Chemical Design and Synthesis of Functionalized Probes for Imaging and Treating Tumor Hypoxia

Long afterglow hybrid nanoplatform for integrated NIR-Ⅱ imaging diagnosis and triple-synergistic treatment of choroidal melanoma

The key to the treatment of choroidal melanoma (CM) is to improve diagnostic efficiency and find a high-performance treatment to replace the traditional treatment of radiotherapy and enucleation. In this paper, for the first time, long afterglow luminescence material was applied to the integrated diagnosis and treatment of eyes, with its unique advantages in photoluminescence and afterglow luminescence to solve the bottleneck problem of real-time irradiation required for photothermal and photodynamic therapy (PTT and PDT). Based on the excellent photoluminescence and afterglow properties of Zn1.3Ga1.4Ge0.3O4:Cr0.004Yb0.04Er0.004 (ZGGO) nanoparticles, a nanoplatform ZGGO@Au@UiO-66@ZnPc:Dox-FA (GAUZD-FA) for NIR-Ⅱ imaging and triple-synergistic therapy (PTT, PDT and sustained-release drug) was constructed. GAUZD-FA showed excellent imaging and therapeutic ability for CM in vitro and in vivo under a systematic comparison of NIR imaging detection and anti-tumor activity. In addition, the precise active targeting of folic acid (FA) on tumor cells protected normal tissues from damage and stayed intraocularly for a relatively long time. This multi-functional nanoplatform provides a new strategy for an ideal mode of single injection and multiple treatments of CM.

A Brain-Targeting NIR-II Polymeric Phototheranostic Nanoplatform toward Orthotopic Drug-Resistant Glioblastoma

Glioblastoma is the most common and devastating brain tumor owing to its high invasiveness and high-frequency drug resistance. Near infrared-II (NIR-II) imaging-guided phototherapy based on polymer luminogens provides a promising remedy against drug-resistant glioma, but it is difficult to maximize photoenergy utilization. Herein, we designed a series of semiconducting polymers to boost the visualization and ablation of glioblastoma. By subtly engineering the side chains or substituents on the phenothiazine and thiophene moieties, an NIR-II polymer luminogen with high-quality fluorescence performance, good solubility, superior photothermal conversion, and balanced reactive oxygen species generation is achieved. The optimal polymer possesses a branched alkyl chain and tetraphenylethylene pendant to manipulate the equilibrium between the radiative and nonradiative energy-dissipating channels. High-sensitivity NIR-II imaging was used to monitor the blood-brain barrier penetration and glioma cell targeting of apolipoprotein E-modified polymer nanoparticles. The NIR irradiation triggers and maximizes the photon utilization in prominent photodynamic/photothermal synergistic therapy in orthotopic drug-resistant glioblastoma.

A One Stone Three Birds Paradigm of Photon-Driven Pyroptosis Dye for Amplifying Tumor Immunotherapy

Activating the pyroptosis pathway of tumor cells by photodynamic therapy (PDT) for immunogenic cell death (ICD) is considered a valid strategy in pursuit of antitumor immunotherapy, but it remains a huge challenge due to the lack of reliable design guidelines. Moreover, it is often overlooked that conventional PDT can exacerbate the development of tumor immunosuppressive microenvironment, which is apparently unfavorable to clinical immunotherapy. The endoplasmic reticulum's (ER) pivotal role in cellular homeostasis and its emerging link to pyroptosis have galvanized interest in ER-centric imaging and therapeutics. Herein, using the targeted group-assisted strategy (TAGS), an intriguing cyclooxygenase-2-targeted photodynamic conjugate, Indo-Cy, strategically created, which exploits the enzyme's overabundance in the tumoral ER, especially under proinflammatory hypoxic conditions. This conjugate, with its highly precise ER imaging, embodies a trifunctional strategy: i) innovating an electron transfer mechanism, converting the hemicyanine moiety into an oxygen-independent type I photosensitizer, thereby navigating around the hypoxia constraints of traditional PDT; ii) executing precise ER-targeted PDT, amplifying caspase-1/GSDMD-mediated pyroptosis for ICD; 3) attenuating immunosuppressive pathways by inhibiting cyclooxygenase-2 downstream factors, including HIF-1α, PGE2, and VEGF. Indo-Cy's multimodal approach potently induces in vivo tumor pyroptosis and bolsters antitumor immunity, underscoring cyclooxygenase-2-targeted dyes' potential as a versatile oncotherapeutics.

A turn on fluorescent probe for nitroreductase activity and its application in real-time imaging of tumor hypoxia

Nitroreductase (NTR) is an endogenous reductase overexpressed in hypoxic tumors, with its levels closely correlated to the degree of hypoxia. This correlation has significant clinical implications for the analysis of tumor hypoxia, as it allows for the indirect detection of nitroreductases. Due to their simplicity, noninvasive nature, and excellent spatiotemporal resolution, various fluorescence methods have been developed for the analysis of nitroreductase and tumor hypoxia. In this study, we present the design, synthesis, in vitro evaluation, and biological application of an NTR-activated fluorescent probe, F-NTR. Utilizing an oxanthrene fluorophore as the core component, F-NTR incorporates a 4-nitrobenzene recognition group. This innovative probe, which introduces a nitro group, demonstrates high selectivity and reactivity towards nitroreductase (NTR) due to its reducing properties. Furthermore, probe F-NTR is capable of accurately identifying hypoxic environments, which provides a basis for precise detection and localization of tumors. This work lays the groundwork for future investigations into cell metabolism, tumor metabolism, and the surgical management of solid tumors under hypoxic conditions.

A near infrared fluorescent probe for hypoxia based on dicyanoisophorone and its application in Hela cells imaging

Hypoxia will accelerate tumors metastasis and deterioration, thereby limiting the effects of chemotherapy or radiotherapy. Thus, developing efficient techniques for detecting hypoxia in tumor cells is extremely important for cancer diagnosis and therapy. In this work, we reported a dicyanoisophorone-based probe (DCI-Azo) that specifically switched on its near infrared emission with hypoxia up-regulated azo-reductase (AzoR). In order to reduce the difficulty of synthesis and simplify the post-processing process, we adopted a one-pot-synthesis method to synthesized NIR fluorophore (DCI-Am) with yield 97 %. Based on the fluorophore, DCI-Azo was designed and synthesized. The sensitivity of DCI-Azo for hypoxia in vitro was evaluated with Na2S2O4 and rat liver microsomes. It exhibited near-infrared emission (λem = 650 nm), large Stokes Shift (>160 nm), high sensitivity (LOD 0.53 μg mL-1 rat liver microsomes), high selectivity, and low cytotoxicity (cell viability > 80 % after incubation for 24 h). Moreover, the probe was successfully used for detecting hypoxia (1% O2) in Hela cells and tumor tissue in mouse model. The fluorescence intensity in Hela cells has increased ∼ 26-fold when the oxygen level is reduced to 1 % from 21 % O2. The fluorescence intensity of the tumor area enhanced ∼ 5 folds compared to the normal area nearby. All these features demonstrated that the probe DCI-Azo was a versatile tool for in vivo assay and imaging for cancer diagnosis studies.

Using a stable radical as an "electron donor" to develop a radical photosensitizer for efficient type-I photodynamic therapy

Among type I photosensitizers, stable organic radicals are superior candidate molecules for hypoxia-overcoming photodynamic therapy. However, their wide applications are limited by complicated preparation processes and poor stabilities. Herein, a nitroxide radical was simply synthesized by introducing a commercially available "TEMPO" moiety. The radical exhibits efficient type-I ROS generation and appreciable photo-cytotoxicity under hypoxia, which open up a new avenue for the exploration of a novel and efficient type-I photosensitizer.

