Uptake and intracellular release kinetics of liposome formulations in glioma cells

A Comparison of Cellular Uptake Mechanisms, Delivery Efficacy, and Intracellular Fate between Liposomes and Extracellular Vesicles

A key aspect for successful drug delivery via lipid-based nanoparticles is their internalization in target cells. Two prominent examples of such drug delivery systems are artificial phospholipid-based carriers, such as liposomes, and their biological counterparts, the extracellular vesicles (EVs). Despite a wealth of literature, it remains unclear which mechanisms precisely orchestrate nanoparticle-mediated cargo delivery to recipient cells and the subsequent intracellular fate of therapeutic cargo. In this review, internalization mechanisms involved in the uptake of liposomes and EVs by recipient cells are evaluated, also exploring their intracellular fate after intracellular trafficking. Opportunities are highlighted to tweak these internalization mechanisms and intracellular fates to enhance the therapeutic efficacy of these drug delivery systems. Overall, literature to date shows that both liposomes and EVs are predominantly internalized through classical endocytosis mechanisms, sharing a common fate: accumulation inside lysosomes. Studies tackling the differences between liposomes and EVs, with respect to cellular uptake, intracellular delivery and therapy efficacy, remain scarce, despite its importance for the selection of an appropriate drug delivery system. In addition, further exploration of functionalization strategies of both liposomes and EVs represents an important avenue to pursue in order to control internalization and fate, thereby improving therapeutic efficacy.

Liposomes and Extracellular Vesicles as Drug Delivery Systems: A Comparison of Composition, Pharmacokinetics, and Functionalization

Over the past decades, lipid-based nanoparticle drug delivery systems (DDS) have caught the attention of researchers worldwide, encouraging the field to rapidly develop improved ways for effective drug delivery. One of the most prominent examples is liposomes, which are spherical shaped artificial vesicles composed of lipid bilayers and able to encapsulate both hydrophilic and hydrophobic materials. At the same time, biological nanoparticles naturally secreted by cells, called extracellular vesicles (EVs), have emerged as promising more complex biocompatible DDS. In this review paper, the differences and similarities in the composition of both vesicles are evaluated, and critical mediators that affect their pharmacokinetics are elucidate. Different strategies that have been assessed to tweak the pharmacokinetics of both liposomes and EVs are explored, detailing the effects on circulation time, targeting capacity, and cytoplasmic delivery of therapeutic cargo. Finally, whether a hybrid system, consisting of a combination of only the critical constituents of both vesicles, could offer the best of both worlds is discussed. Through these topics, novel leads for further research are provided and, more importantly, gain insight in what the liposome field and the EV field can learn from each other.

Influence of a lipophilic edaravone on physical state and activity of antioxidant liposomes: An experimental and in silico study

The influence of a lipophilic derivative of Edaravone (C18Edv) on a POPC liposomal bilayer has been investigated by a combined computational-experimental approach. The order and hydration degree of three different systems composed by 10%, 20% and 40% in w/w percentage of C18Edv respect to POPC were investigated through Molecular Dynamics (MD) simulations and fluorescence spectroscopy experiments. Dynamic Light Scattering measurements showed how the presence of different amounts of C18EdV determines differences on liposome size and stability. The survey revealed that the content of lipophilic antioxidant tunes liposome rigidity and influences cellular uptake and antioxidant activity which are maximized for formulation containing 20% of C18Edv.

Lithocholic acid-tryptophan conjugate (UniPR126) based mixed micelle as a nano carrier for specific delivery of niclosamide to prostate cancer via EphA2 receptor

Targeted delivery of chemotherapeutic agents is considered a prominent strategy for the treatment of cancer due to its site-specific delivery, augmented penetration, bioavailability, and improved therapeutic efficiency. In the present study, we employed UniPR126 as a carrier in a mixed nanomicellar delivery system to target and deliver anticancer drug NIC specifically to cancer cells via EphA2 receptors as these receptors are overexpressed in cancer cells but not in normal cells. The specificity of the carrier was confirmed from the significant enhancement in the uptake of coumarin-6 loaded mixed nanomicelle by EphA2 highly expressed PC-3 cells compared to EphA2 low expressed H4 cells. Further, niclosamide-loaded lithocholic acid tryptophan conjugate-based mixed nanomicelle has shown significant synergistic cytotoxicity in PC-3 but not in H4 cells. In vivo anticancer efficacy data in PC-3 xenograft revealed a significant reduction in the tumor volume (66.87%) with niclosamide-loaded lithocholic acid tryptophan conjugate nanomicelle, where pure niclosamide showed just half of the activity. Molecular signaling data by western blotting also indicated that niclosamide-loaded lithocholic acid tryptophan conjugate nanomicelle interfered with the EphA2 receptor signaling and inhibition of the Wnt/beta-catenin pathway and resulted in the synergistic anticancer activity compared to niclosamide pure drug.

