BODIPY Fluorophores for Membrane Potential Imaging

Pd and Pt Complexes of Benzo-Fused Dipyrrins: Synthesis, Structure, Electrochemical, and Optical Properties

Benzo-fused dipyrrins are π-extended analogs of conventional dipyrrins, which exhibit bathochromically shifted absorption and possess the synthetic capability to bind various metal ions. We aimed to investigate the synthetic potential of benzo-fused dipyrrins in the complexation with transition metals. Two new complexes with Pd2+ and Pt2+ were synthesized and characterized. X-ray crystallography reveals that both complexes exhibit a zigzag geometry with square planar coordination of the central metal. The Pd2+ complex possesses a very weak fluorescence at 665 nm, while the Pt2+ complex is completely nonemissive. Transient absorption spectroscopy confirmed triplet excited state formation for both complexes; however, they are short-lived and no phosphorescence was observed even at 77K. DFT calculations support the experimental observation, revealing the existence of the low-lying ligand-metal charge-transfer (LMCT) triplet state acting as an energy sink.

Design, synthesis, and biological application of A-D-A-type boranil fluorescent dyes

For the first time, three acceptor-donor-acceptor (A-D-A)-type boranil fluorescent dyes, CSU-BF-R (R = H, CH3, and OCH3), featuring phenothiazine as the donor, were designed and synthesized. CSU-BF-R exhibited remarkable photophysical characteristics, including large Stokes shifts (>150 nm), high fluorescence quantum yields (up to 40%), long-wavelength emissions, and strong red solid-state fluorescence. Moreover, these CSU-BF-R fluorescent dyes were demonstrated to function as highly selective and sensitive ratiometric fluorescent probes for detecting hypochlorous acid (HClO). The preliminary biological applications of CSU-BF-OCH3 for sensing intracellular HClO in living cells and zebrafish were demonstrated. Therefore, CSU-BF-R possess the potential to further explore the physiological and pathological functions associated with HClO and provide valuable insights into the design of high-performance A-D-A-type fluorescent dyes.

Water-Soluble Small Organic Fluorophores for Oncological Theragnostic Applications: Progress and Development

Cancer is one of the major noncommunicable diseases, responsible for millions of deaths every year worldwide. Though various cancer detection and treatment modalities are available today, many deaths occur owing to its late-stage detection and metastatic nature. Noninvasive detection using luminescence-based imaging tools is considered one of the promising techniques owing to its low cost, high sensitivity, and brightness. Moreover, these tools are unique and valuable as they can detect even the slightest changes in the cellular microenvironment. To achieve this, a fluorescent probe with strong tumor uptake and high spatial and temporal resolution, especially with high water solubility, is highly demanded. Recently, several water-soluble molecules with emission windows in the visible (400-700 nm), first near-infrared (NIR-I, 700-1000 nm), and second near-infrared (NIR-II, 1000-1700 nm) windows have been reported in literature. This review highlights recently reported water-soluble small organic fluorophores/dyes with applications in cancer diagnosis and therapeutics. We systematically highlight and describe the key concepts, structural classes of fluorophores, strategies for imparting water solubility, and applications in cancer therapy and diagnosis, i.e., theragnostics. We discuss examples of water-soluble fluorescent probes based on coumarin, xanthene, boron-dipyrromethene (BODIPY), and cyanine cores. Some other emerging classes of dyes based on carbocyclic and heterocyclic cores are also discussed. Besides, emerging molecular engineering methods to obtain such fluorophores are discussed. Finally, the opportunities and challenges in this research area are also delineated.

Linear Amine-Linked Oligo-BODIPYs: Convergent Access via Buchwald-Hartwig Coupling

A convergent route toward nitrogen-bridged BODIPY oligomers has been developed. The synthetic key step is a Buchwald-Hartwig cross-coupling reaction of an α-amino-BODIPY and the respective halide. Not only does the selective synthesis provide control of the oligomer size, but the facile preparative procedure also enables easy access to these types of dyes. Furthermore, functionalized examples were accessible via brominated derivatives.

Design and Application of Fluorescent Probes to Detect Cellular Physical Microenvironments

The microenvironment is indispensable for functionality of various biomacromolecules, subcellular compartments, living cells, and organisms. In particular, physical properties within the biological microenvironment could exert profound effects on both the cellular physiology and pathology, with parameters including the polarity, viscosity, pH, and other relevant factors. There is a significant demand to directly visualize and quantitatively measure the fluctuation in the cellular microenvironment with spatiotemporal resolution. To satisfy this need, analytical methods based on fluorescence probes offer great opportunities due to the facile, sensitive, and dynamic detection that these molecules could enable in varying biological settings from in vitro samples to live animal models. Herein, we focus on various types of small molecule fluorescent probes for the detection and measurement of physical parameters of the microenvironment, including pH, polarity, viscosity, mechanical force, temperature, and electron potential. For each parameter, we primarily describe the chemical mechanisms underlying how physical properties are correlated with changes of various fluorescent signals. This review provides both an overview and a perspective for the development of small molecule fluorescent probes to visualize the dynamic changes in the cellular environment, to expand the knowledge for biological process, and to enrich diagnostic tools for human diseases.

