Selective modifications at the different positions of cyclodextrins: a review of strategies

Multifunctionality of cyclodextrin-based polymeric nanoparticulate delivery systems for chemotherapeutics, combination therapy, and theranostics

As cancer being the most difficult disease to treat, different kinds of medications and therapeutic approaches have been prominently developed by scientists. For certain families of drugs, such as immuno-therapeutics or antibody-drug conjugates, efficient delivery systems are required during administration to protect the drugs from chemical degradation or biological inactivation. Delivery systems with the ability to carry different therapeutics or diagnostic agents or both, hold promising potential to tackle the abnormalities behind cancer. In this context, this review provides updated insights on how cyclodextrin-based polymeric nanosystems have become an effective treatment approach against cancer. Cyclodextrins (CDs) are natural oligosaccharides that are famously exploited in pharmaceutical research due to their exceptional quality of entrapping water-insoluble molecules inside their hydrophobic core and providing enhanced solubility with the help of their hydrophilic exterior. Combining the properties of CDs with polymeric nanoparticles (PNPs) brings out excellent versatile and tunable profiles, thanks to the submicron-sized PNPs. By introducing the significance of CD as a delivery system, a collective discussion on different binding approaches and release mechanisms of CD-drug complexation, followed by their characterization studies has been done in this review. Further, in light of recent studies, the article majorly focuses on conveying how promoting CD to a polymeric and nanoscale elevates the multifunctional advantages against cancer that can be successfully applied in combination therapy and theranostics. Moreover, CD-based delivery systems including CALAA-01, CRLX101, and CRLX301, have demonstrated improved tumor targeting, reduced side effects, and prolonged drug release in preclinical studies and clinical trials.

Hydroxypropyl-Beta Cyclodextrin Barrier Prevents Respiratory Viral Infections: A Preclinical Study

The emergence and mutation of pathogenic viruses have been occurring at an unprecedented rate in recent decades. The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has developed into a global public health crisis due to extensive viral transmission. In situ RNA mapping has revealed angiotensin-converting enzyme 2 (ACE2) expression to be highest in the nose and lower in the lung, pointing to nasal susceptibility as a predominant route for infection and the cause of subsequent pulmonary effects. By blocking viral attachment and entry at the nasal airway using a cyclodextrin-based formulation, a preventative therapy can be developed to reduce viral infection at the site of entry. Here, we assess the safety and antiviral efficacy of cyclodextrin-based formulations. From these studies, hydroxypropyl beta-cyclodextrin (HPBCD) and hydroxypropyl gamma-cyclodextrin (HPGCD) were then further evaluated for antiviral effects using SARS-CoV-2 pseudotypes. Efficacy findings were confirmed with SARS-CoV-2 Delta variant infection of Calu-3 cells and using a K18-hACE2 murine model. Intranasal pre-treatment with HPBCD-based formulations reduced viral load and inflammatory signaling in the lung. In vitro efficacy studies were further conducted using lentiviruses, murine hepatitis virus (MHV), and influenza A virus subtype H1N1. These findings suggest HPBCD may be used as an agnostic barrier against transmissible pathogens, including but not limited to SARS-CoV-2.

Cyclodextrins and derivatives in drug delivery: New developments, relevant clinical trials, and advanced products

Cyclodextrins (CD) and derivatives are functional excipients that can improve the bioavailability of numerous drugs. Because of their drug solubility improving properties they are used in many pharmaceutical products. Furthermore, the stability of small molecular drugs can be improved by the incorporation in CDs and an unpleasant taste and smell can be masked. In addition to well-established CD derivatives including hydroxypropyl-β-CD, hydroxypropyl-γ-CD, methylated- β-CD and sulfobutylated- β-CD, there are promising new derivatives in development. In particular, CD-based polyrotaxanes exhibiting cellular uptake enhancing properties, CD-polymer conjugates providing sustained drug release, enhanced cellular uptake, and mucoadhesive properties, and thiolated CDs showing mucoadhesive, in situ gelling, as well as permeation and cellular uptake enhancing properties will likely result in innovative new drug delivery systems. Relevant clinical trials showed various new applications of CDs such as the formation of CD-based nanoparticles, stabilizing properties for protein drugs or the development of ready-to-use injection systems. Advanced products are making use of various benefical properties of CDs at the same time. Within this review we provide an overview on these recent developments and take an outlook on how this class of excipients will further shape the landscape of drug delivery.

