title: The bifunctional liposomes constructed by poly(2-ethyl-oxazoline)-cholesteryl methyl carbonate: an effectual approach to enhance liposomal circulation time, pH-sensitivity and endosomal escape.
abstract: OBJECTIVE
  A novel bifunctional liposome with long-circulating and pH-sensitive properties was constructed using poly(2-ethyl-oxazoline)-cholesteryl methyl carbonate (PEtOz-CHMC) in this study.
  
  
  METHODS
  PEtOz-CHMC was synthesized and characterized by TLC, IR and (1)H-NMR. The obtained PEtOz lipid was inserted into liposomes by the post-insertion method. Through a series of experiments, such as drug release, tumor cell uptake, cytotoxicity, calcium-induced aggregation, pharmacokinetic experiments, etc., the pH-sensitive and long-circulating properties of PEtOzylated liposomes was identified.
  
  
  RESULTS
  PEtOz-CHMC modified liposomes (PEtOz-L) showed increased calcein release at low pH. Flow cytometric analysis results showed that the fusion and cellular uptake of PEtOz-L could be promoted significantly at pH 6.4 compared with those at pH 7.4. Confocal laser scanning microscope observations revealed that PEtOz-L could respond to low endosomal pH and directly released the fluorescent tracer into the cytoplasm. MTT assays in HeLa cells demonstrated that doxorubicin hydrochloride (DOX) loaded PEtOz-L exhibited stronger anti-tumor activity in a medium at pH 6.4 than in a medium pH 7.4. PEtOz-L remained stable when these liposomes were incubated in calcium chloride solution. The cumulative calcein release rate of PEtOz-L was significantly lower than that of CL when the liposomes were dialysed in PBS. The pharmacokinetic experiments of liposomes in rats showed that t 1/2 and AUC of PEtOz-L were 4.13 times and 4.71 times higher than those of CL.
  
  
  CONCLUSIONS
  PEtOzylated liposomes exhibits excellent long-circulating and pH-sensitive properties. Our results suggest that PEtOz is a promising biomaterial for the modification of liposome in drug delivery.
authors.affiliation: Department of Pharmacy, School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, 116029, People's Republic of China, huan.xu1@163.com.
authors.forename: Huan
authors.initials: H
authors.lastname: Xu
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Fei F
authors.initials: FF
authors.lastname: Ye
authors.forename: Peng P
authors.initials: PP
authors.lastname: Yin
authors.forename: Xiu
authors.initials: X
authors.lastname: Yu
authors.forename: Mei N
authors.initials: MN
authors.lastname: Hu
authors.forename: Yuan S
authors.initials: YS
authors.lastname: Fu
authors.forename: Che
authors.initials: C
authors.lastname: Wang
authors.forename: De J
authors.initials: de J
authors.lastname: Shang
mesh_terms: D000818:Animals; D001776:Blood Circulation Time / Q000187:drug effects*; D002122:Calcium Chloride / Q000737:chemistry; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000737:chemistry / Q000378:metabolism; D016503:Drug Delivery Systems / Q000379:methods; D011992:Endosomes / Q000737:chemistry* / Q000378:metabolism*; D005452:Fluoresceins / Q000378:metabolism; D005561:Formates / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D008081:Liposomes / Q000737:chemistry* / Q000378:metabolism*; D008297:Male; D011073:Polyamines / Q000737:chemistry*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D005452:Fluoresceins; D005561:Formates; D008081:Liposomes; D011073:Polyamines; C511916:poly(2-ethyl-2-oxazoline); D004317:Doxorubicin; C023025:methyl carbonate; D002122:Calcium Chloride; C007740:fluorexon