Ting Zhong

Tumor-specific pH-responsive peptide-modified pH-sensitive liposomes containing doxorubicin for enhancing glioma targeting and anti-tumor activity.

The pH environment in gliomas is acidic. Therefore, in the present research, we selected our previously reported tumor-specific pH-responsive peptide H7K(R2)2 as a targeting ligand, which could respond to the acidic pH environment in gliomas, possessing CPP characteristics. The pH-sensitive liposomes were selected as carriers which could also respond to the acidic pH environment in gliomas triggering encapsulated drug release from these pH-sensitive liposomes. The H7K(R2)2-modified pH-sensitive liposomes containing doxorubicin (DOX-PSL-H7K(R2)2) were designed and prepared in order to evaluate their potential targeting of glioma tumor cells and their anti-tumor activity in mice with glioma tumor cells. DOX-PSL-H7K(R2)2 was prepared by the thin-film hydration method followed by remote loading using an ammonium sulfate gradient method. The in vitro release of DOX from pH-sensitive liposomes was tested and the in vitro targeting characteristics of H7K(R2)2-modified liposomes regarding C6 (rat C6 glioma cells) and U87-MG (human glioblastoma cells) were evaluated. The in vivo anti-tumor activity of DOX-PSL-H7K(R2)2 was also investigated in C6 tumor-bearing mice and in U87-MG orthotopic tumor-bearing nude mice. A specific targeting effect triggered by an acidic pH was observed in our in vitro experiments in C6 and U87-MG glioma cells. The pH-triggered DOX release from the pH-sensitive liposomes under acidic conditions was also confirmed in our in vitro experiment. Anti-tumor activity of DOX-PSL-H7K(R2)2 was found in C6 tumor-bearing mice and U87-MG orthotopic tumor-bearing nude mice in in vivo experiments. The antiangiogenic activity of DOX-PSL-H7K(R2)2 was confirmed in C6 tumor-bearing mice in the in vivo experiment. These H7K(R2)2-modified pH-sensitive liposomes containing anti-tumor drugs developed in this study are a promising delivery system involving the response stimuli at the acidic pH in the glioma tumor microenvironment and are suitable for anti-tumor therapy.

The development of site-specific drug delivery nanocarriers based on receptor mediation

Since they were first reported in 1980, site-specific drug delivery nanocarriers have progressed greatly with the development of nanotechnology and biotechnology, especially in the anti-tumor field. Currently, some of the ligand peptides like RGD have become hot targeting molecules with extensive academic studies and some receptor-medicated nanocarriers are now in clinical trials. Homing peptides have been the preferred ligands thus far due to their low molecular weight, low antigenicity, high modification ratios and low interference in vivo. The major benefit of receptor-mediated nanocarriers over passive ones may be their accumulation within tumors for longer period of time due to their binding to and/or their uptake by cancer cells, preventing them from fast redistribution into systemic circulation. The studies on receptor-mediated nanocarriers are very dynamic currently, advancing gradually from these against non-therapeutic targets to these against therapeutic targets. And recently, more studies were focused on these systems against multiple receptors and the combination therapies with receptor-mediated nanocarriers. However, we still face great challenges, especially in the understanding of receptors, the key issue for receptor-mediated delivery. This review presents the past and ongoing studies on various types of drug delivery systems based on receptor mediation, discusses the prospective and challenges, and introduces the possible trend of study in the future.

The antitumor activity of tumor-homing peptide-modified thermosensitive liposomes containing doxorubicin on MCF-7/ADR: in vitro and in vivo

