Noncovalently Caged Firefly Luciferins Enable Amplifiable Bioluminescence Sensing of Hyaluronidase-1 Activity in Vivo

In vivo bioluminescence imaging of labile iron in xenograft models and liver using FeAL-1, an iron-activatable form of D-luciferin

Dysregulated iron homeostasis underlies diverse pathologies, from ischemia-reperfusion injury to epithelial-mesenchymal transition and drug-tolerant "persister" cancer cell states. Here, we introduce ferrous iron-activatable luciferin-1 (FeAL-1), a small-molecule probe for bioluminescent imaging of the labile iron pool (LIP) in luciferase-expressing cells and animals. We find that FeAL-1 detects LIP fluctuations in cells after iron supplementation, depletion, or treatment with hepcidin, the master regulator of systemic iron in mammalian physiology. Utilizing FeAL-1 and a dual-luciferase reporter system, we quantify LIP in mouse liver and three different orthotopic pancreatic ductal adenocarcinoma tumors. We observed up to a 10-fold increase in FeAL-1 bioluminescent signal in xenograft tumors as compared to healthy liver, the major organ of iron storage in mammals. Treating mice with hepcidin further elevated hepatic LIP, as predicted. These studies reveal a therapeutic index between tumoral and hepatic LIP and suggest an approach to sensitize tumors toward LIP-activated therapeutics.

A Reaction-Based Ratiometric Bioluminescent Platform for Point-of-Care and Quantitative Detection Using a Smartphone

Fluorescent probes have emerged as powerful tools for the detection of different analytes by virtue of structural tenability. However, the requirement of an excitation source largely hinders their applicability in point-of-care detection, as well as causing autofluorescence interference in complex samples. Herein, based on bioluminescence resonance energy transfer (BRET), we developed a reaction-based ratiometric bioluminescent platform, which allows the excitation-free detection of analytes. The platform has a modular design consisting of a NanoLuc-HaloTag fusion as an energy donor, to which a synthetic fluorescent probe is bioorthogonally labeled as recognition moiety and energy acceptor. Once activated by the target, the fluorescent probe can be excited by NanoLuc to generate a remarkable BRET signal, resulting in obvious color changes of luminescence, which can be easily recorded and quantitatively analyzed by a smartphone. As a proof of concept, a fluorescent probe for HOCl was synthesized to construct the bioluminescent system. Results demonstrated the system showed a constant blue/red emission ratio which is independent to the signal intensity, allowing the quantification of HOCl concentration with high sensitivity (limit of detection (LOD) = 13 nM) and accuracy. Given the universality, this reaction-based bioluminescent platform holds great potential for point-of-care and quantitative detection of reactive species.

Polymeric agents for activatable fluorescence, self-luminescence and photoacoustic imaging

Numerous polymeric agents have been widely applied in biology and medicine by virtue of the facile chemical modification, feasible nano-engineering approaches and fine-tuned pharmacokinetics. To endow polymeric imaging agents with ability to monitor and measure subtle molecular or cellular alterations at diseased sites, activatable polymeric probes that can elicit signal changes in response to biomolecular interactions or the analytes of interest have to be developed. Herein, this review aims to provide a systemic interpretation and summarization of the design methodology and imaging utility of recently emerged activatable polymeric probes. An introduction of activatable probes allowing for precise imaging and classification of polymeric imaging agents is reported first. Then, we give a detailed discussion of the contemporary design approaches toward activatable polymeric probes in diverse imaging modes for the detection of various stimuli and their imaging applications. Finally, current challenges and future advances are discussed and highlighted.

