2019 年 67 巻 4 号 p. 289-298
Recently, active pharmaceutical ingredients (APIs) have been dramatically expanding from low-molecular weight drugs to peptides, proteins, antibodies, genes, oligonucleotides, cells, and machines. Therefore to develop pharmaceutical technologies and drug delivery systems (DDS) for these APIs, advanced molecules and novel concepts are needed. In this review, we introduce cyclodextrin-based supramolecular accessories such as molecular necklace, molecular earring, and intelligent molecular necklace, and describe their application for pharmaceutical technology and DDS. In addition, we also introduce utility of supramolecular accessories as antitumor drugs. Finally, we propose a new concept in pharmaceutical sciences termed as “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.
A person may choose to wear an accessory so as to enhance their appearance and give them confidence and thus a change of character. So what happens when accessories are decorated with drugs? We have developed molecular accessories for drugs through supramolecular chemistry to create new medicines and pharmaceutical technologies.
Supramolecular chemistry is defined as the chemistry of intermolecular bonds, covering the structure and functions of the entities formed by the association of two or more chemical species.1–3) Recently, numerous supermolecules have been developed with various cyclic compounds, such as cyclodextrin4–6) (CyD, Fig. 1), cryptand,7) cucurbituril,8) crown ethers,9) calixarene,10) and pillar[n]arenes.11,12) Especially, CyDs are widely used to fabricate supermolecules, such as inclusion complex, pseudorotaxane, rotaxane, catenane, daisy chain, poly[2]rotaxane, stacking polymer, polyvalent complex, polypseudorotaxane, polyrotaxane, and polycatenane4,5,13,14) (Fig. 2). Of these supermolecules, polypseudorotaxane, polyrotaxane, and polycatenane are called molecular necklaces because of their unique structures.
(Color figure can be accessed in the online version.)
Reproduced with permission from Chem. Pharm. Bull., 66 207–216. Copyright [2018]. The Pharmaceutical Society of Japan. (Color figure can be accessed in the online version.)
In this review, we introduce various CyD-based supramolecular accessories (molecular necklace, molecular earring, and intelligent molecular necklace) (Fig. 3) and their applications for drug discovery and drug delivery. Moreover, we propose a new concept for pharmaceutical sciences termed “supramolecular pharmaceutical sciences,” which involves the combination of supramolecular chemistry and pharmaceutical sciences.
(Color figure can be accessed in the online version.)
We have developed various drug carriers for low-molecular weight drugs, proteins, and nucleic acids using a molecular necklace, polypseudorotaxanes (Fig. 4). Polypseudorotaxanes are spontaneously formed by mixing parent CyDs and axile molecules in water15–17) (Fig. 5). α- and β-CyDs form polypseudorotaxanes with one polyethylene glycol (PEG) chain and one polypropylene glycol (PPG) chain, respectively.15–18) On the other hand, γ-CyD forms polypseudorotaxane with two PEG chains or one PPG chain.17,19) These polypseudorotaxanes are less soluble in water because adjacent CyD molecules form hydrogen bonds, resulting in dehydration and aggregation. However, polypseudorotaxanes are easily dissociated by dilution and soluble in water.17,18) On the basis of these properties of polypseudorotaxanes, we developed sustained release systems for PEGylated proteins.
(Color figure can be accessed in the online version.)
(Color figure can be accessed in the online version.)
Both PEGylated insulin and PEGylated lysozyme (molecular weight (m.w.) of PEG, 2000 Da), model proteins, formed precipitates derived from the polypseudorotaxanes with α- and γ-CyDs20–23) (Fig. 4c). The enzymatic stability of the PEGylated proteins was improved by polypseudorotaxane formation. Importantly, activities of PEGylated insulin and PEGylated lysozyme released from the polypseudorotaxanes were completely retained. Moreover, hypoglycemic effect of PEGylated insulin/γ-CyD polypseudorotaxane was prolonged after subcutaneous administration to rats compared with PEGylated insulin (Fig. 6). Furthermore, duration of the hypoglycemic effect was controllable by adjusting the concentration of γ-CyD in the medium. Thus polypseudorotaxanes may be useful as controlled release systems for PEGylated proteins. To our best knowledge, this is the first report investigating the utility of CyD-based molecular necklaces as drug carriers in vivo.