Rational Design and Biological Application of Hybrid Fluorophores

Fluorophores are considered powerful tools for not only enabling the visualization of cell structures, substructures, and biological processes, but also making for the quantitative and qualitative measurement of various analytes in living systems. However, most fluorophores do not meet the diverse requirements for biological applications in terms of their photophysical and biological properties. Hybridization is an important strategy in molecular engineering that provides fluorophores with complementarity and multifunctionality. This review summarizes the basic strategies of hybridization with four classes of fluorophores, including xanthene, cyanine, coumarin, and BODIPY with a focus on their structure-property relationship (SPR) and biological applications. This review aims to provide rational hybrid ideas for expanding the reservoir of knowledge regarding fluorophores and promoting the development of newly produced fluorophores for applications in the field of life sciences.

Zwitterionic Polysulfobetaine Inhibits Cancer Cell Migration Owing to Actin Cytoskeleton Dynamics

Cell migration is an essential dynamic process for most living cells, mainly driven by the reorganization of actin cytoskeleton. To control actin dynamics, a molecular architecture that can serve as a nucleator has been designed by polymerizing sulfobetaine methacrylate. The synthesized zwitterionic polymer, poly(sulfobetaine methacrylate) (PZI), effectively nucleates the polymerization process of G-actin and substantially accelerates the rate of polymerization. Isothermal titration calorimetry (ITC) and bioinformatics analysis indicated binding between PZI and monomeric G-actin. Thus, in vitro actin dynamics was studied by dynamic light scattering (DLS), pyrene-actin polymerization assay, and total internal reflection fluorescence microscopy (TIRFM). Furthermore, a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophore-containing monomeric unit was incorporated into the sulfobetaine zwitterionic architecture to visualize the effect of polymer in the cellular environment. The BODIPY-containing zwitterionic sulfobetaine polymer (PZI-F) successfully penetrated the cell and remained in the lysosome with minimal cytotoxicity. Confocal microscopy revealed the influence of this polymer on the cellular actin cytoskeleton dynamics. The PZI-F polymer was successfully able to inhibit the collective migration of the human cervical cancer cell line (HeLa cell) and breast cancer cell line (MDA-MB-231 cell), as confirmed by a wound healing assay. Therefore, polyzwitterionic sulfobetaine could be explored as an inhibitor of cancer cell migration.

Visualizing intracellular membrane interactions and cell type-specific differentiation in ferroptosis and apoptosis with Boranil-Carbazole derivative

Intracellular lipid systems play essential roles in various physiological functions and cell growth processes. However, our understanding of the intricate interactions within this system, especially between mitochondria and lipid droplets, is limited, particularly in the context of cancer cells' altered lipid metabolism. To address this, our study introduces an N-B-O BODIPY-hexylcarbazole derivative, named Cz-Boranil, that sets a new benchmark in visualizing these critical interactions. Cz-Boranil's unique capability lies in its ability to display distinct intracellular distribution patterns in both normal and cancer cells, offering nuanced cell type-specific differentiation. More impressively, this probe tracks the coordinated interactions of lipid droplets and mitochondria during the critical processes of ferroptosis and apoptosis. We believe that the innovative capabilities of Cz-Boranil will revolutionize our understanding of intracellular lipid interactions and prove pivotal in identifying and studying cancerous cells.

Self-Assembly Induced Photosensitization of Long-Tailed Heavy-Atom-Free BODIPY Derivatives for Photodynamic Therapy

Type I photosensitizers (PSs) are a promising approach for photodynamic therapy (PDT) since they can generate radicals that are tolerant to hypoxia. Thus, the development of highly efficient type I PSs is essential. Self-assembly is a promising strategy for developing novel PSs with desirable properties. Here, a simple and effective approach is developed to create heavy-atom-free PSs for PDT by self-assembling long-tailed boron dipyrromethene dyes (BODIPYs). The resulting aggregates BY-I16 and BY-I18 can efficiently convert their excited energy to the triplet state, producing reactive oxygen species that are essential for PDT. Furthermore, the aggregation and PDT performance can be regulated by adjusting the length of the tailed alkyl chains. As proof of concept, the efficacy of these heavy-atom-free PSs both in vitro and in vivo under both normoxic and hypoxic conditions is demonstrated.

Novel Molecular Vehicle-Based Approach for Cardiac Cell Transplantation Leads to Rapid Electromechanical Graft-Host Coupling