Covalently Labeled Fluorescent Exosomes for In Vitro and In Vivo Applications

The vertiginous increase in the use of extracellular vesicles and especially exosomes for therapeutic applications highlights the necessity of advanced techniques for gaining a deeper knowledge of their pharmacological properties. Herein, we report a novel chemical approach for the robust attachment of commercial fluorescent dyes to the exosome surface with covalent binding. The applicability of the methodology was tested on milk and cancer cell-derived exosomes (from U87 and B16F10 cancer cells). We demonstrated that fluorescent labeling did not modify the original physicochemical properties of exosomes. We tested this nanoprobe in cell cultures and healthy mice to validate its use for in vitro and in vivo applications. We confirmed that these fluorescently labeled exosomes could be successfully visualized with optical imaging.

Design of 18 nm Doxorubicin-Loaded 3-Helix Micelles: Cellular Uptake and Cytotoxicity in Patient-Derived GBM6 Cells

The fate of nanocarrier materials at the cellular level constitutes a critical checkpoint in the development of effective nanomedicines, determining whether tissue level accumulation results in therapeutic benefit. The cytotoxicity and cell internalization of ∼18 nm 3-helix micelle (3HM) loaded with doxorubicin (DOX) were analyzed in patient-derived glioblastoma (GBM) cells in vitro. The half-maximal inhibitory concentration (IC₅₀) of 3HM-DOX increased to 6.2 μg/mL from <0.5 μg/mL for free DOX in patient-derived GBM6 cells, to 15.0 μg/mL from 6.5 μg/mL in U87MG cells, and to 21.5 μg/mL from ∼0.5 μg/mL in LN229 cells. Modeling analysis of previous 3HM biodistribution results predicts that these cytotoxic concentrations are achievable with intravenous injection in rodent GBM models. 3HM-DOX formulations were internalized intact and underwent intracellular trafficking distinct from free DOX. 3HM was quantified to have an internalization half-life of 12.6 h in GBM6 cells, significantly longer than that reported for some liposome and polymer systems. 3HM was found to traffic through active endocytic processes, with clathrin-mediated endocytosis being the most involved of the pathways studied. Inhibition studies suggest substantial involvement of receptor recognition in 3HM uptake. As the 3HM surface is PEG-ylated with no targeting functionalities, protein corona-cell surface interactions, such as the apolipoprotein-low-density lipoprotein receptor, are expected to initiate internalization. The present work gives insights into the cytotoxicity, pharmacodynamics, and cellular interactions of 3HM and 3HM-DOX relevant for ongoing preclinical studies. This work also contributes to efforts to develop predictive mathematical models tracking the accumulation and biodistribution kinetics at a systemic level.

Preparation of T‑2 toxin‑containing pH‑sensitive liposome and its antitumor activity

T‑2 toxin is a type A trichothecene mycotoxin. In order to reduce the side effects of T‑2 toxin and increase the tumor targeting ability, a pH‑sensitive liposome of T‑2 toxin (LP‑pHS‑T2) was prepared and characterized in the present study. The cytotoxicity of LP‑pHS‑T2 on A549, Hep‑G2, MKN‑45, K562 and L929 cell lines was tested by 3‑(4,5‑dimethylthiazolyl‑2)‑2,5‑diphenyltetrazolium bromide assay, with T‑2 toxin as the control. The apoptotic and migratory effects of LP‑pHS‑T2 on Hep‑G2 cells were investigated. The preparation process of LP‑pHS‑T2 involved the following parameters: Dipalmitoyl phosphatidylcholine: dioleoylphosphatidylethanolamine, 1:2; total phospholipid concentration, 20 mg/ml; phospholipid:cholesterol, 3:1; 4‑(2‑hydroxyethyl)‑1‑piperazineethanesulfonic acid buffer (pH 7.4), 10 ml; drug:lipid ratio, 2:1; followed by ultrasound for 10 min and extrusion. The encapsulation efficiency reached 95±2.43%. The average particle size of LP‑pHS‑T2 after extrusion was 100 nm; transmission electron microscopy showed that the shape of LP‑pHS‑T2 was round or oval and of uniform size. The release profile demonstrated a two‑phase downward trend, with fast leakage of T‑2 toxin in the first 6 h (~20% released), followed by sustained release up to 48 h (~46% released). From 48‑72 h, the leakage rate increased (~76% released), until reaching a minimum at 72 h. When LP‑pHS‑T2 was immersed in 0.2 mol/l disodium phosphate‑sodium dihydrogen phosphate buffers (pH 6.5), the release speed was significantly increased and the release rate reached 91.2%, demonstrating strong pH sensitivity. Overall, antitumor tests showed that LP‑pHS‑T2 could promote the apoptosis and inhibit the migration of Hep‑G2 cells. The present study provided a new approach for the development of T‑2 toxin‑based anti‑cancer drugs.

