In this work we investigated how the surface charge and the presence of polyethylene glycol (PEG) on liposome carriers affect the delivery of the encapsulated doxorubicin in P-glycoprotein (Pgp)-overexpressing cells. We found that neutral net charge was critical to favour the liposome uptake and decrease the Vmax of doxorubicin efflux. PEG-coating was necessary to increase the Km of doxorubicin for Pgp. In particular the PEGylated phospholipid present in neutral liposomes, i.e. PEGylated distearoyl-phosphatidylethanolamine (DSPE-PEG), was a Pgp allosteric inhibitor, increased doxorubicin Km and inhibited Pgp ATPase activity. Site-directed mutagenesis experiments suggested that the domain centred around glycine 185 of Pgp was necessary for these inhibitory properties of DSPE-PEG and PEGylated neutral liposomes. We conclude that both surface charge and PEGylation must be considered to optimize the doxorubicin delivery within chemoresistant cells. DSPE-PEG-enriched particles may represent promising tools for therapeutic and diagnostic applications in tissues with high levels of Pgp.
From the clinical editor: These authors investigated how surface charge and PEGylation of liposome carriers affect the delivery of encapsulated doxorubicin to Pgp-overexpressing cells, concluding that both factors need to be considered in order to optimize doxorubicin delivery to chemoresistant cells.
Keywords: 1,2-dioleoyloxy-3-trimethylammoniumpropanchloride; 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-glycerol; 1,2-dipalmitoyl-sn-glycero-3-phosphocholine; BCRP; Chemoresistance; DOTAP; DPPC; DPPG; DSPE-PEG; Doxorubicin; Liposome; MRPs; P-glycoprotein; PEG; PEGylated distearoyl-phosphatidylethanolamine; Pgp; Polyethylene glycol; breast cancer resistance protein; multidrug-resistance related proteins; polyethylene glycol.