Clotted plasma proteins are present on the walls of tumor vessels and in tumor stroma. Tumor-homing peptide Cys-Arg-Glu-Lys-Ala (CREKA) could recognize the clotted plasma proteins in tumor vessels. Thermosensitive liposomes could immediately release the encapsulated drug in the vasculature of the heated tumor. In this study, we designed a novel form of targeted thermosensitive liposomes, CREKA-modified lysolipid-containing thermosensitive liposomes (LTSLs), containing doxorubicin (DOX) (DOX-LTSL-CREKA), to investigate the hypothesis that DOX-LTSL-CREKA might target the clotted plasma proteins in tumor vessels as well as tumor stroma and then exhibit burst release of the encapsulated DOX at the heated tumor site. We also hypothesized that the high local drug concentration produced by these thermosensitive liposomes after local hyperthermia treatment will be useful for treatment of multidrug resistance. The multidrug-resistant human breast adenocarcinoma (MCF-7/ADR) cell line was chosen as a tumor cell model, and the targeting and immediate release characteristics of DOX-LTSL-CREKA were investigated in vitro and in vivo. Furthermore, the antitumor activity of DOX-LTSL-CREKA was evaluated in MCF-7/ADR tumor-bearing nude mice in vivo. The targeting effect of the CREKA-modified thermosensitive liposomes on the clotted plasma proteins was confirmed in our in vivo imaging and immunohistochemistry experiments. The burst release of this delivery system was observed in our in vitro temperature-triggered DOX release and flow cytometry analysis and also by confocal microscopy experiments. The antitumor activity of the DOX-LTSL-CREKA was confirmed in tumor-bearing nude mice in vivo. Our findings suggest that the combination of targeting the clotted plasma proteins in the tumor vessel wall as well as tumor stroma by using CREKA peptide and temperature-triggered drug release from liposomes by using thermosensitive liposomes offers an attractive strategy for chemotherapeutic drug delivery to tumors.

Antitumor effect of iRGD-modified liposomes containing conjugated linoleic acid-paclitaxel (CLA-PTX) on B16-F10 melanoma

In the present study, we prepared a novel delivery system of iRGD (CRGDK/RGPD/EC)-modified sterically stabilized liposomes (SSLs) containing conjugated linoleic acid–paclitaxel (CLA-PTX). The anti-tumor effect of iRGD-SSL-CLA-PTX was investigated on B16-F10 melanoma in vitro and in vivo. The in vitro targeting effect of iRGD-modified SSLs was investigated in a real-time confocal microscopic analysis experiment. An endocytosis-inhibition assay was used to evaluate the endocytosis pathways of the iRGD-modified SSLs. In addition, the in vitro cellular uptake and in vitro cytotoxicity of iRGD-SSL-CLA-PTX were evaluated in B16-F10 melanoma cells. In vivo biodistribution and in vivo antitumor effects of iRGD-SSL-CLA-PTX were investigated in B16-F10 tumor-bearing mice. The induction of apoptosis by iRGD-SSL-CLA-PTX was evaluated in tumor-tissue sections. Real-time confocal microscopic analysis results indicated that the iRGD-modified SSLs internalized into B16-F10 cells faster than SSLs. The identified endocytosis pathway of iRGD-modified SSLs indicated that energy- and lipid raft-mediated endocytosis played a key role in the liposomes’ cellular uptake. The results of the cellular uptake experiment indicated that the increased cellular uptake of CLA-PTX in the iRGD-SSL-CLA-PTX-treated group was 1.9-, 2.4-, or 2.1-fold compared with that in the CLA-PTX group after a 2-, 4-, or 6-hour incubation, respectively. In the biodistribution test, the CLA-PTX level in tumor tissues from iRGD-SSL-CLA-PTX-treated mice at 1 hour (1.84±0.17 μg/g) and 4 hours (1.17±0.28 μg/g) was 2.3- and 2.0-fold higher than that of CLA-PTX solution at 1 hour (0.79±0.06 μg/g) and 4 hours (0.58±0.04 μg/g). The value of the area under the curve for the first 24 hours in the tumors of iRGD-SSL-CLA-PTX-treated mice was significantly higher than that in the SSL-CLA-PTX and CLA-PTX solution-treated groups (P<0.01). The in vivo antitumor results indicated that iRGD-SSL-CLA-PTX significantly inhibited the growth of B16-F10 tumors compared with the SSL-CLA-PTX or CLA-PTX solution-treatment groups (P<0.01). The results of tumor-cell apoptosis showed that tumors from the iRGD-SSL-CLA-PTX-treated group exhibited more advanced cell apoptosis compared with the control, CLA-PTX solution-, and SSL-CLA-PTX-treated groups. In conclusion, the antitumor effect of iRGD-SSL-CLA-PTX was confirmed on B16-F10 melanoma in vitro and in vivo.

