Comparison of polymerically stabilized PEG-grafted liposomes and physically adsorbed carboxymethylchitin and carboxymethyl/glycolchitin liposomes for biological applications

Aptamer-Conjugated Chitosan-Anchored Liposomal Complexes for Targeted Delivery of Erlotinib to EGFR-Mutated Lung Cancer Cells

Lung cancer is the leading cancer and has the highest death rate. The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) erlotinib has had a promising response in lung cancer therapy. Unfortunately, individuals with TKI-resistant EGFR mutations often develop acquired resistance against erlotinib. To overcome this resistance, in the present study, we developed liposomes anchored with anti-EGFR aptamer (Apt)-conjugated chitosan (Apt-Cs) as stable carriers to deliver erlotinib to the target. We loaded erlotinib into Apt-Cs-anchored liposomal complexes (Apt-CL-E) and characterized the physicochemistry of Apt-CL-E. The nanoparticles showed good biostability and a binding specificity for EGFR-mutated cancer cells guided by the Apt. The specific binding facilitated the uptake of Apt-CL-E into EGFR-mutated cancer cells. A cytotoxicity study showed an advantage of Apt-CL-E over their nontargeted liposomal counterparts in delivering erlotinib to EGFR-mutated cancer cells, resulting in cell cycle arrest and apoptosis. These results provide a good platform for future in vivo animal studies with Apt-CL-E.

Preparation and evaluation of PCL–PEG–PCL polymeric nanoparticles for doxorubicin delivery against breast cancer

DOX-loaded polymeric NPs based on PCL–PEG–PCL triblock copolymers were successfully prepared and showed highly efficient targeting and accumulation in tumor via EPR effect. The prepared NPs would be a promising nanosized DDS for cancer therapy.

Poly(ethylene glycol)-block-poly(ε-caprolactone)-and phospholipid-based stealth nanoparticles with enhanced therapeutic efficacy on murine breast cancer by improved intracellular drug delivery

BACKGROUND

Effective anticancer drug delivery to the tumor site without rapid body clearance is a prerequisite for successful chemotherapy. 1,2-distearoyl-sn-glycero-3-phospho-ethanolamine-N-(methoxy[polyethyleneglycol]-2000) (DSPE-PEG2000) has been widely used in the preparation of stealth liposomes. Although PEG chains can efficiently preserve liposomes from rapid clearance by the reticuloendothelial system (RES), its application has been hindered by poor cellular uptake and unsatisfactory therapeutic effect.

METHODS

To address the dilemma, we presented a facile approach to fabricate novel stealth nanoparticles generated by poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL), soybean phosphatidylcholine (SPC), and cholesterol, namely LPPs (L represented lipid and PP represented PEG-b-PCL), for the delivery of anticancer drug paclitaxel (PTX). LPPs were prepared using the thin film hydration method. Two PEG-b-PCL polymers with different molecular weights (MW; PEG2000-b-PCL2000, MW: 4,000 Da and PEG5000-b-PCL5000, MW: 10,000 Da) were used to fabricate stealth nanoparticles. Conventional PEGylated liposome (LDP2000, L represented lipid and DP2000 represented DSPE-PEG2000) composed of SPC, cholesterol, and DSPE-PEG2000 was used as the control. The physical properties, cellular uptake, endocytosis pathway, cytotoxicity, pharmacokinetics, tumor accumulation, and anticancer efficacy of free PTX, PTX-loaded LPPs, and LDP2000 were systemically investigated after injection into 4T1 breast tumor-bearing mice.

