A self-immolative prodrug nanosystem capable of releasing a drug and a NIR reporter for in vivo imaging and therapy

Strategies for the development of stimuli-responsive small molecule prodrugs for cancer treatment

Approved anticancer drugs typically face challenges due to their narrow therapeutic window, primarily because of high systemic toxicity and limited selectivity for tumors. Prodrugs are initially inactive drug molecules designed to undergo specific chemical modifications. These modifications render the drugs inactive until they encounter specific conditions or biomarkers in vivo, at which point they are converted into active drug molecules. This thoughtful design significantly improves the efficacy of anticancer drug delivery by enhancing tumor specificity and minimizing off-target effects. Recent advancements in prodrug design have focused on integrating these strategies with delivery systems like liposomes, micelles, and polymerosomes to further improve targeting and reduce side effects. This review outlines strategies for designing stimuli-responsive small molecule prodrugs focused on cancer treatment, emphasizing their chemical structures and the mechanisms controlling drug release. By providing a comprehensive overview, we aim to highlight the potential of these innovative approaches to revolutionize cancer therapy.

Self-Immolative Domino Dendrimers as Anticancer-Drug Delivery Systems: A Review

Worldwide cancer statistics have indicated about 20 million new cancer cases and over 10 million deaths in 2022 (according to data from the International Agency for Research on Cancer). One of the leading cancer treatment strategies is chemotherapy, using innovative drug delivery systems (DDSs). Self-immolative domino dendrimers (SIDendr) for triggered anti-cancer drugs appear to be a promising type of DDSs. The present review provides an up-to-date survey on the contemporary advancements in the field of SIDendr-based anti-cancer drug delivery systems (SIDendr-ac-DDSs) through an exhaustive analysis of the discovery and application of these materials in improving the pharmacological effectiveness of both novel and old drugs. In addition, this article discusses the designing, chemical structure, and targeting techniques, as well as the properties, of several SIDendr-based DDSs. Approaches for this type of targeted DDSs for anti-cancer drug release under a range of stimuli are also explored.

Glutathione-triggered prodrugs: Design strategies, potential applications, and perspectives

The burgeoning prodrug strategy offers a promising avenue toward improving the efficacy and specificity of cytotoxic drugs. Elevated intracellular levels of glutathione (GSH) have been regarded as a hallmark of tumor cells and characteristic feature of the tumor microenvironment. Considering the pivotal involvement of elevated GSH in the tumorigenic process, a diverse repertoire of GSH-triggered prodrugs has been developed for cancer therapy, facilitating the attenuation of deleterious side effects associated with conventional chemotherapeutic agents and/or the attainment of more efficacious therapeutic outcomes. These prodrug formulations encompass a spectrum of architectures, spanning from small molecules to polymer-based and organic-inorganic nanomaterial constructs. Although the GSH-triggered prodrugs have been gaining increasing interests, a comprehensive review of the advancements made in the field is still lacking. To fill the existing lacuna, this review undertakes a retrospective analysis of noteworthy research endeavors, based on a categorization of these molecules by their diverse recognition units (i.e., disulfides, diselenides, Michael acceptors, and sulfonamides/sulfonates). This review also focuses on explaining the distinct benefits of employing various chemical architecture strategies in the design of these prodrug agents. Furthermore, we highlight the potential for synergistic functionality by incorporating multiple-targeting conjugates, theranostic entities, and combinational treatment modalities, all of which rely on the GSH-triggering. Overall, an extensive overview of the emerging field is presented in this review, highlighting the obstacles and opportunities that lie ahead. Our overarching goal is to furnish methodological guidance for the development of more efficacious GSH-triggered prodrugs in the future. By assessing the pros and cons of current GSH-triggered prodrugs, we expect that this review will be a handful reference for prodrug design, and would provide a guidance for improving the properties of prodrugs and discovering novel trigger scaffolds for constructing GSH-triggered prodrugs.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Activatable Near-Infrared Versatile Fluorescent and Chemiluminescent Dyes Based on the Dicyanomethylene-4H-pyran Scaffold: From Design to Imaging and Theranostics

Activatable fluorescent and chemiluminescent dyes with near-infrared emission have indispensable roles in the fields of bioimaging, molecular prodrugs, and phototheranostic agents. As one of the most popular fluorophore scaffolds, the dicyanomethylene-4H-pyran scaffold has been applied to fabricate a large number of versatile activatable optical dyes for analytes detection and diseases diagnosis and treatment by virtue of its high photostability, large Stokes shift, considerable two-photon absorption cross-section, and structural modifiability. This review discusses the molecular design strategies, recognition mechanisms, and both in vitro and in vivo bio-applications (especially for diagnosis and therapy of tumors) of activatable dicyanomethylene-4H-pyran dyes. The final section describes the current shortcomings and future development prospects of this topic.

Versatile Click Linker Enabling Native Peptide Release from Nanocarriers upon Redox Trigger

