Clickable Cubosomes for Antibody-Free Drug Targeting and Imaging Applications

Liposomes to Cubosomes: The Evolution of Lipidic Nanocarriers and Their Cutting-Edge Biomedical Applications

Lipidic nanoparticles have undergone extensive research toward the exploration of their diverse therapeutic applications. Although several liposomal formulations are in the clinic (e.g., DOXIL) for cancer therapy, there are many challenges associated with traditional liposomes. To address these issues, modifications in liposomal structure and further functionalization are desirable, leading to the emergence of solid lipid nanoparticles and the more recent liquid lipid nanoparticles. In this context, "cubosomes", third-generation lipidic nanocarriers, have attracted significant attention due to their numerous advantages, including their porous structure, structural adaptability, high encapsulation efficiency resulting from their extensive internal surface area, enhanced stability, and biocompatibility. Cubosomes offer the potential for both enhanced cellular uptake and controlled release of encapsulated payloads. Beyond cancer therapy, cubosomes have demonstrated effectiveness in wound healing, antibacterial treatments, and various dermatological applications. In this review, the authors provide an overview of the evolution of lipidic nanocarriers, spanning from conventional liposomes to solid lipid nanoparticles, with a special emphasis on the development and application of cubosomes. Additionally, it delves into recent applications and preclinical trials associated with cubosome formulations, which could be of significant interest to readers from backgrounds in nanomedicine and clinicians.

pH-Dependent Lyotropic Liquid Crystalline Mesophase and Ionization Behavior of Phytantriol-Based Ionizable Lipid Nanoparticles

Self-assembled lipid nanoparticles (LNPs), serving as essential nanocarriers in recent COVID-19 mRNA vaccines, provide a stable and versatile platform for delivering a wide range of biological materials. Notably, LNPs with unique inverse mesostructures, such as cubosomes and hexosomes, are recognized as fusogenic nanocarriers in the drug delivery field. This study delves into the physicochemical properties, including size, lyotropic liquid crystalline mesophase, and apparent pKa of LNPs with various lipid components, consisting of two ionizable lipids (ALC-0315 and SM-102) used in commercial COVID-19 mRNA vaccines and a well-known inverse mesophase structure-forming helper lipid, phytantriol (PT). Two partial mesophase diagrams are generated for both ALC-0315/PT LNPs and SM-102/PT LNPs as a function of two factors, ionizable lipid ratio (α, 0-100 mol%) and pH condition (pH 3-11). Furthermore, the impact of different LNP stabilizers (Pluronic F127, Pluronic F108, and Tween 80) on their pH-dependent phase behavior is evaluated. The findings offer insights into the self-assembled mesostructure and ionization state of the studied LNPs with potentially enhanced endosomal escape ability. This research is relevant to developing innovative next-generation LNP systems for delivering various therapeutics.

Clicking in harmony: exploring the bio-orthogonal overlap in click chemistry

In the quest to scrutinize and modify biological systems, the global research community has continued to explore bio-orthogonal click reactions, a set of reactions exclusively targeting non-native molecules within biological systems. These methodologies have brought about a paradigm shift, demonstrating the feasibility of artificial chemical reactions occurring on cellular surfaces, in the cell cytosol, or within the body - an accomplishment challenging to achieve with the majority of conventional chemical reactions. This review delves into the principles of bio-orthogonal click chemistry, contrasting metal-catalyzed and metal-free reactions of bio-orthogonal nature. It comprehensively explores mechanistic details and applications, highlighting the versatility and potential of this methodology in diverse scientific contexts, from cell labelling to biosensing and polymer synthesis. Researchers globally continue to advance this powerful tool for precise and selective manipulation of biomolecules in complex biological systems.