Reproduced with permission from Yakugaku Zasshi, 139, 175–183. Copyright [2019]. The Pharmaceutical Society of Japan. (Color figure can be accessed in the online version.)
High-molecular weight PEGs (>2000 Da) form polypseudorotaxane hydrogels, not precipitates, with α- and γ-CyDs, because the polypseudorotaxane moiety works as crosslinking points.24,25) Therefore we prepared polypseudorotaxane hydrogels containing insulin and lysozyme, relatively low-molecular weight proteins, and evaluated their utility as sustained release carriers26,27) (Fig. 4e). First, we prepared polypseudorotaxane hydrogels by mixing α- or γ-CyD solution and PEG (m.w., 20000 Da) solution in the presence of insulin or lysozyme. The reaction solution became a gel within a few hours. The release of the proteins from the gels was markedly prolonged in vitro, and the lytic activity of the released lysozyme was completely retained. In addition, serum insulin levels and hypoglycemic effects were significantly prolonged after subcutaneous administration of γ-CyD polypseudorotaxane hydrogel containing insulin. Thus polypseudorotaxane hydrogels are useful as sustained-release carriers for protein drugs.
Polypseudorotaxanes are also useful as sustained release carriers for low-molecular weight drugs. We previously prepared polypseudorotaxane of PEGylated liposome as a sustained-release carrier for doxorubicin28) (Fig. 4b). Unfortunately, α-CyD disrupted PEGylated liposome; therefore we could not obtain polypseudorotaxane of PEGylated liposome with α-CyD. However, γ-CyD gave the polypseudorotaxane without disrupting PEGylated liposome because of weak interaction between γ-CyD cavity and lipid membrane of PEGylated liposome. In addition, the release rate of doxorubicin and/or PEGylated liposome encapsulating doxorubicin from the γ-CyD polypseudorotaxane was sustained, suggesting the potential of PEGylated liposome/γ-CyD polypseudorotaxane as sustained-release carriers for low-molecular weight drugs.
We also developed polypseudorotaxane-based sustained-release carriers for genes or small interfering RNA (siRNA).29,30) First, PEGylated polyamidoamine dendrimer conjugate with α-CyD (PEG-α-CDE) was prepared as a transfection reagent for gene and siRNA. Then, α- and γ-CyDs were added to the solution containing the polyplexes with PEG-α-CDE to obtain the polypseudorotaxanes (Fig. 4a). The resulting polypseudorotaxanes provided sustained-release profiles of gene or siRNA in vitro. Moreover, γ-CyD polypseudorotaxanes of PEG-α-CDE/plasmid DNA complex showed sustained gene-transfer activity after intramuscular injection to mice for at least 14 d. These findings suggest good usefulness of polypseudorotaxanes as sustained-release carriers for nucleic acids.
Isoprenoid compounds such as β-carotene, lycopene, teprenone, vitamins, and coenzyme Q10 (CoQ10) have been widely used as functional foods and active pharmaceutical ingredients (APIs). However, solubility and stability of isoprenoid compounds are extremely low. Therefore pharmaceutical excipients that improve pharmaceutical properties of isoprenoid compounds are needed. In this context, we reported that β- and γ-CyDs form pseudorotaxane-like supramolecular complexes with a number of isoprenoid compounds such as CoQ10, reduced CoQ10, squalene, tocotrienol, β-carotene, and teprenone by threading isoprenoid chain into β- and γ-CyDs31–33) (Fig. 4f). This probably results from similar girth of isoprenoid chain compared with PPG chain. Interestingly, the resulting pseudorotaxane-like complexes showed significantly higher dispersibility in water than the drugs alone. Namely, pseudorotaxane formation worked as solubilizing technique of isoprenoid compounds. Unlike PEGylated compounds, isoprenoid compounds possess extremely low solubility and dispersibility in water. Therefore pseudorotaxane formation enhanced the solubility and dispersibility of isoprenoid compounds in water. Importantly, photostability of teprenone in the β- and γ-CyD complexes was also significantly improved compared with teprenone alone and the physical mixtures. Hence dispersibility and stability of isoprenoid compounds are improved by formation of pseudorotaxane-like complexes.