RESULTS

LPPs were vesicles around 100 nm in size with negative zeta potential. With enhanced stability, LPPs achieved sustainable release of cancer therapeutics. The cellular uptake level was closely related to the PEG chain length of PEG-b-PCL; a shorter PEG chain resulted in higher cellular uptake. Moreover, the cellular internalization of LPP2000 modified by PEG2000-b-PCL2000 on 4T1 cells was 2.1-fold higher than LDP2000 due to the improved stability of LPP2000. The cytotoxicity of PTX-loaded LPP2000 was also higher than that of LDP2000 and LPP5000 as observed using a WST-8 assay, while blank LPPs showed negligible toxicity. Consistent with the results of the in vitro study, in vivo experiments showed that LPPs allowed significantly improved bioavailability and prolonged T1/2β as compared to free PTX injection. More importantly, LPPs mainly accumulated at the tumor site, probably due to the enhanced permeation and retention effect (EPR effect). As a nanomedicine, LPP2000 (tumor inhibition rate of 75.1%) significantly enhanced the therapeutic effect of PTX in 4T1 breast tumor-bearing mice by inhibiting tumor growth compared to LDP2000 and LPP5000 (tumor inhibition rates of 56.3% and 49.5%, respectively).

CONCLUSION

Modification of liposomes with PEG2000-b-PCL2000 can simultaneously improve drug accumulation at the target tumor site and tumor cells, showing great promise for utilization as a PEG modification tool in the fabrication of stealth nanoparticles for cancer chemotherapy.

Recent advancements in the cardiovascular drug carriers

Cardiovascular disease is the disease that affects the cardiovascular system, vascular diseases of the brain and kidney, and peripheral arterial disease. Despite of all advances in pharmacological and clinical treatment, heart failure is a leading cause of morbidness and mortality worldwide. Many new therapeutic advance strategies, including cell transplantation, gene delivery or therapy, and cytokines or other small molecules, have been research to treat heart failure. The main aim of this review article is to focus on nano carriers advancement and addressing the problems associated with old and modern therapeutics such as nonspecific effects and poor stability.

Polystyrene microsphere and 5-fluorouracil release from custom-designed wound dressing films

Custom-designed wound dressing films of chitosan and alginate have been prepared by a casting/solvent evaporation method for hydrophobic therapeutic agent encapsulation. In this parametric study, the propylene glycol (PG) and calcium chloride (CaCl2) concentrations were varied for chitosan and alginate films, respectively. Mechanical and chemical inter-related responses under observations included thickness (th), elasticity (E), tensile strength (TS), sorption ability (S%) and kinetics of in-vitro drug release, specifically in terms of membrane time to burst (t B ) and duration of release (t R ). As shown by results of a one tailed t-test significance testing at the 95% confidence interval (α = 0.05), alginate films were significantly more elastic (p = 0.003), thinner (p = 0.004) and more susceptible to osmotic burst (p = 0.011) and characterized by a longer duration of release (p = 0.03). Meanwhile chitosan films exhibited superior moisture permeability (p = 0.006) and sorption characteristics (p = 0.001), indicative of higher hydrophilicity. There were no significant differences in tensile strength (p = 0.324) for alginate and chitosan-based formulations. Preliminary testing was conducted using 0.71 μm in diameter microspheres for modeling film dissolution into Lactated Ringer's solution. Experimental release profiles were modeled for each film from which the average release from alginate films (M AGCa  = 81%) was estimated to be twice the percentage associated with chitosan films (M CD  = 42%). The film comprised of 2.5% (w/v) medium MW chitosan/dextran 70 kDa (5:1) was selected for studying the release of 5-Fluorouracil (5-FU) as a model hydrophobic drug. Diffusion coupled with film disintegration is immediate (t B  = 0) in case of encapsulated 5-FU as compared to the control film encapsulating microspheres characterized by t B  = 70 min ± 7 min. This shift in release profile and the ability to modulate the timing of membrane burst can be attributed to the approximate ratio (1: 505) in molecular size between drug and microsphere. This hypothesis has been validated by the film pore size measured to be 430 nm ± 88 nm using atomic force microscopy.

In-vitro and in-vivo evaluation of austocystin D liposomes

OBJECTIVES

The purpose this study is to enhance the anti-tumour activity of austocystin D (AD) by AD-loaded liposomes (AD-Ls).

