Targeted drug delivery crossing cytoplasmic membranes of intended cells via ligand-grafted sterically stabilized liposomes

Receptor-targeted drug delivery: current perspective and challenges

Receptor-targeted drug delivery has been extensively explored for active targeting. However, the scarce clinical applications of such delivery systems highlight the implicit hurdles in development of such systems. These hurdles begin with lack of knowledge of differential expression of receptors, their accessibility and identification of newer receptors. Similarly, ligand-specific challenges range from proper choice of ligand and conjugation chemistry, to release of drug/delivery system from ligand. Finally, nanocarrier systems, which offer improved loading, biocompatibility and reduced premature degradation, also face multiple challenges. This review focuses on understanding these challenges, and means to overcome such challenges to develop efficient, targeted drug-delivery systems.

Micromixer Based Preparation of Functionalized Liposomes and Targeting Drug Delivery

We present here a specific targeting nanocarrier system by functionalization of liposomes with one new type of breast cancer targeting peptide (H6, YLFFVFER) by a micromixer with high efficiency. Antitumor drugs could be successfully delivered into human epidermal growth factor receptor 2 (HER2) positive breast cancer cells with high efficiency in both in vivo and ex vivo models.

Transcytosis-Targeting Peptide: A Conductor of Liposomal Nanoparticles through the Endothelial Cell Barrier

The ultimate goal in the area of drug-delivery systems is the development of a nanoparticle that can penetrate the endothelial cell monolayer for the targeting of tissue parenchyma. In the present study, we identify a transcytosis-targeting peptide (TTP) that permits polyethyleneglycol (PEG)-modified liposomes (PEG-LPs) to penetrate through monolayers of brain-derived endothelial cells. These endothelial cells were layered on a gelatin nanofiber sheet, a nanofiber meshwork that allows the evaluation of transcellular transport of nanosized particles (ca. 100 nm). Systematic modification of the sequences results in the identification of the consensus sequence of TTP as L(R/K)QZZZL, where Z denotes hydrophilic amino acids (R/K/S and partially D). The TTP-modified liposomes are bound on the heparin sulfate proteoglycan, and are then taken up via lipid raft-mediated endocytosis. Subsequent intracellular imaging of the particles reveals a unique intracellular sorting of TTP-modified PEG liposomes (TTP-PEG-LPs); namely the TTP-LPs are not localized with the lysosomes, whereas this co-localization is dominant in the unmodified PEG liposomes (PEG-LPs). The in vivo endothelial penetration of liposomes in adipose tissue is conferred by the dual modification of the particles with TTP and tissue-targeting ligands. This technology promises innovations in intravenously available delivery system to tissue parenchyma.

Neuroprotection against degeneration of sk-N-mc cells using neuron growth factor-encapsulated liposomes with surface cereport and transferrin

Liposomes with Cereport (RMP-7) and transferrin (Tf) (RMP-7/Tf/liposomes) were employed to target the blood-brain barrier (BBB) and to inhibit the degeneration of neurons insulted with fibrillar β-amyloid peptide 1-42 (Aβ1-42). Neuron growth factor (NGF)-encapsulated RMP-7/Tf/liposomes (RMP-7/Tf/NGF-liposomes) were used to permeate a monolayer of human brain-microvascular endothelial cells (HBMECs) regulated by human astrocytes (HAs) and to treat Aβ1-42 -attacked SK-N-MC cells. An increase in RMT-7 concentration increased the particle size, zeta potential, propidium iodide (PI) permeability, and NGF permeability, but decreased the cross-linking efficiency of RMT-7, viability of HBMECs and HAs, and transendothelial electrical resistance (TEER). In addition, an increase in Tf concentration enhanced the particle size, viability of HBMECs, HAs, and SK-N-MC cells, PI permeability, and NGF permeability, but reduced the zeta potential, cross-linking efficiency of RMT-7 and Tf, and TEER. RMP-7/Tf/NGF-liposomes can transport NGF across the BBB and improve the neuroprotection for Alzheimer's disease therapy in preclinical trials.

