Polyethylene glycol in the design of tumor-targetting radiolabelled macromolecules -- lessons from liposomes and monoclonal antibodies.

Radiolabelled macromolecules such as liposomes and monoclonal antibodies (Mab) are attractive agents for tumour-targetting studies. In addition to their potential diagnostic role, they can also provide vital information on the targetting capacity of therapeutic agents. Certainly in the case of liposome development, this ability to track the pharmacokinetics and biodistribution of the agents in a non-invasive fashion has assisted the design and application of therapeutic liposomal agents. A significant limitation of unmodified liposomes and Mab is their tendency to be cleared rapidly from the circulation. The use of polyethylene glycol (PEG) in the formulation of these agents has the capacity to alter their biological behaviour in such a way as to improve their ability to target tumours. In this paper we review the data relating to the use of PEG-modified liposomes and Mab in the context of nuclear medicine studies.