Following the Fate of Dye-Containing Liposomes In Vitro

The rather limited success of translation from basic research to clinical application has been highlighted as a major issue in the nanomedicine field. To identify the factors influencing the applicability of nanosystems as drug carriers and potential nanomedicine, we focused on following their fate through fluorescence-based assays, namely flow cytometry and imaging. These methods are often used to follow the nanocarrier internalization and targeting; however, the validity of the obtained results strictly depends on how much the nanosystem’s fate can be inferred from the fate of fluorescent dyes. To evaluate the parameters that affect the physicochemical and biological stability of the labeled nanosystems, we studied the versatility of two lipid dyes, TopFluor^®-PC and Cy5-DSPE, in conventional liposomes utilizing well-defined in vitro assays. Our results suggest that the dye can affect the major characteristics of the system, such as vesicle size and zeta-potential. However, a nanocarrier can also affect the dye properties. Medium, temperature, time, fluorophore localization and its concentration, as well as their interplay, affect the outcome of tracing experiments. Therefore, an in-depth characterization of the labeled nanosystem should be fundamental to understand the conditions that validate the results within the screening process in optimization of nanocarrier.

Zn phthalocyanines loaded into liposomes: Characterization and enhanced performance of photodynamic activity on glioblastoma cells

Photodynamic therapy (PDT) is considered a promising strategy for cancer treatment. PDT utilizes light in combination with a photosensitizer (PS) to induce several phototoxic reactions. Phthalocyanines (Pcs), a second generation of photosensitizers, have been studied in several cancer models. Among these, Pcs, have become of interest for the treatment of glioblastomas which are one of the most common and aggressive forms of tumors of the central nervous system. Due to the lipophilic nature of Pcs and their limited solubility in water, Pcs can be loaded in liposomes. In this work, we characterized liposomes of ZnPc and TAZnPc and their effectiveness to photoinactivate glioblastoma cells, was evaluated. Both Pcs show an increase in their photosensitizing activity when they were administrated in Dipalmitoylphosphatidylcholine-cholesterol liposomes compared to Pcs administrated in dimethylformamide.

PEGylated nanocarriers: A promising tool for targeted delivery to the brain

Targeted drug delivery across the blood-brain barrier is an extremely challenging quest in the fight with fatal brain ailments, with the major hurdles being short circulation time, reticuloendothelial system (RES) uptake, and excretion of nanocarriers. PEGylation has emerged as a boon for targeted drug delivery to the brain. It is well established that PEGylation can increase the circulation time of nanocarriers by avoiding RES uptake, which is indispensable for increasing the brain's uptake of nanocarriers. PEGylation also acts as a linker for ligand molecules to achieve active targeting to the brain. Using PEGylation, novel approaches are being investigated to facilitate ligand-receptor interactions at the brain endothelium to ease the entry of therapeutic drugs into the brain. In addition, PEGylation made it simpler to assess the brain tissue for delivering diagnostic molecules and theranostic nanocarriers. The potential of PEGylated nanocarriers is being investigated vastly to boost the therapeutic effect several fold in the treatment of brain diseases. This review sheds light on the contribution of PEGylated nanocarriers, especially liposomes, polymeric nanoparticles, and dendrimers for brain-specific delivery of bioactives.

Exploring the influence of inhaled liposome membrane fluidity on its interaction with pulmonary physiological barriers

Liposome membrane fluidity can influence its interaction with pulmonary physiological barriers, including mucus permeation, macrophage uptake and trachea permeation.

