Remote loading of doxorubicin into liposomes driven by a transmembrane phosphate gradient

In vitro localized release of thermosensitive liposomes with ultrasound-induced hyperthermia

Localized drug delivery with ultrasound-induced hyperthermia can enhance the therapeutic index of chemotherapeutic drugs by improving efficacy and reducing systemic toxicity. A novel in vitro method for the activation of drug-loaded thermosensitive liposomes is described. In particular, a dual-compartment, acoustically transparent container is used in which thermosensitive liposomes suspended in cell culture medium are immersed in a thermally absorptive medium, glycerol. Hyperthermia is induced with ultrasound in the glycerol, which in turn heats the culture medium by thermal conduction. The method approximately mimics the in vivo scenario of thermosensitive liposomes collected in the interstitial spaces of tumors, where ultrasound induces hyperthermia in the tumor tissue, which in turn heats the thermosensitive liposomes by conduction and induces release of the encapsulated drug. The acoustic conditions for the desired hyperthermia are derived theoretically and validated experimentally. Eighty percent release of doxorubicin from thermosensitive liposomes is achieved.

Nanoparticles containing insoluble drug for cancer therapy

Nanoparticle drug formulations have been extensively researched and developed in the field of drug delivery as a means to efficiently deliver insoluble drugs to tumor cells. By mechanisms of the enhanced permeability and retention effect, nanoparticle drug formulations are capable of greatly enhancing the safety, pharmacokinetic profiles and bioavailability of the administered treatment. Here, the progress of various nanoparticle formulations in both research and clinical applications is detailed with a focus on the development of drug/gene delivery systems. Specifically, the unique advantages and disadvantages of polymeric nanoparticles, liposomes, solid lipid nanoparticles, nanocrystals and lipid-coated nanoparticles for targeted drug delivery will be investigated in detail.

Chemical and physical characterization of remotely loaded bupivacaine liposomes: comparison between large multivesicular vesicles and small unilamellar vesicles

Large multivesicular liposomes (LMVV) remotely loaded with bupivacaine (Bupisome) were previously demonstrated to be a stable, long-acting local anesthetic. We demonstrate that this is not the case for small unilamellar vesicles (SUV) of the same lipid composition also remotely loaded with bupivacaine. We show that the trapped volume in LMVV is 21-fold higher and the drug-to-lipid mole ratio is 10-fold higher than in SUV. Cryo-transmission electron micrographs and differential interference contrast microscopy show that there are no bupivacaine crystals inside LMVV and SUV. The thermotropic characterization studied by DSC demonstrates that the drug interacts with the liposome membrane, which, together with the above results on the drug-to-lipid ratio, explains the small in vitro drug release from the SUV and large (but <100%) release from the LMVV after 24 h at 37 °C. The absence of analgesia in mice treated locally with SUV loaded with bupivacaine compared with prolonged analgesia from LMVV correlates well with the in vitro results. The study indicates that in LMVV and SUV, part of the bupivacaine is associated with the liposomal membrane, which is poorly available for analgesia. The membrane fraction is very high in SUV and much smaller in LMVV. The much larger trapped volume of the LMVV explains the higher drug availability and better analgesia of LMVV.

Radiolabeled lipid nanoparticles for diagnostic imaging

BACKGROUND

Nanoparticles are increasingly being incorporated into the design of diagnostic imaging agents. Significant research efforts have been conducted with one class of lipid nanoparticle (liposomes) radiolabeled with gamma-emitting radionuclides as radiopharmaceuticals for scintigraphic imaging of cancer, inflammation/infection and sentinel lymph node detection.

OBJECTIVE

This article reviews the current literature with special emphasis on the clinical studies performed with liposome radiopharmaceuticals for detection of tumors, infectious/inflammatory sites or metastatic lymph nodes. Future uses of liposome radiopharmaceuticals are also described.

METHODS

Characteristics required of the radionuclide, liposome formulation and radiolabeling method for an effective radiopharmaceutical are discussed. A description of the procedures and instrumentation for conducting an imaging study with liposome radiopharmaceutical is included. Clinical studies using liposome radiopharmaceuticals are summarized. Future imaging applications of first- and second-generation radiolabeled liposomes for chemodosimetry and the specific targeting of a disease process are also described.

RESULTS/CONCLUSION

The choice of radionuclide, liposome formulation and radiolabeling method must be carefully considered during the design of a liposome radiopharmaceutical for a given application. After-loading and surface chelation methods are the most efficient and practical. Clinical studies with liposome radiopharmaceuticals demonstrated that a wide variety of tumors could be detected with good sensitivity and specificity. Liposome radiopharmaceuticals could also clearly detect various soft tissue and bone inflammatory/infectious lesions, and performed equal to or better than infection imaging agents that are approved at present. Yet, despite these favorable results, no liposome radiopharmaceutical has been approved for any indication. Some of the reasons for this can be attributed to reports of an unexpected infusion-related adverse reaction in two studies, the requirement of more complex liposome manufacturing procedures, and the adoption of other competing imaging procedures. Continued research of liposome radiopharmaceutical design based on a better understanding of liposome biology, improved radiolabeling methodologies and advances in gamma camera technology is warranted.

Enhanced brain distribution and pharmacodynamics of rivastigmine by liposomes following intranasal administration

Alzheimer's disease (AD) is a common progressive neurodegenerative disorder associated with cholinergic neurons degeneration. The blood-brain barrier (BBB) not only provides protection for the brain but also hinders the treatment and diagnosis of this neurological disease, because the drugs must cross BBB to reach the lesions. The present work was aimed at formulating rivastigmine liposomes (Lp) and cell-penetrating peptide (CPP) modified liposomes (CPP-Lp) to improve rivastigmine distribution in brain and proceed to enhance pharmacodynamics by intranasal (IN) administration and minimize side effects. The results revealed that Lp especially the CPP-Lp can enhance the permeability across the BBB by murine brain microvascular endothelial cells model in vitro. IN administration of rivastigmine solution and rivastigmine liposomes demonstrated the capacity to improve rivastigmine distribution and adequate retention in CNS regions especially in hippocampus and cortex, which were the regions most affected by AD, than that of IV administration. Importantly, the lagging but intense inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities were relative to the extended release, absorption and retention. In addition, there was very mild nasal toxicity of liposomal formulations. The data suggest that rivastigmine liposomes especially CPP-Lp improve the brain delivery and enhance pharmacodynamics which respect to BBB penetration and nasal olfactory pathway into brain after IN administration, and simultaneously decrease the hepatic first pass metabolism and gastrointestinal adverse effects.

