Design and Engineering of Hypoxia and Acidic pH Dual-Stimuli-Responsive Intelligent Fluorescent Nanoprobe for Precise Tumor Imaging

A "Dual-Key-and-Lock" MRI Contrast Agent with T1-T2 Switchable Function for Accurate Diagnosis of Tumors

Extremely small iron oxide nanoparticle (ESIONP)-based stimuli-responsive switchable MRI contrast agents (CAs) show great promise for accurate detection of tumors due to their outstanding advantages of high specificity and low background signal. However, currently developed ESIONP-based switchable CAs often suffer single-biomarker-induced responses, which lack absolute specificity to pathological tissues, potentially diminishing diagnostic accuracy. In this study, weak acidity and hypoxia, two of the most remarkable characteristics of tumors, are introduced as dual biomarker stimuli to construct an ESIONP-based switchable MRI CA (DKL-CA), with its signal switch controlled by a "dual-key-and-lock" strategy. Only when DKL-CA is exposed to a coexisting weakly acidic and hypoxic environment can monodispersed ESIONPs form nanoclusters, thereby realizing a switch from the T1 to T2 contrast. Moreover, DKL-CA exhibits favorable biosafety and the capacity for precise tumor diagnosis in tumor-bearing mice. Overall, DKL-CA paves the way for designing highly accurate ESIONP-based MRI CAs for tumor diagnosis.

Scutellarin-loaded pH/H2O2 dual-responsive polymer cyclodextrin mesoporous silicon framework nanocarriers for enhanced cancer therapy

Stimulus-responsive nanomaterials, particularly with targeting capabilities, have garnered significant attention in the cancer therapy. However, the biological safety of these innovative materials in vivo remains unknown, posing a hurdle to their clinical application. Here, a pH/H2O2 dual-responsive and targeting nano carrier system (NCS) was developed using core shell structure of Fe3O4 mesoporous silicon (MSN@Fe3O4) as main body, scutellarin (SCU) as antitumor drug and polymer cyclodextrin (PCD) as molecular switch (denoted as PCD@SCU@MSN@Fe3O4, abbreviated as NCS). The NCS, with an average particle size of 100 nm, displayed exceptional SCU loading capacity, a result of its uniform radial channel structure. The in vitro investigation under condition of pH and H2O2 indicated that NCS performed excellent pH/H2O2-triggered SCU release behavior. The NCS displayed a higher cytotoxicity against tumor cells (Huh7 and HCT116) due to its pH/H2O2 dual-triggered responsiveness, while the PCD@MSN@Fe3O4 demonstrated lower cytotoxicity for both Huh7 and HCT116 cells. In vivo therapeutic evaluation of NCS indicates significant inhibition of tumor growth in mouse subcutaneous tumor models, with no apparent side-effects detected. The NCS not only enhances the bioavailability of SCU, but also utilizes magnetic targeting technology to deliver SCU accurately to tumor sites. These findings underscore the substantial clinical application potential of NCS.

Accelerated Activity-Based Sensing by Fluorogenic Reporter Engineering Enables to Rapidly Determine Unstable Analyte

Accurate detection of labile analytes through activity based fluorogenic sensing is meaningful but remains a challenge because of nonrapid reaction kinetic. Herein, we present a signaling reporter engineering strategy to accelerate azoreduction reaction by positively charged fluorophore promoted unstable anion recognition for rapidly sensing sodium dithionite (Na2S2O4), a kind of widespread used but harmful inorganic reducing agent. Its quick decomposition often impedes application reliability of traditional fluorogenic probes in real samples because of their slow responses. In this work, four azo-based probes with different charged fluorophores (positive, zwitterionic, neutral, and negative) were synthesized and compared. Among of them, with sequestration effect of positively charged anthocyanin fluorophore for dithionite anion via electrostatic attraction, the cationic probe Azo-Pos displayed ultrafast fluorogenic response (∼2 s) with the fastest response kinetic (kpos' = 0.373 s-1) that is better than other charged ones (kzwi' = 0.031 s-1, kneu' = 0.013 s-1, kneg' = 0.003 s-1). Azo-Pos was demonstrated to be capable to directly detect labile Na2S2O4 in food samples and visualize the presence of Na2S2O4 in living systems in a timely fashion. This new probe has potential as a robust tool to fluorescently monitor excessive food additives and biological invasion of harmful Na2S2O4. Moreover, our proposed accelerating strategy would be versatile to develop more activity-based sensing probes for quickly detecting other unstable analytes of interest.

MiRNA and mRNA-Controlled Double-Cascaded Amplifying Circuit Nanosensor for Accurate Discrimination of Breast Cancers in Living Cells, Animals, and Organoids

Metastasis is the leading cause of death in patients with breast cancer. Detecting high-risk breast cancer, including micrometastasis, at an early stage is vital for customizing the right and efficient therapies. In this study, we propose an enzyme-free isothermal cascade amplification-based DNA logic circuit in situ biomineralization nanosensor, HDNAzyme@ZIF-8, for simultaneous imaging of multidimensional biomarkers in live cells. Taking miR-21 and Ki-67 mRNA as the dual detection targets achieved sensitive logic operations and molecular recognition through the cascade hybridization chain reaction and DNAzyme. The HDNAzyme@ZIF-8 nanosensor has the ability to accurately differentiate breast cancer cells and their subtypes by comparing their relative fluorescence intensities. Of note, our nanosensor can also achieve visualization within breast cancer organoids, faithfully recapitulating the functional characteristics of parental tumor. Overall, the combination of these techniques offers a universal strategy for detecting cancers with high sensitivity and holds vast potential in clinical cancer diagnosis.

