Doxorubicin loaded tumor-triggered targeting ammonium bicarbonate liposomes for tumor-specific drug delivery.

Ammonium bicarbonate (ABC) liposomes can only release drugs extracellularly while intracellular drug delivery could be more promising than extracellular release in chemotherapy. The purpose of this work was to endow the ABC liposomes with tumor-triggered targeting effect, to realize the intracellular drug release and retain the long circulation characteristics of the liposomes. The tumor-triggered targeting ABC (TT-ABC) liposomes were proposed to improve uptake of tumor cells owing to folate (FA) - specific binding. To retain the long circulation characteristics of the TT-ABC liposomes, we synthesized PEGylated phospholipid with a pH-sensitive imine bond (DSPE-PEG5000) and added it to the liposomes. After endocytosis by tumor cells via active targeting, the TT-ABC liposomes produced carbon dioxide (CO2) bubbles at elevated temperature or in the acidic endo/lysosome. The permeable defects could be created in the phospholipid bilayer by the generating CO2 bubbles, so the liposomes could quickly release the drugs intracellularly. Doxorubicin (DOX) loaded TT-ABC (DOX@TT-ABC) liposomes exhibited good stability at physiological pH (7.4) and released DOX quickly at reduced pH (6.4) and hyperthermia (42 °C). DOX@TT-ABC liposomes showed significantly enhanced cellular uptake, intracellular accumulation of DOX, and cytotoxicity at pH 6.4 and 42 °C.