Influence of pH gradients on the transbilayer transport of drugs, lipids, peptides and metal ions into large unilamellar vesicles

Building Asymmetric Lipid Bilayers for Molecular Dynamics Simulations: What Methods Exist and How to Choose One?

The compositional asymmetry of biological membranes has attracted significant attention over the last decade. Harboring more differences from symmetric membranes than previously appreciated, asymmetric bilayers have proven quite challenging to study with familiar concepts and techniques, leaving many unanswered questions about the reach of the asymmetry effects. One particular area of active research is the computational investigation of composition- and number-asymmetric lipid bilayers with molecular dynamics (MD) simulations. Offering a high level of detail into the organization and properties of the simulated systems, MD has emerged as an indispensable tool in the study of membrane asymmetry. However, the realization that results depend heavily on the protocol used for constructing the asymmetric bilayer models has sparked an ongoing debate about how to choose the most appropriate approach. Here we discuss the underlying source of the discrepant results and review the existing methods for creating asymmetric bilayers for MD simulations. Considering the available data, we argue that each method is well suited for specific applications and hence there is no single best approach. Instead, the choice of a construction protocol-and consequently, its perceived accuracy-must be based primarily on the scientific question that the simulations are designed to address.

Local pH at Nonionic and Zwitterionic Lipid/Water Interfaces Revealed by Heterodyne-Detected Electronic Sum-Frequency Generation: A Unified View to Predict Interfacial pH of Biomembranes

For biomembranes, which are composed of neutral as well as charged lipids, the local pH at lipid/water interfaces is extremely important in their structural formation and functional activity. In our previous study of the charged lipid/water interfaces, we found that the local pH at the interface is governed by the positive or negative sign of the charge of the lipid: i.e., the local pH is dictated by the repulsive or attractive electrostatic interaction between the charged lipid headgroup and the proton. Because of the lack of net charge in the headgroup of the neutral lipid, the factor determining the local pH at neutral lipid/water interfaces is less straightforward, and therefore it is more challenging to predict the local pH. Here we apply heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy to nonionic and zwitterionic lipids to investigate the local pH at the neutral lipid/water interfaces. The obtained results indicate that the local pH at the nonionic lipid/water interface is higher than in bulk water by 0.8 whereas the local pH at the zwitterionic lipid/water interface is lower by 0.6, although the latter is subject to significant uncertainty. The present HD-ESFG study on neutral lipids, combined with the previous study on charged lipids, presents a unified view to consider the local pH at biomembranes based on the balance between the electrostatic interaction and the hydrophobicity provided by the lipid.

Liposomal Nanodrug Based on Norcantharidin Derivative for Increased in Vivo Activity

To address the limitations of norcantharidin (NCTD) in clinical applications, including restricted tumor accumulation and intense irritation, we have developed a new derivative of NCTD with (S)-1-benzyl-3-pyrrolidinol, which can be actively loaded into liposomes to achieve drug encapsulation and sustained release properties by using pH gradient loading technique. Cytotoxicity tests against cancer cell lines (Hepa 1-6 and 4 T1 cells) have demonstrated that this derivative exhibits comparable activity to NCTD in vitro. The NCTD derivative can be efficiently loaded into liposomes with high encapsulation efficiency (98.7%) and high drug loading (32.86%). Tolerability and antitumor efficacy studies showed that the liposomal NCTD derivative was well tolerated at intravenous injection doses of 3 folds higher than the parent drug solution, while significantly improved anticancer activity in vivo was achieved. This liposomal nanodrug could become a potent and safe NCTD formulation alternative for cancer therapy.

Drug Stability and Minimized Acid-/Drug-Catalyzed Phospholipid Degradation in Liposomal Irinotecan

Therapeutics at or close to the nanoscale, such as liposomal irinotecan, offer significant promise for the treatment of solid tumors. Their potential advantage over the unencapsulated or free form of the drug is due in part to their altered biodistribution. For slow and sustained release, significant optimization of formulation is needed to achieve the required level of stability and allow long-term storage of the drug product. Gradient-based liposomal formulation of camptothecins such as irinotecan poses unique challenges owing to the camptothecin- and acid-catalyzed hydrolysis of phospholipid esters in the inner monolayer of the liposomal membrane. We demonstrated that a narrow set of conditions related to the external pH, temperature, intraliposomal concentration, identity of the drug-trapping agent, physical form of the drug inside the liposomes, and final drug load have a marked impact on the stability of the liposome phospholipid membrane. The physical form of the drug inside the liposome was shown to be an insoluble gel with an irinotecan-to-sulfate ratio approximating 1:1, reducing the potential for irinotecan-catalyzed phospholipid hydrolysis in the internal phospholipid monolayer. As a result of this work, a stable and active liposome formulation has been developed that maintains phospholipid chemical stability following long-term storage at 2-8°C.

Assembly methods for asymmetric lipid and polymer-lipid vesicles

Asymmetric unilamellar vesicles are aqueous bodies surrounded by two dissimilar leaflets made from lipids, polymers, or both. They are great models for cell membranes and attractive vehicles in potential biomedicine applications. Despite their promise, asymmetric unilamellar vesicles are not widely studied or adopted in applications. This is largely due to the complexity in generating asymmetric membranes. Recent technical advances in microfluidics have opened doors to high throughput fabrication of asymmetric unilamellar vesicles. In this review, we focus on microfluidic methods for generating asymmetric lipid vesicles, with two dissimilar lipid leaflets, and asymmetric lipid-polymer vesicles, with one lipid leaflet and one polymer leaflet. We also review a few standard non-microfluidic methods for generating asymmetric vesicles. We hope to highlight the improved capability in obtaining asymmetric vesicles through a variety of methods and encourage the wider scientific community to adopt some of these for their own work.

Proton‐Gradient‐Driven Sensitivity Enhancement of Liposome‐Encapsulated Supramolecular Chemosensors

An overarching challenge in the development of supramolecular sensor systems is to enhance their sensitivity, which commonly involves the synthesis of refined receptors with increased affinity to the analyte. We show that a dramatic sensitivity increase by 1–2 orders of magnitude can be achieved by encapsulating supramolecular chemosensors inside liposomes and exposing them to a pH gradient across the lipid bilayer membrane. This causes an imbalance of the influx and efflux rates of basic and acidic analytes leading to a significantly increased concentration of the analyte in the liposome interior. The utility of our liposome‐enhanced sensors was demonstrated with various host–dye reporter pairs and sensing mechanisms, and we could easily increase the sensitivity towards multiple biologically relevant analytes, including the neurotransmitters serotonin and tryptamine.