Recent Advances in Fluorescent Probes for Cancer Biomarker Detection

Many important biological species have been identified as cancer biomarkers and are gradually becoming reliable targets for early diagnosis and late therapeutic evaluation of cancer. However, accurate quantitative detection of cancer biomarkers remains challenging due to the complexity of biological systems and the diversity of cancer development. Fluorescent probes have been extensively utilized for identifying biological substances due to their notable benefits of being non-invasive, quickly responsive, highly sensitive and selective, allowing real-time visualization, and easily modifiable. This review critiques fluorescent probes used for detecting and imaging cancer biomarkers over the last five years. Focuses are made on the design strategies of small-molecule and nano-sized fluorescent probes, the construction methods of fluorescence sensing and imaging platforms, and their further applications in detection of multiple biomarkers, including enzymes, reactive oxygen species, reactive sulfur species, and microenvironments. This review aims to guide the design and development of excellent cancer diagnostic fluorescent probes, and promote the broad application of fluorescence analysis in early cancer diagnosis.

Light-Enhanced Hypoxia-Responsive Gene Editing for Hypoxia-Resistant Photodynamic and Immunotherapy

Hypoxia is a key hallmark of solid tumors and can cause resistance to various treatments such as photodynamics and immunotherapy. Microenvironment-responsive gene editing provides a powerful tool to overcome hypoxia resistance and remodel hypoxic microenvironments for enhanced tumor therapy. Here, a light-enhanced hypoxia-responsive multifunctional nanocarrier is developed to perform spatiotemporal specific dual gene editing for enhanced photodynamic and immunotherapy in breast cancer. As a gated molecule of nanocarrier, the degradation of azobenzene moieties under hypoxic conditions triggers controllable release of Cas9 ribonucleoprotein in hypoxic site of the tumor. Hyaluronic acid is conjugated with chloramine e6 to coat mesoporous silica nanoparticles for targeted delivery in tumors and generation of high levels of reactive oxygen species, which can result in increased hypoxia levels for effective cleavage of azobenzene bonds to improve gene editing efficiency and reduce toxic side effects with light irradiation. Moreover, dual targeting HIF-1α and PD-L1 in the anoxic microenvironments can overcome hypoxia resistance and remodel immune microenvironments, which reduces tumor plasticity and resistance to photodynamic and immunotherapy. In summary, a light-enhanced hypoxia responsive nanocomposite is developed for controllable gene editing which holds great promise for synergistic hypoxia-resistant photodynamic and immunotherapy.

Tumor microenvironment-responsive degradable silica nanoparticles: design principles and precision theranostic applications

Silica nanoparticles have emerged as promising candidates in the field of nanomedicine due to their remarkable versatility and customizable properties. However, concerns about their potential toxicity in healthy tissues and organs have hindered their widespread clinical translation. To address this challenge, significant attention has been directed toward a specific subset of silica nanoparticles, namely degradable silica nanoparticles, primarily because of their excellent biocompatibility and responsive biodegradability. In this review, we provide a comprehensive understanding of degradable silica nanoparticles, categorizing them into two distinct groups: inorganic species-doped and organic moiety-doped silica nanoparticles based on their framework components. Next, the recent progress of tumor microenvironment (TME)-responsive degradable silica nanoparticles for precision theranostic applications is summarized in detail. Finally, current bottlenecks and future opportunities of theranostic nanomedicines based on degradable silica nanoparticles in clinical applications are also outlined and discussed. The aim of this comprehensive review is to shed light on the potential of degradable silica nanoparticles in addressing current challenges in nanomedicine, offering insights into their design, applications in tumor diagnosis and treatment, and paving the way for future advancements in clinical theranostic nanomedicines.

Diverse drug delivery systems for the enhancement of cancer immunotherapy: an overview

Despite the clear benefits demonstrated by immunotherapy, there is still an inevitable off-target effect resulting in serious adverse immune reactions. In recent years, the research and development of Drug Delivery System (DDS) has received increased prominence. In decades of development, DDS has demonstrated the ability to deliver drugs in a precisely targeted manner to mitigate side effects and has the advantages of flexible control of drug release, improved pharmacokinetics, and drug distribution. Therefore, we consider that combining cancer immunotherapy with DDS can enhance the anti-tumor ability. In this paper, we provide an overview of the latest drug delivery strategies in cancer immunotherapy and briefly introduce the characteristics of DDS based on nano-carriers (liposomes, polymer nano-micelles, mesoporous silica, extracellular vesicles, etc.) and coupling technology (ADCs, PDCs and targeted protein degradation). Our aim is to show readers a variety of drug delivery platforms under different immune mechanisms, and analyze their advantages and limitations, to provide more superior and accurate targeting strategies for cancer immunotherapy.

Hypoxia-responsive AIEgens for precise disease theranostics

Specific biomarker-activatable probes have revolutionized theranostics, being beneficial for precision medicine. Hypoxia is a critical pathological characteristic prevalent in numerous major diseases such as cancers, cardiovascular disorders, inflammatory diseases, and acute ischemia. Aggregation-induced emission luminogens (AIEgens) have emerged as a promising tool to tackle the biomedical issues. Of particular significance are the hypoxia-responsive AIEgens, representing a kind of crucial probe capable of delicately sensing and responding to the hypoxic microenvironment, thereby enhancing the precision of disease diagnosis and treatment. In this review, we summarize the recent advances of hypoxia-responsive AIEgens for varied biomedical applications. The hypoxia-responsive structures based on AIEgens, such as azobenzene, nitrobenzene, and N-oxide are presented, which are in response to the reduction property to bring about significant alternations in response spectra and/or fluorescence intensity. The bioapplications including imaging and therapy of tumor and ischemia diseases are discussed. Moreover, the review sheds light on the future challenges and prospects in this field. This review aims to provide comprehensive guidance and understanding into the development of activatable bioprobes, especially the hypoxia-responsive AIEgens for improving the diagnosis and therapy outcome of related diseases.

