Tetraphenylethene-based highly emissive metallacage as a component of theranostic supramolecular nanoparticles

Uncovering tetrazoles as building blocks for constructing discrete and polymeric assemblies

Metal-organic self-assembly with flexible moieties is a budding field of research due to the possibility of the formation of unique architectures. Tetrazole, characterised by four nitrogen atoms in a five-member ring, exhibits immense potential as a component. Tetrazole offers four coordination sites for binding to the metal centre with nine distinct binding modes, leading to various assemblies. This review highlights different polymeric and discrete tetrazole-based assemblies and their functions. The meticulous manipulation of stoichiometry, ligands, and metal ions required for constructing discrete assemblies has also been discussed. The different applications of these architectures in separation, catalysis and detection have also been accentuated. The latter section of the review consolidates tetrazole-based cage composites, highlighting their applications in cell imaging and photocatalytic applications.

Supramolecular Coordination Complexes for Synergistic Cancer Therapy

Supramolecular coordination complexes (SCCs) are predictable and size-tunable supramolecular self-assemblies constructed through directional coordination bonds between readily available organic ligands and metallic receptors. Based on planar and 3D structures, SCCs can be mainly divided into two categories: metallacycles (e.g., rhomboidal, triangular, rectangular, and hexagonal) and metallacages (e.g., tetrahedral, hexahedral, and dodecahedral). The directional coordination bonds enable the efficient formation of metallacycles and metallacages with well-defined architectures and geometries. SCCs exhibit several advantages, including good directionality, strong interaction force, tunable modularity, and good solution processability, making them highly attractive for biomedical applications, especially in cellular imaging and cancer therapy. Compared with their molecular precursors, SCCs demonstrate enhanced cellular uptake and a strengthened tumor accumulation effect, owing to their inherently charged structures. These properties and the chemotherapeutic potential inherent to organic platinum complexes have promoted their widespread application in antitumor therapy. Furthermore, the defined structures of SCCs, achieved via the design modification of assembly elements and introduction of different functional groups, enable them to combat malignant tumors through multipronged treatment modalities. Because the development of cancer-treatment methodologies integrated in clinics has evolved from single-modality chemotherapy to synergistic multimodal therapy, the development of functional SCCs for synergistic cancer therapy is crucial. While some pioneering reviews have explored the bioapplications of SCCs, often categorized by a specific function or focusing on the specific metal or ligand types, a comprehensive exploration of their synergistic multifunctionality is a critical gap in the current literature.In this Account, we focus on platinum-based SCCs and their applications in cancer therapy. While other metals, such as Pd-, Rh-, Ru-, and Ir-based SCCs, have been explored for cancer therapy by Therrien and Casini et al., platinum-based SCCs have garnered significant interest, owing to their unique advantages in antitumor therapy. These platinum-based SCCs, which enhance antitumor efficacy, are considered prominent candidates for cancer therapies owing to their desirable properties, such as potent antitumor activity, exceptionally low systemic toxicity, active tumor-targeting ability, and enhanced cellular uptake. Furthermore, diverse diagnostic and therapeutic modalities (e.g., chemotherapy, photothermal therapy, and photodynamic therapy) can be integrated into a single platform based on platinum-based SCCs for cancer therapy. Consequently, herein, we summarize our recent research on platinum-based SCCs for synergistic cancer therapy with particular emphasis on the cooperative interplay between different therapeutic methods. In the Conclusions section, we present the key advancements achieved on the basis of our research findings and propose future directions that may significantly impact the field.

Strategies to address key challenges of metallacycle/metallacage-based supramolecular coordination complexes in biomedical applications

Owing to their capacity for dynamically linking two or more functional molecules, supramolecular coordination complexes (SCCs), exemplified by two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages, have gained increasing significance in biomedical applications. However, their inherent hydrophobicity and self-assembly driven by heavy metal ions present common challenges in their applications. These challenges can be overcome by enhancing the aqueous solubility and in vivo circulation stability of SCCs, alongside minimizing their side effects during treatment. Addressing these challenges is crucial for advancing the fundamental research of SCCs and their subsequent clinical translation. In this review, drawing on extensive contemporary research, we offer a thorough and systematic analysis of the strategies employed by SCCs to surmount these prevalent yet pivotal obstacles. Additionally, we explore further potential challenges and prospects for the broader application of SCCs in the biomedical field.

Combining Multiple Photosensitizer Modules into One Supramolecular System for Synergetic Enhanced Photodynamic Therapy

Photodynamic therapy (PDT), as an emerging cancer treatment, requires the development of highly desirable photosensitizers (PSs) with integrated functional groups to achieve enhanced therapeutic efficacy. Coordination-driven self-assembly (CDSA) would provide an alternative approach for combining multiple PSs synergistically. Here, we demonstrate a simple yet powerful strategy of combining conventional chromophores (tetraphenylethylene, porphyrin, or Zn-porphyrin) with pyridinium salt PSs together through condensation reactions, followed by CDSA to construct a series of novel metallo-supramolecular PSs (S1-S3). The generation of reactive oxygen species (ROS) is dramatically enhanced by the direct combination of two different PSs, and further reinforced in the subsequent ensembles. Among all the ensembles, S2 with two porphyrin cores shows the highest ROS generation efficiency, specific interactions with lysosome, and strong emission for probing cells. Moreover, the cellular and living experiments confirm that S2 has excellent PDT efficacy, biocompatibility, and biosafety. As such, this study will enable the development of more efficient PSs with potential clinical applications.

