Lysosomal pH-inducible supramolecular dissociation of polyrotaxanes possessing acid-labile N-triphenylmethyl end groups and their therapeutic potential for Niemann-Pick type C disease

Synthesis of cyclodextrin-based polyrotaxanes and polycatenanes for supramolecular pharmaceutical sciences

Cyclodextrins (CDs) are essential in the pharmaceutical industry and have long been used as food and pharmaceutical additives. CD-based interlocked molecules, such as rotaxanes, polyrotaxanes, catenanes, and polycatenanes, have been synthesized and have attracted considerable attention in supramolecular chemistry. Among them, CD polyrotaxanes have been employed as slide-ring materials and biomaterials. CD polycatenanes are new materials; therefore, to date, no examples of applied research on CD polycatenanes have been reported. Consequently, we expect that applied research on CD polycatenanes will accelerate in the future. This review article summarizes the syntheses and structural analyses of CD polyrotaxanes and polycatenanes to facilitate their applications in the pharmaceutical industry. We believe that this review will promote further research on CD-based interlocked molecules.

Enhanced Tumor Targeting and Antitumor Activity of Methylated β-Cyclodextrin-Threaded Polyrotaxanes by Conjugating Cyclic RGD Peptides

We previously reported that acid-degradable methylated β-cyclodextrins (Me-β-CDs)-threaded polyrotaxanes (Me-PRXs) can induce autophagic cell death through endoplasmic reticulum (ER) stress-related autophagy, even in apoptosis-resistant cells. Hence, Me-PRXs show great potential as anticancer therapeutics. In this study, peptide-supermolecule conjugates were designed to achieve the targeted delivery of Me-PRX to malignant tumors. Arg-Gly-Asp peptides are well-known binding motifs of integrin αvβ3, which is overexpressed on angiogenic sites and many malignant tumors. The tumor-targeted cyclic Arg-Gly-Asp (cRGD) peptide was orthogonally post-modified to Me-PRX via click chemistry. Surface plasmon resonance (SPR) results indicated that cRGD-Me-PRX strongly binds to integrin αvβ3, whereas non-targeted cyclic Arg-Ala-Glu (cRGE) peptide conjugated to Me-PRX (cRGE-Me-PRX) failed to interact with integrins αvβ3. In vitro, cRGD-Me-PRX demonstrated enhanced cellular internalization and antitumor activity in 4T1 cells than that of unmodified Me-PRX and non-targeted cRGE-Me-PRX, due to its ability to recognize integrin αvβ3. Furthermore, cRGD-Me-PRX accumulated effectively in tumors, leading to antitumor effects, and exhibited excellent biocompatibility and safety in vivo. Therefore, cRGD conjugation to enhance selectivity for integrin αvβ3-positive cancer cells is a promising design strategy for Me-PRXs in antitumor therapy.

Lysosomal cholesterol overload in macrophages promotes liver fibrosis in a mouse model of NASH

Accumulation of lipotoxic lipids, such as free cholesterol, induces hepatocyte death and subsequent inflammation and fibrosis in the pathogenesis of nonalcoholic steatohepatitis (NASH). However, the underlying mechanisms remain unclear. We have previously reported that hepatocyte death locally induces phenotypic changes in the macrophages surrounding the corpse and remnant lipids, thereby promoting liver fibrosis in a murine model of NASH. Here, we demonstrated that lysosomal cholesterol overload triggers lysosomal dysfunction and profibrotic activation of macrophages during the development of NASH. β-cyclodextrin polyrotaxane (βCD-PRX), a unique supramolecule, is designed to elicit free cholesterol from lysosomes. Treatment with βCD-PRX ameliorated cholesterol accumulation and profibrotic activation of macrophages surrounding dead hepatocytes with cholesterol crystals, thereby suppressing liver fibrosis in a NASH model, without affecting the hepatic cholesterol levels. In vitro experiments revealed that cholesterol-induced lysosomal stress triggered profibrotic activation in macrophages predisposed to the steatotic microenvironment. This study provides evidence that dysregulated cholesterol metabolism in macrophages would be a novel mechanism of NASH.

Polymer-based drug delivery systems under investigation for enzyme replacement and other therapies of lysosomal storage disorders

Lysosomes play a central role in cellular homeostasis and alterations in this compartment associate with many diseases. The most studied example is that of lysosomal storage disorders (LSDs), a group of 60 + maladies due to genetic mutations affecting lysosomal components, mostly enzymes. This leads to aberrant intracellular storage of macromolecules, altering normal cell function and causing multiorgan syndromes, often fatal within the first years of life. Several treatment modalities are available for a dozen LSDs, mostly consisting of enzyme replacement therapy (ERT) strategies. Yet, poor biodistribution to main targets such as the central nervous system, musculoskeletal tissue, and others, as well as generation of blocking antibodies and adverse effects hinder effective LSD treatment. Drug delivery systems are being studied to surmount these obstacles, including polymeric constructs and nanoparticles that constitute the focus of this article. We provide an overview of the formulations being tested, the diseases they aim to treat, and the results observed from respective in vitro and in vivo studies. We also discuss the advantages and disadvantages of these strategies, the remaining gaps of knowledge regarding their performance, and important items to consider for their clinical translation. Overall, polymeric nanoconstructs hold considerable promise to advance treatment for LSDs.

