Tumor-Triggered Geometrical Shape Switch of Chimeric Peptide for Enhanced in Vivo Tumor Internalization and Photodynamic Therapy

Adaptive Polymeric Assemblies for Applications in Biomimicry and Nanomedicine

Dynamic and adaptive self-assembly systems are able to sense an external or internal (energy or matter) input and respond via chemical or physical property changes. Nanomaterials that show such transient behavior have received increasing interest in the field of nanomedicine due to improved spatiotemporal control of the nanocarrier function. In this regard, much can be learned from the field of systems chemistry and bottom-up synthetic biology, in which complex and intelligent networks of nanomaterials are designed that show transient behavior and function to advance our understanding of the complexity of living systems. In this Perspective, we highlight the recent advancements in adaptive nanomaterials used for nanomedicine and trends in transient responsive self-assembly systems to envisage how these fields can be integrated for the formation of next-generation adaptive stimuli-responsive nanocarriers in nanomedicine.

Cell Membrane-Coated Porphyrin Metal-Organic Frameworks for Cancer Cell Targeting and O2-Evolving Photodynamic Therapy

Photodynamic therapy (PDT) has attracted great attention as an alternative tumor treatment method. Unfortunately, it suffers from some limitations like poor targeting capability and insufficient therapeutic efficiency caused by tumor hypoxia. In this work, we introduce a novel O₂-evolving PDT nanoparticle for homologous cancer cell targeting as well as dual-mode imaging [i.e., magnetic resonance imaging (MRI) and fluorescence imaging]. Specifically, the nanostructure consists of a MnO₂ nanosheet-coated metal-organic framework core and cancer cell membrane shell (defined as CM-MMNPs). The MnO₂ layer displays H⁺ and H₂O₂ responsiveness, which can produce O₂ to enhance O₂-mediated singlet oxygen (¹O₂) generation for PDT. Moreover, the resulted Mn²⁺ can also be used as an optimal MRI contrast agent. The introduction of cell membrane and membrane proteins endow the CM-MMNPs with good stability and integrity in the process of cellular endocytosis, as well as strong homologous cell-targeting ability. This multifunctional nanoparticle has the potential to overcome the hypoxia of cancer cells in PDT, and provides a new paradigm for tumor targeting, detection, and therapy, which is promising for biomedical applications in the future.

Construction of Dually Responsive Nanotransformers with Nanosphere-Nanofiber-Nanosphere Transition for Overcoming the Size Paradox of Anticancer Nanodrugs

Tumor microenvironment (TME)-responsive nanosystems represent a category of intelligent nanomaterials for precise anticancer drug delivery. Herein, we report a smart size-/morphology-switchable nanodrug that can respond to the acidic TME and near-infrared (NIR) laser irradiation for effective tumor ablation and tumor metastasis inhibition. The nanoagent is physically assembled by a cytolytic peptide, melittin (MEL), an NIR-absorbing molecule, cypate, and a tumor-targeting polymer, hyaluronic acid (HA). At pH 7.4, the as-formed MEL/Cypate@HA complexes are negatively charged nanospheres (∼50 nm), which are suitable for long-term systemic circulation. When these nanospheres actively target tumors, the weakly acidic TME triggers an in situ transformation of the nanospheres to net-like nanofibers. Compared with the nanospheres, the nanofibers not only exhibit an inhibitory effect on tumor cell mobility but also significantly prolong the retention time of MEL/Cypate@HA in tumor tissues for MEL-based chemotherapy. Moreover, the nanofibers can be photodegraded into small nanospheres (∼25 nm) by NIR laser irradiation during cypate-mediated photothermal therapy, which enables deep tumor penetration of the loaded MEL and thus achieves effective tumor eradication. This work provides a facile strategy for converting naturally occurring therapeutic peptides into a TME-responsive drug delivery system and may inspire the development of nanomaterials with changeable structures for therapeutic purposes.