Coordination-Induced Emissive Poly-NHC-Derived Metallacage for Pesticide Detection

Developing sensitive, rapid, and convenient methods for the detection of residual toxic pesticides is immensely important to prevent irreversible damage to the human body. Luminescent metal-organic cages and macrocycles have shown great applications, and designing highly emissive supramolecular systems in dilute solution using metal-ligand coordination-driven self-assembly is demanded. In this study, we have demonstrated the development of a silver-carbene bond directed tetranuclear silver(I)-octacarbene metallacage [Ag4(L)2](PF6)4 (1) based on an aggregation-induced emissive (AIE) cored 1,1',1″,1‴-((1,4-phenylenebis(ethene-2,1,1-triyl))tetrakis(benzene-4,1-diyl))tetrakis(3-methyl-1H-imidazol-3-ium) salt (L). A 36-fold enhanced emission was observed after metallacage (1) formation when compared with the ligand (L) in dilute solution due to the restriction of intramolecular motions imparted by metal-ligand coordination. Such an increase in fluorescence made 1 a potential candidate for the detection of a broad-spectrum pesticide, 2,6-dichloro-nitroaniline (DCN). 1 was able to detect DCN efficiently by the fluorescence quenching method with a significant detection limit (1.64 ppm). A combination of static and dynamic quenching was applicable depending on the analyte concentration. The use of silver-carbene bond directed self-assembly to exploit coordination-induced emission as an alternative to AIE in dilute solution and then apply this approach to solve health and safety concerns is noteworthy and carries a lot of potential for future developments.

Multimodal Therapeutic Platforms Based on Self-Assembled Metallacycles/Metallacages for Cancer Radiochemotherapy

Discrete organometallic complexes with defined structures are proceeding rapidly in combating malignant tumors due to their multipronged treatment modalities. Many innovative superiorities, such as high antitumor activity, extremely low systemic toxicity, active targeting ability, and enhanced cellular uptake, make them more competent for clinical applications than individual precursors. In particular, coordination-induced regulation of luminescence and photophysical properties of organic light-emitting ligands has demonstrated significant potential in the timely evaluation of therapeutic efficacy by bioimaging and enabled synergistic photodynamic therapy (PDT) or photothermal therapy (PTT). This review highlights instructive examples of multimodal radiochemotherapy platforms for cancer ablation based on self-assembled metallacycles/metallacages, which would be classified by functions in a progressive manner. Finally, the essential demands and some plausible prospects in this field for cancer therapy are also presented.

Platinum Drug-Incorporating Polymeric Nanosystems for Precise Cancer Therapy

Platinum (Pt) drugs are widely used in clinic for cancer therapy, but their therapeutic outcomes are significantly compromised by severe side effects and acquired drug resistance. With the emerging immunotherapy and imaging-guided cancer therapy, precise delivery and release of Pt drugs have drawn great attention these days. The targeting delivery of Pt drugs can greatly increase the accumulation at tumor sites, which ultimately enhances antitumor efficacy. Further, with the combination of Pt drugs and other theranostic agents into one nanosystem, it not only possesses excellent synergistic efficacy but also achieves real-time monitoring. In this review, after the introduction of Pt drugs and their characteristics, the recent progress of polymeric nanosystems for efficient delivery of Pt drugs is summarized with an emphasis on multi-modal synergistic therapy and imaging-guided Pt-based cancer treatment. In the end, the conclusions and future perspectives of Pt-encapsulated nanosystems are given.

Solvent Induced Conversion of a Self-Assembled Gyrobifastigium to a Barrel and Encapsulation of Zinc-Phthalocyanine within the Barrel for Enhanced Photodynamic Therapy

A rare gyrobifastigium architecture (GB) was constructed by self-assembly of a tetradentate donor (L) with Pd^II acceptor in DMSO. The GB was converted to its isomeric tetragonal barrel (MB) upon treatment with water. The hydrophobic cavity of MB has been explored for the encapsulation of zinc-phthalocyanine (ZnPc), which is an excellent photosensitizer for photodynamic therapy (PDT). However, the poor water-solubility and aggregation tendency are the main reasons for the suboptimal PDT performance of free ZnPc in the aqueous medium. Effective solubilization of ZnPc in an aqueous medium was achieved by encapsulating it in the cavity of MB. The inclusion complex (ZnPc⊂MB) showed enhanced singlet oxygen generation in water. Higher cellular uptake and anticancer activity of the ZnPc⊂MB compared to free ZnPc on HeLa cells indicate that encapsulation of ZnPc in an aqueous host is a potential strategy for enhancement of its PDT activity in water.

Pt(II) metallacycles encapsulated by ferritin enable precise cancer combination chemo-photodynamic therapy

Different from common anti-tumor drugs, organoplatinum(II) metallacycles can integrate imaging and other therapeutic capabilities by incorporating corresponding functional donor ligands to enable potential applications in biomedicine. However, most of the emerging therapeutic agents not only show poor solubility and selectivity but also have serious side effects and unsatisfactory efficacy and encounter the tendency to develop drug resistance due to their single treatment model. Herein, an organoplatinum(II) metallacycle (PtM) was designed and synthesized using coordination-driven self-assembly via the combination of a metallic chemotherapy precursor and a reactive oxygen species generating organic precursor. The hydrophobic PtM molecules were encapsulated in the cavity of human heavy chain ferritin (HFn) during the reassembly of HFn to prepare the active targeting nanoagent HFn-PtM for use in chemo-photodynamic combination therapy. The HFn-PtM nanoagents exhibited excellent stability in buffer (pH from 5 to 7.2), alleviating the concern of drug leakage during circulation. A cellular uptake assay indicated that HFn-PtM could efficiently enter specific cells that overexpress the transferrin receptor 1. In vitro and in vivo anti-tumor investigations revealed that HFn-PtM exhibited excellent anti-tumor efficiency with negligible systemic toxicity. This work provides a strategy for the easy construction of multifunctional organoplatinum-based tumor-targeted drugs.