Exploring Receptor Binding Affinities and Hepatic Cell Association of N-Acetyl-d-Galactosamine-Modified β-Cyclodextrin-Based Polyrotaxanes for Liver-Targeted Therapies

Acid-degradable polyrotaxanes (PRXs) containing threading β-cyclodextrins (β-CDs) are promising candidates for therapeutic applications of β-CDs in metabolic diseases with cholesterol overload or imbalance. To improve cellular uptake specificity and efficiency of PRXs in hepatocytes, N-acetyl-d-galactosamine (GalNAc)-modified PRXs were developed to facilitate asialoglycoprotein receptor (ASGR)-mediated endocytosis. Binding affinity studies revealed that the dissociation constant (K_D) values between recombinant ASGR and GalNAc-PRXs decreased with an increase in the number of modified GalNAc units. Additionally, the K_D values for GalNAc-PRXs were smaller than those for GalNAc-modified β-CD and amylose, suggesting that the PRX backbone structure improves the binding affinity with ASGR. However, the intracellular uptake levels of GalNAc-PRXs in HepG2 cells increased with a decrease in the number of modified GalNAc units, which was opposite to the trend observed in the binding affinity study. We found that GalNAc-PRXs had a large number of GalNAc units localized in recycling endosomes, resulting in the low intracellular uptake. The cholesterol-reducing abilities of GalNAc-PRXs were assessed using cholesterol-overloaded HepG2 cells. GalNAc-PRXs with a small number of GalNAc units were demonstrated to show superior cholesterol-reducing effects compared to previously designed acid-degradable PRX and clinically tested β-CD derivatives. Thus, we conclude that GalNAc modification is a promising molecular design for the therapeutic application of β-CD-threaded PRXs in various metabolic diseases with cholesterol overload or imbalance in the liver.

Supermolecule—Drug Conjugates Based on Acid-Degradable Polyrotaxanes for pH-Dependent Intracellular Release of Doxorubicin

Doxorubicin (DOX)-conjugated acid-degradable polyrotaxanes (PRXs) were designed as supramolecular drug carriers capable of releasing drugs in acidic cellular environments. Acid-degradable PRXs composed of α-cyclodextrin (α-CD) as a cyclic molecule, poly(ethylene glycol) (PEG) as a polymer axis, and N-triphenylmethyl (N-Trt) groups as an acid-labile stopper molecules were synthesized and DOX was conjugated with the threaded α-CDs in the PRXs. Because the acid-induced cleavage of N-Trt groups in PRXs leads to PRX dissociation, the DOX-modified α-CDs were released under acidic conditions (pH 5.0). The cytotoxicity of DOX-conjugated PRXs in colon-26 cells revealed significant cell death for DOX-conjugated PRXs after 48 h of treatment. Confocal laser scanning microscopy (CLSM) analysis revealed that the fluorescence signals derived from DOX-conjugated PRXs were observed in cellular nuclei after 48 h, suggesting that the DOX-modified α-CDs were released and accumulated in cellular nuclei. These results confirmed that acid-degradable PRXs can be utilized as drug carriers capable of releasing drug-modified α-CDs in acidic lysosomes and eliciting cytotoxicity. Overall, acid-degradable PRXs represent a promising supramolecular framework for the delivery and intracellular release of drug-modified α-CDs, and PRX–drug conjugates are expected to contribute to the development of pH-responsive drug carriers for cancer therapy.

Cyclodextrins applied to the treatment of lysosomal storage disorders

Cyclodextrin (CD), a cyclic oligosaccharide, is a pharmaceutical additive that improves the solubility of hydrophobic compounds. Recent research has focused on the potential active pharmaceutical abilities of CD. Lysosomal storage diseases are inherited metabolic diseases characterized by lysosomal dysfunction and abnormal lipid storage. Niemann-Pick disease type C (NPC) is caused by mutations in cholesterol transporter genes (NPC1, NPC2) and is characterized by cholesterol accumulation in lysosomes. A biocompatible cholesterol solubilizer 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was recently used in NPC patients for compassionate use and in clinical trials. HP-β-CD is an attractive drug candidate for NPC; however, its adverse effects, such as ototoxicity, should be solved. In this review, we discuss the current use of HP-β-CD in basic and clinical research and discuss alternative CD derivatives that may outperform HP-β-CD, which should be considered for clinical use. The potential of CD therapy for the treatment of other lysosomal storage diseases is also discussed.

Activated cholesterol metabolism is integral for innate macrophage responses by amplifying Myd88 signaling

Recent studies have shown that cellular metabolism is tightly linked to the regulation of immune cells. Here, we show that activation of cholesterol metabolism, involving cholesterol uptake, synthesis, and autophagy/lipophagy, is integral to innate immune responses in macrophages. In particular, cholesterol accumulation within endosomes and lysosomes is a hallmark of the cellular cholesterol dynamics elicited by Toll-like receptor 4 activation and is required for amplification of myeloid differentiation primary response 88 (Myd88) signaling. Mechanistically, Myd88 binds cholesterol via its CLR recognition/interaction amino acid consensus domain, which promotes the protein's self-oligomerization. Moreover, a novel supramolecular compound, polyrotaxane (PRX), inhibited Myd88‑dependent inflammatory macrophage activation by decreasing endolysosomal cholesterol via promotion of cholesterol trafficking and efflux. PRX activated liver X receptor, which led to upregulation of ATP binding cassette transporter A1, thereby promoting cholesterol efflux. PRX also inhibited atherogenesis in Ldlr-/- mice. In humans, cholesterol levels in circulating monocytes correlated positively with the severity of atherosclerosis. These findings demonstrate that dynamic changes in cholesterol metabolism are mechanistically linked to Myd88‑dependent inflammatory programs in macrophages and support the notion that cellular cholesterol metabolism is integral to innate activation of macrophages and is a potential therapeutic and diagnostic target for inflammatory diseases.