Nanotechnology-based strategies as novel therapies in gliomas

Gliomas are the most common malignancies of the brain and have a mean survival of 12 months with only 5-10% of the patients surviving for more than 5 years, independent of treatment after diagnosis. Conventional treatment modalities have found the modest success in reducing tumor burden and metastases. Presence of different biological barriers and drug-resistance efflux transporters are crucial for tumor recurrence and treatment failure. Nanotechnology may amend these circumstances by targeting residual infiltrating malignant cells with minimal damage to normal cells, on-demand release and an improved cellular uptake by tumor cells. This review highlights the current status and advances in nanotechnology for treatment of gliomas.

Liposomal formulations of carboplatin injected by convection-enhanced delivery increases the median survival time of F98 glioma bearing rats

BACKGROUND

Effectiveness of chemotherapy for treating glioblastoma (GBM) brain tumors is hampered by the blood-brain barrier which limits the entry into the brain of most drugs from the blood. To bypass this barrier, convection-enhanced delivery (CED) was proposed to directly inject drugs in tumor. However, the benefit of CED may be hampered when drugs diffuse outside the tumor to then induce neurotoxicity. Encapsulation of drugs into liposome aims at increasing tumor cells specificity and reduces neurotoxicity. However, the most appropriate liposomal formulation to inject drugs into brain tumor by CED still remains to be determined. In this study, four liposomal carboplatin formulations were prepared and tested in vitro on F98 glioma cells and in Fischer rats carrying F98 tumor implanted in the brain. Impact of pegylation on liposomal surface and relevance of positive or negative charge were assessed.

RESULTS

The cationic non-pegylated (L1) and pegylated (L2) liposomes greatly improved the toxicity of carboplatin in vitro compared to free carboplatin, whereas only a modest improvement and even a reduction of efficiency were measured with the anionic non-pegylated (L3) and the pegylated (L4) liposomes. Conversely, only the L4 liposome significantly increased the median survival time of Fisher rats implanted with the F98 tumor, compared to free carboplatin. Neurotoxicity assays performed with the empty L4' liposome showed that the lipid components of L4 were not toxic. These results suggest that the positive charge on liposomes L1 and L2, which is known to promote binding to cell membrane, facilitates carboplatin accumulation in cancer cells explaining their higher efficacy in vitro. Conversely, negatively charged and pegylated liposome (L4) seems to diffuse over a larger distance in the tumor, and consequently significantly increased the median survival time of the animals.

CONCLUSIONS

Selection of the best liposomal formulation based on in vitro studies or animal model can result in contradictory conclusions. The negatively charged and pegylated liposome (L4) which was the less efficient formulation in vitro showed the best therapeutic effect in animal model of GBM. These results support that relevant animal model of GBM must be considered to determine the optimal physicochemical properties of liposomal formulations.

Development and evaluation of injectable nanosized drug delivery systems for apigenin

The purpose of this study was to develop different injectable nanosized drug delivery systems (NDDSs) i.e. liposome, lipid nanocapsule (LNC) and polymeric nanocapsule (PNC) encapsulating apigenin (AG) and compare their characteristics to identify the nanovector(s) that can deliver the largest quantity of AG while being biocompatible. Two liposomes with different surface characteristics (cationic and anionic), a LNC and a PNC were prepared. A novel tocopherol modified poly(ethylene glycol)-b-polyphosphate block-copolymer was used for the first time for the PNC preparation. The NDDSs were compared by their physicochemical characteristics, AG release, storage stability, stability in serum, complement consumption and toxicity against a human macrovascular endothelial cell line (EAhy926). The diameter and surface charge of the NDDSs were comparable with previously reported injectable nanocarriers. The NDDSs showed good encapsulation efficiency and drug loading. Moreover, the NDDSs were stable during storage and in fetal bovine serum for extended periods, showed low complement consumption and were non-toxic to EAhy926 cells up to high concentrations. Therefore, they can be considered as potential injectable nanocarriers of AG. Due to less pronounced burst effect and extended release characteristics, the nanocapsules could be favorable approaches for achieving prolonged pharmacological activity of AG using injectable NDDS.

