title: PEG-poly(amino acid) block copolymer micelles for tunable drug release.
abstract: OBJECTIVE
  To achieve tunable pH-dependent drug release in tumor tissues.
  
  
  METHODS
  Poly(ethylene glycol)-poly(aspartic acid) [PEG-p(Asp)] containing 12 kDa PEG and pAsp (5, 15, and 35 repeating units) were prepared. Hydrazide linkers with spacers [glycine (Gly) and 4-aminobenzoate (Abz)] were introduced to PEG-p(Asp), followed by drug conjugation [doxorubicin (DOX)]. The block copolymer-drug conjugates were either reconstituted or dialyzed in aqueous solutions to prepare micelles. Drug release patterns were observed under sink conditions at pH 5.0 and 7.4, 37°C, for 48 h.
  
  
  RESULTS
  A collection of six block copolymers with different chain lengths and spacers was synthesized. Drug binding yields were 13-43.6%. The polymer-drug conjugates formed <50 nm polymer micelles irrespective of polymer compositions. Gly-introduced polymer micelles showed marginal change in particle size (40 ± 10 nm), while the size of Abz-micelles increased gradually from 10 to 40 nm as the polymer chain lengths increased. Drug release patterns of both Gly and Abz micelles were pH-dependent and tunable. The spacers appear to play a crucial role in controlling drug release and stability of polymer micelles in combination with block copolymer chain lengths.
  
  
  CONCLUSIONS
  A drug delivery platform for tunable drug release was successfully developed with polymer micelles possessing spacer-modified hydrazone drug-binding linkers.
authors.affiliation: Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 789 South Limestone, Lexington, Kentucky 40536, USA.
authors.forename: Andrei
authors.initials: A
authors.lastname: Ponta
authors.forename: Younsoo
authors.initials: Y
authors.lastname: Bae
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D004337:Drug Carriers; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D004337:Drug Carriers; D008823:Micelles; D011108:Polymers; D011092:Polyethylene Glycols