A selenamorpholine-based redox-responsive fluorescent probe for targeting lysosome and visualizing exogenous/endogenous hydrogen peroxide in living cells and zebrafish

AIE-active large Stokes-shift BODIPY Functionalized with Carbazolyl for Lysosome-Targeted Imaging in Living Cells

A large number of studies have shown that lysosomal microcircumstances changes can affect many physiological and pathological processes at the cellular level. However, the visual detection of lysosomal microcircumstances is relatively difficult due to low pH (4.5-6.0) value in lysosomal that require the probe not only stable under acidic condition but also has a good localization effect to lysosomal. Obviously, novel fluorescent which possessed both acidic stability and lysosomal-target property together with lysosomal viscosity active is highly demanded. Herein, a novel BODIPY molecular CarBDP based on carbazole group was rationally designed and synthesized for the lysosomal imaging. CarBDP exhibited AIE feature with a large Stokes shift of up to 157 nm. More importantly, co-localization assay of the CarBDP-treated MCF-7 cells indicated that CarBDP has a good localization effect on lysosomal (Rr = 0.7109) due to the carbazole group while the normal BODIPY that without carbazole group (PhBDP) shows poor localization performance, this was the first time that a small molecule can locate lysosomes only based on carbazole group. CarBDP exhibits strong solid emission with long fluorescence decay lifetime (τ = 44.54 ns) and was stable under acid condition.The probe CarBDP assembled with carbazole group was successfully utilized for lysosomal localization and mapping lysosomal viscosity in live cells, which provides a novel candidate tool for the determination of lysosomal microcircumstances.

meso-Methyl Amination of BODIPYs by Regiospecific Cross Dehydrogenative Coupling via Direct C(sp3)-N(sp3) Bond Formation

Herein, we report a direct meso-methyl amination of BODIPY dyes by C(sp3)-N(sp3) bond formation using PIDA as an oxidant with a wide range of aliphatic secondary amines. This metal free cross dehydrogenative coupling reaction is regiospecific at the meso-methyl position of BODIPY in the presence of C1, C3, C5, and C7 methyl groups. Detailed nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, and X-ray crystallographic studies were performed to establish the reaction mechanism and the regiospecificity of the reaction. Finally, the photophysical and electrochemical properties of the newly synthesized dyes were evaluated and rationalized.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Diphenylbutadiene Fluorescent Analogues in Sub-Cellular Imaging and Monitoring Mitophagy

A series of donor-acceptor (D-π-A) substituted diphenylbutadienes exhibiting solvatochromic emission and a large Stokes shift (100-200 nm) were designed and synthesized for distinctive organelle labelling, enabling real-time monitoring of organelle behaviour such as lysosomal dynamics, mitophagy monitoring, and stress responses. The morpholine-substituted D-A-D diphenylbutadiene (M2) was employed to investigate selective imaging of lysosomes, the uptake of damaged mitochondria through mitophagy, and monitoring lysosomal viscosity or pH changes. Other diphenylbutadiene derivatives (M1, M3, M4) selectively accumulated in lipid droplets. All the synthesized derivatives demonstrated significant uptake in 5-day post-fertilization zebrafish larvae, with M2 showing maximum uptake in the enterocyte-containing heart and intestinal regions, which include the lysosomes.

An indole-based near-infrared fluorescent "Turn-On" probe for H2O2: Selective detection and ultrasensitive imaging of zebrafish gallbladder

Fluorescent probes play essential roles in medical imaging, where the researchers can select one of many molecules to use to help monitor the status of living systems under investigation. To date, a few scaffolds that allow the in vivo detection of H2O2 are available only. Herein, we provide a highly sensitive and selective near-infrared fluorescent probe that detects H2O2 based on the ICT sensing mechanism. We report the first indole-incorporated fluorescent probe Indo-H2O2 that allows H2O2 detection with a LOD of 25.2 nM featuring a boronate group conjugated to an indole scaffold; the boronate cleaves upon reaction with H2O2. A 5-membered malononitrile derivative was incorporated; Indo-H2O2 has near-infrared (NIR) properties and the reaction time is low (∼25 min) compared to other related probes. Indo-H2O2 was successfully employed in both endogenous and exogenous imaging trials of H2O2 in living cells. Indo-H2O2 also allows the real-time monitoring of H2O2in vivo. It preferentially accesses the gallbladder of zebrafish. Our findings support Indo-H2O2 as a highly sensitive fluorescent NIR probe for detecting H2O2, and an idea to incorporate a central indole unit in future fluorescent probe designs.