Innovative perspectives on metal free contrast agents for MRI: Enhancing imaging efficacy, and AI-driven future diagnostics

The U.S. Food and Drug Administration (FDA) has issued a boxed warning and mandated additional safety measures for all gadolinium-based contrast agents (GBCAs) used in clinical magnetic resonance imaging (MRI) due to their prolonged retention in the body and associated adverse health effects. This review explores recent advancements in CAs for MRI, highlighting four innovative probes: ORCAs, CEST CAs, 19F CAs, and HP 13C MRI. ORCAs offer a metal-free alternative that enhances imaging through nitroxides. CEST MRI facilitates the direct detection of specific molecules via proton exchange, aiding in disease diagnosis and metabolic assessment. 19F MRI CAs identify subtle biological changes, enabling earlier detection and tailored treatment approaches. HP 13C MRI improves visualization of metabolic processes, demonstrating potential in cancer diagnosis and monitoring. Finally, this review concludes by addressing the challenges facing the field and outlining future research directions, with a particular focus on leveraging artificial intelligence to enhance diagnostic capabilities and optimize both the performance and safety profiles of these innovative CAs. STATEMENT OF SIGNIFICANCE: The review addresses the urgent need for safer MRI contrast agents in light of FDA warnings about GBCAs. It highlights the key factors influencing the stability and functionality of metal-free CAs and recent advancements in designing ORCAs, CEST CAs, 19F CAs, and HP 13C probes and functionalization that enhance MRI contrast. It also explores the potential of these agents for multimodal imaging and targeted diagnostics while outlining future research directions and the integration of artificial intelligence to optimize their clinical application and safety. This contribution is pivotal for driving innovation in MRI technology and improving patient outcomes in disease detection and monitoring.

Aggregation control of anionic pentamethine cyanine enabling excitation wavelength selective NIR-II fluorescence imaging-guided photodynamic therapy

Near-infrared (NIR)-II fluorescence imaging-guided photodynamic therapy (PDT) has shown great potential for precise diagnosis and treatment of tumors in deep tissues; however, its performance is severely limited by the undesired aggregation of photosensitizers and the competitive relationship between fluorescence emission and reactive oxygen species (ROS) generation. Herein, we report an example of an anionic pentamethine cyanine (C5T) photosensitizer for high-performance NIR-II fluorescence imaging-guided PDT. Through the counterion engineering approach, a triphenylphosphine cation (Pco) modified with oligoethylene glycol chain is synthesized and adopted as the counterion of C5T, which can effectively suppress the excessive and disordered aggregation of the resulting C5T-Pco by optimizing the dye amphipathicity and enhancing the cyanine-counterion interactions. Dynamic tuning of fluorescence characteristics and ROS generation is achieved at the aggregate level, resulting in an impressive type I ROS generation under 760 nm light irradiation, accompanied by efficient NIR-II fluorescence emission excited at 808 nm. As a result, excitation wavelength selective NIR-II fluorescence imaging-guided PDT has been successfully demonstrated for tumor diagnosis and therapeutics of female mice.

Naphthalimide and Carbazole Based Mechanochromic Molecular Dyads and Triads for Selective Lysosome Imaging

In this study, we report the design and development of a stable fluorescent probe that is selectively localized in the cytosol of Hela cells. We designed two probes, 1 and 2, with D-π-A (carbazole (Cbz)-vinyl-naphthalimide (NPI)) and A-π-D-π-A (NPI-vinyl-Cbz-vinyl-NPI) architecture, respectively. Probes 1 and 2 exhibit broad photoluminescence (PL) spectra ranging from green (550 nm) to far-red (800 nm) in solutions and aggregated states. In the solid-state, the PL of these probes shows a bathochromic shift, which can be attributed to intermolecular interactions. In a water-rich medium, Probe 1, with a single NPI moiety, shows aggregation-caused quenching (ACQ) but retains a moderate quantum yield of 13.7 % (Φsoln=61.4 %). On the other hand, probe 2, with two NPI units, showed aggregation-induced enhanced emission AIEE, where the PLQY is increased nearly 4 times (Φsoln=3.5 %, Φagg=12.8 %). In-vitro cell studies revealed that these probes are non-toxic and effectively stain cells in green and red channels. Notably, Probe 1 demonstrated excellent cellular uptake and selectivity for lysosome, with a Pearson overlap coefficient of 0.91.

Engineered hypoxia-responsive albumin nanoparticles mediating mitophagy regulation for cancer therapy

Hypoxic tumors present a significant challenge in cancer therapy due to their ability to adaptation in low-oxygen environments, which supports tumor survival and resistance to treatment. Enhanced mitophagy, the selective degradation of mitochondria by autophagy, is a crucial mechanism that helps sustain cellular homeostasis in hypoxic tumors. In this study, we develop an azocalix[4]arene-modified supramolecular albumin nanoparticle, that co-delivers hydroxychloroquine and a mitochondria-targeting photosensitizer, designed to induce cascaded oxidative stress by regulating mitophagy for the treatment of hypoxic tumors. These nanoparticles are hypoxia-responsive and release loaded guest molecules in hypoxic tumor cells. The released hydroxychloroquine disrupts the mitophagy process, thereby increasing oxidative stress and further weakening the tumor cells. Additionally, upon laser irradiation, the photosensitizer generates reactive oxygen species independent of oxygen, inducing mitochondria damage and mitophagy activation. The dual action of simultaneous spatiotemporal mitophagy activation and mitophagy flux blockade results in enhanced autophagic and oxidative stress, ultimately driving tumor cell death. Our work highlights the effectiveness of hydroxychloroquine-mediated mitophagy blockade combined with mitochondria-targeted photosensitizer for cascade-amplified oxidative stress against hypoxic tumors.

Highly specific GSH-triggered bifunctional molecules to enable precise imaging and targeted therapy of cancer

The utilization of diagnostic-integrated molecules can enable targeted delivery and controlled release to significantly enhance therapeutic effectiveness and minimize toxic effects. Herein, we developed a novel class of glutathione (GSH)-activated bifunctional molecules that respond to elevated levels of GSH in tumor microenvironment. These bifunctional molecules retained the pharmacodynamic effects of parent molecules and mitigated cytotoxicity. Meanwhile, controlled release was monitored using fluorescent signals, enabling detection of drug distribution and accumulation in situ and in real time. Moreover, the correlation between GSH levels and fluorescence intensity offers the possibility of monitoring the effectiveness of responsive drugs. In conclusion, bifunctional molecules, as novel diagnostic-integrated molecules with both fluorescence imaging and therapeutic effects, exhibited potential applications in cancer therapy and imaging.

Anthracene-Based Endoperoxides as Self-Sensitized Singlet Oxygen Carriers for Hypoxic-Tumor Photodynamic Therapy

Singlet oxygen is a crucial reactive oxygen species (ROS) in photodynamic therapy (PDT). However, the hypoxic tumor microenvironment limits the production of cytotoxic singlet oxygen through the light irradiation of PDT photosensitizers (PSs). This restriction poses a major challenge in improving the effectiveness of PDT. To overcome this challenge, researchers have explored the development of singlet oxygen carriers that can capture and release singlet oxygen in physiological conditions. Among these developments, anthracene-based endoperoxides, initially discovered almost 100 years ago, have shown the ability to generate singlet oxygen controllably under thermal or photo stimuli. Recent advancements have led to the development of a new class of self-sensitized anthracene-endoperoxides, with potential applications in enhancing PDT effects for hypoxic tumors. This review discusses the current research progress in utilizing self-sensitized anthracene-endoperoxides as singlet oxygen carriers for improved PDT. It covers anthracene-conjugated small organic molecules, metal-organic complexes, polymeric structures, and other self-sensitized nano-structures. The molecular structural designs, mechanisms, and characteristics of these systems will be discussed. This review aims to provide valuable insights for developing high-performance singlet oxygen carriers for hypoxic-tumor PDT.