Anti-glioma activity and the mechanism of cellular uptake of asiatic acid-loaded solid lipid nanoparticles

Asiatic acid (AA), a pentacyclic triterpene found in Centella Asiatica, has shown neuroprotective and anti-cancer activity against glioma. However, owing to its poor aqueous solubility, effective delivery and absorption across biological barriers, in particular the blood brain barrier (BBB), are challenging. Solid lipid nanoparticles (SLNs) have shown a promising potential as a drug delivery system to carry lipophilic drugs across the BBB, a major obstacle in brain cancer therapy. Nevertheless, limited information is available about the cytotoxic mechanisms of nano-lipidic carriers with AA on normal and glioma cells. This study assessed the anti-cancer efficacy of AA-loaded SLNs against glioblastoma and their cellular uptake mechanism in comparison with SVG P12 (human foetal glial) cells. SLNs were systematically investigated for three different solid lipids; glyceryl monostearate (MS), glyceryl distearate (DS) and glyceryl tristearate (TS). The non-drug containing MS-SLNs (E-MS-SLNs) did not show any apparent toxicity towards normal SVG P12 cells, whilst the AA-loaded MS-SLNs (AA-MS-SLNs) displayed a more favourable drug release profile and higher cytotoxicity towards U87 MG cells. Therefore, MS-SLNs were chosen for further in vitro studies. Cytotoxicity studies of SLNs (± AA) were performed using MTT assay where AA-SLNs showed significantly higher cytotoxicity towards U87 MG cells than SVG P12 normal cells, as confirmed by flow cell cytometry. Cellular uptake of SLNs also appeared to be preferentially facilitated by energy-dependent endocytosis as evidenced by fluorescence imaging and flow cell cytometry. Using the Annexin V-PI double staining technique, it was found that these AA-MS-SLNs displayed concentration-dependent apoptotic activity on glioma cells, which further confirms the potential of exploiting these AA-loaded MS-SLNs for brain cancer therapy.

Membrane Microdomain Structures of Liposomes and Their Contribution to the Cellular Uptake Efficiency into HeLa Cells

The purpose of this study is to obtain a comprehensive relationship between membrane microdomain structures of liposomes and their cellular uptake efficiency. Model liposomes consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/cholesterol (Ch) were prepared with various lipid compositions. To detect distinct membrane microdomains in the liposomes, fluorescence-quenching assays were performed at temperatures ranging from 25 to 60 °C using 1,6-diphenyl-1,3,5-hexatriene-labeled liposomes and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl. From the data analysis using the response surface method, we gained a better understanding of the conditions for forming distinct domains (Lo, Ld, and gel phase membranes) as a function of lipid composition. We further performed self-organizing maps (SOM) clustering to simplify the complicated behavior of the domain formation to obtain its essence. As a result, DPPC/DOPC/Ch liposomes in any lipid composition were integrated into five distinct clusters in terms of similarity of the domain structure. In addition, the findings from synchrotron small-angle X-ray scattering analysis offered further insight into the domain structures. As a last phase of this study, an in vitro cellular uptake study using HeLa cells was conducted using SOM clusters' liposomes with/without PEGylation. As a consequence of this study, higher cellular uptake was observed from liposomes having Ch-rich ordered domains.

Sui generis: gene therapy and delivery systems for the treatment of glioblastoma

Gene therapy offers a multidimensional set of approaches intended to treat and cure glioblastoma (GBM), in combination with the existing standard-of-care treatment (surgery and chemoradiotherapy), by capitalizing on the ability to deliver genes directly to the site of neoplasia to yield antitumoral effects. Four types of gene therapy are currently being investigated for their potential use in treating GBM: (i) suicide gene therapy, which induces the localized generation of cytotoxic compounds; (ii) immunomodulatory gene therapy, which induces or augments an enhanced antitumoral immune response; (iii) tumor-suppressor gene therapy, which induces apoptosis in cancer cells; and (iv) oncolytic virotherapy, which causes the lysis of tumor cells. The delivery of genes to the tumor site is made possible by means of viral and nonviral vectors for direct delivery of therapeutic gene(s), tumor-tropic cell carriers expressing therapeutic gene(s), and "intelligent" carriers designed to increase delivery, specificity, and tumoral toxicity against GBM. These vehicles are used to carry genetic material to the site of pathology, with the expectation that they can provide specific tropism to the desired site while limiting interaction with noncancerous tissue. Encouraging preclinical results using gene therapies for GBM have led to a series of human clinical trials. Although there is limited evidence of a therapeutic benefit to date, a number of clinical trials have convincingly established that different types of gene therapies delivered by various methods appear to be safe. Due to the flexibility of specialized carriers and genetic material, the technology for generating new and more effective therapies already exists.