METHODS

AD-Ls were prepared by the film dispersion-ultrasonication method and characterized in terms of particle size and zeta potential, encapsulation efficiency and in-vitro drug release. In vivo, the pharmacokinetics, biodistribution and anti-tumour effect were also compared with those of the solution.

KEY FINDINGS

The obtained liposomes were a mildly translucent suspension, with a particle size of 71.26 ± 6.43 nm, a polydispersity index of 0.259 ± 0.017 and a zeta potential of -9.9 ± 1.8 mV. Transmission electron microscope examination showed that the liposomes had a spherical shape and a multilayer structure. The encapsulation efficiency ofAD-Ls was 83.74 ± 1.26%. AD was continuously released from liposomes up to 72 h in in-vitro experiments. The growth of HT-29 tumours in animal models was controlled more effectively by AD-LS than by AD solution. Pharmacokinetic study showed that AD-Ls had higher t½β and mean retention time. Biodistribution results in tumour-bearing mice showed that the AD-LS could target to liver and tumour.

CONCLUSIONS

This study indicates that AD-Ls are a potential carrier of AD for the treatment of tumours in the liver, increasing the cure efficiency and decreasing the side effects on other tissues.

Preparation and evaluation of liposome-encapsulated codrug LMX

A novel codrug (LMX) consisting of Lamivudine and Ursolic acid has been shown to possess the dual action of anti-hepatitis B virus activity and hepatoprotective effects against acute liver injury in vivo. Because of the limited water solubility of LMX, our aims were to design and optimize a liposomal formulation that could facilitate its in vivo administration, and to estimate the potential of LMX-loaded liposomes as oral or intravenous delivery system. In this work, LMX-loaded liposomes were prepared by the thin film hydration method coupled with sonication. LMX-loaded liposomes showed spherical morphology under transmission electron microscope (TEM) analysis. The mean particle size of liposomes was about 210 nm, and the drug entrapment efficiency was more than 90%. Stability data indicated that lyophilized liposomes were stable for at least 6 months at 4 °C. In vitro drug release profile of LMX-loaded liposomes showed a sustained release profile of LMX and an initial mild burst was observed. The relative bioavailability of LMX-loaded liposomes was 1074.8% compared with LMX suspension after oral administration, and 135.2% relative to 50% alcohol solution after intravenous (i.v.) administration. These results indicated that LMX-loaded liposomes were valued to develop as a practical preparation for oral or i.v. administration.

Effect of phospholipid composition on pharmacokinetics and biodistribution of epirubicin liposomes

The effects of phospholipid composition on the pharmacokinetics (PK) and biodistribution of epirubicin (EPI) liposomes, as well as the in vitro macrophage uptake of various liposome formulations, were investigated. Three liposome formulations were investigated: HSPC:Chol (L-EPI; 5:4 molar ratio), HSPC:Chol:DSPG (D-EPI; 5:4:1 molar ratio), and HSPC:Chol:DSPG:DSPE-mPEG(2000) (S-EPI; 5:4:1:0.3 molar ratio). Small unilamellar liposomes were prepared by the modified thin-film hydration method with extrusion through polycarbonate filters, and EPI was remote loaded into liposomes by the transmembrane ammonium sulfate gradient method. Macrophages were used to evaluate in vitro the cellular uptake of EPI-loaded liposomes. The following decreasing order of uptake amount was observed: L-EPI>D-EPI>S-EPI. D-EPI showed a relatively low level of uptake, probably because of the steric hindrance provided by the glycerol head group on DSPG, protecting it from the direct recognization by cell-membrane receptors. With the presence of serum, uptake values for all liposome formulations were increased for the activation of the complement system. In the PK study, S-EPI showed significantly prolonged circulating time and reduced clearance. The following increasing order of area under the concentration versus time curve was observed among the various liposome formulations: L-EPI<D-EPI<S-EPI. The biodistribution study indicated that S-EPI decreased drug disposition in the liver, spleen, lung, and heart and increased that in the kidney with respect to the other liposomes. The encouraging property of S-EPI, in terms of prolonging circulating time and reducing heart toxicity, might describe a promising perspective toward clinical application, and all the results would support further research into liposome-based drug carriers.