Branched PEG-modification: A new strategy for nanocarriers to evade of the accelerated blood clearance phenomenon and enhance anti-tumor efficacy

PEGylation is one of the most successful technologies for reducing immunogenicity, improving the stability and circulation time of nanocarriers, and has been applied in the clinic for over three decades. However, linear PEG-modified nanocarriers have been found to induce anti-PEG IgM at the first injection, which triggers the accelerated blood clearance (ABC) phenomenon upon repeated injections. Furthermore, clinical and research evidence has revealed that anti-PEG antibodies also cause serious complement activation-related pseudoallergies (CARPA), which greatly reduce the safety of linear PEGylated nanocarriers. In this study, as an alternative to linear PEG, branched PEG was selected owing to its low antigenicity. We pioneer the use of branched PEG lipid derivatives [DSPE-mPEG_2,n (n = 2, 10, and 20 kDa)] to modify nanoemulsions (PE_2,n) and liposomes (PL_2,n). Upon characterization, PE_2,n and PL_2,n showed similar physicochemical properties to linear DSPE-mPEG₂₀₀₀-modified nanocarriers in terms of size, polydispersity index (PDI), and zeta potential. However, our pharmacokinetics study surprisingly indicated that PE_2,n and PL_2,n did not induce the ABC phenomenon after repeated injection. This may be attributed to the fact that PE_2,n and PL_2,n induced noticeably lower levels of anti-PEG IgM than linear PEG-modified nanocarriers and did not activate the complement system. Furthermore, we are the first to investigate the anti-tumor efficacy of DSPE-mPEG_2,n-modified liposomal doxorubicin (DOX). The pharmacodynamic experiments showed that DSPE-mPEG_2,n-m-modified liposomal DOX had better in vivo anti-tumor effects than linear DSPE-mPEG₂₀₀₀-modified liposomes. Therefore, we speculate that DSPE-mPEG_2,n-modified nanocarriers possess promising prospects in avoiding the ABC phenomenon, reducing CARPA, and improving the anti-tumor efficacy of encapsulated drugs.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

Therapeutic nanoreactors for detoxification of xenobiotics: Concepts, challenges and biotechnological trends with special emphasis to organophosphate bioscavenging

The introduction of enzyme nanoreactors in medicine is relatively new. However, this technology has already been experimentally successful in cancer treatments, struggle against toxicity of reactive oxygen species in inflammatory processes, detoxification of drugs and xenobiotics, and correction of metabolic and genetic defects by using encapsulated enzymes, acting in single or cascade reactions. Biomolecules, e.g. enzymes, antibodies, reactive proteins capable of inactivating toxicants in the body are called bioscavengers. In this review, we focus on enzyme-containing nanoreactors for in vivo detoxification of organophosphorous compounds (OP) to be used for prophylaxis and post-exposure treatment of OP poisoning. A particular attention is devoted to bioscavenger-containing injectable nanoreactors operating in the bloodstream. The nanoreactor concept implements single or multiple enzymes and cofactors co-encapsulated in polymeric semi-permeable nanocontainers. Thus, the detoxification processes take place in a confined space containing highly concentrated bioscavengers. The article deals with historical and theoretical backgrounds about enzymatic detoxification of OPs in nanoreactors, nanoreactor polymeric enveloppes, realizations and advantages over other approaches using bioscavengers.

Life in the lumen: The multivesicular endosome

The late endosomes/endo‐lysosomes of vertebrates contain an atypical phospholipid, lysobisphosphatidic acid (LBPA) (also termed bis[monoacylglycero]phosphate [BMP]), which is not detected elsewhere in the cell. LBPA is abundant in the membrane system present in the lumen of this compartment, including intralumenal vesicles (ILVs). In this review, the current knowledge on LBPA and LBPA‐containing membranes will be summarized, and their role in the control of endosomal cholesterol will be outlined. Some speculations will also be made on how this system may be overwhelmed in the cholesterol storage disorder Niemann‐Pick C. Then, the roles of intralumenal membranes in endo‐lysosomal dynamics and functions will be discussed in broader terms. Likewise, the mechanisms that drive the biogenesis of intralumenal membranes, including ESCRTs, will also be discussed, as well as their diverse composition and fate, including degradation in lysosomes and secretion as exosomes. This review will also discuss how intralumenal membranes are hijacked by pathogenic agents during intoxication and infection, and what is the biochemical composition and function of the intra‐endosomal lumenal milieu. Finally, this review will allude to the size limitations imposed on intralumenal vesicle functions and speculate on the possible role of LBPA as calcium chelator in the acidic calcium stores of endo‐lysosomes.

A Comparative Study on DMSO-Induced Modulation of the Structural and Dynamical Properties of Model Bilayer Membranes

Modulating the structures and properties of biomembranes via permeation of small amphiphilic molecules is immensely important, having diverse applications in cell biology, biotechnology, and pharmaceuticals, because their physiochemical and biological interactions lead to new pathways for transdermal drug delivery and administration. In this work, we have elucidated the role of dimethyl sulfoxide (DMSO), broadly used as a penetration-enhancing agent and cryoprotective agent on model lipid membranes, using a combination of fluorescence microscopy and time-resolved fluorescence spectroscopy. Spatially resolved fluorescence lifetime imaging microscopy (FLIM) has been employed to unravel how the fluidity of the DMSO-induced bilayer regulates the structural alteration of the vesicles. Moreover, we have also shown that the dehydration effect of DMSO leads to weakening of the hydrogen bond between lipid headgroups and water molecules and results in faster solvation dynamics as demonstrated by femtosecond time-resolved fluorescence spectroscopy. It has been gleaned that the water dynamics becomes faster because bilayer rigidity decreases in the presence of DMSO, which is also supported by time-resolved rotational anisotropy measurements. The enhanced diffusivity and increased membrane fluidity in the presence of DMSO are further ratified at the single-molecule level through fluorescence correlation spectroscopy (FCS) measurements. Our results indicate that while the presence of DMSO significantly affects the 1,2-dimyristoyl-rac-glycero-3-phosphocholine (DMPC) and 1,2-dipalmitoyl-rac-glycero-3-phosphatidylcholine (DPPC) bilayers, it has a weak effect on 1,2-dimyristoyl-sn-glycero-3-phospho-rac-glycerol (DMPG) vesicles, which might explain the preferential interaction of DMSO with the positively charged choline group present in DMPC and DPPC vesicles. The experimental findings have also been further verified with molecular dynamics simulation studies. Moreover, it has been observed that DMSO is likely to have a differential effect on heterogeneous bilayer membranes depending on the structure and composition of their headgroups. Our results illuminate the importance of probing the lipid structure and composition of cellular membranes in determining the effects of cryoprotective agents.