Nanocarriers have shown their ability to extend the circulation time of drugs, enhance tumor uptake, and tune drug release. Therapeutic peptides are a class of drug compounds in which nanocarrier-mediated delivery can potentially improve their therapeutic index. To this end, there is an urgent need for orthogonal covalent linker chemistry facilitating the straightforward on-the-resin peptide generation, nanocarrier conjugation, as well as the triggered release of the peptide in its native state. Here, we present a copper-free clickable ring-strained alkyne linker conjugated to the N-terminus of oncolytic peptide LTX-315 via standard solid-phase peptide synthesis (SPPS). The linker contains (1) a recently developed seven-membered ring-strained alkyne, 3,3,6,6-tetramethylthiacycloheptyne sulfoximine (TMTHSI), (2) a disulfide bond, which is sensitive to the reducing cytosolic and tumor environment, and (3) a thiobenzyl carbamate spacer enabling release of the native peptide upon cleavage of the disulfide via 1,6-elimination. We demonstrate convenient "clicking" of the hydrophilic linker-peptide conjugate to preformed pegylated core-cross-linked polymeric micelles (CCPMs) of 50 nm containing azides in the hydrophobic core under aqueous conditions at room temperature resulting in a loading capacity of 8 mass % of peptide to polymer (56% loading efficiency). This entrapment of hydrophilic cargo into/to a cross-linked hydrophobic core is a new and counterintuitive approach for this class of nanocarriers. The release of LTX-315 from the CCPMs was investigated in vitro and rapid release upon exposure to glutathione (within minutes) followed by slower 1,6-elimination (within an hour) resulted in the formation of the native peptide. Finally, cytotoxicity of LTX CCPMs as well as uptake of sulfocyanine 5-loaded CCPMs was investigated by cell culture, demonstrating successful tumor cell killing at concentrations similar to that of the free peptide treatment.

Camptothecin-based prodrug nanomedicines for cancer therapy

Camptothecin (CPT) is a cytotoxic alkaloid that attenuates the replication of cancer cells via blocking DNA topoisomerase 1. Despite its encouraging and wide-spectrum antitumour activity, its application is significantly restricted owing to its instability, low solubility, significant toxicity, and acquired tumour cell resistance. This has resulted in the development of many CPT-based therapeutic agents, especially CPT-based nanomedicines, with improved pharmacokinetic and pharmacodynamic profiles. Specifically, smart CPT-based prodrug nanomedicines with stimuli-responsive release capacity have been extensively explored owing to the advantages such as high drug loading, improved stability, and decreased potential toxicity caused by the carrier materials in comparison with normal nanodrugs and traditional delivery systems. In this review, the potential strategies and applications of CPT-based nanoprodrugs for enhanced CPT delivery toward cancer cells are summarized. We appraise in detail the chemical structures and release mechanisms of these nanoprodrugs and guide materials chemists to develop more powerful nanomedicines that have real clinical therapeutic capacities.

Recent Advancements on Self-Immolative System Based on Dynamic Covalent Bonds for Delivering Heterogeneous Payloads

The precisely spatial-temporal delivery of heterogeneous payloads from a single system with the same pulse is in great demand in realizing versatile and synergistic functions. Very few molecular architectures can satisfy the strict requirements of dual-release translated from single triggers, while the self-immolative systems based on dynamic covalent bonds represent the "state-of-art" of ultimate solution strategy. Embedding heterogeneous payloads symmetrically onto the self-immolative backbone with dynamic covalent bonds as the trigger, can respond to the quasi-bio-orthogonal hallmarks which are higher at the disease's microenvironment to simultaneously yield the heterogeneous payloads (drug A/drug B or drug/reporter). In this review, the modular design principles are concentrated to illustrate the rules in tailoring useful structures, then the rational applications are enumerated on the aspects of drug codelivery and visualized drug-delivery. This review, hopefully, can give the general readers a comprehensive understanding of the self-immolative systems based on dynamic covalent bonds for delivering heterogeneous payloads.

A JAK tyrosine kinase and pseudokinase Co-inhibition strategy combines enhanced potency and on-demand activation

Janus tyrosine kinase (JAK) inhibitors have been on the market for several years, but their use is limited by drug resistance and intolerable side effects. Herein, we propose a novel strategy of JAK tyrosine kinase (TK) and pseudokinase (PK) domain co-inhibition system to consolidate robust JAK inhibition and on-demand activation. A photoexcited prodrug PAT-SIL-TG-1&AT exhibits the synergy effects of TK-PK co-inhibition and enable the spatiotemporal control of JAK2 signaling. The hypoxia-activated prodrug HAT-SIL-TG-1&AT significantly inhibited HEL cells proliferation and downregulated phosphorylated STAT3/5 under hypoxic conditions. Importantly, HAT-SIL-TG-1&AT showed synergistic antitumor effects and selectively inhibited the JAK-STAT signaling in tumor tissues in vivo. This work demonstrates a viable solution to achieve superior JAK2 inhibition, and provides an inspiration for other kinases containing PK domain.

Nitro-Containing Self-Immolative Systems for Biological Applications

Since its introduction in 1981, the chemistry of self-immolative systems has received increasing attention in different application areas, such as analytical chemistry, medicinal chemistry, and materials science. This strategy is based on a stimulation that triggers a cascade of disassembling reactions leading to the release of smaller molecules. The particular reactivity of the nitro group, due to its powerful electron-withdrawing nature, has been exploited in the field of self-immolative chemistry. In this context, the present review describes the major role of the nitro group in self-immolative processes depending on its position.

Emerging Strategies in Stimuli-Responsive Prodrug Nanosystems for Cancer Therapy

Prodrugs are chemically modified drug molecules that are inactive before administration. After administration, they are converted in situ to parent drugs and induce the mechanism of action. The development of prodrugs has upgraded conventional drug treatments in terms of bioavailability, targeting, and reduced side effects. Especially in cancer therapy, the application of prodrugs has achieved substantial therapeutic effects. From serendipitous discovery in the early stage to functional design with pertinence nowadays, the importance of prodrugs in drug design is self-evident. At present, studying stimuli-responsive activation mechanisms, regulating the stimuli intensity in vivo, and designing nanoscale prodrug formulations are the major strategies to promote the development of prodrugs. In this review, we provide an outlook of recent cutting-edge studies on stimuli-responsive prodrug nanosystems from these three aspects. We also discuss prospects and challenges in the future development of such prodrugs.