Smart Unimolecular Micelle-Based Polyprodrug with Dual-Redox Stimuli Response for Tumor Microenvironment: Enhanced in Vivo Delivery Efficiency and Tumor Penetration

Low delivery efficiency and limited tumor penetration of nanoparticle-based drug delivery systems (DDSs), the two most concerned issues in tumor therapy, have been considered as the "Achilles' heel" for tumor treatment. In this study, we have designed a highly sensitive dual-redox-responsive prodrug-based starlike polymer β-CD-b-P(CPT_GSH-co-CPT_ROS-co-OEGMA) (CP_GR) for synergistic chemotherapy. The high glutathione (GSH) concentration and high reactive oxygen species (ROS) levels are in a dynamic equilibrium in the tumor microenvironment (TME) and could trigger the disintegration of CP_GR micelles, which can promote the release of anticancer drug camptothecin (CPT) completely and intelligently. In order to verify the synergistic antitumor mechanism, two corresponding single-responsive β-CD-b-P(CPT_GSH-co-OEGMA) (CP_G) and β-CD-b-P(CPT_ROS-co-OEGMA) (CP_R) were altogether prepared as contrast. Both in vitro and in vivo studies confirmed the enhanced anticancer activity of CP_GR micelles in comparison of single responsive micelles. This work contributes to the orchestrated design of dual-redox-responsive DDSs for synergetic antitumor chemotherapy, which provides a good approach for the development of dual-redox-responsive nanomedicine.

A theranostic saponin nano-assembly based on FRET of an aggregation-induced emission photosensitizer and photon up-conversion nanoparticles

A photodynamic aggregation-induced emissive (AIE) fluorophore, characterized by near-infrared (NIR) emission, was created based on a fluorescence resonance energy transfer (FRET) donor of appreciable NIR up-conversion nanoparticles (UCNPs) and acceptor of immense fluorescence emissive AIEgen. Hence, the entrapment of the FRET couple into an amphiphilic saponin-based nanoscaled self-assembly demonstrated appealing theranostic functions in producing immense fluorescence emission and cytotoxic reactive oxygen species (ROS).

Transition from vesicles to nanofibres in the enzymatic self-assemblies of an amphiphilic peptide as an antitumour drug carrier

Amphiphilic peptides modified by molecular design can self-assemble into specific nanostructures with interesting applications in the fields of biomedicine and biotechnology. Lysyl oxidase (LO) is ubiquitous in human serum. However, enzymatic self-assembly of amphiphilic peptides remains a challenge for lipid-soluble drug delivery under the induction of LO. Here, we designed a positively charged amphiphilic peptide, A₆K₂, that could stably self-assemble to form nanovesicles. The lysine in the peptide molecule could be covalently cross-linked under enzyme catalysis, and the major transition was from random coil to β-sheet secondary structures, eventually leading to the destruction of the peptide nanovesicles. The lipid-soluble antitumour drug doxorubicin (DOX) as a model drug could be loaded into the hydrophobic core of the nanovesicles formed by the amphiphilic peptide A₆K₂, even though DOX was not covalently linked to the peptide monomer. The amount of DOX-encapsulated A₆K₂ nanovesicles in human hepatocellular carcinoma BEL-7402 cells was significantly higher than that in human liver L02 cells, indicating excellent selectivity. The amphiphilic peptide A₆K₂ inhibited tumour cell growth and had low cytotoxicity to mammalian cells, and it showed antibacterial activity against G⁺ and G^- bacteria. These advantages make enzymatic self-assembling A₆K₂ nanovesicles of great interest in drug delivery for biomedical applications.

