Smart Molecular Imaging and Theranostic Probes by Enzymatic Molecular In Situ Self-Assembly

Enzymatic molecular in situ self-assembly (E-MISA) that enables the synthesis of high-order nanostructures from synthetic small molecules inside a living subject has emerged as a promising strategy for molecular imaging and theranostics. This strategy leverages the catalytic activity of an enzyme to trigger probe substrate conversion and assembly in situ, permitting prolonging retention and congregating many molecules of probes in the targeted cells or tissues. Enhanced imaging signals or therapeutic functions can be achieved by responding to a specific enzyme. This E-MISA strategy has been successfully applied for the development of enzyme-activated smart molecular imaging or theranostic probes for in vivo applications. In this Perspective, we discuss the general principle of controlling in situ self-assembly of synthetic small molecules by an enzyme and then discuss the applications for the construction of "smart" imaging and theranostic probes against cancers and bacteria. Finally, we discuss the current challenges and perspectives in utilizing the E-MISA strategy for disease diagnoses and therapies, particularly for clinical translation.

A Golgi Apparatus-Targeted Photothermal Agent with Protein Anchoring for Enhanced Cancer Photothermal Therapy

The Golgi apparatus (GA) is central in shuttling proteins from the endoplasmic reticulum to different cellular areas. Therefore, targeting the GA to precisely destroy its proteins through local heat could induce apoptosis, offering a potential avenue for effective cancer therapy. Herein, a GA-targeted photothermal agent based on protein anchoring is introduced for enhanced photothermal therapy of tumor through the modification of near-infrared molecular dye with maleimide derivative and benzene sulfonamide. The photothermal agent can actively target the GA and covalently anchor to its sulfhydryl proteins, thereby increasing its retention within the GA. Under laser irradiation, the heat generated by the photothermal agent efficiently disrupts sulfhydryl proteins in situ, leading to GA dysfunction and ultimately inducing cell apoptosis. In vivo experiments demonstrate that the photothermal agent can precisely treat tumors and significantly reduce side effects.

Smart Stimuli-Responsive Spherical Nucleic Acids: Cutting-Edge Platforms for Biosensing, Bioimaging, and Therapeutics

Spherical nucleic acids (SNAs) with exceptional colloidal stability, multiple modularity, and programmability are excellent candidates to address common molecular delivery-related issues. Based on this, the higher targeting accuracy and enhanced controllability of stimuli-responsive SNAs render them precise nanoplatforms with inestimable prospects for diverse biomedical applications. Therefore, tailored diagnosis and treatment with stimuli-responsive SNAs may be a robust strategy to break through the bottlenecks associated with traditional nanocarriers. Various stimuli-responsive SNAs are engineered through the incorporation of multifunctional modifications to meet biomedical demands with the development of nucleic acid functionalization. This review provides a comprehensive overview of prominent research in this area and recent advancements in the utilization of stimuli-responsive SNAs in biosensing, bioimaging, and therapeutics. For each aspect, SNA nanoplatforms that exhibit responsive behavior to both internal stimuli (including sequence, enzyme, redox reactions, and pH) and external stimuli (such as light and temperature) are highlighted. This review is expected to offer inspiration and guidance strategies for the rational design and development of stimuli-responsive SNAs in the field of biomedicine.

Fine-tuning of stable organic free-radical photosensitizers for photodynamic immunotherapy

Photodynamic immunotherapy (PDI) is an innovative approach to cancer treatment that utilizes photodynamic therapy (PDT) and photosensitizers (PSs) to induce immunogenic cell death (ICD). However, currently most commonly used PSs have restricted capabilities to generate reactive oxygen species (ROS) via a type-II mechanism under hypoxic environments, which limits their effectiveness in PDI. To overcome this, we propose a novel approach for constructing oxygen independent PSs based on stable organic free-radical molecules. By fine-tuning the characteristics of tris(2,4,6-trichlorophenyl)-methyl (TTM) radicals through the incorporation of electron-donating moieties, we successfully found that TTMIndoOMe could produce substantial amounts of ROS even in hypoxic environments. In vitro experiments showed that TTMIndoOMe could effectively produce O2˙-, kill tumor cells and trigger ICD. Moreover, in vivo experiments also demonstrated that TTMIndoOMe could further trigger anti-tumor immune response and exhibit a superior therapeutic effect compared with PDT alone. Our study offers a promising approach towards the development of next-generation PSs functioning efficiently even under hypoxic conditions and also paves the way for the creation of more effective PSs for PDI.

Ligand Regulation Strategy to Modulate ROS Nature in a Rhodamine-Iridium(III) Hybrid System for Phototherapy

The efficacy of photodynamic therapy (PDT) is highly dependent on the photosensitizer features. The reactive oxygen species (ROS) generated by photosensitizers is proven to be associated with immunotherapy by triggering immunogenic cell death (ICD) as well. In this work, we establish a rhodamine-iridium(III) hybrid model functioning as a photosensitizer to comprehensively understand its performance and potential applications in photodynamic immunotherapy. Especially, the correlation between the ROS generation efficiency and the energy level of the Ir(III)-based excited state (T1'), modulated by the cyclometalating (C∧N) ligand, is systematically investigated and correlated. We prove that in addition to the direct population of the rhodamine triplet state (T1) formed through the intersystem crossing process with the assistance of a heavy Ir(III) metal center, the fine-tuned T1' state could act as a relay to provide an additional pathway for promoting the cascade energy transfer process that leads to enhanced ROS generation ability. Moreover, type I ROS can be effectively produced by introducing sulfur-containing thiophene units in C∧N ligands, providing a stronger M1 macrophage-activation efficiency under hypoxia to evoke in vivo antitumor immunity. Overall, our work provides a fundamental guideline for the molecular design and exploration of advanced transition-metal-based photosensitizers for biomedical applications.

