An evaluation of transmembrane ion gradient-mediated encapsulation of topotecan within liposomes

A Critical Scrutiny on Liposomal Nanoparticles Drug Carriers as Modelled by Topotecan Encapsulation and Release in Treating Cancer

The medical field is looking for drugs and/or ways of delivering drugs without harming patients. A number of severe drug side effects are reported, such as acute kidney injury (AKI), hepatotoxicity, skin rash, and so on. Nanomedicine has come to the rescue. Liposomal nanoparticles have shown great potential in loading drugs, and delivering drugs to specific targeted sites, hence achieving a needed bioavailability and steady state concentration, which is achieved by a controlled drug release ability by the nanoparticles. The liposomal nanoparticles can be conjugated to cancer receptor tags that give the anticancer-loaded nanoparticles specificity to deliver anticancer agents only at cancerous sites, hence circumventing destruction of normal cells. Also, the particles are biocompatible. The drugs are shielded by attack from the liver and other cytochrome P450 enzymes before reaching the desired sites. The challenge, however, is that the drug release is slow by these nanoparticles on their own. Scientists then came up with several ways to enhance drug release. Magnetic fields, UV light, infrared light, and so on are amongst the enhancers used by scientists to potentiate drug release from nanoparticles. In this paper, synthesis of liposomal nanoparticle formulations (liposomal-quantum dots (L-QDs), liposomal-quantum dots loaded with topotecan (L-QD-TPT)) and their analysis (cytotoxicity, drug internalization, loading efficiency, drug release rate, and the uptake of the drug and nanoparticles by the HeLa cells) are discussed.

Hypoxia-targeted cupric-tirapazamine liposomes potentiate radiotherapy in prostate cancer spheroids

In this study, novel cupric-tirapazamine [Cu(TPZ)₂]-liposomes were developed as an effective hypoxia-targeted therapeutic, which potentiated radiotherapy in a three dimensional (3D) prostate cancer (PCa) model. To overcome the low water solubility of the Cu(TPZ)₂, a remote loading method was developed to efficiently load the lipophilic complex into different liposomal formulations. The effect of pH, temperature, PEGylation, lipid composition, liposome size, lipid: complex ratio on the liposome properties, and drug loading was evaluated. The highest loading efficiency was obtained at neutral pH, which was independent of lipid composition and incubation time. In addition, enhanced drug loading was achieved upon decreasing the lipid:complex molar ratio with minimal effects on liposomes' morphology. Interestingly, the in vitro potency of the developed liposomes was easily manipulated by changing the lipid composition. The hydrophilic nature of our liposomal formulations improved the complex's solubility, leading to enhanced cellular uptake and toxicity, both in PCa monolayers and tumour spheroids. Moreover, Cu(TPZ)₂-loaded liposomes combined with radiation, showed a significant reduction in PCa spheroids growth rate, compared to the free complex or radiation alone, which could potentiate radiotherapy in patients with localised advanced PCa.

A novel drug delivery system -- Drug crystallization encapsulated liquid crystal emulsion

Liquid crystals (LCs) are widely used for drug delivery due to their controlled and sustained drug release properties. In this paper, drug crystallization encapsulated liquid crystal emulsion, a novel drug delivery system, was proposed. The lamellar liquid crystals formed by hydrogenated lecithin, which are similar to the skin stratum corneum lipid structure, are adopted as the drug carrier to encapsulate non-steroidal anti-inflammatory drugs (NSAIDs). As the model drug, ketoprofen exists in the hydrophobic core of emulsion as a drug crystal when squalane is used as the oil phase. The microstructure, sustained drug release behaviors, physicochemical property and biocompatibility of the system were examined by polarized light microscopy, rheological measurements, differential scanning calorimetry, X-ray diffraction, small-angle X-ray scattering, in vitro release study, and in vitro cellular cytotoxicity assay. The results have shown that the novel system lowers the drug crystal melting point and improves the thermal stability of liquid crystal structure. Besides, the excellent biocompatibility and sustained release property through the additional dissolution step of drug crystal show its application potentials in the topical cosmeceuticals. The results will also be helpful for in-depth understanding of the physical state of encapsulated drug in the liquid crystal carrier systems.

Recent advances in liposome formulations for breast cancer therapeutics

Among many nanoparticle-based delivery platforms, liposomes have been particularly successful with many formulations passed into clinical applications. They are well-established and effective gene and/or drug delivery systems, widely used in cancer therapy including breast cancer. In this review we discuss liposome design with the targeting feature and triggering functions. We also summarise the recent progress (since 2014) in liposome-based therapeutics for breast cancer including chemotherapy and gene therapy. We finally identify some challenges on the liposome technology development for the future clinical translation.

Cholesterol Levels Affect the Performance of AuNPs-Decorated Thermo-Sensitive Liposomes as Nanocarriers for Controlled Doxorubicin Delivery

Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly useful in cancer therapy. This research was focused on the evaluation of the effects of cholesterol levels in the performance of gold nanoparticles (AuNPs)-functionalized L for controlled doxorubicin (D) delivery. Their interfacial and morphological properties, drug release behavior against temperature changes and cytotoxic activity against breast and ovarian cancer cells were studied. Langmuir isotherms were performed to identify the most stable combination of lipid components. Two mole fractions of cholesterol (3.35 mol% and 40 mol%, L1 and L2 series, respectively) were evaluated. Thin-film hydration and transmembrane pH-gradient methods were used for preparing the L and for D loading, respectively. The cationic surface of L allowed the anchoring of negatively charged AuNPs by electrostatic interactions, even inducing a shift in the zeta potential of the L2 series. L exhibited nanometric sizes and spherical shape. The higher the proportion of cholesterol, the higher the drug loading. D was released in a controlled manner by diffusion-controlled mechanisms, and the proportions of cholesterol and temperature of release media influenced its release profiles. D-encapsulated L preserved its antiproliferative activity against cancer cells. The developed liposomal formulations exhibit promising properties for cancer treatment and potential for hyperthermia therapy.

