Fluorescence-Based Assay for Carbonic Anhydrase Inhibitors

Ru(ii)/Os(ii)-based carbonic anhydrase inhibitors as photodynamic therapy photosensitizers for the treatment of hypoxic tumours

Photodynamic therapy (PDT) is a medical technique for the treatment of cancer. It is based on the use of non-toxic molecules, called photosensitizers (PSs), that become toxic when irradiated with light and produce reactive oxygen specious (ROS) such as singlet oxygen (1O2). This light-induced toxicity is rather selective since the physician only targets a specific area of the body, leading to minimal side effects. Yet, a strategy to improve further the selectivity of this medical technique is to confine the delivery of the PS to cancer cells only instead of spreading it randomly throughout the body prior to light irradiation. To address this problem, we present here novel sulfonamide-based monopodal and dipodal ruthenium and osmium polypyridyl complexes capable of targeting carbonic anhydrases (CAs) that are a major target in cancer therapy. CAs are overexpressed in the membrane or cytoplasm of various cancer cells. We therefore anticipated that the accumulation of our complexes in or outside the cell prior to irradiation would improve the selectivity of the PDT treatment. We show that our complexes have a high affinity for CAs, accumulate in cancer cells overexpressing CA cells and importantly kill cancer cells under both normoxic and hypoxic conditions upon irradiation at 540 nm. More importantly, Os(ii) compounds still exhibit some phototoxicity under 740 nm irradiation under normoxic conditions. To our knowledge, this is the first description of ruthenium/osmium-based PDT PSs that are CA inhibitors for the selective treatment of cancers.

Sub-100 ms Level Ultrafast Detection and Near-Infrared Ratiometric Fluorescence Imaging of Norepinephrine in Live Neurons and Brains

Norepinephrine (NE) is a key neurotransmitter in the central and sympathetic nervous systems, whose content fluctuates dynamically and rapidly in various brain regions during different physiological and pathophysiological processes. However, it remains a great challenge to directly visualize and precisely quantify the transient NE dynamics in living systems with high accuracy, specificity, sensitivity, and, in particular, high temporal resolution. Herein, we developed a series of small-molecular probes that can specifically detect NE through a sequential nucleophilic substitution-cyclization reaction, accompanied by a ratiometric near-infrared fluorescence response, within an impressively short time down to 60 ms, which is 3 orders of magnitude faster than that of present small-molecular probes. A unique water-promoted intermolecular proton transfer mechanism is disclosed, which dramatically boosted the recognition kinetics by ∼680 times. Benefiting from these excellent features, we quantitatively imaged the transient endogenous NE dynamics under external stimuli at the single living neuron level and further revealed the close correlations between NE fluctuations and Parkinson's disease pathology at the level of acute brain slices and live mouse brains in vivo.

Imaging of Carbonic Anhydrase Level in Epilepsy with an Environment-Sensitive Fluorescent Probe

Carbonic anhydrases (CAs) participate in various physiological and pathological activities by catalyzing the interconversion between carbon dioxide and bicarbonate ions. Under normal circumstances, they guarantee that the relevant biological reactions in our body occur within an appropriate time scale. Abnormal expression or activity alteration of CAs is closely related to the pathogenesis of diverse diseases. This work reports an inhibitor-directed fluorescent probe FMRs-CA for the detection of CAs. Excellent selectivity, favorable biocompatibility, and desirable blood-brain barrier (BBB) penetration endow the probe with the ability to image the fluctuation of CAs in cells and mice. We achieved in situ visualization of the increased CAs in hypoxic cells with this probe. Additionally, probe FMRs-CA was mainly enriched within the liver and gradually metabolized by the liver. With the help of FMRs-CA, the increase of CAs in epileptic mouse brains was revealed first from the perspective of imaging, providing the mechanism connection between abnormal CA expressions and epilepsy.

Two-photon fluorescence imaging and specifically biosensing of norepinephrine on a 100-ms timescale

Norepinephrine (NE) is a key neurotransmitter in the central nervous system of organisms; however, specifically tracking the transient NE dynamics with high spatiotemporal resolution in living systems remains a great challenge. Herein, we develop a small molecular fluorescent probe that can precisely anchor on neuronal cytomembranes and specifically respond to NE on a 100-ms timescale. A unique dual acceleration mechanism of molecular-folding and water-bridging is disclosed, which boosts the reaction kinetics by ˃10⁵ and ˃10³ times, respectively. Benefiting from its excellent spatiotemporal resolution, the probe is applied to monitor NE dynamics at the single-neuron level, thereby, successfully snapshotting the fast fluctuation of NE levels at neuronal cytomembranes within 2 s. Moreover, two-photon fluorescence imaging of acute brain tissue slices reveals a close correlation between downregulated NE levels and Alzheimer's disease pathology as well as antioxidant therapy.