Polypseudorotaxane hydrogels consisting of α- or γ-CyD and PEG (m.w., 20000 Da) are also useful as stabilizer for antibodies.34–36) First, we prepared polypseudorotaxane hydrogels containing highly concentrated human immunoglobulin G (IgG) (>100 mg/mL)34) (Fig. 7). The hydrogels markedly improved stabilities of human IgG against heating and shaking. Therefore we next evaluated the stability of commercially available antibody drugs such as omalizumab, palivizumab, panitumumab, and ranibizumab in the polypseudorotaxane hydrogels. As expected, the polypseudorotaxane hydrogels markedly improved the stability of these antibody drugs. In addition, stabilizing effect of the polypseudorotaxane hydrogels was markedly higher than that of the other macromolecular gelling agents such as carmellose, pectin, pullulan, locust bean gum, and guar gum (unpublished data). Importantly, the in vitro activity of omalizumab released from the polypseudorotaxane hydrogels was completely retained. Unlike insulin and lysozyme, plasma levels of omalizumab after subcutaneous administration of the γ-CyD polypseudorotaxane hydrogel to rats were equivalent to those of omalizumab alone, because of markedly long blood half-life of omalizumab alone. These findings suggest that polypseudorotaxane hydrogels work as a stabilizer for antibody drugs without changing their pharmacokinetics.
Reproduced with permission from Yakugaku Zasshi, 139, 175–183. Copyright [2019]. The Pharmaceutical Society of Japan. (Color figure can be accessed in the online version.)
Subcutaneous administration of α- and γ-CyD polypseudorotaxane hydrogels to rat did not affect their blood biochemistry values, weights of organs, and histological observations, suggesting no serious adverse effects.
Covalent PEGylation is a useful approach to improve stability, reduce immunogenicity, and improve blood retention of proteins. However, bioactivities of proteins are extremely reduced by PEGylation, resulting from steric hindrance of PEG chains or structural changes to the proteins. Meanwhile, we recently developed novel PEGylation based on host–guest interaction between β-CyD and adamantane (Ad), and termed it “self-assembly PEGylation-retaining activity” (SPRA) technology. Namely, we firstly prepared Ad conjugate with model proteins such as insulin and lysozyme (Ad-insulin and Ad-lysozyme) then mixed with PEGylated β-CyD (m.w. of PEG, 20000 Da) (Fig. 8). As a result, both proteins were PEGylated by host–guest interaction between β-CyD and Ad. The resulting PEGylated proteins (SPRA-proteins) possessed higher enzymatic and thermal stabilities than the proteins alone. Importantly, SPRA-lysozyme completely retained lytic activity compared with native lysozyme, because this supramolecular PEGylation was reversible. In contrast, 77% of the activity of lysozyme was lost by covalent PEGylation. Moreover, SPRA-insulin showed prolonged hypoglycemic effect compared with insulin and insulin glargine with completely retained biologic activity, although covalently PEGylated insulin showed less than 6% of the activity. Of note, the stability constants of SPRA-proteins was ca. ≥104 M−1, and the value seems low to maintain the complex in vivo. However, not only stability constants but also low protein-binding ability of guest molecules and high blood retention of host/guest molecules are important factors for complexation in vivo.13) Therefore low protein binding of Ad-proteins in blood and high blood retention of PEGylated β-CyD were probably important for complexation in vivo. Thus SPRA technology can improve pharmaceutical properties of proteins without reducing their activity. Because this technology resembles earring decoration of protein drugs, we termed it “molecular earring technology.” The combination of “molecular necklace technology” and “molecular earring technology” is also available as a controllable and sustained-release carrier for insulin37) (Figs. 3, 4d).
(Color figure can be accessed in the online version.)
Molecular earring technology (SPRA technology) is also useful to fabricate an antitumor drug carrier for pancreatic cancer (unpublished data). Bromelain is one of the cysteine and sulfhydryl proteases and can digest the extracellular matrix (ECM) and thereby improve penetration of drugs into solid tumors. However, blood retention and tumor accumulation of bromelain are low. We recently prepared PEGylated bromelain through SPRA technology (SPRA-bromelain) to improve its blood retention and tumor accumulation (Fig. 9). SPRA-bromelain possessed 100% of ECM-degrading activity, and enhanced permeability of fluorescein isothiocyanate (FITC)-dextran (2 MDa) against a gelatin gel, a model of ECM. Moreover, accumulation of FITC-dextran in the tumor and antitumor activities of doxorubicin and DOXIL were significantly improved by the pre-administration of SPRA-bromelain to pancreatic cancer model mice. Therefore SPRA-bromelain could be a promising drug carrier for the treatment of pancreatic cancer.