PET Imaging of Self-Assembled 18 F-Labelled Pd2 L4 Metallacages for Anticancer Drug Delivery

To advance the design of self-assembled metallosupramolecular architectures as new generation theranostic agents, the synthesis of ¹⁸ F-labelled [Pd₂ L₄ ]⁴⁺ metallacages is reported. Different spectroscopic and bio-analytical methods support the formation of the host-guest cage-cisplatin complex. The biodistribution profiles of one of the cages, alone or encapsulating cisplatin have been studied by PET/CT imaging in healthy mice in vivo, in combination to ICP-MS ex vivo.

Bioinorganic supramolecular coordination complexes and their biomedical applications

The field of Bioinorganic Supramolecular Chemistry is an emerging research area including metal-based supramolecules resulting from coordination-driven self-assembly (CDSA), whereby metal ions and organic ligands can be easily linked by metal-ligand bonds via Lewis' acid/base interactions. The focus of this 'In a Nutshell' review will be on the family of supramolecular coordination complexes, discrete entities formed by CDSA, which have recently captured widespread attention as a new class of versatile multifunctional materials with broad biological applications including molecular recognition, biosensing, therapy, imaging and drug delivery. Herein, we provide a summary of the state-of-the-art use of these systems in biomedicine, with some selected representative examples, as well as our visions of the challenges and possible directions in the field.

Synergistically Enhancing Tumor Chemotherapy Using an Aggregation-Induced Emission Photosensitizer on Covalently Conjugated Molecularly Imprinted Polymer Nanoparticles

Due to the polygenic and heterogeneous nature of the tumorigenesis process, traditional chemotherapy is far from desirable. Fabricating multifunctional nanoplatforms integrating photodynamic effect can synergistically enhance chemotherapy because they can make the cancer cells much sensitive to chemotherapeutics. However, how to assemble different units in nanoplatforms and minimize side effects caused by chemodrugs and photosensitizers (PSs) still needs to be explored. Herein, a nanoplatform CPP/PS-MIP@DOX is developed using a simultaneously covalently conjugated new aggregation-induced emission (AIE) PS and a cell-penetrating peptide (CPP) on the surface of silica-based molecularly imprinted polymer (MIP) nanoparticles, prepared with doxorubicin (DOX) as the template in the water system via a sol-gel technique. CPP/PS-MIP@DOX has good biocompatibility, high DOX-loading ability, promoted cellular uptake, and sustained and pH-sensitive drug release capability. Furthermore, it can efficiently penetrate into tumor tissue, accurately home to, and accumulate at the tumor site. As a result, a better efficacy with lower cytotoxicity is achieved with a smaller dosage of DOX by utilizing either the photodynamic effect or unique characteristics of the MIP. It is the first nanoplatform fabricated by chemically conjugating AIE PSs directly on the surface of the scaffold via the surface-decorated strategy and successfully applied in cancer therapy. This work provides an effective strategy by constructing AIE PS-based cancer nanomedicines with MIPs as scaffolds.

Aggregation-Induced Emission Metallocuboctahedra for White Light Devices

Materials for organic light-emitting devices which exhibit superior emission properties in both the solution and solid states with a high fluorescence quantum yield have been extensively sought after. Herein, two metallocages, S1 and S2, were constructed, and both showed typical aggregation-induced emission (AIE) features with intense yellow fluorescence. By adding blue-emissive 9,10-dimethylanthracene, pure white light emission can be produced in the solution of S1 and S2. Furthermore, due to the remarkable AIE feature and good fluorescence quantum yield in the solid state, metallocages are highly emissive in the solid state and can be utilized to coat blue LED bulbs or integrate with blue-emitting chips to obtain white light. This study advances the usage of metallocages as practical solid-state fluorescent materials and provides a fresh perspective on highly emissive AIE materials.

Stereoisomeric engineering of aggregation-induced emission photosensitizers towards fungal killing

Fungal infection poses and increased risk to human health. Photodynamic therapy (PDT) as an alternative antifungal approach garners much interest due to its minimal side effects and negligible antifungal drug resistance. Herein, we develop stereoisomeric photosensitizers ((Z)- and (E)-TPE-EPy) by harnessing different spatial configurations of one molecule. They possess aggregation-induced emission characteristics and ROS, viz. ¹O₂ and O₂^-• generation capabilities that enable image-guided PDT. Also, the cationization of the photosensitizers realizes the targeting of fungal mitochondria for antifungal PDT killing. Particularly, stereoisomeric engineering assisted by supramolecular assembly leads to enhanced fluorescence intensity and ROS generation efficiency of the stereoisomers due to the excited state energy flow from nonradiative decay to the fluorescence pathway and intersystem (ISC) process. As a result, the supramolecular assemblies based on (Z)- and (E)-TPE-EPy show dramatically lowered dark toxicity without sacrificing their significant phototoxicity in the photodynamic antifungal experiments. This study is a demonstration of stereoisomeric engineering of aggregation-induced emission photosensitizers based on (Z)- and (E)-configurations.

Wavelength-tunable AIEgens based on 6-methoxy-2-naphthaldehyde: AIE behavior and bioimaging performance

AIE-active dyes have lately received considerable attention due to their versatile applications, especially in bioimaging and theranostics. Herein, 6-methoxy-2-naphthaldehyde was used to construct fluorophores through Knoevenagel condensation with various active methylene compounds. All the obtained compounds showed varying degrees of AIE characteristics. It was worth mentioning that the condensation product of 6-methoxy-2-naphthaldehyde and malononitrile (MOP-e) exhibited a large redshift and a large Stokes shift when forming aggregates. Furthermore, it showed an ultra-wide AIE band which enabled it to be utilized for dual-channel bioimaging. The single crystal X-ray diffraction analysis showed that two different molecular arrangement modes, the monomolecular stacking and the discrete π-π dimeric stacking, existed in the aggregates of MOP-e. The discrete dimeric stacking leads to excimer-induced enhanced emission, which results in its unique AIE behavior. Moreover, MOP-e displayed an excellent bioimaging performance in living cells in green channel and in red channel respectively.