One-Step Integration of Tumor Microenvironment-Responsive Calcium and Copper Peroxides Nanocomposite for Enhanced Chemodynamic/Ion-Interference Therapy

Recently, various metal peroxide nanomaterials have drawn increasing attention as an efficient hydrogen peroxide (H₂O₂) self-supplying agent for enhanced tumor therapy. However, a single kind of metal peroxide is insufficient to achieve more effective antitumor performance. Here, a hyaluronic acid modified calcium and copper peroxides nanocomposite has been synthesized by a simple one-step strategy. After effective accumulation at the tumor site due to the enhanced permeability and retention (EPR) effect and specific recognition of hyaluronate acid with CD44 protein on the surface of tumor cells, plenty of Ca²⁺, Cu²⁺, and H₂O₂ can be simultaneously released in acid and hyaluronidase overexpressed tumor microenvironment (TME), generating abundant hydroxyl radical through enhanced Fenton-type reaction between Cu²⁺ and self-supplying H₂O₂ with the assistance of glutathione depletion. Overloaded Ca²⁺ can lead to mitochondria injury and thus enhance the oxidative stress in tumor cells. Moreover, an unbalanced calcium transport channel caused by oxidative stress can further promote tumor calcification and necrosis, which is generally defined as ion-interference therapy. As a result, the synergistic effect of Fenton-like reaction by Cu²⁺ and mitochondria dysfunction by Ca²⁺ in ROS generation is performed. Therefore, a TME-responsive calcium and copper peroxides nanocomposite based on one-step integration has been successfully established and exhibits a more satisfactory antitumor efficiency than any single kind of metal peroxide.

Self-Immolative Dye-Doped Polymeric Probe for Precisely Imaging Hydroxyl Radicals by Avoiding Leakage

For sensing low abundance of biomarkers, utilizing nanocarriers to load dyes is an efficient method to amplify the detected signal. However, the non-specific leak of the internal dyes in this approach is accompanied by false positive signals, resulting in inaccurate signal acquirement. To address this issue, in this work, we reported a novel signal amplification strategy with dye as a scaffold to construct a self-immolative dye-doped polymeric probe (SDPP). In our proposed approach, the dyes were covalently integrated into the main chain of a polymer, which can avoid the non-specific leak of the dye when used in a rigorous biological environment, thus evading the false positive signal. As a prototype of this concept, a SDPP, which responds to hydroxyl radicals (^•OH), was rationally fabricated. Upon being activated by ^•OH, SDPP will liberate the dye through a self-immolative reaction to bind with protein for amplifying the fluorescence signal. Compared with a dye-loaded nanoprobe, SDPP can precisely track intracellular basal ^•OH levels and visualize the ^•OH associated with myocarditis in vivo. More importantly, the attempt in this work not only provides an effective molecular tool to investigate the role of ^•OH in cardiopathy, but also puts forward a new direction to current signal-amplifying strategies for precisely and reliably acquiring the intracellular molecular information.

Enhancing the anticancer efficacy of a LL-37 peptide fragment analog using peptide-linked PLGA conjugate micelles in tumor cells

LL-37, a well-known antimicrobial human peptide, is a cationic peptide that provides an important antimicrobial defense mechanism in damaged skin. Accumulating evidence indicates that LL-37 also displays an anticancer effect in colon cancer, gastric cancer, hematologic malignancy and oral squamous cell carcinoma. However, anticancer activity of LL-37 peptide fragment analogs has not been reported. Poor intercellular translocation may be one of the causes for this lack of observed anticancer activity. In this study, a LL-37 peptide fragment analog with cysteine at the N-terminus was conjugated with the biodegradable polymer, lactic acid/glycolic acid copolymer (PLGA), using the thiol group of cysteine. The purpose of this study was to improve the cell permeability of the peptide using a micellar system and then evaluate the anticancer activity. Cell proliferation, migration, and invasion assays were performed to evaluate the anticancer activity in four cancer cell lines with high metastasis, HM-1, B16/BL6, HeLa, and HepG2. The LL-37 fragment peptide analog-linked PLGA conjugate was shown to effectively inhibit cell proliferation, migration, and invasion and had increased cell permeability in all the cancer cell lines, compared with the peptide alone. These results suggested that LL-37 fragment peptide analog (CKR12)-linked PLGA conjugate micelles could be useful in the development of cancer therapeutics.