Biopharmaceutical and nanotoxicological aspects of cyclodextrins for non-invasive topical treatments: A critical review

Cyclodextrins are nanometric cyclic oligosaccharides with amphiphilic characteristics that increase the stability of drugs in pharmaceutical forms and bioavailability, in addition to protecting them against oxidation and UV radiation. Some of their characteristics are low toxicity, biodegradability, and biocompatibility. They are divided into α-, β-, and γ-cyclodextrins, each with its own particularities. They can undergo surface modifications to improve their performances. Furthermore, their drug inclusion complexes can be made by various methods, including lyophilization, spray drying, magnetic stirring, kneading, and others. Cyclodextrins can solve several problems in drug stability when incorporated into dosage forms (including tablets, gels, films, nanoparticles, and suppositories) and allow better topical biological effects of drugs at administration sites such as skin, eyeballs, and oral, nasal, vaginal, and rectal cavities. However, as they are nanostructured systems and some of them can cause mild toxicity depending on the application site, they must be evaluated for their nanotoxicology and nanosafety aspects. Moreover, there is evidence that they can cause severe ototoxicity, killing cells from the ear canal even when applied by other administration routes. Therefore, they should be avoided in otologic administration and should have their permeation/penetration profiles and the in vivo hearing system integrity evaluated to certify that they will be safe and will not cause hearing loss.

Cyclodextrin Inclusion Complexes for Improved Drug Bioavailability and Activity: Synthetic and Analytical Aspects

Many active pharmaceutical ingredients show low oral bioavailability due to factors such as poor solubility and physical and chemical instability. The formation of inclusion complexes with cyclodextrins, as well as cyclodextrin-based polymers, nanosponges, and nanofibers, is a valuable tool to improve the oral bioavailability of many drugs. The microencapsulation process modifies key properties of the included drugs including volatility, dissolution rate, bioavailability, and bioactivity. In this context, we present relevant examples of the stabilization of labile drugs through the encapsulation in cyclodextrins. The formation of inclusion complexes with drugs belonging to class IV in the biopharmaceutical classification system as an effective solution to increase their bioavailability is also discussed. The stabilization and improvement in nutraceuticals used as food supplements, which often have low intestinal absorption due to their poor solubility, is also considered. Cyclodextrin-based nanofibers, which are polymer-free and can be generated using environmentally friendly technologies, lead to dramatic bioavailability enhancements. The synthesis of chemically modified cyclodextrins, polymers, and nanosponges based on cyclodextrins is discussed. Analytical techniques that allow the characterization and verification of the formation of true inclusion complexes are also considered, taking into account the differences in the procedures for the formation of inclusion complexes in solution and in the solid state.

Effect of Substitution Degree and Homogeneity on Cyclodextrin-Ligand Complex Stability: Comparison of Fenbufen and Fenoprofen Using CD and NMR Spectroscopy

The stability of host-guest complexes of two NSAID drugs with similar physicochemical properties, fenbufen and fenoprofen, was investigated by comparing induced circular dichroism and ¹H nuclear magnetic resonance methods using eight cyclodextrins of different degrees of substitution and isomeric purity as guest compounds. These cyclodextrins include native β-cyclodextrin (BCyD), 2,6-dimethyl-β-cyclodextrin 50 (DIMEB50), 80 (DIMEB80) and 95% (DIMEB95) isomerically pure versions, low-methylated CRYSMEB, randomly methylated β-cyclodextrin (RAMEB) and 4.5 and 6.3 average substitution grade hydroxypropyl-β-cyclodextrin (HPBCyD). The stability constants obtained by the two methods show good agreement in most cases. For fenbufen complexes, there is a clear trend that the stability constant increases with the degree of substitution while isomer purity has a smaller effect on the magnitude of stability constants. A significant difference was found in the case of DIMEB50 when compared to DIMEB80/DIMEB95, while the latter two are similar. In the fenbufen-fenoprofen comparison, fenbufen, with its linear axis, gives a more stable complex, while fenoprofen shows lower constants and poorly defined trends.