Application of response surface methodology in development of sirolimus liposomes prepared by thin film hydration technique

Introduction : The present investigation was aimed to optimize the formulating process of sirolimus liposomes by thin film hydration method. Methods : In this study, a 3(2) factorial design method was used to investigate the influence of two independent variables in the preparation of sirolimus liposomes. The dipalmitoylphosphatidylcholine (DPPC) /Cholesterol (Chol) and dioleoyl phosphoethanolamine(DOPE) /DPPC molar ratios were selected as the independent variables. Particle size (PS) and Encapsulation Efficiency (EE %) were selected as the dependent variables. To separate the un-encapsulated drug, dialysis method was used. Drug analysis was performed with a validated RP-HPLC method. Results : Using response surface methodology and based on the coefficient values obtained for independent variables in the regression equations, it was clear that the DPPC/Chol molar ratio was the major contributing variable in particle size and EE %. The use of a statistical approach allowed us to see individual and/or interaction effects of influencing parameters in order to obtain liposomes with desired properties and to determine the optimum experimental conditions that lead to the enhancement of characteristics. In the prediction of PS and EE % values, the average percent errors are found to be as 3.59 and 4.09%. This value is sufficiently low to confirm the high predictive power of model. Conclusion : Experimental results show that the observed responses were in close agreement with the predicted values and this demonstrates the reliability of the optimization procedure in prediction of PS and EE % in sirolimus liposomes preparation.

The effect of liposomal size on the targeted delivery of doxorubicin to Integrin αvβ3-expressing tumor endothelial cells

Size of the liposomes (LPs) specially governs its biodistribution. In this study, LPs were developed with controlled sizes, where variation in LP size dictates the ligand-receptor interaction, cellular internalization and its distribution within the tumor microenvironment. The therapeutic efficacies of doxorubicin (DOX)-loaded RGD modified small size (~100 nm in diameter, dnm) and large size (~300 dnm) PEGylated LPs (RGD-PEG-LPs) were compared to that of Doxil (a clinically used DOX-loaded PEG-LP, ~100 dnm) in DOX resistant OSRC-2 (Renal cell carcinoma, RCC) tumor xenografts. Doxil, which accumulated in tumor tissue via the enhanced permeability and retention (EPR) effect, failed to suppress tumor growth. Small size RGD-PEG-LP, that targets the tumor endothelial cells (TECs) and extravasates to tumor cells, failed to provide anti-tumor effect. Large size RGD-PEG-LP preferentially targets the TECs via minimization of the EPR effect, and significantly reduced the tumor growth, which was exerted through its strong anti-angiogenic activity on the tumor vasculature rather than having a direct effect on DOX resistant RCC. The prepared large size RGD-PEG-LP that targets the TECs via interacting with Integrin αvβ3, is a potentially effective and alternate therapeutic strategy for the treatment of DOX resistant tumor cells by utilizing DOX, in cases where Doxil is ineffective.

Lyophilisomes as a new generation of drug delivery capsules

Nanoparticulate drug delivery systems are currently explored to overcome critical challenges associated with classical administration forms. In this study, we present a drug delivery system based on a novel class of proteinaceous biodegradable nano/micro capsules, lyophilisomes. Lyophilisomes can be prepared from biomolecules without the need for amphiphilicity. Albumin-based lyophilisomes were prepared by freezing, annealing and lyophilizing, resulting in capsules ranging from 100 to 3000 nm. Lyophilisomes were loaded with the anti-tumor drugs doxorubicin and curcumin using different concentrations and time/temperature regimes. Incubation in 0.1 mg/ml doxorubicin or 1.0 mg/ml curcumin resulted in an entrapment efficiency of 95±1% and 4±1%, respectively. This corresponds to a drug loading of 0.24 mg doxorubicin per milligram albumin and 0.10 mg curcumin per milligram albumin. Drug release profiles from doxorubicin and curcumin-loaded lyophilisomes were studied in culture medium and showed slow release for doxorubicin (2.7% after 72 h), and rapid release for curcumin (55% after 72 h). When applied to cells, non-loaded lyophilisomes did not influence cell viability, even at high concentrations (1 mg/ml). Lyophilisomes were internalized by cells. When loaded with doxorubicin and curcumin, lyophilisomes strongly reduced cell proliferation and viability of SKOV-3 and HeLa cells, respectively, to a level similar or better compared to an equal amount of free drugs. In conclusion, albumin lyophilisomes show potential as (nano)carriers of drugs for tumor cell elimination.

Improving the transport of chemotherapeutic drugs across the blood-brain barrier

The successful treatment of brain tumors or metastases in the brain is still hampered by the very efficient blood-brain barrier, which prevents the cerebral accumulation of a pharmacologically sufficient amount of a drug. Beside the possibility of disintegrating the functionality of this effective working barrier, a nanocarrier-mediated transport is presently an interesting and promising method to increase the drug concentration in the brain. Nanocarriers are small vesicles (<200 nm) and can be prepared by polymerization, resulting in nanoparticles, or by producing superficial lipid structures to incorporate the drug. In this context, liposomes are of importance owing to their ability to adapt their properties to the pharmacological requirements. In this article, we will give an overview of current possibilities of enhancing anticancer drug transport across the blood-brain barrier, based on its structure and functionality. Special consideration will be given to recent liposomal approaches that use active targeting for receptor-mediated transport across this physiological barrier.

