Polysaccharide Nanoparticles for Efficient siRNA Targeting in Cancer Cells by Supramolecular pKa Shift

Synthetic Receptors for Early Detection and Treatment of Cancer

Over recent decades, synthetic macrocyclic compounds have attracted interest from the scientific community due to their ability to selectively and reversibly form complexes with a huge variety of guest moieties. These molecules have been studied within a wide range of sensing and other fields. Within this review, we will give an overview of the most common synthetic macrocyclic compounds including cyclodextrins, calixarenes, calixresorcinarenes, pillarenes and cucurbiturils. These species all display the ability to form a wide range of complexes. This makes these compounds suitable in the field of cancer detection since they can bind to either cancer cell surfaces or indeed to marker compounds for a wide variety of cancers. The formation of such complexes allows sensitive and selective detection and quantification of such guests. Many of these compounds also show potential for the detection and encapsulation of environmental carcinogens. Furthermore, many anti-cancer drugs, although effective in in vitro tests, are not suitable for use directly for cancer treatment due to low solubility, inherent instability in in vivo environments or an inability to be adsorbed by or transported to the required sites for treatment. The reversible encapsulation of these species in a macrocyclic compound can greatly improve their solubility, stability and transport to required sites where they can be released for maximum therapeutic effect. Within this review, we intend to present the use of these species both in cancer sensing and treatment. The various macrocyclic compound families will be described, along with brief descriptions of their synthesis and properties, with an outline of their use in cancer detection and usage as therapeutic agents. Their use in the sensing of environmental carcinogens as well as their potential utilisation in the clean-up of some of these species will also be discussed.

Reliable and accurate prediction of basic pK a values in nitrogen compounds: the pK a shift in supramolecular systems as a case study

This article presents a quantitative structure-activity relationship (QSAR) approach for predicting the acid dissociation constant (pKa ) of nitrogenous compounds, including those within supramolecular complexes based on cucurbiturils. The model combines low-cost quantum mechanical calculations with QSAR methodology and linear regressions to achieve accurate predictions for a broad range of nitrogen-containing compounds. The model was developed using a diverse dataset of 130 nitrogenous compounds and exhibits excellent predictive performance, with a high coefficient of determination (R2 ) of 0.9905, low standard error (s) of 0.3066, and high Fisher statistic (F) of 2142. The model outperforms existing methods, such as Chemaxon software and previous studies, in terms of accuracy and its ability to handle heterogeneous datasets. External validation on pharmaceutical ingredients, dyes, and supramolecular complexes based on cucurbiturils confirms the reliability of the model. To enhance usability, a script-like tool has been developed, providing a streamlined process for users to access the model. This study represents a significant advancement in pKa prediction, offering valuable insights for drug design and supramolecular system optimization.

An in situ protonation-activated supramolecular self-assembly for selective suppression of tumor growth

An in situ supramolecular self-assembly in the subcellular organelles could provide a new strategy to treat diseases. Herein, we report a protonation-activated in situ supramolecular self-assembly system in the lysosomes, which could destabilize the lysosome membrane, resulting in the selective suppression of cancer cells. In this system, pyridyl-functionalized tetraphenylethylene (TPE-Py) was protonated in the lysosomes of A549 lung cancer cells to form octahedron-like structures with cucurbit[8]uril (CB[8]), which impaired the integrity of the lysosome membrane, resulting in selective suppression of cancer cells. Moreover, its anticancer efficiency was also systematically evaluated in vivo, triggering the apoptosis of tumor tissues with ignorable effects on normal organs. Overall, the protonation-activated self-assembly in the lysosomes based on the host-guest complexation would provide a method for novel anti-cancer systems.