A Tumor-Microenvironment-Responsive Nanocomposite for Hydrogen Sulfide Gas and Trimodal-Enhanced Enzyme Dynamic Therapy

Recently, enzyme dynamic therapy (EDT) has drawn much attention as a new type of dynamic therapy. However, the selection of suitable nanocarriers to deliver chloroperoxidase (CPO) and enhancement of the level of hydrogen peroxide (H2 O2 ) in the tumor microenvironment (TME) are critical factors for improving the efficiency of EDT. In this study, a rapidly decomposing nanocomposite is designed using tetra-sulfide-bond-incorporating dendritic mesoporous organosilica (DMOS) as a nanocarrier, followed by loading CPO and sodium-hyaluronate-modified calcium peroxide nanoparticles (CaO2 -HA NPs). The nanocomposite can effectively generate singlet oxygen (1 O2 ) for tumor therapy without any exogenous stimulus via trimodal-enhanced EDT, including DMOS-induced depletion of glutathione (GSH), H2 O2 compensation from CaO2 -HA NPs in mildly acidic TME, and oxidative stress caused by overloading of Ca2+ . As tetra-sulfide bonds are sensitive to GSH, DMOS can generate hydrogen sulfide (H2 S) gas as a new kind of H2 S gas nanoreactor. Additionally, the overloading of Ca2+ can cause tumor calcification to accelerate in vivo tumor necrosis and promote computed tomography imaging efficacy. Therefore, a novel H2 S gas, EDT, and Ca2+ -interference combined therapy strategy is developed.

Ultralong and Color-Tunable Room-Temperature Phosphorescence Based on Commercial Melamine for Anticounterfeiting and Information Recognition

Advances have been made in the research on color-tunable organic ultralong room-temperature phosphorescence (OURTP) materials. Due to the high cost of raw materials, complex and strict synthesis conditions, and low yields, it is hard to obtain cheap commercial OURTP materials within a short time. Therefore, it is of practical significance to research and develop new OURTP functions based on commercialized organic materials. In this study, the OURTP characteristics of melamine (MEL), a kind of commercially available, cheap, and pure organic material, were investigated and explored. MEL was found with color-tunable and excellent OURTP, the average lifetime can reach 0.74 s, and the phosphorescence quantum yield can reach 17%. Since the ratio of molecular phosphorescence of MEL to the ultralong phosphorescence mediated by H-aggregation differs with the excitation wavelength and their luminescence life spans are also different, the color of OURTP materials is dependent on both excitation wavelength and time. Moreover, the OURTP characteristics of MEL can be utilized in anticounterfeiting and information identification.

Electrochemiluminescence-Repurposed Abiological Catalysts in Full Protein Tag for Ultrasensitive Immunoassay

Being announced as one of the "2019 Top Ten Emerging Technologies in Chemistry" by IUPAC, the directed evolution of artificial metalloenzymes has led to a broad scope of abiotic processes. Here, inspired by those key proteins in bioluminescence, a rudimentary expression of bio-electrochemiluminescent (ECL) macromolecules was achieved via the complexation of zinc proto-porphyrin IX (ZnPPIX) within apo-hemoglobin (apo-Hb). A high-yield monochromic irradiation at 644 nm could be provoked potentiostatically from the reconstituted holo-Hb^ZnPPIX in solutions. Its secondary structure integrity was elucidated by UV and circular dichroism spectrometry, while voltammetry-hyphenated surface plasmon resonance authenticated its ligation conservativeness in electrical fields. Further conjugation with streptavidin rendered a homogeneous Janus fusion of both receptor and reporter domains, enabling a new abiological catalyst-linked ECL bioassay. On the other hand, singular ZnPPIX inside each tetrameric subunit of Hb accomplished an overall signal amplification without the bother of luminogenic heterojunctions. This pH-tolerant and non-photobleaching optics was essentialized to be the unique configuration interaction between Zn and O₂, by which the direct electrochemistry of proteins catalyzed the transient progression of O₂ → O₂^·- → O₂* + hυ selectively. Such principle was implemented as a signal-on strategy for the determination of a characteristic cancer biomarker, the vascular endothelial growth factor, resulting in competent performance at a low detection limit of 0.6 pg·mL^-1 and a wide calibration range along with good stability and reliability in real practices. This simple mutation repurposed the O₂-transport Hb in the erythrocytes of almost all vertebrates into a cluster of oxidoreductases with intrinsic ECL activity, which would enrich the chromophore library. More importantly, its genetically engineered variants may come in handy in biomedical diagnosis and visual electrophysiology.