Self-immolative polyprodrug-based tumor-specific cascade amplificated drug release nanosystem for orchestrated synergistic cancer therapy

Reactive oxygen species (ROS)-activated prodrugs can potentially improve the selectivity of chemotherapeutics. However, the inability to release sufficient drugs at tumor sites due to the paucity of ROS, which is required for prodrug activation usually limits the antitumor potency. Herein, a delivery nanosystem with self-amplifiable drug release pattern is constructed by encapsulating a tumor specificity ROS inducer NAD(P)H: quinone oxidoreductase-1 (NQO1)-responsive hemicyanine fluorescent dye (NCyNH₂) in a ROS-responsive self-immolative polyprodrug nanoparticle for orchestrated oxidation-chemotherapy. In response to ROS stimulation, the self-immolative polyprodrug can degrade and release doxorubicin (DOX) through a domino-like fragmentation, which can impart advanced attributes of this nanosystem such as minimum cleavage events required and maximum cleavage speed for disintegration. Thus, the NCyNH₂-loaded self-immolative polyprodrug nanoparticle (SIPN) could be dissociated in response to endogenous ROS, triggering the release of DOX and NCyNH₂. Subsequently, the NCyNH₂ could be activated by intratumoral overexpressed NQO1 to generate additional ROS, which further induces the amplifiable degradation of self-immolative polyprodrug to release sufficient drugs. The in vitro and in vivo studies consistently demonstrate that SIPN amplifies the drug release efficiency of ROS-responsive polyprodrug by specifically upregulating intratumoral ROS levels, resulting in significant antitumor efficacy with minimal side effects.

Semiconducting Polymer Nanoparticles with Surface-Mimicking Protein Secondary Structure as Lysosome-Targeting Chimaeras for Self-Synergistic Cancer Immunotherapy

Immunotherapy has received tremendous attention for tumor treatment, but the efficacy is greatly hindered by insufficient tumor-infiltration of immune cells and immunosuppressive tumor microenvironment. The strategy that can efficiently activate cytotoxic T lymphocytes and inhibit negative immune regulators will greatly amplify immunotherapy outcome, which is however very rare. Herein, a new kind of semiconducting polymer (SP) nanoparticles is developed, featured with surface-mimicking protein secondary structure (SPSS NPs) for self-synergistic cancer immunotherapy by combining immunogenic cell death (ICD) and immune checkpoint blockade therapy. The SPs with excellent photodynamic property are synthesized by rational fluorination, which can massively induce ICD. Additionally, the peptide antagonists are introduced and self-assembled into β-sheet protein secondary structures on the photodynamic NP surface via preparation process optimization, which function as efficient lysosome-targeting chimaeras (LYTACs) to mediate the degradation of programmed cell death ligand-1 (PD-L1) in lysosome. In vivo experiments demonstrate that SPSS NPs can not only elicit strong antitumor immunity to suppress both primary tumor and distant tumor, but also evoke long-term immunological memory against tumor rechallenge. This work introduces a new kind of robust immunotherapy agents by combining well-designed photosensitizer-based ICD induction and protein secondary structures-mediated LYTAC-like multivalence PD-L1 blockade, rendering great promise for synergistic immunotherapy.

Phenylthiol-BODIPY-based supramolecular metallacycles for synergistic tumor chemo-photodynamic therapy

The development of more effective tumor therapy remains challenging and has received widespread attention. In the past decade, there has been growing interest in synergistic tumor therapy based on supramolecular coordination complexes. Herein, we describe two triangular metallacycles (1 and 2) constructed by the formation of pyridyl boron dipyrromethene (BODIPY)-platinum coordination. Metallacycle 2 had considerable tumor penetration, as evidenced by the phenylthiol-BODIPY ligand imparting red fluorescent emission at ∼660 nm, enabling bioimaging, and transport visualization within the tumor. Based on the therapeutic efficacy of the platinum(II) acceptor and high singlet oxygen (¹O₂) generation ability of BODIPY, 2 was successfully incorporated into nanoparticles and applied in chemo-photodynamic tumor therapy against malignant human glioma U87 cells, showing excellent synergistic therapeutic efficacy. A half-maximal inhibitory concentration of 0.35 μM was measured for 2 against U87 cancer cells in vitro. In vivo experiments indicated that 2 displayed precise tumor targeting ability and good biocompatibility, along with strong antitumor effects. This work provides a promising approach for treating solid tumors by synergistic chemo-photodynamic therapy of supramolecular coordination complexes.