Galactosyl BODIPY-based nanoparticles as a type-I photosensitizer for HepG2 cell targeted photodynamic therapy

We report a galactosyl diiodo-BODIPY-based nanoparticles as type-I photosensitizer (PS) with high water solubility for HepG2 cell targeted photodynamic therapy. Functionalized galactoside and glucoside were introduced into diiodo-BODIPY to obtain BP1 and BP2, respectively. The glycolyl PSs could self-assemble to form the nanoparticles BP1-NP and BP2-NP with red-shifted near-infrared (NIR) absorption and fluorescence at 682 nm and 780 nm, as well as excellent chemo- and photo-stability. In comparison to the monomer in DMSO, the aggregated photosensitizers in the nanoparticles enabled the sensitization of oxygen to superoxide (O2˙-) through a type-I process, while repressing the generation of singlet oxygen (1O2) through a type-II process. The galactosyl-modified BP1-NPs could target and concentrate on HepG2 cells, subsequently generating O2˙- and 1O2 to trigger cell death under 660 nm light irradiation. This work provides an efficient strategy for the construction of glycoside-recognized type-I photosensitizers for tumor cell imaging and photodynamic therapy.

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.

Self-amplified activatable nanophotosensitizers for HIF-1α inhibition-enhanced photodynamic therapy

Activatable photodynamic therapy (PDT) has shown great potential in cancer therapy owing to its high tumor specificity and minimized side effect. However, the relatively low level of biomarkers within tumor tissue rescricts the photosensitizer to get thoroughly activated. In this study, we design a self-amplified activatable nanophotosensitizer (CPPa NP) for enhanced PDT. CPPa NP is prepared by encapsulating a hypoxia-inducible factor 1α (HIF-1α) inhibitor CI-994 with an amphiphilic hydrogen peroxide (H2O2) responsive copolymer PPa-CA-PEG. Upon the addition of H2O2, the thioketal linker within CPPa NP is cleaved, resulting in the simultaneous release of thiol-modified pyropheophorbide a (PPa-SH), cinnamic aldehyde (CA), and CI-994. PPa-SH can be encapsulated by albumin to turn on its photodynamic efficiency, while CI-994 may inhibit the expression of HIF-1α to improve the PDT efficacy. CA is able to deplete glutathione (GSH) and upregulate reactive oxygen species (ROS) within tumor cells, accelerating the dissociation of nanoparticles and disrupting the redox balance of tumor cells. In vitro and in vivo studies showed that CPPa NP can successfully elevate the ROS level within 4T1 cells and has a better anticancer efficacy than PPa NP without CI-994 under laser irradiation. This study thus provides an effective approach to develop self-amplified activatable nanoparticles for enhanced PDT.

Development of Human Serum Albumin Fluorescent Probes in Detection, Imaging, and Disease Therapy

Human serum albumin (HSA) acts as a repository and transporter of substances in the blood. An abnormal concentration may indicate the occurrence of liver- and kidney-related diseases, which has attracted people to investigate the precise quantification of HSA in body fluids. Fluorescent probes can combine with HSA covalently or noncovalently to quantify HSA in urine and plasma. Moreover, probes combined with HSA can improve its photophysical properties; probe-HSA has been applied in real-time monitoring and photothermal and photodynamic therapy in vivo. This Review will introduce fluorescent probes for quantitative HSA according to the three reaction mechanisms of spatial structure, enzymatic reaction, and self-assembly and systematically introduce the application of probes combined with HSA in disease imaging and phototherapy. It will help develop multifunctional applications for HSA probes and provide assistance in the early diagnosis and treatment of diseases.

A selenium-based NIR-II photosensitizer for a highly effective and safe phototherapy plan

High efficiency, stability, long emission wavelength (NIR-II), and good biocompatibility are crucial for photosensitizers in phototherapy. However, current Food and Drug Administration (FDA)-approved organic fluorophores exhibit poor chemical stability and photostability as well as short emission wavelength, limiting their clinical usage. To address this, we developed Se-IR1100, a novel organic photosensitizer with a photostable and thermostable benzobisthiadiazole (BBTD) backbone. By incorporating selenium as a heavy atom and constructing a D-A-D structure, Se-IR1100 exhibits a maximum fluorescence emission wavelength of 1100 nm. Compared with FDA-approved indocyanine green (ICG), DSPE-PEGylated Se-IR1100 nanoparticles exhibit prominent photostability and long-lasting photothermal effects. Upon 808 nm laser irradiation, Se-IR1100 NPs efficiently convert light energy into heat and reactive oxygen species (ROS), inducing cancer cell death in cellular studies and living organisms while maintaining biocompatibility. With salient photostability and a photothermal conversion rate of 55.37%, Se-IR1100 NPs hold promise as a superior photosensitizer for diagnostic and therapeutic agents in oncology. Overall, we have designed and optimized a multifunctional photosensitizer Se-IR1100 with good biocompatibility that performs NIR-II fluorescence imaging and phototherapy. This dual-strategy method may offer novel approaches for the development of multifunctional probes using dual-strategy or even multi-strategy methods in bioimaging, disease diagnosis, and therapy.

Cascade In Situ Self-Assembly and Bioorthogonal Reaction Enable the Enrichment of Photosensitizers and Carbonic Anhydrase Inhibitors for Pretargeted Cancer Theranostics

We report here a tumor-pretargted theranostic approach for multimodality imaging-guided synergistic cancer PDT by cascade alkaline phosphatase (ALP)-mediated in situ self-assembly and bioorthogonal inverse electron demand Diels-Alder (IEDDA) reaction. Using the enzymatic catalysis of ALP that continuously catalyses the dephosphorylation and self-assembly of trans-cyclooctene (TCO)-bearing P-FFGd-TCO, a high density of fluorescent and magnetic TCO-containing nanoparticles (FMNPs-TCO) can be synthesized and retained on the membrane of tumor cells. They can act as 'artificial antigens' amenable to concurrently capture lately administrated tetrazine (Tz)-decorated PS (775NP-Tz) and carbonic anhydrase (CA) inhibitor (SA-Tz) via the fast IEDDA reaction. This two-step pretargeting process can further induce FMNPs-TCO regrowth into microparticles (FMNPs-775/SA) directly on tumor cell membranes, which is analyzed by bio-SEM and fluorescence imaging. Thus, efficient enrichment of both SA-Tz and 775NP-Tz in tumors can be achieved, allowing to alleviate hypoxia by continuously inhibiting CA activity and improving PDT of tumors. Findings show that subcutaneous HeLa tumors could be completely eradicated and no tumor recurred after irradiation with an 808 nm laser (0.33 W cm-2 , 10 min). This pretargeted approach may be applied to enrich other therapeutic agents in tumors to improve targeted therapy.