Efficient discovery of potent α-glucosidase inhibitors from Paeoniae lactiflora using enzyme-MOF nanocomposites and competitive indicators

A great deal of attention has been paid to the seeds of Paeoniae lactiflora pall., an underutilized food resource, since its extract exhibits excellent α-glucosidase (GAA) inhibitory activity. In the present study, to gain further insight into this plant and find out potent GAA inhibitors, we established a novel ligand fishing strategy by introducing a competitive inhibitor as an indicator. After the successful establishment of this approach was verified by a series of methods, including kinetic assay, fluorescence determination, and HPLC, the newly developed ligand fishing method was applied to acquire potent GAA inhibitors from P. lactiflora seeds. Nine bioactive compounds were captured, and seven of them were identified as suffruticosol A, suffruticosol B, resveratrol, vitisin E, luteolin, trans-δ-viniferin, and ampelopsin E. The data of their GAA inhibitory activity demonstrated that these constituents were vigorously active against GAA with IC₅₀ values of 1.67-30.47 μM, while such value of 1-DNJ was 228.77 μM. Among them, vitisin E and ampelopsin E were reported to show such inhibitory activity for the first time. Collectively, our findings provide valuable clues for the further utilization of P. lactiflora seeds as a functional food, and offer a new avenue for acquiring potent inhibitors from natural resources.

Pillar[5]arene-Based Fluorescent Sensor Array for Biosensing of Intracellular Multi-neurotransmitters through Host-Guest Recognitions

Neurotransmitters are very important for neuron events and brain diseases. However, effective probes for analyzing specific neurotransmitters are currently lacking. Herein, we design and create a supramolecular fluorescent probe (CN-DFP5) by synthesizing a dual-functionalized fluorescent pillar[5]arene derivative with borate naphthalene and aldehyde coumarin recognition groups to identify large-scale neurotransmitters. The developed probe can detect seven model neurotransmitters by generating different fluorescence patterns through three types of host-guest interactions. The obtained signals are statistically processed by principal component analysis, thus the high-throughput analysis of neurotransmitters is realized under dual-channel fluorescence responses. The present probe combines the advantages of small-molecule-based probes to easily enter into living neurons and cross-reactive sensor arrays. Thus, the selective binding enables this probe to identify specific neurotransmitters in biofluids, living neurons, and tissues. High selectivity and sensitivity further demonstrate that the molecular device could extend to more applications to detect and image neurotransmitters.

Machine Learning-Assisted Pattern Recognition of Amyloid Beta Aggregates with Fluorescent Conjugated Polymers and Graphite Oxide Electrostatic Complexes

Five fluorescent positively charged poly(para-aryleneethynylene) (P1-P5) were designed to construct electrostatic complexes C1-C5 with negatively charged graphene oxide (GO). The fluorescence of conjugated polymers was quenched by the quencher GO. Three electrostatic complexes were enough to distinguish between 12 proteins with 100% accuracy. Furthermore, using these sensor arrays, we could identify the levels of Aβ40 and Aβ42 aggregates (monomers, oligomers, and fibrils) via employing machine learning algorithms, making it an attractive strategy for early diagnosis of Alzheimer's disease.

Excimer-monomer fluorescence changes by supramolecular disassembly for protein sensing and quantification

A protein binding-induced supramolecular dissociation strategy is developed with the ratio of monomer and excimer fluorescence as the tool for protein sensing and quantification. Due to the "lock-and-key" strategy based on specific ligand-protein binding, the probe exhibits excellent selectivity and quantification accuracy to the protein of interest. The ratiometric approach is immune to interference from extrinsic quenchers, while preserving the opportunity to be protein specific.

7-Hydroxycoumarins Are Affinity-Based Fluorescent Probes for Competitive Binding Studies of Macrophage Migration Inhibitory Factor

Macrophage migration inhibitory factor (MIF) is a cytokine with key roles in inflammation and cancer, which qualifies it as a potential drug target. Apart from its cytokine activity, MIF also harbors enzyme activity for keto–enol tautomerization. MIF enzymatic activity has been used for identification of MIF binding molecules that also interfere with its biological activity. However, MIF tautomerase activity assays are troubled by irregularities, thus creating a need for alternative methods. In this study, we identified a 7-hydroxycoumarin fluorophore with high affinity for the MIF tautomerase active site (K_i = 18 ± 1 nM) that binds with concomitant quenching of its fluorescence. This property enabled development of a novel competition-based assay format to quantify MIF binding. We also demonstrated that the 7-hydroxycoumarin fluorophore interfered with the MIF–CD74 interaction and inhibited proliferation of A549 cells. Thus, we provide a high-affinity MIF binder as a novel tool to advance MIF-oriented research.

