Purpose: To investigate the potential of a reduction-sensitive and fusogenic liposomes, enabled by surface-coating with chotooligosaccharides (COS) via a disulfide linker, for tumor-targeted cytoplasmic drug delivery.
Methods: COS (MW2000-5000) were chemically tethered onto the liposomes through a disulfide linker (-SS-) to cholesterol (Chol). Doxorubicin (DOX) was actively loaded in the liposomes. Their reduction-sensitivities, cellular uptake, cytotoxicity, pharmacokinetics and antitumor efficacy were investigated.
Results: The Chol-SS-COS/DOX liposomes (100 nm) had zeta potential of 33.9 mV and high drug loading (13% w/w). The liposomes were stable with minimal drug leakage under physiological conditions but destabilized in the presence of reducing agents, dithiothreitol (DTT) or glutathione (GSH) at 10 mM, the cytosolic level. MTT assay revealed that the cationic Chol-SS-COS/DOX liposomes had higher cytotoxicity to MG63-osteosarcoma cells than non-reduction sensitive liposome (Chol-COS/DOX). Flow cytometry and confocal microscopy revealed that Chol-SS-COS/DOX internalized more efficiently than Chol-COS/DOX with more content to cytoplasm whereas Chol-COS/DOX located around the cell membrane. Chol-SS-COS/DOX preferentially internalized into MG63 cancer cell over LO2 normal liver cells. In rats both liposomes produced a prolonged half-life of DOX by 4 - 5.5 fold (p < 0.001) compared with the DOX solution. Chol-SS-COS/DOX exhibited strong inhibitory effect on tumor growth in MG63 cell-bearing nude mice (n = 6), and extended animal survival rate.
Conclusions: Reduction-responsive Chol-SS-COS liposomes may be an excellent platform for cytoplasmic delivery of anticancer drugs. Conjugation of liposomes with COS enhanced tumor cell uptake, antitumor effect and survival rate in animal models.
Keywords: Cationic liposomes; Chotooligosaccharides (COS); Cytoplasmic delivery; Reduction-sensitivity; Survival rate; Tumor-suppression.