Nanoparticles Escaping RES and Endosome: Challenges for siRNA Delivery for Cancer Therapy

Small interfering RNAs (siRNAs) technology has emerged as a promising potential treatment for viral, genetic diseases and cancers. Despite the powerful therapeutic potential of siRNA, there are challenges for developing efficient and specific delivery systems for systemic administration. There are extracellular and intracellular barriers for nanoparticle-mediated delivery. First, nanoparticles are rapidly cleared from the circulation by the reticuloendothelial system (RES). Second, following their cellular uptake, nanoparticles are trapped in endosomes/lysosomes, where siRNA would be degraded by enzymes. In this review, we describe strategies for grafting a polyethylene glycol (PEG) brush to the nanoparticles for evading RES, such that they may effectively accumulate in the tumor by the enhanced permeability and retention (EPR) effect. PEG has to shed from the nanoparticles to allow close interaction with the tumor cells. Current strategies for facilitating endosome escape, such as ion pair formation, “proton sponge effect”, destabilizing endosome membrane, and hydrophobic modification of the vector, are discussed.

Influence of polyelectrolyte chemical structure on their interaction with lipid membrane of zwitterionic liposomes

In this paper we extend our previous experimental work on interaction between polyelectrolytes and liposomes. First, the adsorption of chitosan and alkylated chitosan (cationic polyelectrolytes) with different alkyl chain lengths on lipid membranes of liposomes is examined. The amount of both chitosans adsorbed remains the same even if more alkylated polysaccharide has to be added to get saturation if compared with unmodified chitosan. It is demonstrated that alkyl chains do not specifically interact with the lipid bilayer and that electrostatic interaction mechanism governs the chitosan adsorption. The difference observed between unmodified and alkylated chitosans behavior to reach the plateau can be interpreted in terms of a competition between electrostatic polyelectrolyte adsorption on lipid bilayer and hydrophobic autoassociation in solution (which depends on the alkyl chain length). Second, interaction of liposomes with hyaluronan (HA) and alkylated hyaluronan (anionic polyelectrolytes) is analyzed. The same types of results as discussed for chitosan are obtained, but in this case, autoassociation of alkylated HA only occurs in the presence of salt excess. Finally, a first positive layer of chitosan is adsorbed on the lipid membrane, followed by a second negative layer of HA at three different pHs. This kind of multilayer decoration allows the control of the net charge of the composite vesicles. A general conclusion is that whatever the pH and, consequently, the initial charge of the liposomes, chitosan adsorption gives positively charged composite systems, which upon addition of hyaluronan, give rise to negatively charged composite vesicles.

Layersome: Development and optimization of stable liposomes as drug delivery system

This paper describes the development of stable drug delivery systems named layersomes. The layersomes are conventional liposomes coated with one or multiple layers of biocompatible polyelectrolytes in order to stabilise their structure. The formulation strategy is based on an alternative coating procedure of positive poly(lysine) (pLL) and negative poly(glutamic acid) (pGA) polypeptides on initially charged small unilamellar liposomes (SUVs). The size distribution and the zeta potential of the final entity depend on the number of polyelectrolyte layers and the charge of the last coating layer. Morphological studies were achieved by flux cytometry and cryo electron microscopy. Release studies of encapsulated hydrophilic 5(6)-carboxyfluorescein (5,6CF) in the presence of Triton or ethanol showed an increased membrane resistance of the layersomes compared to classical SUVs. Finally, encapsulation of piroxicam (PX) was performed with success.