BODIPY-Based Molecules for Biomedical Applications

BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives have attracted attention as probes in applications like imaging and sensing due to their unique properties like (1) strong absorption and emission in the visible and near-infrared regions of the electromagnetic spectrum, (2) strong fluorescence and (3) supreme photostability. They have also been employed in areas like photodynamic therapy. Over the last decade, BODIPY-based molecules have even emerged as candidates for cancer treatments. Cancer remains a significant health issue world-wide, necessitating a continuing search for novel therapeutic options. BODIPY is a flexible fluorophore with distinct photophysical characteristics and is a fascinating drug development platform. This review provides a comprehensive overview of the most recent breakthroughs in BODIPY-based small molecules for cancer or disease detection and therapy, including their functional potential.

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Photoinduced electron transfer (PeT) based fluorescent probes for cellular imaging and disease therapy

Typical PeT-based fluorescent probes are multi-component systems where a fluorophore is connected to a recognition/activating group by an unconjugated linker. PeT-based fluorescent probes are powerful tools for cell imaging and disease diagnosis due to their low fluorescence background and significant fluorescence enhancement towards the target. This review provides research progress towards PeT-based fluorescent probes that target cell polarity, pH and biological species (reactive oxygen species, biothiols, biomacromolecules, etc.) over the last five years. In particular, we emphasise the molecular design strategies, mechanisms, and application of these probes. As such, this review aims to provide guidance and to enable researchers to develop new and improved PeT-based fluorescent probes, as well as promoting the use of PeT-based systems for sensing, imaging, and disease therapy.

A novel hydrogen peroxide fluorescent probe for bioimaging detection and enables multiple redox cycles

In this subject, a novel hydrogen peroxide (H₂O₂) fluorescent probe (MNG) was designed and developed using naphthalimide derivatives and selenomorpholine. In PBS buffer (10 mM, pH = 7.4, 1 %DMSO), the selenomorpholine on the probe is capable of qualitatively and quantitatively detecting (H₂O₂) at a small amount under a detection limit of 61 nM. The probe follows a mechanism that Se (Ⅱ) in selenomorpholine is transformed to Se (Ⅳ), thus changing the spectra of the probe MNG. It is noteworthy that MNG can continuously make a cyclic response to H₂O₂ and glutathione (GSH), so it can potentially achieve redox process imaging in vivo. Moreover, this subject verified the redox process of the probe's continuous redox response in the Gaussian 09 programme through simulation calculation and mass spectrometry. The probe exhibits high biocompatibility. Moreover, it can detect H₂O₂ in MCF-7 cells and Argentine Bloodfin.

Recent Progress in Organic Small-Molecule Fluorescent Probe Detection of Hydrogen Peroxide

The fluorescent probe has become an important method for accurate detection of H2O2, with advantages of simple operation, high sensitivity, good selectivity, and real-time dynamic monitoring. This paper reviews the research progress in organic small-molecule fluorescent probe H2O2 detection methods that are based on different recognition reactions. In addition, the application prospect of fluorescent probes in the detection of trace H2O2 is anticipated.

A redox reversible endoplasmic reticulum-targeted fluorescent probe for revealing the redox status of living cells

The endoplasmic reticulum (ER) is one of the most important organelles in cells and is involved in protein synthesis, folding and orderly transport. Redox balance is the key to its normal function. In this work, we designed and synthesized an endoplasmic reticulum-targeted fluorescent probe N-Se with selenomorpholine as the redox reversible detection moiety. N-Se could selectively respond to ClO^- within only 8 s with a LOD of 28.8 nM. Furthermore, such a response is reversible in the regulation of GSH. Confocal fluorescence imaging confirmed the excellent endoplasmic reticulum targeting ability of N-Se. Thus, it could real-time monitor the dynamic changes of the redox status in the endoplasmic reticulum through the variation of the fluorescence intensity.