Hyaluronic acid derivative-based self-assembled nanoparticles for the treatment of melanoma

PURPOSE

Hyaluronic acid-ceramide (HACE)-based nanoparticles (NPs) were developed for the targeted delivery of doxorubicin (DOX), and their antitumor efficacy for melanoma was evaluated.

METHODS

DOX-loaded HACE-based self-assembled NPs were prepared and their physicochemical properties were characterized. The in vitro cytotoxicity of HACE was measured using an MTS-based assay. The cellular uptake efficiency of DOX into mouse melanoma B16F10 cells was assessed by confocal laser scanning microscopy and flow cytometry. Tumor growth and body weight were monitored after the intratumoral and intravenous injection of DOX-loaded NPs into a B16F10 tumor-bearing mouse model.

RESULTS

DOX-loaded NPs, with a mean diameter of ~110 nm, a narrow size distribution, and high drug entrapment efficiency, were prepared. A sustained DOX release pattern was shown, and drug release was enhanced at pH 5.5 compared with pH 7.4. The cytotoxicity of HACE to B16F10 cells was negligible. It was assumed that DOX was taken up into the B16F10 cells through receptor-mediated endocytosis. A significant inhibitory effect was observed on tumor growth, without any serious changes in body weight, after the injection of DOX-loaded NPs into the B16F10 tumor-bearing mouse model.

CONCLUSIONS

DOX-loaded HACE-based NPs were successfully developed and their antitumor efficacy against B16F10 tumors was demonstrated.

Biomimetic Design of Protein Nanomaterials for Hydrophobic Molecular Transport

Biomaterials such as self-assembling biological complexes have demonstrated a variety of applications in materials science and nanotechnology. The functionality of protein-based materials, however, is often limited by the absence or locations of specific chemical conjugation sites. In this investigation, we developed a new strategy for loading organic molecules into the hollow cavity of a protein nanoparticle that relies only on non-covalent interactions, and we demonstrated its applicability in drug delivery. Based on a biomimetic model that incorporates multiple phenylalanines to create a generalized binding site, we retained and delivered the antitumor compound doxorubicin by redesigning a caged protein scaffold. Through an iterative combination of structural modeling and protein engineering, we obtained new variants of the E2 subunit of pyruvate dehydrogenase with varying levels of drug-carrying capabilities. We found that an increasing number of introduced phenylalanines within the scaffold cavity generally resulted in greater drug loading capacities. Drug loading levels could be achieved that were greater than conventional nanoparticle delivery systems. These protein nanoparticles containing doxorubicin were taken up by breast cancer cells and induced significant cell death. Our novel approach demonstrates a universal strategy to design de novo hydrophobic binding domains within protein-based scaffolds for molecular encapsulation and transport, and it broadens the ability to attach guest molecules to this class of materials.

Targeted delivery of transferrin-conjugated liposomes to an orthotopic model of lung cancer in nude rats

BACKGROUND

Lung cancer is the leading cause of cancer death worldwide. Pulmonary anticancer therapy might offer several advantages over systemic delivery, leading to an increased exposure of the lung tumor to the drug, while minimizing side effects, due to regional containment. Here, we studied if a combination of inhalation therapy and drug targeting holds potential as an even more efficient lung cancer therapy.

METHODS

Transferrin (Tf )-conjugated PEG liposomes loaded with doxorubicin (DOX) were administered using an intracorporeal nebulizing catheter to an orthotopic lung cancer model established in athymic Rowett nude rats. Different DOX formulations and doses (0.2 and 0.4 mg/kg) were tested and the influence on tumor progression and life span of rats was evaluated in comparison with the i.v. administration of Tf-PEG-liposomes loaded with DOX at a therapeutic dose of 2 mg/kg.

RESULTS

Rats in the untreated control group showed significant weight loss 2 weeks after tumor induction and died between days 19 and 29. Lungs of these animals showed multiple foci of neoplastic deposits, ranging up to 20 mm replacing the entire lobe. Empty Tf-liposomes showed a significant effect on survival time. This might be caused by the secondary cytotoxicity via stimulation of pulmonary macrophages. All animal treated intravenously also perished before the end of the study. No significant (p<0.05) improvement in survival was observed between the groups treated with aerosols of free drug, DOX encapsulated in plain and in Tf-modified liposomes. However, more animals survived in the Tf-liposome groups than in the other treatment regimes, and their lung tissue generally had fewer and smaller tumors. Nevertheless, the size of the groups, and the duration of the trial render it impossible to come to a definite conclusion.

CONCLUSIONS

Drug targeting demonstrated potential for improving the aerosol treatment of lung cancer.

pH-sensitive degradable chimaeric polymersomes for the intracellular release of doxorubicin hydrochloride

pH-sensitive degradable chimaeric polymersomes were developed based on asymmetric poly(ethylene glycol)-b-poly(2,4,6-trimethoxybenzylidene-1,1,1-tris(hydroxymethyl)ethane methacrylate)-b-poly(acrylic acid) (PEG-PTTMA-PAA) triblock copolymers for active loading as well as triggered intracellular release of hydrophilic doxorubicin hydrochloride (DOX·HCl). PEG-PTTMA-PAA copolymers were readily prepared with M(n PAA) ranging from 1.5, 2.1 to 2.7 kg/mol by sequential reversible addition-fragmentation chain transfer (RAFT) copolymerization of 2,4,6-trimethoxybenzylidene-1,1,1-tris(hydroxymethyl)ethane methacrylate (TTMA) and acrylic acid (AA) using PEG-CPADN (M(n PEG) = 5.0 kg/mol; CPADN: 4-cyanopentanoic acid dithionaphthalenoate) as a macro-RAFT agent. PEG-PTTMA-PAA copolymers formed mono-disperse polymersomes with average sizes of 63.9-112.1 nm, which decreased with increasing M(n PAA). The polymersomal structure was confirmed by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). Notably, the acetals in polymersomes while sufficiently stable at pH 7.4 were prone to rapid hydrolysis at mildly acidic pHs of 4.0 and 5.0, which resulted in swelling and eventually disassembly of polymersomes. These chimaeric polymersomes could actively load DOX·HCl resulting in remarkably high drug loading contents (up to 15.9 wt.%) and loading efficiencies (up to 88.8%). The in vitro release studies showed that DOX·HCl was released from chimaeric polymersomes in a controlled and pH-dependent manner. CLSM observations revealed that these chimaeric polymersomes could efficiently deliver and release DOX·HCl into the nuclei of HeLa cells. MTT assays in HeLa cells demonstrated that DOX·HCl-loaded PEG-PTTMA-PAA polymersomes exhibited high anti-tumor activity with IC(50) (inhibitory concentration to produce 50% cell death) of 1.48-1.67 μg/mL, close to that of free DOX·HCl, while blank polymersomes were practically non-toxic up to a tested concentration of 2.0 mg/mL. These pH-sensitive degradable chimaeric polymersomes have appeared to be a promising alternative to liposomes for tumor-targeted delivery of DOX·HCl.