New power of self-assembling carbonic anhydrase inhibitor: Short peptide-constructed nanofibers inspire hypoxic cancer therapy

Carbonic anhydrase (CA) IX overexpresses exclusively on cell membranes of hypoxic tumors, regulating the acidic tumor microenvironment. Small molecules of CA inhibitor modified with short peptide successfully achieve CA IX-targeted self-assembly that localizes CA inhibitors on hypoxic cancer cell surfaces and enhances their inhibition efficacy and selectivity. CA IX-related endocytosis also promotes selective intracellular uptake of these nanofibers under hypoxia, in which nanofiber structures increase in size with decreasing pH. This effect subsequently causes intracellular acid vesicle damage and blocks protective autophagy. The versatility of tunable nanostructures responding to cell milieu impressively provokes selective toxicities and provides strategic therapy for hypoxic tumors. Moreover, in vivo tests demonstrate considerable antimetastatic and antiangiogenesis effects in breast tumors, and particularly remarkable enhancement of antitumor efficacy in doxorubicin administration. With its biocompatible components and distinctive hypoxia therapies, this nanomaterial advances current chemotherapy, providing a new direction for hypoxic cancer therapy.

Molecular Programming of Biodegradable Nanoworms via Ionically Induced Morphology Switch toward Asymmetric Therapeutic Carriers

Engineering biodegradable nanostructures with precise morphological characteristics is a key objective in nanomedicine. In particular, asymmetric (i.e., nonspherical) nanoparticles are desirable due to the advantageous effects of shape in a biomedical context. Using molecular engineering, it is possible to program unique morphological features into the self-assembly of block copolymers (BCPs). However, the criteria of biocompatibility and scalability limit progress due to the prevalence of nondegradable components and the use of toxic solvents during fabrication. To address this shortfall, a robust strategy for the fabrication of morphologically asymmetric nanoworms, comprising biodegradable BCPs, has been developed. Modular BCPs comprising poly (ethylene glycol)-block-poly(caprolactone-gradient-trimethylene carbonate) (PEG-PCLgTMC), with a terminal chain of quaternary ammonium-TMC (PTMC-Q), undergo self-assembly via direct hydration into well-defined nanostructures. By controlling the solution ionic strength during hydration, particle morphology switches from spherical micelles to nanoworms (of varying aspect ratio). This ionically-induced switch is driven by modulation of chain packing with salts screening interchain repulsions, leading to micelle elongation. Nanoworms can be loaded with cytotoxic cargo (e.g., doxorubicin) at high efficiency, preferentially interact with cancer cells, and increase tumor penetration. This work showcases the ability to program assembly of BCPs and the potential of asymmetric nanosystems in anticancer drug delivery.

A lanthanide-peptide-derived bacterium-like nanotheranostic with high tumor-targeting, -imaging and -killing properties

Nanostructures formed with bioactive peptides offer an exciting prospect in clinical oncology as a novel class of therapeutic agents for human cancers. Despite their therapeutic potential, however, peptide-based nanomedicines are often inefficacious in vivo due to low cargo-loading efficiency, poor tumor cell-targeting specificity and limited drug accumulation in tumor tissues. Here, we describe the design, via assembly of a p53-activating peptide termed PMI, functionalized PEG and fluorescent lanthanide oxyfluoride nanocrystals, of a novel nanotheranostic shaped in flexible rods. This lanthanide-peptide nanorod or LProd of bionic nature exhibited significantly enhanced tumor-targeting and -imaging properties compared to its spherical counterpart. Importantly, LProd potently inhibited tumor growth in a mouse model of human colon cancer through activating tumor suppressor protein p53 via MDM2/MDMX antagonism, while maintaining a highly favorable biosafety profile. Our data demonstrate that LProd as a multifunctional theranostic platform is ideally suited for tumor-specific peptide drug delivery with real-time disease tracking, thereby broadly impacting clinical development of antitumor peptides.