Crosstalk between Hepatic Glutathione Efflux and Tumor Targeting Efficiency of Indocyanine Green-Conjugated Gold Nanoparticles

The elevated glutathione (GSH) level in solid tumors has been used as a major hallmark for GSH-responsive nanoparticles to enhance targeting efficiency and specificity. Meanwhile, GSH is mainly synthesized inside the hepatocytes of the liver in the body and constantly released into the blood through hepatic GSH efflux to regulate redox potential of the entire body. However, it remains largely unknown how this hepatic GSH efflux affects the tumor targeting of GSH-responsive nanoparticles. Herein, we report that depletion of hepatic GSH enhanced the tumor targeting of GSH-responsive indocyanine green-conjugated Au25 nanoclusters coated with 18 GSH ligand (ICG-Au25 SG18 ). The dissociation of ICG from Au25 SG18 by the hepatic GSH through thiol-exchange reaction and the subsequent hepatobiliary clearance of the detached ICG were slowed down by GSH depletion, which in turn prolonged the blood circulation of intact ICG-Au25 SG18 and enhanced its tumor targeting. Our work highlights glutathione-mediated crosstalk between the liver and tumor, in addition to well-known Kupffer cell-mediated uptake, in the tumor targeting of engineered nanoparticles, which could be modulated to enhance targeting efficiency and specificity of cancer nanomedicines while reducing their nonspecific accumulation.

Prolonging Treatment Window of Photodynamic Therapy with Self-Amplified H2 O2 -Activated Photodynamic/Chemo Combination Therapeutic Nanomedicines

Photodynamic therapy (PDT) is a promising approach to cancer therapy. However, the relatively short tumor retention time of photosensitizers (PSs) makes it difficult to catch the optimal treatment time and restricts multiple PDT within a single injection. In this study, a tumor-specific phototheranostic nanomedicine (DPPa NP) is developed for photodynamic/chemo combination therapy with a prolonged PDT treatment window. DPPa NP is prepared via encapsulating a hydrophobic oxidized bovine serum albumin (BSA-SOH)-conjugatable PS DPPa with amphiphilic H2 O2 -activatable chlorambucil (CL) prodrug mPEG-TK-CL. The released CL under H2 O2 treatment can not only kill tumor cells but also upregulate reactive oxygen species levels within tumor cells, leading to the almost full release of cargoes. The released DPPa may conjugate with overexpressed BSA-SOH, which results in the recovery of the fluorescence signal and photodynamic effect. More importantly, such conjugation transfers DPPa from a small molecule PS into a macromolecular PS with a long tumor retention time and treatment window of PDT, which enables multiple PDT. This study thus provides an effective strategy to prolong the treatment window of PDT and enables tumor-specific fluorescence imaging-guided combination therapy.

A DNA Logic Circuit Equipped with a Biological Amplifier Loaded into Biomimetic ZIF-8 Nanoparticles Enables Accurate Identification of Specific Cancers In Vivo

DNA logic circuits (DLC) enable the accurate identification of specific cell types, such as cancer cells, but they face the challenges of weak output signals and a lack of competent platforms that can efficiently deliver DLC components to the target site in the living body. To address these issues, we rationally introduced a cascaded biological amplifier module based on the Primer Exchange Reaction inspired by electronic circuit amplifier devices. As a paradigm, three abnormally expressed Hela cell microRNAs (-30a, -17, and -21) were chosen as "AND" gate inputs. DLC response to these inputs was boosted by the amplifier markedly enhancing the output signal. More importantly, the encapsulation of DLC and amplifier components into ZIF-8 nanoparticles resulted in their efficient delivery to the target site, successfully distinguishing the Hela tumor subtype from other tumors in vivo. Thus, we envision that this strategy has great potential for clinical cancer diagnosis.

β-Glucuronidase-Activated Bioluminescence Probe for In Vivo Tumor Imaging

β-Glucuronidase (GLU) is a hallmark enzyme for many malignant tumors, but bioluminescence (BL) probes that enable GLU imaging in vivo have not been reported. Herein, we rationally designed the BL probe Glc-Luc to address this issue. In vitro results demonstrated the specific responsiveness of Glc-Luc toward GLU with a calculated catalytic efficiency (kcat/Km) of 0.0109 μM-1 min-1 and a limit of detection (LOD) of 1.39 U/mL. Moreover, Glc-Luc rendered 3.1-fold and 15.9-fold higher BL intensities over the control groups in cell lysates and tumor-bearing mice, respectively. We anticipate that Glc-Luc could be further applied for the sensitive diagnosis of GLU-related diseases.

Nanoprobe-based molecular imaging for tumor stratification

The responses of patients to tumor therapies vary due to tumor heterogeneity. Tumor stratification has been attracting increasing attention for accurately distinguishing between responders to treatment and non-responders. Nanoprobes with unique physical and chemical properties have great potential for patient stratification. This review begins by describing the features and design principles of nanoprobes that can visualize specific cell types and biomarkers and release inflammatory factors during or before tumor treatment. Then, we focus on the recent advancements in using nanoprobes to stratify various therapeutic modalities, including chemotherapy, radiotherapy (RT), photothermal therapy (PTT), photodynamic therapy (PDT), chemodynamic therapy (CDT), ferroptosis, and immunotherapy. The main challenges and perspectives of nanoprobes in cancer stratification are also discussed to facilitate probe development and clinical applications.