Folate-targeted supramolecular vesicular aggregates as a new frontier for effective anticancer treatment in in vivo model

Supramolecular vesicular aggregates (SVAs), made up by self-assembling liposomes and polyasparthydrazide co-polymers conjugated to folic acid molecules were extensively investigated in this manuscript as potential active targeting formulation for anticancer drug delivery. Folate-targeted systems (FT-SVAs) were used to treat breast cancer and to further proof the potential in vivo administration of these systems for the therapeutic treatment for several aggressive solid tumors. The physicochemical and technological parameters of FT-SVAs are suitable for their potential in vivo administration. The chemotherapeutic activity of GEM-loaded FT-SVAs was increased during in vivo experiments. NOD-SCID mice bearing MCF-7 human xenograft is used as breast cancer model. The measurement of the volume and weight of tumor masses decreased when animal models are treated by using GEM-loaded FT-SVAs, compared to data obtained by using GEM-loaded mPEG-SUVs and the free form of GEM. An almost complete regression of the tumor (≈ 0.2 cm(3)) was observed in NOD-SCID mice bearing MCF-7 human xenografts treated by GEM-loaded FT-SVAs due to the noticeable improvement of GEM pharmacokinetic parameters provided by FT-SVAs with respect to native anticancer drug. The obtained data showed that supramolecular systems could represent an innovative drug delivery system by self-assembling liposomes and biocompatible polymers to be potentially used for anticancer treatment.

Doxorubicin and chloroquine coencapsulated liposomes: preparation and improved cytotoxicity on human breast cancer cells

Doxorubicin, as a widely used chemotherapeutic, always causes multidrug resistance in human cancer cells. To circumvent drug resistance, we developed a novel formulation where doxorubicin hydrochloride (DOX) and chloroquine phosphate (CQ) were simultaneously loaded into liposomes by a pH-gradient method where CQ played the role of a chemical sensitizer. The various factors were investigated to optimize the formulation and manufacturing conditions of DOX and CQ coencapsulated liposomes (DCL). The resultant DCLs achieved the high encapsulation efficiency of both drugs over 90%. Further, DCLs significantly displayed resistance reversal action on a doxorubicin-resistant human breast cancer cell line (MCF-7/ADR) through the cooperation of CQ with DOX. The reversal fold of DCL with the DOX/CQ/soybean phosphatidylcholine weight ratio of 0.5:1:50 was 5.7, compared to free DOX. These results demonstrate that DCL is a promising formulation for the treatment of DOX-resistant breast cancer.

Peptide-modified liposomes for selective targeting of bombesin receptors overexpressed by cancer cells: a potential theranostic agent

Objectives

Drug delivery systems consisting of liposomes displaying a cell surface receptor-targeting peptide are being developed to specifically deliver chemotherapeutic drugs to tumors overexpressing a target receptor. This study addresses novel liposome composition approaches to specifically target tissues overexpressing bombesin (BN) receptors.

Methods

A new amphiphilic peptide derivative (MonY-BN) containing the BN(7–14) peptide, the DTPA (diethylenetriaminepentaacetate) chelating agent, a hydrophobic moiety with two C₁₈ alkyl chains, and polyethylene glycol spacers, has been synthesized by solid-phase methods. Liposomes have been generated by co-aggregation of MonY-BN with 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). The structural and biological properties of these new target-selective drug-delivery systems have been characterized.

Results

Liposomes with a DSPC/MonY-BN (97/3 molar ratio) composition showed a diameter of 145.5 ± 31.5 nm and a polydispersity index of 0.20 ± 0.05. High doxorubicin (Dox) loading was obtained with the remote pH gradient method using citrate as the inner buffer. Specific binding to PC-3 cells of DSPC/MonY-BN liposomes was obtained (2.7% ± 0.3%, at 37°C), compared with peptide-free DSPC liposomes (1.4% ± 0.2% at 37°C). Incubation of cells with DSPC/ MonY-BN/Dox showed significantly lower cell survival compared with DSPC/Dox-treated cells, in the presence of 100 ng/mL and 300 ng/mL drug amounts, in cytotoxicity experiments. Intravenous treatment of PC-3 xenograft-bearing mice with DSPC/MonY-BN/Dox at 10 mg/kg Dox dose produced higher tumour growth inhibition (60%) compared with nonspecific DSPC/ Dox liposomes (36%) relative to control animals.

Conclusion

The structural and loading properties of DSPC/MonY-BN liposomes along with the observed in-vitro and in-vivo activity are encouraging for further development of this approach for target-specific cancer chemotherapy.

Treatment of experimental brain metastasis with MTO-liposomes: impact of fluidity and LRP-targeting on the therapeutic result

PURPOSE

To test targeted liposomes in an effort to improve drug transport across cellular barriers into the brain.

METHODS

Therefore we prepared Mitoxantrone (MTO) entrapping, rigid and fluid liposomes, equipped with a 19-mer angiopeptide as ligand for LDL lipoprotein receptor related protein (LRP) targeting.