Coarse-grained simulation of the translational and rotational diffusion of globular proteins by dissipative particle dynamics

With simplified interactions and degrees of freedom, coarse-grained (CG) simulations have been successfully applied to study the translational and rotational diffusion of proteins in solution. However, in order to reach larger lengths and longer timescales, many CG simulations employ an oversimplified model for proteins or an implicit-solvent model in which the hydrodynamic interactions are ignored, and thus, the real kinetics are more or less unfaithful. In this work, we develop a CG model based on the dissipative particle dynamics (DPD) that can be universally applied to different types of proteins. The proteins are modeled as a group of rigid DPD beads without conformational changes. The fluids (including solvent and ions) are also modeled as DPD beads. The electrostatic interactions between charged species are explicitly considered by including charge distributions on DPD particles. Moreover, a surface friction between the protein and fluid beads is applied to control the slip boundary condition. With this model, we investigate the self-diffusion of a single globular protein in bulk solution. The translational and rotational diffusion coefficients of the protein can be tuned by the surface frictional constant to fit the predictions of the Stokes-Einstein (SE) relation. We find that both translational and rotational diffusion coefficients that meet with the prediction of the SE relation based on experimental results of the hydrodynamic radius are reached at almost the same frictional constant for different types of proteins. Such scaling behavior indicates that the model can be applied to simulate the translational and rotational diffusion together for various types of proteins.

Contrastive Studies of Cytarabine/Daunorubicin Dual-Loaded Liposomes Prepared by pH Gradient and Cu2+ Gradient Method

Conventional combination chemotherapy often leads to unsatisfactory clinical outcomes due to the different distribution characteristics in vivo and the superimposed systemic toxicity of the drug cocktail. Co-encapsulated nano preparations have been gradually developed in recent years. In this work, cytarabine (Ara-C)/daunorubicin (DNR) liposomes were prepared by the pH gradient (ADL-pH) and Cu²⁺ gradient (ADL-Cu) methods. Ara-C did not show significant release from either ADL-Cu or ADL-pH in vitro during 168 h, which related to its logP_oct. Different drug-loading patterns showed different release characteristics of DNR due to the different existence forms, ADL-pH contains the citrate form, while in ADL-Cu, there is the Cu²⁺ complex. To evaluate the release behavior, daunorubicin liposome (DL) and daunorubicin-Cu²⁺ complex (DNR-Cu) were prepared. The addition of EDTA in the release medium significantly increased the release rate of DNR from DL-Cu, while lower pH accelerated DNR release from both DL-pH and DL-Cu. The PK confirmed that ADL-Cu and ADL-pH could prolong the drug circulation time, and ADL-Cu had a mean retention time 1.5 times that of ADL-pH. Furthermore, both liposomes allowed the two drugs to maintain a relatively constant plasma concentration ratio for a prolonged time. Cytotoxicity assays showed that Ara-C/DNR with a molar ratio of 5:1 and 3:1 exhibited an excellent synergistic effect, which was more obvious at 5:1. In vitro antitumor results revealed that ADL-Cu exhibited more cytotoxicity than ADL-pH. All factors tested in this work suggest the considerable potential of ADL-Cu and ADL-pH for anticancer treatment.

Enhanced In Vitro Magnetic Cell Targeting of Doxorubicin-Loaded Magnetic Liposomes for Localized Cancer Therapy

The lack of efficient targeting strategies poses significant limitations on the effectiveness of chemotherapeutic treatments. This issue also affects drug-loaded nanocarriers, reducing nanoparticles cancer cell uptake. We report on the fabrication and in vitro characterization of doxorubicin-loaded magnetic liposomes for localized treatment of liver malignancies. Colloidal stability, superparamagnetic behavior and efficient drug loading of our formulation were demonstrated. The application of an external magnetic field guaranteed enhanced nanocarriers cell uptake under cell medium flow in correspondence of a specific area, as we reported through in vitro investigation. A numerical model was used to validate experimental data of magnetic targeting, proving the possibility of accurately describing the targeting strategy and predict liposomes accumulation under different environmental conditions. Finally, in vitro studies on HepG2 cancer cells confirmed the cytotoxicity of drug-loaded magnetic liposomes, with cell viability reduction of about 50% and 80% after 24 h and 72 h of incubation, respectively. Conversely, plain nanocarriers showed no anti-proliferative effects, confirming the formulation safety. Overall, these results demonstrated significant targeting efficiency and anticancer activity of our nanocarriers and superparamagnetic nanoparticles entrapment could envision the theranostic potential of the formulation. The proposed magnetic targeting study could represent a valid tool for pre-clinical investigation regarding the effectiveness of magnetic drug targeting.

Comprehensive Survey on Nanobiomaterials for Bone Tissue Engineering Applications

One of the most important ideas ever produced by the application of materials science to the medical field is the notion of biomaterials. The nanostructured biomaterials play a crucial role in the development of new treatment strategies including not only the replacement of tissues and organs, but also repair and regeneration. They are designed to interact with damaged or injured tissues to induce regeneration, or as a forest for the production of laboratory tissues, so they must be micro-environmentally sensitive. The existing materials have many limitations, including impaired cell attachment, proliferation, and toxicity. Nanotechnology may open new avenues to bone tissue engineering by forming new assemblies similar in size and shape to the existing hierarchical bone structure. Organic and inorganic nanobiomaterials are increasingly used for bone tissue engineering applications because they may allow to overcome some of the current restrictions entailed by bone regeneration methods. This review covers the applications of different organic and inorganic nanobiomaterials in the field of hard tissue engineering.