(Color figure can be accessed in the online version.)
Recently, CyDs and their derivatives are expected as APIs against various diseases such as Niemann–Pick disease type C (NPC),38–52) Alzheimer’s disease,53–58) leukemia,59) cerebral ischemic injury,60) chronic renal failure,61) hyperlipidemia,62) atherosclerosis,63) AIDS,64,65) diabetic kidney disease,66) influenza,67) sterility,68–70) peripheral artery disease,71) bacterial growth,72) solid cancers,73–78) GM1-gangliosidosis,79) septic shock,80–82) α-synucleinopathy,83) hypervitaminosis,84) and transthyretin-related familial amyloidotic polyneuropathy (FAP).85,86) In addition, γ-CyD derivative (Bridion®) is already used as an inhibiter against neuromuscular blockade by rocuronium.87)
We have developed a CyD-based antitumor drug, namely folate appended-methyl-β-CyD (FA-M-β-CyD), thus far.75,76,78) FA-M-β-CyD induced mitophagy after uptake into folate receptor-overexpressing tumor cells, leading to tumor-selective antitumor activity.78) More recently, to improve tumor selectivity, blood retention, and safety of FA-M-β-CyD, we newly prepared a molecular necklace (polyrotaxane) consisting of FA-M-β-CyD (Fig. 10) (unpublished data). FA-M-β-CyD polyrotaxane possessed high molecular weight and a number of folate moieties, leading to high blood retention and high tumor selectivity, respectively. In addition, the axile molecule occupied cavity of FA-M-β-CyD, and FA-M-β-CyD was probably released from the polyrotaxane in tumor cells. This results in negligible adverse effect on normal tissues, but tumor-selective cytotoxic activity in tumor tissue. Indeed, intravenous administration of FA-M-β-CyD polyrotaxane showed higher in vivo antitumor activity than FA-M-β-CyD without changing blood chemistry values. Thus CyD-based supermolecules could be a promising antitumor drug.
Reproduced with permission from Yakugaku Zasshi, 139, 175–183. Copyright [2019]. The Pharmaceutical Society of Japan. (Color figure can be accessed in the online version.)
To create future pharmaceutical sciences, fabrication of smart pharmaceutical materials is necessary. We recently developed thermoresponsive molecular necklaces (polyrotaxanes) consisting of 2,6-di-O-methyl-CyDs (DM-CyDs).88) DM-α-CyD/PEG or DM-β-CyD/PPG formed no polypseudorotaxanes at room temperature, but formed them at >50°C and >35°C, respectively (Fig. 11). After cooling, the precipitates of the polypseudorotaxanes were rapidly dissolved because of dissociation of DM-CyDs. Additionally, DM-α- and DM-β-CyD polyrotaxanes were obtained by capping with one and two 2,4,6-trinitrobenzenesulfonic acid (TNBS) molecules, respectively. Thus DM-CyD polyrotaxanes were prepared by one-pot synthesis with water solvent. These methods are very useful to obtain polyrotaxane derivatives easily. Moreover, DM-CyD polyrotaxanes could be useful for fabrication of thermoresponsive pharmaceutical materials.
(Color figure can be accessed in the online version.)
Recently, slide-ring materials based on CyD polyrotaxanes have attracted considerable attention. Indeed, they are commercially used as coating materials for devices such as cellular phones and speakers.89,90) In addition, a large number of drug carriers and biomaterials based on CyD polyrotaxanes are aggressively reported.25,91–95) In spite of many reports regarding CyD polyrotaxanes, very few reports on CyD polycatenanes are available, thus far.96) Most recently, we first prepared polycatenanes consisting of β- or γ-CyD and PEG-PPG-PEG copolymer (pluronic) in a one-pot synthesis (submitted) (Fig. 12). First, CyD/thiolized PEG-PPG-PEG polypseudorotaxanes were prepared, then cyclized by disulfide formation in water. This method is very useful to obtain interlocked molecules consisting of β- and γ-CyDs easily, because preparations of β- and γ-CyD polyrotaxanes are laborious works resulting from lack of endcap molecules. Moreover, the resulting polycatenanes degraded in the reduced condition, and released CyDs. Therefore CyD polycatenanes could be useful to fabricate redox-responsive pharmaceutical materials.