RESULTS

Fluid, ligand bearing liposomes showed in vitro the highest cellular uptake and transcytosis and were significantly better than the corresponding ligand-free liposomes and rigid, ligand-bearing vesicles. Treatment of mice, transplanted with human breast cancer cells subcutaneously and into the brain, with fluid membrane liposomes resulted in a significant reduction in the tumor volume by more than 80% and in a clear reduction in drug toxicity. The improvement was mainly depended on liposome fluidity while the targeting contributed only to a minor degree. Pharmacokinetic parameters were also improved for liposomal MTO formulations in comparison to the free drug. So the area under the curve was increased and t(1/2) was extended for liposomes.

CONCLUSION

Our data show that it is possible to significantly improve the therapy of brain metastases if MTO-encapsulating, fluid membrane liposomes are used instead of free MTO. This effect could be further enhanced by fluid, ligand bearing liposomes.

E-selectin liposomal and nanotube-targeted delivery of doxorubicin to circulating tumor cells

The presence of circulating tumor cells (CTCs) is believed to lead to the formation of secondary tumors via an adhesion cascade involving interaction between adhesion receptors of endothelial cells and ligands on CTCs. Many CTCs express sialylated carbohydrate ligands on their surfaces that adhere to selectin protein found on inflamed endothelial cells. We have investigated the feasibility of using immobilized selectin proteins as a targeting mechanism for CTCs under flow. Herein, targeted liposomal doxorubicin (L-DXR) was functionalized with recombinant human E-selectin (ES) and polyethylene glycol (PEG) to target and kill cancer cells under shear flow, both when immobilized along a microtube device or sheared in a cone-and-plate viscometer in a dilute suspension. Healthy circulating cells such as red blood cells were not targeted by this mechanism and were left to freely circulate, and minimal leukocyte death was observed. Halloysite nanotube (HNT)-coated microtube devices immobilized with nanoscale liposomes significantly enhanced the targeting, capture, and killing of cancer cells. This work demonstrates that E-selectin functionalized L-DXR, sheared in suspension or immobilized onto microtube devices, provides a novel approach to selectively target and deliver chemotherapeutics to CTCs in the bloodstream.

Nanostructured Surfaces to Target and Kill Circulating Tumor Cells While Repelling Leukocytes

Hematogenous metastasis, the process of cancer cell migration from a primary to distal location via the bloodstream, typically leads to a poor patient prognosis. Selectin proteins hold promise in delivering drug-containing nanocarriers to circulating tumor cells (CTCs) in the bloodstream, due to their rapid, force-dependent binding kinetics. However, it is challenging to deliver such nanocarriers while avoiding toxic effects on healthy blood cells, as many possess ligands that adhesively interact with selectins. Herein, we describe a nanostructured surface to capture flowing cancer cells, while preventing human neutrophil adhesion. Microtube surfaces with immobilized halloysite nanotubes (HNTs) and E-selectin functionalized liposomal doxorubicin (ESPEG L-DXR) significantly increased the number of breast adenocarcinoma MCF7 cells captured from flow, yet also significantly reduced the number of captured neutrophils. Neutrophils firmly adhered and projected pseudopods on surfaces coated only with liposomes, while neutrophils adherent to HNT-liposome surfaces maintained a round morphology. Perfusion of both MCF7 cells and neutrophils resulted in primarily cancer cell adhesion to the HNT-liposome surface, and induced significant cancer cell death. This work demonstrates that nanostructured surfaces consisting of HNTs and ES-PEG L-DXR can increase CTC recruitment for chemotherapeutic delivery, while also preventing healthy cell adhesion and uptake of therapeutic intended for CTCs.

Quantitative structure-property relationship modeling of remote liposome loading of drugs

Remote loading of liposomes by trans-membrane gradients is used to achieve therapeutically efficacious intra-liposome concentrations of drugs. We have developed Quantitative Structure Property Relationship (QSPR) models of remote liposome loading for a data set including 60 drugs studied in 366 loading experiments internally or elsewhere. Both experimental conditions and computed chemical descriptors were employed as independent variables to predict the initial drug/lipid ratio (D/L) required to achieve high loading efficiency. Both binary (to distinguish high vs. low initial D/L) and continuous (to predict real D/L values) models were generated using advanced machine learning approaches and 5-fold external validation. The external prediction accuracy for binary models was as high as 91-96%; for continuous models the mean coefficient R(2) for regression between predicted versus observed values was 0.76-0.79. We conclude that QSPR models can be used to identify candidate drugs expected to have high remote loading capacity while simultaneously optimizing the design of formulation experiments.

Gemcitabine-loaded innovative nanocarriers vs GEMZAR: biodistribution, pharmacokinetic features and in vivo antitumor activity

INTRODUCTION

Gemcitabine, an anticancer drug, is a nucleoside analog deoxycytidine antimetabolite, which acts against a wide range of solid tumors. The limitation of gemcitabine is its rapid inactivation by the deoxycytidine deaminase enzyme following its in vivo administration.

AREAS COVERED

One of the most promising new approaches for improving the biopharmaceutical properties of gemcitabine is the use of innovative drug delivery devices. This review explains the current status of gemcitabine drug delivery, which has been under development over the past 5 years, with particular emphasis on liposomal delivery. In addition, the use of novel supramolecular vesicular aggregates (SVAs), polymeric nanoparticles and squalenoylation were treated as interesting innovative approaches for the administration of the nucleoside analog.

EXPERT OPINION

Different colloidal systems containing gemcitabine have been realized, with the aim of providing important potential advancements through traditional ways of therapy. A possible future commercialization of modified gemcitabine is desirable, as was true in the case of liposomal doxorubicin (Doxil(®), Caely(®)).