Recent advances of lipid droplet-targeted AIE-active materials for imaging, diagnosis and therapy

Lipid droplets (LDs) are cellular organelles specialized in the storage and regulating the release of lipids critical for energy metabolism. As investigation on LDs deepens, the complex biological functions of LDs are revealed and their relationships with various diseases such as atherosclerosis, fatty liver, obesity, and cancer are uncovered. Fluorescence-based techniques with simple operations, visible results and high non-invasiveness are ideal tools for investigating LD-related biological processes and diseases. Materials with aggregation-induced emission (AIE) characteristics have emerged as promising candidates for investigating LDs due to their high signal-to-noise ratio (S/N), strong photostability, and large Stokes shift. This review discusses the principles and advantages of LD-targeting AIE probes for imaging LDs, diagnosis of LD-associated diseases including atherosclerotic plaques, liver diseases, acute kidney diseases and cancer, therapies with LD-targeting AIE-active photosensitizers and other relevant fields in the past five years. Through typical examples, we illustrate the status of investigating LD-related imaging, diagnosis of diseases and therapy with AIE materials. This review is expected to attract attentions from scientists with different research backgrounds and contribute to the further development of LD-targeting AIE materials.

Covalent assembly-based two-photon fluorescent probes for in situ visualizing nitroreductase activities: From cancer cells to human cancer tissues

Nitroreductase (NTR) is widely regarded as a biomarker whose enzymatic activity correlates with the degree of hypoxia in solid malignant tumors. Herein, we utilized 2-dimethylamino-7-hydroxynaphthalene as fluorophore linked diverse nitroaromatic groups to obtain four NTR-activatable two-photon fluorescent probes based on covalent assembly strategy. With the help of computer docking simulation and in vitro assay, the sulfonate-based probe XN3 was proved to be able to identify NTR activity with best performances in rapid response, outstanding specificity, and sensitivity in comparison with the other three probes. Furthermore, XN3 could detect the degree of hypoxia by monitoring NTR activity in kinds of cancer cells with remarkable signal-to-noise ratios. In cancer tissue sections of the breast and liver in mice, XN3 had the ability to differentiate between healthy and tumorous tissues, and possessed excellent fluorescence stability, high tissue penetration and low tissue autofluorescence. Finally, XN3 was successfully utilized for in situ visualizing NTR activities in human transverse colon and rectal cancer tissues, respectively. The findings suggested that XN3 could directly identify the boundary between cancer and normal tissues by monitoring NTR activities, which provides a new method for imaging diagnosis and intraoperative navigation of tumor tissue.

NIR-II Light-Driven Multifunctional Nanozymes PS@CS for Efficient Therapy against Melanoma and Post-tumor Surgery Infection

Melanoma, the most prevalent form of skin cancer, is primarily treated with surgical intervention. However, complete tumor cell removal is challenging, and surgical wounds are prone to infection, complicating treatment and increasing costs. The successful treatment of melanoma generally requires multifunctional agents that are coordinated in tumor therapy and wound healing. In this study, we developed platinum (Pt)- and selenium (Se)-based nanozymes, Pt-Se@Chitosan (PS@CS), which exhibit synergistic antitumor and bactericidal efficacy attributed to their multienzyme activity and strong photothermal conversion efficiency. Furthermore, we engineered PS@CS hydrogels capable of inhibiting tumor regrowth postsurgery and accelerating healing of infected wounds. The PS@CS and PS@CS hydrogels presented herein incorporate characteristics including catalytic therapy, photothermal therapy, antibacterial properties, and skin damage healing, providing an innovative and comprehensive therapeutic approach for melanoma treatment.

A Nitroreductase-Activatable Metabolic Reporter for Covalent Labeling of Pathological Hypoxic Cells in Tumorigenesis

Aberrant hypoxic stress will initiate a cascade of pathological consequence observed prominently in tumorigenesis. Understanding of hypoxia's role in tumorigenesis is highly essential for developing effective therapeutics, which necessitates reliable tools to specifically distinguish hypoxic tumor cells (or tissues) and correlate their dynamics with the status of disease in complex living settings for precise theranostics. So far, disparate hypoxia-responsive probe molecules and prodrugs were designed via chemical or enzymatic reactions, yet their capability in real-time reporting pathogenesis development is often compromised due to unrestricted diffusion and less selectivity towards the environmental responsiveness. Herein we present an oxygen-insensitive nitroreductase (NTR)-activatable glycan metabolic reporter (pNB-ManNAz) capable of covalently labeling hypoxic tumor cells and tissues. Under pathophysiological hypoxic environments, the caged non-metabolizable precursor pNB-ManNAz exhibited unique responsiveness to cellular NTR, culminating in structural self-immolation and the resultant ManNAz could incorporate onto cell surface glycoproteins, thereby facilitating fluorescence labeling via bioorthogonal chemistry. This NTR-responsive metabolic reporter demonstrated broad applicability for multicellular hypoxia labeling, particularly in the dynamic monitoring of orthotopic tumorigenesis and targeted tumor phototherapy in vivo. We anticipate that this approach holds promise for investigating hypoxia-related pathological progression, offering valuable insights for accurate diagnosis and treatment.

Advancements in nanotechnology-driven photodynamic and photothermal therapies: mechanistic insights and synergistic approaches for cancer treatment

Cancer is a disease that involves uncontrolled cell division triggered by genetic damage to the genes that control cell growth and division. Cancer starts as a localized illness, but subsequently spreads to other areas in the human body (metastasis), making it incurable. Cancer is the second most prevalent cause of mortality worldwide. Every year, almost ten million individuals get diagnosed with cancer. Although different cancer treatment options exist, such as chemotherapy, radiation, surgery and immunotherapy, their clinical efficacy is limited due to their significant side effects. New cancer treatment options, such as phototherapy, which employs light for the treatment of cancer, have sparked a growing fascination in the cancer research community. Phototherapies are classified into two types: photodynamic treatment (PDT) and photothermal therapy (PTT). PDT necessitates the use of a photosensitizing chemical and exposure to light at a certain wavelength. Photodynamic treatment (PDT) is primarily based on the creation of singlet oxygen by the stimulation of a photosensitizer, which is then used to kill tumor cells. PDT can be used to treat a variety of malignancies. On the other hand, PTT employs a photothermal molecule that activates and destroys cancer cells at the longer wavelengths of light, making it less energetic and hence less hazardous to other cells and tissues. While PTT is a better alternative to standard cancer therapy, in some irradiation circumstances, it can cause cellular necrosis, which results in pro-inflammatory reactions that can be harmful to therapeutic effectiveness. Latest research has revealed that PTT may be adjusted to produce apoptosis instead of necrosis, which is attractive since apoptosis reduces the inflammatory response.

Responsive Magnetic Particle Imaging Tracer: Overcoming "Always-On" Limitation, Eliminating Interference, and Ensuring Safety in Adaptive Therapy

Magnetic particle imaging (MPI) has emerged as a novel technology utilizing superparamagnetic nanoparticles as tracers, essential for disease diagnosis and treatment guidance in preclinical animal models. Unlike other modalities, MPI provides high sensitivity, deep tissue penetration, and no signal attenuation. However, existing MPI tracers suffer from "always-on" signals, which complicate organ-specific imaging and hinder accuracy. To overcome these challenges, we have developed a responsive MPI tracer using pH-responsive PdFe alloy particles coated with a gatekeeper polymer. This tracer exhibits pH-sensitive Fe release and modulation of the MPI signal, enabling selective imaging with a higher signal-to-noise ratio and intratumoral pH quantification. Notably, this responsive tracer facilitates subtraction-enhanced MPI imaging, effectively eliminating interference from liver uptake and expanding the scope of abdominal imaging. Additionally, the tracer employs a dual-function mechanism for adaptive cancer therapy, combining pH-switchable enzyme-like catalysis with dual-key co-activation of ROS generation, and Pd skeleton that scavenges free radicals to minimize Fe-related toxicity. This advancement promises to significantly expand MPI's applicability in diagnostics and therapeutic monitoring, marking a leap forward in imaging technology.