Myocardial remodeling is an inevitable risk factor for cardiac arrhythmias and can potentially be corrected with cell therapy. Although the generation of cardiac cells ex vivo is possible, specific approaches to cell replacement therapy remain unclear. On the one hand, adhesive myocyte cells must be viable and conjugated with the electromechanical syncytium of the recipient tissue, which is unattainable without an external scaffold substrate. On the other hand, the outer scaffold may hinder cell delivery, for example, making intramyocardial injection difficult. To resolve this contradiction, we developed molecular vehicles that combine a wrapped (rather than outer) polymer scaffold that is enveloped by the cell and provides excitability restoration (lost when cells were harvested) before engraftment. It also provides a coating with human fibronectin, which initiates the process of graft adhesion into the recipient tissue and can carry fluorescent markers for the external control of the non-invasive cell position. In this work, we used a type of scaffold that allowed us to use the advantages of a scaffold-free cell suspension for cell delivery. Fragmented nanofibers (0.85 µm ± 0.18 µm in diameter) with fluorescent labels were used, with solitary cells seeded on them. Cell implantation experiments were performed in vivo. The proposed molecular vehicles made it possible to establish rapid (30 min) electromechanical contact between excitable grafts and the recipient heart. Excitable grafts were visualized with optical mapping on a rat heart with Langendorff perfusion at a 0.72 ± 0.32 Hz heart rate. Thus, the pre-restored grafts' excitability (with the help of a wrapped polymer scaffold) allowed rapid electromechanical coupling with the recipient tissue. This information could provide a basis for the reduction of engraftment arrhythmias in the first days after cell therapy.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications

The use of boron dipyrromethene (BODIPY) in biomedicine is reviewed. To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

Boron-containing compounds on neurons: Actions and potential applications for treating neurodegenerative diseases

Boron-containing compounds (BCC) exert effects on neurons. After the expanding of both the identification and synthesis of new BCC, novel effects in living systems have been reported, many of these involving neuronal action. In this review, the actions of BCC on neurons are described; the effects have been inferred by boron deprivation or addition. Also, the effects can be related to those mediated by interaction on ionic channels, G-protein coupled receptors, or other receptors exerting modification on neuronal behavior. Additionally, BCC have exhibited effects by the modulation of inflammation or oxidative processes. BCC are expanding as drugs. Deprivation of boron sources from the diet shows the role of some natural BCC. However, the observations of several new synthesized compounds suggest their ability to act with attractive potency, efficacy, and long-term action on neuronal receptors or processes related with the origin and evolution of neurodegenerative processes. The details of BCC-target interactions are currently being elucidated in progress, as those observed from BCC-protein crystal complexes. Taking all of the above into account, the expansion is presumably near to having studies on the application of BCC as drugs on specific targets for treating neurodegenerative diseases.

Sulfone Rhodamines for Voltage Imaging

Fluorescent indicators that respond to changes in biological membrane potentials provide a powerful complement to existing methods for monitoring neuronal activity. Indicators that absorb and emit in the near infrared window are especially attractive, since lower energy wavelengths excite fewer biological molecules and can penetrate more deeply into biological tissues. In this work, we incorporate sulfone rhodamine chromophores into a voltage-sensitive scaffold in order to generate voltage sensitive fluorophores which absorb and emit above 700 nm. These Sulfone Rhodamine Voltage Reporters (SuRhoVRs) partition into cell membranes and display good sensitivity to membrane potential changes. The most sensitive SuRhoVR derivative also displays excellent photostability and can track membrane potential changes in dissociated rat hippocampal neurons.

Computational Analysis of the Behavior of BODIPY Decorated Monofunctional Platinum(II) Complexes in the Dark and under Light Irradiation

Dual-action drugs are occupying an important place in the scientific landscape of cancer research owing to the possibility to combine different therapeutic strategies into a single molecule. In the present work, the behavior of two BODIPY-appended monofunctional Pt(II) complexes, one mononuclear and one binuclear, recently synthesized and tested for their cytotoxicity have been explored both in the dark and under light irradiation. Quantum mechanical DFT calculations have been used to carry out the exploration of the key steps, aquation and guanine attack, of the mechanism of action of Pt(II) complexes in the dark. Due to the presence of the BODIPY chromophore and the potential capability of the two investigated complexes to work as photosensitizers in PDT, time dependent DFT has been employed to calculate their photophysical properties and to inspect how the sensitizing properties of BODIPY are affected by the presence of the platinum "heavy atom". Furthermore, also the eventual influence on of the photophysical properties due to the displacement of chlorido ligands by water and of water by guanine has been taken into consideration.

BODIPY-based metal-organic frameworks as efficient electrochemiluminescence emitters for telomerase detection

A boron dipyrromethene (BODIPY)-based metal-organic framework (MOF) nanoemitter was for the first time designed with enhanced electrochemiluminescence (ECL) intensity due to the suppression of non-radiative dissipation originating from the ordered arrangement of BODIPY molecules in the framework. Thus, an ECL biosensor was developed for telomerase detection with excellent performance in real samples.

Synthesis and bioimaging of a BODIPY-based fluorescence quenching probe for Fe3

Iron is the main substance for maintaining life. Real-time determination of ferric ion (Fe³⁺) in living cells is of great significance for understanding the relationship of Fe³⁺ concentration changes with various physiological and pathological processes. Fluorescent probes are suitable for the detection of trace metal ions in cells due to their low toxicity and high sensitivity. In this work, a boron-dipyrromethene-based fluorescent probe (BODIPY-CL) for selective detection of Fe³⁺ was synthesized. The fluorescence emission of BODIPY-CL was determined at 516 nm. In a pH range of 1 to 10, the probe BODIPY-CL exhibits a quenching response to Fe³⁺. Meanwhile, BODIPY-CL showed a highly selective response to Fe³⁺ compared with 16 kinds of metal ions. The stoichiometry ratio of BODIPY-CL bound to Fe³⁺ was nearly 2 : 1. The fluorescence quenching response obtained by the sensor was linear with the Fe³⁺ concentration in the range of 0-400 μM, and the detection limit was 2.9 μM. BODIPY-CL was successfully applied to image Fe³⁺ in cells. This study provides a promising fluorescent imaging probe for further research on the physiological and pathological effects of Fe³⁺.