Flip-flop asymmetry of cholesterol in model membranes induced by thermal gradients

Lipid asymmetry is a crucial property of biological membranes and significantly influences their physical and mechanical properties. It is responsible for maintaining different chemical environments on the external and internal surfaces of cells and organelles and plays a vital role in many biological processes such as cell signalling and budding. In this work we show, using non-equilibrium molecular dynamics (NEMD) simulations, that thermal fields can induce lipid asymmetry in biological membranes. We focus our investigation on cholesterol, an abundant lipid in the plasma membrane, with a rapid flip-flop rate, significantly influencing membrane properties. We demonstrate that thermal fields induce membrane asymmetry with cholesterol showing thermophobic behaviour and therefore accumulating on the cold side of the membrane. This work highlights a possible experimental route to preparing and controlling asymmetry in synthetic membranes.

On the physiological and cellular homeostasis of ascorbate

Recent interest in the role of ascorbate in crucial metabolic processes is driven by the growing number of medical reports that show beneficial effects of ascorbate supplementation for maintaining general well-being and recovery from a variety of medical conditions. The effect of ascorbate on the local body environment highly depends on its local concentration; at low concentrations it can cause the reduction of reactive oxygen and facilitate activities of enzymes, while at high concentrations it generates free radicals by reducing ferric ions. Ascorbate serving as an electron donor assists the iron-containing proteins and the iron transfer between various aqueous compartments. These functions require effective and adjustable mechanisms responsible for ascorbate biodistribution. In the paper we propose a new biophysical model of ascorbate redistribution between various aqueous body compartments. It combines recent experimental evidence regarding the ability of ascorbate to cross the lipid bilayer by unassisted diffusion, with active transport by well-characterized sodium vitamin C transporter (SVCT) membrane proteins. In the model, the intracellular concentration of ascorbate is maintained by the balance of two opposing fluxes: fast active and slow passive transport. The model provides a mechanistic understanding of ascorbate flux across the epidermal barrier in the gut as well as the role of astrocytes in ascorbate recycling in the brain. In addition, ascorbate passive diffusion across biological membranes, which depends on membrane electric potentials and pH gradients, provides the rationale for the correlation between ascorbate distribution and the transfer of iron ions inside a cell. The proposed approach provides, for the first time, a mechanistic account of processes leading to ascorbate physiological and cellular distribution, which helps to explain numerous experimental and clinical observations.

Liposomal OTS964, a TOPK inhibitor: a simple method to estimate OTS964 association with liposomes that relies on enhanced OTS964 fluorescence when bound to albumin

OTS964 is an inhibitor of T-lymphokine-activated killer cell-originated protein kinase (TOPK), a protein kinase important for mitosis and highly expressed in ovarian and lung cancers. This compound demonstrated potent anti-proliferative activity in a panel of cell lines positive for TOPK; however, when administered to mouse xenograft models, adverse hematopoietic toxicities were observed. To overcome this problem, OTS964 was encapsulated into liposomes and a liposomal formulation of OTS964 is now considered a lead candidate for clinical development. To support clinical development of this formulation, it is critically important to define assays that can easily distinguish between free and liposomal OTS964. Here, we develop a new assay to determine liposomal OTS964 encapsulation (percentage of drug associated with the liposomes) and OTS964 that is dissociated from the liposomes (percentage of drug released from liposomes) by monitoring the enhanced OTS964 fluorescence after its binding to albumin. The optical properties of OTS964 were investigated and three absorbance peaks were identified (235 nm, 291 nm, and 352 nm). Fluorescence was observed at 350 nm (excitation) and 470 nm (emission). Interestingly, the fluorescence of OTS964 increased 18-fold in the presence of serum proteins and more specifically albumin. This phenomenon was used to discriminate between the amounts of drug associated with the liposomes or released from the liposomes. Controls consisting of liposomal OTS964 permeabilized with saponins or octyl glucopyranoside served to confirm that drug release could be monitored by albumin-associated increases in fluorescence. The OTS964 liposomal formulation proved to be very stable with less than 10% release after 4 days in phosphate-buffered saline at 37 °C. The quantity of drug associated with the liposomal surface but not inside the liposomes could also be estimated using this approach. These studies present a novel approach to characterize liposomal release of OTS964, in real time and in a non-invasive manner while acquiring additional information about the spatial distribution of liposomal drug.

Chromogranin A preferential interaction with Golgi phosphatidic acid induces membrane deformation and contributes to secretory granule biogenesis

Chromogranin A (CgA) is a key luminal actor of secretory granule biogenesis at the trans-Golgi network (TGN) level but the molecular mechanisms involved remain obscure. Here, we investigated the possibility that CgA acts synergistically with specific membrane lipids to trigger secretory granule formation. We show that CgA preferentially interacts with the anionic glycerophospholipid phosphatidic acid (PA). In accordance, bioinformatic analysis predicted a PA-binding domain (PABD) in CgA sequence that effectively bound PA (36:1) or PA (40:6) in membrane models. We identified PA (36:1) and PA (40:6) as predominant species in Golgi and granule membranes of secretory cells, and we found that CgA interaction with these PA species promotes artificial membrane deformation and remodeling. Furthermore, we demonstrated that disruption of either CgA PABD or phospholipase D (PLD) activity significantly alters secretory granule formation in secretory cells. Our findings show for the first time the ability of CgA to interact with PLD-generated PA, which allows membrane remodeling and curvature, key processes necessary to initiate secretory granule budding.

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.

Association equilibria of divalent ions on the surface of liposomes formed from phosphatidylcholine

Divalent ions, in particular calcium ions, constitute important macroelements in living organisms. They are also found in cell membranes, i.e., ensuring their stabilization or participating in synaptic transmission of nerve impulses. The aim of this work is to describe the interactions of divalent ions, such as Ca²⁺, Ba²⁺, and Sr²⁺, in electrolytes with the functional groups on the surface of liposomes formed from phosphatidylcholine (PC). Microelectrophoresis is used to determine the surface charge density as a function of pH. The interactions between ions found in solution and the functional groups of PC are described with the use of a seven-equilibrium mathematical model. Using this model along with experimental data on the charge density of the membrane surface, the association constants characterizing this equilibrium are determined. These parameters are used to calculate the theoretical model curves. The validity of the proposed model is confirmed by comparing the theoretically calculated changes in charge density on the liposome surface with the experimental results.