Modular and Fast Assembly of Self-Immobilizing Fluorogenic Probes for β-Galactosidase Detection

β-Galactosidase (β-gal) has emerged as a pivotal biomarker in primary ovarian cancer. Despite the existence of numerous fluorescent probes for β-gal activity detection, quinone methide-based immobilizing probes were shown to avoid rapid diffusion of the activated fluorophore and improve the resolution. However, the synthesis of these fluorophores, particularly near-infrared fluorophores, still exhibits lower efficiency. In this study, we introduce modular and rapidly assembled self-immobilizing fluorogenic probes, capitalizing on the proximity labeling properties of quinone methide (QM). Compared to conventional fluorescent probes, these new probes not only exhibit a fluorogenic response but also achieve permanent retention, demonstrating improved detection sensitivity, particularly after cell fixation and in vivo animal model studies. This straightforward synthesis approach holds promise for broader applications in detecting other analytes.

Recent progress of porphyrin metal-organic frameworks for combined photodynamic therapy and hypoxia-activated chemotherapy

Nanoscale metal-organic frameworks integrated with porphyrins (Por-nMOFs) have emerged as efficient nanoplatforms for photodynamic therapy (PDT), which relies on the conversion of molecular oxygen into cytotoxic singlet oxygen. However, the hypoxic microenvironment within tumors significantly limits the efficacy of PDT. To address this challenge, researchers have explored various strategies to either alter or exploit the hypoxic conditions in tumors. One such strategy involves leveraging the porous structure of Por-nMOFs to load hypoxia-activated prodrugs (HAPs) like tirapazamine (TPZ), thereby utilizing the tumor's intrinsic hypoxic environment to trigger a chemotherapeutic effect that synergizes with PDT. Advances in nanoscience have enabled the development of porphyrin-based nMOFs capable of simultaneously loading both porphyrin photosensitizers and TPZ, ensuring effective release within cancer cells under high-phosphate conditions. The subsequent activation of co-loaded TPZ, by the tumor's own hypoxic microenvironment, and that created during PDT, facilitates a combined PDT and chemotherapy approach. This method not only enhances the suppression of cancer cell proliferation but also improves control over tumor metastasis while mitigating the negative impact of hypoxia on singular Por-nMOFs in PDT. This review summarizes recent advances in Por-nMOFs research, focusing on the design strategies for enhancing water dispersibility, circulatory stability, and targeting specificity through post-synthetic modifications. Additionally, this review highlights the bioapplication of Por-nMOFs by integrating TPZ chemotherapy and other therapeutic modalities to combat hypoxic and metastatic malignancies. We anticipate that this review will inspire further research into Por-nMOFs and advance their application in biomedicine.

Intrinsic 77 K Phosphorescence Characteristics and Computational Modeling of Ru(II)-(Bidentate Cyclometalated-Aromatic Ligand) Chromophores: Their Relatively Low Nonradiative Rate Constants Originating from Low Spin-Orbit Coupling Driven Vibronic Coupling Amplitudes between Emitting and Ground States

We investigated the photoinduced relaxation of Kasha-type emitting ruthenium-(bidentate cyclometalated aromatic ligand), Ru-CM, chromophores of [Ru(pzpy)2(CM)]+ ions (CM = 1-phenylisoquinoline, 2,3-diphenylpyrazine, and 1,4-diazatriphenylene and pzpy = 2-pyrazol-1-yl-pyridine). This is the first report of the phosphorescence behavior of pure Ru-(bidentate CM) chromophores. The 77 K photoinduced relaxation characteristics of phosphorescence chromophores showed emission quantum yields higher than those of reference Ru-bpy (bpy = 2,2'-bipyridine) chromophores in the emission region of 670-900 nm. This phenomenon of the Ru-CM chromophores could be attributed to their unusually low magnitudes for 77 K nonradiative rate constants (kNRD), although their radiative rate-constants (kRAD) are not remarkable. In order to examine the 77 K photoinduced behavioral relaxation difference between Ru-CM and Ru-bpy chromophores, we used computational simulation, applying the fundamental formalism of kRAD and temperature-independent kNRD equations, which included calculated spin-orbit coupling values.

Oxygen Concentration Effect in Photosensitized Generation of 1O2 from Normoxia to Hypoxia

Photodynamic therapy (PDT) has gained widespread acceptance as a clinical cancer treatment modality and has been attracting intensive attention on developing novel PDT strategies. However, the hypoxic environment in tumors is considered as a significant challenge for efficient type II PDT, based on the inference of the highly oxygen-concentration-related 1O2 generation. Contrary to this conventional understanding, our research demonstrates oxygen concentration independence in the photosensitized generation of 1O2, as evidenced through steady-state and transient spectroscopy for chlorin e6 and methylene blue from normoxic to hypoxic conditions. We propose an oxygen-concentration-independent kinetic model, suggesting that efficient 1O2 generation can take place as long as the triplet-state lifetime ratio of the photosensitizer (τh/τn) is in a similar range to pO2n/pO2h. Our findings provide insights into PDT mechanisms and indicate that the oxygen concentration reduction concerns may not be critical for effective PDT in hypoxic tumor environments.

Ultrasmall Enzyodynamic PANoptosis Nano-Inducers for Ultrasound-Amplified Hepatocellular Carcinoma Therapy and Lung Metastasis Inhibition

Addressing the inefficiency of current therapeutic approaches for hepatocellular carcinoma is an urgent and pressing challenge. PANoptosis, a form of inflammatory programmed cell death, presents a dependable strategy for combating cancer by engaging multiple cell death pathways (apoptosis, pyroptosis, and necroptosis). In this study, an ultrasmall Bi2Sn2O7 nanozyme with ultrasound-magnified multienzyme-mimicking properties is designed and engineered as a PANoptosis inducer through destroying the mitochondrial function of tumor cells and enhancing the intracellular accumulation of toxic reactive oxygen species, finally triggering the activation of PANoptosis process. The role of PANoptosis inducer has been verified by the expression of related proteins, including cleaved Caspase 3, NLRP3, N-GSDMD, cleaved Caspase 1, p-MLKL, and RIPK3. The inclusion of external ultrasonic irradiation significantly augments the enzyodynamic therapeutic efficiency. In vitro and in vivo antineoplastic efficacy, along with inhibition of lung metastasis, validate the benefits of the Bi2Sn2O7-mediated PANoptosis pathway. This study not only elucidates the intricate mechanisms underlying Bi2Sn2O7 as a PANoptosis inducer, but also offers a novel perspective for the treatment of hepatocellular carcinoma.

Metal-Coordinated Polydopamine Structures for Tumor Imaging and Therapy

Meticulously engineered nanomaterials achieve significant advances in the diagnosis and therapy of solid tumors by improving tumor delivery efficiency; and thereby, enhancing imaging and therapeutic efficacy. Currently, polydopamine (PDA) attracts widespread attention because of its biocompatibility, simplicity of preparation, abundant surface groups, and high photothermal conversion efficiency, which can be applied in drug delivery, photothermal therapy, theranostics, and other nanomedicine fields. Inspired by PDA structures that are rich in catechol and amino functional groups that can coordinate with various metal ions, which have charming qualities and characteristics, metal-coordinated PDA structures are exploited for tumor theranostics, but are not thoroughly summarized. Herein, this review summarizes the recent progress in the fabrication of metal-coordinated PDA structures and their availabilities in tumor imaging and therapy, with further in-depth discussion of the challenges and future perspectives of metal-coordinated PDA structures, with the aim that this systematic review can promote interdisciplinary intersections and provide inspiration for the further growth and clinical translation of PDA materials.

