Assembly and Applications of Macrocyclic-Confinement-Derived Supramolecular Organic Luminescent Emissions from Cucurbiturils

Cucurbit[n]urils (Q[n]s or CB[n]s), as a classical of artificial organic macrocyclic hosts, were found to have excellent advantages in the fabricating of tunable and smart organic luminescent materials in aqueous media and the solid state with high emitting efficiency under the rigid pumpkin-shaped structure-derived macrocyclic-confinement effect in recent years. This review aims to give a systematically up-to-date overview of the Q[n]-based supramolecular organic luminescent emissions from the confined spaces triggered host-guest complexes, including the assembly fashions and the mechanisms of the macrocycle-based luminescent complexes, as well as their applications. Finally, challenges and outlook are provided. Since this class of Q[n]-based supramolecular organic luminescent emissions, which have essentially derived from the cavity-dependent confinement effect and the resulting assembly fashions, emerged only a few years ago, we hope this review will provide valuable information for the further development of macrocycle-based light-emitting materials and other related research fields.

A novel pH-responsive Fe-MOF system for enhanced cancer treatment mediated by the Fenton reaction

A novel pH-responsive Fe-MOF system for enhancing cancer treatment mediated by a Fenton reaction.

Activation Strategies in Image-Guided Nanotherapeutic Delivery

Therapeutic nanomaterials serve as an important platform for drug delivery under image guidance. Despite significant growth and broad applications, their design specifics remain a subject of continued interest primarily due to multifunctional factors involved, ranging from nanomaterial properties, imaging modalities, and therapeutic agents to activation strategies. This review article summarizes key findings on their design characteristics with a particular interest in strategies developed for therapeutic activation (release). First, their activation can be controlled using either an endogenous factor including low pH and glutathione or an external stimulation by light, ultrasound, or electromagnetic field. The former is passively controlled from a spatiotemporal aspect compared to the latter, which is otherwise actively controlled through drug linker photolysis, nanomaterial disassembly, or gate opening. Second, light stimulation serves a most notable strategy due to its essential role in controlled drug release, photothermal activation (hyperthermia), and photodynamic production of reactive oxygen species (ROS). Third, some of those activation strategies that rely on ultrasound, photothermal, photoacoustic, magnetic field, or X-ray radiation are dually functional due to their role in imaging modalities. In summary, this review article presents recent advances and new insights that pertain to nanotherapeutic delivery systems. It also addresses their technical limitations associated with tissue penetration (light), spatial resolution (ultrasound, hyperthermia), and occurrence of cellular resistance (ROS).

Supramolecular Hydrogels via Light-Responsive Homoternary Cross-Links

Host-guest physical cross-linking has been used to prepare supramolecular hydrogels for various biomedical applications. More recent efforts to endow these materials with stimuli-responsivity offers an opportunity to precisely tune their function for a target use. In the context of light-responsive materials, azobenzenes are one prevailing motif. Here, an asymmetric azobenzene was explored for its ability to form homoternary complexes with the cucurbit[8]uril macrocycle, exhibiting an affinity (K_eq) of 6.21 × 10¹⁰ M^-2 for sequential binding, though having negative cooperativity. Copolymers were first prepared from different and tunable ratios of NIPAM and DMAEA, and DMAEA groups were then postsynthetically modified with this asymmetric azobenzene. Upon macrocycle addition, these polymers formed supramolecular hydrogels; relaxation dynamics increased with temperature due to temperature-dependent affinity reduction for the ternary complex. Application of UV light disrupted the supramolecular motif through azobenzene photoisomerization, prompting a gel-to-sol transition in the hydrogel. Excitingly, within several minutes at room temperature, thermal relaxation of azobenzene to its trans state afforded rapid hydrogel recovery. By revealing this supramolecular motif and employing facile means for its attachment onto pre-synthesized polymers, the approach described here may further enable stimuli-directed control of supramolecular hydrogels for a number of applications.

Integrating Stimuli-Responsive Properties in Host-Guest Supramolecular Drug Delivery Systems

Host-guest motifs are likely the most recognizable manifestation of supramolecular chemistry. These complexes are characterized by the organization of small molecules on the basis of preferential association of a guest within the portal of a host. In the context of their therapeutic use, the primary application of these complexes has been as excipients which enhance the solubility or improve the stability of drug formulations, primarily in a vial. However, there may be opportunities to go significantly beyond such a role and leverage key features of the affinity, specificity, and dynamics of the interaction itself toward "smarter" therapeutic designs. One approach in this regard would seek stimuli-responsive host-guest recognition, wherein a complex forms in a manner that is sensitive to, or can be governed by, externally applied triggers, disease-specific proteins and analytes, or the presence of a competing guest. This review will highlight the general and phenomenological design considerations governing host-guest recognition and the specific types of chemistry which have been used and are available for different applications. Finally, a discussion of the molecular engineering and design approaches which enable sensitivity to a variety of different stimuli are highlighted. Ultimately, these molecular-scale approaches offer an assortment of new chemistry and material design tools toward improving precision in drug delivery.