Construction of hyperbranched polysiloxane-based multifunctional fluorescent prodrug for preferential cellular uptake and dual-responsive drug release

Hyperbranched polymers hold great promise in nanomedicine for their controlled chemical structures, sizes, multiple terminal groups and enhanced stability than linear amphiphilic polymer assemblies. However, the rational design of hyperbranched polymer-based nanomedicine with low toxic materials, selective cellular uptake, controlled drug release, as well as real-time drug release tracking remains challenging. In this work, a hyperbranched multifunctional prodrug HBPSi-SS-HCPT is constructed basing on the nonconventional aggregation-induced emission (AIE) featured hyperbranched polysiloxanes (HBPSi). The HBPSi is a biocompatible AIE macromolecule devoid of conjugates, showing a high quantum yield of 17.88% and low cytotoxicity. By covalently grafting the anticancer drug, 10-hydroxycamptothecin (HCPT), to the HBPSi through 3,3'-dithiodipropionic acid, HBPSi-SS-HCPT is obtained. The HBPSis demonstrate obvious AIE features and it turned to aggregation-caused quenching (ACQ) after grafting HCPT owing to the FRET behavior between HBPSi and HCPT in HBPSi-SS-HCPT. In addition to on-demand HCPT release in response to changes in environmental pH and glutathione, a series of in vitro and in vivo studies revealed that HBPSi-SS-HCPT exhibits enhanced accumulation in tumor tissues through the enhanced permeation and retention (EPR) effect and preferential cancer cell uptake by charge reversal, thus resulting in apoptotic cell death subsequently. This newly developed multifunctional HBPSi-SS-HCPT prodrug provides a biocompatible strategy for controlled drug delivery, preferential cancer cell uptake, on-demand drug release and enhanced antitumor efficacy.

Pt(ii)-coordinated tricomponent self-assemblies of tetrapyridyl porphyrin and dicarboxylate ligands: are they 3D prisms or 2D bow-ties?

Thermodynamically favored simultaneous coordination of Pt(ii) corners with aza- and carboxylate ligands yields tricomponent coordination complexes with sophisticated structures and functions, which require careful structural characterization to paint accurate depiction of their structure-function relationships. Previous reports claimed that heteroleptic coordination of cis-(Et3P)2PtII with tetrapyridyl porphyrins (M'TPP, M' = Zn or H2) and dicarboxylate ligands (XDC) yielded 3D tetragonal prisms containing two horizontal M'TPP faces and four vertical XDC pillars connected by eight Pt(ii) corners, even though such structures were not supported by their 1H NMR data. Through extensive X-ray crystallographic and NMR studies, herein, we demonstrate that self-assembly of cis-(Et3P)2PtII, M'TPP, and four different XDC linkers having varied lengths and rigidities actually yields bow-tie (⋈)-shaped 2D [{cis-(Et3P)2Pt}4(M'TPP) (XDC)2]4+ complexes featuring a M'TPP core and two parallel XDC linkers connected by four heteroleptic PtII corners instead of 3D prisms. This happened because (i) irrespective of their length (∼7-11 Å) and rigidity, the XDC linkers intramolecularly bridged two adjacent pyridyl-N atoms of a M'TPP core via PtII corners instead of connecting two cofacial M'TPP ligands and (ii) bow-tie complexes are entropically favored over prisms. The electron-rich ZnTPP core of a representative bow-tie complex selectively formed a charge-transfer complex with highly π-acidic 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-heaxacarbonitrile but not with a π-donor such as pyrene. Thus, this work not only produced novel M'TPP-based bow-tie complexes and demonstrated their selective π-acid recognition capability, but also underscored the importance of proper structural characterization of supramolecular assemblies to ensure accurate depiction of their structure-property relationships.

An NIR Discrete Metallacycle Constructed from Perylene Bisimide and Tetraphenylethylene Fluorophores for Imaging-Guided Cancer Radio-Chemotherapy

To promote the clinical theranostic performances of platinum-based anticancer drugs, imaging capability is urgently desired, and their chemotherapeutic efficacy needs to be upgraded. Herein, a theranostic metallacycle (M) is developed for imaging-guided cancer radio-chemotherapy using perylene bisimide fluorophore (PPy) and tetraphenylethylene-based di-Pt(II) organometallic precursor (TPE-Pt) as building blocks. The formation of this discrete supramolecular coordination complex facilitates the encapsulation of M by a glutathione (GSH)-responsive amphiphilic block copolymer to prepare M-loaded nanoparticles (MNPs). TPE-Pt acts as a chemotherapeutic drug and also an excellent radiosensitizer, thus incorporating radiotherapy into the nanomedicine to accelerate the therapeutic efficacy and overcome drug resistance. The NIR-emission of PPy is employed to detect the intracellular delivery and tissue distribution of MNPs in real time. In vitro and in vivo investigations demonstrate the excellent anticancer efficacy combining chemotherapy and radiotherapy; the administration of this nanomedicine effectively inhibits the tumor growth and greatly extends the survival rate of cisplatin-resistant A2780CIS-tumor-bearing mice. Guided by in vivo fluorescence imaging, radio-chemotherapy is precisely carried out, which facilitates boosting of the therapeutic outcomes and minimizing undesired side effects. The success of this theranostic system brings new hope to supramolecular nanomedicines for their potential clinical translations.

Design of a Metallacycle-Based Supramolecular Photosensitizer for In Vivo Image-Guided Photodynamic Inactivation of Bacteria

Bacterial infection is one of the greatest threats to public health. In vivo real-time monitoring and effective treatment of infected sites through non-invasive techniques, remain a challenge. Herein, we designed a PtII metallacycle-based supramolecular photosensitizer through the host-guest interaction between a pillar[5]arene-modified metallacycle and 1-butyl-4-[4-(diphenylamino)styryl]pyridinium. Leveraging the aggregation-induced emission supramolecular photosensitizer, we improved fluorescence performance and antimicrobial photodynamic inactivation. In vivo studies revealed that it displayed precise fluorescence tracking of S. aureus-infected sites, and in situ performed image-guided efficient PDI of S. aureus without noticeable side effects. These results demonstrated that metallacycle combined with host-guest chemistry could provide a paradigm for the development of powerful photosensitizers for biomedicine.