Reproduced with permission from Yakugaku Zasshi, 139, 175–183. Copyright [2019]. The Pharmaceutical Society of Japan. (Color figure can be accessed in the online version.)
In this review, we described various CyD-based supramolecular accessories (molecular necklace, molecular earring, and intelligent molecular necklace) and their applications for drug discovery and drug delivery. Currently, APIs are dramatically expanding from low-molecular weight drugs to peptides, proteins, antibodies, genes, oligonucleotides, cells, and machines. However, pharmaceutical technologies used in commercially available products are often common methods. Meanwhile, supramolecular chemistry and supermolecules provide superior pharmaceutical properties to drugs beyond the existing chemistry and molecules. Indeed, as described in this review, decoration of polypseudorotaxane (i.e. supermolecule) improved the pharmaceutical properties of proteins compared with conventional modification with PEG (i.e. macromolecules) (Fig. 6). In addition, stabilizing effects of polypseudorotaxane hydrogels (i.e. supermolecule) were superior to other gelling agents (i.e. macromolecules) (Fig. 7). Moreover, PEGylated proteins prepared by SPRA technology (i.e. supramolecular chemistry) improved pharmaceutical properties over conventional covalent PEGylation (i.e. chemistry) (Figs. 8, 9). Thus supramolecular chemistry and supermolecules are useful for developing advanced pharmaceutical technologies and drug delivery systems (DDS). Furthermore, FA-M-β-CyD polyrotaxane possessed antitumor activity by itself (Fig. 10), indicating that supermolecules could be promising candidates as future APIs together with peptides, proteins, antibodies, genes, oligonucleotides, cells, and machines.
On the basis of these findings, we here propose a new concept in pharmaceutical sciences termed “supramolecular pharmaceutical sciences,” which combines pharmaceutical sciences and supramolecular chemistry.13,14) This concept could be useful for developing new ideas, methods, hypotheses, strategies, materials, and mechanisms in pharmaceutical sciences (Fig. 13). For example, as described in this review, substitution of supramolecular chemistry and supermolecules for chemistry and molecules renders new functions and properties in pharmaceutical sciences. Moreover, in conventional drug discovery we usually synthesize compounds that strongly bind to target molecules (Fig. 14A). Based on the supramolecular pharmaceutical sciences, new types of drugs may be rendered, e.g. 1) multivalent type that can bind multiple points of target molecules (Fig. 14B), 2) prodrug type that dissociates at the disease site and exerts treatment effects (Fig. 14C), and 3) prodrug type that forms bioactive supramolecular complex with endogenous substances at the disease site and exerts treatment effects (Fig. 14D).
Chem. Pharm. Bull. Vol. 66 No. 3, 207–216 Copyright [2018] The Pharmaceutical Society of Japan and Yakugaku Zasshi, 139, 175–183. Copyright [2019]. The Pharmaceutical Society of Japan. (Color figure can be accessed in the online version.)
(Color figure can be accessed in the online version.)
In this review article, we introduced various supramolecular accessories such as molecular necklace, molecular earring, and intelligent molecular necklace. We believe that supramolecular accessories are useful to fabricate future pharmaceutical technologies and DDS beyond the conventional molecules. In addition, supramolecular accessories are promising candidates as future APIs. Moreover, supramolecular pharmaceutical sciences should be useful for creating new ideas, methods, hypotheses, strategies, materials, and mechanisms in pharmaceutical sciences.
The author would like to express sincere thanks to Drs. H. Arima, K. Motoyama, K. Uekama, F. Hirayama, D. Iohara, R. Onodera, J. Li, and students of Graduate School of Pharmaceutical Sciences, Kumamoto University, for their valuable advice, inspiration, and kind help. In addition, the author thanks Chie and Akari for warm support.
The author declares no conflict of interest.
This review of the author’s work was written by the author upon receiving the 2018 Pharmaceutical Society of Japan Award for Young Scientists.