Smart multifunctional nanostructure for targeted cancer chemotherapy and magnetic resonance imaging

Targeted chemotherapy and magnetic resonance imaging of cancer cells in vitro has been achieved using a smart multifunctional nanostructure (SMN) constructed from a porous hollow magnetite nanoparticle (PHMNP), a heterobifunctional PEG ligand, and an aptamer. The PHMNPs were prepared through a three-step reaction and loaded with the anticancer drug doxorubicin while being functionalized with PEG ligands. Targeting aptamers were then introduced by reaction with the PEG ligands. The pores of the PHMNPs are stable at physiological pH, but they are subject to acid etching. Specific binding and uptake of the SMN to the target cancer cells induced by aptamers was observed. In addition, multiple aptamers on the surface of one single SMN led to enhanced binding and uptake to target cancer cells due to the multivalent effect. Upon reaching the lysosomes of target cancer cells through receptor-mediated endocytosis, the relatively low lysosomal pH level resulted in corrosion of the PHMNP pores, facilitating the release of doxorubicin to kill the target cancer cells. In addition, the potential of using SMN for magnetic resonance imaging was also investigated.

Fabrication principles and their contribution to the superior in vivo therapeutic efficacy of nano-liposomes remote loaded with glucocorticoids

We report here the design, development and performance of a novel formulation of liposome- encapsulated glucocorticoids (GCs). A highly efficient (>90%) and stable GC encapsulation was obtained based on a transmembrane calcium acetate gradient driving the active accumulation of an amphipathic weak acid GC pro-drug into the intraliposome aqueous compartment, where it forms a GC-calcium precipitate. We demonstrate fabrication principles that derive from the physicochemical properties of the GC and the liposomal lipids, which play a crucial role in GC release rate and kinetics. These principles allow fabrication of formulations that exhibit either a fast, second-order (t(1/2) ~1 h), or a slow, zero-order release rate (t(1/2) ~ 50 h) kinetics. A high therapeutic efficacy was found in murine models of experimental autoimmune encephalomyelitis (EAE) and hematological malignancies.

Clickable functionalization of liposomes with the gH625 peptide from Herpes simplex virus type I for intracellular drug delivery

Liposomes externally modified with the nineteen residues gH625 peptide, previously identified as a membrane-perturbing domain in the gH glycoprotein of Herpes simplex virus type I, have been prepared in order to improve the intracellular uptake of an encapsulated drug. An easy and versatile synthetic strategy, based on click chemistry, has been used to bind, in a controlled way, several copies of the hydrophobic gH625 peptide on the external surface of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPG)-based liposomes. Electron paramagnetic resonance studies, on liposomes derivatized with gH625 peptides, which are modified with the 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) spin label in several peptide positions, confirm the positioning of the coupled peptides on the liposome external surface, whereas dynamic light scattering measurements indicate an increase of the diameter of the liposomes of approximately 30% after peptide introduction. Liposomes have been loaded with the cytotoxic drug doxorubicin and their ability to penetrate inside cells has been evaluated by confocal microscopy experiments. Results suggest that liposomes functionalized with gH625 may act as promising intracellular targeting carriers for efficient delivery of drugs, such as chemotherapeutic agents, into tumor cells.

Folate-decorated nanogels for targeted therapy of ovarian cancer

Nanogels are comprised of swollen polymer networks and nearly 95% water and can entrap diverse chemical and biological agents for cancer therapy with very high loading capacities. Here we use diblock copolymer poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMA) to form nanogels with the desired degree of cross-linking. The nanogels are further conjugated to folic acid (FA) and loaded with different types of drugs (cisplatin, doxorubicin). For the first time we demonstrate a tumor-specific delivery and superior anti-tumor effect in vivo of an anti-cancer drug using these polyelectrolyte nanogels decorated with folate-targeting groups. This reinforces the use of nanogels for the therapy of ovarian and other cancers, where folate receptor (FR) is overexpressed.

The targeted delivery of multicomponent cargos to cancer cells by nanoporous particle-supported lipid bilayers

Encapsulation of drugs within nanocarriers that selectively target malignant cells promises to mitigate side effects of conventional chemotherapy and to enable delivery of the unique drug combinations needed for personalized medicine. To realize this potential, however, targeted nanocarriers must simultaneously overcome multiple challenges, including specificity, stability and a high capacity for disparate cargos. Here we report porous nanoparticle-supported lipid bilayers (protocells) that synergistically combine properties of liposomes and nanoporous particles. Protocells modified with a targeting peptide that binds to human hepatocellular carcinoma exhibit a 10,000-fold greater affinity for human hepatocellular carcinoma than for hepatocytes, endothelial cells or immune cells. Furthermore, protocells can be loaded with combinations of therapeutic (drugs, small interfering RNA and toxins) and diagnostic (quantum dots) agents and modified to promote endosomal escape and nuclear accumulation of selected cargos. The enormous capacity of the high-surface-area nanoporous core combined with the enhanced targeting efficacy enabled by the fluid supported lipid bilayer enable a single protocell loaded with a drug cocktail to kill a drug-resistant human hepatocellular carcinoma cell, representing a 10(6)-fold improvement over comparable liposomes.

Active methods of drug loading into liposomes: recent strategies for stable drug entrapment and increased in vivo activity

INTRODUCTION

The use of liposomes increases the therapeutic index of many drugs, and also offers drug targeting and controlled release. The commercial impact of liposomes is strengthened by the invention of several active drug encapsulation methods, allowing the encapsulation of several weak base or weak acid drugs with very high drug-to-lipid ratios.

AREAS COVERED

In recent years, there have been reports on several new approaches to retain more hydrophobic drugs inside liposomes, in the circulation. Most of these methods apply drug precipitation inside preformed liposomes, as low soluble complexes with ions or chemicals. In some cases, drug derivatization was applied to enable active encapsulation of hydrophobic drugs, previously not reported to encapsulate, by active or remote loading. This review presents and compares most of the existing methods of active drug encapsulation and outlines recent strategies to achieve stable drug encapsulation in vivo.

EXPERT OPINION

At present, there is no single universal encapsulation method that offers stable encapsulation of most drugs; each drug requires a different approach to manage all of its properties. Now is the time to combine all these strategies to achieve the goal of a complex, but successful, anticancer therapy.

