ABSTRACT
A new strategy for the reversible attachment of methoxypoly(ethylene glycol) (mPEG) to an amino-containing substrate is described. The strategy is based on formation of a benzyl carbamate linkage substituted with a disulfide in the para or ortho position. While being stable under nonreducing conditions, the dithiobenzyl (DTB) urethane linkage is susceptible to cleavage by mild thiolysis with cysteine resulting in release of the parent amino component of the conjugate in its original form. The method is exemplified by preparation of mPEG-DTB-alcohol, its activation and attachment to distearoylphosphatidylethanolamine (DSPE). The resulting lipopolymer incorporates into liposomes, which are capable of losing their polymer coating under conditions approximating those existing in vivo. Implications for drug delivery are briefly discussed.
Subject(s)
Cysteine/chemistry , Phosphatidylethanolamines/chemistry , Phospholipids/chemistry , Polyethylene Glycols/chemistry , Urethane/chemistry , Carbamates/chemical synthesis , Carbamates/chemistry , Drug Delivery Systems , Liposomes , Phospholipids/chemical synthesis , Polyethylene Glycols/chemical synthesis , Urethane/analogs & derivativesABSTRACT
This report characterizes a procedure for rapidly and accurately determining the entrapment of vincristine or other water-soluble drugs in polyethylene glycol-derivatized liposomes. Rapid liposome aggregation with poly(methacrylic acid) and pelleting by mild centrifugation separates liposome-associated vincristine from unentrapped drug. After collecting the supernatant fraction, the pellet is resuspended and solubilized in isopropyl alcohol. Quantitative uv spectrophotometry determines vincristine mass in both fractions. The mean accuracy (recovery) is 100.6% over an entrapped drug range from 70 to 99%. Within and between day precision of the method has a relative standard deviation of 0.76% for a single measurement.