Surfactant Assisted Rapid-Release Liposomal Strategies Enhance the Antitumor Efficiency of Bufalin Derivative and Reduce Cardiotoxicity

Background

BF211, a derivative of bufalin (BF), shows significantly improved solubility and potent antitumor efficiency compared to BF. Unfortunately, the unwanted toxicity such as cardiotoxicity caused by unspecific distribution has hindered its clinical use.

Methods

PEGylated BF211 liposomes (BF211@Lipo) were designed and optimizely prepared based on the pre-prescription research. In vitro and in vivo cardiotoxicity was evaluated. In vivo pharmacokinetics and biodistribution of BF211@Lipo were investigated. In vivo antitumor activity and toxicity were evaluated in HepG2 cell xenograft models. The rapid-release triggered by Poloxamer 188 (P188) was assessed in vitro and in vivo.

Results

The optimized BF211@Lipo displayed a spherical morphology with a size of (164.6 ± 10.3) nm and a high encapsulation efficiency of (93.24 ± 2.15) %. The in vivo concentration–time curves of BF211 loaded in liposomes showed a prolonged half-life in plasma and increased tumor accumulation. No obvious abnormality in electrocardiograms was observed in guinea pigs even at 9 mg/kg. Moreover, to improve the efficient release of BF211@Lipo, a surfactant-assisted rapid-release strategy was developed, and the release-promoting mechanism was revealed by the fluorescence resonance energy transfer (FRET) and fluorescence nanoparticle tracking analysis (fl-NTA) technology. Sequential injection of BF211@Lipo and P188 could ignite the “cold” liposomes locally in tumor regions, facilitating the burst release of BF211 and enhancing the therapeutic index.

Conclusion

Our progressive efforts that begin with preparation technology and dosage regimen enable BF211 to like a drug, providing a promising nano platform to deliver the cardiac glycosides and alleviate the side effects by decreasing unspecific biodistribution.

Nanoplatforms for Targeted Stimuli-Responsive Drug Delivery: A Review of Platform Materials and Stimuli-Responsive Release and Targeting Mechanisms

To achieve the promise of stimuli-responsive drug delivery systems for the treatment of cancer, they should (1) avoid premature clearance; (2) accumulate in tumors and undergo endocytosis by cancer cells; and (3) exhibit appropriate stimuli-responsive release of the payload. It is challenging to address all of these requirements simultaneously. However, the numerous proof-of-concept studies addressing one or more of these requirements reported every year have dramatically expanded the toolbox available for the design of drug delivery systems. This review highlights recent advances in the targeting and stimuli-responsiveness of drug delivery systems. It begins with a discussion of nanocarrier types and an overview of the factors influencing nanocarrier biodistribution. On-demand release strategies and their application to each type of nanocarrier are reviewed, including both endogenous and exogenous stimuli. Recent developments in stimuli-responsive targeting strategies are also discussed. The remaining challenges and prospective solutions in the field are discussed throughout the review, which is intended to assist researchers in overcoming interdisciplinary knowledge barriers and increase the speed of development. This review presents a nanocarrier-based drug delivery systems toolbox that enables the application of techniques across platforms and inspires researchers with interdisciplinary information to boost the development of multifunctional therapeutic nanoplatforms for cancer therapy.

Modeling of a spray drying method to produce ciprofloxacin nanocrystals inside the liposomes utilizing a response surface methodology: Box-Behnken experimental design

Spray drying was previously used to modify the physical form of the encapsulated ciprofloxacin drug to produce ciprofloxacin nanocrystals inside the liposomes (CNL). The purpose of the present study was to optimize CNL powder production by evaluating the response surface via design of experiments (DoE). Using the Box-Behnken (BB) design, the study independent variables were the protectant type (sucrose, trehalose or lactose), protectant amount, drying temperature, and spray gas flow. Individual spray drying experiments were performed at various set points for each variable followed by characterization of the produced powders. Liposomal particle size, drug encapsulation efficiency (EE%), liposomal surface zeta potential, and nanocrystal dimensions were the design dependant variables. By applying the least square regression method on the experimental data, mathematical models were developed using the mathematical software package MATLAB R2018b. Model reliability and the significance of the model's factors were estimated using analysis of variance (ANOVA). The generated CNL powders showed spherical to elliptical liposomal vesicles with particle sizes ranging from 98 to 159 nm. The EE (%) ranged from 30 to 95% w/w while the zeta potential varied between -3.5 and -10.5 mV. The encapsulated ciprofloxacin nanocrystals were elongated cylindrical structures with an aspect ratio of 4.0-7.8. Coefficients of determination (R² > 0.9) revealed a good agreement between the predicted and experimental values for all responses except for the nanocrystal dimensions. Sucrose and lactose were superior to trehalose in protecting the liposomes during spray drying. The amount of sugar significantly affected the characteristics of the CNL powders (p-value < 0.05). In conclusion, the DoE approach using BB design has efficiently modelled the generation of CNL by spray drying. The optimum processing conditions which produced high drug encapsulation (90%) after formation of nanocrystals and a vesicle size of ~125 nm utilized 57% (w/w) sucrose, an 80 °C inlet temperature, and an atomization rate of 742 L/hr.