Intracellular Physical Properties with Small Organic Fluorescent Probes: Recent Advances and Future Perspectives

The intracellular physical parameters i. e., polarity, viscosity, fluidity, tension, potential, and temperature of a live cell are the hallmark of cellular health and have garnered immense interest over the past decade. In this context, small molecule organic fluorophores exhibit prominent useful properties including easy functionalizability, environmental sensitivity, biocompatibility, and fast yet efficient cellular uptakability which has made them a popular tool to understand intra-cellular micro-environmental properties. Throughout this discussion, we have outlined the basic design strategies of small molecules for specific organelle targeting and quantification of physical properties. The values of these parameters are indicative of cellular homeostasis and subtle alteration may be considered as the onset of disease. We believe this comprehensive review will facilitate the development of potential future probes for superior insight into the physical parameters that are yet to be quantified.

Green‐Light Activatable BODIPY and Coumarin 5’‐Caps for Oligonucleotide Photocaging

We synthesized two green‐light activatable 5’‐caps for oligonucleotides based on the BODIPY and coumarin scaffold. Both bear an alkyne functionality allowing their use in numerous biological applications. They were successfully incorporated in oligonucleotides via solid‐phase synthesis. Copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) using a bisazide photo‐tether gave cyclic oligonucleotides that could be relinearized by activation with green light and were shown to exhibit high stability against exonucleases. Chemical ligation as another example for bioconjugation yielded oligonucleotides with an internal strand break site. Irradiation at 530 nm or 565 nm resulted in complete photolysis of both caging groups.

Synthesis and Optical Properties of Excited-State Intramolecular Proton Transfer (ESIPT) Emitters with Sulfobetaine Fragments

This article describes the synthetic efforts towards the solubilization of organic fluorescent emitters based on a 2-(2'-hydroxybenzofuranyl)benzazole (HBBX) scaffold in aqueous media under physiological conditions (PBS, pH 7.4). These dyes are well-known to display the excited-state intramolecular proton transfer (ESIPT) process which leads to a Stokes-shifted fluorescence with enhanced photostability and strong environment dependent features. Organic dyes are hydrophobic by nature and their vectorization into aqueous media usually necessitates amphiphilic polymers. In this study, we show that the incorporation of one or two sulfobetaine fragments, a highly biocompatible zwitterionic unit leads to the vectorization in buffer solution at pH 7.4 while keeping a reasonable ESIPT fluorescence emission. The photophysical properties of all dyes were studied in multiple solvents and showed that, depending on structure and environment, different excited-state species are observed: normal or tautomeric species, as well as a competitive anionic fluorescent derivative. This study shows that it is not only possible to solubilize fluorescent ESIPT dyes in water using sulfobetaine(s) but also that the optical properties can be finely tuned depending on small structural inputs.

Chemical Targeting of Rhodol Voltage-Sensitive Dyes to Dopaminergic Neurons

Optical imaging of changes in the membrane potential of living cells can be achieved by means of fluorescent voltage-sensitive dyes (VSDs). A particularly challenging task is to efficiently deliver these highly lipophilic probes to specific neuronal subpopulations in brain tissue. We have tackled this task by designing a solubilizing, hydrophilic polymer platform that carries a high-affinity ligand for a membrane protein marker of interest and a fluorescent VSD. Here, we disclose an improved design of polymer-supported probes for chemical, nongenetic targeting of voltage sensors to axons natively expressing the dopamine transporter in ex vivo mouse brain tissue. We first show that for negatively charged rhodol VSDs functioning on the photoinduced electron transfer principle, poly(ethylene glycol) as a carrier enables targeting with higher selectivity than the polysaccharide dextran in HEK cell culture. In the same experimental setting, we also demonstrate that incorporation of an azetidine ring into the rhodol chromophore substantially increases the brightness and voltage sensitivity of the respective VSD. We show that the superior properties of the optimized sensor are transferable to recording of electrically evoked activity from dopaminergic axons in mouse striatal slices after averaging of multiple trials. Finally, we suggest the next milestones for the field to achieve single-scan recordings with nongenetically targeted VSDs in native brain tissue.