A New Computational Method for Membrane Compressibility: Bilayer Mechanical Thickness Revisited

Because lipid bilayers can bend and stretch in ways similar to thin elastic sheets, physical models of bilayer deformation have utilized mechanical constants such as the moduli for bending rigidity (κ_C) and area compressibility (K_A). However, the use of these models to quantify the energetics of membrane deformation associated with protein-membrane interactions, and the membrane response to stress is often hampered by the shortage of experimental data suitable for the estimation of the mechanical constants of various lipid mixtures. Although computational tools such as molecular dynamics simulations can provide alternative means to estimate K_A values, current approaches suffer significant technical limitations. Here, we present a novel, to our knowledge, computational framework that allows for a direct estimation of K_A values for individual bilayer leaflets. The theory is based on the concept of elasticity and derives K_A from real-space analysis of local thickness fluctuations sampled in molecular dynamics simulations. We explore and validate the model on a large set of single and multicomponent bilayers of different lipid compositions and sizes, simulated at different temperatures. The calculated bilayer compressibility moduli agree with values estimated previously from experiments and those obtained from a standard computational method based on a series of constrained tension simulations. We further validate our framework in a comparison with an existing polymer brush model and confirm the polymer brush model's predicted linear relationship with proportionality coefficient of 24, using elastic parameters calculated from the simulation trajectories. The robustness of the results that emerge from the method allows us to revisit the origins of the bilayer mechanical (compressible) thickness and in particular its dependence on acyl-chain unsaturation and the presence of cholesterol.

Remote loading of liposomes with a 124I-radioiodinated compound and their in vivo evaluation by PET/CT in a murine tumor model

Long circulating liposomes entrapping iodinated and radioiodinated compounds offer a highly versatile theranostic platform. Here we report a new methodology for efficient and high-yield loading of such compounds into liposomes, enabling CT/SPECT/PET imaging and ¹³¹I-radiotherapy.

Methods: The CT contrast agent diatrizoate was synthetically functionalized with a primary amine, which enabled its remote loading into PEGylated liposomes by either an ammonium sulfate- or a citrate-based pH transmembrane gradient. Further, the amino-diatrizoate was radiolabeled with either ¹²⁴I (t_1/2 = 4.18 days) for PET or ¹²⁵I (t_1/2 = 59.5 days) for SPECT, through an aromatic Finkelstein reaction.

Results: Quantitative loading efficiencies (>99%) were achieved at optimized conditions. The ¹²⁴I-labeled compound was remote-loaded into liposomes, with an overall radiolabeling efficiency of 77 ± 1%, and imaged in vivo in a CT26 murine colon cancer tumor model by PET/CT. A prolonged blood circulation half-life of 19.5 h was observed for the radiolabeled liposomes, whereas injections of the free compound were rapidly cleared. Lower accumulation was observed in the spleen, liver, kidney and tumor than what is usually seen for long-circulating liposomes.

Conclusion: The lower accumulation was interpreted as release of the tracer from the liposomes within these organs after accumulation. These results may guide the design of systems for controlled release of remote loadable drugs from liposomes.

Neutrophil-mediated delivery of pixantrone-loaded liposomes decorated with poly(sialic acid)-octadecylamine conjugate for lung cancer treatment

Poly(sialic acid) (PSA) is a natural hydrophilic biodegradable and non-immunogenic biopolymer, receptors for its monomer are expressed on peripheral blood neutrophils (PBNs), which plays important roles in the progression and invasion of tumors. A poly(sialic acid)-octadecylamine conjugate (PSA-ODA) was synthesized and then anchor it on the surface of liposomal pixantrone (Pix-PSL), to achieve an improved anticancer effect. The liposomes were prepared using a remote loading method via a pH gradient, and then assessed for particle size, zeta potential encapsulation efficiency, in vitro release, and in vitro cytotoxicity. Simultaneously, in vitro and in vivo cellular uptake studies confirmed that PSA-decorated liposomes provided an enhanced accumulation of liposomes in PBNs. An in vivo study presented that the anti-tumor activity of Pix-PSL was superior to that of other Pix formulations, probably due to the efficient targeting of PBNs by Pix-PSL, after which PBN containing Pix-PSL (Pix-PSL/PBNs) in the blood circulation are recruited by the tumor microenvironment. These findings suggest that PSA-decorated liposomal Pix may provide a neutrophil-mediated drug delivery system (DDS) for the eradication of tumors, which represents a promising approach for the tumor targeting of chemotherapeutic treatments.

Targeted delivery of pixantrone to neutrophils by poly(sialic acid)-p-octadecylamine conjugate modified liposomes with improved antitumor activity

Based on the knowledge that poly(sialic acid) is a critical element for tumour development and that the receptors for its monomer are expressed on neutrophils, which play important roles in the progression and invasion of tumours, a poly(sialic acid)-p-octadecylamine conjugate (PSA-p-ODA) was synthesised and used to modify the surface of liposomal pixantrone (Pix-PSL) to improve the delivery of Pix to peripheral blood neutrophils (PBNs). The liposomes were fabricated using a remote loading technology via a pH gradient, and were then assessed for particle size, encapsulation efficiency, in vitro release, in vitro cytotoxicity, and pharmacokinetics. Simultaneously, in vitro and in vivo cellular uptake studies demonstrated that Pix-PSL provided an enhanced accumulation of Pix in PBNs. An in vivo study showed that the anti-tumour activity of Pix-PSL was superior to that of other formulations, probably owing to the efficient targeting of PBNs by Pix-PSL, after which PBNs containing Pix-PSL (Pix-PSL/PBNs) in the circulatory system are recruited by the tumour microenvironment. These findings suggest that PSA-p-ODA-decorated liposomal Pix may provide a neutrophil-mediated drug delivery system (DDS) for the eradication of tumours, and thus represents a promising approach for the tumour targeting of chemotherapeutic treatments.