Calibrated liposomal release of the anti-mitotic agent BI-2536 increases the targeting of mitotic tumor cells

Cancer drugs which are specifically targeted at mitosis have generally under-delivered as a class. One likely reason is that only a small percentage of cancer cells in a tumor are actually dividing at any moment. If this is the case, then prolonged bioavailability in the tumor should significantly increase the efficacy of antimitotic agents. Here, we show that if the Plk1 inhibitor BI 2536 is co-encapsulated in a liposome with a pair of anions, its release rate is dependent on both the identity and stoichiometry of the anions. We created a library of liposomes with varying release rates using this approach and found that liposomal drug release rates correlated inversely with in vitro cancer cell killing. Xenografted mice treated with a single dose of slow-releasing liposomal BI 2536 experienced tumor volume decreases lasting 12 days and complete responses in 20% of mice. Treatment with two doses a week apart increased the response rate to 75%. This approach, which we termed Paired Anion Calibrated Release (PACeR), has the potential to revive the clinical utility of antimitotic cancer drugs which have failed clinical trials.

Liposomes: Advancements and innovation in the manufacturing process

Liposomes are well recognised as effective drug delivery systems, with a range of products approved, including follow on generic products. Current manufacturing processes used to produce liposomes are generally complex multi-batch processes. Furthermore, liposome preparation processes adopted in the laboratory setting do not offer easy translation to large scale production, which may delay the development and adoption of new liposomal systems. To promote advancement and innovation in liposome manufacturing processes, this review considers the range of manufacturing processes available for liposomes, from laboratory scale and scale up, through to large-scale manufacture and evaluates their advantages and limitations. The regulatory considerations associated with the manufacture of liposomes is also discussed. New innovations that support leaner scalable technologies for liposome fabrication are outlined including self-assembling liposome systems and microfluidic production. The critical process attributes that impact on the liposome product attributes are outlined to support potential wider adoption of these innovations.

Nanobowl-Supported Liposomes Improve Drug Loading and Delivery

Liposomal drug delivery for cancer therapy can be limited due to drug leakage in circulation. Here, we develop a new method to enhance the stability of actively loaded liposomal doxorubicin (DOX) through embedding a stiff nanobowl in the liposomal water cavity. Nanobowl-supported liposomal DOX (DOX@NbLipo) resists the influence of plasma protein and blood flow shear force to prevent drug leakage. This approach yields improved drug delivery to tumor sites and enhanced antitumor efficacy. Compared to alternative methods of modifying liposome surface and composition for stability, this approach designs a physical support for an all-aqueous nanoliposomal cavity. Nanobowl stabilization of liposomes is a simple and effective method to improve carrier stability and drug delivery.

Rapid Microfluidic Preparation of Niosomes for Targeted Drug Delivery

Niosomes are non-ionic surfactant-based vesicles with high promise for drug delivery applications. They can be rapidly prepared via microfluidics, allowing their reproducible production without the need of a subsequent size reduction step, by controlled mixing of two miscible phases of an organic (lipids dissolved in alcohol) and an aqueous solution in a microchannel. The control of niosome properties and the implementation of more complex functions, however, thus far are largely unknown for this method. Here we investigate microfluidics-based manufacturing of topotecan (TPT)-loaded polyethylene glycolated niosomes (PEGNIO). The flow rate ratio of the organic and aqueous phases was varied and optimized. Furthermore, the surface of TPT-loaded PEGNIO was modified with a tumor homing and penetrating peptide (tLyp-1). The designed nanoparticular drug delivery system composed of PEGNIO-TPT-tLyp-1 was fabricated for the first time via microfluidics in this study. The physicochemical properties were determined through dynamic light scattering (DLS) and zeta potential analysis. In vitro studies of the obtained formulations were performed on human glioblastoma (U87) cells. The results clearly indicated that tLyp-1-functionalized TPT-loaded niosomes could significantly improve anti-glioma treatment.

PEGylation and surface functionalization of liposomes containing drug nanocrystals for cell-targeted delivery

Liposomal formulations have important therapeutic applications in anti-cancer treatments but current formulations suffer from serious side effects, high dosage requirements and prolonged treatment. In this study, PEGylated azide-functionalized liposomes containing drug nanocrystals were investigated with the aim of increasing the drug payload and achieving functionalization for targeted delivery. Liposomes were characterized using cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small and ultra-small angle neutron scattering (SANS/USANS) and small and wide angle X-ray scattering (SAXS/WAXS). Cryo-TEM experiments revealed the dimensions of the nanocrystal-loaded liposomes and the change of shape from spherical to elongated after the formation of nanocrystals. Results from SANS/USANS experiments confirmed the asymmetric particle shape. SAXS/WAXS experiments confirmed that the crystalline drug only occurred in freeze-thawed samples and correlated with a new unidentified polymorphic form of ciprofloxacin. Using a small molecule dye, dibenzocyclooctyne (DBCO)-cy5, specific conjugation between DBCO groups and surface azide groups on the liposomes was confirmed; this indicates the promise of this system for tumour-targeted delivery.

What Drives Innovation: The Canadian Touch on Liposomal Therapeutics

Liposomes are considered one of the most successful drug delivery systems (DDS) given their established utility and success in the clinic. In the past 40–50 years, Canadian scientists have made ground-breaking discoveries, many of which were successfully translated to the clinic, leading to the formation of biotech companies, the creation of research tools, such as the Lipex Extruder and the NanoAssemblr™, as well as contributing significantly to the development of pharmaceutical products, such as Abelcet^®, MyoCet^®, Marqibo^®, Vyxeos^®, and Onpattro™, which are making positive impacts on patients’ health. This review highlights the Canadian contribution to the development of these and other important liposomal technologies that have touched patients. In this review, we try to address the question of what drives innovation: Is it the individual, the teams, the funding, and/or an entrepreneurial spirit that leads to success? From this perspective, it is possible to define how innovation will translate to meaningful commercial ventures and products with impact in the future. We begin with a brief history followed by descriptions of drug delivery technologies influenced by Canadian researchers. We will discuss recent advances in liposomal technologies, including the Metaplex technology from the author’s lab. The latter exemplifies how a nanotechnology platform can be designed based on multidisciplinary groups with expertise in coordination chemistry, nanomedicines, disease, and business to create new therapeutics that can effect better outcomes in patient populations. We conclude that the team is central to the effort; arguing if the team is entrepreneurial and well positioned, the funds needed will be found, but likely not solely in Canada.