Brefeldin A delivery nanomicelles in hepatocellular carcinoma therapy: Characterization, cytotoxic evaluation in vitro, and antitumor efficiency in vivo

Hepatocellular carcinoma (HCC) is one of the major cancers with high mortality rate. Traditional drugs used in clinic are usually limited by the drug resistance and side effect and novel agents are still needed. Macrolide brefeldin A (BFA) is a well-known lead compound in cancer chemotherapy, however, with poor solubility and instability. In this study, to overcome these disadvantages, BFA was encapsulated in mixed nanomicelles based on TPGS and F127 copolymers (M-BFA). M-BFA was conferred high solubility, colloidal stability, and capability of sustained release of intact BFA. In vitro, M-BFA markedly inhibited the proliferation, induced G0/G1 phase arrest, and caspase-dependent apoptosis in human liver carcinoma HepG2 cells. Moreover, M-BFA also induced autophagic cell death via Akt/mTOR and ERK pathways. In HepG2 tumor-bearing xenograft mice, indocyanine green (ICG) as a fluorescent probe loaded in M-BFA distributed to the tumor tissue rapidly, prolonged the blood circulation, and improved the tumor accumulation capacity. More importantly, M-BFA (10 mg/kg) dramatically delayed the tumor progression and induced extensive necrosis of the tumor tissues. Taken together, the present work suggests that M-BFA has promising potential in HCC therapy.

A novel methylenemalononitrile-BODIPY-based fluorescent probe for highly selective detection of hydrogen peroxide in living cells

Hydrogen peroxide (H₂O₂) plays vital roles in oxidative stress and signal transduction in living organisms, and its abnormal levels could be linked to many diseases. Despite numerous efforts spent, it is still urgent and of high importance to develop better H₂O₂ probes with good selectivity, high sensitivity and low backgrounds. To this end, a novel boron dipyrromethene (BODIPY)-based fluorescent probe with an electron-withdrawing methylenemalononitrile at the meso position has been rationally designed, successfully synthesized and investigated for detection of H₂O₂ in aqueous solutions and living cells, which exhibited high selectivity and sensitivity, fluorescent "turn-on" phenomenon at 540 nm, and ratiometric changes from 506 to 540 nm. Upon exposure to H₂O₂, a strong fluorescent emission at 540 nm appeared and the corresponding quantum yields changed from 0.009 to 0.13. The detection limit towards H₂O₂ was calculated to be 31 nM by the linear fluorescence change at 540 nm in the H₂O₂-concentration ranging from 2 to 10 μM. This probe was applicable in a pH range from 6 to 10. Meanwhile, the sensing mechanism was also confirmed by the ¹H NMR and mass spectrometry, suggesting that the above changes might be ascribed to the quick addition and oxidization of the double bond. Furthermore, confocal imaging results also showed great enhancement of intracellular fluorescence upon exposure to H₂O₂ and PMA in RAW264.7 cells, unambiguously confirming its great potentials as a fluorescent probe for highly sensitive detection of both exogenous and endogenous H₂O₂ in living cells.

A Novel Photosensitizer for Lipid Droplet-Location Photodynamic Therapy

Lipid droplets (LDs), an extremely important cellular organelle, are responsible for the storage of neutral lipids in multiple biological processes, which could be a potential target site for photodynamic therapy (PDT) of cancer. Herein, a lipid droplet–targeted photosensitizer (BODSeI) is developed, allowing for fluorescence imaging–guided PDT. Owing to the location of lipid droplets, BODSeI demonstrates enhanced PDT efficiency with an extremely low IC50 value (around 125 nM). Besides, BODSeI shows good biocompatibility and high photostability. Therefore, BODSeI is promising for droplet-location PDT, which may trigger wide interest for exploring the pathway of lipid droplet–location PDT.