Resolution V fractional factorial design for screening of factors affecting weakly basic drugs liposomal systems

This study aims to investigate factors affecting weakly basic drugs liposomal systems. Resolution V fractional factorial design (2_V^5-1) is used as an example of screening designs that would better be used as a wise step before proceeding with detailed factors effects or optimization studies. Five factors probable to affect liposomal systems of weakly basic drugs were investigated using Amisulpride as a model drug. Factors studied were; A: Preparation technique B: Phosphatidyl choline (PhC) amount (mg) C: Cholesterol: PhC molar ratio, D: Hydration volume (ml) and E: Sonication type. Levels investigated were; Ammonium sulphate-pH gradient technique or Transmembrane zinc chelation-pH gradient technique, 200 or 400 mg, 0 or 0.5, 10 or 20 ml and bath or probe sonication for A, B, C, D and E respectively. Responses measured were Particle size (PS) (nm), Zeta potential (ZP) (mV) and Entrapment efficiency percent (EE%). Ion selective electrode was used as a novel method for measuring unentrapped drug concentration and calculating entrapment efficiency without the need for liposomal separation. Factors mainly affecting the studied responses were Cholesterol: PhC ratio and hydration volume for PS, preparation technique for ZP and preparation technique and hydration volume for EE%. The applied 2_V^5-1 design enabled the use of only 16 trial combinations for screening the influence of five factors on weakly basic drugs liposomal systems. This clarifies the value of the use of screening experiments before extensive investigation of certain factors in detailed optimization studies.

From dynamic self-assembly to networked chemical systems

Although dynamic self-assembly, DySA, is a relatively new area of research, the past decade has brought numerous demonstrations of how various types of components - on scales from (macro)molecular to macroscopic - can be arranged into ordered structures thriving in non-equilibrium, steady states. At the same time, none of these dynamic assemblies has so far proven practically relevant, prompting questions about the field's prospects and ultimate objectives. The main thesis of this Review is that formation of dynamic assemblies cannot be an end in itself - instead, we should think more ambitiously of using such assemblies as control elements (reconfigurable catalysts, nanomachines, etc.) of larger, networked systems directing sequences of chemical reactions or assembly tasks. Such networked systems would be inspired by biology but intended to operate in environments and conditions incompatible with living matter (e.g., in organic solvents, elevated temperatures, etc.). To realize this vision, we need to start considering not only the interactions mediating dynamic self-assembly of individual components, but also how components of different types could coexist and communicate within larger, multicomponent ensembles. Along these lines, the review starts with the discussion of the conceptual foundations of self-assembly in equilibrium and non-equilibrium regimes. It discusses key examples of interactions and phenomena that can provide the basis for various DySA modalities (e.g., those driven by light, magnetic fields, flows, etc.). It then focuses on the recent examples where organization of components in steady states is coupled to other processes taking place in the system (catalysis, formation of dynamic supramolecular materials, control of chirality, etc.). With these examples of functional DySA, we then look forward and consider conditions that must be fulfilled to allow components of multiple types to coexist, function, and communicate with one another within the networked DySA systems of the future. As the closing examples show, such systems are already appearing heralding new opportunities - and, to be sure, new challenges - for DySA research.

Mesoporous silica nanocarriers encapsulated antimalarials with high therapeutic performance

The use of nanocarriers in drug delivery is a breakeven research and has received a clarion call in biomedicine globally. Herein, two newly nano-biomaterials: MCM-41 encapsulated quinine (MCM-41 ⊃ QN) (1) and 3-phenylpropyl silane functionalized MCM-41 loaded QN (pMCM-41 ⊃ QN) (2) were synthesized and well characterized. 1 and 2 along with our two already reported nano-antimalarial drugs (MCM-41 ⊃ ATS) (3) and 3-aminopropyl silane functionalized MCM-41 contained ATS (aMCM-41 ⊃ ATS) (4) were screened in vitro for their activity against P. falciparium W2 strain, cytotoxicity against BGM cells and in vivo for their activity against Plasmodium bergheiNK65. 1 has the highest antimalarial activity in vivo against P. berghei NK65, (ED50: < 0.0625 mg/kg body weight) and higher mean survival time compared to the other nano biomaterials or unencapsulated drugs at doses higher than 0.0625 mg/kg body weight. This encapsulation strategy of MCM-41 ⊃ QN (1) stands very useful and effective in delivering the drug to the target cells compared to other delivery systems and therefore, this encapsulated drug may be considered for rational drug design.

In vitro lung epithelial cell transport and anti-interleukin-8 releasing activity of liposomal ciprofloxacin

As a promising long-acting inhaled formulation, liposomal ciprofloxacin (Lipo-CPFX) was characterized in the in vitro human lung epithelial Calu-3 cell monolayer system, compared to ciprofloxacin in solution (CPFX). Its modulated absorptive transport and uptake, and sustained inhibitory activity against induced pro-inflammatory interleukin-8 (IL-8) release were examined. The absorptive transport and uptake kinetics for Lipo-CPFX and CPFX were determined at 0.1-50 mg/ml in the Transwell system. The Lipo-CPFX transport was then challenged for mechanistic exploration via cell energy depletion, a reduced temperature, endocytosis and/or lipid fusion inhibition, and addition of excess non-loaded liposomes. The inhibitory activities of Lipo-CPFX and CPFX against lipopolysaccharide (LPS)-induced IL-8 release were assessed in a co-incubation or pre-incubation mode. In the tight Calu-3 cell monolayers, Lipo-CPFX yielded 15-times slower ciprofloxacin flux of absorptive transport and 5-times lower cellular drug uptake than CPFX. Its transport appeared to be transcellular; kinetically linear, proportional to encapsulated ciprofloxacin concentration; and consistent with the cell energy-independent lipid bilayer fusion mechanism. Lipo-CPFX was equipotent to CPFX in the anti-IL-8 releasing activity upon 24 h co-incubation with LPS. Additionally, Lipo-CPFX, but not CPFX, retained the anti-IL-8 releasing activity even 24 h after pre-incubation. In conclusion, Lipo-CPFX enabled slower absorptive lung epithelial cell transport and uptake of ciprofloxacin, apparently via the lipid bilayer fusion mechanism, and the sustained inhibitory activity against LPS-induced IL-8 release, compared to CPFX.

Microniosomes for concurrent doxorubicin and iron oxide nanoparticles loading; preparation, characterization and cytotoxicity studies

The current work deals with developing a suitable drug delivery system of doxorubicin (DOX) for intraperitoneal chemotherapy using niosomes through formulating non-ionic surfactants consisting of Brij™ 52, span™ 60 and Solulan™ C24. Entrapping the magnetite nanoparticles in the hydrophilic parts of niosomes was accompanied with high-efficient DOX loading by the current novel remote-loading method. Cytotoxicity of the prepared formulations was evaluated in vitro against A549 and PC-12 cell lines using the colorimetric WST-1 assay test. The obtained results revealed that, the cytotoxicity of DOX increased up to 22% especially on A549 cells by the current delivery system.