A short review on the applicability and use of cubosomes as nanocarriers

Abstract

Cubosomes are nanostructured lipid-based particles that have gained significant attention in the field of drug delivery and nanomedicine. These unique structures consist of a three-dimensional cubic lattice formed by the self-assembly of lipid molecules. The lipids used to construct cubosomes are typically nonionic surfactants, such as monoolein, which possess both hydrophilic and hydrophobic regions, allowing them to form stable, water-dispersible nanoparticles. One of the key advantages of cubosomes is their ability to encapsulate and deliver hydrophobic as well as hydrophilic drugs. The hydrophobic regions of the lipid bilayers provide an ideal environment for incorporating lipophilic drugs, while the hydrophilic regions can encapsulate water-soluble drugs. This versatility makes cubosomes suitable for delivering a wide range of therapeutic agents, including small molecules, proteins, peptides, and nucleic acids. The unique structure of cubosomes also offers stability and controlled release benefits. The lipid bilayers provide a protective barrier, shielding the encapsulated drugs from degradation and improving their stability. Moreover, the cubic lattice arrangement enables the modulation of drug release kinetics by varying the lipid composition and surface modifications. This allows for the development of sustained or triggered drug release systems, enhancing therapeutic efficacy and reducing side effects. Furthermore, cubosomes can be easily modified with targeting ligands or surface modifications to achieve site-specific drug delivery, enhancing therapeutic selectivity and reducing off-target effects. In conclusion, cubosomes offer a versatile and promising platform for the delivery of therapeutic agents. In this manuscript, we will highlight some of these applications.

Graphical abstract

Affimer Tagged Cubosomes: Targeting of Carcinoembryonic Antigen Expressing Colorectal Cancer Cells Using In Vitro and In Vivo Models

Nanomedicines, while having been approved for cancer therapy, present many challenges such as low stability, rapid clearance, and nonspecificity leading to off-target toxicity. Cubosomes are porous lyotropic liquid crystalline nanoparticles that have shown great premise as drug delivery vehicles; however, their behavior in vivo is largely underexplored, hindering clinical translation. Here, we have engineered cubosomes based on the space group Im3m that are loaded with copper acetylacetonate as a model drug, and their surfaces are functionalized for the first time with Affimer proteins via copper-free click chemistry to actively target overexpressed carcinoembryonic antigens on LS174T colorectal cancer cells. Unlike nontargeted cubosomes, Affimer tagged cubosomes showed preferential accumulation in cancer cells compared to normal cells not only in vitro (2D monolayer cell culture and 3D spheroid models) but also in vivo in colorectal cancer mouse xenografts, while exhibiting low nonspecific absorption and toxicity in other vital organs. Cancerous spheroids had maximum cell death compared to noncancerous cells upon targeted delivery. Xenografts subjected to targeted drug-loaded cubosomes showed a 5-7-fold higher drug accumulation in the tumor tissue compared to the liver, kidneys, and other vital organs, a significant decrease in tumor growth, and an increased survival rate compared to the nontargeted group. This work encompasses the first thorough preclinical investigation of Affimer targeted cubosomes as a cancer therapeutic.

Cubosomes as an emerging platform for drug delivery: a state-of-the-art review

Lipid-based drug delivery nanoparticles, including non-lamellar type, mesophasic nanostructured materials of lyotropic liquid crystals (LLCs), have been a topic of interest for researchers for their applications in encapsulation of drugs...

Comprehensive and comparative studies on nanocytotoxicity of glyceryl monooleate- and phytantriol-based lipid liquid crystalline nanoparticles

Background

Lipid liquid crystalline nanoparticles (LLCNPs) emerge as a suitable system for drug and contrast agent delivery. In this regard due to their unique properties, they offer a solubility of a variety of active pharmaceutics with different polarities increasing their stability and the possibility of controlled delivery. Nevertheless, the most crucial aspect underlying the application of LLCNPs for drug or contrast agent delivery is the unequivocal assessment of their biocompatibility, including cytotoxicity, genotoxicity, and related aspects. Although studies regarding the cytotoxicity of LLCNPs prepared from various lipids and surfactants were conducted, the actual mechanism and its impact on the cells (both cancer and normal) are not entirely comprehended. Therefore, in this study, LLCNPs colloidal formulations were prepared from two most popular structure-forming lipids, i.e., glyceryl monooleate (GMO) and phytantriol (PHT) with different lipid content of 2 and 20 w/w%, and the surfactant Pluronic F-127 using the top-down approach for further comparison of their properties. Prepared formulations were subjected to physicochemical characterization and followed with in-depth biological characterization, which included cyto- and genotoxicity towards cervical cancer cells (HeLa) and human fibroblast cells (MSU 1.1), the evaluation of cytoskeleton integrity, intracellular reactive oxygen species (ROS) generation upon treatment with prepared LLCNPs and finally the identification of internalization pathways.