Fluorescence Enhancement of Adamantane-Modified Dyes in Aqueous Solution via Supramolecular Interaction with Methyl-β-cyclodextrin and Their Application in Cell Imaging

The fluorescence of functional dyes was generally quenched in aqueous solution, which hindered their application in water-bearing detections. In this work, a novel strategy based on host-guest interaction was provided for the purpose of fluorescence enhancement in aqueous solution and cell imaging. Three adamantane-modified fluorescent dyes (Coum-Ad, NP-Ad, NR-Ad) with coumarin, 1,8-naphthalimide and Nile Red as fluorophores were initially designed and prepared. The ((adamantan-1-yl)methyl)amino group, as the auxochrome of those dyes, complexed with methylated β-cyclodextrin (M-β-CD) via supramolecular interaction, and then fluorescent supramolecular nanoparticles (FSNPs) were formed by self-assembly in water. The inclusion equilibrium constant (K) could be as high as 3.94×104  M-1 . With the addition of M-β-CD, fluorescence quantum yields of these dyes were separately improved to 69.8 %, 32.9 % and 41.3 %. Inspired by the above satisfactory results, six adamantane-modified probes organelle-NPAds with organelle-targeting capability were further obtained. As the formation of hydrogen bonds between organelle-NPAd2 and M-β-CD verified by theoretical calculation, K of organelle-NPAd2 (5.13×104  M-1 ~4.53×105  M-1 ) with M-β-CD was higher than that of organelle-NPAd1 (1.15×104  M-1 ~3.66×104  M-1 ) and their fluorescence quantum yields increased to 32.8 %~83.6 % in aqueous solution. In addition, fluorescence enhancement was realized in cell imaging with the addition of M-β-CD.

Iron-Rich Semiconducting Polymer Dots for the Combination of Ferroptosis-Starvation and Phototherapeutic Cancer Therapy

Chemodynamic therapy (CDT) has emerged as an outstanding antitumor therapeutic method due to its selectivity and utilization of tumor microenvironment. However, there are still unmet requirements to achieve a high antitumor efficiency, including the tumor accumulation of catalyst and enrichment of reactants of Fenton reaction. Here, an iron-loaded semiconducting polymer dot modified with glucose oxidase (Pdot@Fe@GOx) is reported to deliver iron ions into tumor tissues and in situ generation of hydrogen peroxide in tumors. On one hand, Pdot@Fe@GOx converts glucose to gluconic acid and hydrogen peroxide (H2 O2 ) in tumor, which not only consumes glucose of tumor cells, but also provides the H2 O2 for the following Fenton reaction. On the other hand, the Pdot@Fe@GOx delivers active iron ions in tumor to perform CDT with the combination of the generated H2 O2 . In addition, the Pdot@Fe@GOx has both photothermal and photodynamic effects under the irradiation of near-infrared laser, which can improve and compensate the CDT effect to kill cancer cells. This Pdot@Fe@GOx-based multiple-mode therapeutic strategy has successfully achieved a synergistic anticancer effect with minimal side effects and has the potential to be translated into preclinical setting for tumor therapy.

A light-up fluorescence probe for wash-free analysis of Mu-opioid receptor and ligand-binding events

With the aggravated burden of opioid use disorder spreading worldwide, demands for new forms of opioid receptor agonist/antagonist constitute immense research interest. The Mu-opioid receptor (MOR) is currently in the spotlight on account of its general involvement in opioid-induced antinociception, tolerance and dependence. MOR binding assay, however, is often complicated by difficulty in MOR separation and purification, as well as the tedious procedure in standard biolayer interferometry and surface plasmon resonance measurements. To this end, we present TPE2N as a light-up fluorescent probe for MOR, which exhibits satisfactory performance in both live cells and lysates. TPE2N was elaborately designed based on the synergistic effect of twisted intramolecular charge-transfer and aggregation-induced emission by incorporating a tetraphenylethene unit to emit strong fluorescence in a restrained environment upon binding with MOR through the naloxone pharmacore. The developed assay enabled high-throughput screening of a compound library, and successfully identified three ligands as lead compounds for further development.

Polysaccharide-Based Stimulus-Responsive Nanomedicines for Combination Cancer Immunotherapy

Cancer immunotherapy is a promising antitumor approach, whereas nontherapeutic side effects, tumor microenvironment (TME) intricacy, and low tumor immunogenicity limit its therapeutic efficacy. In recent years, combination immunotherapy with other therapies has been proven to considerably increase antitumor efficacy. However, achieving codelivery of the drugs to the tumor site remains a major challenge. Stimulus-responsive nanodelivery systems show controlled drug delivery and precise drug release. Polysaccharides, a family of potential biomaterials, are widely used in the development of stimulus-responsive nanomedicines due to their unique physicochemical properties, biocompatibility, and modifiability. Here, the antitumor activity of polysaccharides and several combined immunotherapy strategies (e.g., immunotherapy combined with chemotherapy, photodynamic therapy, or photothermal therapy) are summarized. More importantly, the recent progress of polysaccharide-based stimulus-responsive nanomedicines for combination cancer immunotherapy is discussed, with the focus on construction of nanomedicine, targeted delivery, drug release, and enhanced antitumor effects. Finally, the limitations and application prospects of this new field are discussed.

An AND-gate bioluminescent probe for precise tumor imaging

Sensitivity and specificity are two indispensable requirements to ensure diagnostic accuracy. Dual-locked probes with "AND-gate" logic theory have emerged as a powerful tool to enhance imaging specificity, avoid "false positive" results, and realize correlation analysis. In addition, bioluminescence imaging (BLI) is an excitation-free optical modality with high sensitivity and low background and can thus be combined with a dual-locked strategy for precise disease imaging. Here, we developed a novel AND-gate bioluminescent probe, FK-Luc-BH, which is capable of responding to two different tumor biomarkers (cathepsin L and ClO^-). The good specificity of FK-Luc-BH was proven, as an obvious BL signal could only be observed in the solution containing both cathepsin L (CTSL) and ClO^-. 4T1-fLuc cells and tumors treated with FK-Luc-BH exhibited significantly higher BL signals than those treated with unresponsive control compound Ac-Luc-EA or cotreated with FK-Luc-BH and a ClO^- scavenger/cathepsin inhibitor, demonstrating the ability of FK-Luc-BH to precisely recognize tumors in which CTSL and ClO^- coexist.

