Anti-tumor and anti-angiogenic effect of metronomic cyclic NGR-modified liposomes containing paclitaxel

In the present study, we prepared NGR-modified sterically stabilized liposomes containing paclitaxel (NGR-SSL-PTX) in order to evaluate their potential targeting to aminopeptidase N receptors expressed on tumor endothelial cells and the tumor cell surface and its anti-angiogenic activity following metronomic administration. NGR-SSL-PTX was prepared by a thin-film hydration method. The in vitro targeting characteristics of NGR-modified liposomes on HUVEC (human umbilical vein endothelial cells), HT1080 (human fibrosarcoma cells) and MCF-7 (human breast adenocarcinoma cells) were then investigated. The effect of NGR-SSL-PTX on HUVEC proliferation and migration was also tested. The pharmacokinetics of NGR-SSL-PTX was studied in rats. The in vivo targeting activity of NGR-modified liposomes was investigated in HT1080 tumor-bearing mice. The anti-tumor activity of NGR-SSL-PTX following metronomic administration was evaluated in HT1080 tumor-bearing mice in vivo. The targeting activity of the NGR-modified liposomes was demonstrated by in vitro flow cytometry and confocal microscopy as well as in vivo confocal immunofluorescence microscopy and bio-distribution experiments. The results of endothelial cell proliferation and migration and microvessel density (MVD) confirmed the anti-angiogenic activity of NGR-SSL-PTX in vitro and in vivo. The sustained circulation of NGR-SSL-PTX was shown in the pharmacokinetic study. NGR-SSL-PTX is able to improve treatment efficacy producing the most significant anti-tumor activity and anti-angiogenic following metronomic administration.