BODIPY Cored A-D-A'-D-A Type Nonfused-Ring Electron Acceptor for Efficient Polymer Solar Cells

In this work, boron dipyrromethene (BODIPY) is for the first time employed as electron-deficient core (A') to construct an A-D-A'-D-A type nonfused-ring electron acceptor (NFREA) for polymer solar cells (PSCs). Among, cyclopentadithiophene (CPDT) and fluorinated dicyanoindanone (DFIC) are involved as electron-donating (D) bridges and terminal A groups, respectively. Bearing with the steric BODIPY core, tMBCIC exhibits twisted configuration with dihedral angles >45^o  between BODIPY and CPDT bridges. Thus, compared with the BODIPY-free planar A-D-D-A structured bCIC, reduced aggregation, weakened intramolecular D-A interactions with up-shifted LUMO by 0.4 eV as well as blue-shifted absorption by up to 150 nm is observed in tMBCIC. Moreover, owing to the intrinsic large molar extinction coefficient from BODIPY, promoted light-harvest ability is achieved for tMBCIC, particularly in its blend films. Therefore, PSCs by using PBDB-T as donor, tMBCIC as NFREA afford superior power conversion efficiency (PCE) of 9.22% and higher open-circuit voltage (V_oc ) of 0.954 V compared to 4.47% and 0.739 V from bCIC-devices. Moreover, compared to other BODIPY-flanked electron acceptors (<5%) reported so far, BODIPY-cored tMBCIC realizes a remarkable progress in PCE. This article is protected by copyright. All rights reserved.

A nitroreductase responsive and photoactivated fluorescent probe for dual-controlled tumor hypoxia imaging

Tumor hypoxia has great importance in tumor progression and resistance to antitumor therapies. To precisely monitor tumor hypoxia, a controllable hypoxia imaging method is meaningful but still lacking. Herein, we develop a dual-controlled tumor hypoxia probe (TNB) by introducing a nitrophenol group and methyltetrazine group to the boron-dipyrromethene (BODIPY) dye. The fluorescence-quenching group nitrophenol is reduced to aminophenol by upregulated nitroreductase in hypoxic tumors, and the photocage methyltetrazine is cleaved by light irradiation. Hence the fluorescence of TNB is dual-controlled by hypoxia and photoactivation. We first evaluated TNB's potential for controllable hypoxia imaging in solution and tumor cells. The fluorescence of TNB under nitroreductase incubation and photoactivation increased more than 60 fold over that which was untreated or only treated with nitroreductase. Furthermore, results validate that TNB possesses photo-controllable activation features in tumor sections. We believe that the probe design based on enzyme and photoactivation responsiveness provides potential for spatiotemporal detection of other biomarkers.

Tumor hypoxia has great importance in tumor progression and resistance to antitumor therapies.

Intracellular Localization Studies of the Luminescent Analogue of an Anticancer Ruthenium Iminophosphorane with High Efficacy in a Triple-Negative Breast Cancer Mouse Model

The potential of ruthenium(II) compounds as an alternative to platinum-based clinical anticancer agents has been unveiled after extensive research for over 2 decades. As opposed to cisplatin, ruthenium(II) compounds have distinct mechanisms of action that do not rely solely on interactions with DNA. In a previous report from our group, we described the synthesis, characterization, and biological evaluation of a cationic, water-soluble, organometallic ruthenium(II) iminophosphorane (IM) complex of p-cymene, ([(η6-p-cymene)Ru{(Ph3P═N-CO-2N-C5H4)-κ-N,O}Cl]Cl (1 or Ru-IM), that was found to be highly cytotoxic against a panel of cell lines resistant to cisplatin, including triple-negative breast cancer (TNBC) MDA-MB-231, through canonical or caspase-dependent apoptosis. Studies on a MDA-MB-231 xenograft mice model (after 28 days of treatment) afforded an excellent tumor reduction of 56%, with almost negligible systemic toxicity, and a favored ruthenium tumor accumulation compared to other organs. 1 is known to only interact weakly with DNA, but its intracellular distribution and ultimate targets remain unknown. To gain insight on potential mechanisms for this highly efficacious ruthenium compound, we have developed two luminescent analogues containing the BOPIPY fluorophore (or a modification) in the IM scaffold with the general structure of [(η6-p-cymene)Ru{(BODIPY-Ph2P═N-CO-2-NC5H4)-κ-N,O}Cl]Cl {BODIPY-Ph2P = 8-[(4-diphenylphosphino)phenyl]-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3a) and 4,4-difluoro-8-[4-[[2-[4-(diphenylphosphino)benzamido]ethyl]carbamoyl]phenyl]-1,3,5,7-tetramethyl,2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3b)}. We report on the synthesis, characterization, lipophilicity, stability, luminescence properties, and cell viability studies in the TNBC cell line MDA-MB-231, nonmalignant breast cells (MCF10a), and lung fibroblasts (IMR-90) of the new compounds. The ruthenium derivative 3b was studied by fluorescence confocal microscopy. These studies point to a preferential accumulation of the compound in the endoplasmic reticulum, mitochondria, and lysosomes. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis also confirms a greater ruthenium accumulation in the cytoplasmic fraction, including endoplasmic reticulum and lysosomes, and a smaller percentage of accumulation in mitochondria and the nucleus. ICP-OES analysis of the parent compound 1 indicates that it accumulates preferentially in the mitochondria and cytoplasm. Subsequent experiments in 1-treated MDA-MB-231 cells demonstrate significant reactive oxygen species generation.

Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers

In photosensitizers, long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which were efficiently generated from easily accessible meso-mesityldipyrrinone and arylboronic acids in one pot. Arylboronic acid, for the first time, was used to provide a boron source for BODIPY derivatives. Due to the well-defined and orthogonally aligned BODIPY cores as verified by X-ray crystallography, these BODIPY arrays show strong exciton coupling effects and efficient intersystem crossings, and are novel heavy-atom-free photosensitizers with a long-lived triplet excited state (lifetime up to 257.5 μs) and good reactive oxygen species generation efficiency (up to 0.72) contributed by both 1O2 and O2 -˙ under light irradiation.

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

Singlet Oxygen "Afterglow" Therapy with NIR-II Fluorescent Molecules

Improving singlet oxygen (1 O2 ) lifespan by fractionated delivery in dark and hypoxic conditions is a better way to achieve enhanced phototherapeutic efficacy. Herein, three boron dipyrromethene (BODIPY) dyes are synthesized to demonstrate that anthracence-functionalized BODIPY, namely ABDPTPA is an efficient heavy-atom-free photosensitizer for the reversible capture and release of 1 O2 . The spin-orbit charge-transfer intersystem crossing of ABDPTPA promises a high 1 O2 quantum yield of 60% in dichloromethane. Under light irradiation, the anthracene group reacts with 1 O2 to produce endoperoxide. Interestingly, after termination of irradiation, the endoperoxide undergoes thermal cycloreversion to produce 1 O2 , and regenerates the anthracene module to achieve 1 O2 "afterglow," which results in a prolonged half lifetime of 1 O2 for 9.2 min. In vitro cytotoxicity assays indicate that ABDPTPA nanoparticles have a low half-maximal inhibitory concentration (IC50 ) of 3.6 µg mL-1 on U87MG cells. Further, the results of near-infrared-II fluorescence-imaging-guided phototherapy indicate that ABDPTPA nanoparticles can inhibit tumor proliferation even at a low dose (200 µg mL-1 , 100 µL) without any side effects. Therefore, the study provides a generalized 1 O2 "afterglow" strategy to enhance phototheranostics for complete tumor regression.

A bright, red-emitting water-soluble BODIPY fluorophore as an alternative to the commercial Mito Tracker Red for high-resolution mitochondrial imaging

With the emergence and rapid development of super-resolution fluorescence microscopy, monitoring of mitochondrial morphological changes has aroused great interest for exploring the role of mitochondria in the process of cell metabolism. However, in the absence of water-soluble, photostable and low-toxicity fluorescent dyes, ultra-high-resolution mitochondrial imaging is still challenging. Herein, we designed two fluorescent BODIPY dyes, namely Mito-BDP 630 and Mito-BDP 760, for mitochondrial imaging. The results proved that Mito-BDP 760 underwent aggregation-caused quenching (ACQ) in the aqueous matrix owing to its hydrophobicity and was inaccessible to the cells, which restricted its applications in mitochondrial imaging. In stark contrast, water-soluble Mito-BDP 630 readily penetrated cellular and mitochondrial membranes for mitochondrial imaging with high dye densities under wash-free conditions as driven by membrane potential. As a comparison, Mito Tracker Red presented high photobleaching (the fluorescence intensity dropped by nearly 50%) and high phototoxicity after irradiation by a laser for 30 min. However, Mito-BDP 630 possessed excellent biocompatibility, photostability and chemical stability. Furthermore, clear and bright mitochondria distribution in living HeLa cells after incubation with Mito-BDP 630 could be observed by CLSM. Convincingly, the morphology and cristae of mitochondria could be visualized using an ultra-high-resolution microscope. In short, Mito-BDP 630 provided a powerful and convenient tool for monitoring mitochondrial morphologies in living cells. Given the facile synthesis, photobleaching resistance and low phototoxicity of Mito-BDP 630, it is an alternative to the commercial Mito Tracker Red.

A Structure-Activity Relationship Study of Bimodal BODIPY-Labeled PSMA-Targeting Bioconjugates

The aim of this study was to identify a high-affinity BODIPY peptidomimetic that targets the prostate-specific membrane antigen (PSMA) as a potential bimodal imaging probe for prostate cancer. For the structure-activity study, several BODIPY (difluoroboron dipyrromethene) derivatives with varying spacers between the BODIPY dye and the PSMA Glu-CO-Lys binding motif were prepared. Corresponding affinities were determined by competitive binding assays in PSMA-positive LNCaP cells. One compound was identified with comparable affinity (IC50 =21.5±0.1 nM) to Glu-CO-Lys-Ahx-HBED-CC (PSMA-11) (IC50 =18.4±0.2 nM). Radiolabeling was achieved by Lewis-acid-mediated 19 F/18 F exchange in moderate molar activities (∼0.7 MBq nmol-1 ) and high radiochemical purities (>99 %) with mean radiochemical yields of 20-30 %. Cell internalization of the 18 F-labeled high-affinity conjugate was demonstrated in LNCaP cells showing gradual increasing PSMA-mediated internalization over time. By fluorescence microscopy, localization of the high-affinity BODIPY-PSMA conjugate was found in the cell membrane at early time points and also in subcellular compartments at later time points. In summary, a high-affinity BODIPY-PSMA conjugate has been identified as a suitable candidate for the development of PSMA-specific dual-imaging agents.