Recent Advances in Supramolecular-Macrocycle-Based Nanomaterials in Cancer Treatment

Cancer is a severe threat to human life. Recently, various therapeutic strategies, such as chemotherapy, photodynamic therapy, and combination therapy have been extensively applied in cancer treatment. However, the clinical benefits of these therapeutics still need improvement. In recent years, supramolecular chemistry based on host-guest interactions has attracted increasing attention in biomedical applications to address these issues. In this review, we present the properties of the major macrocyclic molecules and the stimulus-response strategies used for the controlled release of therapeutic agents. Finally, the applications of supramolecular-macrocycle-based nanomaterials in cancer therapy are reviewed, and the existing challenges and prospects are discussed.

Macrocyclic Supramolecular Assemblies Based on Hyaluronic Acid and Their Biological Applications

Hyaluronic acid (HA), which contains multiple carboxyl, hydroxyl, and acetylamino groups and is an agent that targets tumors, has drawn great attention in supramolecular diagnosis and treatment research. It can not only assemble directly with macrocyclic host-guest complexes through hydrogen bonding and electrostatic interactions but also can be modified with macrocyclic compounds or functional guest molecules by an amidation reaction and used for further assembly. Macrocycles play a main role in the construction of supramolecular drug carriers, targeted imaging agents, and hydrogels, such as cyclodextrins and cucurbit[n]urils, which can encapsulate photosensitizers, drugs, or other functional guest molecules via host-guest interactions. Therefore, the formed supramolecular assemblies can respond to various stimuli, such as enzymes, light, electricity, and magnetism for controlled drug delivery, enhance the luminescence intensity of the assembly, and improve drug loading capacity. In addition, the nanosupramolecular assembly formed with HA can also improve the biocompatibility of drugs, reduce drug toxicity and side effects, and enhance cell permeability; thus, the assembly has extensive application value in biomedical research. This Account mainly focuses on macrocyclic supramolecular assemblies based on HA, especially their biological applications and progress in the field, and these assemblies include (i) guest-modified HA, such as pyridinium-, adamantane-, peptide-, and other functional-group-modified HA, along with their cyclodextrin and cucurbit[n]uril assemblies; (ii) macrocycle-modified HA, such as HA modified with cyclodextrins and cucurbit[n]uril derivatives and their assembly with various guests; (iii) direct assembly between unmodified HA and cyclodextrin- or cucurbit[n]uril-based host-guest complexes. Particularly, we discussed the important role of macrocyclic host-guest complexes in HA-based supramolecular assembly, and the roles included improving the water solubility and efficacy of hydrophobic drugs, enhancing the luminescent intensity of assemblies, inducing room temperature phosphorescence and providing energy transfer systems, constructing multi-stimulus-responsive supramolecular assemblies, and in situ formation of hydrogels. Additionally, we believe that obtaining in-depth knowledge of these HA-based macrocyclic supramolecular assemblies and their biological applications encompasses many challenges regarding drug carriers, targeted imaging agents, wound healing, and biomedical soft materials and would certainly contribute to the rapid development of supramolecular diagnosis and treatment.

Carbohydrate anchored lipid nanoparticles

Nanotechnology has been a dynamic field for formulation scientists with multidisciplinary research being conducted worldwide. Advancements in development of functional nanosystems have led to evolution of breakthrough technologies. Lipidic nanosystems, in particular, are highly preferred owing to their non-immunogenic safety profiles along with a range of versatile intrinsic properties. Surface modification of lipid nanoparticles by anchoring carbohydrates to these systems is one such attractive drug delivery technology. Carbohydrates confer interesting properties to the nanosystems such as stealth, biostability, bioavailability, reduced toxicity due to decreased immunogenic response, targeting potential as well as ease of commercial availability. The carbohydrate anchored systems can be developed using methods such as adsorption, incorporation (nanoprecipitation or solvent displacement method), crosslinking and grafting. Current review provides a detailed overview of potential lipid based nanoparticulate systems with an emphasis on liposomes, solid lipid nanoparticles, nanostructures lipid carriers and micelles. Review further explores basics of surface modification, methods applied therein, advantages of carbohydrates as surface modifiers, their versatile applications, techniques for characterization of carbohydrate anchored systems and vital regulatory aspects concerned with these specialized systems.

