Salinomycin（SAL）,a polyether antibiotic isolated from Streptomyces albus,is widely used as an anticoccidial drug in poultry and other livestock and is furthermore fed to ruminescent animals to improve nutrient absorption and feed efficiency.It has recently been shown to act as a specific inhibitor of cancer stem cells.At present,the price of salinomycin sodium（SAL-Na） is 10 fold lower than that of salinomycin,however,there is no report about the comparison of the inhibitory effects of SAL and SAL-Na on cancer stem cells as well as cancer cells.In the present study,side population cells（SP cells）and non-SP cells （NSP cells）sorted from human breast cancer cell line MCF-7 were chosen as the models of cancer stem cells and cancer cells, respectively.SRB assay was performed to compare the cytotoxicity of SAL and SAL-Na.First of all,SP cells were sorted from MCF-7 cells via FACSDiva flow cytometry.Secondly,the sorted SP cells were identified with the surface makers（CD44~＋/CD24^-） of breast cancer stem cells.Finally,the inhibitory effects of SAL and SAL-Na were evaluated on the sorted SP cells and NSP cells.Results showed that,as compared to breast cancer cells,the inhibitory effect of free SAL or free SAL-Na was more potent in breast cancer stem cells.Furthermore,the inhibitory effects of free SAL and free SAL-Na had no significant difference for the SP cells as well as the NSP cells when they were in the same concentration.Thus,it suggested that salinomycin sodium should be considered as a potential candidate to take the place of salinomycin in cancer stem cells research,due to their similar inhibitory effects on cancer stem cells.
To improve the pharmacological profile of tumor necrosis factor alpha(TNF-α),we have synthesized a new PEGylated prodrug,PEG-vcTNF-α,using a cathepsin B-sensitive dipeptide(valine-citrulline,vc) to link branched PEG and TNF-α.PEG-modified TNF-α without the dipeptide linker(PEG-TNF-α) and unconjugated TNF-α were also tested as controls.It was found for the first time that TNF-α released from PEG-vcTNF-α was specifically dependent on the presence of cathepsin B.PEG-vcTNF-α induced higher cytotoxicity and greater apoptosis against L929 murine fibrosarcoma cells than PEG-TNF-α.Reversal of these effects by a cathepsin-B inhibitor confirmed that these effects were mediated by cathepsin B-specific release of TNF-α.In vivo pharmacokinetics studies demonstrated that the plasma stability of PEG-vcTNF-α was significantly increased compared to TNF-α.Finally,the improved anticancer efficacy of PEG-vcTNF-α and the distinct activities among the three formulations confirmed the positive contribution of both PEGylation and the dipeptide linkage to the improved drug-like properties of PEG-vcTNF-α.The results here indicate that linking proteins and PEG via the cathepsin B-sensitive dipeptide may be a promising strategy for developing protein therapeutics.
DAI ChuanYunFU YaLI BiaoWANG YiGuangZHANG XuanWANG JianChengZHANG Qiang
Aminopeptidase N(APN)/CD13 is a transmembrane glycoprotein,which is overexpressed on tumor neovascular endothelial cells and most tumor cells,where it plays an important role in tumor angiogenesis.Peptides containing the Asn-Gly-Arg(NGR)motif can specifically recognize APN/CD13 allowing them to act as tumor-homing peptides for the targeted delivery of anti-tumor drugs to tumor neovascular endothelial cells and tumor cells.This article reviews the literature and recent developments related to APN/CD13,its role in tumor growth and some antitumor drug delivery systems containing NGR peptides designed to target APN/CD13.
Active targeting drug delivery systems （TDDS）, which could improve drug therapeutic efficacy and reduce toxicity, are still the focus of many scientific researches in cancer therapy. The drug circulation time and tumor accumulation could be significantly increased with the application of sterically stabilized liposome （SSL）. SSL could also be modified easily with certain ligands to achieve targeting drug delivery. Because many tumors overexpress somatostatin receptors （SSTRs）, octreotide （OCT） becomes a potential targeting ligand due to its high affinity to SSTRs, especially to subtype 2 （SSTR2）. In this study, OCT was conjugated to methoxypolyethyleneglycol-distearoyl-phosphatidylethanolamine （DSPE-PEG2000）, and doxorubicin （DOX）-loaded SSL with a variable percentage of octreotide-methoxypolyethyleneglycol-distearoyl-phosphatidylethanolamine （DSPE-PEG/00o-OCT） were prepared （OCT-SSL-DOX）. All liposomes were about 90 nm in diameter and negatively charged on the surface, with DOX encapsulation efficiency at above 95%. OCT modification exhibited little effect on the physicochemical properties of SSL. In this study, cellular delivery efficacy of all prepared liposomes was evaluated in SSTIL2-positive cells in vitro by flow cytometry for the optimization of the OCT density on the surface of liposomes. Lipid formulation containing 1.5% DSPE-PEG20oo-OCT exhibited the highest efficiency of intracellular drug delivery. The modification of OCT did not alter the release behaviors of liposomal DOX in vitro, but OCT-SSL-DOX increased the cytotoxicity and improved the anti-tumor effect of liposomal DOX in SST1L2- positive cells and tumor-bearing mice models. In summary, OCT-modified SSL succeeded in increasing intracellular delivery and enhancing therapeutic efficacy of encapsulated anticancer agent, suggesting that it might be a promising TDDS for the treatment of SSTR2-overexpressing cancers.