Effects of Hydroxypropyl-Beta-Cyclodextrin on Cultured Brain Endothelial Cells

The application of 2-hydroxypropyl-beta-cyclodextrin (HPBCD) in the treatment of the rare cholesterol and lipid storage disorder Niemann-Pick disease type C opened new perspectives in the development of an efficient therapy. Even if the systemic administration of HPBCD was found to be effective, its low permeability across the blood-brain barrier (BBB) limited the positive neurological effects. Nevertheless, the cellular interactions of HPBCD with brain capillary endothelial cells have not been investigated in detail. In this study, the cytotoxicity, permeability, and cellular internalization of HPBCD on primary rat and immortalized human (hCMEC/D3) brain capillary endothelial cells were investigated. HPBCD shows no cytotoxicity on endothelial cells up to 100 µM, measured by impedance kinetics. Using a fluorescent derivative of HPBCD (FITC-HPBCD) the permeability measurements reveal that on an in vitro triple co-culture BBB model, FITC-HPBCD has low permeability, 0.50 × 10^-6 cm/s, while on hCMEC/D3 cell layers, the permeability is higher, 1.86 × 10^-5 cm/s. FITC-HPBCD enters brain capillary endothelial cells, is detected in cytoplasmic vesicles and rarely localized in lysosomes. The cellular internalization of HPBCD at the BBB can help to develop new strategies for improved HPBCD effects after systemic administration.

Mitigating RANKL-induced cholesterol overload in macrophages with β-cyclodextrin-threaded polyrotaxanes suppresses osteoclastogenesis

Free cholesterol acts as an endogenous agonist for estrogen-related receptor α (ERRα), a nuclear receptor that regulates osteoclastogenesis. Because stimulation of macrophages with receptor activator of nuclear factor κB ligand (RANKL) induces an overload of free cholesterol and activates ERRα, we hypothesized that direct removal of cellular cholesterol would suppress osteoclastogenesis. In this study, the effect of 2-hydroxypropyl β-cyclodextrin (HP-β-CD), a highly water-soluble cyclic glucopyranose, and β-CD-threaded polyrotaxanes (PRXs), supramolecular polymers designed to release threaded β-CDs in acidic lysosomes, on RANKL-induced cholesterol overload and osteoclast differentiation of murine macrophage-like RAW264.7 cells were investigated. PRXs suppressed RANKL-induced cholesterol overload. Additionally, RANKL-induced osteoclast differentiation of RAW264.7 cells was inhibited by PRXs. In contrast, HP-β-CD did not reduce cholesterol levels or inhibit osteoclast differentiation in RAW264.7 cells. Gene expression analysis of osteoclast markers suggested that PRXs suppress only the early stage of osteoclast differentiation, as PRXs cannot be internalized into multinucleated osteoclasts. However, modification of PRXs with cell-penetrating peptides facilitated their cellular uptake into multinucleated osteoclasts and inhibited osteoclast maturation. Thus, PRXs are promising candidates for inhibiting osteoclast differentiation by suppressing cholesterol overload and may be useful for treating osteoporosis or other bone defects caused by the overactivity of osteoclasts.

Cografting of Zwitterionic Sulfobetaines and Cationic Amines on β-Cyclodextrin-Threaded Polyrotaxanes Facilitates Cellular Association and Tissue Accumulation with High Biocompatibility

β-Cyclodextrins (β-CDs) and β-CD-containing polymers have attracted considerable attention as potential candidates for the treatment of cholesterol-related metabolic and intractable diseases. We have advocated the use of β-CD-threaded acid-degradable polyrotaxanes (PRXs) as intracellular delivery carriers for β-CDs. As unmodified PRXs are insoluble in aqueous solutions, chemical modification of PRXs is an essential process to improve their solubility and impart novel functionalities. In this study, we investigated the effect of the modification of zwitterionic sulfobetaines on PRXs due to their excellent solubility, biocompatibility, and bioinert properties. Sulfobetaine-modified PRXs were synthesized by converting the tertiary amino groups of precursor 2-(N,N-dimethylamino)ethyl carbamate-modified PRXs (DMAE-PRXs) using 1,3-propanesultone. The resulting sulfobetaine-modified PRXs showed high solubility in aqueous solutions and no cytotoxicity, while their intracellular uptake levels were low. To further improve this system, we designed PRXs cografted with zwitterionic sulfobetaine and cationic DMAE groups via partial betainization of the DMAE groups. Consequently, the interaction with proteins, intracellular uptake levels, and liver accumulation of partly betainized PRXs were found to be higher than those of completely betainized PRXs. Additionally, partly betainized PRXs showed no toxicity in vitro or in vivo despite the presence of residual cationic DMAE groups. Furthermore, partly betainized PRXs ameliorated the abnormal free cholesterol accumulation in Niemann-Pick type C disease patient-derived cells at lower concentrations than β-CD derivatives and previously designed PRXs. Overall, the cografting of sulfobetaines and amines on PRXs is a promising chemical modification for therapeutic applications due to the high cholesterol-reducing ability and biocompatibility of such modified PRXs. In addition, modification with both zwitterionic and cationic groups can be used for the design of various polymeric materials exhibiting both bioinert and bioactive characteristics.

