Insertion of poly(ethylene glycol) derivatized phospholipid into pre‐formed liposomes results in prolonged in vivo circulation time

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Abstract
Transfer of MPEG1900‐DSPE from micellar phase to pre‐formed liposomes imparts long in vivo circulation half‐life to an otherwise rapidly cleared lipid composition. MPEG1900‐DSPE transfers efficiently and quickly in a time and temperature dependent manner. There is negligible content leakage and a strong correlation between assayed mol% MPEG1900‐DSPE, liposome diameter increase, and pharmacokinetic parameters such as distribution phase half‐life. Since a biological attribute (liposome clearance rate) can be modified by the insertion process, it suggests a simple and economical way to impart site‐specific targeting to a variety of liposome delivery systems. This method is also a convenient way to measure the ‘brush’ thickness of such conjugates directly.