Cyclodextrins as eminent constituents in nanoarchitectonics for drug delivery systems

Cyclodextrins have been widely employed for drug delivery systems (DDSs) in which drugs are selectively delivered to a target site in the body. Recent interest has been focused on the construction of cyclodextrin-based nanoarchitectures that show sophisticated DDS functions. These nanoarchitectures are precisely fabricated based on three important features of cyclodextrins, namely (1) the preorganized three-dimensional molecular structure of nanometer size, (2) the easy chemical modification to introduce functional groups, and (3) the formation of dynamic inclusion complexes with various guests in water. With the use of photoirradiation, drugs are released from cyclodextrin-based nanoarchitectures at designated timing. Alternatively, therapeutic nucleic acids are stably protected in the nanoarchitectures and delivered to the target site. The efficient delivery of the CRISPR-Cas9 system for gene editing was also successful. Even more complicated nanoarchitectures can be designed for sophisticated DDSs. Cyclodextrin-based nanoarchitectures are highly promising for future applications in medicine, pharmaceutics, and other relevant fields.

Bioconjugated β-Cyclodextrin-Perfluorohexane Nanocone Clusters as Functional Nanoparticles for Nanoparticle-Mediated Histotripsy

Nanocone clusters (NCCs) are new-generation agents of nanoparticle-mediated histotripsy (NMH) recently developed to address the limitations of previously designed nanodroplets (NDs). NCCs can be obtained by simply mixing FDA-approved cyclodextrins (CD) and suitable perfluorocarbons (PFCs), which result in smaller size aggregates, detectable PFC amount, and more stable long-term storage since the obtained powder can be stored and redispersed as needed. Previous experimental and computational studies showed that NCCs consist of an organization of inclusion complexes of CD and PFC around free PFC droplets, and their aggregate behavior depends on the localization of PFC in the cavity and the water solubility of CD derivatives. It has been shown that β-cyclodextrin (βCD) and perfluorohexane (PFH) are ideal candidates for NCCs that can be isolated as a powder with high PFC content among various CD and PFC derivatives. This study focuses on the further development of the selected NCC composition to enhance the potential of NMH therapy while also enabling more detailed future experiments in vitro and in vivo. It is aimed to show the bioconjugation potential of NCCs through the example of the most commonly used functionalization methods such as targeting, PEGylation, and fluorescent labeling. For this purpose, βCD as a building block was monofunctionalized with groups such as azide, alkyne, and amine groups that allow for effective coupling reactions such as the "click" reaction and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) coupling. These monofunctional βCDs were used as building blocks of NCCs in the presence of PFH to obtain functional NCCs as precursors of bioconjugation. EPPT1 as a synthetic peptide specific to uMUC1 and folic acid (FA) as the most commonly used targeting agent along with PEGylation were successfully shown as bioconjugation examples. Lastly, fluorescently labeled NCCs were obtained via fluorescein isothiocyanate (FITC) and alkyne functional NCC reaction through propargyl amine and isothiocyanate group reaction. The obtained bioconjugates were tested in vitro to validate the conjugation, and the ability to lower the histotripsy cavitation threshold, which is necessary for NMH, was demonstrated for all bioconjugates. Overall, the results showed that all obtained bioconjugates successfully lowered the cavitation threshold pressure while also fulfilling the desired bioconjugation metrics to serve as improved tools to enhance NMH as a targeted noninvasive ablation method.

Synthesis of Mono-Amino Substituted γ-CD: Host–Guest Complexation and In Vitro Cytotoxicity Investigation

Cyclodextrins (CDs) are cyclic oligosaccharides which can trap hydrophobic molecules and improve their chemical, physical, and biological properties. γ-CD showed the highest aqueous solubility with the largest cavity diameter among other CD types. The current study describes a direct and easy method for nucleophilic mono-aminos to be substituted with γ-CD and tested for their ability to host the guest curcumin (CUR) as a hydrophobic drug model. The mass spectrometry and NMR analyses showed the successful synthesis of three amino-modified γ-CDs: mono-6-amino-6-deoxy-cyclodextrine (γ-CD-NH₂), mono-6-deoxy-6-ethanolamine-γ-cyclodextrine (γ-CD-NHCH₂CH₂OH), and mono-6-deoxy-6-aminoethylamino)-γ-cyclodextrin (γ-CD-NHCH₂CH₂NH₂). These three amino-modified γ-CDs were proven to be able to host CUR as native γ-CDs with formation constants equal to 6.70 ± 1.02, 5.85 ± 0.80, and 8.98 ± 0.90 mM⁻¹, respectively. Moreover, these amino-modified γ-CDs showed no significant toxicity against human dermal fibroblast cells. In conclusion, the current work describes a mono-substitution of amino-modified γ-CDs that can still host guests and showed low toxicity in human dermal fibroblasts cells. Therefore, the amino-modified γ-CDs can be used as a carrier host and be conjugated with a wide range of molecules for different biomedical applications, especially for active loading methods.

