Reexamining the effects of drug loading on the in vivo performance of PEGylated liposomal doxorubicin.

Higher drug loading employed in nanoscale delivery platforms is a goal that researchers have long sought after. But such viewpoint remains controversial because the impacts that nanocarriers bring about on bodies have been seriously overlooked. In the present study we investigated the effects of drug loading on the in vivo performance of PEGylated liposomal doxorubicin (PLD). We prepared PLDs with two different drug loading rates: high drug loading rate, H-Dox, 12.9% w/w Dox/HSPC; low drug loading rate, L-Dox, 2.4% w/w Dox/HSPC (L-Dox had about 5 folds drug carriers of H-Dox at the same Dox dose). The pharmaceutical properties and biological effects of H-Dox and L-Dox were compared in mice, rats or 4T1 subcutaneous tumor-bearing mice. We showed that the lowering of doxorubicin loading did not cause substantial shifts to the pharmaceutical properties of PLDs such as in vitro and in vivo stability (stable), anti-tumor effect (equivalent effective), as well as tissue and cellular distribution. Moreover, it was even more beneficial for mitigating the undesired biological effects caused by PLDs, through prolonging blood circulation and alleviating cutaneous accumulation in the presence of pre-existing anti-PEG Abs due to less opsonins (e.g. IgM and C3) deposition on per particle. Our results warn that the effects of drug loading would be much more convoluted than expected due to the complex intermediation between nanocarriers and bodies, urging independent investigation for each individual delivery platform to facilitate clinical translation and application.

Effects of interferon-gamma liposomes targeted to platelet-derived growth factor receptor-beta on hepatic fibrosis in rats.

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-ß (PDGFR-ß), 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.