A self-assembling nanomedicine of conjugated linoleic acid-paclitaxel conjugate (CLA-PTX) with higher drug loading and carrier-free characteristic

The main objective of this study was to demonstrate the proof-of-principle for the hypothesis that conjugated linoleic acid-paclitaxel conjugate (CLA-PTX), a novel fatty acid modified anti-cancer drug conjugate, could self-assemble forming nanoparticles. The results indicated that a novel self-assembling nanomedicine, CLA-PTX@PEG NPs (about 105 nm), with Cremophor EL (CrEL)-free and organic solvent-free characteristics, was prepared by a simple precipitation method. Being the ratio of CLA-PTX:DSPE-PEG was only 1:0.1 (w/w), the higher drug loading CLA-PTX@PEG NPs (about 90%) possessed carrier-free characteristic. The stability results indicated that CLA-PTX@PEG NPs could be stored for at least 9 months. The safety of CLA-PTX@PEG NPs was demonstrated by the MTD results. The anti-tumor activity and cellular uptake were also confirmed in the in vitro experiments. The lower crystallinity, polarity and solubility of CLA-PTX compared with that of paclitaxel (PTX) might be the possible reason for CLA-PTX self-assembling forming nanoparticles, indicating a relationship between PTX modification and nanoparticles self-assembly. Overall, the data presented here confirm that this drug self-delivery strategy based on self-assembly of a CLA-PTX conjugate may offer a new way to prepare nanomedicine products for cancer therapy involving the relationship between anticancer drug modification and self-assembly into nanoparticles.

Multi-targeting NGR-modified liposomes recognizing glioma tumor cells and vasculogenic mimicry for improving anti-glioma therapy

Like the anti-angiogenic strategy, anti-vascular mimicry is considered as a novel targeting strategy for glioma. In the present study, we used NGR as a targeting ligand and prepared NGR-modified liposomes containing combretastatin A4 (NGR-SSL-CA4) in order to evaluate their potential targeting of glioma tumor cells and vasculogenic mimicry (VM) formed by glioma cells as well as their anti-VM activity in mice with glioma tumor cells. NGR-SSL-CA4 was prepared by a thin-film hydration method. The in vitro targeting of U87-MG (human glioma tumor cells) by NGR-modified liposomes was evaluated. The in vivo targeting activity of NGR-modified liposomes was tested in U87-MG orthotopic tumor-bearing nude mice. The anti-VM activity of NGR-SSL-CA4 was also investigated in vitro and in vivo. The targeting activity of the NGR-modified liposomes was demonstrated by in vitro flow cytometry and in vivo biodistribution. The in vitro anti-VM activity of NGR-SSL-CA4 was indicated in a series of cell migration and VM channel experiments. NGR-SSL-CA4 produced very marked anti-tumor and anti-VM activity in U87-MG orthotopic tumor-bearing mice in vivo. Overall, the NGR-SSL-CA4 has great potential in the multi-targeting therapy of glioma involving U87-MG cells, and the VM formed by U87-MG cells as well as endothelial cells producing anti-U87-MG cells, and anti-VM formed by U87-MG cells as well as anti-endothelial cell activity.

Improving anti-tumor activity of sorafenib tosylate by lipid- and polymer-coated nanomatrix

Abstract In the present study, we select the Sylysia 350 (Sylysia) as mesoporous material, distearoylphosphatidylethanolamine-poly(ethylene glycol)2000 (DSPE-PEG) as absorption enhancer and hydroxy propyl methyl cellulose (HPMC) as crystallization inhibitor to prepare sorafenib tosylate (SFN) nanomitrix (MSNM@SFN) for improving the anti-tumor activity of SFN. The MSNM@SFN was prepared by solvent evaporation method. The solubility, dissolution, and bioavailability of SFN in MSNM@SFN were also investigated. The anti-tumor activity of MSNM@SFN was evaluated in vitro and in vivo. Our results indicated that the solubility and dissolution of SFN in MSNM@SFN were significantly increased. The oral bioavailability of SFN in MSNM@SFN was greatly improved 7.7-fold compared with that in SFN suspension. The enhanced anti-tumor activity of MSNM@SFN was confirmed in vitro and in vivo experiments. This nanomatrix developed in this study could be a promising drug delivery platform for improving the therapeutic efficacy of poorly water-soluble drugs.