A Versatile Carbon Monoxide Nanogenerator for Enhanced Tumor Therapy and Anti-Inflammation

Carbon monoxide (CO) is regarded as a potential therapeutic agent with multiple beneficial functions for biomedical applications. In this study, a versatile CO nanogenerator (designated as PPOSD) was fabricated and developed for tumor therapy and anti-inflammation. Partially oxidized tin disulfide (SnS₂) nanosheets (POS NSs) were decorated with a tumor-targeting polymer (polyethylene glycol-cyclo(Asp-d-Phe-Lys-Arg-Gly), PEG-cRGD), followed by the loading of chemotherapeutic drug doxorubicin (DOX) to prepare polymer@POS@DOX, or PPOSD. After injected intravenously, PPOSD could selectively accumulate in tumor tissue via the cRGD-mediated tumor recognition. Upon 561 nm laser irradiation, the POS moiety in PPOSD can photoreduce CO₂ to CO, which significantly sensitized the chemotherapeutic effect of DOX. The POS in PPOSD can also act as a photothermal agent for effective photothermal therapy (PTT) of the tumor upon 808 nm laser irradiation. Furthermore, the generated CO can simultaneously decrease the inflammatory reaction caused by PTT. Blood analysis and hematoxylin-eosin staining of major organs showed that no obvious systemic toxicity was induced after the treatment, suggesting good biosafety of PPOSD. This versatile CO nanogenerator will find great potential for both enhanced tumor inhibition and anti-inflammation.

Anti-biofouling therapeutic nanoparticles with removable shell and highly efficient internalization by cancer cells

Cationic gelatin nanoparticles ((+)nGNPs) were prepared by in situ polymerization upon the surfaces of monodispersed gelatin nanoparticles (GNPs) using N-(3-Aminopropyl)methacrylamide (APm) as monomer, which were then decorated with doxorubicin terminated poly(2-methylacryloyloxyethyl phosphorylcholine) (DOX-pMPC) via EDC/NHS conjugation to obtain core-shell nanoparticles ((+)nGNPs@DOX-pMPC) for cancer therapy. The non-fouling pMPC shell could effectively shield the positively charged surface of inner nanoparticle and prevent non-specific protein adsorption, thus endowing the materials with potential for long-acting cancer treatment. Furthermore, the acyl hydrazone bond connecting DOX and pMPC chain could be easily hydrolyzed in the weakly acidic tumor microenvironment. After decladding of the pMPC shell, electropositive (+)nGNPs carrying the drugs can be effectively internalized by cancer cells to induce apoptosis, avoiding undesirable hindrance caused by the superhydrophilic outer layer. On combining the above properties, this drug delivery system can be a promising candidate for long-acting, low-toxicity and high-efficiency cancer therapy.

MMP-2-Controlled Transforming Micelles for Heterogeneic Targeting and Programmable Cancer Therapy

Herein, through the active-peptide-functionalization, we developed a nanoscale micelles system (named HEKM) which consists of tumor microenvironment-regulated shape-changing with specific recognition abilities for enhanced cellular targeting, internalization and therapy of heterogeneic tumors. As a result, HEKMs could recognize and bind the tumor heterogeneity marker EGFR-HER2 complex, which led to an enhanced tumor targeting effect. In particular, HEKMs could self-assemble into nanorods under normal physiological conditions while transform into nanospheres in the tumor extracellular microenvironment by a sensitive response to matrix metalloproteinase-2 (MMP-2). The nanorods could prolong the blood circulation time while the nanospheres could accelerate tissue penetration in tumors. In vivo dual-modal targeted imaging was realized by FRET-fluorophore conjugation and gadolinium loading in HEKMs. Tumor cell apoptosis was achieved by proapoptotic element integration. The in vitro and in vivo studies both demonstrated that these rationally designed, shape-changing and targeting micelles could achieve maximized drug efficacy and minimum side effects.