The Role of Optical Imaging in Translational Nanomedicine

Nanomedicines have been a major research focus in the past two decades and are increasingly emerging in a broad range of clinical applications. However, a proper understanding of their biodistribution is required to further progress the field of nanomedicine. For this, imaging methods to monitor the delivery and therapeutic efficacy of nanoparticles are urgently needed. At present, optical imaging is the most common method used to study the biodistribution of nanomaterials, where the unique properties of nanomaterials and advances in optical imaging can jointly result in novel methods for optimal monitoring of nanomaterials in preclinical animal models. This review article aims to give an introduction to nanomedicines and their translational impact to highlight the potential of optical imaging to study the biodistribution of nanoparticles and to monitor the delivery and therapeutic efficacy at the preclinical level. After introducing both domains, the review focuses on different techniques that can be used to overcome some intrinsic limitations of optical imaging and how this can specifically benefit nanoparticle studies. Finally, we point out some important key features of nanoparticles that currently hinder their full potential in the clinic and how the advances in optical imaging can help to provide us with the information needed to further boost the clinical translation and expand the field of nanomedicines.

Self-boosting stimulus activation of a polyprodrug with cascade amplification for enhanced antitumor efficacy

The use of polyprodrugs, which bind drugs to polymer chains through responsive linkers, is a potential technique for cancer therapy; however, a lack of endogenous triggering factors limits drug activation in tumor tissue. Herein, we rationally created a reactive oxygen species (ROS)-sensitive polyprodrug (TS_CA/DOX) with cascade amplification of triggering agents and drug activation by incorporating both an ROS signal amplifier (TA_CA) and a drug activation amplifier (SIP_DOX) into a delivery system. Endogenous ROS as a triggering mechanism kicked off the initial circulation phase to increase intracellular ROS signals. Subsequently, the enhanced ROS initiated the second degradation step, allowing the polyprodrug SIP_DOX to fracture spontaneously in a domino-like fashion, resulting in self-accelerated drug activation in tumor tissue. Therefore, the polyprodrug created in this study with cascade amplification of drug activation holds great promise for effective cancer treatment.

A Smart Theranostic Prodrug System Activated by Reactive Oxygen Species for Regional Chemotherapy of Metastatic Cancer

Metastatic cancer is difficult to cure because of its uncontrollable nature and side effects during treatment. We constructed a reactive oxygen species (ROS)-activated smart theranostic prodrug system based on an ROS active site linked with both a targeting group and an anticancer drug for efficient regional chemotherapy of metastatic cancers. The optimized prodrug (Bio-(8)-MB-CPT) with biotin as the targeting group displayed high sensitivity towards ROS and selectively targeting ability towards cervical cancer cells, showing highly efficient drug release (up to 92 %) in vitro. Bio-(8)-MB-CPT thus exerted strong toxicity towards cervical cancer cells, but unlike the parent drug (camptothecin), showed no toxicity towards normal cells. Moreover, the prodrug displayed significantly enhanced antitumor efficacy in vivo and eradicated the tumor with no obvious side effects (inhibition of the tumor reached up to 99.9 %).

IRE-1-Targeting Caged Prodrug with Endoplasmic Reticulum Stress-Inducing and XBP-1S-Inhibiting Activities for Cancer Therapy

Activation of the IRE-1/XBP-1s pathway supports tumor progression. Here, we report a novel prodrug, TC-D-F07, in which a thiol-reactive dinitrobenzenesulfonyl (Dns) cage was installed onto the C8 hydroxyl of the covalent IRE-1 inhibitor D-F07. The electron-withdrawing Dns group in TC-D-F07 stabilizes the neighboring 1,3-dioxane acetal, allowing for stimulus-mediated control of its inhibitory activity. TC-D-F07 exhibits high sensitivity to intracellular thiols. Because tumor cells exhibit higher concentrations of glutathione and cysteine, treatment with TC-D-F07 results in more sustained levels of D-F07 in transformed versus normal cells. In addition, we show that a dinitrophenyl cysteine adduct resulting from cleavage of the Dns group induces endoplasmic reticulum (ER) stress, causing tumor cells to increase the expression of XBP-1s. The accumulated levels of D-F07 and its gradual decomposition into the active IRE-1 inhibitor eventually deprive tumor cells of XBP-1s, leading to more severe apoptosis than those treated with its uncaged analogue.

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

A self-immolated fluorogenic agent triggered by H2S exhibiting potential anti-glioblastoma activity

Glioblastoma is the most common and aggressive type of malignant brain tumor with poor survival and limited therapeutic options. Theranostic anticancer agents with dual functions of diagnosis and therapy are highly attractive. Self-immolation reaction is a promising approach for theranostic prodrugs triggered by the tumor microenvironment. Overexpression of hydrogen sulfide (H₂S) in glioma cells becomes a potential stimulus for activating prodrugs. Herein, a novel H₂S responsive agent (SNF) containing amonafide (ANF), a self-immolative linker and a trigger group has been developed for imaging and chemotherapy in living cells. SNF exhibited high selectivity and sensitivity towards H₂S and also showed excellent lysosome-targeted capability. The activated SNF could translocate to the nucleus, causing DNA damage and blocking the cell cycle. More mechanistic studies indicated that SNF altered the mitochondrial membrane potential and induced autophagy in human glioblastoma-astrocytoma (U87MG). In addition, 3D multicellular U87MG tumor spheroids were used to further confirm the active drug release and high anti-proliferative activity of SNF. This approach may provide a general strategy for developing H₂S-triggered prodrugs for synergic cancer therapy.