Lipid somersaults: Uncovering the mechanisms of protein-mediated lipid flipping

Membrane lipids diffuse rapidly in the plane of the membrane but their ability to flip spontaneously across a membrane bilayer is hampered by a significant energy barrier. Thus spontaneous flip-flop of polar lipids across membranes is very slow, even though it must occur rapidly to support diverse aspects of cellular life. Here we discuss the mechanisms by which rapid flip-flop occurs, and what role lipid flipping plays in membrane homeostasis and cell growth. We focus on conceptual aspects, highlighting mechanistic insights from biochemical and in silico experiments, and the recent, ground-breaking identification of a number of lipid scramblases.

Long-Circulating Polymeric Nanovectors for Tumor-Selective Gene Delivery

Significant advances in the understanding of the genetic abnormalities that lead to the development, progression, and metastasis of neoplastic diseases has raised the promise of gene therapy as an approach to medical intervention. Most of the clinical protocols that have been approved in the United States for gene therapy have used the viral vectors because of the high efficiency of gene transfer. Conventional means of gene delivery using viral vectors, however, has undesirable side effects such as insertion of mutational viral gene into the host genome and development of replication competent viruses. Among non-viral gene delivery methods, polymeric nanoparticles are increasingly becoming popular as vectors of choice. The major limitation of these nanoparticles is poor transfection efficiency at the target site after systemic administration due to uptake by the cells of reticuloendothelial system (RES). In order to reduce the uptake by the cells of the RES and improve blood circulation time, these nanoparticles are coated with hydrophilic polymers such as poly(ethylene glycol) (PEG). This article reviews the use of such hydrophilic polymers employed for improving the circulation time of the nanocarriers. The mechanism of polymer coating and factors affecting the circulation time of these nanocarriers will be discussed. In addition to the long circulating property, modifications to improve the target specificity of the particles and the limitations of steric protection will be analyzed.

Tactic, reactive, and functional droplets outside of equilibrium

Droplets subject to non-equilibrium conditions can exhibit a range of biomimetic and “intelligent” behaviors.

Emerging delivery systems to reduce doxorubicin cardiotoxicity and improve therapeutic index: focus on liposomes

Anthracyclines are powerful anticancer agents and among the most important tools in the chemotherapy armamentarium of medical oncologists. They are approved for use in the treatment of a broad variety of solid and hematologic neoplasms. However, the usefulness of these agents, particularly doxorubicin, the most widely used anthracycline, is limited by considerable toxicity, especially damage to the cardiac muscle, which is cumulative and mostly irreversible, restricting extended use of this drug. In the last 30 years, extensive research with a variety of drug-delivery systems has attempted to overcome this limitation, with clinical success mostly confined to liposome formulations. Liposomal doxorubicin, and particularly pegylated liposomal doxorubicin, has shown significant pharmacologic advantages and an added clinical value over doxorubicin. Here, we review the mechanisms of action and toxicity of doxorubicin, and ways to reduce toxicity, with a focus on liposome-based drug-delivery systems.

Confocal Raman Microscopy for pH-Gradient Preconcentration and Quantitative Analyte Detection in Optically Trapped Phospholipid Vesicles

The ability of a vesicle membrane to preserve a pH gradient, while allowing for diffusion of neutral molecules across the phospholipid bilayer, can provide the isolation and preconcentration of ionizable compounds within the vesicle interior. In this work, confocal Raman microscopy is used to observe (in situ) the pH-gradient preconcentration of compounds into individual optically trapped vesicles that provide sub-femtoliter collectors for small-volume samples. The concentration of analyte accumulated in the vesicle interior is determined relative to a perchlorate-ion internal standard, preloaded into the vesicle along with a high-concentration buffer. As a guide to the experiments, a model for the transfer of analyte into the vesicle based on acid-base equilibria is developed to predict the concentration enrichment as a function of source-phase pH and analyte concentration. To test the concept, the accumulation of benzyldimethylamine (BDMA) was measured within individual 1 μm phospholipid vesicles having a stable initial pH that is 7 units lower than the source phase. For low analyte concentrations in the source phase (100 nM), a concentration enrichment into the vesicle interior of (5.2 ± 0.4) × 10(5) was observed, in agreement with the model predictions. Detection of BDMA from a 25 nM source-phase sample was demonstrated, a noteworthy result for an unenhanced Raman scattering measurement. The developed model accurately predicts the falloff of enrichment (and measurement sensitivity) at higher analyte concentrations, where the transfer of greater amounts of BDMA into the vesicle titrates the internal buffer and decreases the pH gradient. The predictable calibration response over 4 orders of magnitude in source-phase concentration makes it suitable for quantitative analysis of ionizable compounds from small-volume samples. The kinetics of analyte accumulation are relatively fast (∼15 min) and are consistent with the rate of transfer of a polar aromatic molecule across a gel-phase phospholipid membrane.

Membrane permeation of a peptide: it is better to be positive

A joint experimental and computational study investigates the translocation of a tryptophan molecule through a phospholipid membrane. Time dependent spectroscopy of the tryptophan side chain determines the rate of permeation into 150 nm phospholipid vesicles. Atomically detailed simulations are conducted to calculate the free energy profiles and the permeation coefficient. Different charging conditions of the peptide (positive, negative, or zwitterion) are considered. Both experiment and simulation reproduce the qualitative trend and suggest that the fastest permeation is when the tryptophan is positively charged. The permeation mechanism, which is revealed by molecular dynamics simulations, is of a translocation assisted by a local defect. The influence of long-range electrostatic interactions, such as the membrane dipole potential on the permeation process, is not significant.