A Fast and Reversible Responsive Bionic Transmembrane Nanochannel for Dynamic Single-Cell Quantification of Glutathione

Biological channels can rapidly and continuously modulate ion transport behaviors in response to external stimuli, which play essential roles in manipulating physiological and pathological processes in cells. Here, to mimic the biological channels, a bionic nanochannel is developed by synergizing a cationic silicon-substituted rhodamine (SiRh) with a glass nanopipette for transmembrane single-cell quantification. Taking the fast and reversible nucleophilic addition reaction between glutathione (GSH) and SiRh, the bionic nanochannel shows a fast and reversible response to GSH, with its inner-surface charges changing between positive and negative charges, leading to a distinct and reversible switch in ionic current rectification (ICR). With the bionic nanochannel, spatiotemporal-resolved operation is performed to quantify endogenous GSH in a single cell, allowing for monitoring of intracellular GSH fluctuation in tumor cells upon photodynamic therapy and ferroptosis. Our results demonstrate that it is a feasible tool for in situ quantification of the endogenous GSH in single cells, which may be adapted to addressing other endogenous biomolecules in single cells by usage of other stimuli-responsive probes.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Self-Assembled Nano-PROTAC Enables Near-Infrared Photodynamic Proteolysis for Cancer Therapy

Confining the protein degradation activity of proteolysis-targeting chimera (PROTAC) to cancer lesions ensures precision treatment. However, it still remains challenging to precisely control PROTAC function in tumor regions in vivo. We herein describe a near-infrared (NIR) photoactivatable nano-PROTAC (NAP) for remote-controllable proteolysis in tumor-bearing mice. NAP is formed by molecular self-assembly from an amphiphilic conjugate of PROTAC linked with an NIR photosensitizer through a singlet oxygen (1O2)-cleavable linker. The activity of PROTAC is initially silenced but can be remotely switched on upon NIR photoirradiation to generate 1O2 by the photosensitizer. We demonstrated that NAP enabled tumor-specific degradation of bromodomain-containing protein 4 (BRD4) in an NIR light-instructed manner. This in combination with photodynamic therapy (PDT) elicited an effective suppression of tumor growth. This work thus presents a novel approach for spatiotemporal control over targeted protein degradation by PROTAC.

Apoptosis-Amplified Assembly of Porphyrin Nanofiber Enhances Photodynamic Therapy of Oral Tumor

Oral squamous cell carcinoma (OSCC) is the most common oral cancer, having high recurrence and metastasis features. In addition to surgery, photodynamic therapy (PDT) is considered as another effective approach for OSCC treatment. The water solubility of currently available PDT photosensitizers (PSs) is poor, lowering their singlet oxygen (¹O₂) yield and consequent PDT efficiency. Strategies of PS assembly have been reported to increase ¹O₂ yield, but it is still possible to further enhance PDT efficiency. In this work, we utilized apoptosis to amplify the assembly of porphyrin nanofibers for enhanced PDT of OSCC. A water-soluble porphyrin derivative, Ac-Asp-Glu-Val-Asp-Asp-TPP (Ac-DEVDD-TPP), was designed for this purpose. Upon caspase-3 (Casp3, an activated enzyme during apoptosis) cleavage and laser irradiation, Ac-DEVDD-TPP was converted to D-TPP, which spontaneously self-assembled into porphyrin nanofibers, accompanied by 1.4-fold and 2.1-fold ¹O₂ generations in vitro and in cells, respectively. The as-formed porphyrin nanofiber induced efficient cell apoptosis and pyroptosis. In vivo experiments demonstrated that, compared with the scrambled control compound Ac-DEDVD-TPP, Ac-DEVDD-TPP led to 6.2-fold and 1.3-fold expressions of Casp3 in subcutaneous and orthotopic oral tumor models, respectively, and significantly suppressed the tumors. We envision that our strategy of apoptosis-amplified porphyrin assembly might be applied for OSCC treatment in the clinic in the near future.

Acceptor engineering of metallacycles with high phototoxicity indices for safe and effective photodynamic therapy

Although metallacycle-based photosensitizers have attracted increasing attention in biomedicine, their clinical application has been hindered by their inherent dark toxicity and unsatisfactory phototherapeutic efficiency. Herein, we employ a π-expansion strategy for ruthenium acceptors to develop a series of Ru(ii) metallacycles (Ru1-Ru4), while simultaneously reducing dark toxicity and enhancing phototoxicity, thus obtaining a high phototoxicity index (PI). These metallacycles enable deep-tissue (∼7 mm) fluorescence imaging and reactive oxygen species (ROS) production and exhibit remarkable anti-tumor activity even under hypoxic conditions. Notably, Ru4 has the lowest dark toxicity, highest ROS generation ability and an optimal PI (∼146). Theoretical calculations verify that Ru4 exhibits the largest steric bulk and the lowest singlet-triplet energy gap (ΔE _ST, 0.62 eV). In vivo studies confirm that Ru4 allows for effective and safe phototherapy against A549 tumors. This work thus is expected to open a new avenue for the design of high-performance metal-based photosensitizers for potential clinical applications.

Crosslinked albumin-manganese nanoaggregates with sensitized T1 relaxivity and indocyanine green loading for multimodal imaging and cancer phototherapy

Albumin-manganese-based nanocomposites (AMNs) characterized by simple preparation and good biocompatibility have been widely used for in vivo T₁-weighted magnetic resonance imaging (MRI) and cancer theranostics. Herein, an aggregation and crosslinking assembly strategy was proposed to achieve the sensitization to T₁ relaxivity of the albumin-manganese nanocomposite. At a relatively low Mn content (0.35%), the aggregation and crosslinking of bovine serum albumin-MnO₂ (BM) resulted in a dramatic increase of T₁ relaxivity from 5.49 to 67.2 mM^-1 s^-1. Upon the loading of indocyanine green (ICG) into the crosslinked BM nanoaggregates (C-BM), the T₁ relaxivity of the C-BM/ICG nanocomposite (C-BM/I) was further increased to 97.3 mM^-1 s^-1, which was much higher than those reported previously even at high Mn contents. Moreover, the presence of C-BM greatly enhanced the photoacoustic (PA) and photothermal effects of ICG at 830 and 808 nm, respectively, and the second near infrared fluorescence (NIR-II FL) of ICG also showed better stability. Therefore, the synthesized C-BM/ICG nanocomposite exhibited remarkable performance in in vivo multimodal imaging of tumors, such as T₁-weighted MRI, NIR-II FL imaging and PA imaging, and cancer phototherapy with little side effects. This work provided a highly efficient and promising multifunctional nanoprobe for breaking through the limits of cancer theranostics, and opened a new avenue for the development of high-relaxivity AMNs and multimodal imaging methodology.