Recent Advances in Improved Anticancer Efficacies of Camptothecin Nano-Formulations: A Systematic Review

Camptothecin (CPT), a natural plant alkaloid, has indicated potent antitumor activities via targeting intracellular topoisomerase I. The promise that CPT holds in therapies is restricted through factors that include lactone ring instability and water insolubility, which limits the drug oral solubility and bioavailability in blood plasma. Novel strategies involving CPT pharmacological and low doses combined with nanoparticles have indicated potent anticancer activity in vitro and in vivo. This systematic review aims to provide a comprehensive and critical evaluation of the anticancer ability of nano-CPT in various cancers as a novel and more efficient natural compound for drug development. Studies were identified through systematic searches of PubMed, Scopus, and ScienceDirect. Eligibility checks were performed based on predefined selection criteria. Eighty-two papers were included in this systematic review. There was strong evidence for the association between antitumor activity and CPT treatment. Furthermore, studies indicated that CPT nano-formulations have higher antitumor activity in comparison to free CPT, which results in enhanced efficacy for cancer treatment. The results of our study indicate that CPT nano-formulations are a potent candidate for cancer treatment and may provide further support for the clinical application of natural antitumor agents with passive targeting of tumors in the future.

Highly Photostable Fluorescent Tracker with pH-Insensitivity for Long-Term Imaging of Lysosomal Dynamics in Live Cells

Visualizing and tracking lysosomal dynamic changes is crucially important in the fields of physiology and pathology. Most currently used pH-dependent small-molecule lysotrackers and sensors usually fail to visualize and track the changes due to (1) their leakage from lysosomes when the lysosomal pH increases and (2) their low photostability. Therefore, it is of significant interest to develop lysosomal probes for visualizing and tracking lysosomal dynamics independent of pH fluctuations and with high photostability. Herein, we found that the popular dicyanomethylene-4H-pyran (DCM) derivative DCM-NH₂ can selectively target and label lysosomes with bright red fluorescence regardless of pH changes. The fluorescence enhancement in lysosomes has probably resulted from their microenvironment of polarity and viscosity. Compared with the commonly used commercial lysosomal molecular probes (LysoTracker Deep Red (LTDR) and LysoTracker Red DND-99), DCM-NH₂ was demonstrated to exhibit a much stronger tolerance in lysosomes against various treatments and microenvironmental changes, and lysosomal membrane permeability could not cause DCM-NH₂ to lose imaging of their targets as well. Moreover, DCM-NH₂ exhibited a superior anti-photobleaching ability and low (photo-) cytotoxicity, which, along with pH-insensitivity, ensured its capability of long-term visualizing and tracking lysosomal dynamics. Lysosomal dynamic events such as the kiss-and-run process, fusion-fission, and mitophagy were successfully recorded with DCM-NH₂. Our study thus confirms that DCM-NH₂ is highly competitive for lysosomal imaging by overcoming the limitations of the commercial LysoTrackers and highlights the unexplored application of DCM-NH₂ in bioimaging.

Indication of Dynamic Peroxynitrite Fluctuations in the Rat Epilepsy Model with a Near-Infrared Two-Photon Fluorescent Probe

Epilepsy is a chronic neurodegenerative disease that has seriously threatened human health. Accumulating evidence reveals that the pathological progression of epilepsy is closely related to peroxynitrite (ONOO^-). Unfortunately, understanding the physiological roles of ONOO^- in epilepsy is still challenging due to the lack of powerful imaging probes for the determination of the level of fluctuations of ONOO^- in the epileptic brain. Herein, a near-infrared (NIR) two-photon (TP) fluorescent probe [dicyanomethylene-4H-pyran (DCM)-ONOO] is presented to trace ONOO^- in living cells and in kainate (KA)-induced rat epilepsy models with satisfactory sensitivity and selectivity. The probe is composed of a NIR TP DCM fluorophore and a recognition moiety diphenylphosphinamide. The phosphoramide bond of the probe is interrupted after reacting with ONOO^- for 10 min, and then, the released amino groups emit strong fluorescence due to the restoration of the intramolecular charge transfer process. The probe can effectively detect the changes of endogenous ONOO^- with excellent temporal and spatial resolution in living cells and in rat epileptic brain. The imaging results demonstrate that the increasing level of ONOO^- is closely associated with epilepsy and severe neuronal damage in the brain under KA stimulation. In addition, the low-dose resveratrol can effectively inhibit ONOO^- overexpression and further relieve neuronal damage. With the assistance of TP fluorescence imaging in the epileptic brain tissue, we hypothesize that the abnormal levels of ONOO^- may serve as a potential indicator for the diagnosis of epilepsy. The TP fluorescence imaging based on DCM-ONOO provides a great potential approach for understanding the epilepsy pathology and diagnosis.

A dicyanomethylene-4H-pyran-based fluorescence probe with high selectivity and sensitivity for detecting copper (II) and its bioimaging in living cells and tissue

Copper (Cu) plays a significant role in the process of oxygenic photosynthesis in living systems. The detection of copper ion (Cu²⁺) is valuable and meaningful for further investigating the functions of Cu²⁺ under physiological and pathological conditions. In this paper, a novel fluorescence probe DCM-Cu based on the near-infrared (NIR) fluorophore dicyanomethylene-4H-pyran (DCM) was designed for Cu²⁺ detection. The probe DCM-Cu possessed characteristic of "turn-on" fluorescent signal in the presence of Cu²⁺ through the enhanced ICT process. It exhibited satisfactory sensitivity and selectivity toward Cu²⁺. A good linear correlation was observed between the concentrations of Cu²⁺ and the fluorescence intensities at 700 nm. The detection limit (LOD) of DCM-Cu toward Cu²⁺ was calculated to be 2.54 × 10^-8 M. Importantly, DCM-Cu was successfully applied in the detection of Cu²⁺ in living MCF-7 cells and tumor tissue with low cytotoxicity. Therefore, this probe would have the potential to monitor cellular Cu²⁺ in the living system and be applied to the diagnosis of related diseases.