Bringing Inherent Charges into Aggregation-Induced Emission Research

Charged organic molecules, such as DNA, RNA, proteins, and polysaccharides, are ubiquitous and indispensable in natural living systems, which possess specific biological functions to interact with oppositely charged species via electrostatic attraction. The molecules with inherent charges typically differentiate themselves from the neutral ones with unique attributes (e.g., ionic interactions and high polarity), thereby playing a pivotal role in a broad spectrum of areas, including supramolecular chemistry, structural biology, and materials science. It is thus of great importance to explore and develop various charged organic systems for biomimicry and the creation of functional materials. In 2001, our group reported a peculiar luminogen that exhibited weak emission in solution but had significantly enhanced emission in aggregates, and we, for the first time, coined this phenomenon as aggregation-induced emission (AIE). The AIE concept significantly changes the cognition of the scientific community toward classic photophysical phenomena. Since the discovery of this unusual luminescence phenomenon, AIE luminogens (AIEgens) have attracted extensive attention from researchers in a plethora of disciplines because of their high brightness in aggregates, large Stokes shift, excellent photostability, and good biocompatibility. In the past 10 years, our laboratory has expended a great amount of effort to bring inherent charges into AIE research and acquired fruitful achievements.In this Account, we summarize the progress of charged AIE systems primarily made by our laboratory. We start with a brief introduction to charged AIEgens and then discuss their design strategies from molecular and topological perspectives, respectively. Next, we review the unique properties of charged AIEgens, including D-A interactions, anion-π⁺ interactions, and intermolecular electrostatic interactions, with an emphasis on how they differentiate themselves from the neutral analogs. On the one hand, positively charged AIEgens exhibit unique photophysical properties by forming typical donor-acceptor structures to manipulate the emission wavelength or initiate ultralong persistent luminescence. On the other hand, positively charged AIEgens exhibit unique physiochemical properties, such as an adjustable targeting capability toward biological targets and a strong capability for the generation of reactive oxygen species. Furthermore, we showcase the applications of charged AIEgens in imaging and diagnosis, photodynamic therapy, gas separation, and solar desalination. Finally, we conclude this Account with a summary and some perspectives regarding the existing challenges and future directions. We hope that this Account can spark new ideas and inspire scientists from different disciplines to explore this nascent yet promising research area.

Light-emitting self-assembled metallacages

Coordination-driven self-assembly of metallacages has garnered significant interest because of their 3D layout and cavity-cored nature. The well-defined, highly tunable metallacage structures render them particularly attractive for investigating the properties of luminophores, as well as for inducing novel photophysical characters that enable widespread applications. In this review, we summarize the recent advances in synthetic methodologies for light-emitting metallacages, and highlight some representative applications of these metallacages. In particular, we focus on the favorable photophysical properties—including high luminescence efficiency in various physical states, good modularity in photophysical properties and stimulus responsiveness—that have resulted from incorporating ligands displaying aggregation-induced emission (AIE) into metallacages. These features show that the synergy between carrying out coordination-driven self-assembly and using luminophores with novel photophysical characteristics like AIE could stimulate the development of supramolecular luminophores for applications in fields as diverse as sensing, biomedicine and catalysis.

Photo-responsive polymeric nanocarriers for target-specific and controlled drug delivery

Conventional drug delivery systems often have several pharmacodynamic and pharmacokinetic limitations related to their low efficacy and bad safety. It is because these traditional systems cannot always be selectively addressed to their therapeutic target sites. Currently, target-specific and controlled drug delivery is one of the foremost challenges in the biomedical field. In this context, stimuli-responsive polymeric nanomaterials have been recognized as a topic of intense research. They have gained immense attention in therapeutics - particularly in the drug delivery area - due to the ease of tailorable behavior in response to the surroundings. Light irradiation is of particular interest among externally triggered stimuli because it may be specifically localized in a contact-free manner. Light-human body interactions may sometimes be harmful due to photothermal and photomechanical reactions that lead to cell death by photo-toxicity and/or photosensitization. However, these limitations may also be overcome by the use of photo-responsive polymeric nanostructures. This review summarizes recent developments in photo-responsive polymeric nanocarriers used in the field of drug delivery systems, including nanoparticles, nanogels, micelles, nanofibers, dendrimers, and polymersomes, as well as their classification and mechanisms of drug release.

Metal-Coordinated Supramolecular Self-Assemblies for Cancer Theranostics

Metal-coordinated supramolecular nanoassemblies have recently attracted extensive attention as materials for cancer theranostics. Owing to their unique physicochemical properties, metal-coordinated supramolecular self-assemblies can bridge the boundary between traditional inorganic and organic materials. By tailoring the structural components of the metal ions and binding ligands, numerous multifunctional theranostic nanomedicines can be constructed. Metal-coordinated supramolecular nanoassemblies can modulate the tumor microenvironment (TME), thus facilitating the development of TME-responsive nanomedicines. More importantly, TME-responsive organic-inorganic hybrid nanomaterials can be constructed in vivo by exploiting the metal-coordinated self-assembly of a variety of functional ligands, which is a promising strategy for enhancing the tumor accumulation of theranostic molecules. In this review, recent advancements in the design and fabrication of metal-coordinated supramolecular nanomedicines for cancer theranostics are highlighted. These supramolecular compounds are classified according to the order in which the coordinated metal ions appear in the periodic table. Furthermore, the prospects and challenges of metal-coordinated supramolecular self-assemblies for both technical advances and clinical translation are discussed. In particular, the superiority of TME-responsive nanomedicines for in vivo coordinated self-assembly is elaborated, with an emphasis on strategies that enhance the accumulation of functional components in tumors for an ideal theranostic outcome.

