No drugs have been approved clinically for the therapy of hepatic fibrosis. Though interferon-γ (IFN-γ) is a highly effective anti-fibrotic agent in vitro and in some animal models in vivo, its anti-fibrotic potential in clinical trials has been disappointing, due to unwanted off-target effects and a short half-life period which results in poor efficacy. The aims of this study are to develop a new targeted drug delivery system to selectively deliver IFN-γ to hepatic stellate cells (HSCs) and to investigate whether it will improve the anti-fibrotic effect of IFN-γ and reduce its side effects in fibrotic livers. Sterically stable liposomes (SSLs) were modified by cyclic peptides (pPB) with a specific affinity for platelet-derived growth factor receptor-β (PDGFR-β), and then IFN-γ was encapsulated in the targeted liposomes (pPB-SSL-IFN-γ). In vitro, pPB-SSL was found to be taken up and internalized by cultured activated HSCs. The binding of FITC-labeled pPB-SSL to activated HSCs was in a time-dependent and concentration-dependent manner, which could be inhibited by excess unlabelled pPB-SSL, PDGF-BB, suramin or monensin. The inhibitory effect of pPB-SSL-IFN-γ on the proliferation of activated HSCs was respectively 7.24-fold and 2.95-fold higher than that of free IFN-γ and IFN-γ encapsulated in untargeted SSLs. In healthy rats, the tissue distribution, living-body tracing image analyses and pharmacokinetics study showed that pPB-SSL-IFN-γ accumulated mainly in the livers and had a longer half-life than free IFN-γ (3.98±0.52h vs. 0.21±0.03h). Furthermore, in rats with hepatic fibrosis induced by thioacetamide injection, FITC-labeled pPB-SSL was found to predominantly localize in activated HSCs by immunofluorescent double staining for FITC and albumin or α-smooth muscle actin (α-SMA). The enhanced anti-fibrotic effect of pPB-SSL-IFN-γ treatnment was indicated by significant decreases in the histologic Ishak stage, collagen I-staining positive areas, and α-SMA expression levels in fibrotic livers. In addition, pPB-SSL-IFN-γ treatment improved the leukopenia caused by low- and high-dosage free IFN-γ treatments. In conclusion, IFN-γ encapsulated in pPB-SSL had an extended circulation half-life and was selectively delivered to activated HSCs, which enhanced the anti-fibrotic effect of IFN-γ and reduced its side-effects in rats with hepatic fibrosis. Thus, pPB-SSL-IFN-γ may be an effective agent for the therapy of hepatic fibrosis.
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