Calcium phosphate-adsorbable and acid-degradable carboxylated polyrotaxane consisting of β-cyclodextrins suppresses osteoclast resorptive activity

Recently, the potential of β-cyclodextrin-thread acid-degradable polyrotaxane (AdPRX) has been emphasized as a therapeutic agent for cholesterol-related metabolic disorders. In this study, we investigated whether carboxymethyl carbamate-modified AdPRX (CMC-AdPRX) can be used for adsorption to calcium phosphate to treat bone diseases. We first synthesized CMC-AdPRX and used it to coat the calcium phosphate plate. RAW264.7 cells were then differentiated into osteoclasts via a receptor activator of nuclear factor-κB ligand, and the number of osteoclasts and the area of absorption lacunae were determined. The number of tartrate-resistant acid phosphatase-positive multinucleated cells was reduced on the CMC-AdPRX-coated plate. The area of the absorption lacunae was smaller with CMC-AdPRX than with AdPRX, which was not carboxy-modified. Our results suggest that CMC-AdPRX can adsorb to calcium phosphate and act on differentiated osteoclasts to suppress their functional expression.

A bifunctional sensitive fluorescence probe based on pyrene for the detection of pH and viscosity in lysosome

Lysosome is one of the important organelles in intracellular transport. It plays a significant role in the physiological process. The lysosomal microenvironment affects the functions of lysosome. When the original acidic environment of lysozyme is destroyed or the fluid viscosity increases gradually, various diseases are easily induced. However, most fluorescent probes can only locate in cells. The fewer probes of subcellular organelles were found and their functions are often single. So, it is of great importance to design multifunctional fluorescent probes with the capable of localizing in lysosome. In this study, a novel lysosome probe, 4-(4-Pyren-1-yl-but-3-enyl)-morpholine (PIM), was synthesized using pyrene as a fluorescent group and morpholine as a target group. The introduction of morpholine group made PIM localize in lysosome with high selectivity. The fluorescence will be enhanced with the increased viscosity because of restricting the rotation of CC bond and CN in PIM, and the detecting linear range is from 4.05 cP to 393.48 cP, which qualified the requirement of the viscosity monitoring in body. Meanwhile, the fluorescence intensity of PIM declines with the decrease of pH because the Schiff base of PIM is hydrolyzed, which was affirmed by ¹H NMR, LC-MS and fluorescence spectra. Moreover, cell imaging and MTT experiments confirmed that PIM as a novel bifunctional probe can be used to detect pH and endogenous viscosity in lysosome.

Terminal Structure of Triethylene Glycol-Tethered Chains on β-Cyclodextrin-Threaded Polyrotaxanes Dominates Temperature Responsivity and Biointeractions

Pharmacological and biomedical applications of cyclodextrin (CD)-threaded polyrotaxanes (PRXs) have gained increasing attention. We had previously investigated the therapeutic effects of oligo(ethylene glycol) (OEG)-modified β-CD PRXs in congenital metabolic disorders. Although the chemical modification of PRXs is crucial for these applications, the influences of the chemical structure of OEG modified on PRXs were not completely understood. The current study focuses on the terminal group structures of triethylene glycol (TEG)-tethered chains, wherein three series of TEG-tethered PRXs (TEG-PRXs) with various TEG terminal group structures (hydroxy, methoxy, and ethoxy) were synthesized to investigate their physicochemical properties and biointeractions. The methoxy and ethoxy-terminated TEG-PRXs exhibited temperature-dependent phase transitions in phosphate buffer saline and formed coacervate droplets above their cloud points. A comprehensive analysis revealed that the hydrophobicity of the terminal group structures of the TEG-tethered chains played a dominant role in exhibiting temperature-dependent phase transition. Furthermore, the hydrophobicity of the terminal group structures of TEG-tethered chains on PRXs also affected the interactions with lipids and proteins, with the hydrophobic ethoxy-terminated TEG-tethered chains showing the highest interactions. However, in normal human skin fibroblasts, the moderately hydrophobic methoxy-terminated TEG-modified PRXs showed the highest intracellular uptake levels. As a result, we concluded that methoxy-terminated TEG is a suitable chemical modification for the biomedical applications of PRXs due to the negligible temperature responsivity around physiological temperature and significant intracellular uptake levels. The findings of this study shall contribute significantly to the rational design of PRXs and CD-based materials for future pharmacological and biomedical applications.