Nanocarriers and Their Loading Strategies

Nanocarriers are of paramount significance for drug delivery and nanomedicine technology. Given the imperfect systems and nonideal therapeutic effects, there are works to be done in synthesis as much as in biological studies, if not more so. Building the foundation of synthesis would offer more tools and deeper insights for exploring the biological systems with extreme complexity. This review aims at a broad-scope summary and classification of nanocarriers for drug delivery, with focus on the synthetic strategy and structural implications. The nanocarriers are divided into four categories according to the loading principle: molecular-level loading, surface loading, matrix loading, and cavity loading systems. Making comparisons across diverse nanocarrier systems would make it easier to see the fundamental characteristics, from where the weakness can be addressed and the strengths combined. The systematic comparisons may also inspire new ideas and methods.

Ion quantification in liposomal drug products using high performance liquid chromatography

A simple, straightforward analytical method based on liquid chromatography has been optimized to quantify total, internal, and external ions in drug-loaded liposomal products. The quantification of ammonium and sulfate ions in Doxil is detailed; although, the methodology has been extrapolated to quantitate a variety of ions, including calcium, acetate, and others in several different liposomal formulations. Total ion concentrations were measured after disruption of the liposome via lyophilization, to liberate all components. External ion concentrations were made following membrane centrifugation, without disruption of the liposome structure, where the permeate fraction was analyzed for external ion quantities. The internal ion fraction was derived from mass balance of the total and external ion measurements. High performance liquid chromatography (HPLC), equipped with different separation columns, and coupled to a charged aerosol detector, was employed for all ion quantifications. The analytical measurements were confirmed using simple stoichiometry based on the drug crystallization of doxorubicin within the liposome interior. The method presented herein is quick, highly accurate, and has significantly improved lower limits of detection and quantification over other traditional methods. As more follow-on versions of Doxil are being developed, this facile approach to ion quantitation can be used to help establish compositional similarity to the reference listed drug.

Solid State Characterization of Ciprofloxacin Liposome Nanocrystals

Liposomes have been widely researched as drug delivery systems; however, the solid state form of drug inside the liposome, whether it is in solution or in a solid state, is often not studied. The solid state properties of the drug inside the liposomes are important, as they dictate the drug release behavior when the liposomes come into contact with physiological fluid. Recently, a new approach of making liposomal ciprofloxacin nanocrystals was proposed by the use of an additional freeze-thawing step in the liposomal preparation method. This paper aims to determine the solid state properties of ciprofloxacin inside the liposomes after this additional freeze-thawing cycle using cryo-TEM, small-angle X-ray scattering (SAXS), and cross-polarized light microscopy (CPLM). Ciprofloxacin precipitated in the ciprofloxacin hydrate crystal form with a unit cell dimension of 16.7 Å. The nanocrystals also showed a phase transition at 93 °C, which represents dehydration of the hydrate crystals to the anhydrate form of ciprofloxacin, verified by temperature-dependent SAXS measurements. Furthermore, the dependence of the solid state form of the nanocrystals on pH was investigated in situ, and it was shown that the liposomal ciprofloxacin nanocrystals retained their crystalline form at pH 6-10. Understanding the solid state attributes of nanocrystals inside liposomes provides improved understanding of drug dissolution and release as well as opening avenues to new applications where the nanosized crystals can provide a dissolution benefit.

Investigation on Physicochemical Characteristics of a Nanoliposome-Based System for Dual Drug Delivery

Synergistic effects of multiple drugs with different modes of action are utilized for combinatorial chemotherapy of intractable cancers. Translation of in vitro synergistic effects into the clinic can be realized using an efficient delivery system of the drugs. Despite a few studies on nano-sized liposomes containing erlotinib (ERL) and doxorubicin (DOX) in a single liposome vesicle, reliable and reproducible preparation methods as well as physicochemical characteristics of a non-PEGylated nanoliposome co-encapsulated with ERL and DOX have not been yet elucidated. In this study, ERL-encapsulated nanoliposomes were prepared using the lipid film-hydration method. By ultrasonication using a probe sonicator, the liposome diameter was reduced to less than 200 nm. DOX was loaded into the ERL-encapsulated nanoliposomes using ammonium sulfate (AS)-gradient or pH-gradient method. Effects of DOX-loading conditions on encapsulation efficiency (EE) of the DOX were investigated to determine an efficient drug-loading method. In the EE of DOX, AS-gradient method was more effective than pH gradient. The dual drug-encapsulated nanoliposomes had more than 90% EE of DOX and 30% EE of ERL, respectively. Transmission electron microscopy and selected area electron diffraction analyses of the dual drug-encapsulated nanoliposomes verified the highly oriented DOX-sulfate crystals inside the liposome as well as the less oriented small crystals of ERL in the outermost region of the nanoliposome. The nanoliposomes were stable at different temperatures without an increase of the nanoliposome diameter. The dual drug-encapsulated nanoliposomes showed a time-differential release of ERL and DOX, implying proper sequential releases for their synergism. The preparation methods and the physicochemical characteristics of the dual drug delivery system contribute to the development of the optimal process and more advanced systems for translational researches.