The Directional Observation of Highly Dynamic Membrane Tubule Formation Induced by Engulfed Liposomes

Highly dynamic tubular structures in cells are responsible for exchanges between organelles. Compared with bacterial invasion, the most affordable and least toxic lipids were found in this study to be gentle and safe exogenous stimuli for the triggering of membrane tubules. A specific lipid system was internalized by NIH3T3 cells. Following cellular uptake, the constructed liposomes traveled towards the nucleus in aggregations and were gradually distributed into moving vesicles and tubules in the cytosol. The triggered tubules proceeded, retreated or fluctuated along the cytoskeleton and were highly dynamic, moving quickly (up to several microns per second), and breaking and fusing frequently. These elongated tubules could also fuse with one another, giving rise to polygonal membrane networks. These lipid systems, with the novel property of accelerating intracellular transport, provide a new paradigm for investigating cellular dynamics.

PEGylation improves the receptor-mediated transfection efficiency of peptide-targeted, self-assembling, anionic nanocomplexes

Non-viral vector formulations comprise typically complexes of nucleic acids with cationic polymers or lipids. However, for in vivo applications cationic formulations suffer from problems of poor tissue penetration, non-specific binding to cells, interaction with serum proteins and cell adhesion molecules and can lead to inflammatory responses. Anionic formulations may provide a solution to these problems but they have not been developed to the same extent as cationic formulations due to difficulties of nucleic acid packaging and poor transfection efficiency. We have developed novel PEGylated, anionic nanocomplexes containing cationic targeting peptides that act as a bridge between PEGylated anionic liposomes and plasmid DNA. At optimized ratios, the components self-assemble into anionic nanocomplexes with a high packaging efficiency of plasmid DNA. Anionic PEGylated nanocomplexes were resistant to aggregation in serum and transfected cells with a far higher degree of receptor-targeted specificity than their homologous non-PEGylated anionic and cationic counterparts. Gadolinium-labeled, anionic nanoparticles, administered directly to the brain by convection-enhanced delivery displayed improved tissue penetration and dispersal as well as more widespread cellular transfection than cationic formulations. Anionic PEGylated nanocomplexes have widespread potential for in vivo gene therapy due to their targeted transfection efficiency and ability to penetrate tissues.

pH-sensitive liposomes for drug delivery in cancer treatment

In recent years, liposomes have been employed with growing success as pharmaceutical carriers for antineoplastic drugs. One specific strategy used to enhance in vivo liposome-mediated drug delivery is the improvement of intracytoplasmic delivery. In this context, pH-sensitive liposomes (pHSLip) have been designed to explore the endosomal acidification process, which may lead to a destabilization of the liposomes, followed by a release of their contents into the cell cytoplasm. This review considers the current status of pHSLip development and its applicability in cancer treatment, focusing on the mechanisms of pH sensitivity and liposomal composition of pHSLip. The final section will discuss the application of these formulations in both in vitro and in vivo studies of antitumor efficacy.

pH-responsive biodegradable assemblies containing tunable phenyl-substituted vinyl ethers for use as efficient gene delivery vehicles

Novel pH-responsive assemblies (PEG-lipid:DOPE liposomes) containing tunable and bifunctional phenyl-substituted vinyl ether (PIVE) cross-linkers were prepared. The assemblies consisted of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), acid-cleavable poly(ethylene glycol) (PEG)-conjugated lipids, pDNA, and protamine sulfate (PS). The PIVE linkage was designed to hydrolyze under acidic conditions, and the hydrolysis studies of PEG-lipid compounds containing PIVE at pH 4.2, 5.4, and 7.4 indicated that the hydrolysis rates of PIVE linker were influenced by the substitution of electron withdrawing or electron donating groups on the phenyl ring. Acid-catalyzed hydrolysis of PIVE leads to destabilization of the acid labile PEG-PIVE-lipid:DOPE liposomes via dePEGylation, thereby triggering content release. Content release assays showed that dePEGylation was highly pH-dependent and correlated with the PIVE proton affinity of the phenyl group. These results indicated that the dePEGylative triggering based on a new pH-sensitive PIVE linkage can be controlled. In vitro transfection studies on the pH-responsive assemblies containing mPEG-(MeO-PIVE)-conjugated 1,3-dioctadecyl-rac-glycerol lipids (mPEG-(MeO-PIVE])-DOG) showed higher transfection efficiency compared to that of polyethylenimine (PEI), a positive control, on HEK 293 and COS-7 cells. In addition, lower cytotoxicity of PEG-PIVE-lipid:DOPE liposomes/PS/DNA was observed in comparison to PEI. These results suggest that PEG-PIVE-lipid:DOPE liposomes can be considered as nonviral vehicles for drug and gene delivery applications.