Weakly acidic carboxy group-grafted β-cyclodextrin-threaded acid-degradable polyrotaxanes for modulating protein interaction and cellular internalization

To improve the therapeutic potential of β-cyclodextrin (β-CD)-threaded acid-degradable polyrotaxanes (β-CD PRXs) in cholesterol-related metabolic disorders, we investigated the effect of carboxylation of β-CD PRXs on intracellular uptake. In this study, we established a synthetic method for the modification of carboxylalkyl carbamates on β-CD PRXs without degradation and synthesized three series of carboxyalkyl carbamate group-modified β-CD PRXs with different alkyl spacer lengths. The modification of carboxymethyl carbamate (CMC), carboxyethyl carbamate (CEC), and carboxypropyl carbamate (CPC) on the β-CD PRXs slightly reduced the interaction of the PRXs with the lipid layer model compared with the modification of 2-(2-hydroxyethoxy)ethyl carbamate (HEE-PRX), which was used in our previous studies. However, all the carboxylated β-CD PRXs showed a significantly stronger interaction with a protein model compared with HEE-PRX. The carboxylated β-CD PRXs showed significantly high intracellular uptake, through macrophage scavenger receptor A (MSR-A)-mediated endocytosis, in MSR-A-positive RAW 264.7 cells compared with HEE-PRX. Interestingly, the carboxylated β-CD PRXs also showed significantly higher intracellular uptake even in MSR-A-negative cells compared with HEE-PRX. Carboxylated β-CD PRXs are considered to strongly interact with other membrane proteins, resulting in high intracellular uptake. The length of the alkyl spacer affected the intracellular uptake levels of carboxylated PRXs, however, this relationship was varied for different cell types. Furthermore, none of the carboxylated β-CD PRXs exhibited cytotoxicity in the RAW 264.7 and NIH/3T3 cells. Altogether, carboxylation of β-CD PRXs is a promising chemical modification approach for their therapeutic application because carboxylated β-CD PRXs exhibit high cellular internalization efficiency in MSR-A-negative cells and negligible toxicity.

An antibody-supermolecule conjugate for tumor-specific targeting of tumoricidal methylated β-cyclodextrin-threaded polyrotaxanes

We previously found that acid-labile polyrotaxane containing methylated β-cyclodextrin (Me-PRX) induces endoplasmic reticulum (ER) stress-related autophagy and autophagic cell death. Me-PRX-induced autophagic cell death occurs even in apoptosis-resistant cells; tumor-targeted Me-PRX delivery could thus be an effective cancer treatment approach. In this study, antibody-supermolecule conjugates, consisting of a tumor-specific antibody and Me-PRX, were designed to achieve a tumor-specific delivery of Me-PRX. Trastuzumab, a monoclonal antibody against HER2 expressed in various malignant tumors, was selected as a tumor-targeting antibody, and phenyl maleimide group-modified Me-PRX (Mal-Me-PRX) was conjugated to the cysteine residue of the reduced Trastuzumab to obtain a Trastuzumab-Me-PRX conjugate (Tras-Me-PRX). The cellular association of Tras-Me-PRX to HER2-expressing tumor cells was remarkably greater than that of unmodified Me-PRX. Moreover, Tras-Me-PRX effectively reduced the viability of HER2-expressing tumor cells at a lower concentration compared to the unmodified Me-PRX. In conclusion, antibody-Me-PRX conjugates are regarded as a new class of antibody-drug conjugates that would contribute to the chemotherapy of cancers.

Specific Modification with TPGS and Drug Loading of Cyclodextrin Polyrotaxanes and the Enhanced Antitumor Activity Study in Vitro and in Vivo

A kind of specific cyclodextrin polyrotaxanes (PRs) drug delivery system was developed for an effective drug delivery and enhancing antitumor effect. In this work, we prepared the PR by using α-CD derivatives and dicarboxyl-PEG (M_n = 4200) self-assembling and end-capping with β-CD derivatives. Then, we chose d-a-Tocopheryl polyethylene glycol 1000 succinate (TPGS) with an antitumor effect to modify the PR. The modified PRs have a certain anticancer effect and can assist the anticancer drug to treat cancer. The 10-hydroxycamptothecin (HCPT) was combined to the specific PRs by covalent bonds to prepare drug-loaded specificity PRs (PR-TPGS-HCPT). The enhanced antitumor activities of PR-TPGS-HCPT were studied by in vitro and in vivo experiments, and the experiment results proved that the TPGS could effectively assist the drug to treat cancer and prolong the lifetime of the tumor-bearing mice. Therefore, this research provides a promising drug-loaded material for the cancer treatment and the specific water-soluble PRs will have potential applications in the biomedical field.

Doxorubicin-Loaded Delta Inulin Conjugates for Controlled and Targeted Drug Delivery: Development, Characterization, and In Vitro Evaluation

Delta inulin, also known as microparticulate inulin (MPI), was modified by covalently attaching doxorubicin to its nanostructured surface for use as a targeted drug delivery vehicle. MPI is readily endocytosed by monocytes, macrophages, and dendritic cells and in this study, we sought to utilize this property to develop a system to target anti-cancer drugs to lymphoid organs. We investigated, therefore, whether MPI could be used as a vehicle to deliver doxorubicin selectively, thereby reducing the toxicity of this antibiotic anthracycline drug. Doxorubicin was covalently attached to the surface of MPI using an acid–labile linkage to enable pH-controlled release. The MPI-doxorubicin conjugate was characterized using FTIR and SEM, confirming covalent attachment and indicating doxorubicin coupling had no obvious impact on the physical nanostructure, integrity, and cellular uptake of the MPI particles. To simulate the stability of the MPI-doxorubicin in vivo, it was stored in artificial lysosomal fluid (ALF, pH 4.5). Although the MPI-doxorubicin particles were still visible after 165 days in ALF, 53% of glycosidic bonds in the inulin particles were hydrolyzed within 12 days in ALF, reflected by the release of free glucose into solution. By contrast, the fructosidic bonds were much more stable. Drug release studies of the MPI-doxorubicin in vitro, demonstrated a successful pH-dependent controlled release effect. Confocal laser scanning microscopy studies and flow cytometric analysis confirmed that when incubated with live cells, MPI-doxorubicin was efficiently internalized by immune cells. An assay of cell metabolic activity demonstrated that the MPI carrier alone had no toxic effects on RAW 264.7 murine monocyte/macrophage-like cells, but exhibited anti-cancer effects against HCT116 human colon cancer cells. MPI-doxorubicin had a greater anti-cancer cell effect than free doxorubicin, particularly when at lower concentrations, suggesting a drug-sparing effect. This study establishes that MPI can be successfully modified with doxorubicin for chemotherapeutic drug delivery.