Naltrexone: a review of existing sustained drug delivery systems and emerging nano-based systems

Narcotic antagonists such as naltrexone (NTX) have shown some efficiency in the treatment of both opiate addiction and alcohol dependence. A few review articles have focused on clinical findings and pharmacogenetics of NTX, advantages and limitations of sustained release systems as well as pharmacological studies of NTX depot formulations for the treatment of alcohol and opioid dependency. To date, three NTX implant systems have been developed and tested in humans. In this review, we summarize the latest clinical data on commercially available injectable and implantable NTX-sustained release systems and discuss their safety and tolerability aspects. Emphasis is also laid on recent developments in the area of nanodrug delivery such as NTX-loaded micelles and nanogels as well as related research avenues. Due to their ability to increase the therapeutic index and to improve the selectivity of drugs (targeted delivery), nanodrug delivery systems are considered as promising sustainable drug carriers for NTX in addressing opiate and alcohol dependence.

Functionalized nanoscale micelles improve drug delivery for cancer therapy in vitro and in vivo

Poor penetration of therapeutic drugs into tumors is a major challenge in anticancer therapy, especially in solid tumors, leading to reduced therapeutic efficacy in vivo. In the study, we used a new tumor-penetrating peptide, CRGDK, to conjugate onto the surface of doxorubicin encapsulated nanoscale micelles. The CRGDK peptide triggered specific binding to neuropilin-1, leading to enhanced cellular uptake and cytotoxicity in vitro and highly accumulation and penetration in the tumors in vivo.

Synergistic anticancer effect of RNAi and photothermal therapy mediated by functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) are special nano-materials which exhibit interesting physical and chemical properties, presenting new opportunities for biomedical research and applications. In this study, we have successfully adopted a novel strategy to chemically functionalize SWNTs with polyethylenimine (PEI) through purification, oxidation, amination and polymerization, which were then bound by DSPE-PEG2000-Maleimide for further conjugation with the tumor targeting NGR (Cys-Asn-Gly-Arg-Cys-) peptide via the maleimide group and sulfhydryl group of cysteine, and finally hTERT siRNA was loaded to obtain a novel tumor targeting siRNA delivery system, designated as SWNT-PEI/siRNA/NGR. The results showed that SWNT-PEI/siRNA/NGR could efficiently cross cell membrane, induced more severe apoptosis and stronger suppression in proliferation of PC-3 cells in vitro. Furthermore, in tumor-bearing mice model the delivery system exhibited higher antitumor activity due to more accumulation in tumor without obvious toxicity in main organs. The combination of RNAi and near-infrared (NIR) photothermal therapy significantly enhanced the therapeutic efficacy. In conclusion, SWNT-PEI/siRNA/NGR is a novel and promising anticancer system by combining gene therapy and photothermal therapy.

A MSLN-targeted multifunctional nanoimmunoliposome for MRI and targeting therapy in pancreatic cancer