Biomimetic Gold Nanorods-Manganese Porphyrins with Surface-Enhanced Raman Scattering Effect for Photoacoustic Imaging-Guided Photothermal/Photodynamic Therapy

Surface-enhanced Raman scattering (SERS) imaging integrating photothermal and photodynamic therapy (PTT/PDT) is a promising approach for achieving accurate diagnosis and effective treatment of cancers. However, most available Raman reporters show multiple signals in the fingerprint region, which overlap with background signals from cellular biomolecules. Herein, a 4T1 cell membrane-enveloped gold nanorods-manganese porphyrins system (GMCMs) is designed and successfully fabricated as a biomimetic theranostic nanoplatform. Manganese porphyrins are adsorbed on the surface of Au nanorods via the terminal alkynyl group. Cell membrane encapsulation protects the manganese porphyrins from falling off the gold nanorods. The biomimetic GMCMs confirm specific homologous targeting to 4T1 cells with good dispersibility, excellent photoacoustic (PA) imaging properties, and preferable photothermal and 1O2 generation performance. GMCMs exhibit distinct SERS signals in the silent region without endogenous biomolecule interference both in vitro and in vivo. Manganese ions could not only quench the fluorescence of porphyrins to enhance the SERS imaging effect but also deplete cellular GSH to increase 1O2 yield. Both in vitro and in vivo studies demonstrate that GMCMs effectively eradicate tumors through SERS/PA imaging-guided PTT/PDT. This study provides a feasible strategy for augmenting the Raman imaging effects of the alkynyl group and integrating GSH-depletion to enhance PTT/PDT efficacy.

Zinc oxide nanoparticles with catalase-like nanozyme activity and near-infrared light response: A combination of effective photodynamic therapy, autophagy, ferroptosis, and antitumor immunity

We prepared biocompatible and environment-friendly zinc oxide nanoparticles (ZnO NPs) with upconversion properties and catalase-like nanozyme activity. Photodynamic therapy (PDT) application is severely limited by the poor penetration of UV-Visible light and a hypoxic tumor environment. Here, we used ZnO NPs as a carrier for the photosensitizer chlorin e6 (Ce6) to construct zinc oxide-chlorin e6 nanoparticles (ZnO-Ce6 NPs), simultaneously addressing both problems. In terms of penetration, ZnO NPs convert 808 nm near-infrared light into 401 nm visible light to excite Ce6, achieving deep-penetrating photodynamic therapy under long-wavelength light. Interestingly, the ability to emit short-wavelength light under long-wavelength light is usually observed in upconversion nanoparticles. As nanozymes, ZnO NPs can catalyze the decomposition of hydrogen peroxide in tumors, providing oxygen for photodynamic action and relieving hypoxia. The enhanced photodynamic action produces a large amount of reactive oxygen species, which overactivate autophagy and trigger immunogenic cell death (ICD), leading to antitumor immunotherapy. In addition, even in the absence of light, ZnO and ZnO-Ce6 NPs can induce ferroptosis of tumor cells and exert antitumor effects.

ROS-responsive self-assembly nanoplatform overcomes hypoxia for enhanced photodynamic therapy

Photodynamic therapy (PDT) has emerged as a promising treatment for malignant tumours in recent decades due to its impressive spatiotemporal selectivity, minimal invasiveness, and few adverse effects. Despite these advancements, there remain significant challenges in effectively delivering photosensitizers to tumours and overcoming tumour hypoxia to maximize the therapeutic benefits of PDT. Ongoing research efforts are focused on developing innovative strategies to overcome the above-mentioned challenges, such as nanoplatforms and combination therapy approaches. Hence, reactive oxygen species (ROS)-responsive polymeric micelles are promising candidates to enhance the distribution and retention of photosensitizers within tumours. Additionally, efforts to alleviate tumour hypoxia may further improve the anti-tumour effects of PDT. In this study, we designed ROS-responsive polymeric micelles (TC@PTP) co-loaded with a Tapp-COF, a porphyrin derivative, and capsaicin for PDT of melanoma. These ROS-responsive nanocarriers, constructed from thioketal (TK)-linked amphiphilic di-block copolymers (PEG5K-TK-PLGA5K), could accumulate in the tumor microenvironment and release drugs under the action of ROS. Capsaicin, acting as a biogenic respiratory inhibitor, suppressed mitochondrial respiration and the hypoxia-inducible factor 1 (HIF-1) signaling pathway, thereby increasing oxygen levels at the tumour site. These PDT-triggered ROS-responsive nanoparticles effectively alleviated the tumour hypoxic microenvironment and enhanced anti-tumour efficacy. With superior biocompatibility and tumour-targeting abilities, the platform holds great promise for advancing anti-tumour combination therapy.

Harnessing J-aggregation for dual-color cellular imaging with chromenoquinoline-benzimidazole dyes

Fluorescence imaging has revolutionized the visualization of cellular structures and biomolecules due to its non-invasive nature and high sensitivity. Chromenoquinoline (CQ)-based dyes offer promising optical properties, yet their widespread application is hindered by aggregation-caused quenching (ACQ). In contrast, J-aggregates, characterized by distinctive photophysical properties, present a solution to ACQ. Here, we introduce a novel platform employing chromenoquinoline-benzimidazole (CQ-BI) dyes, capable of forming J-aggregates, for dual-color cellular imaging. The incorporation of a methyl group into the benzimidazole moiety enhances J-aggregate formation, leading to robust emission in both dilute solutions and aggregated states. Our study demonstrates that methyl moiety-modified CQ-BI derivatives enable simultaneous imaging of mitochondria and lipid droplets in living cells. This work underscores the potential of CQ-BI dyes for dual-channel fluorescence imaging, leveraging the unique properties of J-aggregation.

Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

Leveraging Non-Radiative Transitions in Asphaltenes-Derived Carbon Dots for Cancer Photothermal Therapy

Cancer photothermal therapy leverages the capability of photothermal agents to convert light to heat for cancer cell ablation and necrosis. However, most conventional photothermal agents (Au, CuS, Pd, mesoporous silica nanoparticles, and indocyanine green dye) either face scalability challenges or photobleached upon prolonged irradiation which jeopardizes practical applications. Here, asphaltenes-derived carbon dots (ACDs, 5 nm) are rationally engineered as a low-cost and photostable photothermal agent with negligible in vivo cytotoxicity. The abundant water-solvating functional groups on the ACDs surface endows them with excellent water re-dispersibility that outperforms those of most commercial nanomaterials. Photothermal therapeutic property of the ACDs is mechanistically described by non-radiative transitions of excited electrons at 808 nm via internal conversions and vibrational relaxations. Consequently, the ACDs offer cancer photothermal therapy in mice within 15 days post-exposure to one-time near infrared irradiation. This pioneering study showcases the first utilization of asphaltenes-based materials for cancer therapy and is expected to arouse further utilization of such materials in various cancer theranostics.

Cancer-Targeting and Viscosity-Activatable Near-Infrared Fluorescent Probe for Precise Cancer Cell Imaging

Small-molecule fluorescent probes have emerged as potential tools for cancer cell imaging-based diagnostic and therapeutic applications, but their limited selectivity and poor imaging contrast hinder their broad applications. To address these problems, we present the design and construction of a novel near-infrared (NIR) biotin-conjugated and viscosity-activatable fluorescent probe, named as QL-VB, for selective recognition and imaging of cancer cells. The designed probe exhibited a NIR emission at 680 nm, with a substantial Stokes shift of 100 nm and remarkably sensitive responses toward viscosity changes in solution. Importantly, QL-VB provided an evidently enhanced signal-to-noise ratio (SNR: 6.2) for the discrimination of cancer cells/normal cells, as compared with the control probe without biotin conjugation (SNR: 1.8). Moreover, we validated the capability of QL-VB for dynamic monitoring of stimulated viscosity changes within cancer cells and employed QL-VB for distinguishing breast cancer tissues from normal tissues in live mice with improved accuracy (SNR: 2.5) in comparison with the control probe (SNR: 1.8). All these findings indicated that the cancer-targeting and viscosity-activatable NIR fluorescent probe not only enables the mechanistic investigations of mitochondrial viscosity alterations within cancer cells but also holds the potential as a robust tool for cancer cell imaging-based applications.