A Concise Route to Water-Soluble 2,6-Disubstituted BODIPY-Carbohydrate Fluorophores by Direct Ferrier-Type C-Glycosylation

Novel, linker-free, BODIPY-carbohydrate derivatives containing sugar residues at positions C2 and C6 are efficiently obtained by, hitherto unreported, Ferrier-type C-glycosylation of 8-aryl-1,3,5,7-tetramethyl BODIPYs with commercially available tri-O-acetyl-d-glucal followed by saponification. This transformation, which involves the electrophilic aromatic substitution (S_EAr) of the dipyrrin framework with an allylic oxocarbenium ion, provides easy access to BODIPY-carbohydrate hybrids with excellent photophysical properties and a weaker tendency to aggregate in concentrated water solutions.

Near-Infrared absorbing J-Aggregates of boron dipyrromethene for high efficient photothermal therapy

Constructing bioactive materials remains a big challenge through the aggregates of molecules. Herein, a boron dipyrromethene (BODIPY) derivative containing three nitro groups (BDP-(NO₂)₃) was synthesized, which displays the characteristic of J-aggregate with pronounced red-shifted absorption in nonpolar solvent and aqueous media. The bathochromic shift from 635 to 765 nm facilitates photothermal transition upon the irradiation of near-infrared (NIR) light. Interestingly, BDP-(NO₂)₃ nanoparticles (NPs) fabricated from BDP-(NO₂)₃ and poly(oxyethylene)-poly(oxypropylene) copolymer (F-127), still exhibit obvious J-aggregate, which possess the merits of hydrophilicity, NIR absorption, high photothermal conversion efficiency, excellent biosafety, and can behave as unique candidates for photothermal therapy. In vitro and in vivo experiments validate that BDP-(NO₂)₃ NPs can effectively suppress the proliferation of cancer cells and lead to tumor ablation. This assembly method would be a generic and efficient mode for reasonable design of functional nanomaterials, and could inspire more study on aggregates of organic molecules.

GlycoBODIPYs: Sugars Serving as a Natural Stock for Water-soluble Fluorescent Probes of Complex Chiral Morphology

A range of unprocessed, reducing sugar substrates (mono-, di-, and trisaccharides) is shown to take part in a straightforward four-step synthetic route to water-soluble, uncharged BODIPY derivatives with unimpaired chiral integrity and high fluorescence efficiency. A wide compatibility with several postfunctionalizations is demonstrated, thus suggesting a universal utility of the multifunctional glycoconjugates, which we call GlycoBODIPYs. Knoevenagel condensations are able to promote a red-shift in the spectra, thereby furnishing strongly fluorescent red and far-red glycoconjugates of high hydrophilicity. The synthetic outcome was studied by X-ray crystallography and by comprehensive photophysical investigations in several solvent systems. Furthermore, cell experiments illustrate efficient cell uptake and demonstrate differential cell targeting as a function of the integrated chiral information.

Genetically Encoded Supramolecular Targeting of Fluorescent Membrane Tension Probes within Live Cells: Precisely Localized Controlled Release by External Chemical Stimulation

To image membrane tension in selected membranes of interest (MOI) inside living systems, the field of mechanobiology requires increasingly elaborated small-molecule chemical tools. We have recently introduced HaloFlipper, i.e., a mechanosensitive flipper probe that can localize in the MOI using HaloTag technology to report local membrane tension changes using fluorescence lifetime imaging microscopy. However, the linker tethering the probe to HaloTag hampers the lateral diffusion of the probe in all the lipid domains of the MOI. For a more global membrane tension measurement in any MOI, we present here a supramolecular chemistry strategy for selective localization and controlled release of flipper into the MOI, using a genetically encoded supramolecular tag. SupraFlippers, functionalized with a desthiobiotin ligand, can selectively accumulate in the organelle having expressed streptavidin. The addition of biotin as a biocompatible external stimulus with a higher affinity for Sav triggers the release of the probe, which spontaneously partitions into the MOI. Freed in the lumen of endoplasmic reticulum (ER), SupraFlippers report the membrane orders along the secretory pathway from the ER over the Golgi apparatus to the plasma membrane. Kinetics of the process are governed by both the probe release and the transport through lipid domains. The concentration of biotin can control the former, while the expression level of a transmembrane protein (Sec12) involved in the stimulation of the vesicular transport from ER to Golgi influences the latter. Finally, the generation of a cell-penetrating and fully functional Sav-flipper complex using cyclic oligochalcogenide (COC) transporters allows us to combine the SupraFlipper strategy and HaloTag technology.