A sequentially responsive and structure-transformable nanoparticle with a comprehensively improved 'CAPIR cascade' for enhanced antitumor effect

An intravenously administered drug delivery system should undergo a five-step 'CAPIR' cascade (circulation, accumulation, penetration, internalization and release), and the maximal efficiency of each step is of great importance to obtain the improved final therapeutic benefits and overall survival rate. Here, a pH/matrix metalloproteinase-9 (MMP9) sequentially responsive and continuously structure-transformable nanoparticle assembled from a doxorubicin (DOX)-conjugated peptide was exploited for comprehensively improving the 'CAPIR cascade' and eventually enhancing the therapeutic efficacy. The chimeric peptide can self-assemble into spherical nanoparticles (RGD-sNPs) at pH 7.4 with a particle size of 45.7 ± 5.4 nm. By a combination of passive and active targeting mechanisms, RGD-sNPs achieved efficient accumulation at the tumor site (∼15.1% ID g-1 within 24 h). Both in vitro and in vivo experiments revealed that RGD-sNPs can be transformed into rod-like nanoparticles (S-NFs) triggered by MMP9 that overexpressed in the tumor microenvironment, demonstrating remarkable advantages of deep tumor penetration, prolonged drug retention with ∼3.7% ID g-1 at 96 h, and 2-fold enhanced internalization. Subsequently, S-NFs would respond to the intracellular weakly acidic stimuli to rapidly release DOX for induction of cytotoxicity and apoptosis. Meanwhile, the remaining peptide was further converted into long fibers (length >5 μm) with significant cytotoxicity, thereby exerting a synergistic antitumor effect. Thus RGD-sNPs displayed superior antitumor efficacy and extended the median survival period to 55 days. This provides a new horizon for the exploration of high-performance antitumor nanomedicines.

Enzyme-instructed self-assembly of a novel histone deacetylase inhibitor with enhanced selectivity and anticancer efficiency

A novel peptide-based prodrug molecule could be activated in situ via ALP catalysis and further self-assembled into a nanodrug with enhanced selectivity and anticancer efficacy.

Advances in nanoparticle development for improved therapeutics delivery: nanoscale topographical aspect

Nanoparticle-based therapeutics delivery holds great promise for the treatment of intractable diseases. The high loading of drug molecules and their precise delivery to target sites are needed to gain optimal therapeutic functions of the nanoparticle delivery system. In this communication, we highlight, among other properties of nanoparticles (e.g. size, shape, surface chemistry, and degradation), the nanoscale topography, which has recently been shown to be an important parameter, ultimately determining drug loading, cell penetration, and body clearance. This nanotopographical aspect is considered to offer a new effective strategy to the development of nanoparticles for drug and gene delivery with enhanced therapeutic outcome.

Enhancing the Accumulation of Polymer Micelles by Selectively Dilating Tumor Blood Vessels with NO for Highly Effective Cancer Treatment

The accumulation of nanoparticles in tumors by the enhanced permeability and retention (EPR) effect is effective and well known. However, how to maximize accumulation is still a bottleneck in the development of nanomedicine. Herein, a tumor vascular-targeted hybrid polymeric micelle, which has a great capacity to selectively augment the EPR effect of nanoparticles by dilating tumor blood vessels via the activity of nitric oxide (NO), is presented. Under neutral conditions, the micelle is stable, with a long blood circulation half-life due to the carboxylated poly(ethylene glycol) (PEG) layer; in mildly acidic tumor tissues, the micelle can selectively target the tumor blood vessels by the exposed cyclic Arg-Gly-Asp peptide (cRGD) peptides, which is realized with a pH-dependent hydrolysis of the monomethoxy PEG layer. Simultaneously, exposed copper ions catalyze the decomposition of endogenous NO donors, which generates NO in situ, leading to vasodilation and increased tumor vascular permeability. As a result, the accumulation of nanoparticles is significantly enhanced, and a high accumulation of doxorubicin in tumors is achieved at 48 h after injection. This high dose of therapeutic agent produces a large inhibition of tumor growth (94%) in cancer treatment, and shows no general toxicity, with 100% of the mice surviving the treatment regimen.