Confocal microscopic oxygen imaging of xenograft tumors using Ir(III) complexes as in vivo intravascular and intracellular probes

Hypoxia is an important feature of the tumor microenvironment (TME) of most solid tumors, and it is closely linked to cancer cell proliferation, therapy resistance, and the tumor immune response. Herein, we describe a method for hypoxia-induced heterogeneous oxygen distribution in xenograft tumors based on phosphorescence imaging microscopy (PLIM) using intravascular and intracellular oxygen probes. We synthesized Ir(III) complexes with polyethylene glycol (PEG) units of different molecular weights into the ligand as intravascular oxygen probes, BTP-PEGm (m = 2000, 5000, 10000, 20000). BTP-PEGm showed red emission with relatively high emission quantum yield and high oxygen sensitivity in saline. Cellular and in vivo experiments using these complexes revealed that BTP-PEG10000 was the most suitable probe in terms of blood retention and ease of intravenous administration in mice. PLIM measurements of xenograft tumors in mice treated with BTP-PEG10000 allowed simultaneous imaging of the tumor microvasculature and quantification of oxygen partial pressures. From lifetime images using the red-emitting intracellular oxygen probe BTPDM1 and the green-emitting intravascular fluorescent probe FITC-dextran, we demonstrated hypoxic heterogeneity in the TME with a sparse vascular network and showed that the oxygen levels of tumor cells gradually decreased with vascular distance.

Totally Caged Type I Pro-Photosensitizer for Oxygen-Independent Synergistic Phototherapy of Hypoxic Tumors

Activatable type I photosensitizers are an effective way to overcome the insufficiency and imprecision of photodynamic therapy in the treatment of hypoxic tumors, however, the incompletely inhibited photoactivity of pro-photosensitizer and the limited oxidative phototoxicity of post-photosensitizer are major limitations. It is still a great challenge to address these issues using a single and facile design. Herein, a series of totally caged type I pro-photosensitizers (Pro-I-PSs) are rationally developed that are only activated in tumor hypoxic environment and combine two oxygen-independent therapeutic mechanisms under single-pulse laser irradiation to enhance the phototherapeutic efficacy. Specifically, five benzophenothiazine-based dyes modified with different nitroaromatic groups, BPN 1-5, are designed and explored as latent hypoxia-activatable Pro-I-PSs. By comparing their optical responses to nitroreductase (NTR), it is identified that the 2-methoxy-4-nitrophenyl decorated dye (BPN 2) is the optimal Pro-I-PSs, which can achieve NTR-activated background-free fluorescence/photoacoustic dual-modality tumor imaging. Furthermore, upon activation, BPN 2 can simultaneously produce an oxygen-independent photoacoustic cavitation effect and a photodynamic type I process at single-pulse laser irradiation. Detailed studies in vitro and in vivo indicated that BPN 2 can effectively induce cancer cell apoptosis through synergistic effects. This study provides promising potential for overcoming the pitfalls of hypoxic-tumor photodynamic therapy.

Recent Advances in the Application of Nitro(het)aromatic Compounds for Treating and/or Fluorescent Imaging of Tumor Hypoxia

This review delves into recent advancements in the field of nitro(het)aromatic bioreductive agents tailored for hypoxic environments. These compounds are designed to exploit the low-oxygen conditions typically found in solid tumors, making them promising candidates for targeted cancer therapies. Initially, this review focused on their role as gene-directed enzyme prodrugs, which are inert until activated by specific enzymes within tumor cells. Upon activation, these prodrugs undergo chemical transformations that convert them into potent cytotoxic agents, selectively targeting cancerous tissue while sparing healthy cells. Additionally, this review discusses recent developments in prodrug conjugates containing nitro(het)aromatic moieties, designed to activate under low-oxygen conditions within tumors. This approach enhances their efficacy and specificity in cancer treatment. Furthermore, this review covers innovative research on using nitro(het)aromatic compounds as fluorescent probes for imaging hypoxic tumors. These probes enable non-invasive visualization of low-oxygen regions within tumors, providing valuable insights for the diagnosis, treatment planning, and monitoring of therapeutic responses. We hope this review will inspire researchers to design and synthesize improved compounds for selective cancer treatment and early diagnostics.

H2O2 Photosynthesis from H2O and O2 under Weak Light by Carbon Nitrides with the Piezoelectric Effect

Driven by the essential need of a green, safe, and low-cost approach to producing H2O2, a highly valuable multifunctional chemical, artificial photosynthesis emerges as a promising avenue. However, current catalyst systems remain challenging, due to the need of high-density sunlight, poor selectivity and activity, or/and unfavorable thermodynamics. Here, we reported that an indirect 2e- water oxidation reaction (WOR) in photocatalytic H2O2 production was unusually activated by C5N2 with piezoelectric effects. Interestingly, under ultrasonication, C5N2 exhibited an overall H2O2 photosynthesis rate of 918.4 μM/h and an exceptionally high solar-to-chemical conversion efficiency of 2.6% after calibration under weak light (0.1 sun). Mechanism studies showed that the piezoelectric effect of carbon nitride overcame the high uphill thermodynamics of *OH intermediate generation, which enabled a new pathway for 2e- WOR, the kinetic limiting step in the overall H2O2 production from H2O and O2. Benefiting from the outstanding sonication-assisted photocatalytic H2O2 generation under weak light, the concept was further successfully adapted to biomedical applications in efficient sono-photochemodynamic therapy for cancer treatment and water purification.

Nitroreductase-Triggered Fluorophore Labeling of Cells and Tissues under Hypoxia

Several reductases, including nitroreductase, are upregulated under hypoxic conditions characterized by an oxygen-deficient microenvironment. Given that hypoxia is a prominent feature of solid tumors, our investigation focused on developing a bioconjugative probe designed for staining tissue under hypoxic conditions, particularly activated by nitroreductase. This probe, developed using our trigger-release-bioconjugation system rooted in the ortho-quinone methide chemistry, exhibited selective activation by nitroreductase and fluorophore labeling within mitochondria and endoplasmic reticulum. As a result, it displayed sustained fluorescence that persisted even after washing steps in cells and tissues. We applied this innovative probe to stain mouse kidney tissue in an acute kidney injury model induced by inadequate oxygen supply. Among various organ tissues examined, only kidney tissue showed significantly higher fluorescence in the injury model compared with the control tissue, as revealed by two-photon microscopic imaging. This research presents a promising avenue for the development of practical staining agents for image-guided tumor surgery.

Nitroreductase-Responsive Fluorescent "Off-On" Photosensitizer for Hypoxic Tumor Imaging and Dual-Modal Therapy

Photothermal therapy synergized with photodynamic therapy for the treatment of tumors has emerged as a promising strategy. However, designing photosensitizers with both high photothermal efficiency and high photodynamic performance remains challenging. In contrast, the strategy of rationalizing the design of photosensitizers using the physiological properties of tumors to improve the photon utilization of photosensitizers during phototherapy is more advantageous than the approach of endowing a single photosensitizer with complex functions. Herein, we propose a molecular design (CyNP) to convert from photothermal therapy to photodynamic synergistic photothermal therapy based on the prevalent properties of hypoxic tumors. In the normoxic region of tumors, the deactivation pathway of CyNP excited state is mainly the conversion of photon energy to thermal energy; in the hypoxic region of tumors, CyNP is reduced to CyNH by nitroreductase, and the deactivation pathway mainly includes radiation leap, energy transfer between CyNP and oxygen, and conversion of photons energy to heat energy. This strategy enables real-time fluorescence detection of hypoxic tumors, and it also provides dual-mode treatment for photothermal and photodynamic therapy of tumors, achieving good therapeutic effects in vivo tumor treatment. Our study achieves more efficient tumor photoablation and provides a reference for the design ideas of smart photosensitizers.