The Role of Cyclodextrin in the Construction of Nanoplatforms: From Structure, Function and Application Perspectives

Cyclodextrins (CyDs) in nano drug delivery systems have received much attention in pursuit of good compatibility, negligible toxicity, and improved pharmacokinetics of drugs. Their unique internal cavity has widened the application of CyDs in drug delivery based on its advantages. Besides this, the polyhydroxy structure has further extended the functions of CyDs by inter- and intramolecular interactions and chemical modification. Furthermore, the versatile functions of the complex contribute to alteration of the physicochemical characteristics of the drugs, significant therapeutic promise, a stimulus-responsive switch, a self-assembly capability, and fiber formation. This review attempts to list recent interesting strategies regarding CyDs and discusses their roles in nanoplatforms, and may act as a guideline for developing novel nanoplatforms. Future perspectives on the construction of CyD-based nanoplatforms are also discussed at the end of this review, which may provide possible direction for the construction of more rational and cost-effective delivery vehicles.

Quercetin Nanoparticle-Based Hypoxia-Responsive Probe for Cancer Detection

In this study, we developed functional nanomaterials via a phenolic-enabled nanotechnology strategy for hypoxia detection employing quercetin (QCT), an abundant flavonoid, as a polyphenolic system. The nano form of QCT was stabilized by coating it with polyethylene glycol (PEG) before loading it with a flavylium dye (Flav) as a pH indicator. The nanosystem, Flav@QCT-PEG, collapsed when it was in an acidic environment, i.e., pH 5, leading to the release of Flav, which activated the fluorescent signal. Therefore, Flav@QCT-PEG was applied to detect hypoxic tumors, known to be acidic, and responded to hypoxic environments in a dose- and time-dependent manner.

De novo design of a novel AIE fluorescent probe tailored to autophagy visualization via pH manipulation

BACKGROUND

Macroautophagy is an essential cellular self-protection mechanism, and defective autophagy has been considered to contribute to a variety of diseases. During the process, cytoplasmic components are transported via autophagosomes to acidic lysosomes for metabolism and recycling, which represents application niches for lysosome-targeted fluorescent probes. Additionally, in view of the complexity of the autophagy pathway, it entails more stringent requirements for probes suitable for monitoring autophagy. Meanwhile, aggregation-induced emission (AIE) fluorescent probes have been impressively demonstrated in the biomedical field, which bring fascinating possibilities to the autophagy visualization.

METHODS

We reported a generalizable de novo design of a novel pH-sensitive AIE probe ASMP-AP tailored to lysosome targeting for the interpretation of autophagy. Firstly, the theoretical calculation was carried out followed by the investigation of optical properties. Then, the performance of ASMP-AP in visualizing autophagy was corroborated by starvation or drugs treatments. Furthermore, the capability of ASMP-AP to monitor autophagy was demonstrated in ex vivo liver tissue and zebrafish in vivo.

RESULTS

ASMP-AP displays a large stokes shift, great cell permeability and good biocompatibility. More importantly, ASMP-AP enables a good linear response to pH, which derives from the fact that its aggregation state can be manipulated by the acidity. It was successfully applied for imaging autophagy in living cells and was proved capable of monitoring mitophagy. Moreover, this novel molecular tool was validated by ex vivo visualization of activated autophagy in drug-induced liver injury model. Interestingly, it provided a meaningful pharmacological insight that the melanin inhibitor 1-phenyl-2-thiourea (PTU)-induced autophagy was clearly presented in wild-type zebrafish.

CONCLUSIONS

ASMP-AP offers a simple yet effective tool for studying lysosome and autophagy. This is the first instance to visualize autophagy in zebrafish using a small-molecule probe with AIE characters, accurate lysosome targeting and simultaneous pH sensitivity. Ultimately, this novel fluorescent system has great potential for in vivo translation to fuel autophagy research.

Multi-stimuli-responsive molecular fluorescent probes for bioapplications

Stimuli-responsive fluorescent probes have been widely utilized in detecting the physiological and pathological states of living systems. Numerous stimuli-responsive fluorescent probes have been developed due to their advantages of good sensitivity, high resolution, and high contrast fluorescent signals. In this feature article, the progress of multi-stimuli-responsive probes, including organic molecules and metal complexes, for the detection of various biomarkers for bio-applications is summarized. The feature article focuses on the applications of organic-molecule- and metal-complex-based molecular probes in biological systems for detecting different biomarkers of cancer or other diseases. The current challenges and potential future directions of these probes for applications in biological systems are also discussed.

Carboxylated paclitaxel prodrug nanofibers for enhanced chemotherapy

The facile availability of nanoformulations with enhanced antitumor performance remains a big challenge. Herein, we synthesize paclitaxel prodrugs with amphiphilic structures and robust assembling ability. Carboxylated paclitaxel prodrugs (PSCB) containing disulfide bonds prefer to form exquisite nanofibers, while phenylcarbinol end capped paclitaxel prodrugs (PSP) assemble into spherical nanoparticles. The transformation of morphology from nanofibers to nanorods can be realized via tuning the content of paclitaxel. Hydrophilic domains of PSCB nanofibers accelerate the cleavage of disulfide bond for rapid drug release in tumor cells, thus exhibiting the enhanced cytotoxicity and antitumor activity. This study provides a crucial insight into the functional design of hydrophobic drugs to improve chemotherapy.

Fluorescence-Activating and Absorption-Shifting Nanoprobes for Anaerobic Tracking of Gut Microbiota Derived Vesicles

Outer membrane vesicles (OMVs) are crucial for bacterial intercellular communication and the crosstalk between the gut microbiota and its host. Methods capable of visualizing gut microbiota derived OMVs would be of great significance but have been rarely reported. Here, nanoprobes carrying a fluorescence-activating and absorption-shifting tag are prepared by combining genetic engineering and antibiotic-boosted vesicle formation and release. Benefiting from their natural structure and molecular oxygen-independent emission, the resulting nanovesicles can be applied as endogenous fluorescence probes to anaerobically track gut microbiota associated OMVs. These nanoprobes show flexibility in on-demand fluorescence turn-on/off and reversibly switchable emission bands for intelligent and dual-color imaging. With these special characteristics, the behaviors of microbiota OMVs to not only inhibit specific pathogenic strains through membrane fusion but also repair the intestinal barrier via entering intestinal epithelia and promoting the expressions of tight junctions are tracked and identified in the gut. Based on these discoveries, OMVs are disclosed to be able to remit inflammation in a murine model of colitis following transplantation to the intestine by oral delivery. This work provides an approach to visualize the dynamics of the gut microbiota and disclose potential targets for disease intervention.