Functional Polymer Nanocarriers for Photodynamic Therapy

Photodynamic therapy (PDT) is an appealing therapeutic modality in management of some solid tumors and other diseases for its minimal invasion and non-systemic toxicity. However, the hydrophobicity and non-selectivity of the photosensitizers, inherent serious hypoxia of tumor tissues and limited penetration depth of light restrict PDT further applications in clinic. Functional polymer nanoparticles can be used as a nanocarrier for accurate PDT. Here, we elucidate the mechanism and application of PDT in cancer treatments, and then review some strategies to administer the biodistribution and activation of photosensitizers (PSs) to ameliorate or utilize the tumor hypoxic microenvironment to enhance the photodynamic therapy effect.

Biological Stimulus-Driven Assembly/Disassembly of Functional Nanoparticles for Targeted Delivery, Controlled Activation, and Bioelimination

Nanoassembly technology has emerged as a powerful tool for targeted drug delivery and provides a basis for fabricating medical theranostic nanosystems. However, it is extremely difficult to concentrate nanoparticles at tumor sites, and the poor target-to-background ratio undoubtedly obstructs the accurate diagnosis and effective therapy of cancerous tissues. Importantly, the addition of biological stimulus-responsive groups to nanoassembly systems can enable a biological stimulus-driven assembly-disassembly mutual switch or structural composition/conformation change, thereby amplifying the imaging signal and/or enhancing the therapeutic effect. This progress report provides an overview of well-designed biological stimulus-responsive nanosystems that can realize precise assembly-disassembly switches by disrupting or rebuilding the intricate balance between the entropy and enthalpy of the nanosystems in response to stimuli (pH, redox, enzymes, etc.) in tumor tissues. The discussion encompasses different biological stimulus-responsive groups, fabrication approaches, and outstanding selective "turn-on" performance for efficient tumor imaging, therapy, and bioelimination. This progress report is expected to inspire more extensive research for the development of smart "turn-on" nanomaterials with increased signal-to-noise (S/N) ratios for diagnosis and drug delivery, which may pave the way for precise nanomedicine with site-specific theranostic features and biocompatibility.

Peptide-Induced Self-Assembly of Therapeutics into a Well-Defined Nanoshell with Tumor-Triggered Shape and Charge Switch

Peptide-tuned self-assembly of macromolecular agents (>500 Da) such as therapeutic peptides offers a strategy to improve the properties and biofunctions of degradable nanomaterials, but the tough requirement of macromolecular therapeutics delivery and a lack of understanding of peptide-based self-assembly design present high barriers for their applications. Herein, we developed a new strategy for nanoengineering macromolecular drugs by an elaborate peptide, termed PSP (VVVVVHHRGDC), capable of directly conjugating with cargo to be a PSP-cargo monomer as building block tending to self-assemble into a well-defined nanoshell with tumor-triggered shape and charge switch. As a proof of concept, conjugation PSP to a D-peptide activator of tumor suppressor p53 termed DPMI (1492.5 Da) generated hollow spheres ~80 nm in diameter named PSP-DPMI that disintegrated only in the acidic microenvironment of tumor tissues, followed by integrin-mediated cellular uptake of PSP-DPMI monomers. Importantly, PSP-based self-assembly successfully endowed the DPMI with long circulation time and high cancer-cell-specific intracellular accumulation. PSP-DPMI nanoshells potently inhibited tumor growth in vitro and in vivo by the p53 restoration, while maintaining a highly favorable in vivo safety profile. Out of conventional encapsulation and conjugation, our study showcases a clinically viable novel method to nanoengineer macromolecular agents such as peptide for anticancer therapy and provides a hazard-free alternative strategy for the theranostics delivery.