An NIR Type I Photosensitizer Based on a Cyclometalated Ir(III)-Rhodamine Complex for a Photodynamic Antibacterial Effect toward Both Gram-Positive and Gram-Negative Bacteria

Type I photosensitizers offer an advantage in photodynamic therapy (PDT) due to their diminished reliance on oxygen levels, thus circumventing the challenge of hypoxia commonly encountered in PDT. In this study, we present the synthesis and comprehensive characterization of a novel type I photosensitizer derived from a cyclometalated Ir(III)-rhodamine complex. Remarkably, the complex exhibits a shift in absorption and fluorescence, transitioning from "off" to "on" states in aprotic and protic solvents, respectively, contrary to initial expectations. Upon exposure to light, the complex demonstrates the effective generation of O2- and ·OH radicals via the type I mechanism. Additionally, it exhibits notable photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria, demonstrated through in vitro and in vivo experiments. This research offers valuable insights for the development of novel type I photosensitizers.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

Nanoparticles Encapsulated in Red Blood Cell Membranes for Near-Infrared Second Window Imaging-Guided Photothermal-Enhanced Immunotherapy on Tumors

Photothermal therapy (PTT), which uses the high thermal conversion ability of photothermal agents to ablate tumor cells at high temperatures, has gained significant attention because it has the advantages of high selectivity and specificity, precise targeting of tumor sites, and low invasiveness and trauma. However, PTT guided by the NIR-I has limitations in tissue penetration depth, resulting in limited imaging monitoring and therapeutic effects on deep-seated tumor tissues. Moreover, nanoparticles are easily cleared by the immune system and difficult to passively target tumor sites during the process of treatment. To address these issues, we prepared nanoparticles using NIR-II dyes IR1048 and DSPE-PEG-OH and further encapsulated them in red blood cell membranes derived from mice. These biomimetic nanoparticles, called RDIR1048, showed reduced clearance by the immune system and had long circulation characteristics. They effectively accumulated at tumor sites, and strong fluorescence could still be observed at the tumor site 96 h after administration. Furthermore, through mouse thermal imaging experiments, we found that RDIR1048 exhibited good PTT ability. When used in combination with an immune checkpoint inhibitor, anti-PD-L1 antibodies, it enhanced the immunogenic cell death of tumor cells caused by PTT and improved the therapeutic effect of immunotherapy, which demonstrated good therapeutic efficacy in the treatment of tumor-bearing mice. This study provides a feasible basis for the future development of NIR-II nanoparticles with long circulation properties.

A near-infrared fluorescence probe with large Stokes shift for selectively monitoring nitroreductase in living cells and mouse tumor models

Hypoxia is commonly regarded as a typical feature of solid tumors, which originates from the insufficient supply of oxygen. Herein, the development of an efficient method for assessing hypoxia levels in tumors is strongly desirable. Nitroreductase (NTR) is an overexpressed reductase in the solid tumors, has been served as a potential biomarker to evaluate the degrees of hypoxia. In this work, we elaborately synthesized a new near-infrared (NIR) fluorescence probe (MR) to monitor NTR activity for assessment of hypoxia levels in living cells and in tumors. Upon exposure of NTR, the nitro-unit of MR could be selectively reduced to amino-moiety with the help of nicotinamide adenine dinucleotide. Moreover, the obtained fluorophore emitted a prominent NIR fluorescence, because it possessed a classical "push-pull" structure. The MR displayed several distinguished characters toward NTR, including intense NIR fluorescent signals, large Stokes shift, high selectivity and low limit of detection (46 ng/mL). Furthermore, cellular confocal fluorescence imaging results validated that the MR had potential of detecting NTR levels in hypoxic cells. Significantly, using the MR, the elevated of NTR levels were successfully visualized in the tumor-bearing mouse models. Therefore, this detecting platform based on this probe may be tactfully constructed for monitoring the variations of NTR and estimating the degrees of hypoxia in tumors.

Cleavable azobenzene linkers for the design of stimuli-responsive materials

The azo linkage (NN) is one of the very few functional groups in organic chemistry that exhibits sensitivity towards thermal, chemical, photochemical, and biological stimuli. Consequently, this property has given rise to a distinct class of responsive materials. For example, thermal sensitivity has led to generation of free radical initiators useful in curing and polymerization applications. Chemically-induced cleavage has aided the development of self-immolative polymers and reactive scaffolds for proteomics applications. Photo-isomerization capability has given rise to photo-responsive systems. Azobenzene cleavage in biologically reducing environments, such as that of the colon, and under tumor hypoxia conditions has led to diagnostic, therapeutic, and delivery materials. Such conditions have also allowed for control over formation (assembly) and disruption (disassembly) of micellar nanoparticles. The aim of this review article is to look beyond the prevalent photosensitivity aspect of the aromatic azo compounds and draw attention to the azo scission reaction as a trigger of the change in the structure and properties of organic materials. Thus, the main discussion begins with the mechanism of the reductive cleavage. Then, its application in the design of molecules that can be activated as drugs and fluorescent sensors, (nano)materials with potential to release active substances, and polymers with side-chain and main-chain self-immolative capacity is discussed. Finally, the status and future challenges in this field are discussed.

An Enzymatically Activated and Catalytic Hairpin Assembly-Driven Intelligent AND-Gated DNA Network for Tumor Molecular Imaging

Due to the potential off-tumor signal leakage and limited biomarker content, there is an urgent need for stimulus-responsive and amplification-based tumor molecular imaging strategies. Therefore, two tetrahedral framework DNA (tFNA-Hs), tFNA-H1AP, and tFNA-H2, were rationally engineered to form a polymeric tFNA network, termed an intelligent DNA network, in an AND-gated manner. The intelligent DNA network was designed for tumor-specific molecular imaging by leveraging the elevated expression of apurinic/apyrimidinic endonuclease 1 (APE1) in tumor cytoplasm instead of normal cells and the high expression of miRNA-21 in tumor cytoplasm. The activation of tFNA-H1AP can be achieved through specific recognition and cleavage by APE1, targeting the apurinic/apyrimidinic site (AP site) modified within the stem region of hairpin 1 (H1AP). Subsequently, miRNA-21 facilitates the hybridization of activated H1AP on tFNA-H1AP with hairpin 2 (H2) on tFNA-H2, triggering a catalytic hairpin assembly (CHA) reaction that opens the H1AP at the vertices of tFNA-H1AP to bind with H2 at the vertices of tFNA-H2 and generate fluorescence signals. Upon completion of hybridization, miRNA-21 is released, initiating the subsequent cycle of the CHA reaction. The AND-gated intelligent DNA network can achieve specific tumor molecular imaging in vivo and also enables risk stratification of neuroblastoma patients.

Novel angiogenesis inhibitors with superoxide anion radical amplification effect: Surmounting the Achilles' heels of angiogenesis inhibitors and photosensitizers

Angiogenesis inhibitors and photosensitizers are pivotal in tumor clinical treatment, yet their utilization is constrained. Herein, eleven novel angiogenesis inhibitors were developed through hybridization strategy to overcome their clinical limitations. These title compounds boast excitation wavelengths within the "therapeutic window", enabling deep tissue penetration. Notably, they could generate superoxide anion radicals via the Type I mechanism, with compound 36 showed the strongest superoxide anion radical generating capacity. Biological evaluation demonstrated remarkable cellular activity of all the title compounds, even under hypoxic conditions. Among them, compound 36 stood out for its superior anti-proliferative activity in both normoxic and hypoxic environments, surpassing individual angiogenesis inhibitors and photosensitizers. Compound 36 induced cell apoptosis via superoxide anion radical generation, devoid of dark toxicity. Molecular docking revealed that the target-recognizing portion of compound 36 was able to insert into the ATP binding pocket of the target protein similar to sorafenib. Collectively, our results suggested that hybridization of angiogenesis inhibitors and photosensitizers was a potential strategy to address the limitations of their clinical use.