Afterglow/Fluorescence Dual-Emissive Ratiometric Oxygen Probe for Tumor Hypoxia Imaging

Hypoxia is a common feature of many diseases such as solid tumors. The measurement and imaging of oxygen (O₂) are extremely important for disease diagnosis and therapy evaluation. In this work, the afterglow/fluorescence dual-emissive ratiometric O₂ probe based on a photochemical reaction-based afterglow system is reported. The afterglow is highly sensitive to O₂ because the O₂ content is directly related to the ¹O₂ yield and eventually affects the afterglow intensity. The O₂-insensitive fluorescence of an emitter can serve as an internal reference. As the O₂ concentration changes from 0.08 to 18.5 mg L^-1, the ratio value shows a remarkable 53-fold increase. Compared with the intensity of a single peak, the ratiometric signal can eliminate the interference of the probe concentration to achieve higher accuracy. This afterglow/fluorescence dual-emissive ratiometric O₂ probe is successfully applied to hypoxia imaging in tumor-bearing mice, which may further promote the development of O₂ sensing in the biomedical field.

Intelligent Dual-Lock Deoxyribonucleic Acid Automatons Boosting Precise Tumor Imaging

An early and accurate cancer diagnosis holds the potential to improve treatment and prognosis. Nevertheless, the complexity of the biological system limits the selectivity of existing approaches and makes tumor imaging in vivo particularly challenging. In this study, tumor-specific fluorescence imaging was achieved by building intelligent dual-lock deoxyribonucleic acid automatons (IDEAs) that employed a DNA walking system standing on ZrMOF@MnO₂ multifunctional nanocomposites for controllable molecular recognition. The IDEAs exhibited significantly enhanced fluorescence signals only in the coexistence of both miRNA and GSH of tumor cells, enabling accurate distinguishing of tumor cells from healthy ones. Furthermore, the feasibility and specificity of IDEAs were also validated in vivo with tumor bearing mice successfully. This work highlights the potential of the proposed IDEA strategy for tumor-specific imaging, paving the way for successful precision diagnosis and treatment.

Trityl Quinodimethane Derivatives as Unimolecular Triple-Function Extracellular EPR Probes for Redox, pH, and Oxygen

Electron paramagnetic resonance (EPR) spectroscopy and imaging coupled with the use of suitable probes is a promising tool for assessment of the tumor microenvironment (TME). Measurement of multiple TME parameters by EPR is very desirable but challenging. Herein, we designed and synthesized a class of negative-charged trityl quinodimethane MTPs as unimolecular triple-function extracellular probes for redox, pH, and oxygen (O2) levels. Using the deuterated analogue, dMTP5, which has an optimal pKa as well as high sensitivity to bioreduction and O2, we reasonably evaluated pH effects on efflux of reducing agents from HepG2 cells and cellular O2 consumption.

Bioresponsive Immunotherapeutic Materials

The human immune system is an interaction network of biological processes, and its dysfunction is closely associated with a wide array of diseases, such as cancer, infectious diseases, tissue damage, and autoimmune diseases. Manipulation of the immune response network in a desired and controlled fashion has been regarded as a promising strategy for maximizing immunotherapeutic efficacy and minimizing side effects. Integration of "smart" bioresponsive materials with immunoactive agents including small molecules, biomacromolecules, and cells can achieve on-demand release of agents at targeted sites to reduce overdose-related toxicity and alleviate off-target effects. This review highlights the design principles of bioresponsive immunotherapeutic materials and discusses the critical roles of controlled release of immunoactive agents from bioresponsive materials in recruiting, housing, and manipulating immune cells for evoking desired immune responses. Challenges and future directions from the perspective of clinical translation are also discussed.

Hypoxia-responsive Immunostimulatory Nanomedicines Synergize with Checkpoint Blockade Immunotherapy for Potentiating Cancer Immunotherapy

Inducing cell death while simultaneously enhancing antitumor immune responses is a promising therapeutic approach for multiple cancers. Celastrol (Cel) and 7-ethyl-10-hydroxycamptothecin (SN38) have contrasting physicochemical properties, but strong synergy in immunogenic cell death induction and anticancer activity. Herein, a hypoxia-sensitive nanosystem (CS@TAP) was designed to demonstrate effective immunotherapy for colorectal cancer by systemic delivery of an immunostimulatory chemotherapy combination. Furthermore, the combination of CS@TAP with anti-PD-L1 mAb (αPD-L1) exhibited a significant therapeutic benefit of delaying tumor growth and increased local doses of immunogenic signaling and T-cell infiltration, ultimately extending survival. We conclude that CS@TAP is an effective inducer of immunogenic cell death (ICD) in cancer immunotherapy. Therefore, this study provides an encouraging strategy to synergistically induce immunogenic cell death to enhance tumor cytotoxic T lymphocytes (CTLs) infiltration for anticancer immunotherapy.