Liposomes for brain delivery

INTRODUCTION

Development of drug delivery systems for brain delivery is one of the most challenging research topics in pharmaceutical areas, mainly due to the presence of the blood-brain barrier (BBB), which separates the blood from the cerebral parenchyma thus limiting the brain uptake of the majority of therapeutic agents. Among the several carriers, which have been studied to overcome this problem, liposomes have gained increasing attention as promising strategies for brain-targeted drug delivery. The most advantageous features of liposomes are their ability to incorporate and deliver large amounts of drug and the possibility to decorate their surface with different ligands.

AREAS COVERED

The purpose of this review is to explore the different approaches studied to transport and deliver therapeutics and imaging agents to the brain by using liposomes. In the first part of the review, particular attention is paid to describe the anatomy of the BBB and different physiological transport mechanisms available for drug permeation. In the second part, the different strategies for the delivery of a drug to the brain using liposomes are reviewed for each transport mechanism.

EXPERT OPINION

Over the last decade, there have been significant developments concerning liposomal brain delivery systems conjugated with selected ligands with high specificity and low immunogenicity. An universally useful liposomal formulation for brain targeting does not exist but liposome design must be modulated by the appropriate choice of the specific homing device and transport mechanism.

Lipid peptide nanocomplexes for gene delivery and magnetic resonance imaging in the brain

Gadolinium-labelled nanocomplexes offer prospects for the development of real-time, non-invasive imaging strategies to visualise the location of gene delivery by MRI. In this study, targeted nanoparticle formulations were prepared comprising a cationic liposome (L) containing a Gd-chelated lipid at 10, 15 and 20% by weight of total lipid, a receptor-targeted, DNA-binding peptide (P) and plasmid DNA (D), which electrostatically self-assembled into LPD nanocomplexes. The LPD formulation containing the liposome with 15% Gd-chelated lipid displayed optimal peptide-targeted, transfection efficiency. MRI conspicuity peaked at 4h after incubation of the nanocomplexes with cells, suggesting enhancement by cellular uptake and trafficking. This was supported by time course confocal microscopy analysis of transfections with fluorescently-labelled LPD nanocomplexes. Gd-LPD nanocomplexes delivered to rat brains by convection-enhanced delivery were visible by MRI at 6 h, 24 h and 48 h after administration. Histological brain sections analysed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) confirmed that the MRI signal was associated with the distribution of Gd(3+) moieties and differentiated MRI signals due to haemorrhage. The transfected brain cells near the injection site appeared to be mostly microglial. This study shows the potential of Gd-LPD nanocomplexes for simultaneous delivery of contrast agents and genes for real-time monitoring of gene therapy in the brain.

Impacts of blood-brain barrier in drug delivery and targeting of brain tumors

INTRODUCTION

Entry of blood circulating agents into the brain is highly selectively con-trolled by specific transport machineries at the blood brain barrier (BBB), whose excellent barrier restrictiveness make brain drug delivery and targeting very challenging.

METHODS

Essential information on BBB cellular microenvironment were reviewed and discussed towards impacts of BBB on brain drug delivery and targeting.

RESULTS

Brain capillary endothelial cells (BCECs) form unique biological structure and architecture in association with astrocytes and pericytes, in which microenvironment the BCECs express restrictive tight junctional complexes that block the paracellular inward/outward traverse of biomolecules/compounds. These cells selectively/specifically control the transportation process through carrier and/or receptor mediated transport machineries that can also be exploited for the delivery of pharmaceuticals into the brain. Intelligent molecular therapies should be designed using such transport machineries for the efficient delivery of designated drugs into the brain. For better clinical outcomes, these smart pharmaceuticals should be engineered as seamless nanosystems to provide simultaneous imaging and therapy (multimodal theranostics).

CONCLUSION

The exceptional functional presence of BBB selectively controls inward and outward transportation mechanisms, thus advanced smart multifunctional nanomedicines are needed for the effective brain drug delivery and targeting. Fully understanding the biofunctions of BBB appears to be a central step for engineering of intelligent seamless therapeutics consisting of homing device for targeting, imaging moiety for detecting, and stimuli responsive device for on-demand liberation of therapeutic agent.

