

Abstract

PEGylated liposome, a liposome coated with polyethylene glycol (PEG), is understood to be biologically inert and, therefore, a suitable vehicle for in vivo applications. The most successful example is the doxorubicin-containing PEGy- lated liposome, known under the commercial name Doxil/Caelyx for cancer ther- apy. However, several researchers have found evidence that unexpected immune responses occur even to such polymer-coated liposomes after intravenous injection not only in animals but also in humans. An understanding of the immunological and pathological factors that control the pharmacokinetic and biological behavior of PEGylated liposomes is crucial for the design and safety of a system with optimal therapeutic and/or diagnostic performance. In this study, the interaction of PEGy- lated liposomes within the biological milieu following parenteral administration is discussed.