Hypoxia-responsive Immunostimulatory Nanomedicines Synergize with Checkpoint Blockade Immunotherapy for Potentiating Cancer Immunotherapy

Inducing cell death while simultaneously enhancing antitumor immune responses is a promising therapeutic approach for multiple cancers. Celastrol (Cel) and 7-ethyl-10-hydroxycamptothecin (SN38) have contrasting physicochemical properties, but strong synergy in immunogenic cell death induction and anticancer activity. Herein, a hypoxia-sensitive nanosystem (CS@TAP) was designed to demonstrate effective immunotherapy for colorectal cancer by systemic delivery of an immunostimulatory chemotherapy combination. Furthermore, the combination of CS@TAP with anti-PD-L1 mAb (αPD-L1) exhibited a significant therapeutic benefit of delaying tumor growth and increased local doses of immunogenic signaling and T-cell infiltration, ultimately extending survival. We conclude that CS@TAP is an effective inducer of immunogenic cell death (ICD) in cancer immunotherapy. Therefore, this study provides an encouraging strategy to synergistically induce immunogenic cell death to enhance tumor cytotoxic T lymphocytes (CTLs) infiltration for anticancer immunotherapy.

Tumor Microenvironment-Activable Manganese-Boosted Catalytic Immunotherapy Combined with PD-1 Checkpoint Blockade

Immune checkpoint blockade (ICB) therapy has attracted widespread attention in cancer treatment. Due to the low immunogenicity and immune suppression state in the tumor microenvironment (TME), the therapeutic effects are only moderate. Herein, a TME-activable manganese-boosted catalytic immunotherapy is designed for synergism with ICB therapy to kill tumors efficiently. The tumor cell membrane (CM)-wrapping multienzyme-mimic manganese oxide (MnO_x) nanozyme termed CM@Mn showed intrinsic peroxidase and oxidase-like activities in an acidic TME. These activities can generate toxic hydroxyl (^•OH) and superoxide radicals (^•O₂^-) for tumor cell killing and evoking immunogenic cell death (ICD). Furthermore, the TME-responsive release of Mn²⁺ directly promotes dendritic cell maturation and macrophage M1 repolarization, resulting in the reversal of an immunosuppressive TME into an immune-activating environment. Additionally, tumor hypoxia relief caused by catalase-like activity also contributes to the process of TME reversal. Finally, a robust tumor-specific T cell-mediated antitumor response occurs with the support of the PD-1 checkpoint blockade. The proliferation of primary and metastatic tumors was inhibited, and a long-term immune memory effect was induced. The therapeutic strategy outlined here may serve as a promising candidate for tumor-integrated treatment.

Tannic Acid-Assisted Biomineralization Strategy for Encapsulation and Intracellular Delivery of Protein Drugs

Protein therapy has been considered to be one of the most direct and safe ways to regulate cell function and treat tumors. However, safe and effective intracellular delivery of protein drugs is still a key challenge. Herein, we developed a tannic acid-assisted biomineralization strategy for the encapsulation and intracellular delivery of protein drugs. RNase A and glucose oxidase (GOD) were choose as the protein drug model. RNase A, GOD, TA, and Mn²⁺ are mixed in one pot to attain RG@MT, and CaCO₃ coating is subsequently carried out to construct RG@MT@C through biomineralization. Once RG@MT@C is endocytosed, the acidic environment of the lysosome will dissolve the protective layer of CaCO₃ and produce plenty of CO₂ to cause lysosome bursting, ensuring the lysosome escape of the RG@MT@C and thus releasing the generated TA-Mn²⁺, RNase A, and GOD into the cytoplasm. The released substances would activate starvation therapy, chemodynamic therapy, and protein therapy pathways to ensure a high performance of cancer therapy. Due to simple preparation, low toxicity, and controlled release in the tumor microenvironment, we expect it can realize efficient and nondestructive delivery of protein drugs and meet the needs for precise, high performance of synergistically antitumor therapy in biomedical applications.

Potential of fluorescent nanoprobe in diagnosis and treatment of Alzheimer's disease

Alzheimer's disease (AD) is well known for its insidious nature, slow progression and high incidence as a neurodegenerative disease. In the past, diagnosis of AD mainly depended on analysis of a patient's cognitive ability and behavior. Without a unified standard for analysis methods, this is prone to produce incorrect diagnoses. Currently, definitive diagnosis mainly relies on histopathological examination. Because of the advantages of precision, noninvasiveness, low toxicity and high spatiotemporal resolution, fluorescent nanoprobes are suitable for the early diagnosis of AD. This review summarizes the research progress of different kinds of fluorescent nanoprobes for AD diagnosis and therapy in recent years and provides an outlook on the development prospects of fluorescent nanoprobes.

Self-Assembly of Small Organic Molecules into Luminophores for Cancer Theranostic Applications

Self-assembled biomaterials have been widely explored for real-time fluorescence imaging, imaging-guided surgery, and targeted therapy for tumors, etc. In particular, small molecule-based self-assembly has been established as a reliable strategy for cancer theranostics due to the merits of small-sized molecules, multiple functions, and ease of synthesis and modification. In this review, we first briefly introduce the supramolecular chemistry of small organic molecules in cancer theranostics. Then, we summarize and discuss advanced small molecule-based self-assembly for cancer theranostics based on three types, including peptides, amphiphilic molecules, and aggregation-induced emission luminogens. Finally, we conclude with a perspective on future developments of small molecule-based self-assembled biomaterials integrating diagnosis and therapy for biomedical applications. These applications highlight the opportunities arising from the rational design of small organic molecules with self-assembly properties for precision medicine.

Stimuli-responsive nanoassemblies for targeted delivery against tumor and its microenvironment

Despite the emergence of various cancer treatments, such as surgery, chemotherapy, radiotherapy, and immunotherapy, their use remains restricted owing to their limited tumor elimination efficacy and side effects. The use of nanoassemblies as delivery systems in nanomedicine for tumor diagnosis and therapy is flourishing. These nanoassemblies can be designed to have various shapes, sizes, and surface charges to meet the requirements of different applications. It is crucial for nanoassemblies to have enhanced delivery of payloads while inducing minimal to no toxicity to healthy tissues. In this review, stimuli-responsive nanoassemblies capable of combating the tumor microenvironment (TME) are discussed. First, various TME characteristics, such as hypoxia, oxidoreduction, adenosine triphosphate (ATP) elevation, and acidic TME, are described. Subsequently, the unique characteristics of the vascular and stromal TME are differentiated, and multiple barriers that have to be overcome are discussed. Furthermore, strategies to overcome these barriers for successful drug delivery to the targeted site are reviewed and summarized. In conclusion, the possible challenges and prospects of using these nanoassemblies for tumor-targeted delivery are discussed. This review aims at inspiring researchers to develop stimuli-responsive nanoassemblies for tumor-targeted delivery for clinical applications.