Pancreatic cancer is a highly lethal disease with a 5-year survival rate less than 5% due to the lack of an early diagnosis method and effective therapy. To provide a novel early diagnostic method and targeted therapy for pancreatic cancer, a multifunctional nanoimmunoliposome with high loading of ultrasmall superparamagnetic iron oxides (USPIOs) and doxorubicin (DOX) was prepared by transient binding and reverse-phase evaporation method, and was conjugated with anti-mesothelin monoclonal antibody by post-insertion method to target anti-mesothelin-overexpressed pancreatic cancer cells. The in vitro and in vivo properties of this anti-mesothelin antibody-conjugated PEGlyated liposomal DOX and USPIOs (M-PLDU; and PEGlyated nanoimmunoliposome without antibody conjugation [PLDU]) were evaluated both in human pancreatic cancer cell line Panc-1 cell and in a pancreatic cancer xenograft animal model. Results showed that M-PLDUs were spherical and uniform with a diameter about ∼180 nm, with a zeta potential of about −28∼−30 mV, and had good efficacy encapsulating DOX and USPIOs. The in vitro study demonstrated that M-PLDUs possessed good magnetic resonance imaging (MRI) capability with a transverse relaxivity (r²) of about 58.5 mM^–1 · s^–1. Confocal microscopy showed more efficient uptake of M-PLDU in Panc-1 cells by antibody-mediated targeting. Methyl thiazolyl tetrazolium assay results showed significant inhibitory effect of M-PLDU against Panc-1 cells (half-maximal inhibitory concentration, 1.95 μM). The in vivo imaging study showed that the tumor signal intensity (SI) dropped significantly about 4 hours after intravenous injection of M-PLDU. The decrease in tumor SI induced by M-PLDUs (ΔSI = 145.98 ± 20.45) or PLDUs (ΔSI = 75.69 ± 14.53) was much more significant than that by free USPIOs (ΔSI = 42.78 ± 22.12; P < 0.01). The in vivo antitumor study demonstrated that compared with FD (free DOX) and PLDU, M-PLDU possessed higher inhibitory effect on tumor growth and the tissue distribution assay further proved that M-PLDUs could selectively accumulate in the tumor xenograft. These results indicated that M-PLDU not only well retained the inherent MRI capability of USPIOs, but significantly improved the targeting distribution of USPIOs and therapeutic agents in pancreatic tumor tissues. They may serve as a promising theranostic nanomedicine not only for early detection but also for MRI-monitored targeting therapy of human pancreatic cancer.

Synergistic enhancement of cancer therapy using a combination of docetaxel and photothermal ablation induced by single-walled carbon nanotubes

Background

Single-walled carbon nanotubes (SWNT) are poorly soluble in water, so their applications are limited. Therefore, aqueous solutions of SWNT, designed by noncovalent functionalization and without toxicity, are required for biomedical applications.

Methods

In this study, we conjugated docetaxel with SWNT via π-π accumulation and used a surfactant to functionalize SWNT noncovalently. The SWNT were then conjugated with docetaxel (DTX-SWNT) and linked with NGR (Asn-Gly-Arg) peptide, which targets tumor angiogenesis, to obtain a water-soluble and tumor-targeting SWNT-NGR-DTX drug delivery system.

Results

SWNT-NGR-DTX showed higher efficacy than docetaxel in suppressing tumor growth in a cultured PC3 cell line in vitro and in a murine S180 cancer model. Tumor volumes in the S180 mouse model decreased considerably under near-infrared radiation compared with the control group.

Conclusion

The SWNT-NGR-DTX drug delivery system may be promising for high treatment efficacy with minimal side effects in future cancer therapy.

Preparation and Cytotoxicity Effect of Anti-Hepatocellular Carcinoma Scfv Immunoliposome on Hepatocarcinoma Cell in Vitro

The use of PE38 for cancer therapy has attracted considerable attention for a long time. However, the extensive use of PE38 is prohibited by its severe side effects. Even though immunotoxin PE38 has been researched for cancer therapy, it has displayed low antitumor activity. The aim of this study is to compare the killing efficacy on Hepatocellular carcinoma (HCC) SMMC-7721 cell of immunoliposome PE38, immunotoxin PE38 and liposome PE38. In this study, the sterically stabilized liposomal PE38 was prepared using soybean phosphatidylcholine, cholesterol, and Cholesterol-PEG-COOH. The humanized anti-hepatoma disulfide-stabilized Fv (hdsFv25) was coupled to sterically stabilized liposomes using the N-hydroxysuccinimide ester method. The immunoliposome PE38 was prepared in our lab using the above-mentioned single-chain antibody. The hdsFv25-immunoliposomes were immunoreactive as determined by ELISA assay. Immunoliposome PE38 can kill SMMC-7721 cells in vitro with higher efficiency than non-targeted liposomes. These results indicate that immunoliposome PE38 may be potential in the treatment of hepatocarcinoma.