Hexameric Lanthanide-Organic Capsules with Tertiary Structure and Emergent Functions

Biological macromolecules always function through a collective behavior of the aggregated constituents, which usually are self-assembled together via noncovalent interactions. Likewise, artificial supramolecular assemblies, whose properties and functions are mainly derived from their primary and secondary structures, may also aggregate into high-order architectures with emergent functions not available on the individual components. Here we report the first example of an insulin-like hexamerization of lanthanide triple helicates toward a 4 nm diameter hexameric capsule via consecutive metal-directed and anion-directed assembly processes. Hierarchical chiral-sorting self-assembly endows hexamers with aggregation-induced stability and emission enhancement. Furthermore, emergent guest-encapsulation function and enantioselectivity toward terpene drugs have been realized in the late-formed central cavity of the hexamers. This study not only provides a feasible strategy for constructing sophisticated and multifunctional lanthanide-organic materials but also sheds some light on the self-assembly processes in nature.

Platinum-Containing Supramolecular Drug Self-Delivery Nanomicelles for Efficient Synergistic Combination Chemotherapy

Supramolecular drug self-delivery systems (SDSDSs) involving active drugs as building blocks linked by supramolecular interactions have been well defined as an advanced chemotherapy strategy. However, the lack of detecting release of drugs from SDSDSs at specific tumor sites inevitably leads to unsatisfactory therapeutic effects, owing to the lack of information regarding the administration of these drugs. In this work, predesigned platinum-containing supramolecular drug self-delivery nanomicelles (SDSDNMs) were employed to synchronously realize drug monitoring by computed tomography imaging, immediately reflecting the evolution of drug release and real-time treatment at the tumor site. The appropriate administration dosage (1.2 mg mL^-1,100 μL) and the injection interval (once every 3 days) needed to guide the antitumor activity of SDSDNMs were then defined, thereby attaining the aim of efficient synergistic combination chemotherapy. In vivo tumor inhibition and histological analyses showed that SDSDNMs exhibited a strong tumor inhibition effect and good safety with respect to normal organs. Such a supramolecular drug self-delivery strategy with monitored functions may offer new potential opportunities for application in the field of synergistic combination chemotherapy.

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Coordination-Driven Self-Assembly of Cyclometalated Iridium Squares Using Linear Aromatic Diisocyanides

Here, we demonstrate facile [4 + 4] coordination-driven self-assembly of cyclometalated iridium(III) using linear aryldiisocyanide bridging ligands (BLs). A family of nine new [Ir(C^N)₂(μ-BL)]₄⁴⁺ coordination cages is described, where C^N is the cyclometalating ligand-2-phenylpyridine (ppy), 2-phenylbenzothiazole (bt), or 1-phenylisoquinoline (piq)-and BL is the diisocyanide BL, with varying spacer lengths between the isocyanide binding sites. These supramolecular coordination compounds are prepared via a one-pot synthesis, with isolated yields of 40-83%. ¹H NMR spectroscopy confirms the selective isolation of a single product, which is affirmed to be the M₄L₄ square by high-resolution mass spectrometry. Detailed photophysical studies were carried out to reveal the nature of the luminescent triplet states in these complexes. In most cases, phosphorescence arises from the [Ir(C^N)₂]⁺ nodes, with the emission color determined by the cyclometalating ligand. However, in two cases, the lowest-energy triplet state resides on the aromatic core of the BL, and weak phosphorescence from that state is observed. This work shows that aromatic diisocyanide ligands enable coordination-driven assembly of inert iridium(III) nodes under mild conditions, producing supramolecular coordination complexes with desirable photophysical properties.

Enhancing near-infrared AIE of photosensitizer with twisted intramolecular charge transfer characteristics via rotor effect for AIE imaging-guided photodynamic ablation of cancer cells

Near-infrared (NIR) aggregation-induced emission (AIE) of previous organic photosensitizers is usually weak because of the competition between twisted intramolecular charge transfer (TICT) effect and AIE. Herein, we report a rational molecular design strategy to boost NIR AIE of photosensitizers and still to keep strong ¹O₂ production capacity via rotor effect. To this end, one new triphenylamine (TPA)-based AIE photosensitizer, TPAM-1, is designed to give strong ability to generate ¹O₂ but weak NIR fluorescence in the aggregate state due to the strong TICT effect. Another new TPA-based AIE photosensitizer, TPAM-2, is designed by introducing three p-methoxyphenyl units as rotors into the structure of TPAM-1 to modulate the competition between AIE and TICT. TPAM-1 and TPAM-2 exhibit stronger ability to generate ¹O₂ in the aggregate state than the commercial photosensitizer, Ce6. Furthermore, TPAM-2 gives much brighter NIR luminescence (25-times higher quantum yield) than TPAM-1 in the aggregate state due to the rotor effect. TPAM-2 with strong NIR AIE and ¹O₂ production capability was encapsulated by DSPE-PEG₂₀₀₀ to give good biocompatibility. The DSPE-PEG₂₀₀₀-encapsulated TPAM-2 nanoparticles show good cell imaging performance and remarkable photosensitive activity for killing HeLa cells. This work provides a new way for designing ideal photosensitizers for AIE imaging-guided photodynamic therapy.