Dimeric camptothecin-loaded RGD-modified targeted cationic polypeptide-based micelles with high drug loading capacity and redox-responsive drug release capability

Camptothecin (CPT) is a broad spectrum anticancer drug, but its application is limited due to the poor water solubility, lactone ring instability, and low drug loading potential. In this study, biocompatible cationic polypeptide-based micelles were developed to deliver dimeric CPT (DCPT) with the aim of overcoming the above-mentioned obstacles and achieving favorable therapeutic effects. Cationic polypeptide poly-lysine-block-poly-leucine (PLys-b-PLeu) was fabricated via the ring-opening polymerization of N-ε-carbobenzoxy-l-lysine (ε-Lys(Z)) and l-leucine (Leu) and further grafted with polyethylene glycol (PEG) and an arginine-glycine-aspartic acid (RGD) peptide. DCPT was synthesized by reacting CPT and 2-hydroxyethyl disulfide, and micelles were prepared using a dialysis method. The obtained DCPT-loaded RGD-PEG-g-poly-l-lysine-b-poly-l-leucine (DRPPP) micelles showed a high encapsulation efficiency of 89.7% and a high drug loading capacity of 46.1%. In addition, the DRPPP micelles remained stable under physiological conditions (PBS at a pH of 7.4) but showed rapid release when triggered by a reductive environment (PBS at a pH of 7.4 with 10 mM dithiothreitol). Compared to micelles without RGD decoration, the DRPPP micelles exhibited an increased cellular uptake through RGD targeting and were internalized into cells via caveolae-mediated endocytosis and macropinocytosis. Furthermore, the DRPPP micelles exerted an enhanced cytotoxicity against MDA-MB-231 cells compared to MCF-7 cells, which expressed less α_vβ₃ receptors. Besides, the DRPPP micelles induced cell apoptosis and caused a decrease of mitochondrial membrane potential. These results indicate that dimeric camptothecin-loaded cationic polypeptide-based micelle is a promising strategy for cancer therapy.

Quantum Dot-Dye Conjugates for Biosensing, Imaging, and Therapy

Adding value to the intrinsic properties of quantum dots (QDs), a strategy to conjugate dyes on the surface of QDs offers new opportunities, since the coupling between QD and dyes can be designed to allow Förster resonance energy transfer (FRET) and/or electron transfer (eT). These processes are accompanied by the change of QD and/or dye fluorescence and subsequent photochemical reactions (e.g., generation of 1 O2 ). Based on the change of fluorescence signals by the interaction with biomolecules, QD-dye conjugates are exploited as biosensors for the detection of pH, O2 , nicotinamide adenine dinucleotide (phosphate), ions, proteases, glutathione, and microRNA. QD-dye conjugates also can be modulated by the irradiation of external light; this concept is demonstrated for fluorescence super-resolution imaging as photoactivatable or photoswitchable probes. When QDs are conjugated with photosensitizing dyes, the QD-dye conjugates can generate 1 O2 in a repetitive manner for better cancer treatment, and can also be available for approaches using two-photon excitation or bioluminescence resonance energy transfer mechanisms for deep tissue imaging. Here, the recent advances in QD-dye conjugates, where FRET or eT produces fluorescence readouts or photochemical reactions, are reviewed. Various QD-dye conjugate systems and their biosensing/imaging and photodynamic therapeutics are summarized.

Fabrication of Charge-Conversion Nanoparticles for Cancer Imaging by Flash Nanoprecipitation

Traditional charge-conversion nanoparticles (NPs) need the breakage of acid-labile groups on the surface, which impedes the rapid response to the acidic microenvironment. Here, we developed novel rodlike charge-conversion NPs with amphiphilic dextran- b-poly(lactic- co-glycolic acid), poly(2-(dimethylamino) ethylmethylacrylate)- b-poly(ε-caprolactone), and an aggregation-induced emission-active probe through flash nanoprecipitation (FNP). These NPs exhibit reversible negative-to-positive charge transition at a slightly acidic pH relying on the rapid protonation/deprotonation of polymers. The size and the critical charge-conversion pH can be further tuned by varying the flow rate and polymer ratio. Consequently, the charge conversion endows NPs with resistance to protein adsorption at physiological pH and enhanced internalization to cancer cells under acidic conditions. Ex vivo imaging on harvest organs shows that charge-conversion NPs were predominantly distributed in tumors after intravenous administration to mice due to the robust response of NPs to the acidic microenvironment in tumor tissue, whereas control NPs or free probes were broadly accumulated in tumor, liver, kidney, and lung. These results suggest the great potential of the current FNP strategy in the facile and generic fabrication of charge-conversion NPs for tumor-targeting delivery of drugs or fluorescent probes.