[Intracellularly Degradable Polyrotaxanes for Therapeutic Applications]

Recently, the application of β-cyclodextrins (β-CDs) as therapeutic agents has received considerable attention. β-CDs have been reported to have therapeutic effects on various diseases, such as Niemann-Pick type C (NPC) disease, a family of lysosomal storage disorders characterized by the lysosomal accumulation of cholesterol. To further improve the therapeutic efficacy of β-CDs, the use of β-CD-threaded polyrotaxanes (PRXs) has been proposed as a carrier of β-CDs for NPC disease. PRXs are supramolecular polymers composed of many CDs threaded onto a linear polymer chain and capped with bulky stopper molecules. In this review, the design of PRXs and their therapeutic applications are described. To achieve the intracellular release of threaded β-CDs from PRXs, stimuli-cleavable linkers are introduced in an axle polymer of PRXs. The stimuli-labile PRXs can dissociate into their constituent molecules by a cleavage reaction under specific stimuli, such as pH reduction in lysosomes. The release of the threaded β-CDs from acid-labile PRXs in acidic lysosomes leads to the formation of an inclusion complex with the cholesterol that has accumulated in NPC disease patient-derived fibroblasts, thus promoting the extracellular excretion of the excess cholesterol. Moreover, the administration of PRXs to a mouse model of NPC disease caused significant suppression of the tissue accumulation of cholesterol, resulting in a prolonged life span in the model mice. Additionally, the induction of autophagy by the methylated β-CD-threaded PRXs (Me-PRXs) is described. Accordingly, the stimuli-labile PRXs are expected to be effective carriers of CDs for therapeutic applications.

Self-assembly as a key player for materials nanoarchitectonics

The development of science and technology of advanced materials using nanoscale units can be conducted by a novel concept involving combination of nanotechnology methodology with various research disciplines, especially supramolecular chemistry. The novel concept is called 'nanoarchitectonics' where self-assembly processes are crucial in many cases involving a wide range of component materials. This review of self-assembly processes re-examines recent progress in materials nanoarchitectonics. It is composed of three main sections: (1) the first short section describes typical examples of self-assembly research to outline the matters discussed in this review; (2) the second section summarizes self-assemblies at interfaces from general viewpoints; and (3) the final section is focused on self-assembly processes at interfaces. The examples presented demonstrate the strikingly wide range of possibilities and future potential of self-assembly processes and their important contribution to materials nanoarchitectonics. The research examples described in this review cover variously structured objects including molecular machines, molecular receptors, molecular pliers, molecular rotors, nanoparticles, nanosheets, nanotubes, nanowires, nanoflakes, nanocubes, nanodisks, nanoring, block copolymers, hyperbranched polymers, supramolecular polymers, supramolecular gels, liquid crystals, Langmuir monolayers, Langmuir-Blodgett films, self-assembled monolayers, thin films, layer-by-layer structures, breath figure motif structures, two-dimensional molecular patterns, fullerene crystals, metal-organic frameworks, coordination polymers, coordination capsules, porous carbon spheres, mesoporous materials, polynuclear catalysts, DNA origamis, transmembrane channels, peptide conjugates, and vesicles, as well as functional materials for sensing, surface-enhanced Raman spectroscopy, photovoltaics, charge transport, excitation energy transfer, light-harvesting, photocatalysts, field effect transistors, logic gates, organic semiconductors, thin-film-based devices, drug delivery, cell culture, supramolecular differentiation, molecular recognition, molecular tuning, and hand-operating (hand-operated) nanotechnology.

Mannosylated Polyrotaxanes for Increasing Cellular Uptake Efficiency in Macrophages through Receptor-Mediated Endocytosis

Macrophages play an important role in the regulation of inflammation and immune response as well as the pathogenesis of chronic inflammatory diseases and cancer. Therefore, targeted delivery of therapeutic reagents to macrophages is an effective method for treatment and diagnosis. We previously examined the therapeutic applications of polyrotaxanes (PRXs) comprised of multiple cyclodextrins (CDs) threaded on a polymer chain and capped with bulky stopper molecules. In the present study, we designed an α-d-mannose-modified α-CD/poly(ethylene glycol)-based PRX (Man-PRX). The intracellular uptake of Man-PRX through the interaction with macrophage mannose receptor (MMR) in macrophage-like RAW264.7 cells was examined. Intracellular Man-PRX uptake was observed in MMR-positive RAW264.7 cells but was negligible in MMR-negative NIH/3T3 cells. In addition, the intracellular Man-PRX uptake in RAW264.7 cells was significantly inhibited in the presence of free α-d-mannose and an anti-MMR antibody, which suggests that MMR is involved in the intracellular uptake of Man-PRX. Moreover, the polarization of RAW264.7 cells affected the Man-PRX internalization efficiency. These results indicate that Man-PRX is an effective candidate for selective targeting of macrophages through a specific interaction with the MMR.