An ultrasound-activated nanoplatform remodels tumor microenvironment through diverse cell death induction for improved immunotherapy

Although nanomaterial-based nanomedicine provides many powerful tools to treat cancer, most focus on the "immunosilent" apoptosis process. In contrast, ferroptosis and immunogenic cell death, two non-apoptotic forms of programmed cell death (PCD), have been shown to enhance or alter the activity of the immune system. Therefore, there is a need to design and develop nanoplatforms that can induce multiple modes of cell death other than apoptosis to stimulate antitumor immunity and remodel the immunosuppressive tumor microenvironment for cancer therapy. In this study, a new type of multifunctional nanocomposite mainly consisting of HMME, Fe3+ and Tannic acid, denoted HFT NPs, was designed and synthesized to induce multiple modes of cell death and prime the tumor microenvironment (TME). The HFT NPs consolidate two functions into one nano-system: HMME as a sonosensitizer for the generation of reactive oxygen species (ROS) 1O2 upon ultrasound irradiation, and Fe3+ as a GSH scavenger for the induction of ferroptosis and the production of ROS ·OH through inorganic catalytic reactions. The administration of HFT NPs and subsequent ultrasound treatment caused cell death through the consumption of GSH, the generation of ROS, ultimately inducing apoptosis, ferroptosis, and immunogenic cell death (ICD). More importantly, the combination of HFT NPs and ultrasound irradiation could reshape the TME and recruit more T cell infiltration, and its combination with immune checkpoint blockade anti-PD-1 antibody could eradicate tumors with low immunogenicity and a cold TME. This new nano-system integrates sonodynamic and chemodynamic properties to achieve outstanding therapeutic outcomes when combined with immunotherapy. Collectively, this study demonstrates that it is possible to potentiate cancer immunotherapy through the rational and innovative design of relatively simple materials.

Portably and Visually Sensing Cytisine through Smartphone Scanning Based on a Post-Modified Luminescence Center Strategy in Zinc-Organic Frameworks

Cytisine (CTS) is a useful medicine for treating nervous disorders and smoking addiction, and exploring a convenient method to detect CTS is of great significance for long-term/home medication to avoid the risk of poisoning, but it is full of challenges. Here, a modified metal-organic framework sensor Tb@Zn-TDA-80 with dual emission centers was prepared using a post-modified luminescence center strategy. The obtained Tb@Zn-TDA-80 can serve as a CTS sensor with high sensitivity and selectivity. To achieve portable detection, Tb@Zn-TDA-80 was further fabricated as a membrane sensor, M-Tb@Zn-TDA-80, which displayed an obvious CTS-responsive color change by simply dropping a CTS solution onto its surface. Benefiting from this unique functionality, M-Tb@Zn-TDA-80 successfully realized the visual detection and quantitative monitoring of CTS in the range of 5.26-52.6 mM by simply scanning the color with a smartphone. The results of nuclear magnetic resonance spectroscopy and theoretical computation illustrated that the high sensing efficiency of Tb@Zn-TDA-80 for CTS was attributed to the N-H⋅⋅⋅π and π⋅⋅⋅π interactions between the ligand and CTS. And luminescence quenching may result from the intramolecular charge transfer. This study provides a convenient method for ensuring long-term medication safety at home.

Size-Switchable Ru Nanoaggregates for Enhancing Phototherapy: Hyaluronidase-Triggered Disassembly to Alleviate Deep Tumor Hypoxia

Hypoxia is a critical factor for restricting photodynamic therapy (PDT) of tumor, and it becomes increasingly severe with increasing tissue depth. Thus, the relief of deep tumor hypoxia is extremely important to improve the PDT efficacy. Herein, tumor microenvironment (TME)-responsive size-switchable hyaluronic acid-hybridized Ru nanoaggregates (HA@Ru NAs) were developed via screening reaction temperature to alleviate deep tumor hypoxia for improving the tumor-specific PDT by the artful integration multiple bioactivated chemical reactions in situ and receptor-mediated targeting (RMT). In this nanosystem, Ru NPs not only enabled HA@Ru NAs to have near infrared (NIR)-mediated photothermal/photodynamic functions, but also could catalyze endogenous H2O2 to produce O2 in situ. More importantly, hyaluronidase (HAase) overexpressed in the TME could trigger disassembly of HA@Ru NAs via the hydrolysis of HA, offering the smart size switch capability from 60 to 15 nm for enhancing tumor penetration. Moreover, the RMT characteristics of HA ensured that HA@Ru NAs could specially enter CD44-overexpressed tumor cells, enhancing tumor-specific precision of phototherapy. Taken together these distinguishing characteristics, smart HA@Ru NAs successfully realized the relief of deep tumor hypoxia to improve the tumor-specific PDT.

Improved effectiveness of X-PDT against human triple-negative breast cancer cells through the use of liposomes co-loaded with protoporphyrin IX and perfluorooctyl bromide

In this study, we utilized X-ray-induced photodynamic therapy (X-PDT) against triple-negative breast cancer (TNBC) cells. To achieve this, we developed a liposome delivery system that co-loaded protoporphyrin IX (PPIX) and perfluorooctyl bromide (PFOB) in a rational manner. Low-dose X-ray at 2 Gy was employed to activate PPIX for the generation of reactive oxygen species (ROS), and the co-loading of PFOB provided additional oxygen to enhance ROS production. The resulting highly toxic ROS effectively induced cell death in TNBC. In vitro X-PDT effects, including intracellular ROS generation, cell viability, and apoptosis/necrosis assays in TNBC cells, were thoroughly investigated. Our results indicate that the nanocarriers effectively induced X-PDT effects with very low-dose radiation, making it feasible to damage cancer cells. This suggests the potential for the effective utilization of X-PDT in treating hypoxic cancers, including TNBC, with only a fraction of conventional radiotherapy.

Tumor microenvironment-activated theranostic nanozymes for trimodal imaging-guided combined therapy

Synergistic therapy is expected to be a promising strategy for highly effective cancer treatment. However, the rational design of a simple and multifunctional nanoplatform still remains a grand challenge. Considering the nature of weak acidic, hypoxic, and H2O2 abundant tumor microenvironment, we constructed an indocyanine green (ICG) modified platinum nanoclusters (Pt NCs) decorated gold nanobipyramids (Au NBPs) to form the multifunctional nanocomposites (Au NBPs@Pt NCs-ICG) for multimodal imaging mediated phototherapy and chemodynamic cancer therapy. The photosensitizer ICG was covalently linked to Au NBPs@Pt NCs by bridging molecules of SH-PEG-NH2 for both photodynamic therapy (PDT) and fluorescence imaging. Besides, Au NBPs@Pt NCs-ICG nanocomposites exhibited catalase- and peroxidase-like activities to generate O2 and ·OH, which relieved the tumor hypoxia and upregulated antitumoral ROS level. Moreover, the combination of Au NBPs and ICG endowed the Au NBPs@Pt NCs-ICG with super photothermal conversion for effective photothermal imaging and therapy. In addition, the Au NBPs@Pt NCs-ICG nanoplatform displayed excellent X-ray computed tomography (CT) imaging ability due to the presence of high-Z elements (Au and Pt). Overall, our results demonstrated that Au NBPs@Pt NCs-ICG nanoplatform exhibited a multimodal imaging guided synergistic PTT/PDT/CDT therapeutic manners and held great potential as an efficient treatment for breast cancer.