Synthesis of PEGylated cationic curdlan derivatives with enhanced biocompatibility

Cationic polysaccharides have shown excellent ability of nucleic acids delivery. However, cationic curdlan derivatives with high degree of amination cause damage to the cell membrane and induce considerable cytotoxicity, limiting their in vivo application. Herein, we synthesized PEGylated 6-amino-6-deoxy-curdlan derivatives containing cleavable disulfide bonds. The resulting polymers (denote 6AC-2S PEGx) not only showed high affinity to siRNA but also exhibited significantly decreased cytotoxicity and hemolysis effect, while showing remarkable in vitro transfection efficiency. In vivo study demonstrated that 6AC-2S PEG40, which had a lower LD50 value than that of 6AC-100, did not cause liver damage, as the i.v. injection of 6AC-2S PEG40 to mouse did not increase serum level of ALT/AST. Furthermore, tissue distribution results showed that 6AC-2S PEG40 successfully delivered siRNA to liver, lung and spleen. Collectively, our data confirmed that PEGylation can increase the biocompatibility of cationic curdlan derivatives, which is a promising carrier for nucleic acid therapeutics.

Non-viral nanoparticles for RNA interference: Principles of design and practical guidelines

Ribonucleic acid interference (RNAi) is an innovative treatment strategy for a myriad of indications. Non-viral synthetic nanoparticles (NPs) have drawn extensive attention as vectors for RNAi due to their potential advantages, including improved safety, high delivery efficiency and economic feasibility. However, the complex natural process of RNAi and the susceptible nature of oligonucleotides render the NPs subject to particular design principles and requirements for practical fabrication. Here, we summarize the requirements and obstacles for fabricating non-viral nano-vectors for efficient RNAi. To address the delivery challenges, we discuss practical guidelines for materials selection and NP synthesis in order to maximize RNA encapsulation efficiency and protection against degradation, and to facilitate the cytosolic release of oligonucleotides. The current status of clinical translation of RNAi-based therapies and further perspectives for reducing the potential side effects are also reviewed.

Cucurbiturils in nucleic acids research

During the past ten years, the importance of cucurbiturils (CB[n]) as macrocyclic hosts in supramolecular assemblies with various types of natural and synthetic nucleic acids (NAs) has increased explosively. As a component of such systems, CB[n] macrocycles can play a wide spectrum of roles from drug and gene delivery vehicles to catalysts/inhibitors of biochemical reactions and even building blocks for NA-based materials. The aim of this highlight article is to describe the development of the CB[n] applications in nucleic acids research and to outline the current situation and perspectives of this fascinating synergistic combination of supramolecular chemistry of CB[n] and NAs.

High-Efficiency Synergistic Effect of Supramolecular Nanoparticles Based on Cyclodextrin Prodrug on Cancer Therapy

Novel cyclodextrin-prodrug supramolecular nanoparticles (NPs) with cooperative-enhancing cancer therapy were constructed from a reduction-sensitive disulfide bond-linked permethyl-β-cyclodextrin-camptothecin prodrug, water-soluble adamantane-porphyrin photosensitizer, and hyaluronic acid grafted by triphenylphosphine and β-cyclodextrin through an orthogonal host-guest recognition strategy, displaying uniform nanoparticles with a diameter around 100 nm as revealed by dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Compared with 293T normal cells, the supramolecular NPs could be easily taken up by mitochondria of A549 cancer cells, then release the active anticancer drug camptothecin (CPT) in situ via the cleavage of the disulfide bond by the overexpressed glutathione, and could initiate the effective singlet oxygen (¹O₂) generation by porphyrin under light irradiation, ultimately resulting in severe mitochondrial dysfunction and a rising cell death rate with increasing micromolar concentration of NPs. These multicomponent supramolecular nanoassemblies effectively combined the two-step synergistic chemo-photodynamic therapy of reduction-release of CPT and light-triggered ¹O₂ generation within cancer cells presenting the synergistic effect of supramolecular nanoparticles on cancer therapy, which provide a new approach for efficient step-by-step cancer therapy.