The anti-tumor efficacy of 3-(2-Nitrophenyl) propionic acid-paclitaxel (NPPA-PTX): a novel paclitaxel bioreductive prodrug

Hypoxia is an important microenvironmental pressure present in the majority of solid tumors and, so, tumor hypoxia might be considered an attractive target for tumor therapy. One strategy for targeting hypoxia is to develop bioreductive prodrugs. In the present research, we synthesized a bioreductive paclitaxel prodrug, 3-(2-Nitrophenyl) propionic acid-paclitaxel (NPPA-PTX). The stability of NPPA-PTX in PBS and rat plasma was investigated. The anti-tumor activity of NPPA-PTX was also evaluated in vitro and in vivo. The results of our stability study indicated that NPPA-PTX was stable in PBS and rat plasma as well as in the blood circulation. The in vitro and in vivo anti-tumor activity of NPPA-PTX was confirmed in both KB cells and MDA-MB-231 cells. Our results also indicated that NPPA-PTX could completely convert to active PTX in tumor tissues and produced the anti-tumor activity in both KB and MDA-MB-231 tumor-bearing nude mice. We suggest that the dissociated PTX which converted from NPPA-PTX in tumor tissues played a key role in producing anti-tumor activity. Considering all our results, we suggest that NPPA-PTX is a novel bioreductive PTX prodrug which could undergo further evaluation.

The theranostic efficiency of tumor-specific, pH-responsive, peptide-modified, liposome-containing paclitaxel and superparamagnetic iron oxide nanoparticles

Background In the present study, the tumor-specific, pH-responsive peptide H7K(R2)2-modified, theranostic liposome-containing paclitaxel (PTX) and superparamagnetic iron oxide nanoparticles (SPIO NPs), PTX/SPIO-SSL-H7K(R2)2, was prepared by using H7K(R2)2 as the targeting ligand, SPIO NPs as the magnetic resonance imaging (MRI) agent, PTX as antitumor drug. Methods The PTX/SPIO-SSL-H7K(R2)2 was prepared by a thin film hydration method. The characteristics of PTX/SPIO-SSL-H7K(R2)2 were evaluated. The targeting effect, MRI, and antitumor activity of PTX/SPIO-SSL-H7K(R2)2 were investigated detail in vitro and in vivo in human breast carcinoma MDA-MB-231 cell models. Results Our results of in vitro flow cytometry, in vivo imaging, and in vivo MR imaging confirmed the pH-responsive characteristic of H7K(R2)2 in MDA-MB-231 cell line in vitro and in vivo. The results of in vivo MRI and in vivo antitumor activity confirmed the theranostic effect of PTX/SPIO-SSL-H7K(R2)2 in MDA-MB-231 tumor-bearing model. Conclusion Considering all our in vitro and in vivo results, we conclude that we developed targeting modified theranostic liposome which could achieve both role of antitumor and MRI.

Does ligand–receptor mediated competitive effect or penetrating effect of iRGD peptide when co-administration with iRGD-modified SSL?

Abstract Ligand-mediated targeting of anticancer therapeutic agents is a useful strategy for improving anti-tumor efficacy. It has been reported that co-administration of a tumor-penetrating peptide iRGD (CRGDK/RGPD/EC) enhances the efficacy of anticancer drugs. Here, we designed an experiment involving co-administration of iRGD-SSL-DOX with free iRGD to B16-F10 tumor bearing mice to examine the action of free iRGD. We also designed an experiment to investigate the location of iRGD-modified SSL when co-administered with free iRGD or free RGD to B16-F10 tumor bearing nude mice. Considering the sequence of iRGD, we selected the GPDC, RGD and CRGDK as targeting ligands to investigate the targeting effect of these peptides compared with iRGD on B16-F10 and MCF-7 cells, with or without enzymatic degradation. Finally, we selected free RGD, free CRGDK and free iRGD as ligand to investigate the inhibitory effect on RGD-, CRGDK- or iRGD-modified SSL on B16-F10 or MCF-7 cells. Our results indicated that iRGD targeting to tumor cells was ligand–receptor mediated involving RGD to αv-integrin receptor and CRGDK to NRP-1 receptor. Being competitive effect, the administration of free iRGD would not be able to further enhance the anti-tumor activity of iRGD-modified SSL. There is no need to co-administrate of free iRGD with the iRGD-modified nanoparticles for further therapeutic benefit.