Preparation and evaluation of norcantharidin-encapsulated liposomes modified with a novel CD19 monoclonal antibody 2E8

In this study, norcanthridin (NCTD)-encapsulated liposomes were modified with a novel murine anti-human CD19 monoclonal antibody 2E8 (2E8-NCTD-liposomes) and the targeting efficiency and specific cytotoxicity of 2E8-NCTD-liposomes to CD19(+) leukemia cells were evaluated. BALB/c mice were injected with 2E8 hybridoma cells to obtain 2E8 monoclonal antibody (mAb). NCTD-liposomes were prepared by using film dispersion method. 2E8 mAbs were linked to NCTD-liposomes using post-incorporation technology. Flow cytometry showed that the targeting efficiency of purified 2E8 mAbs on CD19(+) Nalm-6 cells was 99.93%. The purified 2E8 mAbs were conjugated with NCTD-liposomes to prepare 2E8-NCTD-liposomes whose targeting efficiency on CD19(+) Nalm-6 was also 95.82%. The average size of 2E8-NCTD-liposomes was 118.32 nm in diameter. HPLC showed that the encapsulation efficiency of NCTD was 46.51%. When the molar ratio of 2E8/Mal-PEG(2000)-DSPE reached 1:50, we obtained the liposomes with 9 2E8 molecules per liposome. The targeting efficiency of 2E8-NCTD-liposomes on CD19(+) leukemia cells was significantly higher than that on CD19-leukemia cells. Similarly, the targeting efficiency of the immunoliposomes was also higher than that of the NCTD-liposomes on CD19(+) leukemia cells. Those results were consistent with those observed by laser scanning confocal microscopy. 3-(4, 5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay demonstrated that 2E8-NCTD-liposomes specifically killed Nalm-6 cells in a dose- and time-dependent manner. The viability of Nalm-6 cells treated by 2E8-NCTD-liposomes was significantly lower than that of Molt-3 cells and it was also significantly lower than that of Nalm-6 cells treated with the same concentration of NCTD-liposomes or free NCTD. We are led to concluded that 2E8 antigen can serve as a specific targeting molecule of B lineage hematopoietic malignancies for liposome targeting, and 2E8-NCTD-liposomes can be used as a new and effective means for the treatment of B lineage hematopoietic malignancies.

Leptin-derived peptide, a targeting ligand for mouse brain-derived endothelial cells via macropinocytosis

Leptin is an appetite regulatory hormone that is secreted into the blood circulation by adipose tissue, and functions in the central nerve system (i.e. hypothalamus) by crossing the blood brain barrier (BBB). In the present study, we investigated the function of a leptin-derived peptide (Lep(70-89)) as a ligand for mouse brain-derived endothelial cells (MBEC4). Lep(70-89)-modified liposomes, prepared with a polyethyleneglycol (PEG) spacer (Lep(70-89)-PEG-LPs) exhibited a significantly higher cellular uptake than peptide-unmodified liposomes (PEG-LPs). Furthermore, cellular uptake was inhibited by amiloride, while no significant inhibitory effect was observed by the presence of chlorpromazine and filipin III, suggesting that macropinocytosis largely contributed to the cellular uptake of Lep(70-89)-PEG-LPs. Imaging studies revealed that Lep(70-89)-PEG-LPs were not colocalized with endosome/lysosomes, whereas neutral dextran (70 kDa) was predominantly colocalized with these compartments. This indicates that Lep(70-89)-PEG-LPs are taken up via macropinocytosis and are subject to non-classical intracellular trafficking, resulting in the circumvention of lysosomal degradation in endothelial cells.