Cyclodextrins inclusion complex: Preparation methods, analytical techniques and food industry applications

This review offers a vision of the chemical behaviour of natural ingredients, synthetic drugs and other related compounds complexed using cyclodextrins. The review takes care of different sections related to i) the inclusion complexes formation with cyclodextrins, ii) the determination of the inclusion formation constant, iii) the most used methods to prepare host inclusion in the non-polar cavity of cyclodextrins and iv) the analytical techniques to evidence host inclusion. The review provides different literature that shows the application of cyclodextrins to improve physical, chemical, and biological characteristics of food compounds including solubility, stability and their elimination/masking. Moreover, the review also offers examples of commercial food/supplement products of cyclodextrins to indicate that cyclodextrins can be used to generate biotechnological substances with innovative properties and improve the development of food products.

Readily accessible azido-alkyne-functionalized monomers for the synthesis of cyclodextrin analogues using click chemistry

A set of linear and cyclic oligomers were synthesized starting from a suitable azido-alkyne monomer through click oligomerization. The synthesis of these monomers starting from bromobenzene features an enzymatic dihydroxylation...

Cyclodextrin-based adsorbents for the removal of pollutants from wastewater: a review

Water is a vital substance that constitutes biological structures and sustains life. However, water pollution is currently among the major environmental challenges and has attracted increasing study attention. How to handle contaminated water now mainly focuses on removing or reducing the pollutants from the wastewater. Cyclodextrin derivatives, possessing external hydrophilic and internal hydrophobic properties, have been recognized as new-generation adsorbents to exert positive effects on water pollution treatment. This article outlines recent contributions of cyclodextrin-based adsorbents on wastewater treatment, highlighting different adsorption mechanisms of cyclodextrin-based adsorbents under different influencing factors. The crosslinked and immobilized cyclodextrin-based adsorbents all displayed outstanding adsorption capacities. Particularly, according to specific pollutants including metal ions, organic chemicals, pesticides, and drugs in wastewater, this article has classified and organized various cyclodextrin-based adsorbents into tables, which could pave an intuitive shortcut for designing and developing efficient cyclodextrin-based adsorbents for targeted wastewater pollutants. Besides, this article specially discusses cost-effectiveness and regeneration performance of current cyclodextrin-based adsorbents. Finally, the challenges and future directions of cyclodextrin-based adsorbents are prospected in this article, which may shed substantial light on practical industrial applications of cyclodextrin-based adsorbents.

Smart stimuli-responsive drug delivery systems based on cyclodextrin: A review

Stimulated by researches in materials chemistry and medicine fields, drug delivery has entered a new stage of development. Drug delivery systems have been extensively studied according to the differences in the drug therapeutic environment such as pH, light, temperature, magnet, redox, enzymes, etc. Cyclodextrin is a smart tool that has been proven to be used in the preparation of drug delivery, and has become a new area of concern in recent years. In this review, we discuss recent research advances in smart stimuli-responsive cyclodextrin-based drug delivery. First, different stimuli-responsive drug delivery systems based on cyclodextrin are introduced and classified. Then, the characteristics of different types of stimuli-responsive drug delivery systems are described, and their applications are emphasized. Finally, current challenges and future development opportunities of smart stimuli-responsive drug delivery systems based on cyclodextrin are discussed.

Cyclodextrin as a magic switch in covalent and non-covalent anticancer drug release systems

Cancer has been a threat to human health, so its treatment is a huge challenge to the present medical field. One of commonly used methods is the controlled release of anticancer drug to reduce the dose for patients, increase the stability of drug treatment and minimize side effects. Cyclodextrin is a kind of cyclic oligosaccharide produced by amylase hydrolysis. Because cyclodextrin contains a cavity structure and active hydroxyl groups, it has a positive effect on the study of the controlled release of anticancer drugs. This article reviews the controlled release of current anticancer drugs based on cyclodextrins as a "flexible switch", and discusses the classification of different types of release systems, highlighting their role in cancer treatment. Moreover, the opportunities and challenges of cyclodextrin as a magic switch in the controlled release of anticancer drugs are discussed.

The classification and application of cyclodextrin polymers: a review

After introducing the concept of cyclodextrin polymers, their classification and applications have been summarized.