Mesoporous Silica Nanoparticles

Integration of nanotechnology and biomedicine has offered great opportunities for the development of nanoscaled therapeutic platforms. Amongst various nanocarriers, mesoporous silica nanoparticles (MSNs) is one of the most developed and promising inorganic materials-based drug delivery system for clinical translations due to their simple composition and nanoporous structure. MSNs possess unique structural features, for example, well-defined morphology, large surface areas, uniform size, controllable structure, flexible pore volume, tunable pore sizes, extraordinarily high loading efficiency, and excellent biocompatibility. Progress in structure control and functionalization may endow MSNs with functionalities that enable medical applications of these integrated nanoparticles such as molecularly targeted drug delivery, multicomponent synergistic therapy, in vivo imaging and therapeutic capability, on-demand/stimuli-responsive drug release, etc. In this chapter, the authors overview MSNs' characteristics and the scientific efforts developed till date involving drug delivery and biomedical applications.

Targeting protein-loaded CB[8]-mediated supramolecular nanocarriers to cells

Supramolecular amphiphiles, consisting of ternary complexes of cucurbit[8]uril (CB[8]), an alkylated paraquat derivative and a tetraethylene glycol-functionalized azobenzene, self-assemble into vesicles of about 200 nm in diameter. The outer surface of the vesicles was functionalized with cell-targeting ligands. These vesicles were employed for loading and delivery of proteins into cells. Supramolecular amphiphile-derived vesicles show great promise as nanocarriers of functional molecules to be transferred into cells.

Phosphonated Pillar[5]arene-Valved Mesoporous Silica Drug Delivery Systems

To explore the diversity and promising applications of pillararene-based molecular machines, phosphonated pillar[5]arenes (PPA[5]) were synthesized to construct novel supramolecular nanovalves for the first time, based on mesoporous silica nanoparticles (MSNs) functionalized with choline and pyridinium moieties, respectively. PPA[5] encircled the choline or pyridinium stalks to construct supramolecular nanovalves for encapsulation of drugs within the MSN pores. PPA[5] showed a high binding affinity for the quaternary ammonium stalks through the host-guest interactions primarily via ion pairing between the phosphonate and quaternary ammonium moieties, in comparison with carboxylated pillar[5]arene (CPA[5]), to minimize premature drug release. The specific ion pairing between the phosphonate and quaternary ammonium moieties was elaborated for the first time to construct supramolecular nanovalves. The supramolecular nanovalves were activated by low pH, Zn²⁺ coordination, and competitive agents for controlled drug release, and release efficiency and antitumor efficacy were further enhanced when gold nanorod (GNR)-embedded MSNs (GNR@MSNs) were used instead under illumination of near-infrared (NIR) light, attributed to the synergistic effect of photothermo-chemotherapy. The constructed PPA[5]-valved GNR@MSN delivery system has promising applications in tumor photothermo-chemotherapy.

A redox-responsive mesoporous silica nanoparticle with a therapeutic peptide shell for tumor targeting synergistic therapy

In this study, we report a novel redox-responsive mesoporous silica nanoparticle (MSN)-based nanocarrier, capping with a therapeutic peptide ((RGDWWW)₂KC) containing a RGD target motif, for tumor targeting synergistic therapy, which is designated as TTSTMSN. The MSN was decorated with a tumor-targeting therapeutic peptide as a potential gatekeeper. The two branched peptides containing rich tryptophans allowed the pores to be blocked via π-π stacking and hydrophobic interactions. Once the drug loaded nanoparticles were taken up by the cancer cells through integrin-mediated endocytosis, the therapeutic peptide capping shells on the surface of MSNs were released, inducing the loaded drug to diffuse into the cytoplasm after breaking of the disulfide bonds, triggered by the high concentration of glutathione (GSH) in cancer cells. At the same time, the falling therapeutic rich tryptophans in the branched chains interacted with DNA due to the indole rings, leading to disturbance of the DNA structure through the strong π interactions and causing cell apoptosis. There is no such report on capping of drug loaded porous silica with a therapeutic peptide shell, co-delivering an anticancer drug and therapeutic agent for tumor targeting synergistic therapy, which will have great potential in developing multifunctional nanocarriers based on therapeutic peptides for synergistic treatment.