Scavenger Receptor A-Mediated Targeting of Carboxylated Polyrotaxanes to Macrophages and the Impacts of Supramolecular Structure

Because macrophages are involved in the pathology of many diseases, targeting delivery of therapeutic molecules to macrophages is important issue. Polyrotaxanes (PRXs) composed of multiple cyclodextrins threaded with a linear polymer were utilized as a therapeutic agent for metabolic disease and for regulating cellular metabolism. For targeting delivery of PRXs to macrophages, carboxyethyl ether group-modified PRXs (CEE-PRXs) are designed for promoting interaction to macrophage scavenger receptor class A (SR-A). The cellular internalization of anionic CEE-PRXs in SR-A-positive macrophage-like cells (RAW264.7) is remarkably higher than that of nonionic PRX, whereas the cellular internalization efficiency in SR-A-negative cells is comparable between anionic and nonionic PRX. Furthermore, the molecular weight of axle polymer and the number of CEE groups modified on PRX are found to be the predominant factors governing cellular internalization efficiency in SR-A-positive RAW264.7 cells. Thus, CEE-PRXs are a promising design for targeting delivery of PRXs to macrophages.

Polysaccharide-Based Controlled Release Systems for Therapeutics Delivery and Tissue Engineering: From Bench to Bedside

Polysaccharides or polymeric carbohydrate molecules are long chains of monosaccharides that are linked by glycosidic bonds. The naturally based structural materials are widely applied in biomedical applications. This article covers four different types of polysaccharides (i.e., alginate, chitosan, hyaluronic acid, and dextran) and emphasizes their chemical modification, preparation approaches, preclinical studies, and clinical translations. Different cargo fabrication techniques are also presented in the third section. Recent progresses in preclinical applications are then discussed, including tissue engineering and treatment of diseases in both therapeutic and monitoring aspects. Finally, clinical translational studies with ongoing clinical trials are summarized and reviewed. The promise of new development in nanotechnology and polysaccharide chemistry helps clinical translation of polysaccharide-based drug delivery systems.

Supramolecular Pharmaceutical Sciences: A Novel Concept Combining Pharmaceutical Sciences and Supramolecular Chemistry with a Focus on Cyclodextrin-Based Supermolecules

Supramolecular chemistry is an extremely useful and important domain for understanding pharmaceutical sciences because various physiological reactions and drug activities are based on supramolecular chemistry. However, it is not a major domain in the pharmaceutical field. In this review, we propose a new concept in pharmaceutical sciences termed "supramolecular pharmaceutical sciences," which combines pharmaceutical sciences and supramolecular chemistry. This concept could be useful for developing new ideas, methods, hypotheses, strategies, materials, and mechanisms in pharmaceutical sciences. Herein, we focus on cyclodextrin (CyD)-based supermolecules, because CyDs have been used not only as pharmaceutical excipients or active pharmaceutical ingredients but also as components of supermolecules.

ER stress-mediated autophagic cell death induction through methylated β-cyclodextrins-threaded acid-labile polyrotaxanes

Autophagy plays a pivotal role in the development and prevention of numerous diseases, and the induction of autophagy is regarded as a potential therapeutic approach for intractable diseases. In this study, the induction of autophagy by methylated β-cyclodextrins (Me-β-CDs)-threaded acid-labile polyrotaxane (Me-PRX) that can release the threaded Me-β-CDs in response to acidic pH in lysosomes was investigated. We hypothesized that the Me-β-CDs released from the Me-PRX interact with the membrane of organelles and cause autophagy. The Me-PRX preferentially accumulated in endoplasmic reticulum (ER) and caused ER stress, which was confirmed by gene expression analysis and the expression of an ER stress-marker protein. Accompanying the ER stress, cells treated with Me-PRX showed autophagy, which was not observed in cells treated with non-labile Me-PRX, other chemically modified PRXs, or free Me-β-CD. Furthermore, the Me-PRX treatment induced autophagic cell death and caused cell death even in apoptosis-resistant cells. Overall, this study demonstrates that the acid-labile Me-PRX induces ER stress-mediated autophagic cell death, and the Me-PRX would be a promising candidate to induce effective cell death in apoptosis-resistant malignant tumors.

Polyrotaxane-based systemic delivery of β-cyclodextrins for potentiating therapeutic efficacy in a mouse model of Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a fatal metabolic disorder characterized by the lysosomal accumulation of cholesterol. Although 2-hydroxypropyl β-cyclodextrin (HP-β-CD) promotes the excretion of cholesterol and prolongs the life span in animal models of NPC disease, it requires extremely high dose. We developed acid-labile β-CD-based polyrotaxanes (PRXs) comprising multiple β-CDs threaded along a polymer chain capped with acid-cleavable stopper molecules for potentiating therapeutic efficacy of β-CD in NPC disease. The acid-labile PRXs dissociate under the acidic lysosomes and release threaded β-CDs in lysosomes, which promotes cholesterol excretion in NPC disease model cells at lower concentration than HP-β-CD. In this study, the therapeutic effect of the PRXs in a mouse model of NPC disease was investigated. Weekly administration of the PRXs significantly prolonged the life span and suppressed neurodegeneration in mice, even at a dose of 500mg/kg, a markedly lower dose than previously reported for HP-β-CD. Detailed analysis of tissue cholesterol revealed that PRX treatment markedly suppressed the tissue accumulation of cholesterol in the NPC mouse model, but did not alter cholesterol content in wild-type mice. Acid-labile PRX is therefore a promising candidate for potentiating the efficacy of β-CD in the treatment of NPC disease.