pH-controlled preferential binding of cucurbit[7]uril-coated iron-oxide nanoparticles to 6-mercaptonicotinic acid for fluorescent detection of cadmium ions in the solid state

A host-guest complex of 6-mercaptonicotinic acid (MNA) and cucurbit[7]uril (CB7) was prepared and conjugated to γ-Fe₃O₄ nanoparticles (NPs) to detect toxic cadmium ions in water as a solid-state sensor. The formation of an inclusion host-guest complex with CB7 was confirmed by UV-vis absorption and proton NMR spectroscopy. CB7 preferentially binds the protonated MNA form compared to the neutral form, demonstrated by a binding constant for the protonated form that is four orders of magnitude higher than that of the neutral form. An increase in the pK_a of MNA by 1.2 units was demonstrated after the addition of CB7, which further supports preferential binding between MNA and CB7. The NMR results confirm binding to cadmium via the carboxylic acid moiety. Stationary and time-resolved fluorescence results, in solution and in the solid state, indicate that cadmium and CB7 cause a blue shift in the MNA emission bands and extend its excited-state lifetime due to dissociation of the MNA dimer. In the solid state, switching the emission signals between Cd²⁺-MNA/CB7NPs (ON state) and MNAH⁺/CB7NPs (OFF state) was achieved by controlling the pH. An efficient, regenerable, and stable sensor device was fabricated for sensitive and selective detection of Cd²⁺ in contaminated water samples. Graphical abstract Regeneration of MNA/CB7 nanoparticles for the detection of cadmium ions in the solid state by a visible blue emission signal upon suppression of photoinduced electron transfer (PET).

Highly efficient photocontrolled targeted delivery of siRNA by a cyclodextrin-based supramolecular nanoassembly

A binary supramolecular nanoassembly that can efficiently load siRNA into A549 cancer cells and inhibited cell growth by photo-irradiation was fabricated using α-CD-modified hyaluronic acid and an azobenzene-modified diphenylalanine derivative.

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions

Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host-guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell-cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.

Acidity constant of pH indicators in the supramolecular systems studied by two CE-based methods compared using the RGB additive color model

Acid-base properties of methyl orange, bromocresol green, bromophenol blue, and bromothymol blue were thoroughly investigated in the past due to their application as colorimetric pH indicators. However, it is still unknown how these properties change upon the supramolecular host-guest interactions. Owing to the growing interest in using supramolecular host-guest interactions to reach expected modification of various physicochemical properties of guests, we decided to address this question in the present article. We estimated the shifts of pK_a values induced by diverse hosts (cyclodextrins, cucurbiturils, calixarenes, micelles, and serum albumin) and performed a thermodynamic analysis of the selected systems. To make a deeper insight, we confronted the aforementioned dyes with the other kinds of molecules studied by us in the past. In overall, the results obtained demonstrate a large multiplicity of possible pK_a behaviors, their poor predictability, and the existence of subtle structure-acidity relationships. In addition, we observed three thermodynamically different mechanisms of pK_a alteration. Therefore, more studies are needed to bring closer the promising perspective of a programmable acidity's tuning. Our methodology was based on capillary electrophoresis (CE) applied in two parallel variants: a classical method based on the fitting of a nonlinear function, and an alternative two-value method (TVM), which requires over twice less measurements to estimate pK_a. To identify the optimal approach for further studies, both methods were comprehensively compared and discussed based on the RGB additive color model, a user-friendly scale that integrates three primary aspects of an analytical method: analytical performance, green chemistry, and practicality.

