A designed lipopeptide with a leucine zipper as an imbedded on/off switch for lipid bilayers

Abstract

Thermo-sensitive drug carriers are receiving increasing attention for use with localized hyperthermia at abnormal tissue sites or to easily implement hyperthermia. In this study, a thermo-sensitive lipopeptide was designed, consisting of a carbon chain and a leucine zipper with an amino acid sequence CH₃-(CH₂)₄-CO-NH-VAQLEVK-VAQLESK-VSKLESK-VSSLESK-COOH. They could form dimers by the hydrophobic force at body temperature and separate into single random coils above the melting temperature (T_m). The lipopeptide was mixed with phospholipids to form a hybrid liposome (Lipo-LPe). The T_m of the free lipopeptide and lipopeptide in Lipo-LPe was found to be 48.0 °C and 42.5 °C from circular dichroism data, respectively. Compared with the pure liposome, the phase-transition temperature (T_tr) of Lipo-LPe, which was obtained by differential scanning calorimetry, was increased by about 5 °C, showing an improvement of thermal stability. The drug release rate of Lipo-LPe was slightly decreased at body temperature but greatly increased at mild hyperthermia in vitro. Drug release under intermittent heating was performed, and the reversibility of thermo-sensitive on/off switch was confirmed. Furthermore, Lipo-LPe achieved the maximum amount of cell death under mild hyperthermia. We concluded that Lipo-LPe, as a novel thermo-sensitive drug carrier, provides a promising opportunity for controlling drug release.