Octreotide-modification enhances the delivery and targeting of doxorubicin-loaded liposomes to somatostatin receptors expressing tumor in vitro and in vivo.

Octreotide is believed to be the ligand of somatostatin receptors (SSTRs) which are widely used in tumor diagnosis and clinical therapy. In the present work, a new targeting conjugate, octreotide-polyethylene glycol-phosphatidylethanolamine (Oct-PEG-PE), was developed for the assembling of liposome, and the effect of octreotide-modification on the enhancement of the delivery and targeting of doxorubicin-loaded liposomes was investigated in vitro and in vivo. Oct-PEG-PE was synthesized by a three-step reaction involving two derivative intermediate formations of bis (p-nitrophenyl carbonate)-PEG ((pNP)(2)-PEG) and pNP-PEG-PE. The Oct-modified and unmodified liposomes (DOX-OL and DOX-CL) were prepared by the ammonium sulfate gradient method. Both drug uptake assay and cell apoptosis assay suggested that DOX-OL noticeably increased the uptake of DOX in SMMC-7721 cells and showed a more significant cytotoxicity, compared with DOX-CL. The effect of DOX-OL was remarkably inhibited by free octreotide. In contrast, no significant difference in drug cytotoxicity was found between DOX-OL and DOX-CL in CHO cells without obvious expression of SSTRs. The study of ex vivo fluorescence tissues imaging of BALB/c mice and in vivo tissue distribution of B16 tumor-bearing mice indicated that DOX-OL caused remarkable accumulation of DOX in melanoma tumors and the pancreas, in which the SSTRs are highly expressed.