Smart Nanosensitizers for Activatable Sono-Photodynamic Immunotherapy of Tumors by Redox-Controlled Disassembly

Tumor-targeted and stimuli-activatable nanosensitizers are highly desirable for cancer theranostics. However, designing smart nanosensitizers with multiple imaging signals and synergistic therapeutic activities switched on is challenging. Herein, we report tumor-targeted and redox-activatable nanosensitizers (1-NPs) for sono-photodynamic immunotherapy of tumors by molecular co-assembly and redox-controlled disassembly. 1-NPs show a high longitudinal relaxivity (r₁ =18.7±0.3 mM^-1  s^-1 ), but "off" dual fluorescence (FL) emission (at 547 and 672 nm), "off" sono-photodynamic therapy and indoleamine 2,3-dioxygenase 1 (IDO1) inhibition activities. Upon reduction by glutathione (GSH), 1-NPs rapidly disassemble and remotely release small molecules 2-Gd, Zn-PPA-SH and NLG919, concurrently switching on (1) dual FL emission, (2) sono-photodynamic therapy and (3) IDO1 inhibition activities. After systemic injection, 1-NPs are effective for bimodal FL and magnetic resonance (MR) imaging-guided sono-photodynamic immunotherapy of orthotropic breast and brain tumors in mice under combined ultrasound (US) and 671-nm laser irradiation.

Engineered Metallacycle-Based Supramolecular Photosensitizers for Effective Photodynamic Therapy

Although metallacycle-based supramolecular photosensitizers (PSs) have attracted increasing attention in biomedicine, their clinical translation is still hindered by their inherent dark toxicity. Herein, we report what to our knowledge is the first example of a molecular engineering approach to building blocks of metallacycles for constructing a series of supramolecular PSs (RuA-RuD), with the aim of simultaneously reducing dark toxicity and enhancing phototoxicity, and consequently obtaining high phototoxicity indexes (PI). Detailed in vitro investigations demonstrate that RuA-RuD display high cancer cellular uptake and remarkable antitumor activity even under hypoxic conditions. Notably, RuD exhibited no dark toxicity and displayed the highest PI value (≈406). Theoretical calculations verified that RuD has the largest steric hindrance and the lowest singlet-triplet energy gap (ΔE_ST , 0.61 eV). Further in vivo studies confirmed that RuD allows safe and effective phototherapy against A549 tumors.

The design of small-molecule prodrugs and activatable phototherapeutics for cancer therapy

Cancer remains as one of the most significant health problems, with approximately 19 million people diagnosed worldwide each year. Chemotherapy is a routinely used method to treat cancer patients. However, current treatment options lack the appropriate selectivity for cancer cells, are prone to resistance mechanisms, and are plagued with dose-limiting toxicities. As such, researchers have devoted their attention to developing prodrug-based strategies that have the potential to overcome these limitations. This tutorial review highlights recently developed prodrug strategies for cancer therapy. Prodrug examples that provide an integrated diagnostic (fluorescent, photoacoustic, and magnetic resonance imaging) response, which are referred to as theranostics, are also discussed. Owing to the non-invasive nature of light (and X-rays), we have discussed external excitation prodrug strategies as well as examples of activatable photosensitizers that enhance the precision of photodynamic therapy/photothermal therapy. Activatable photosensitizers/photothermal agents can be seen as analogous to prodrugs, with their phototherapeutic properties at a specific wavelength activated in the presence of disease-related biomarkers. We discuss each design strategy and illustrate the importance of targeting biomarkers specific to the tumour microenvironment and biomarkers that are known to be overexpressed within cancer cells. Moreover, we discuss the advantages of each approach and highlight their inherent limitations. We hope in doing so, the reader will appreciate the current challenges and available opportunities in the field and inspire subsequent generations to pursue this crucial area of cancer research.

A pH/GSH dual responsive nanoparticle with relaxivity amplification for magnetic resonance imaging and suppression of tumors and metastases

Engineered magnetic nanoparticles combining diagnosis and therapy functions into one entity hold great potential to rejuvenate cancer treatment; however, they are still constrained by the "always on" signals and unsatisfactory therapeutic effect. Here, we report an intelligent theranostic probe based on Mn₃O₄ tetragonal bipyramids (MnTBs), which simultaneously respond to H⁺ and glutathione (GSH) with high sensitivity and quickly decompose to release Mn²⁺ in mild acidic and reductive intracellular environments. Mn²⁺ binds to the surrounding proteins to achieve a remarkable relaxivity amplification and selectively brighten the tumors. Particularly, this MR signal improvement is also effective in the detection of millimeter-sized liver metastases, with an ultrahigh contrast of 316%. Moreover, Mn²⁺ would trigger chemodynamic therapy (CDT) by exerting the Fenton-like activity to generate ˙OH from H₂O₂. Subsequently, a significant tumor suppression effect can be achieved by the GSH depletion-enhanced CDT. Besides, MnTBs manifest efficient urinary and hepatic excretions with biodegradability and minimal systemic toxicity. A pH/GSH dual responsive nanoprobe that integrates tumor diagnostic and therapeutic activities was developed to provide a new paradigm for precise diagnosis and treatment of tumors and metastases.

