COPOLYMERS OF N-ISOPROPYLACRYLAMIDE CAN TRIGGER PH SENSITIVITY TO STABLE LIPOSOMES

Stable liposomes were rendered pi-I-sensitive by complexation to a pol ymer that undergoes marked temperature- and pH-dependent water solubil ity changes, The N-isopropylacrylamide-methacrylic acid copolymer was prepared with or without octadecyl acrylate, At pH below the phase tra nsition of the polymer, egg phosphatidylcholine liposomes quickly rele ased a part of their contents only when associated with the octadecyl aliphatic chain grafted polymer at 37 degrees C. Similarly, sterically stabilized liposomes also quickly released a significant part of the entrapped fluorescent markers at pH 5.5-4.9, values corresponding to t hose of endosomes/lysosomes. This new pH-sensitive liposome-polymer sy stem may further improve the efficiency of liposomal drug delivery, (C ) 1998 Federation of European Biochemical Societies.