Results

Results denote the higher cytotoxicity of PHT-based nanoparticles on both cell lines on monolayers as well as cellular spheroids, what is in accordance with evaluation of ROS activity level and cytoskeleton integrity. Detected level of ROS in cells upon the treatment with LLCNPs indicates their insignificant contribution to the cellular redox balance for most concentrations, however distinct for GMO- and PHT-based LLCNPs. The disintegration of cytoskeleton after administration of LLCNPs implies the relation between LLCNPs and F-actin filaments. Additionally, the expression of four genes involved in DNA damage and important metabolic processes was analyzed, indicating concentration–dependent differences between PHT- and GMO-based LLCNPs.

Conclusions

Overall, GMO-based LLCNPs emerge as potentially more viable candidates for drug delivery systems as their impact on cells is not as deleterious as PHT-based as well as they were efficiently internalized by cell monolayers and 3D spheroids.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00913-5.

Bicontinuous cubic liquid crystalline phase nanoparticles stabilized by softwood hemicellulose

The colloidal stability of lipid based cubosomes, aqueous dispersion of inverse bicontinuous cubic phase, can be significantly increased by a stabilizer. The most commonly used stabilizers are non-ionic tri-block copolymers, poloxamers, which adsorb at the lipid-water interface and hence sterically stabilize the dispersion. One of the challenges with these synthetic polymers is the effect on the internal structure of the cubosomes and the potential toxicity when these nanoparticles are applied as nanomedicine platforms. The natural polysaccharide, softwood hemicellulose, has been proved to be an excellent stabilizer for oil-in-water emulsions, partially due to the presence of hydrophobic lignin in the extract which to some extent is associated to hemicellulose. Herein, we reported for the first time cubosomes stabilized by two types of softwood hemicelluloses, where one is extracted through thermomechanical pulping (TMP, low lignin content) and the other obtained from sodium-based sulfite liquor (SSL, high lignin content). The effect of the two hemicellulose samples on the colloidal stability and structure of monoolein-based cubosomes have been investigated via DLS, SAXS, AFM and cryo-TEM. The data obtained suggest that both types of the hemicelluloses stabilize monoolein (GMO) based cubosomes in water without significantly affecting their size, morphology and inner structure. SSL-extracted hemicellulose yields the most stable cubosomes, likely due to the higher content of lignin in comparison to TMP-stabilized ones. In addition, the stability of these particles was tested under physiological conditions relevant to possible application as drug carriers.

Understanding selectivity of metabolic labelling and click-targeting in multicellular environments as a route to tissue selective drug delivery

Cancer cells generally exhibit higher metabolic demands relative to that of normal tissue cells. This offers great possibilities to exploit metabolic glycoengineering in combination with bio-orthogonal chemistry reactions to achieve tumour site-targeted therapeutic delivery. This work addresses the selectivity of metabolic glycan labelling in diseased (i.e., cancer) versus normal cells grown in a multicellular environment. Dibenzocylooctyne (DBCO)-bearing acetylated-d-mannosamine (Ac4ManNDBCO) was synthesised to metabolically label three different types of cell lines originating from the human lung tissues: A549 adenocarcinomic alveolar basal epithelial cells, MeT5A non-cancerous mesothelial cells, and MRC5 non-cancerous fibroblasts. These cell lines displayed different labelling sensitivity, which trended with their doubling time in the following order: A549 ≈ MeT5A > MRC5. The higher metabolic labelling efficiency inherently led to a higher extent of specific binding and accumulation of the clickable N3-conjugated gold nanoparticles (N3-AuNps, core diameter = 30 nm) in the DBCO-glycan modified A549 and MeT5A cells, but to a less prominent effect in MRC5 cells. These findings demonstrate that relative rates of cell metabolism can be exploited using metabolic labelling to recruit nanotherapeutics whilst minimising non-specific targeting of surrounding tissues.