Lipid nanoparticle delivery systems for siRNA-based therapeutics

Therapeutics based on small interfering RNA (siRNA) have a huge potential for the treatment of disease but requires sophisticated delivery systems for in vivo applications. Lipid nanoparticles (LNP) are proven delivery systems for conventional small molecule drugs with over eight approved LNP drugs. Experience gained in the clinical development of LNP for the delivery of small molecules, combined with an understanding of the physical properties of lipids, can be applied to design LNP systems for in vivo delivery of siRNA. In particular, cationic lipids are required to achieve efficient encapsulation of oligonucleotides; however, the presence of a charge on LNP systems can result in toxic side effects and rapid clearance from the circulation. To address these problems, we have developed ionizable cationic lipids with pKa values below 7 that allow oligonucleotide encapsulation at low pH (e.g., pH 4) and a relatively neutral surface at physiological pH. Further optimization of cationic lipids to achieve maximized endosomal destabilization following uptake has resulted in LNP siRNA systems that can silence genes in hepatocytes at doses as low as 0.005 mg siRNA/kg body weight in mouse models. These systems have been shown to be highly effective clinically, with promising results for the treatment of hypercholesterolemia and transthyretin-induced amyloidosis among others. More LNP siRNA therapeutics, targeting different tissues and diseases, are expected to become available in the near future.

Formation and characterization of supported lipid bilayers containing phosphatidylinositol-4,5-bisphosphate and cholesterol as functional surfaces

Solid-supported lipid bilayers (SLBs) mimicking a biological membrane are commonly used to investigate lipid-lipid or lipid-protein interactions. Simple binary or ternary lipid systems are well established, whereas more complex model membranes containing biologically important signaling lipids such as phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) and cholesterol have not been extensively described yet. Here we report the generation of such bilayers and their relevant biophysical properties and in particular the accessibility of PI(4,5)P2 for protein binding. Ternary mixtures of POPC with 20% cholesterol and either 3 or 5 mol % dioleoyl-phosphatidylinositol-4,5-bisphosphate were probed by employing the quartz crystal microbalance and atomic force microscopy. We show that these mixtures form homogeneous solid-supported bilayers that exhibit no intrinsic phase separation and are characterized by long-term stability (>8 h). Bilayers were formed in a pH-dependent manner and were characterized by the accessibility of PI(4,5)P2 on the SLB surface as shown by the interaction with the PI(4,5)P2 binding domain of the cortical membrane-cytoskeleton linker protein ezrin. A time-dependent reduction of PI(4,5)P2 levels in the upper leaflet of SLBs was observed, which could be effectively inhibited by the incorporation of a negatively charged lipid such as phosphatidylserine. Furthermore, quartz crystal microbalance measurements revealed that cholesterol affects bilayer adsorption to the solid support.

Physicochemical characterization of asulacrine towards the development of an anticancer liposomal formulation via active drug loading: stability, solubility, lipophilicity and ionization

To facilitate the development of a liposomal formulation for cancer therapy, the physicochemical properties of asulacrine (ASL), an anticancer drug candidate, were characterized. Nano-liposomes were prepared by thin-film hydration in conjugation with active drug loading using ammonium sulphate and post-insertion with Poloxamer 188. A stability-indicating HPLC assay with diode array detection was developed for the determination of ASL concentrations. The U-shaped pH-solubility profile in aqueous solutions, with a lowest solubility at pH 7.4 (0.843 μg/mL), indicated that ASL is an ampholyte, and dilution or neutralization of acidic drug solutions used in clinical trials with physiological fluids may cause drug precipitation. The basic pKa value measured by absorbance spectroscopy was 6.72. The logD value at pH 3.8 was 1.15 which increased to 3.24 as pH increased to 7.4. ASL was found to be the most stable in acidic conditions and degraded most rapidly in alkaline conditions. An extra-liposomal pH of 5.6 during drug loading was found to be optimal to achieve the highest drug loading (DL) of 4.76% and entrapment efficiency (EE) of 99.9%. At this pH, >90% of ASL was ionized conferring high drug solubility (1mg/mL) and acted as a reservoir of unionized ASL to be transported into liposomal cores. As a suspension the optimized liposomes showed great physicochemical stability for five months at 4°C. In summary, the obtained physicochemical parameters provided insightful information useful to maximise DL into the liposomes, and explain a tendency of drug precipitation of pH-solubilized formulations following intravenous infusion.

Formulation design and evaluation of liposomal sepantronium bromide (YM155), a small-molecule survivin suppressant, based on pharmacokinetic modeling and simulation

PURPOSE

Sepantronium bromide (YM155) is administered by 168-hour continuous infusions in clinical studies due to its time-dependent pharmacological efficacy and rapid elimination from plasma. To enable more convenient administration, i.e., bolus injections with low frequency, we prepared liposomal formulations of YM155 and evaluated their antitumor activities.

METHODS

A kinetic simulation model of liposomal YM155 to predict the free drug concentration in both tumor and plasma was developed. A liposomal formulation with the target drug release rate was prepared based on the simulation. Antitumor activities of the formulation were examined in various tumor xenograft mouse models. In addition, antitumor activities of liposomal formulations with different drug release rates were compared in order to confirm the validity of the simulation-based prediction.

RESULTS

Liposomal YM155 with the release half-life of 48 h was prepared as a promising formulation. This formulation showed significantly potent antitumor activities in tumor xenograft models by weekly bolus injections. Further studies demonstrated that this release rate was optimal for YM155 in terms of both efficacy and safety.

CONCLUSIONS

We successfully developed a liposomal formulation of YM155 that could substitute for long-term continuous infusion of the drug solution in clinical settings by being given as weekly bolus injections.

Application of pharmacokinetic and pharmacodynamic analysis to the development of liposomal formulations for oncology

Liposomal formulations of anticancer agents have been developed to prolong drug circulating lifetime, enhance anti-tumor efficacy by increasing tumor drug deposition, and reduce drug toxicity by avoiding critical normal tissues. Despite the clinical approval of numerous liposome-based chemotherapeutics, challenges remain in the development and clinical deployment of micro- and nano-particulate formulations, as well as combining these novel agents with conventional drugs and standard-of-care therapies. Factors requiring optimization include control of drug biodistribution, release rates of the encapsulated drug, and uptake by target cells. Quantitative mathematical modeling of formulation performance can provide an important tool for understanding drug transport, uptake, and disposition processes, as well as their role in therapeutic outcomes. This review identifies several relevant pharmacokinetic/pharmacodynamic models that incorporate key physical, biochemical, and physiological processes involved in delivery of oncology drugs by liposomal formulations. They capture observed data, lend insight into factors determining overall antitumor response, and in some cases, predict conditions for optimizing chemotherapy combinations that include nanoparticulate drug carriers.