A "Dual-Source, Dual-Activation" Strategy for an NIR-II Window Theranostic Nanosystem Enabling Optimal Photothermal-Ion Combination Therapy

The activatable imaging technique in the second near-infrared window (NIR-II) utilizes the stimulation of cancer-associated biomarkers for specific imaging to guide precise NIR-II photothermal therapy. However, most activatable nanoprobes with single-source stimulation are insufficient in providing comprehensive information regarding the tumor, severely restricting the therapeutic optimization, especially in NIR-II photothermal therapy (PTT)-based combination therapy. Herein, a "dual-source, dual-activation" strategy-based multifunctional nanosystem, PPAC, is reported as a promising tool for activatable NIR-II fluorescence (FL)/ratiometric photoacoustic (PA) imaging-guided "localization-timing" photothermal-ion therapy (PTIT). A fibroblast activation protein (FAP)-responsive peptide to modify the surface of Pd nanosheets with excellent NIR-II absorption ability can efficiently cross-link BSA-CQ4T to realize NIR-II FL quenching, followed by the loading of Ag to construct the PPAC. Triggered by the specific cleavage with FAP on the perivascular cancer-associated fibroblasts (first source), the PPAC can correspondingly release BSA-CQ4T for rapid fluorescence recovery. The nanosystems are subsequently taken up by tumor cells, where the overexpressed H₂ O₂ (second source) promotes the oxidation of Ag shell to Ag⁺ , and further leads the real-time ratiometric PA signals (Ag-PA660/Pd-PA1050) that can monitor the Ag⁺ ions-related production efficiency and therapeutic performance. Intelligent integration of dual-modality imaging information can comprehensively provide the right time-point and site-specificity for selective NIR-II PTT.

Preparation and application of pH-responsive drug delivery systems

Microenvironment-responsive drug delivery systems (DDSs) can achieve targeted drug delivery, reduce drug side effects and improve drug efficacies. Among them, pH-responsive DDSs have gained popularity since the pH in the diseased tissues such as cancer, bacterial infection and inflammation differs from a physiological pH of 7.4 and this difference could be harnessed for DDSs to release encapsulated drugs specifically to these diseased tissues. A variety of synthetic approaches have been developed to prepare pH-sensitive DDSs, including introduction of a variety of pH-sensitive chemical bonds or protonated/deprotonated chemical groups. A myriad of nano DDSs have been explored to be pH-responsive, including liposomes, micelles, hydrogels, dendritic macromolecules and organic-inorganic hybrid nanoparticles, and micron level microspheres. The prodrugs from drug-loaded pH-sensitive nano DDSs have been applied in research on anticancer therapy and diagnosis of cancer, inflammation, antibacterial infection, and neurological diseases. We have systematically summarized synthesis strategies of pH-stimulating DDSs, illustrated commonly used and recently developed nanocarriers for these DDSs and covered their potential in different biomedical applications, which may spark new ideas for the development and application of pH-sensitive nano DDSs.

Recent advances in dual-target-activated fluorescent probes for biosensing and bioimaging

Fluorescent probes have been powerful tools for visualizing and quantifying multiple dynamic processes in living cells. However, the currently developed probes are often constructed by conjugation a fluorophore with a recognition moiety and given signal-output after triggering with one singly target interest. Compared with the single-target-activated fluorescent probes mentioned above, the dual-target-activated ones, triggering with one target under stimulus (such as photoirradiation, microenvironment) or another targets, have the advantages of advoiding nonspecific activation and "false positive" results in complicated environments. In recent years, many dual-target-activated fluorescent probes have been developed to detect various biologically relevant species. In view of the importance of a comprehensive understanding of dual-target- activated fluorescent probes, a thorough summary of this topic is urgently needed. However, no comprehensive and critical review on dual target activated fluorescent probes has been published recently. In this review, we focus on the dual-target-activated fluorescent probes and briefly outline their types and current state of development. In each type, the chemical structure, proposed responsive mechanism and application of probes are highlighted. At last, the challenges and prospective opportunities of every type were proposed.

Noncovalent Dual-Locked Near-Infrared Fluorescent Probe for Precise Imaging of Tumor via Hypoxia/Glutathione Activation

Stimulus-responsive fluorescent probes have broad applications in the early detection and treatment of tumors and thus promote the personalized treatment of tumors and improve patient survival. Among the repertoires of probes, dual-locked near-infrared (NIR) fluorescent probes are of great significance due to their improved specificity and multiplex detection in tumor imaging but remain to be explored. In this work, a facile noncovalent strategy for constructing dual-locked probes was proposed. A glutathione (GSH)-activatable single-locked probe CySS (first lock) was preloaded into a hypoxia-responsive molecular container CF3C4A (second lock) through a host-guest interaction to form the dual-locked probe CF3C4A-CySS. Under physiological conditions, CF3C4A-CySS binds strongly to avoid undesired leakage in normal tissues. We have proven that CF3C4A-CySS can be activated and "turn on" its NIR fluorescent signal under the dual key stimulation of hypoxia and GSH in the tumor microenvironment, which enables precise tumor imaging with enhanced accuracy and specificity. Both in vitro and in vivo results indicated the superiority of CF3C4A-CySS in tumor imaging. This work not only provides an effective tool for tumor imaging but also proposes a promising strategy for dual-locked imaging agent construction.

Engineering defected 2D Pd/H-TiO2 nanosonosensitizers for hypoxia alleviation and enhanced sono-chemodynamic cancer nanotherapy

Background

Sonodynamic therapy (SDT) is a burgeoning modality for cancer therapy owing to its high tissue-penetrating capability, controllability and safety. Whereas, the undesirable reactive oxygen species (ROS) yield of sonosensitizers and tumor hypoxia are two vulnerable spots of SDT. Therefore, it is an advisable strategy to augment ROS level and simultaneously relieve hypoxia for SDT to arrive its full potential in cancer treatment.