Phytantriol-Based Cubosome Formulation as an Antimicrobial against Lipopolysaccharide-Deficient Gram-Negative Bacteria

Treatment of multidrug-resistant (MDR) bacterial infections increasingly relies on last-line antibiotics, such as polymyxins, with the urgent need for discovery of new antimicrobials. Nanotechnology-based antimicrobials have gained significant importance to prevent the catastrophic emergence of MDR over the past decade. In this study, phytantriol-based nanoparticles, named cubosomes, were prepared and examined in vitro by minimum inhibitory concentration (MIC) and time-kill assays against Gram-negative bacteria: Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Phytantriol-based cubosomes were highly bactericidal against polymyxin-resistant, lipopolysaccharide (LPS)-deficient A. baumannii strains. Small-angle neutron scattering (SANS) was employed to understand the structural changes in biomimetic membranes that replicate the composition of these LPS-deficient strains upon treatment with cubosomes. Additionally, to further understand the membrane-cubosome interface, neutron reflectivity (NR) was used to investigate the interaction of cubosomes with model bacterial membranes on a solid support. These results reveal that cubosomes might be a new strategy for combating LPS-deficient Gram-negative pathogens.

Surface-modified nanoerythrosomes for potential optical imaging diagnostics

Nanoerythrosomes (NERs), vesicle-like nanoparticles derived from red blood cells, represent a new and interesting vector for therapeutic molecules and imaging probes, mainly thanks to their high stability and excellent biocompatibility. Aiming to present a proof-of-concept of the use of NERs as diagnostic tools for in vitro/in vivo imaging purposes, we report here several functionalization routes to decorate the surfaces of NERs derived from bovine blood with two different fluorophores: 7-amino-4-methylcumarin and dibenzocyclooctinecyanine5.5. Notably, the fluorophores were cross-linked to the NERs surface with glutaraldehyde and, in the case of dibenzocyclooctinecyanine5.5, also using a click-chemistry route, termed strain-promoted azide-alkyne cycloaddition. The physicochemical characterization highlighted the high stability of the NERs derivatives in physiological conditions. Furthermore, the loading efficiency of the fluorophores on the NERs surface was evaluated using both UV-Vis spectroscopy and fluorescence microscopy.

PM-IRRAS Study on the Effect of Phytantriol-Based Cubosomes on DMPC Bilayers as Model Lipid Membranes

The effect of phytantriol (PT)-based liquid-crystalline nanoparticles, cubosomes, on the lipid bilayer membranes has been investigated using the combined Langmuir-Blodgett/Langmuir-Schaefer (LB-LS) technique to form an h-1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) monolayer at the air-water interface and transfer the lipid bilayer onto the Au(111) substrate. Changes of the compression isotherms confirmed incorporation of cubosomes dispersed in the subphase into the h-DMPC monolayer at the air-water interface. The photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements of the gold electrode covered by the transferred DMPC bilayer showed for the first time how the incorporation of cubosome material affects the orientation and conformation of lipid molecules in the membrane. Exposure to cubosomes affected the packing of d₅₄-DMPC bilayers and introduced disorder of chains by increasing the contribution of gauche conformation. The decrease of the tilt angle of the acyl chains of adsorbed DMPC in the whole range of potentials applied to the gold electrode confirmed that incorporation of cubosome material results in a more tightly packed bilayer. The presence of phytantriol molecules within the d₆₃-DMPC matrix was confirmed by PM-IRRAS studies of the PT-related bands. The LB and PM-IRRAS studies demonstrated in a convincing way that PT-based cubosomes change the organization of model lipid layers leading to structural changes of the membranes which have to be taken into consideration when PT-cubosomes are employed as drug carriers.

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.