Enhanced circulation time and antitumor activity of doxorubicin by comblike polymer-incorporated liposomes

Polymer incorporation on liposomal membranes has been extensively studied as a method of enhancing the circulation time of liposomes in the bloodstream. In this study, we investigated the in vitro and in vivo characteristics of liposomes whose surface was modified using a comblike polymer comprised of a poly(methyl methacrylate) (PMMA) backbone and short poly(ethylene oxide) (PEO) side chains. Doxorubicin (DOX)-loaded liposomes incorporating with the comblike polymer were prepared and their circulation time, biodistribution and antitumor activity were evaluated in B16F10 melanoma tumor-bearing mice. The circulation half-life time in the bloodstream of the comblike polymer-incorporated liposomes (CPILs) was approximately 14- or 2-fold higher than those of the conventional or polyethyleneglycol-fixed liposomes (PEG-liposomes), respectively. Additionally, in the biodistribution assay, the accumulation of the CPILs in the tumor was higher than those of the other liposomes. Based on this result, the antitumor activities of the CPILs were higher than those of conventional liposome formulation of DOX or free DOX due to the higher passive targeting efficiency of the long-circulating CPILs to tumor. This study suggests that the incorporation of the comblike polymer on the liposomal membrane is a promising tool to further improve circulation time of liposomes in tumor-bearing mice.

Poly(ethylene glycol)-conjugated phospholipids in aqueous micellar solutions: hydration, static structure, and interparticle interactions

By means of dielectric relaxation spectroscopy (DRS) and small-angle X-ray scattering (SAXS), we have investigated hydration behavior, solvent dynamics, and static structures of aqueous solutions of poly(ethylene glycol)-conjugated distearoyl phosphatidylethanolamine (DSPE-PEG) (molecular weight of PEG: M(PEG)= 2000, 5000, and 12,000 Da). A quantitative analysis of the bulk-water relaxation amplitude revealed the effective hydration number of a DSPE-PEG molecule per ethylene oxide monomer unit to be approximately 5.0-5.5, virtually independent of M(PEG). The overall hydration number of a DSPE-PEG molecule is ca. 20% higher than that of the corresponding normal PEG (without DSPE). This is attributed to both hydration of a charged head group of phosphoric acid in DSPE and a packing effect of PEG chains into micellar structures. The pair-distance distribution functions, p(r), extracted from the GIFT analysis of SAXS intensities show that the DSPE-PEGs form spherical-like micelles in water having the maximum diameter of approximately 16, 22, and 31 nm, respectively, for M(PEG) = 2000, 5000, and 12,000 Da and nearly identical aggregation numbers of 72 (+/-10%). The DSPE-PEG micelles behave as charged colloids whose interparticle interaction potential can be approximated by the screened Coulomb potential model. The extracted pair correlation function g(r) demonstrates that both electrostatic repulsion induced by the charged head group and excluded volume effects of the fully hydrated PEG layer contribute to repulsive interactions among the PEG-lipid micelles. This should be a key factor for the function of PEG lipids as a stabilizer of liposomes.

Coating of negatively charged liposomes by polylysine: drug release study

The present work describes surface coating of carboxyfluorescein(CF)-loaded liposomes with poly-l-lysine (PLL) and liposome membrane permeability. The vesicles were prepared from synthetic or natural lipids. Interaction between PLL and the liposomes leads to the formation of complexes - either single PLL-coated vesicles or vesicle aggregates. Formation of the complexes is strongly affected by PLL/lipid molar ratio and the molecular mass of the PLL chains. Liposome permeability depends strongly on the lipid phase state - vesicles in the solid state retained the entrapped dye for a long time, but continuous CF release was registered for "fluid" vesicles. Crossing the transition temperature leads to intensive dye leakage because of the appearance of leaky interfacial domains between the coexisting solid and liquid phases and also because of a reversible change in the vesicle size upon the solid-liquid state phase transition. PLL coverage does not cause permeabilization of "solid" liposomes, but increases the permeability of "fluid" vesicles. At the same time, the results of differential scanning calorimetry and vesicle fusion suggest that PLL adsorption occurs exclusively on the vesicular surface and that the lipidic organization is not significantly disturbed. Moreover, PLL does not prevent lipid exchange between vesicles induced by temperature change.