Theranostic Liposome-Nanoparticle Hybrids for Drug Delivery and Bioimaging

Advanced theranostic nanomedicine is a multifunctional approach which combines the diagnosis and effective therapy of diseased tissues. Here, we investigated the preparation, characterization and in vitro evaluation of theranostic liposomes. As is known, liposome–quantum dot (L–QD) hybrid vesicles are promising nanoconstructs for cell imaging and liposomal-topotecan (L-TPT) enhances the efficiency of TPT by providing protection against systemic clearance and allowing extended time for it to accumulate in tumors. In the present study, hydrophobic CdSe/ZnS QD and TPT were located in the bilayer membrane and inner core of liposomes, respectively. Dynamic light scattering (DLS), zeta potential (ζ) measurements and fluorescence/absorption spectroscopy were performed to determine the vesicle size, charge and spectroscopic properties of the liposomes. Moreover, drug release was studied under neutral and acidic pH conditions. Fluorescence microscopy and flow cytometry analysis were used to examine the cellular uptake and intracellular distribution of the TPT-loaded L–QD formulation. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was utilized to investigate the in vitro cytotoxicity of the formulations on HeLa cells. According to the results, the TPT-loaded L–QD hybrid has adequate physicochemical properties and is a promising multifunctional delivery vehicle which is capable of a simultaneous co-delivery of therapeutic and diagnostic agents.

Angiopep-2-conjugated poly(ethylene glycol)-co- poly(ε-caprolactone) polymersomes for dual-targeting drug delivery to glioma in rats

The blood–brain barrier is a formidable obstacle for glioma chemotherapy due to its compact structure and drug efflux ability. In this study, a dual-targeting drug delivery system involving Angiopep-2-conjugated biodegradable polymersomes loaded with doxorubicin (Ang-PS-DOX) was developed to exploit transport by the low-density lipoprotein receptor-related protein 1 (LRP1), which is overexpressed in both blood–brain barrier and glioma cells. The polymersomes (PS) were prepared using a thin-film hydration method. The PS were loaded with doxorubicin using the pH gradient method (Ang-PS-DOX). The resulting PS were uniformly spherical, with diameters of ~135 nm and with ~159.9 Angiopep-2 molecules on the surface of each PS. The drug-loading capacity and the encapsulation efficiency for doxorubicin were 7.94%±0.17% and 95.0%±1.6%, respectively. Permeability tests demonstrated that the proton diffusion coefficient across the PS membrane was far slower than that across the liposome membrane, and the common logarithm value was linearly dependent on the dioxane content in the external phase. Compared with PS-DOX, Ang-PS-DOX demonstrated significantly higher cellular uptake and stronger cytotoxicity in C6 cells. In vivo pharmacokinetics and brain distribution experiments revealed that Ang-PS-DOX achieved a more extensive distribution and more abundant accumulation in glioma cells than PS-DOX. Moreover, the survival time of glioma-bearing rats treated with Ang-PS-DOX was significantly prolonged compared with those treated with PS-DOX or a solution of free doxorubicin. These results suggested that Ang-PS-DOX can target glioma cells and enhance chemotherapeutic efficacy.

A simple passive equilibration method for loading carboplatin into pre-formed liposomes incubated with ethanol as a temperature dependent permeability enhancer

A passive equilibration method which relies on addition of candidate drugs to pre-formed liposomes is described as an alternative method for preparing liposome encapsulated drugs. The method is simple, rapid and applicable to liposomes prepared with high (45mol%) or low (<20mol%) levels of cholesterol. Passive equilibration is performed in 4-steps: (i) formation of liposomes, (ii) addition of the candidate drug to the liposomes in combination with a permeability enhancing agent, (iii) incubation at a temperature that facilitates diffusion of the added compound across the lipid bilayer, and (iv) quenching the enhanced membrane permeability by reduction in temperature and/or removal of the permeabilization enhancer. The method is fully exemplified here using ethanol as the permeabilization enhancer and carboplatin (CBDCA) as the drug candidate. It is demonstrated that ethanol can be added to liposomes prepared with 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and Cholesterol (Chol) (55:45mol ratio) in amounts up to 30% (v/v) with no change in liposome size, even when incubated at temperatures>60°C. Super-saturated solutions of CBDCA (40mg/mL) can be prepared at 70°C and these are stable in the presence of ethanol even when the temperature is reduced to <30°C. maximum CBDCA encapsulation is achieved within 1h after the CBDCA solution is added to pre-formed DSPC/Chol liposomes in the presence of 30% (v/v) ethanol at 60°C. When the pre-formed liposomes are mixed with ethanol (30% v/v) at or below 40°C, the encapsulation efficiency is reduced by an order of magnitude. The method was also applied to liposomes prepared from other compositions include a cholesterol free formulations (containing 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[carboxy(polyethylene glycol)-2000] (DSPE-PEG₂₀₀₀)) and a low Chol (<20mol%) formulations prepared with the distearoyl-sn-glycero-3-phospho-(1'-rac-glycerol) DSPG)). The cytotoxic activity of CBDCA was unaffected when prepared in this manner and two of the resultant formulations exhibited good stability in vitro and in vivo. The cytotoxic activity of CBDCA was unaffected when prepared in this manner and the resultant formulations exhibited good stability in vitro and in vivo. Pharmacokinetics studies in CD-1 mice indicated that the resulting formulations increased the circulation half life of the associated CBDCA significantly (AUC_0-24h of CBDCA=0.016μg·hr/mL; AUC_0-24h of the DSPC/Chol CBDCA formulation=1014.0μg·hr/mL and AUC_0-24h of the DSPC/DSPG/Chol CBDCA formulation=583.96μg·hr/mL). Preliminary efficacy studies in Rag-2M mice with established subcutaneous H1975 and U-251 tumors suggest that the therapeutic activity of CBDCA is improved when administered in liposomal formulations. The encapsulation method described here has not been disclosed previously and will have broad applications to drugs that would normally be encapsulated during liposome manufacturing.