Non-Lamellar Lyotropic Liquid Crystalline Lipid Nanoparticles for the Next Generation of Nanomedicine

Nonlamellar lyotropic liquid crystalline (LLC) lipid nanomaterials have emerged as a promising class of advanced materials for the next generation of nanomedicine, comprising mainly of amphiphilic lipids and functional additives self-assembling into two- and three-dimensional, inverse hexagonal, and cubic nanostructures. In particular, the lyotropic liquid crystalline lipid nanoparticles (LCNPs) have received great interest as nanocarriers for a variety of hydrophobic and hydrophilic small molecule drugs, peptides, proteins, siRNAs, DNAs, and imaging agents. Within this space, there has been a tremendous amount of effort over the last two decades elucidating the self-assembly behavior and structure-function relationship of natural and synthetic lipid-based drug delivery vehicles in vitro, yet successful clinical translation remains sparse due to the lack of understanding of these materials in biological bodies. This review provides an overview of (1) the benefits and advantages of using LCNPs as drug delivery nanocarriers, (2) design principles for making LCNPs with desirable functionalities for drug delivery applications, (3) current understanding of the LLC material-biology interface illustrated by more than 50 in vivo, preclinical studies, and (4) current patenting and translation activities in a pharmaceutical context. Together with our perspectives and expert opinions, we anticipate that this review will guide future studies in developing LCNP-based drug delivery nanocarriers with the objective of translating them into a key player among nanoparticle platforms comprising the next generation of nanomedicine for disease therapy and diagnosis.

Cubosomes: The Next Generation of Smart Lipid Nanoparticles?

Cubosomes are highly stable nanoparticles formed from the lipid cubic phase and stabilized by a polymer based outer corona. Bicontinuous lipid cubic phases consist of a single lipid bilayer that forms a continuous periodic membrane lattice structure with pores formed by two interwoven water channels. Cubosome composition can be tuned to engineer pore sizes or include bioactive lipids, the polymer outer corona can be used for targeting and they are highly stable under physiological conditions. Compared to liposomes, the structure provides a significantly higher membrane surface area for loading of membrane proteins and small drug molecules. Owing to recent advances, they can be engineered in vitro in both bulk and nanoparticle formats with applications including drug delivery, membrane bioreactors, artificial cells, and biosensors. This review outlines recent advances in cubosome technology enabling their application and provides guidelines for the rational design of new systems for biomedical applications.

Citrem–phosphatidylcholine nano-self-assemblies: solubilization of bupivacaine and its role in triggering a colloidal transition from vesicles to cubosomes and hexosomes

In concentration- and lipid composition-dependent manners, bupivacaine triggers lamellar–nonlamellar phase transitions in citrem/soy phosphatidylcholine nanodispersions.

Nonlamellar liquid crystals: a new paradigm for the delivery of small molecules and bio-macromolecules

The aim of this article is to collate the recent developments in the field of drug delivery, medical therapeutics and diagnostics specifically involving the nonlamellar liquid crystalline (NLC) systems. This review highlights different NLC phases having cubic, hexagonal and sponge internal structures, and their application in the field of drug delivery, such as dose reduction, toxicity reduction and therapeutic efficacy enhancement either in the form of nanoparticles, colloidal dispersion or gels. In addition, application of NLC systems as vehicles for peptides, proteins and as a theranostic system in cancer and other disease conditions is also elaborated, which is a growing platform of interest. Overall, the present review gives us a complete outlook on applications of NLC systems in the field of medicine.

Application of click chemistry in nanoparticle modification and its targeted delivery

Background

Click chemistry is termed as a group of chemical reactions with favorable reaction rate and orthogonality. Recently, click chemistry is paving the way for novel innovations in biomedical science, and nanoparticle research is a representative example where click chemistry showed its promising potential. Challenging trials with nanoparticles has been reported based on click chemistry including copper-catalyzed cycloaddition, strain-promoted azide-alkyne cycloaddition, and inverse-demand Diels-Alder reaction.

Main body

Herein, we provide an update on recent application of click chemistry in nanoparticle research, particularly nanoparticle modification and its targeted delivery. In nanoparticle modification, click chemistry has been generally used to modify biological ligands after synthesizing nanoparticles without changing the function of nanoparticles. Also, click chemistry in vivo can enhance targeting ability of nanoparticles to disease site.

Conclusion

These applications in nanoparticle research were hard or impossible in case of traditional chemical reactions and demonstrating the great utility of click chemistry.