Alkylation enhances biocompatibility and siRNA delivery efficiency of cationic curdlan nanoparticles

Cationic curdlan derivatives are a class of promising carriers for nucleic acid delivery including short interfering RNA (siRNA). While our previous studies demonstrated the siRNA delivery efficiency of aminated curdlan derivatives, the associated cytotoxicity issue remained unsolved. To investigate the effects of alkylation on the toxicity as well as the transfection efficiency, we conjugated short alkyl chains to 6-amino-6-deoxy-curdlan (6AC-100). The cytotoxicity of alkylated 6AC-100 derivatives (denote CuVa polymers) decreased with the increase of the degree of substitution (DS). CuVa3, with the highest DS, showed a 50% decreased cytotoxicity compared to 6AC-100 to 6AC-100 at a concentration of 140 μg/mL. The CuVa polymers readily complexed with siRNA to form nanoparticles, and induced significant knockdown of a disease related gene (STAT3) in mouse melanoma cell line B16. However, B16 cells transfected with siSTAT3 complexed to CuVa3 showed the highest phenotypic changes. These findings suggest that CuVa polymers have significantly enhanced biocompatibility and may be a promising delivery system for delivery of therapeutic siRNAs.

A Cucurbit[8]uril 2:2 Complex with a Negative pKa Shift

A viologen derivative carrying a benzimidazole group (V-P-I ²⁺ ; viologen-phenylene-imidazole V-P-I) can be dimerized in water using cucurbit[8]uril (CB[8]) in the form of a 2:2 complex resulting in a negative shift of the guest pK_a , by more than 1 pH unit, contrasting with the positive pK_a shift usually observed for CB-based complexes. Whereas 2:2 complex protonation is unclear by NMR, silver cations have been used for probing the accessibility of the imidazole groups of the 2:2 complexes. The protonation capacity of the buried imidazole groups is reduced, suggesting that CB[8] could trigger proton release upon 2:2 complex formation. The addition of CB[8] to a solution containing V-P- I³⁺ indeed released protons as monitored by pH-metry and visualized by a coloured indicator. This property was used to induce a host/guest swapping, accompanied by a proton transfer, between V-P-I ³⁺ ⋅CB[7] and a CB[8] complex of 1-methyl-4-(4-pyridyl)pyridinium. The origin of this negative pK_a shift is proposed to stand in an ideal charge state, and in the position of the two pH-responsive fragments inside the two CB[8] which, alike residues engulfed in proteins, favour the deprotonated form of the guest molecules. Such proton release triggered by a recognition event is reminiscent of several biological processes and may open new avenues toward bioinspired enzyme mimics catalyzing proton transfer or chemical reactions.

Boronate-crosslinked polysaccharide conjugates for pH-responsive and targeted drug delivery

A pH-responsive and targeted polysaccharide conjugate was fabricated from the boronate linkage of N-(2-aminoethyl)-gluconamide-grafted hyaluronic acid with anticancer drug bortezomib, which could exhibit targeted drug release behaviors at acidic pH and possess lower cytotoxicity and a higher inhibition effect toward cancer cells.

Contrasting interactions of DNA-intercalating dye acridine orange with hydroxypropyl derivatives of β-cyclodextrin and γ-cyclodextrin hosts

The present study demonstrates contrasting binding interactions of acridine orange dye with HPβCD and HPγCD hosts, always illustrating fluoresence “turn on” in the case of HPβCD and showing an interesting fluorescence “off/on switching” in the case of the HPγCD host.

Host-guest complexes of imazalil with cucurbit[8]uril and β-cyclodextrin and their effect on plant pathogenic fungi

We report the control of imazalil (IMZ) antifungal activity utilizing its non-covalent assembly with β-cyclodextrins (β-CD) and cucurbit[8]uril (CB8) macrocycles, as well as its stimuli-responsive disassembly with cadaverine. The NMR results are consistent with inclusion of a single IMZ molecule inside the cavities of either CB8 from its aromatic site or β-CD from its aliphatic end. Efficient complex formation with both host molecules and controlled released upon the addition of cadaverine is supported by NMR measurements. The stimuli-responsiveness of the same host-guest assemblies with cadaverine was validated against seven economically important plant pathogenic fungi which cause agriculturally important plant diseases across the globe. While loading the drug into macrocycles cavities suppressed its activity, subsequent adding of cadaverine efficiently restored it up. The results in the present paper enable researchers working in the area of mycology and plant pathology to inhibit or reduce the fungal growth on demand in order to control these economically important plant pathogenic fungi.