Ion-Pairing Contribution to the Liposomal Transport of Topotecan as Revealed by Mechanistic Modeling

Actively loaded liposomal formulations of anticancer agents have been widely explored due to their high drug encapsulation efficiencies and prolonged drug retention. Mathematical models to predict and optimize drug loading and release kinetics from these nanoparticle formulations would be useful in their development and may allow researchers to tune release profiles. Such models must account for the driving forces as influenced by the physicochemical properties of the drug and the microenvironment, and the liposomal barrier properties. This study employed mechanistic modeling to describe the active liposomal loading and release kinetics of the anticancer agent topotecan (TPT). The model incorporates ammonia transport resulting in generation of a pH gradient, TPT dimerization, TPT lactone ring-opening and -closing interconversion kinetics, chloride transport, and transport of TPT-chloride ion-pairs to describe the active loading and release kinetics of TPT in the presence of varying chloride concentrations. Model-based predictions of the kinetics of active loading at varying loading concentrations of TPT and release under dynamic dialysis conditions were in reasonable agreement with experiments. These findings identify key attributes to consider in optimizing and predicting loading and release of liposomal TPT that may also be applicable to liposomal formulations of other weakly basic pharmaceuticals.

Design of cholesterol arabinogalactan anchored liposomes for asialoglycoprotein receptor mediated targeting to hepatocellular carcinoma: In silico modeling, in vitro and in vivo evaluation

We have developed active targeting liposomes to deliver anticancer agents to ASGPR which will contribute to effective treatment of hepatocellular carcinoma. Active targeting is achieved through polymeric ligands on the liposome surface. The liposomes were prepared using reverse phase evaporation method and doxorubicin hydrocholoride, a model drug, was loaded using the ammonium sulphate gradient method. Liposomes loaded with DOX were found to have a particle size of 200nm with more than 90% entrapment efficiency. Systems were observed to release the drug in a sustained manner in acidic pH in vitro. Liposomes containing targeting ligands possessed greater and selective toxicity to ASGPR positive HepG2 cell lines due to specific ligand receptor interaction. Bio-distribution studies revealed that liposomes were concentrated in the liver even after 3h of administration, thus providing conclusive evidence of targeting potential for formulated nanosystems. Tumor regression studies indicated greater tumor suppression with targeted liposomes thereby establishing superiority of the liposomal system. In this work, we used a novel methodology to guide the determination of the optimal composition of the targeting liposomes: molecular dynamics (MD) simulation that aided our understanding of the behaviour of the ligand within the bilayer. This can be seen as a demonstration of the utility of this methodology as a rational design tool for active targeting liposome formulation.

Nanoscale Reaction Vessels Designed for Synthesis of Copper-Drug Complexes Suitable for Preclinical Development

The development of copper-drug complexes (CDCs) is hindered due to their very poor aqueous solubility. Diethyldithiocarbamate (DDC) is the primary metabolite of disulfiram, an approved drug for alcoholism that is being repurposed for cancer. The anticancer activity of DDC is dependent on complexation with copper to form copper bis-diethyldithiocarbamate (Cu(DDC)₂), a highly insoluble complex that has not been possible to develop for indications requiring parenteral administration. We have resolved this issue by synthesizing Cu(DDC)₂ inside liposomes. DDC crosses the liposomal lipid bilayer, reacting with the entrapped copper; a reaction that can be observed through a colour change as the solution goes from a light blue to dark brown. This method is successfully applied to other CDCs including the anti-parasitic drug clioquinol, the natural product quercetin and the novel targeted agent CX-5461. Our method provides a simple, transformative solution enabling, for the first time, the development of CDCs as viable candidate anticancer drugs; drugs that would represent a brand new class of therapeutics for cancer patients.

Formation of drug nanocrystals under nanoconfinement afforded by liposomes

In response to freeze–thaw, liposome-encapsulated antibiotic (A) is converted into nanocrystalline form (B) resulting in an attenuated drug release profile.

Small molecule therapeutic-loaded liposomes as therapeutic carriers: from development to clinical applications

In this review, various methods and mechanisms for encapsulation of small therapeutic molecules in liposomes for targeted delivery and triggered release, as well as their potential in the clinical uses, are discussed.

Porphyrin-phospholipid liposomes with tunable leakiness

Drug bioavailability is a key consideration for drug delivery systems. When loaded with doxorubicin, liposomes containing 5 molar % porphyrin-phospholipid (HPPH liposomes) exhibited in vitro and in vivo serum stability that could be fine-tuned by varying the drug-to-lipid ratio. A higher drug loading ratio destabilized the liposomes, in contrast to standard liposomes which displayed an opposite and less pronounced trend. Following systemic administration of HPPH liposomes, near infrared laser irradiation induced vascular photodynamic damage, resulting in enhanced liposomal doxorubicin accumulation in tumors. In laser-irradiated tumors, the use of leaky HPPH liposomes resulted in improved doxorubicin bioavailability compared to stable standard liposomes. Using this approach, a single photo-treatment with 10mg/kg doxorubicin rapidly eradicated tumors in athymic nude mice bearing KB or MIA Paca-2 xenografts.