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

Research advances in integrated theranostic probes for tumor fluorescence visualization and treatment

At present, cancer is obviously a major threat to human health worldwide. Accurate diagnosis and treatment are in great demand and have become an effective method to alleviate the development of cancer and improve the survival rate of patients. A large number of theranostic probes that combine diagnosis and treatment methods have been developed as promising tools for tumor precision medicine. Among them, fluorescent theranostic probes have developed rapidly in the frontier research field of precision medicine with their real time, low toxicity, and high-resolution merit. Therefore, this review focuses on recent advances in the development of fluorescent theranostic probes, as well as their applications for cancer diagnosis and treatment. Initially, small-molecule fluorescent theranostic probes mainly including tumor microenvironment-responsive fluorescent prodrugs and phototherapeutic probes were introduced. Subsequently, nanocomposite probes are expounded based on four types of nano-fluorescent particles combining different therapies (chemotherapy, photothermal therapy, photodynamic therapy, gene therapy, etc.). Then, the capsule-type "all in one" probes, which occupy an important position in theranostic probes, are summarized according to the surface carrier type. This review aims to present a comprehensive guide for researchers in the field of tumor-related theranostic probe design and development.

Nanoparticles Incorporating a Fluorescence Turn-on Reporter for Real-Time Drug Release Monitoring, a Chemoenhancer and a Stealth Agent: Poseidon's Trident against Cancer?

The rate and extent of drug release under physiological conditions is a key factor influencing the therapeutic activity of a formulation. Real-time detection of drug release by conventional pharmacokinetics approaches is confounded by low sensitivity, particularly in the case of tissue-targeted novel drug delivery systems, where low concentrations of the drug reach systemic circulation. We present a novel fluorescence turn-on platform for real-time monitoring of drug release from nanoparticles based on reversible fluorescence quenching in fluorescein esters. Fluorescein-conjugated carbon nanotubes (CNTs) were esterified with methotrexate in solution and solid phase, followed by supramolecular functionalization with a chemoenhancer (suramin) or/and a stealth agent (dextran sulfate). Suramin was found to increase the cytotoxicity of methotrexate in A549 cells. On the other hand, dextran sulfate exhibited no effect on cytotoxicity or cellular uptake of CNTs by A549 cells, while a decrease in cellular uptake of CNTs and cytotoxicity of methotrexate was observed in macrophages (RAW 264.7 cells). Similar results were also obtained when CNTs were replaced with graphene. Docking studies revealed that the conjugates are not internalized by folate receptors/transporters. Further, docking and molecular dynamics studies revealed the conjugates do not exhibit affinity toward the methotrexate target, dihydrofolate reductase. Molecular dynamics studies also revealed that distinct features of dextran-CNT and suramin-CNT interactions, characterized by π-π interactions between CNTs and dextran/suramin. Our study provides a simple, cost-effective, and scalable method for the synthesis of nanoparticles conferred with the ability to monitor drug release in real-time. This method could also be extended to other drugs and other types of nanoparticles.

Activatable Off-on Near-Infrared QCy7-based Fluorogenic Probes for Bioimaging

The activatable off-on near-infrared QCy7-based fluorogenic probes have emerged as powerful modalities for detecting and monitoring biological analytes and understanding their biological processes in cells and organisms. The use of biomarker-activated QCy7-based probes enables simple synthesis, minimum photo-damage to biological samples, and minimum background interference from biological systems. In this minireview, we aim to provide a rigorous but concise overview of activatable QCy7-based fluorogenic probes by reporting the significant progress made in recent years. The design strategies and the main applications of accurate detection and imaging of disease-related biomarkers (including ROS/RSS, enzymes, metal ions, and other related species) were reasonably analyzed and discussed. The potential challenges and prospects of activatable QCy7-based fluorogenic probes are also emphasized to further advance the development of new methods for biomarker detection and bioimaging.

In vivo real-time tracking of tumor-specific biocatalysis in cascade nanotheranostics enables synergistic cancer treatment

Glucose oxidase (GOD)-based synergistic cancer therapy has aroused great research interest in the context of cancer treatment due to the inherent biocompatibility and biodegradability. However, this emerging therapeutic system still lacks a strategy to predict and regulate the in vivo biocatalytic behavior of GOD in real time to minimize the side effects on normal tissues. Herein, we developed a tumor-specific cascade nanotheranostic system (BNG) that combines GOD-catalyzed oxidative stress and dual-channel fluorescent sensing, significantly improving the synergistic therapeutic efficacy with real-time feedback information. The nanotheranostic system remains completely silent in the blood circulatory system and selectively releases GOD enzymes in the tumor site, with enhanced near-infrared (NIR) fluorescence at 825 nm. Subsequently, GOD catalyzes H2O2 production, triggering cascade reactions with NIR fluorescence at 650 nm as an optical output, along with GSH depletion, enabling synergistic cancer treatment. The designed nanotheranostic system, integrated with tumor-activated cascade reactions and triggering a dual-channel output at each step, represents an insightful paradigm for precise cooperative cancer therapy.