Supramolecular Self-Assembly-Facilitated Aggregation of Tumor-Specific Transmembrane Receptors for Signaling Activation and Converting Immunologically Cold to Hot Tumors

Supramolecular self-assembling peptide systems are attracting increasing interest in the field of cancer theranostics. Additionally, transformation of the immunologically cold tumor microenvironment into hot is of great importance for obtaining high antitumor responses for most immunotherapies. However, as far as it is known, there are nearly no studies on self-assembling peptides reported to be able to convert cold to hot tumors. Herein, a self-assembling peptide-based cancer theranostic agent (named DBT-2FFGYSA) is designed and synthesized, which can target tumor-specific transmembrane Eph receptor A2 (EphA2) receptors selectively and make the receptors form large aggregates. Such aggregate formation promotes the cross-phosphorylations among EphA2 receptors, leading to signal transduction of antitumor pathway. As a consequence, DBT-2FFGYSA can not only visualize EphA2 receptors in a fluorescence turn-on manner, but also specifically suppress the EphA2 receptor-overexpressed cancer cell proliferation and tumor growth. What is more, DBT-2FFGYSA also serves as an effective agent to convert immunologically cold tumors to hot by inducing the immunogenic cell death of EphA2 receptor-overexpressed cancer cells and recruiting massive tumor-infiltrating T cells. This study, thus, introduces a new category of agents capable of converting cold to hot tumors by pure supramolecular self-assembly without any aid of known anticancer drugs.

Biotinylated platinum(ii) metallacage towards targeted cancer theranostics

A biotinylated metallacage was prepared via metal-coordination-driven self-assembly, combining fluorescence, anti-cancer and targeted properties into a single entity. The metallacage was successfully employed for targeted cell imaging and therapy, offering a platform for cancer theranostics.

Polymeric Systems Containing Supramolecular Coordination Complexes for Drug Delivery

Cancer has become a common disease that seriously endangers human health and life. Up to now, the essential treatment method has been drug therapy, and drug delivery plays an important role in cancer therapy. To improve the efficiency of drug therapy, researchers are committed to improving drug delivery methods to enhance drug pharmacokinetics and cancer accumulation. Supramolecular coordination complexes (SCCs) with well-defined shapes and sizes are formed through the coordination between diverse functional organic ligands and metal ions, and they have emerged as potential components in drug delivery and cancer therapy. In particular, micelles or vesicles with the required biocompatibility and stability are synthesized using SCC-containing polymeric systems to develop novel carriers for drug delivery that possess combined properties and extended system tunability. In this study, the research status of SCC-containing polymeric systems as drug carriers and adjuvants for cancer treatment is reviewed, and a special focus is given to their design and preparation.

Coordination-Induced Emission from Tetraphenylethylene Units and Their Applications

Thanks to the potential of aggregation-induced emission (AIE) phenomena, improved stabilities, and the good selectivity and sensitivity of the chemical responses exhibited by the products, coordination-driven self-assembly with tetraphenylethylene (TPE) units has recently received much attention and has been widely investigated for application in chemical sensors, cell imaging agents, light-harvesting systems, and others. Several reviews have emerged on the topics of AIE chemistry and aggregation-induced emission luminogen (AIEgen)-based supramolecular assembles, however, there is still a distinct lack of full overviews of emission enhancement from the viewpoint of metal-coordination effects. Thus, this minireview offers recent advances that have been made in the design and application of TPE-based metallacycles, metallacages, metal-organic frameworks (MOFs) and coordination polymers (CPs).

Single-molecule magnets under dc field with an anion effect: self-assembly of pure dysprosium(iii) metallacycles

The anion-adaptive self-assembly described here not only offers a facile approach to produce large single-molecule magnets but also provides an understanding of how structural factors affect the magnetic properties.

Amphiphilic Rhomboidal Organoplatinum(II) Metallacycles with Encapsulated Doxorubicin for Synergistic Cancer Therapy

Synergistic therapy with nanocarriers is a promising strategy for effective cancer treatment. Here, we synthesized an amphiphilic rhomboidal metallacycle M, in which a glucose-modified pyridine ligand was used to improve water-solubility and an organoplatinum(II) receptor acted as a platinum-based anticancer agent. Moreover, because of the amphiphilic properties, M self-assembled into micelles or nanobelts at different concentrations, and a drug delivery system (DDS) was developed by encapsulating the anticancer drug doxorubicin (DOX) into the micelles. The morphology, cell uptake, cytotoxicity, internalization, and antitumor effect of the DDS were investigated. Under low intracellular pH conditions, the DDS disassembled to release the loaded DOX in situ. The designed DDS exhibited good biocompatibility, synergistic antitumor efficacy, and negligible adverse effects in a U87 tumor-bearing mice model.

Apoptotic effect of novel pyrazolone-based derivative [Cu(PMPP-SAL)(EtOH)] on HeLa cells and its mechanism

Pyrazolone complexes have strong anti-tumor and antibacterial properties, but the anti-tumor mechanism of pyrazolone-based copper complexes has not been fully understood. In this study, the possible mechanism and the inhibitory effect of a novel pyrazolone-based derivative compound [Cu(PMPP-SAL)(EtOH)] on human cervical cancer cells (HeLa cells) was investigated. [Cu(PMPP-SAL)(EtOH)] effectively inhibited proliferation of HeLa cells in vitro with an IC₅₀ value of 2.082 after treatment for 72 h. Cell cycle analysis showed apoptosis was induced by blocking the cell cycle in the S phase. [Cu(PMPP-SAL)(EtOH)] promoted the loss of mitochondrial membrane potential, release of cytochrome c, PARP cleavage, and activation of caspase-3/9 in HeLa cells. Additionally, [Cu(PMPP-SAL)(EtOH)] inhibited the PI3K/AKT pathway and activated the P38/MAPK, and JNK/MAPK pathways. [Cu(PMPP-SAL)(EtOH)] also inhibited the phosphorylation of Iκ-Bα in the NF-κB pathway activated by TNF-α, thus restricting the proliferation of HeLa cells which were activated by TNF-α. In conclusion, [Cu(PMPP-SAL)(EtOH)] inhibited the growth of HeLa cells and induced apoptosis possibly via the caspase-dependent mitochondria-mediated pathway. These results suggest that [Cu(PMPP-SAL)(EtOH)] can be a potential candidate for the treatment of cervical cancer.