Mechanistic model and analysis of doxorubicin release from liposomal formulations

Reliable and predictive models of drug release kinetics in vitro and in vivo are still lacking for liposomal formulations. Developing robust, predictive release models requires systematic, quantitative characterization of these complex drug delivery systems with respect to the physicochemical properties governing the driving force for release. These models must also incorporate changes in release due to the dissolution media and methods employed to monitor release. This paper demonstrates the successful development and application of a mathematical mechanistic model capable of predicting doxorubicin (DXR) release kinetics from liposomal formulations resembling the FDA-approved nanoformulation DOXIL® using dynamic dialysis. The model accounts for DXR equilibria (e.g. self-association, precipitation, ionization), the change in intravesicular pH due to ammonia release, and dialysis membrane transport of DXR. The model was tested using a Box-Behnken experimental design in which release conditions including extravesicular pH, ammonia concentration in the release medium, and the dilution of the formulation (i.e. suspension concentration) were varied. Mechanistic model predictions agreed with observed DXR release up to 19h. The predictions were similar to a computer fit of the release data using an empirical model often employed for analyzing data generated from this type of experimental design. Unlike the empirical model, the mechanistic model was also able to provide reasonable predictions of release outside the tested design space. These results illustrate the usefulness of mechanistic modeling to predict drug release from liposomal formulations in vitro and its potential for future development of in vitro - in vivo correlations for complex nanoformulations.

Thermosensitive, near-infrared-labeled nanoparticles for topotecan delivery to tumors

Liposomal nanoparticles have proven to be versatile systems for drug delivery. However, the progress in clinic has been slower and less efficient than expected. This suggests a need for further development using carefully designed chemical components to improve usefulness under clinical conditions and maximize therapeutic effect. For cancer chemotherapy, PEGylated liposomes were the first nanomedicine to reach the market and have been used clinically for several years. Approaches toward targeted drug delivery using next generation "thermally triggered" nanoparticles are now in clinical trials. However, clinically tested thermosensitive liposomes (TSLs) lack the markers that allow tumor labeling and improved imaging for tissue specific applied hyperthermia. Here we describe the development of optically labeled TSLs for image guidance drug delivery and proof-of-concept results for their application in the treatment of murine xenograft tumors using the anticancer drug topotecan. These labeled TSLs also allow the simultaneous, real-time diagnostic imaging of nanoparticle biodistribution using a near-infrared (NIR; 750-950 nm) fluorophore coupled to a lipidic component of the lipid bilayer. When combined with multispectral fluorescence analysis, this allows for specific and high sensitivity tracking of the nanoparticles in vivo. The application of NIR fluorescence-labeled TSLs could have a transformative effect on future cancer chemotherapy.

Insights into accelerated liposomal release of topotecan in plasma monitored by a non-invasive fluorescence spectroscopic method

A non-invasive fluorescence method was developed to monitor liposomal release kinetics of the anticancer agent topotecan (TPT) in physiological fluids and subsequently used to explore the cause of accelerated release in plasma. Analyses of fluorescence excitation spectra confirmed that unencapsulated TPT exhibits a red shift in its spectrum as pH is increased. This property was used to monitor TPT release from actively loaded liposomal formulations having a low intravesicular pH. Mathematical release models were developed to extract reliable rate constants for TPT release in aqueous solutions monitored by fluorescence and release kinetics obtained by HPLC. Using the fluorescence method, accelerated TPT release was observed in plasma as previously reported in the literature. Simulations to estimate the intravesicular pH were conducted to demonstrate that accelerated release correlated with alterations in the low intravesicular pH. This was attributed to the presence of ammonia in plasma samples rather than proteins and other plasma components generally believed to alter release kinetics in physiological samples. These findings shed light on the critical role that ammonia may play in contributing to the preclinical/clinical variability and performance seen with actively-loaded liposomal formulations of TPT and other weakly-basic anticancer agents.

Supramolecular cyclodextrin-based drug nanocarriers

Hosting of polymers, lipids and drug conjugates makes cyclodextrins suitable to prepare biocompatible, targetable and stimuli-responsive supramolecular drug nanocarriers.

Interactions of anticancer drugs with biomembranes: what can we learn from model membranes?

The interactions of anticancer drugs with cell membranes are of primary importance for drug transport, accumulation and activity. However, these interactions are very difficult to investigate because of the complexity of biological membranes. Lipid model membranes have therefore been built to gain insight into the collective role of lipids in drug-membrane interactions. Membranes can act as a barrier for drug molecules, sequester them or conversely may allow them to freely diffuse, thereby modulating the accumulation of drugs into cells. Lipid membranes also affect the ability of the efflux pump Pgp to bind and efflux anticancer drugs from cells. On the other hand, anticancer drugs can alter the structure and properties of lipid membranes, which are expected to influence the functioning of embedded proteins. The relevance of lipid model membranes to assess interactions between anticancer drugs and biomembranes is evidenced.

Dynamic, nonsink method for the simultaneous determination of drug permeability and binding coefficients in liposomes

Drug release from liposomal formulations is governed by a complex interplay of kinetic (i.e., drug permeability) and thermodynamic factors (i.e., drug partitioning to the bilayer surface). Release studies under sink conditions that attempt to mimic physiological conditions are insufficient to decipher these separate contributions. The present study explores release studies performed under nonsink conditions coupled with appropriate mathematical models to describe both the release kinetics and the conditions in which equilibrium is established. Liposomal release profiles for a model anticancer agent, topotecan, under nonsink conditions provided values for both the first-order rate constant for drug release and the bilayer/water partition coefficient. These findings were validated by conducting release studies under sink conditions via dynamic dialysis at the same temperature and buffer pH. A nearly identical rate constant for drug release could be obtained from dynamic dialysis data when appropriate volume corrections were applied and a mechanism-based mathematical model was employed to account for lipid bilayer binding and dialysis membrane transport. The usefulness of the nonsink method combined with mathematical modeling was further explored by demonstrating the effects of topotecan dimerization and bilayer surface charge potential on the bilayer/water partition coefficient at varying suspension concentrations of lipid and drug.