Target-selective drug delivery through liposomes labeled with oligobranched neurotensin peptides

The structure and the in vitro behavior of liposomes filled with the cytotoxic drug doxorubicin (Doxo) and functionalized on the external surface with a branched moiety containing four copies of the 8-13 neurotensin (NT) peptide is reported. The new functionalized liposomes, DOPC-NT₄Lys(C₁₈)₂, are obtained by co-aggregation of the DOPC phospholipid with a new synthetic amphiphilic molecule, NT₄ Lys(C₁₈)₂, which contains a lysine scaffold derivatized with a lipophilic moiety and a tetrabranched hydrophilic peptide, NT8-13, a neurotensin peptide fragment well known for its ability to mimic the neurotensin peptide in receptor binding ability. Dynamic light scattering measurements indicate a value for the hydrodynamic radius (RH) of 88.3±4.4 nm. The selective internalization and cytotoxicity of DOPC-NT₄ Lys(C₁₈)₂ liposomes containing Doxo, as compared to pure DOPC liposomes, were tested in HT29 human colon adenocarcinoma and TE671 human rhabdomyosarcoma cells, both of which express neurotensin receptors. Peptide-functionalized liposomes show a clear advantage in comparison to pure DOPC liposomes with regard to drug internalization in both HT29 and TE671 tumor cells: FACS analysis indicates an increase in fluorescence signal of the NT₄-liposomes, compared to the DOPC pure analogues, in both cell lines; cytotoxicity of DOPC-NT₄ Lys(C₁₈)₂-Doxo liposomes is increased four-fold with respect to DOPC-Doxo liposomes in both HT29 and TE671 cell lines. These effects could to be ascribed to the higher rate of internalization for DOPC-NT₄ Lys(C₁₈)₂-Doxo liposomes, due to stronger binding driven by a lower dissociation constant of the NT₄-liposomes that bind the membrane onto a specific protein, in contrast to DOPC liposomes, which approach the plasma membrane unselectively.

Self-folding micropatterned polymeric containers

We demonstrate self-folding of precisely patterned, optically transparent, all-polymeric containers and describe their utility in mammalian cell and microorganism encapsulation and culture. The polyhedral containers, with SU-8 faces and biodegradable polycaprolactone (PCL) hinges, spontaneously assembled on heating. Self-folding was driven by a minimization of surface area of the liquefying PCL hinges within lithographically patterned two-dimensional (2D) templates. The strategy allowed for the fabrication of containers with variable polyhedral shapes, sizes and precisely defined porosities in all three dimensions. We provide proof-of-concept for the use of these polymeric containers as encapsulants for beads, chemicals, mammalian cells and bacteria. We also compare accelerated hinge degradation rates in alkaline solutions of varying pH. These optically transparent containers resemble three-dimensional (3D) micro-Petri dishes and can be utilized to sustain, monitor and deliver living biological components.

Improving physicochemical properties and doxorubicin cytotoxicity of novel polymeric micelles by poly(ε-caprolactone) segments

This study constructed a series of novel micelles based on star-shaped amphiphilic copolymers (sPEC/CDs), and aimed to confirm the important role poly(ε-caprolactone) (PCL) segments played to improve the various properties of micelles. sPEC/CDs, consisting of β-cyclodextrin (β-CD) as a core and monomethoxy poly(ethylene glycol) (mPEG) and PCL diblock copolymers as arms, were synthesized by arm-first method. The critical micelle concentrations (CMC) of sPEC/CDs were determined by fluorescence spectrophotometry using pyrene as a probe. 3-(4, 5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide and flow cytometry were used to detect drug cytotoxicity and cellular uptake of the doxorubicin-loaded micelles. Rhodamine-123 cellular accumulation was examined to evaluate the polymer action to P-glycoprotein. It was revealed that, once PCL segment was inserted between β-CD and mPEG, the CMC can be significantly decreased, the drug loading capability greatly improved, and the drug resistance of MCF-7/ADR cells effectively reversed. These findings suggest that sPEC/CDs own potential superiority for cancer therapy as drug carriers.

Development of stealth liposome coencapsulating doxorubicin and fluoxetine

Stealth liposomes form an important subset of liposomes, demonstrating prolonged circulation half-life and improved safety in vivo. Caelyx® (liposomal doxorubicin; Merck & Co., Whitehouse Station, New Jersey, USA) is a successful example of the application of stealth liposomes in anticancer treatment. However, multidrug resistance (MDR) to chemotherapy still remains a critical problem, accounting for more than 90% of treatment failure in patients with advanced cancer. To circumvent MDR, fluoxetine and doxorubicin were tested in combination for synergistic activity in MCF-7 (human breast carcinoma) and MCF-7/adr (doxorubicin-resistant human breast carcinoma) cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell-viability assay. Coencapsulation of doxorubicin and fluoxetine, using an ammonium sulphate gradient, was investigated, and a factorial experiment was designed to determine the optimal drug-to-lipid (D/L) ratio for coencapsulation. Drug release from Dox-Flu-SL (stealth liposome coencapsulating doxorubicin and fluoxetine) under both in vitro and in vivo conditions was determined. In MCF-7 cells, synergism was demonstrated at specific doxorubicin:fluoxetine ratios of between 0.09 and 0.5 (molar ratio), while MCF/7/adr cells demonstrated synergism across all drug ratios. Coencapsulation of doxorubicin and fluoxetine (Dox-Flu-SL) was successfully achieved (optimal doxorubicin:fluoxetine:lipid molar ratio of 0.02:0.05:1), obtaining a mean concentration of 257 ± 12.1 and 513 ± 29.3 μM for doxorubicin and fluoxetine, respectively. Most important, Dox-Flu-SL demonstrated drug release in synergistic ratios in cell-culture media, accounting for the improved cytotoxicity of Dox-Flu-SL over liposomal doxorubicin (LD) in both MCF-7 and MCF-7/adr cells. Pharmacokinetic studies also revealed that Dox-Flu-SL effectively prolonged drug-circulation time and reduced tissue biodistribution. Dox-Flu-SL presents a promising anticancer formulation, capable of effective reversal of drug resistance, and may constitute a novel approach for cancer therapy.