Mitochondria-Targeted BODIPY Nanoparticles for Enhanced Photothermal and Photoacoustic Imaging In Vivo

Short-wavelength absorption and emission (<600 nm), hydrophobicity, and low selectivity have greatly restricted the biomedical applications of BODIPY. Herein, a series of mitochondria-targeted BODIPY nanoparticles with a cationic triphenylphosphine (TPP) group (Mito-BDP1-5 NPs) bearing different lengths of ethylene glycol (0-4 units), along with HO-BDP5 without a cationic TPP group for comparison, have been rationally designed and prepared to investigate the interplay between their structures and the related properties. Our studies found that Mito-BDP1-4 NPs showed a tendency of aggregation and precipitation while Mito-BDP5 NPs could be stable in aqueous solutions. Compared with HO-BDP5, tailor-made Mito-BDP5 possessed a high photothermal conversion efficiency (PCE) of 76.6 vs 9.0% and exhibited the highest photoinduced cytotoxicity. Upon NIR irradiation, the temperature induced by Mito-BDP5 NPs increased rapidly from room temperature to 76.0 °C in vitro and 50.0 °C at the tumor site in vivo within 5 min. Furthermore, effective mitochondrial imaging in vitro, photothermal imaging (PTI), and photoacoustic imaging (PAI) in vivo were achieved. In this paper, we developed tailor-made photothermal agents for targeting mitochondria and enhancing the PTI and PAI performances, which could be potentially applied in clinical precision theranostics.

BODIPY-based monofunctional Pt (II) complexes for specific photocytotoxicity against cancer cells

Photodynamic therapy (PDT) has attracted extensive attention in cancer treatment because of its minimum trauma, less side effects, and so on. Photosensitizers, as one of the core elements of PDT, usually have to face problems such as poor water solubility and light stability, lack of targeting, and other problems, which seriously affect the therapeutic effect. In this work, two BODIPY (boron-dipyrromethene)-based monofunctional Pt (II) complexes, 1a and 2a, were designed and synthesized, and their PDT effect was studied. The Pt atom improved the singlet oxygen quantum yield (0.19 for 1a and 0.14 for 2a, respectively), which effectively improves the efficiency of PDT. MTT assay confirmed that the short time photo-irradiation distinctly promoted antitumor cytotoxicity of Pt (II) compounds against different cell lines. For 1a under irradiation, the IC₅₀ value of cancer cell lines were 13.1 μM for HeLa cells and 7.6 μM for MCF-7 cells, while those of normal cell lines were 32.4 μM for HBL-100 cells and 48.6 μM for L02 cells. The results demonstrated that 1a showed specific phototoxicity to cancer cells. This specific selectivity could be attributed to the synergistic effect of increased cellular uptake (determined by ICP-MS) and higher ROS generation (detected by Cell ROX Deep Red) in cancer cells after irradiation. This study laid the foundation for the future design and synthesis of effective PDT photosensitizers.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

Acetonitrilated Unsymmetric BODIPYs having glycine fluorescence responsive quenching: Design, synthesis and spectroscopic properties

A series of novel N≡C-CH₂-B-F system BODIPY were designed and synthesized by introducing aldehyde and acetonitrile units which gave positive influence to spectroscopic and chemical properties of BODIPY derivatives. The effects of glycine (Gly) on the target products were studied via ultraviolet and visible spectrophotometry (UV-Vis) and photoluminescence (PL) under different conditions of the presence and absence of cations (K⁺, Ca²⁺, Zn²⁺). It was showed that glycine has an intense quenching effect on the compounds in both the presence and absence of ions with a dramatic color change from notable red to light orange owing to the addition of Gly. With regard to cells imaging investigation, the products showed the prominent fluorescence in cholangiocarcinoma cells. The luminescent effect of compounds 1 and 3 entering the cells was significantly stronger than that of compound 2. In addition, pertaining to anticancer properties, two human cancer cell lines (RBE, HCCC-9810) and one normal cell line (L-02) were evaluated for in vitro cytotoxicity. The target compounds, 1-3, exhibited moderate antitumor activity, of which compound 1 was found to be the most potent derivative with IC₅₀ values of 119.31 ± 6.25, 114.73 ± 3.25, and 106.33 ± 5.22 against RBE, HCCC-9810, and L-02 cells, respectively, slightly weaker than the positive control 5-FU.

Near-Infrared Laser-Triggered In Situ Dimorphic Transformation of BF2-Azadipyrromethene Nanoaggregates for Enhanced Solid Tumor Penetration

The shape of a drug delivery system impacts its in vivo behavior such as circulation time, accumulation, and penetration. Considering the advantages of functional dyes in bioapplications, we synthesize a class of nanoaggregates based on BF₂-azadipyrromethene (aza-BODIPY) dyes, which can realize long blood circulation and deep tumor penetration simultaneously in vivo through morphological transformation modulated by a near-infrared (NIR) laser. First, when the temperature increases, the wormlike nanofibers of the aza-BODIPY-1 aggregate, possessing a long blood circulation time, can be transformed into spherical nanoparticles, which are conducive to increasing the penetration in the solid tumor. Second, without any postmodification, the nanofibers exhibit an outstandingly narrow absorption band in the NIR spectral range, so that they possess ideal photothermal properties. Through 655 nm laser irradiation, the intrinsic photothermal effect causes a local temperature increase to ∼48 °C, realizing the transformation of 1-NFs to 1-NPs. Third, the morphological transformation is real-time detected by photoacoustic (PA) imaging. By monitoring the change of the PA signal at a specific wavelength, the in vivo deformation process of nanomaterials can be traced. Consequently, the in situ morphology transformation of aza-BODIPY-based nanomaterials can simultaneously realize long blood circulation and deep penetration, resulting in the enhanced antitumor outcome.