Peptide- and aptamer-functionalized nanovectors for targeted delivery of therapeutics

Targeted delivery of therapeutics is an area of vigorous research, and peptide- and aptamer-functionalized nanovectors are a promising class of targeted delivery vehicles. Both peptide- and aptamer-targeting ligands can be readily designed to bind a target selectively with high affinity, and more importantly are molecules accessible by chemical synthesis and relatively compact compared with antibodies and full proteins. The multitude of peptide ligands that have been used for targeted delivery are covered in this review, with discussion of binding selectivity and targeting performance for these peptide sequences where possible. Aptamers are RNA or DNA strands evolutionarily engineered to specifically bind a chosen target. Although use of aptamers in targeted delivery is a relatively new avenue of research, the current state of the field is covered and promises of future advances in this area are highlighted. Liposomes, the classic drug delivery vector, and polymeric nanovectors functionalized with peptide or aptamer binding ligands will be discussed in this review, with the exclusion of other drug delivery vehicles. Targeted delivery of therapeutics, from DNA to classic small molecule drugs to protein therapeutics, by these targeted nanovectors is reviewed with coverage of both in vitro and in vivo deliveries. This is an exciting and dynamic area of research and this review seeks to discuss its broad scope.

Targeting and internalization of sterically stabilized liposome modified with ZCH-4-2E8

Sterically stabilized liposome (SL) modified with 2E8 monoclonal antibody (2E8-SL) was prepared in order to evaluate its targeting ability and internalization efficiency against tumor cells with high expression of CD19. 2E8 was coupled to the surface of SL using post-insertion technique. The shape of liposomes was observed under a transmission electronic microscope. The average size of liposomes was determined by using the Zetasizer instrument. The binding and internalization of 2E8-SL against tumor cells with higher expression of CD19 were tested by flow cytometry and confocal microscopy. The mean diameter of 2E8-SL was 121.25 nm. 2E8-SL was stable after up to 24 days in various buffers. 2E8-SL showed specific binding to tumor cells with high expression of CD19, including B cells in peripheral blood mononuclear cells (PBMCs). 2E8-SL could efficiently internalize into Nalm6 cells with CD19 high expression. It is suggested that 2E8-SL may serve as useful delivery carrier of anti-cancer drugs targeting to hematological malignant tumors with CD19 high expression.

Preparation and evaluation of paclitaxel-loaded PEGylated immunoliposome

A sterically stabilized paclitaxel-loaded liposome tailored to target human breast cancer cells was developed, thereby promoting the efficiency of intracellular delivery of paclitaxel through receptor-mediated endocytosis. Results indicated that the targeting moiety (thiolated Herceptin) was successfully coupled to the distal reactive maleimide terminus of the poly (ethylene glycol)-phospholipid conjugate as well as being incorporated in the liposomal bilayers. The particle size of the PEGylated immunoliposome was maintained at about 200 nm. Confocal microscopy studies showed that the PEGylated immunoliposome was uptaken into the interior of the tumor cell through the receptor-mediated endocytosis pathway. The PEGylated immunoliposome showed substantially higher cellular uptake than the PEGylated liposome in cancer cells (BT-474 and SK-BR-3) over-expressing human epidermal growth factor receptor 2 (HER2) at 37 degrees C, while no difference was found in low HER2 expressing cells (MDA-MB-231) nor at low temperature (4 degrees C). Pharmacokinetics of paclitaxel in the PEGylated immunoliposome was compared with that in Taxol and in the PEGylated liposome in rats. The circulating time of paclitaxel in the PEGylated immunoliposome was prolonged compared to Taxol while slightly shortened than that in the PEGylated liposome. Therefore, the paclitaxel-loaded PEGylated immunoliposome using Herceptin could serve as a promising model for future tumor specific cancer therapy of HER2 over-expressing breast cancers.

Phosphorylation: A molecular switch in opioid tolerance

Protein phosphorylation is a key posttranslational modification mechanism controlling the conformation and activity of many proteins. Increasing evidence has implicated an essential role of phosphorylation by several major protein kinases in promoting and maintaining opioid tolerance. We review some of the most recent studies on protein kinase C (PKC), cyclic AMP dependent protein kinase A (PKA), calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase G (PKG), and G protein receptor kinase (GRK). These kinases act as the molecular switches to modulate opioid tolerance. Pharmacological interventions at one or more of the protein kinases and phosphatases may provide valuable strategies to improve opioid analgesia by attenuating tolerance to these drugs.