Design, synthesis and biological evaluation of carbohydrate-functionalized cyclodextrins and liposomes for hepatocyte-specific targeting

Targeting glycan-binding receptors is an attractive strategy for cell-specific drug and gene delivery. The C-type lectin asialoglycoprotein receptor (ASGPR) is particularly suitable for liver-specific delivery due to its exclusive expression by parenchymal hepatocytes. In this study, we designed and developed an efficient synthesis of carbohydrate-functionalized β-cyclodextrins (βCDs) and liposomes for hepatocyte-specific delivery. For targeting of ASGPR, rhodamine B-loaded βCDs were functionalized with glycodendrimers. Liposomes were equipped with synthetic glycolipids containing a terminal D-GalNAc residue to mediate binding to ASGPR. Uptake studies in the human hepatocellular carcinoma cell line HepG2 demonstrated that βCDs and liposomes displaying terminal D-Gal/D-GalNAc residues were preferentially endocytosed. In contrast, uptake of βCDs and liposomes with terminal d-Man or D-GlcNAc residues was markedly reduced. The d-Gal/d-GalNAc-functionalized βCDs and liposomes presented here enable hepatocyte-specific targeting. Gal-functionalized βCDs are efficient molecular carriers to deliver doxorubicin in vitro into hepatocytes and induce apoptosis.

Folate-targeted supramolecular vesicular aggregates based on polyaspartyl-hydrazide copolymers for the selective delivery of antitumoral drugs

Supramolecular vesicular aggregates (SVAs) have the advantage of combining the safe and biocompatible properties of colloidal vesicular carriers based on phospholipids with those of polymeric materials, i.e. polyaspartyl-hydrazide (PAHy) copolymers. To provide SVAs with a certain tumour selectivity, folate moieties were chemically conjugated to PAHy copolymers. Physicochemical properties (mean sizes, polydispersity index and zeta potential) of folate-targeted SVAs (FT-SVAs) loaded with gemcitabine were evaluated. The antiproliferative and anticancer activity of gemcitabine-loaded FT-SVAs was evaluated against two cancer cell lines, i.e. MCF-7 cells which over-express the folate receptor and the BxPC-3 cells, which do not over-express this receptor. Gemcitabine-loaded FT-SVAs showed a significantly (p < 0.001) greater and more specific in vitro anticancer activity with respect to both the free drug and the drug-loaded conventional liposomes or untargeted SVAs. Confocal microscopy, flow cytometry analysis and beta-scintillation highlighted that FT-SVAs were able to interact with MCF-7 cells after just 3 h and to increase the amount internalization in cells over-expressing the folate receptor. The in vivo biodistribution and pharmacokinetic experiments showed that gemcitabine-loaded SVAs and FT-SVAs were removed from the circulatory system at a slower rate than the native drug and a prolonged gemcitabine plasma concentration was observed for up to 16 h. SVAs were accumulated mainly in the lungs, spleen and kidneys, while FT-SVAs were also up taken by brain. These interesting and stimulating results suggest the existence of a possible in vivo application of SVAs and encourage the use of folate as a targeting agent in anticancer therapy.

β-cyclodextrin-centered star-shaped amphiphilic polymers for doxorubicin delivery

Aim: Delivery of doxorubicin could be achieved by a novel micellar system based on β-cyclodextrin-centered star-shaped amphiphilic polymers (sPEL/CD). This study specifically explored the effect of polylactide segments in sPEL/CD on various micelle properties, such as the critical micelle concentration, size, drug loading, cytotoxicity and drug resistance reversing effect. Method: The sPEL/CD was synthesized by the arm-first method. The critical micelle concentrations of polymeric micelles were determined by fluorescence spectrophotometry using pyrene as a probe. The oil/water method was applied to prepare doxorubicin-loaded micelles. 3-(4,5-dimethylthi-azol-2-yl)-2,5-diphenyltetrazolium bromide, confocal laser-scanning microscopy and flow cytometry were used to examine cell cytotoxicity and cellular uptake of the doxorubicin-loaded micelles. Finally, rhodamine-123 cellular uptake was determined to evaluate the polymer action on MCF-7 and MCF-7/ADR cells. Results: All polymers exhibited low cytotoxicity and their micelles had a desirable release-acceleration pH (pH 5.0) for cytoplasmic drug delivery. With the introduction of polylactide into the polymer, the micelle critical micelle concentration can be effectively decreased and the drug-loading content was enhanced. Most importantly, the drug resistance of MCF-7/ADR cells was significantly reversed via the interaction between polymer and Pgp. Therefore, this type of polymer has potential superiority for cancer therapy.

Remote loading of anthracyclines into liposomes

The following chapter introduces a remote loading procedure for anthracyclines focussing on the well-established drug doxorubicin. The key advantage of remote loading is that it leads to higher drug to lipid ratios and encapsulation efficiencies compared to conventional passive trapping techniques like hydration of dried lipid films with aqueous drug solutions. The method presented is appropriate to produce sterile liposomal doxorubicin formulations with a final concentration of 2 mg/mL doxorubicin, which can be applied not only in vitro but also in vivo.

Aqueous Compatible Fullerene-Doxorubicin Conjugates

Covalent conjugates of fullerene C(60) and the highly effective anticancer drug doxorubicin (DOX) were prepared and studied. The conjugation was through the amide linkage to preserve the intrinsic properties of DOX and fullerene cage. As designed, the conjugates with hydrophilic ethylene glycol spacers exhibited much improved aqueous compatibility, with significant solubility in water-DMSO mixtures. The anti-neoplastic activities of DOX were apparently unaffected in the conjugates according to evaluations in vitro with a human breast cancer cell line.