Acid-Induced Intracellular Dissociation of β-Cyclodextrin-Threaded Polyrotaxanes Directed toward Attenuating Phototoxicity of Bisretinoids through Promoting Excretion

In the retinal pigment epithelium of patients with age-related macular degeneration (AMD), excess N-retinylidene-N-retinylethanolamine (A2E), a dimer of all-trans-retinal, accumulats to induce inflammatory cytokine secretion and phototoxic effects. Therefore, the reduction of intracellular A2E is a promising approach for the prevention and treatment of AMD. In this study, acid-labile β-cyclodextrin (β-CD)-threaded polyrotaxanes (PRXs) were synthesized and investigated their effects on the removal of A2E accumulated in retinal pigment epithelium cells (ARPE-19) in comparison to nonlabile PRXs and 2-hydroxypropyl β-CD (HP-β-CD) were examined. GC-MS and HPLC studies strongly suggest that the acid-labile PRXs dissociated into their constituent molecules in cells by lysosomal acidification and threaded β-CDs were considered to be released from the PRXs. The released β-CDs formed an inclusion complex with A2E, which promoted the excretion of A2E. Indeed, the acid-labile PRXs effectively reduced intracellular A2E level at approximately a 10-fold lower concentration than HP-β-CD. Accompanied with A2E removal, the toxicity and phototoxicity of A2E were attenuated by treatment with acid-labile PRXs. Because the nonlabile PRX failed to reduce intracellular A2E level and attenuate phototoxicity, intracellular release of threaded β-CDs from the acid-labile PRX might contribute to reducing intracellular A2E. We conclude that acid-labile PRXs are promising candidates for the treatment of macular diseases through the removal of toxic metabolites.

Oligo(ethylene glycol)-modified β-cyclodextrin-based polyrotaxanes for simultaneously modulating solubility and cellular internalization efficiency

We developed stimuli-labile polyrotaxanes (PRXs) composed of β-cyclodextrin (β-CD), Pluronic as an axle polymer, and acid-cleavable N-triphenylmethyl groups as bulky stopper molecules, and found that the PRXs are potent therapeutics for Niemann-Pick type C disease, because the PRX can effectively reduce intracellular cholesterol through the intracellular release of threaded β-CDs. In general, the PRXs need to be chemically modified with hydrophilic functional groups because PRXs are not soluble in aqueous media. Herein, four series of oligo(ethylene glycol)s (OEGs) with different ethylene glycol repeating unit (2 or 3) and chemical structure of OEG terminal (hydroxy or methoxy) were modified onto the threaded β-CDs in PRX. The effects of the structure of OEG on the aqueous solubility, toxicity, and cellular internalization efficiency of OEG-modified PRXs were investigated to optimize the chemical structure of OEG. The hydroxy-terminated OEG-modified PRXs showed excellent solubility in aqueous media and no toxicity, regardless of the number of ethylene glycol repeating units. In the case of the methoxy-terminated OEG-modified PRXs, sufficient solubility in aqueous media and negligible toxicity were observed when the number of ethylene glycol repeating units was 3, while low solubility and toxicity were observed when the ethylene glycol repeating unit was 2. Additionally, cellular uptake levels of methoxy-terminated OEG-modified PRXs in RAW264.7 cells were higher than those of hydroxy-terminated OEG-modified PRXs. Consequently, the chemical structure of the OEG strongly affects the chemical and biological properties of the PRXs, and that a methoxy-terminated OEG with 3 ethylene glycol repeating units is the most preferable modification of PRXs, since the resultant PRX is sufficiently soluble in aqueous media, non-toxic, and possesses high cellular internalization efficiency.

Versatile synthesis of end-reactive polyrotaxanes applicable to fabrication of supramolecular biomaterials

Cyclodextrin (CD)-threaded polyrotaxanes (PRXs) with reactive functional groups at the terminals of the axle polymers are attractive candidates for the design of supramolecular materials. Herein, we describe a novel and simple synthetic method for end-reactive PRXs using bis(2-amino-3-phenylpropyl) poly(ethylene glycol) (PEG-Ph-NH₂) as an axle polymer and commercially available 4-substituted benzoic acids as capping reagents. The terminal 2-amino-3-phenylpropyl groups of PEG-Ph-NH₂ block the dethreading of the α-CDs after capping with 4-substituted benzoic acids. By this method, two series of azide group-terminated polyrotaxanes (benzylazide: PRX-Bn-N_3, phenylazide: PRX-Ph-N_3,) were synthesized for functionalization via click reactions. The PRX-Bn-N₃ and PRX-Ph-N₃ reacted quickly and efficiently with p-(tert-butyl)phenylacetylene via copper-catalyzed click reactions. Additionally, the terminal azide groups of the PRX-Bn-N₃ could be modified with dibenzylcyclooctyne (DBCO)-conjugated fluorescent molecules via a copper-free click reaction; this fluorescently labeled PRX was utilized for intracellular fluorescence imaging. The method of synthesizing end-reactive PRXs described herein is simple and versatile for the design of diverse functional PRXs and can be applied to the fabrication of PRX-based supramolecular biomaterials.