Tetrazine-Mediated Bioorthogonal System for Prodrug Activation, Photothermal Therapy, and Optoacoustic Imaging

Bioorthogonal "bond cleavage" reactions hold great promise in a variety of biological applications such as controlled activation of the drug and probe, while the application of these biocompatible reactions in living animals is still in its infancy and has yet to be further explored. Herein we demonstrate a nanosized and two-component bioorthogonal system for tumor inhibition through the combined action of chemo- and photothermal therapy. The trigger of the system was fabricated by immobilizing PEGylated tetrazine on the gold nanorods, and the bioorthogonal prodrug was synthesized by caging the drug camptothecin with vinyl ether, followed by encapsulating it with phospholipid liposomes. The tetrazine-based trigger effectively mediates the bioorthogonal reaction and triggers the release of camptothecin for chemotherapy, and the gold nanorods exhibit high photothermal capability for photothermal therapy and for three-dimensional optoacoustic imaging. Upon injection into tumor-bearing mice, the two components accumulate in the tumor region and carry out a bioorthogonal reaction therein, hence releasing the parent drug. The combined actions of chemo- and photothermal therapy greatly inhibited tumor growth in mice. This strategy may afford a promising approach for achieving controlled release of an active drug in vivo through an alternative external stimulus-a bioorthogonal reaction.

Depolymerization of Bottlebrush Polypentenamers and Their Macromolecular Metamorphosis

The depolymerization of bottlebrush (BB) polymers with varying lengths of polycyclopentene (PCP) backbone and polystyrene (PS) grafts is investigated. In all cases, ring closing metathesis (RCM) depolymerization of the PCP BB backbone appears to occur through an end-to-end depolymerization mechanism as evidenced by size exclusion chromatography. Investigation on the RCM depolymerization of linear PCP reveals a more random chain degradation process. Quantitative depolymerization occurs under thermodynamic conditions (higher temperature and dilution) that drives RCM into cyclopentenes (CPs), each bearing one of the original PS grafts from the BB. Catalyst screening reveals Grubbs' third (G3) and second (G2) generation catalyst depolymerize BBs significantly faster than Grubbs' first generation (G1) and Hoveyda-Grubbs' second generation (HG2) catalyst under identical conditions while solvent (toluene versus CHCl₃) plays a less significant role. The length of the BB backbone and PS side chains also play a minor role in depolymerization kinetics, which is discussed. The ability to completely deconstruct these BB architectures into linear grafts provides definitive insights toward the ATRP "grafting-from" mechanism originally used to construct the BBs. Core-shell BB block copolymers (BBCPs) are shown to quantitatively depolymerize into linear diblock polymer grafts. Finally, the complete depolymerization of BBs into α-cyclopentenyl-PS allows further transformation to other architectures, such as 3-arm stars, through thiol-ene coupling onto the CP end group. These unique materials open the door to stimuli-responsive reassembly of BBs and BBCPs into new morphologies driven by macromolecular metamorphosis.

Nanoplatform Constructed from a β-Glucan and Polydeoxyadenylic Acid for Cancer Chemotherapy and Imaging

A nanoplatform carrying doxorubicin (Dox) for cancer therapy and a dye for imaging was developed based on a natural triple helix β-glucan (t-LNT) and polydeoxyadenylic acid (poly(dA)). The t-LNT-Dox conjugates were prepared through Schiff-base reaction between the aldehyde group in the oxidized t-LNT and the amino group of Dox, the single chains (s-LNT-Dox) of which interacted with the poly(dA)-dye to form a composite s-LNT-Dox/poly(dA)-dye through hydrogen bonding between s-LNT and poly(dA). t-LNT-Dox was confirmed to acid-responsively release Dox in vitro, showing enhanced cytotoxicity against HeLa cancer cells with time. It was confirmed that Dox and the dye could be simultaneously delivered into HeLa cells or the tumors with a prolonged duration time. Furthermore, LNT-Dox conjugates effectively inhibited tumor growth and decreased adverse effects of the free Dox in vivo. Hence, this work develops a new strategy to fabricate the nanoplatform for therapy and imaging using a natural polysaccharide.

A conjugated-polymer-based ratiometric nanoprobe for evaluating in-vivo hepatotoxicity induced by herbal medicine via MSOT imaging

Herbal medicines are widely used around the world, while some of them are associated with adverse effects like herb-induced liver injury due to oxidative/nitrosative stress resulted from hepatically-generated ROS/RNS. It is of significance to accurately evaluate herbal-medicine-induced hepatotoxicity, since it would help provide effective monitoring method of the safety of herbal remedies. Herein we designed a ratiometric nanoprobe for in vivo imaging hepatic injury induced by herbal medicine (polygonum multiflorum, PM) via specifically responding to NO generated in liver by PM, and with MSOT imaging the precise location of liver injury can be identified. The liposomal nanoprobe consists of a responsive dye (IX-2NH₂) which could specifically respond to NO and the diketopyrrolopyrrole-based conjugated polymer (DPP-TT) as the internal reference. Thus we can realize ratiometric optoacoustic detection of herbal-medicine-induced liver injury with 3D information in mouse model in a noninvasive way.

In situ imaging of aminopeptidase N activity in hepatocellular carcinoma: a migration model for tumour using an activatable two-photon NIR fluorescent probe

CD13/aminopeptidase N (APN), which is a zinc-dependent metalloproteinase, plays a vital role in the growth, migration, angiogenesis, and metastasis of tumours. Thus, in situ molecular imaging of endogenous APN levels is considerably significant for investigating APN and its different functions. In this study, a novel two-photon near-infrared (NIR) fluorescence probe DCM-APN was prepared to perform in vitro and in vivo tracking of APN. The N-terminal alanyl site of probe DCM-APN was accurately hydrolysed to the amino group, thereby liberating strong fluorescence owing to the recovery of the Intramolecular Charge Transfer (ICT) effect. By considering its outstanding selectivity, ultra-sensitivity (DL 0.25 ng mL-1) and favourable biocompatibility, the probe DCM-APN was used to distinguish between normal cells (LO2 cells) and cancer cells (HepG-2 and B16/BL6 cells). Furthermore, migration of hepatocellular carcinoma cells was apparently inhibited by ensuring that the APN catalytic cavity was occupied by bestatin. The identification of three-dimensional (3D) fluorescence in cancer tissues was completed under two-photon excitation coupled with lighting up hepatocellular carcinoma tumours in situ; this revealed that probe DCM-APN is an effective tool for detecting APN, thereby assisting in the early diagnosis of tumour in clinical medicine.