The proton permeability of self-assembled polymersomes and their neuroprotection by enhancing a neuroprotective peptide across the blood-brain barrier after modification with lactoferrin

Biotherapeutics such as peptides possess strong potential for the treatment of intractable neurological disorders. However, because of their low stability and the impermeability of the blood-brain barrier (BBB), biotherapeutics are difficult to transport into brain parenchyma via intravenous injection. Herein, we present a novel poly(ethylene glycol)-poly(d,l-lactic-co-glycolic acid) polymersome-based nanomedicine with self-assembled bilayers, which was functionalized with lactoferrin (Lf-POS) to facilitate the transport of a neuroprotective peptide into the brain. The apparent diffusion coefficient (D*) of H(+) through the polymersome membrane was 5.659 × 10(-26) cm(2) s(-1), while that of liposomes was 1.017 × 10(-24) cm(2) s(-1). The stability of the polymersome membrane was much higher than that of liposomes. The uptake of polymersomes by mouse brain capillary endothelial cells proved that the optimal density of lactoferrin was 101 molecules per polymersome. Fluorescence imaging indicated that Lf101-POS was effectively transferred into the brain. In pharmacokinetics, compared with transferrin-modified polymersomes and cationic bovine serum albumin-modified polymersomes, Lf-POS obtained the greatest BBB permeability surface area and percentage of injected dose per gram (%ID per g). Furthermore, Lf-POS holding S14G-humanin protected against learning and memory impairment induced by amyloid-β25-35 in rats. Western blotting revealed that the nanomedicine provided neuroprotection against over-expression of apoptotic proteins exhibiting neurofibrillary tangle pathology in neurons. The results indicated that polymersomes can be exploited as a promising non-invasive nanomedicine capable of mediating peptide therapeutic delivery and controlling the release of drugs to the central nervous system.

The role of pH and ring-opening hydrolysis kinetics on liposomal release of topotecan

The use of liposomal delivery systems for the treatment of cancer has been extensively researched because of their passive targeting to the vasculature of solid tumors. While their potential to provide prolonged retention and high drug encapsulation is desirable for anticancer agents, a mechanistic understanding is required to optimize and design liposomal drug delivery systems capable of controllable release tailored to tumor type and patient. Topotecan (TPT) is a topoisomerase I inhibitor that undergoes reversible, pH-sensitive ring-opening hydrolysis. TPT may benefit from liposomal formulation using active loading strategies to generate low intravesicular pH to prolong drug retention and increase drug encapsulation. This paper develops a mathematical model to describe TPT's permeability as a function of pH by accounting for the drug's ionization state, membrane binding, and ring-opening interconversion kinetics. Studies were conducted to determine the acid dissociation constant of TPT's phenolic -OH and interconversion kinetics between TPT's lactone and carboxylate forms. Using the constants determined from these studies and release studies conducted at varying pH, permeability coefficients and membrane binding constants for each species of TPT were determined. Based on this model, three permeable species were observed. Interestingly, the two most permeable species were zwitterionic forms of TPT, and the permeability of the lactone zwitterion was comparable to that of the neutral form of another camptothecin analogue. Furthermore, release was affected by based-catalyzed interconversion kinetics between TPT's lactone and carboxylate forms. At neutral pH, release was rate-limited by formation of the TPT lactone from the ring-opened carboxylate form. Based on these findings, the developed model describing liposomal release of TPT may be used in the future to evaluate and optimize loading and subsequent release of liposomal TPT formulations utilizing active loading strategies.

Remote loading of preencapsulated drugs into stealth liposomes

Loading drugs into carriers such as liposomes can increase the therapeutic ratio by reducing drug concentrations in normal tissues and raising their concentrations in tumors. Although this strategy has proven advantageous in certain circumstances, many drugs are highly hydrophobic and nonionizable and cannot be loaded into liposomes through conventional means. We hypothesized that such drugs could be actively loaded into liposomes by encapsulating them into specially designed cyclodextrins. To test this hypothesis, two hydrophobic drugs that had failed phase II clinical trials because of excess toxicity at deliverable doses were evaluated. In both cases, the drugs could be remotely loaded into liposomes after their encapsulation (preloading) into cyclodextrins and administered to mice at higher doses and with greater efficacy than possible with the free drugs.

Physicochemical aspects of the coformulation of colistin and azithromycin using liposomes for combination antibiotic therapies

Remote loading of azithromycin into liposomes, and subsequent release behavior in the presence of colistin, has been investigated with a view to understand the potential of liposomes to enable the coformulation of these two antibiotics for application in inhalation therapy. Azithromycin was successfully encapsulated into liposomes by remote loading (encapsulation efficiency > 98%). Slow release of azithromycin was achieved in the presence of cholesterol in a concentration-dependent manner, with a 4:1 mol ratio of phospholipid-cholesterol releasing 22% azithromycin in 24 h, whereas a 2:1 mol ratio released only 4.9% of azithromycin in 24 h. Addition of colistin to the formulation with increasing concentration did not change the loading behavior, but accelerated drug release, increasing the percentage of released azithromycin from 4.9% to 30% over 24 h. The permeabilizing ability of colistin on liposomes is consistent with its permeabilizing effect on bacterial cells. This behavior opens opportunities to tailor the release rate of drugs coformulated with colistin using liposomes as the carrier.