A hybrid nanoassembly for ultrasound-inducible cytosolic siRNA delivery and cancer sono-gene therapy

Cancer gene therapy by small-interfering RNAs (siRNAs) holds great promise but is impeded by a low cytoplasmic delivery efficiency. The past two decades have witnessed many efforts that are dedicated to discover biomaterials in order to increase cellular uptake efficiency of siRNAs. However, less attention has been paid to the lysosomal trapping dilemma that greatly restricts gene silencing outcomes. Herein, to address this challenge, we developed a sono-controllable strategy for ultrasound-promoted cytosolic siRNA delivery. A hybrid nanoassembly (HNA) was prepared via electrostatic self-assembly of a siRNA and a nona-arginine modified with protoporphyrin IX that is a sonosensitizer. After cellular uptake and exposure to sono-irradiation, HNA generated singlet oxygen to facilitate the lysosomal escape of siRNA to knock down anti-apoptotic Bcl-2 in the cytoplasm. We showed that the colocalization ratios between siRNA and the lysosome decreased from 91 % to 33 % post sono-irradiation; meanwhile, the gene silencing efficacy increased from 46 % to 68 % at 300 nM of HNA. Furthermore, sonodynamic therapy was achieved by the sonosensitizer under ultrasound irradiation, which combined gene therapy to eradicate cancer cells, resulting in a cell death rate of 82 %. This study thus presents a novel ultrasonic approach for effective cytoplasmic delivery of siRNAs and combinational sono-gene therapy of cancer.

Controlling Disassembly of Paramagnetic Prodrug and Photosensitizer Nanoassemblies for On-Demand Orthotopic Glioma Theranostics

Controlling delivery and release of therapeutic agents to accomplish on-demand synergistic therapy of orthotopic gliomas is desired but challenging. Here, we report a glioma targeting and redox activatable theranostic nanoprobe (Co-NP-RGD_1/1) for magnetic resonance (MR) and fluorescence (FL) bimodal imaging-guided on-demand synergistic chemotherapy/photodynamic therapy (Chemo-PDT) of orthotopic gliomas. Co-NP-RGD_1/1 is formed via molecular coassembly of two paramagnetic and fluorogenic small-molecule probes CPT-RGD and PPa-RGD at an optimized molar ratio of 1/1, which shows a high longitudinal relaxivity (r₁ = 17.0 ± 0.6 mM^-1 s^-1, 0.5 T) but weak FL emissions and low Chemo-PDT activity. Upon reduction by endogenous glutathione (GSH), Co-NP-RGD_1/1 disassemble and release small molecules 2-RGD, chemodrug camptothecin (CPT), and near-infrared (NIR) photosensitizer (PS) PPa-SH that further binds to endogenous albumin to form PPa-SH-albumin complex, allowing to turn on FL, chemotherapeutic efficacy, and PDT activity for synergistic Chemo-PDT of orthotopic U87MG or U251 gliomas in living mice. Moreover, Co-NP-RGD_1/1 can also allow noninvasive detection and monitoring of orthotopic brain tumor growth via FL and MR imaging. Findings suggest the potential of cascade coassembly and stimuli-controlled intracellular disassembly strategy for constructing targeted and activatable nanoagents for improving combinational cancer theranostics.

Shifting the Triangle-Square Equilibrium of Self-Assembled Metallocycles by Guest Binding with Enhanced Photosensitization

Shifting a triangle-square equilibrium in one direction is an important problem in supramolecular self-assembly. Reaction of a benzothiadiazole-based diimidazole donor with a cis-Pt(II) acceptor yielded an equilibrium mixture of a triangle ([C₁₈H₂₄N₁₀O₆S₁Pt₁]₃≡ PtMC^T) and a square ([C₁₈H₂₄N₁₀O₆S₁Pt₁]₄≡ PtMC^S). We report here the shifting of such equilibrium toward a triangle using a guest (pyrene aldehyde, G1). While both benzothiadiazole and pyrene aldehyde can form reactive oxygen species (ROS) in organic solvents, their therapeutic use in water is restricted due to aqueous insolubility. The enhanced water solubility of the benzothiadiazole unit and G1 by macrocycle formation and host-guest complexation, respectively, enabled enhanced ROS generation by the host-guest complex (G1' ⊂ PtMC^T) in water (G1' = hydrated form of G1). The guest-encapsulated metallacycle (G1' ⊂ PtMC^T) has shown synergistic antibacterial activity compared to the mixture of macrocycles upon white-light irradiation due to enhanced ROS generation. The mechanism for such enhanced activity was established by measuring the oxidative stress and relative internalization of PtMCs and G1' ⊂ PtMC^T.

NIR-II Ratiometric Chemiluminescent/Fluorescent Reporters for Real-Time Monitoring and Evaluating Cancer Photodynamic Therapy Efficacy

The development of probes for early monitoring tumor therapy response may greatly benefit the promotion of photodynamic therapy (PDT) efficacy. Singlet oxygen (¹ O₂ ) generation is a typical indicator for evaluating PDT efficacy in cancer. However, most existing probes cannot quantitatively detect ¹ O₂ in vivo due to the high reactivity and transient state, and thus have a poor correlation with PDT response. Herein, a ¹ O₂ -responsive theranostic platform comprising thiophene-based small molecule (2SeFT-PEG) and photosensitizer Chlorin e6 (Ce6) micelles for real-time monitoring PDT efficacy is developed. After laser irradiation, the Ce6-produced ¹ O₂ could simultaneously kill cancer and trigger 2SeFT-PEG to produce increased chemiluminescence (CL) and decreased fluorescence (FL) signals variation at 1050 nm in the second near-infrared (NIR-II, 950-1700 nm) window. Significantly, the ratiometric NIR-II CL/FL imaging at 1050 nm could effectively quantify and monitor the concentration of ¹ O₂ and O₂ consumption or recovery, so as to evaluate the therapeutic efficacy of PDT in vivo. Hence, this ¹ O₂ activated NIR-II CL/FL probe provides an efficient ratiometric optical imaging platform for real-time evaluating PDT effect and precisely guiding the PDT process in vivo.