Discussions of Fluorescence in Selenium Chemistry: Recently Reported Probes, Particles, and a Clearer Biological Knowledge

In this review from literature appearing over about the past 5 years, we focus on selected selenide reports and related chemistry; we aimed for a digestible, relevant, review intended to be usefully interconnected within the realm of fluorescence and selenium chemistry. Tellurium is mentioned where relevant. Topics include selenium in physics and surfaces, nanoscience, sensing and fluorescence, quantum dots and nanoparticles, Au and oxide nanoparticles quantum dot based, coatings and catalyst poisons, thin film, and aspects of solar energy conversion. Chemosensing is covered, whether small molecule or nanoparticle based, relating to metal ion analytes, H2S, as well as analyte sulfane (biothiols-including glutathione). We cover recent reports of probing and fluorescence when they deal with redox biology aspects. Selenium in therapeutics, medicinal chemistry and skeleton cores is covered. Selenium serves as a constituent for some small molecule sensors and probes. Typically, the selenium is part of the reactive, or active site of the probe; in other cases, it is featured as the analyte, either as a reduced or oxidized form of selenium. Free radicals and ROS are also mentioned; aggregation strategies are treated in some places. Also, the relationship between reduced selenium and oxidized selenium is developed.

Mitochondria and lysosome-targetable fluorescent probes for hydrogen peroxide

Hydrogen peroxide (H₂O₂), as a key member of the reactive oxygen species (ROS), has a certain regulatory effect on many physiological processes, such as cell proliferation, differentiation and migration. However, abnormal production of H₂O₂ can cause diseases including cancer, Alzheimer's disease, cardiovascular disease, and so on. Therefore, it is important to detect changes in H₂O₂ at the subcellular level. In recent years, many fluorescent probes for H₂O₂ have been developed and used in living cells. In this review, we introduce some typical fluorescent probes for H₂O₂ with mitochondrial and lysosomal targeting. This review contains targeting strategies, detection mechanisms, optical characteristics and cell imaging of these probes.

A novel dual-function fluorescent probe for the rapid detection of bisulfite and hydrogen peroxide in aqueous solution and living cells

In this work, Hcy-OB, a novel hemicyanine-based biocompatible dual-function fluorescence probe for bisulfite and H₂O₂ detection is designed and synthesized. Based on a 1,4-addition reaction, Hcy-OB can be used for bisulfite detection with fast response, high sensitivity and low detection limit (120 nM). In addition, the probe is successfully applied to the detection of bisulfite in aqueous solution. Furthermore, Hcy-OB shows excellent performance for hydrogen peroxide detection with the oxidation of phenylboronic acid. Hcy-OB shows excellent selectivity to H₂O₂ over other interfering substances with detection limit of H₂O₂ is calculated to be 70 nM. Most importantly, due to its good cell membrane permeability and low cytotoxicity, Hcy-OB has been applied to monitor and image H₂O₂ in living cells and mice.

Targeting Delivery Nanocarriers for (+)-Terrein to Enhance Its Anticancer Effects

As a compound from marine fungi, (+)-terrein showed significant anticancer activity. In this study, (+)-terrein was extracted from the marine-derived fungus and showed significant cytotoxicity against cancer cells, especially in A549 cells. To enhance its anticancer effects, redox-responsive nanocarriers based on folic acid-chitosan decorating the mesoporous silica nanoparticles were designed to control (+)-terrein target delivery into cancer cells. (+)-Terrein was loaded in the holes, and folic acid-chitosan worked as a gatekeeper by disulfide linkage controlling (+)-terrein release in the tumor microenvironment. The (+)-terrein drug delivery systems exhibited cytotoxicity toward A549 cells through induction of apoptosis. The apoptosis effect was confirmed by the increase in the expression of cleaved caspase-3, caspase-9, and PARP. Taken together, this work evaluates for the first time the (+)-terrein delivery system and provides a promising nanomedicine platform for (+)-terrein.

SnAP reagents for the synthesis of selenomorpholines and 1,4-selenazepanes and their biological evaluation

Herein, we disclose the first set of unique selenium-containing SnAP reagents for the direct synthesis of C-substituted selenomorpholines and 1,4-selenazepanes, including their amino acid derivatives from commercially available aldehydes under mild conditions. These elusive N-unprotected heterocycles are not accessible by classical routes. Biological evaluation of these compounds revealed promising activities against clinically relevant fungal strains.