Results

In this work, the defected two-dimensional (2D) Pd/H-TiO₂ nanosheets (NSs) with triple antineoplastic properties were dexterously elaborated and engineered using a facile one-pot Pd-catalyzed hydrogenation tactic by loading a tiny amount of Pd and then inletting hydrogen flow at atmospheric pressure and temperature. The 2D black Pd/H-TiO₂ NSs with oxygen defects exerted eximious SDT effect based on the decreased bandgap that made it easier for the separation of electrons and holes when triggered by ultrasound as theoretically guided by density functional theory calculations. Additionally, Pd/H-TiO₂ NSs could serve as Fenton-like agents because of the presence of oxygen defects, facilitating the conversion of hydrogen peroxide into hydroxyl radicals for exerting the chemodynamic therapy (CDT). Simultaneously, the introduced tiny Pd component possessed catalase-like activity responsible for oxygen production to ameliorate hypoxic condition and thus contributed to improving SDT and CDT efficacies. Both in vitro and in vivo results provided compelling evidences of high ROS yield and aggrandized sono-chemodynamic effect of Pd/H-TiO₂ nanosonosensitizers with the detailed underlying mechanism investigation by RNA sequencing.

Conclusion

This work delves the profound potential of Pd-catalyzed hydrogenated TiO₂ on oncotherapy, and the effective antineoplastic performance and ignorable therapeutic toxicity make it a powerful competitor among a cornucopia of nanosonosensitizers.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01398-6.

Triggered azobenzene-based prodrugs and drug delivery systems

Azobenzene-based molecules show unique trans-cis isomerization upon ultraviolet light irradiation, which induce the change of polarity, crystallinity, stability, and binding affinity with pharmacological target. Moreover, azobenzene is the substrate of azoreductase that is often overexpressed in many pathological sites, e.g. hypoxic solid tumor. Therefore, azobenzene can be a multifunctional molecule in material science, pharmaceutical science and biomedicine because of its sensitivity to light, hypoxia and certain enzymes, hence showing potential application in site-specific smart therapy. Herein we focus on the employment of azobenzene and its derivatives for engineering triggered prodrug and drug delivery systems, and provide an overview of photoswitchable azo-based prodrugs, the associated problems regarding ultraviolet light and reversible isomerization, as well as the potential solutions. We also present the advance of azo-bearing delivery vehicles wherein azobenzene act as the linker, capping agent, and building block, and discuss the corresponding mechanisms for controlled cargo release, endocytosis enhancement and sensitization of free radical cancer therapy.

Dual Imaging of Poly(ADP-ribose) Polymerase-1 and Endogenous H2O2 for the Diagnosis of Cancer Cells Using Silver-Coated Gold Nanorods

The imaging of tumor-related multitarget molecules is of great significance to raise the diagnostic accuracy for malignant tumors. Poly(ADP-ribose) polymerase-1 (PARP-1) has emerged as a potential clinical biomarker for tumor diagnosis due to its specific overexpression in cancer cells. High levels of H₂O₂ in the tumor microenvironment play vital roles in driving cancer progression. Inspired by these achievements, we employed a silver-coated gold nanorod (Au@Ag NR) as a plasmonic probe for dual imaging of intracellular PARP-1 and H₂O₂ under a dark-field microscope (DFM). Au@Ag NR was used not only to distinguish tumor cells from normal cells but also to induce the apoptosis of cancer cells owing to the etching of Ag shell by H₂O₂, accompanied by the color change from green to orange. On the other hand, Au@Ag NRs modified with active double-stranded DNA (dsDNA) could be utilized to image PARP-1 in cancer cells and quantitatively detect PARP-1 in vitro by naked eyes or DFM. The reason is that PARP-1 polymerized nicotinamideadenine dinucleotide (NAD⁺) into large and hyperbranched poly(ADP-ribose) polymer (PAR) on the surface of Au@Ag NRs, preventing the Ag shell from being etched by H₂O₂. As the PARP-1 activity increased, a blue-shift of the adsorption peak occurred along with a color change from pale pink to green, which could be recognized by naked eyes. Under DFM, its scattering light varied obviously from red to green. The proposed dual-imaging strategy holds good prospects in cancer diagnosis.

Dual-stimuli-responsive porous polymer enzyme reactor for tuning enzymolysis efficiency

A strategy for preparing a dual-stimuli-responsive porous polymer membrane enzyme reactor (D-PPMER) is described, consisting of poly (styrene-maleic anhydride-N-isopropylacrylamide-acrylate-3',3'-dimethyl-6-nitro-spiro[2H-1-benzopyran-2,2'-indoline]-1'-esterspiropyran ester) [P(S-M-N-SP)] and D-amino acid oxidase. Tunable control via "on/off" 365 nm UV light irradiation and temperature variation was used to change the membrane surface configuration and adjust the enzymolysis efficiency of the D-PPMER. A chiral capillary electrophoresis technique was developed for evaluation of the enzymatic efficiency of D-PPMER with a Zn(II)-dipeptide complex as the chiral selector and D,L-serine as the substrate. Interestingly, the enzymatic kinetic reaction rate of D-PPMER under UV irradiation at 36 °C (9.2 × 10^-2 mM·min^-1) was 3.2-fold greater than that of the free enzyme (2.9 × 10^-2 mM·min^-1). This was because upon UV irradiation at high temperature, the P(SP) and P(N) moieties altered from a "stretched" to a "curled" state to encapsulate the enzyme in smaller cavities. The confinement effect of the cavities further improved the enzymatic efficiency of the D-PPMER. This protocol highlights the outstanding potential of smart polymers, enables tunable control over the kinetic rates of stimuli-responsive enzyme reactors, and establishes a platform for adjusting enzymolysis efficiency using two different stimuli.