Advances in Peptide Functionalization on Mesoporous Silica Nanoparticles for Controlled Drug Release

During the last decade, using versatile, promising, and fascinating mesoporous silica nanoparticles (MSNs) as site-specific and stimuli-responsive drug delivery systems (DDSs) has received concentrated research interest. As one of the most attractive surface modification units, peptides have inherent bioactivity, biodegradability and biocompatibility. Recent progresses in the utilization of versatile peptides for surface functionalization of MSNs to achieve cell-specific targeting, fluorescence imaging, and intracellular diagnosis and treatment of tumors are summarized in this review. The various functional peptides decorated on the MSNs are introduced and classified into three types, including targeting peptides, stimuli-responsive peptides and multifunctional chimeric peptides. The limitations and challenges of peptide modified MSNs and their potential applications are further discussed.

Photoactivated drug delivery and bioimaging

Among the various types of diseases, cancer remains one of the most leading causes of mortality that people are always suffering from and fighting with. So far, the effective cancer treatment demands accurate medical diagnosis, precise surgery, expensive medicine administration, which leads to a significant burden on patients, their families, and the whole national healthcare system around the world. In order to increase the therapeutic efficiency and minimize side effects in cancer treatment, various kinds of stimuli-responsive drug delivery systems and bioimaging platforms have been extensively developed within the past decades. Among them, the strategy of photoactivated approach has attracted considerable research interest because light enables the precise control, in a highly spatial and temporal manner, the release of drug molecules as well as the activation of bioimaging agents. In general, several appropriate photoresponsive systems, which are normally sensitive to ultraviolet (UV) or visible light irradiation to undergo the multiple reaction pathways such as photocleavage and photoisomerization strategy etc. have been mainly involved in the light activated cancer therapies. Considering the potential issues of poor tissue penetration and high photoctotoxicity of short wavelength light, the recently emerged therapies based on long-wavelength irradiation, e.g., near-infrared (NIR) light (700-1000 nm), have displayed distinct advantages in biomedical applications. The light irradiation at NIR window indicates minimized photodamage, deep penetration, and low autofluorescence in living cells and tissues, which are of clinical importance in the desired diagnosis and therapy. In this review article, we introduce the recent advances in light-activated drug release and biological imaging mainly for anticancer treatment. Various types of strategies such as photocage, photo-induced isomerization, optical upconversion, and photothermal release by which different wavelength ranges of light can play the important roles in the controlled therapeutic or imaging agents delivery, and activation will be systemically discussed. In addition, the challenges and future perspectives for photo-based cancer theranostics will be also summarized. WIREs Nanomed Nanobiotechnol 2017, 9:e1408. doi: 10.1002/wnan.1408 For further resources related to this article, please visit the WIREs website.

MMP-responsive theranostic nanoplatform based on mesoporous silica nanoparticles for tumor imaging and targeted drug delivery

In this paper, we report on an intelligent mesoporous silica-based multifunctional theranostic nanoplatform (designated as MMTNP) for tumor imaging as well as controlled drug release. This theranostic nanoplatform consists of MCM-41 typical mesoporous silica nanoparticles (MSNs) as a hydrophobic drug carrier, matrix metalloprotease-2 (MMP-2) activated fluorescence imaging peptides on the surface of MSNs served as diagnostic probes as well as enzyme-responsive nanovalves blocking the pores, and cRGD peptides further functionalized on the surface of MSNs for tumor targeting. In the absence of MMP-2 conditions, the proximity between the fluorescent dye 5(6)-carboxytetramethylrhodamine hydrochloride (TAMRA) and the quencher 4,4-dimethylamino-azobenzene-4'-carboxylic acid (Dabcyl) on the surface of MSNs resulted in no fluorescence. When the drug loaded nanoplatform arrived at tumor tissue with overexpressed MMP-2, the fluorescence of TAMRA became recovered efficiently due to the hydrolysis of the MMP-2 sensitive peptide substrate, realizing tumor imaging and triggering drug release. In addition, the further introduced cRGD peptide significantly enhanced the targeting efficiency through receptor-mediated endocytosis in tumor cells.

Construction of a photo-responsive supra-amphiphile based on a tetracationic cyclobis(paraquat-p-phenylene) and an azobenzene-containing guest in water

A photo-responsive supra-amphiphile was constructed based on the host–guest molecular recognition between a tetracation cyclophane cyclobis(paraquat-p-phenylene) host and an azobenzene-containing guest.