Complexation of phosphocholine liposomes with polylysine. Stabilization by surface coverage versus aggregation

Complexation between linear poly-L-lysine (PLL) and negatively charged phosphocholine unilamellar liposomes has been investigated by means of dynamic light scattering, microelectrophoresis, and differential scanning calorimetry. It is found that complexation results in charge inversion (vesicle coating/stabilization) or vesicle aggregation depending on various experimental conditions. Complexation in dependence on PLL concentration and molecular mass, lipid phase state, rate and order of liposome and PLL mixing and time evolution of complexes are investigated and discussed. Aggregation profiles are determined and size distribution of the aggregates formed is studied, leading to the possibility of aggregation control. The time evolution of vesicle aggregation shows particle enlargement consisting in particle growth up to the irreversible formation of thermodynamically stable aggregates of about 2 microm in diameter. The formation of stable aggregates is in agreement with theoretical predictions of colloid particles aggregation by an interplay of long range electrostatic repulsion and short range attraction. Differential scanning calorimetry reveals that physical adsorption occurs exclusively on the vesicle surface and the lipidic organization is not significantly disturbed. The present study describes multivariable aspects of the complexation process between liposomes and polyions which results in the formation of a new class of still poorly defined colloids. These results allow establishing and optimization of a procedure for fabrication of polycation-stabilized vesicles to be used for various applications such as drug delivery.

Synthesis and Characterization of Oligomaltose-Grafted Lipids with Application to Liposomes

Novel glycolipids, which contain 2 and 15 oligomaltose units and a phosphatidylethanolamine, were synthesized and characterized by FTIR and (1)H-NMR spectroscopies. The well-defined linear structure of the glycolipids was assured by an end-point conjugation strategy using selective oxidation of the reducing end groups of maltose oligosaccharides, followed by aminolysis with distearoylphosphatidylethanolamine. The intermediate acids react selectively with amines to form amide linkages, catalyzed by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. Conformations of the glycolipids at the air-water interface were proposed based on the film balance measurements. The unique conformations of glycolipids at interfaces may offer advantages over traditional PEO-derived lipids in regard to their applications for sterically stabilizing liposomes. The glycolipids demonstrated the ability for sterically stabilizing liposome dispersions, as determined by turbidity measurements.

Interactions of functionalized dextran-coated liposomes with vascular smooth muscle cells

Synthetic polymers are commonly used in the medical field as implants, polymeric drugs, or drug delivery systems. Among them, bioactive sulfated polysaccharides such as chemically modified dextrans are described to exhibit various properties including the inhibition of smooth muscle cell (SMC) growth. SMCs are key cellular components involved in the physiopathology of the vascular walls especially in atherosclerosis or after vascular surgeries. Interestingly, binding sites on vascular SMCs were already observed for an antiproliferative functionalized dextran (FDx). In this context, we hypothesized that this bioactive polymer could be used as a targeting moiety on the surface of drug delivery systems. In this work, liposomes constituted of phosphatidylcholine, phosphatidylethanolamine and cholesterol (70/10/20 mol.%) were prepared and coated with FDx hydrophobized by a cholesterol anchor (CholFDx) which penetrates the lipid bilayer during the liposome formation. The liposome interactions with SMCs were then followed using radiolabeled liposomes and fluorolabeled liposomes. Results of radioactivity on SMCs indicated higher interactions with CholFDx-coated liposomes as compared to uncoated liposomes. The fluorescence of cells incubated with fluorolabeled CholFDx-coated liposomes also evidenced the liposome binding on SMC membranes. These data demonstrated that liposomes coated with FDx interacted with vascular SMCs. Consequently, the coating with such bioactive polymers appears promising for the design of new drug delivery systems for the targeting of vascular cells.