Supramolecular nanoparticles based on β-CD modified hyaluronic acid for DNA encapsulation and controlled release

Supramolecular nanoparticles composed of doubly positively charged adamantane (ADA2+) and β-CD modified hyaluronic acid (HACD) were constructed and the controlled binding and release of pDNA was realized.

An easy gene assembling strategy for light-promoted transfection by combining host-guest interaction of cucurbit[7]uril and gold nanoparticles

Cucurbit[7]uril (CB[7]), a representative member of the host family cucurbit[n]uril, can host-guest interact with many guest molecules such as adamantane, viologen and naphthalene derivatives. This host-guest interaction provides an easy strategy in gene vector assembling. Furthermore, CB[7] can self-assemble on gold nanospheres (AuNSs). Herein, the combination of CB[7] and AuNSs provides both advantages of host-guest interaction and photo-thermal effect of AuNSs. In this study, polyethyleneimine (PEI) and polyethylene glycol (PEG) were separately interacted with CB[7] via host-guest interaction. Then by assembling on AuNSs, PEI and PEG were combined together to condense DNA into polyplexes as well as enhance circulation stability of the polyplexes. These gene vectors were found to have high cellular uptake efficiency and low cytotoxicity. Furthermore, the well distributed AuNSs in the polyplexes could transform light into heat under light exposure because of the photo-thermal effect. This was found to effectively promote the entry of gene into cytoplasm and highly enhanced gene transfection efficiency.

Reversing the Cytotoxicity of Bile Acids by Supramolecular Encapsulation

Supramolecular encapsulation has been developed into a powerful tool in clearance of toxic substances and hazardous waste from living body and external environments. Herein we tested the special efficacy of tyramine-modified β-cyclodextrin (1) in inhibiting and reversing of the inherent cytotoxicity of deoxycholic acid (DCA). The decarboxylation from tyrosine to tyramine in 1 is crucial to the mutual electrostatic communication, ultimately leading to great enhancement in binding affinity and molecular selectivity toward bile acids. As a result, the DCA-mediated cytotoxicity could be largely eliminated by the biocompatible 1. Meanwhile, the excess DCA could be rapidly excreted by 1 via rat urinary clearance, thus facilitating the decrease of DCA concentration in blood. This study presents a proof of principle that the supramolecular encapsulation with functional cyclodextrin derivatives can efficiently modulate the cell progression and remove the cytotoxic DCA, which provides a practical approach to prevent or treat bile acid-involved diseases.

Camptothecin-Polysaccharide Co-assembly and Its Controlled Release

β-Cyclodextrin modified camptothecin (CPT-CD) was synthesized through esterification reaction and "click chemistry" to greatly improve the solubility of CPT in aqueous solution, and then, a supramolecular nanoparticle was constructed by strong noncovalent interaction between β-cyclodextrin and adamantane and amphiphilic interaction by simply mixing CPT-CD and adamantane modified hyaluronic acid (HA-ADA) together. The obtained nanoparticle had a hydrophilic HA shell, which could target and recognize HA receptors overexpressed on the surface of cancer cells, and a hydrophobic CPT core, which could protect CPT from hydrolyzation. The results of cytotoxicity experiments showed that the nanoparticle we have designed in this work exhibited similar anticancer activities to, but with much lower side effects than, the commercial chemotherapeutic drug CPT in vitro. We believe that this work might provide a strategy for improving the treatment performance of CPT in laboratory and clinical settings.

Nanosupramolecular assembly of amphiphilic guest mediated by cucurbituril for doxorubicin delivery

A binary supramolecular nanoparticle was constructed through the complexation of cucurbit[6]uril with an amphiphilic polyamine by macrocycle-assisted aggregation strategy, which exhibited controlled drug loading and release behaviours.