Effective targeted gene delivery to dendritic cells via synergetic interaction of mannosylated lipid with DOPE and BCAT

The efficient delivery of plasmids encoding antigenic determinants into dendritic cells (DCs) that control immune response is a promising strategy for rapid development of new vaccines. In this study, we prepared a series of targeted cationic lipoplex based on two synthetic lipid components, mannose-poly(ethylene glycol, MW3000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (Mannose-PEG3000-DSPE) and O-(2R-1,2-di-O-(1'Z-octadecenyl)-glycerol)-3-N-(bis-2-aminoethyl)-carbamate (BCAT), that were formulated with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) for evaluation as nonviral vectors for transgene expression in DCs. First, we optimized the N/P ratio for maximum transfection and then screened the effects of mannose targeting for further enhancement of transfection levels. Our results indicate that efficient delivery of gWIZ GFP plasmid into DCs was observed for mannose compositions of ∼10%, whereas low transfection efficiencies were observed with nontargeted formulations. Mannose-targeted lipofectamine complexes also showed high GFP expression levels in DCs relative to nontargeted lipofectamine controls. The best transfection performance was observed using 10 mol % Mannose-PEG3000-DSPE, 60 mol % BCAT, and 30 mol % DOPE, indicating that the most efficient delivery into DCs occurs via synergistic interaction between mannose targeting and acid-labile, fusogenic BCAT/DOPE formulations. Our data suggest that mannose-PEG3000-DSPE/BCAT/DOPE formulations may be effective gene delivery vehicles for the development of DC-based vaccines.

Co-delivery of pEGFP-hTRAIL and paclitaxel to brain glioma mediated by an angiopep-conjugated liposome

In this study, we report an angiopep-2 modified cationic liposome (ANG-CLP) for the efficient co-delivery of a therapeutic gene encoding the human tumour necrosis factor-related apoptosis-inducing ligand (pEGFP-hTRAIL) and paclitaxel (PTX) to glioma. The dual targeting co-delivery system (ANG-CLP/PTX/pEGFP-hTRAIL) improved uptake and gene expression not only in U87 MG cells and BCECs, but also in the glioma bed and infiltrating margin of intracranial U87 MG glioma-bearing models. The system selectively induces apoptosis in U87 MG cells while reducing toxicity to BCECs. The results of the pharmacodynamics studies showed that the apoptosis of glioma cells in in vitro BBB models and in U87 MG glioma-bearing mice induced by ANG-CLP/PTX/pEGFP-hTRAIL was more apparent and widespread than that induced by single medication systems and unmodified co-delivery system. More importantly, the median survival time of brain tumour-bearing mice treated with ANG-CLP/PTX/pEGFP-hTRAIL was 69.5 days, significantly longer than that of other groups, even longer than the commercial temozolomide group (47 days). Therefore, the dual targeting co-delivery system is a promising drug delivery strategy against glioma.

Surface-modified gold nanoshells for enhanced cellular uptake

Gold nanoshells have shown a great potential for use as agents in a wide variety of biomedical applications, and some of which require the delivery of large numbers of gold nanoshells onto or into the cells. Here, we develop a ready method to enhance the cellular uptake of gold nanoshells by modifying with meso-2,3-dimercaptosuccinic acid (DMSA). The quantifiable technique of inductively coupled plasma atomic emissions spectroscopy (ICP-AES) and transmission electron microscopy (TEM) were used to investigate the cellular uptake of unmodified and DMSA-modified gold nanoshells. Three cell lines (RAW 264.7, A549, and BEL-7402) were involved and the results indicated that the cellular uptake of the DMSA-modified gold nanoshells was obviously enhanced versus the unmodified gold nanoshells. The reason possibly lies in the nonspecific adsorption of serum protein on the DMSA-modified gold nanoshells (DMSA-GNs), which consequently enhanced the cellular uptake. As a continued effort, in vitro experiments with endocytic inhibitors suggested the DMSA-GNs internalized into cells via receptor-mediated endocytosis (RME) pathway. This study has provided a valuable insight into the effects of surface modification on cellular uptake of nanoparticles.

A review on composite liposomal technologies for specialized drug delivery

The combination of liposomes with polymeric scaffolds could revolutionize the current state of drug delivery technology. Although liposomes have been extensively studied as a promising drug delivery model for bioactive compounds, there still remain major drawbacks for widespread pharmaceutical application. Two approaches for overcoming the factors related to the suboptimal efficacy of liposomes in drug delivery have been suggested. The first entails modifying the liposome surface with functional moieties, while the second involves integration of pre-encapsulated drug-loaded liposomes within depot polymeric scaffolds. This attempts to provide ingenious solutions to the limitations of conventional liposomes such as short plasma half-lives, toxicity, stability, and poor control of drug release over prolonged periods. This review delineates the key advances in composite technologies that merge the concepts of depot polymeric scaffolds with liposome technology to overcome the limitations of conventional liposomes for pharmaceutical applications.