In vitro and in vivo behavior of liposomes decorated with PEGs with different chemical features

The colloidal stability, in vitro toxicity, cell association, and in vivo pharmacokinetic behavior of liposomes decorated with poly(ethylene glycol)-lipids (mPEG-lipids) with different chemical features were comparatively investigated. Structural differences of mPEG-lipids used in the study included: a) surface anchoring moiety [1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), cholesterol (Chol) and cholane (Chln)]; b) mPEG molecular weight, (2 kDa mPEG45 and 5 kDa mPEG114); c) mPEG shape (linear and branched PEG). In vitro results demonstrated that branched (mPEG114)2-DSPE confers the highest stealth properties to liposomes (~31-fold lower cell association than naked liposomes) with respect to all PEGylating agents tested. However, the pharmacokinetic studies showed that the use of cholesterol as anchoring group yields PEGylated liposomes with longer permeance in the circulation and higher systemic bioavailability among the tested formulations. Liposomes decorated with mPEG114-Chol had 3.2- and ~2.1-fold higher AUC than naked liposomes and branched (mPEG114)2-DSPE coated liposomes, respectively, which reflects the high stability of this coating agent. By comparing the PEGylating agents with same size, namely linear 5 kDa PEG derivatives, linear mPEG114-DSPE yielded coated liposomes with the best in vitro stealth performance. Nevertheless, the in vivo the AUC of liposomes decorated with linear mPEG114-DSPE was lower than that obtained with liposomes decorated with linear mPEG114-Chol. Computational molecular dynamics modelling provided additional insights that complement the experimental results.