Co-delivery of doxorubicin and P-gp inhibitor by a reduction-sensitive liposome to overcome multidrug resistance, enhance anti-tumor efficiency and reduce toxicity

To overcome multidrug resistance (MDR) in cancer chemotherapy with high efficiency and safety, a reduction-sensitive liposome (CL-R8-LP), which was co-modified with reduction-sensitive cleavable PEG and octaarginine (R8) to increase the tumor accumulation, cellular uptake and lysosome escape, was applied to co-encapsulate doxorubicin (DOX) and a P-glycoprotein (P-gp) inhibitor of verapamil (VER) in this study. The encapsulation efficiency (EE) of DOX and VER in the binary-drug loaded CL-R8-LP (DOX + VER) was about 95 and 70% (w/w), respectively. The uptake efficiencies, the cytotoxicity, and the apoptosis and necrosis-inducing efficiency of CL-R8-LP (DOX + VER) were much higher than those of DOX and the other control liposomes in MCF-7/ADR cells or tumor spheroids. Besides, CL-R8-LP (DOX + VER) was proven to be uptaken into MCF-7/ADR cells by clathrin-mediated and macropinocytosis-mediated endocytosis, followed by efficient lysosomal escape. In vivo, CL-R8-LP (DOX + VER) effectively inhibited the growth of MCF-7/ADR tumor and reduce the toxicity of DOX and VER, which could be ascribed to increased accumulation of drugs in drug-resistant tumor cells and reduced distribution in normal tissues. In summary, the co-delivery of chemotherapeutics and P-gp inhibitors by our reduction-sensitive liposome was a promising approach to overcome MDR, improve anti-tumor effect and reduce the toxicity of chemotherapy.

A detachable coating of cholesterol-anchored PEG improves tumor targeting of cell-penetrating peptide-modified liposomes

Cell-penetrating peptides (CPPs) have been widely used to enhance the membrane translocation of various carriers for many years, but the non-specificity of CPPs seriously limits their utility in vivo. In this study, cholesterol-anchored, reduction-sensitive PEG (first synthesized by our laboratory) was applied to develop a co-modified liposome with improved tumor targeting. Following optimization of the formulation, the in vitro and in vivo properties of the co-modified liposome were evaluated. The co-modified liposome had a much lower cellular uptake and tumor spheroid uptake, but a much higher tumor accumulation compared to CPP-modified liposome, indicating the non-specific penetration of CPPs could be attenuated by the outer PEG coating. With the addition of exogenous reducing agent, both the in vitro and in vivo cellular uptake was markedly increased, demonstrating that the reduction-sensitive PEG coating achieved a controllable detachment from the surface of liposomes and did not affect the penetrating abilities of CPPs. The present results demonstrate that the combination of cholestervsitive PEG and CPPs is an ideal alternative for the application of CPP-modified carriers in vivo.

Liposomes co-modified with cholesterol anchored cleavable PEG and octaarginines for tumor targeted drug delivery

Tumor targeted drug delivery system with high efficiency of tumor accumulation, cell internalization and endosomal escape was considered ideal for cancer therapy. Herein, a cleavable polyethylene glycol (PEG) and octaarginines (R8) co-modified liposome (CL-R8-LP) was developed, in which the cholesterol was used as an alternative anchor to the commonest phospholipids for the diversified development of surface modification. The in vitro hemolysis assay and bio-distribution study demonstrated that CL-R8-LP improved biocompatibility and tumor accumulation compared with the single R8 modified liposomes (R8-LP), since the strong positive charges, toxicity and non-specificity of R8 were efficiently shielded by the outer cleavable PEG. And the cellular uptake, cytotoxicity and apoptosis of CL-R8-LP on C26 cells were much stronger than that of control liposomes in which R8 was not included or exposed. In addition, it was confirmed that CL-R8-LP entered cells via clathrin-mediated endocytosis and the macropinocytosis, and followed by a more efficient endosomal escape compared with R8-LP due to the topology change of R8. The enhanced in vivo delivery efficiency and anti-tumor efficacy were validated in C26 bearing mice. In conclusion, the results demonstrated that CL-R8-LP was a promising vehicle for enhancing the chemotherapy of solid cancers.