title: Enhanced pH-Responsiveness, Cellular Trafficking, Cytotoxicity and Long-circulation of PEGylated Liposomes with Post-insertion Technique Using Gemcitabine as a Model Drug.
abstract: OBJECTIVE
  The in vitro and in vivo properties of PEGylated pH-sensitive liposomes (PSL) prepared by pre- and post-insertion techniques were investigated.
  
  
  METHODS
  A pre-insertion or post-insertion technique was used for PSL PEGylation. For the first time, confocal laser scanning microscopy coupled with a modified calcein self-quench assay was applied to evaluate the endosome escape capability. PSL cellular uptake was evaluated using macrophages and the cytotoxicity using a gemcitabine (model drug)-resistant MIA PaCa-2 cells. The pharmacokinetics of PSL encapsulated gemcitabine was investigated in rats.
  
  
  RESULTS
  PEGylation reduced the pH-sensitivity in a concentration-dependent manner (0.5-5% mol). Both PEGylation methods reduced the uptake of PSL by macrophages by over 60%. Cytotoxicity was ranked in the order: post-inserted PSL ≥ pre-inserted PSL > non-PSL > gemcitabine solution, consistent with the confocal microscopic observation and pH-sensitivity. Both pre and post-inserted PSL resulted in significant reductions (p < 0.05) in plasma clearance (58.6 and 38.4 ml/h/kg), increases in the area-under-the-concentration-time curve (56.9 and 87.1 μM · h) and half-life (6.1 and 6.2 h) compared to gemcitabine solution (152.9 ml/h/kg, 22.2 μM · h and 1.4 h).
  
  
  CONCLUSIONS
  PEGylation by post-insertion offers advantages over pre-insertion to obtain PSL with enhanced pH-sensitivity, more effective intra-cytoplasmic delivery, and a superior pharmacokinetics.
authors: School of Pharmacy, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand.
authors: Hongtao
authors: H
authors: Xu
authors: James W
authors: JW
authors: Paxton
authors: Zimei
authors: Z
authors: Wu
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004337:Drug Carriers / Q000737:chemistry*; D004339:Drug Compounding; D065546:Drug Liberation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D008264:Macrophages / Q000378:metabolism; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry*; D017207:Rats, Sprague-Dawley; D013499:Surface Properties; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D004337:Drug Carriers; D008081:Liposomes; D003841:Deoxycytidine; D011092:Polyethylene Glycols; D000093542:Gemcitabine