Fluorescence Turn-On Response Amplified by Space Confinement in Metal-Organic Frameworks

Sensitive fluorescence turn-on response to specific substances is highly desired for development of chemical sensors and switches. Here we utilized a "two-in-one" strategy to prepare ionic metal-organic frameworks (MOFs) functionalized with the cationic bipyridinium receptors at the frameworks and anionic fluorescent indicators in the pores. The MOFs are rendered a fluorescence-resting state because the indicator's fluorescence is efficiently quenched by the ground-state charge-transfer (CT) complexation between the indicator and receptor. Addition of an alkylamine efficiently turns on the fluorescence because the indicator is displaced by the CT complexation between alkylamine with receptor. The turn-on response is highly specific to alkylamines. The MOFs can be used as recyclable sensors for selective and sensitive detection of alkylamines, with ultralow detection limits (0.5 nM). The fluorescence in solid state can be reversibly switched on and off with high contrast. The sensitive and high-contrast response can be attributed to the space confinement effects of the porous frameworks. The confined space can significantly enhance indicator-receptor and analyte-receptor interactions, and thereby both the quenching efficiency in the off state and the displacement efficiency in the on state are amplified.

A dual-mode nanoprobe for evaluation of the autophagy level affected by photothermal therapy

A novel dual-mode nanoprobe (Apt@MNPS) was created for the detection of autophagy-related miRNAs to monitor the autophagic level and study the effect of PTT on autophagy. Interestingly, using our developed probe, PTT was found to be able to activate the autophagy by down regulation of miR-18a* and miR-4802, which in turn restricted the PTT efficiency for cancer.

Space-confined indicator displacement assay inside a metal-organic framework for fluorescence turn-on sensing

The indicator displacement assay (IDA) is for the first time performed within a metal-organic framework (MOF) to achieve ultrasensitive fluorescence turn-on sensing. A Zr(iv) ion MOF (UiO-67-DQ-PsO) furnished with electron-deficient diquat units (DQ2+, as the receptor) on the wall and electron-rich 1-pyrenesulfonate anions (PsO-, as the fluorescent indicator) in the pores was prepared by postsynthetic anion exchange. The MOF is capable of sensing alkylamines owing to the competing PsO--DQ2+ and alkylamine-DQ2+ charge-transfer interactions, the former interaction causing a fluorescence OFF state and the latter displacing PsO- to trigger its emission. Significant advantages have been demonstrated for the IDA inside the MOF. The turn-on assay exhibits much higher sensitivity and anti-interference than the turn-off sensing using the MOF without indicators (the sensitivity is enhanced by as much as six orders of magnitude to the subnanomolar level). The integration of both the receptor and indicator in the porous solid enables facile regeneration and recyclability of the IDA ensemble. Furthermore, we show that the confined space provided by the MOF significantly enhances the supramolecular interactions to make possible the IDA impossible in solution. This work not only demonstrates a novel conceptual approach to fabricate superior fluorescence turn-on sensors using porous materials but also has important implications for supramolecular chemistry in porous materials.

Pyrrolidinone-bearing methylated and halogenated benzenesulfonamides as inhibitors of carbonic anhydrases

Two series of benzenesulfonamides bearing methyl groups at ortho/ortho or meta/ortho positions and a pyrrolidinone moiety at para position were synthesized and tested as inhibitors of the twelve catalytically active human carbonic anhydrase (CA) isoforms. Observed binding affinities were determined by fluorescent thermal shift assay and intrinsic binding affinities representing the binding of benzenesulfonamide anion to the Zn(II)-bound water form of CA were calculated. Introduction of dimethyl groups into benzenesulfonamide ring decreased the binding affinity to almost all CA isoforms, but gained in selectivity towards one CA isoform. A chloro group at the meta position of 2,6-dimethylbenzenesulfonamide derivatives did not influence the binding to CA I, but it increased the affinity to all other CAs, especially, CA VII and CA XIII (up to 500 fold). The compounds may be used for further development of CA inhibitors with higher selectivity to particular CA isoforms.