Recent Advances in Polymeric Nanomedicines for Cancer Immunotherapy

Immunotherapy has emerged as a promising approach to treat cancer, since it facilitates eradication of cancer by enhancing innate and/or adaptive immunity without using cytotoxic drugs. Of the immunotherapeutic approaches, significant clinical potentials are shown in cancer vaccination, immune checkpoint therapy, and adoptive cell transfer. Nevertheless, conventional immunotherapies often involve immune-related adverse effects, such as liver dysfunction, hypophysitis, type I diabetes, and neuropathy. In an attempt to address these issues, polymeric nanomedicines are extensively investigated in recent years. In this review, recent advances in polymeric nanomedicines for cancer immunotherapy are highlighted and thoroughly discussed in terms of 1) antigen presentation, 2) activation of antigen-presenting cells and T cells, and 3) promotion of effector cells. Also, the future perspectives to develop ideal nanomedicines for cancer immunotherapy are provided.

Intracellular GSH-responsive camptothecin delivery systems

Smart GSH-responsive camptothecin delivery systems for treatment of tumors and real-time monitoring in vivo and in vitro were described.

A fluorescent probe based on aggregation-induced emission for hydrogen sulfide-specific assaying in food and biological systems

An AIE-based fluorescent probe was developed for monitoring food spoilage via its response toward hydrogen sulfide.

Self-immolative colorimetric, fluorescent and chemiluminescent chemosensors

Self-immolative chemistry features a cascade of disassembly reactions in response to external stimuli, which provides great opportunities to design new self-immolative chemosensors with advanced performance and/or functions. Self-immolative spacers in these chemosensors not only facilitate the linkage of designed triggers to various chromophores or fluorophores, but can also be used to solve inherent problems associated with native chemosensors, such as low reactivities, poor stabilities and slow response times. Their capacity for stimuli-responsive release through operation of a self-immolative reaction further enables integration of sophisticated functions into chemosensors, including signal amplification, enzyme activity localization, and drug monitoring. Significant advances have been made in the field of self-immolative chemosensors, leading to intriguing applications to sensitive detection of analytes, bioimaging and cancer theranostics. This tutorial review summarizes this recent progress with a focus on their design strategies and sensing mechanisms.

A highly GSH-sensitive SN-38 prodrug with an "OFF-to-ON" fluorescence switch as a bifunctional anticancer agent

SN-38 (7-ethyl-10-hydroxy-camptothecin) is an active metabolite of irinotecan (CPT-11) and the most potent camptothecin analogue. In this study, 2,4-dinitrobenzene sulfonyl (DNS) was covalently conjugated as a GSH-sensitive trigger to 10'-OH of SN-38 to yield a GSH-sensitive prodrug, denoted as DNS-SN38, with virtually quenched fluorescence due to donor-excited photo-induced electron transfer (d-PeT). By investigating DNS-SN38's activation properties upon fluorescence restoration and cytotoxic potency against ovarian cancer cell lines (A2780 and m-Cherry + OCSC1-F2), its potential applicability as a useful chemotherapeutic agent was demonstrated.

In Vivo Imaging Tracking and Immune Responses to Nanovaccines Involving Combined Antigen Nanoparticles with a Programmed Delivery

Combined nanovaccine can generate robust and persistent antigen-specific immune responses. A combined nanovaccine was developed based on antigen-loaded genipin-cross-linked-polyethyleneimine-antigen nanoparticles and in vivo multispectral fluorescence imaging tracked the antigen delivery of combined nanovaccine. The inner layer antigen nanoparticles carried abundant antigens by self-cross-linking for persistent immune response, whereas the outer antigen on the surface of antigen nanoparticles provided the initial antigen exposure. The delivery of combined nanovaccine was tracked dynamically and objectively by the separation of inner genipin cross-linked antigen nanoparticle and the outer fluorescent antigen. The immune responses of the combined nanovaccine were evaluated including antigen-specific CD4⁺ and CD8⁺ T-cell responses, IgG antibody level, immunological memory, and CD8⁺ cytotoxic T lymphocyte responses. The results indicated that the inner and outer antigens of combined vaccine can be tracked in real time with a programmed delivery by the dual fluorescence imaging. The programmed delivery of the inner and outer antigens induced strong immune responses with a combination of a quick delivery and a persistent delivery. With adequate antigen exposure, the dendritic cells were effectively activated and matured, and following T cells were further activated for immune response. Compared with a single nanoparticle formulation, the combined nanovaccine exactly elicited a stronger antigen-specific immune response.