Emerging nanobiotechnology-encoded relaxation tuning establishes new MRI modes to localize, monitor and predict diseases

Magnetic resonance imaging (MRI) is one of the most important techniques in the diagnosis of many diseases including cancers, where contrast agents (CAs) are usually necessary to improve its precision and sensitivity. Previous MRI CAs are confined to the signal-to-noise ratio (SNR) elevation of lesions for precisely localizing lesions. As nanobiotechnology advances, some new MRI CAs or nanobiotechnology-enabled MRI modes have been established to vary the longitudinal or transverse relaxation of CAs, which are harnessed to detect lesion targets, monitor disease evolution, predict or evaluate curative effect, etc. These distinct cases provide unexpected insights into the correlation of the design principles of these nanobiotechnologies and corresponding MRI CAs with their potential applications. In this review, first, we briefly present the principles, classifications and applications of conventional MRI CAs, and then elucidate the recent advances in relaxation tuning via the development of various nanobiotechnologies with emphasis on the design strategies of nanobiotechnology and the corresponding MRI CAs to target the tumor microenvironment (TME) and biological targets or activities in tumors or other diseases. In addition, we exemplified the advantages of these strategies in disease theranostics and explored their potential application fields. Finally, we analyzed the present limitations, potential solutions and future development direction of MRI after its combination with nanobiotechnology.

Fluorinated Ionic Liquid Based Multicolor 19 F MRI Nanoprobes for In Vivo Sensing of Multiple Biological Targets

Multicolor imaging, which maps the distribution of different targets, is important for in vivo molecular imaging and clinical diagnosis. Fluorine 19 magnetic resonance imaging (¹⁹ F MRI) is a promising technique because of unique insights without endogenous background or tissue penetration limit. Thus multicolor ¹⁹ F MRI probes, which can sense a wide variety of molecular species, are expected to help elucidate the biomolecular networks in complex biological systems. Here, a versatile model of activatable probes based on fluorinated ionic liquids (ILs) for multicolor ¹⁹ F MRI is reported. Three types of ILs at different chemical shifts are loaded in nanocarriers and sealed by three stimuli-sensitive copolymers, leading to "off" ¹⁹ F signals. The coating polymers specifically respond to their environmental stimuli, then degrade to release the loaded ILs, causing ¹⁹ F signals recovery. The nanoprobes are utilized for non-invasive detection of tumor hallmarks, which are distinguished by their individual colors in one living mouse, without interference between each other. This multicolor imaging strategy, which adopts modular construction of various ILs and stimuli-responsive polymers, will allow more comprehensive sensing of multiple biological targets, thus, opening a new realm in mechanistic understanding of complex pathophysiologic processes in vivo.

Asymmetric, amphiphilic RGD conjugated phthalocyanine for targeted photodynamic therapy of triple negative breast cancer

Targeted photodynamic therapy (TPDT) is considered superior to conventional photodynamic therapy due to the enhanced uptake of photosensitizers by tumor cells. In this paper, an amphiphilic and asymmetric cyclo-Arg-Gly-Asp-d-Tyr-Lys(cRGDyK)-conjugated silicon phthalocyanine (RSP) was synthesized by covalently attaching the tripeptide Arg-Gly-Asp (RGD) to silicone phthalocyanine in the axial direction for TPDT of triple-negative breast cancer (TNBC). RSP was characterized by spectroscopy as a monomer in physiological buffer. Meanwhile, the modification of RSP with RGD led to a high accumulation of the photosensitizer in TNBC cells overexpressing ανβ3 integrin receptors which can bind RGD, greatly reducing the risk of phototoxicity. In vitro photodynamic experiments showed that the IC50 of RSP was 295.96 nM in the 4T1 cell line, which caused significant apoptosis of the tumor cells. The tumor inhibition rate of RSP on the orthotopic murine TNBC achieved 74%, while the untargeted photosensitizer exhibited no obvious tumor inhibition. Overall, such novel targeted silicon phthalocyanine has good potential for clinical translation due to its simple synthesis route, strong targeting, and high therapeutic efficacy for TPDT treatment of TNBC.

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

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

Acidity-Activated Charge Conversion of 177Lu-Labeled Nanoagent for the Enhanced Photodynamic Radionuclide Therapy of Cancer

Nanomaterials in combination with radionuclide therapy (RNT) provide new opportunities for cancer treatment. However, nanomaterials with efficient tumor accumulation have been less exploited for effective radionuclide-based therapy. Here, we report glycol chitosan-based nanoparticles (GCP-NPs) with acidic pH-dependent surface charge conversion for efficient radionuclide-based combination therapy. The nanoplatform can change the surface charge of nanoparticles from slight negative to positive in the acidic tumor microenvironment, which facilitates cellular internalization and penetration and thus improves the tumor accumulation efficiency of nanomaterials. Radiolabeling of GCP-NPs with ^99mTc enables in vivo radioactive imaging in the mouse subcutaneous tumor model, showing 8.1-fold enhanced tumor uptake relative to pH-insensitive control nanoparticles (termed as GCOP-NPs). Afterward, therapeutic radioisotope ¹⁷⁷Lu-labeled GCP-NPs (¹⁷⁷Lu-GCP-NPs) that utilize RNT synergistic with photodynamic therapy (PDT) derived from conjugated pyropheophorbide-a within nanoparticles endow superior antitumor efficacy in living cells and tumor-bearing mouse model. More importantly, the combination of RNT and PDT using ¹⁷⁷Lu-GCP-NPs can effectively inhibit lung metastasis and eliminate splenomegaly, which is not possible for individual RNT or PDT. Therefore, this study proposes a facile radionuclide-based combination therapy strategy toward complete cancer remission.

Albumin-mediated “Unlocking” of supramolecular prodrug-like nanozymes toward selective imaging-guided phototherapy

An adaptive nanozyme without producing off-target toxicity has been successfully applied in phototherapy.