pH-Responsive PEG-Doxorubicin-Encapsulated Aza-BODIPY Nanotheranostic Agent for Imaging-Guided Synergistic Cancer Therapy

Synergistic cancer therapy is of great interest for multiple advantages, such as excellent targeting accuracy, low side effects, and enhanced therapeutic efficiency. Herein, a near-infrared photosensitizer aza-BODIPY (AB) with high singlet oxygen quantum yield (Φ_Δ = 82%) is designed and synthesized. With Schiff's base obtained from condensation reaction between doxorubicin (DOX) and polyethylene glycol-benzaldehyde (PEG-CHO) as the polymer matrix, aza-BODIPY is encapsulated to afford hydrophilic nanoparticles (DAB NPs). The DAB NPs exhibit high reactive oxygen species (ROS) generation rate and outstanding photothermal conversion efficiency (η = 38.3%) under irradiation. In vivo fluorescence- and photothermal-imaging (PTI) results demonstrate that DAB NPs can specifically accumulate at tumor sites and serve as dual-modal imaging probe for cancer diagnosis. Particularly, triggered by acidic tumor microenvironment, the HCN bond of Schiff's base would be broken simultaneously, resulting in the efficient release of DOX from DAB NPs at tumor sites as well as enhancing the targeting performance of chemotherapeutics. Compared with free DOX and aza-BODIPY nanoparticles, DAB NPs can inhibit tumor growth more effectively through pH-responsive photodynamic/photothermal/chemo synergistic therapy. This report may also present a practicable strategy to develop a pH-responsive nanotheranostic agent for tumor targeting, imaging, and therapy.

PA/US dual-modality imaging to guide VEGFR-2 targeted photothermal therapy using ZnPc-/PFH-loaded polymeric nanoparticles

Angiogenesis is a common pathological characteristic of many solid tumors and vulnerable atherosclerotic plaques.

Functional peptide-based nanoparticles for photodynamic therapy

Photodynamic therapy as a non-invasive approach has obtained great research attention during the last decade.

Self-assembled nanomaterials for synergistic antitumour therapy

Recent progress on self-assembled nanodrugs for anticancer treatment was discussed.

Acidity-Triggered Tumor Retention/Internalization of Chimeric Peptide for Enhanced Photodynamic Therapy and Real-Time Monitoring of Therapeutic Effects

Photodynamic therapy (PDT) holds great promise in tumor treatment. Nevertheless, it remains highly desirable to develop easy-to-fabricated PDT systems with improved tumor accumulation/internalization and timely therapeutic feedback. Here, we report a tumor-acidity-responsive chimeric peptide for enhanced PDT and noninvasive real-time apoptosis imaging. Both in vitro and in vivo studies revealed that a tumor mildly acidic microenvironment could trigger rapid protonation of carboxylate anions in chimeric peptide, which led to increased ζ potential, improved hydrophobicity, controlled size enlargement, and precise morphology switching from sphere to spherocylinder shape of the chimeric peptide. All of these factors realized superfast accumulation and prolonged retention in the tumor region, selective cellular internalization, and enhanced PDT against the tumor. Meanwhile, this chimeric peptide could further generate reactive oxygen species and initiate cell apoptosis during PDT. The subsequent formation of caspase-3 enzyme hydrolyzed the chimeric peptide, achieving a high signal/noise ratio and timely fluorescence feedback. Importantly, direct utilization of the acidity responsiveness of a biofunctional Asp-Glu-Val-Asp-Gly (DEVDG, caspase-3 enzyme substrate) peptide sequence dramatically simplified the preparation and increased the performance of the chimeric peptide furthest.