Self-sensibilized polymeric prodrug co-delivering MMP-9 shRNA plasmid for combined treatment of tumors

Polymeric prodrugs are of immense interest as anticancer drug-delivery system owing to their superior drug stability during circulation and satisfactory drug loading capacity. However, they are usually less effective than free drugs due to imperfect degradable characteristics or active sites blockage. A polymeric prodrug (HPAA-MTX) with chemotherapeutic self-sensibilization effect consisting of glutathione (GSH)-triggered hyperbranched poly(amido amine) (HPAA) and methotrexate (MTX) was designed and synthesized in this work. This prodrug not only showed better inhibition effect on the tumor cells proliferation compared with free MTX, but also displayed selective sensibilization to tumor cells rather than normal cells. Meanwhile, HPAA-MTX was also explored as a MMP-9 shRNA plasmid delivery vector due to their rich amino group of HPAA, accompanying with MTX for simultaneous inhibiting tumor cells proliferation and migration. As expected, HPAA-MTX possessed excellent gene delivery capacity with significant down-regulation expression of MMP-9 protein and further inhibition of MCF-7 cells migration. Benefiting from the self-sensibilization effect and MTX/MMP-9 co-delivery strategy, this HPAA-MTX/MMP-9 co-delivery system exhibited significantly improved therapeutic efficacy to breast cancer in a combined manner which was confirmed through in vitro and in vivo assays. The strategy established in this study provided a facile "all-in-one" platform to integrate the drug/gene co-delivery strategy and self-sensibilization effect into one single nanocomposite for potential cancer treatment.

STATEMENT OF SIGNIFICANCE

A cationic polymeric prodrug with chemotherapeutic self-sensibilization effect was designed and showed better inhibition effect on tumor cells proliferation compared with its free drug, as well displayed the selective sensibilization effect to tumor cells rather than normal cells. Moreover, the prodrug could also deliver MMP-9 shRNA plasmid for a combined therapy. As expected, the prodrug possessed excellent gene delivery capacity with significant down-regulation expression of MMP-9 protein and further inhibition of MCF-7 cells migration. Benefiting from the self-sensibilization effect and the drug/gene co-delivery strategy, this prodrug exhibited significantly improved therapeutic efficacy to breast cancer in a combined manner.

Polymer Therapeutics: Biomarkers and New Approaches for Personalized Cancer Treatment

Polymer therapeutics (PTs) provides a potentially exciting approach for the treatment of many diseases by enhancing aqueous solubility and altering drug pharmacokinetics at both the whole organism and subcellular level leading to improved therapeutic outcomes. However, the failure of many polymer-drug conjugates in clinical trials suggests that we may need to stratify patients in order to match each patient to the right PT. In this concise review, we hope to assess potential PT-specific biomarkers for cancer treatment, with a focus on new studies, detection methods, new models and the opportunities this knowledge will bring for the development of novel PT-based anti-cancer strategies. We discuss the various "hurdles" that a given PT faces on its passage from the syringe to the tumor (and beyond), including the passage through the bloodstream, tumor targeting, tumor uptake and the intracellular release of the active agent. However, we also discuss other relevant concepts and new considerations in the field, which we hope will provide new insight into the possible applications of PT-related biomarkers.

Therapeutic Nanosystem Consisting of Singlet-Oxygen-Responsive Prodrug and Photosensitizer Excited by Two-Photon Light

Using light as the sole stimulus and employing the generated singlet oxygen as a therapeutic agent and the trigger to activate chemo-drug release could serve as an elegant way to bring into full play the advantageous features of light and enhance therapeutic efficacy through a combination of chemotherapy and photodynamic therapy. Herein a liposomal drug system has been developed by embedding a fluorescent photosensitizer and a prodrug into phospholipid vesicles. Upon one- or two-photon light irradiation, the photosensitizer generates singlet oxygen, which removes the protecting group of the prodrug and subsequently causes the release of the active drug chlorambucil. With the combined action of O21 and chlorambucil, highly controllable cytotoxicity toward cancer cells was achieved. In addition, the fluorescent photosensitizer gives out fluorescent signal acting as the drug monitoring agent. This strategy may provide an efficient approach for cancer treatment and some useful insights for designing light-stimulated on-demand therapeutic systems.

Recent advances of dicyano-based materials in biology and medicine

We highlight the development of dicyano-based fluorescent materials in biology and medicine.

A unimolecular theranostic system with H2O2-specific response and AIE-activity for doxorubicin releasing and real-time tracking in living cells

A theranostic drug delivery system composed of tetraphenyl-ethene (AIEgen), benzyl boronic ester (trigger), and doxorubicin (drug) was designed and synthesized; its utilities for cell imaging, drug delivery tracking, and cancer cell cytociding were evaluated.

A theranostic drug delivery system composed of tetraphenylethene (AIE-gen), benzyl-boronic ester (trigger) and doxorubicin (drug) was synthesized and its functions in cell imaging, drug delivery tracking, and therapeutic effect were evaluated.

Cationic Poly(benzyl ether)s as Self-Immolative Antimicrobial Polymers

Self-immolative polymers (SIMPs) are macromolecules that spontaneously undergo depolymerization into small molecules when triggered by specific external stimuli. We report here the first examples of antimicrobial SIMPs with potent, rapid, and broad-spectrum bactericidal activity. Their antibacterial and hemolytic activities were examined as a function of cationic functionality. Polymers bearing primary ammonium cationic groups showed more potent bactericidal activity against Escherichia coli, relative to tertiary and quaternary ammonium counterparts, whereas the quaternary ammonium polymers showed the lowest hemolytic toxicity. These antibacterial polycations undergo end-to-end depolymerization when triggered by an externally applied stimulus. Specifically, poly(benzyl ether)s end-capped with a silyl ether group and bearing pendant allyl side chains were converted to polycations by photoinitiated thiol-ene radical addition using cysteamine HCl. The intact polycations are stable in solution, but they spontaneously unzip into their component monomers upon exposure to fluoride ions, with excellent sensitivity and selectivity. Upon triggered depolymerization, the antibacterial potency was largely retained but the hemolytic toxicity was substantially reduced. Thus, we reveal the first example of a self-immolative antibacterial polymer platform that will enable antibacterial materials to spontaneously unzip into biologically active small molecules upon the introduction of a specifically designed stimulus.