Assembly Transformation Jointly Driven by the LAP Enzyme and GSH Boosting Theranostic Capability for Effective Tumor Therapy

Developing intelligent and morphology-transformable nanomaterials that can spatiotemporally undergo stimulus-responsive size transformation holds great promise for improving the tumor delivery efficiency of drugs in vivo. Here, we report a smart size-transformable theranostic probe Ce6-Leu consisting of a leucine amino peptidase (LAP) and glutathione (GSH) dual-responsive moiety, an 1,2-aminothiol group, and a clinically used photosensitizer Ce6. This probe tends to self-assemble into uniform nanoparticles with an initial size of ∼80 nm in aqueous solution owing to the amphiphilic feature. Surprisingly, taking advantage of the biocompatible CBT-Cys condensation reaction, the large nanoprobes can be transformed into tiny nanoparticles (∼23 nm) under the joint action of LAP and GSH in a tumor microenvironment, endowing them with great tumor accumulation and deep tissue penetration. Concomitantly, this LAP/GSH-driven disassembly and size shrinkage of Ce6-Leu can also activate the fluorescence/magnetic resonance signals and the photodynamic effect for enhanced multimodal imaging-guided photodynamic therapy of human liver HepG2 tumors in vivo. More excitingly, the Mn²⁺-chelating probe (Ce6-Leu@Mn²⁺) was demonstrated to have the capability to catalyze endogenous H₂O₂ to persistently release O₂ at the hypoxic tumor site, as a consequence improving the oxygen supply to boost the radiotherapy effect. We thus believe that this LAP/GSH-driven size-transformable nanosystem would offer a novel advanced technology to improve the drug delivery efficiency for achieving precise tumor diagnosis and treatment.

Tumor Microenvironment Responsive "Head-to-Foot" Self-Assembly Nanoplatform for Positron Emission Tomography Imaging in Living Subjects

Sensitivity and specificity of molecular probes are two important factors in determining the accuracy of cancer diagnosis or the efficacy of cancer treatment. However, the development of probes with high sensitivity and strong specificity still poses many challenges. Herein, we report an ¹⁸F-labeled smart tracer ([¹⁸F]1) targeting cancer-associated biotin receptor (BR) and self-assembling into nanoparticles in response to intracellular glutathione. The tracer [¹⁸F]1 selectively targeted BR-positive cancer cells A549 and Hela and formed nanoparticles through self-assembly with an average diameter of 138.2 ± 16.3 nm. The character of self-assembly into nanoparticles enhanced the uptake and extended the retention of probe [¹⁸F]1 in the target tissue and hence improved the quality of positron emission tomography (PET) images. Thus, [¹⁸F]1 is a promising PET tracer for accurately detecting BR-positive cancers. Moreover, the tumor microenvironment responsive "head-to-foot" self-assembly nanoplatform is particularly attractive for development of other smart molecular probes.

An Activatable Afterglow/MRI Bimodal Nanoprobe with Fast Response to H2 S for In Vivo Imaging of Acute Hepatitis

Accurate detection of hepatic hydrogen sulfide (H₂ S) to monitor H₂ S-related enzymes' activity is critical for acute hepatitis diagnosis, but remains a challenge due to the dynamic and transient nature of H₂ S. Here, we report a H₂ S-activatable near-infrared afterglow/MRI bimodal probe F1-GdNP, which shows an "always-on" MRI signal and "off-on" afterglow signal toward H₂ S. F1-GdNP shows fast response, high sensitivity and specificity toward H₂ S, permitting afterglow imaging of H₂ S and evaluation of cystathionine γ-lyase (CSE)'s activity in living mice. We further employ the high spatial-resolution MRI signal of F1-GdNP to track its delivery and accumulation in liver. Importantly, F1-GdNP offers a high signal-to-background ratio (SBR=86.2±12.0) to sensitively report on the increased hepatic H₂ S level in the acute hepatitis mice via afterglow imaging, which correlated well with the upregulated CSE activity in the liver, showcasing the good potential of F1-GdNP for monitoring of acute hepatitis process in vivo.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Degradable FeCuS-Lipid Nanoparticles Confer Ultrasound-Activated CO Release and O2-Independent Radical Production for Synergistic Therapy

Ultrasound (US)-activated nanoagents capable of producing cytotoxic species have been promising for the treatment of deep-seated tumors; however, poor tumor uptake and insufficient generation of cytotoxic agents have largely limited their therapeutic efficacy in vivo. Herein, we report a hybrid FeCuS-lipid nanoparticle (AIBA@FeCuS-FeCO) by amphiphilic lipids-assisted emulsion of a free radical initiator (AIBA), a radical-sensitive CO donor (Fe₃(CO)₁₂), and radical-degradable FeCuS nanodisks for US-activated synergistic therapy of deep-located orthotopic gastric tumors in living mice. Upon US irradiation, AIBA@FeCuS-FeCO could be degraded and release cytotoxic AIBA radicals, CO, Fe²⁺, and Cu²⁺, allowing us to (1) enhance tumor uptake of AIBA@FeCuS-FeCO through CO-mediated vasodilation, (2) promote hydroxyl radical production and induce tumor ferroptosis via intracellular accumulation of Fe²⁺/Cu²⁺, and (3) kill tumor cells. Moreover, the subsequent administration of disulfiram (DSF) could further chelate with the liberated Cu²⁺, yielding toxic bis(N,N-diethyl dithiocarbamato)copper(II) chelates to synergize the therapeutic effect to ablate deep-seated orthotopic gastric tumors.

Tumor-activatable biomineralized nanotherapeutics for integrative glucose starvation and sensitized metformin therapy

Metformin is a clinically-approved anti-diabetic drug with emerging antitumor potential, but its antitumor activity is highly susceptible to local glucose abundance. Herein, we construct a nanotherapeutic platform based on biocompatible constituents to sensitize tumor cells for metformin therapy via cooperative glucose starvation. The nanoplatform was synthesized through the spontaneous biomineralization of glucose oxidase (GOx) and metformin in amorphous calcium phosphate nanosubstrate, which was further modified with polyethylene glycol and cRGD ligands. This biomineralized nanosystem could efficiently deliver the therapeutic payloads to tumor cells in a targeted and bioresponsive manner. Here GOx could catalyze the oxidation of glucose into gluconic acid and H₂O₂, thus depleting the glucose in tumor intracellular compartment while accelerating the release of the entrapped therapeutic payloads. The selective glucose deprivation would not only disrupt tumor energy metabolism, but also upregulate the PP2A regulatory subunit B56δ and sensitize tumor cells to the metformin-induced CIP2A inhibition, leading to efficient apoptosis induction via PP2A-GSK3β-MCL-1 axis with negligible side effects. This study may offer new avenues for targeted tumor therapy in the clinical context.