Dual-site lysosome-targeted fluorescent sensor for fast distinguishing visualization of HClO and ONOO- in living cells and zebrafish

As two of important highly reactive species / nitrogen species, hypochloric acid (HClO) and peroxynitrite (ONOO-) are involved in various pathological and physiological processes, which are important factors that affect and reflect the functional state of lysosome. Nevertheless, many of their roles are still indefinite because of lack of suitable analytical methods for HClO and ONOO- detection in lysosome. Herein, we designed a lysosome-targeted probe to monitor HClO and ONOO-, which was a hydrid of the benzothiazole derivative, methyl thioether (HClO recognition site) and morpholino hydrazone (ONOO- recognition and lysosome target site). The probe exhibited high sensitivity, good selectivity and fast response toward HClO and ONOO- without spectral crosstalk, and can be employed for quantitative monitoring HClO and ONOO- with LOD of 63 and 83 nM, respectively. In addition, the dual-site probe was lysosome targetable and could be used for detection of HClO and ONOO- in living cells. Furthermore, the excellent behavior made it was suitable for imaging of HClO and ONOO- in zebrafish. Thus, the present probe provides a potent tool for distinguishing monitoring HClO and ONOO- and exploring the role of HClO and ONOO- in biological systems.

A lysosome-targeted fluorescent probe for fluorescence imaging of hypochlorous acid in living cells and in vivo

Lysosomes, as crucial acidic organelles in cells, play a significant role in cellular functions. The levels and distribution of hypochlorous acid (HOCl) within lysosomes can profoundly impact their biological functionality. Hence, real-time monitoring of the concentration of HOCl in lysosomes holds paramount importance for further understanding various physiological and pathological processes associated with lysosomes. In this study, we developed a bodipy-based fluorescent probe derived from pyridine and phenyl selenide for the specific detection of HOCl in aqueous solutions. Leveraging the probe's sensitive photoinduced electron transfer effect from phenyl selenide to the fluorophore, the probe exhibited satisfactory high sensitivity (with a limit of detection of 5.2 nM and a response time of 15 s) to hypochlorous acid. Further biological experiments confirmed that the introduction of the pyridine moiety enabled the probe molecule to selectively target lysosomes. Moreover, the probe successfully facilitated real-time monitoring of HOCl in cell models stimulated by N-acetylcysteine (NAC) and lipopolysaccharide (LPS), as well as in a normal zebrafish model. This provides a universal method for dynamically sensing HOCl in lysosomes.

Lysosome-targeted Aza-BODIPY photosensitizers for anti-cancer photodynamic therapy

Developing effective near-infrared (NIR) photosensitizers (PSs) has been an attractive goal of photodynamic therapy (PDT) for cancer treatment. In this study, we synthesized N, N-diethylaminomethylphenyl-containing Aza-BODIPY photosensitizers and comprehensively investigated their photophysical/photochemical properties, as well as cell-based and animal-based anti-tumor studies. Among them, BDP 1 has strong NIR absorption at 680 nm and higher singlet oxygen yield in PBS which showed favorable pH-activatable and lysosome-targeting ability. BDP 1 could be easily taken up by tumor cells and showed negligible dark activity (IC50 > 50 μM), however strong phototoxicity upon exposure to light irradiation. The acceptable fluorescence emission from BDP 1 allowed convenient in vivo fluorescence imaging for organ distribution studies in mice. After PDT treatment with upon single time PDT treatment at the beginning using relatively low light dose (54 J/ cm2), BDP 1 (2 mg/kg, 0.1 mL) was found to have strong efficacy to inhibit tumor growth and even to ablate off tumor without causing body weight loss. Therefore, pH-activatable and lysosome-targeted PS may become an effective way to develop potent PDT agent.

Configurationally regulated half-sandwich iridium(III)-ferrocene heteronuclear metal complexes: Potential anticancer agents

Half-sandwich iridium(III) (IrIII) complexes and ferrocenyl (Fc) derivatives are becoming the research hotspot in the field of anticancer because of their good bioactivity and unique anticancer mechanism different from platinum-based drugs. Then, a series of half-sandwich IrIII-Fc pyridine complexes have been prepared through the structural regulation in this study. The incorporation of half-sandwich IrIII complex with Fc unit successfully improves their anticancer activity, and the optimal performance (IrFc5) is almost 3-fold higher than that of cisplatin against A549 cells, meanwhile, which also shows better anti-proliferative activity against A549/DDP cells. Complexes can aggregate in the intracellular lysosome of A549 cells and induce lysosomal damage, disrupt the cell cycle, increase the level of intracellular reactive oxygen species, and eventually lead to cell apoptosis. Half-sandwich IrIII-Fc heteronuclear metal complexes possess a different anticancer mechanism from cisplatin, which can serve as a potential alternative to platinum-based drugs and show a good application prospect.

Lysosome-targeted cyclometalated iridium(III) complexes: JMJD inhibition, dual induction of apoptosis and autophagy

A series of cyclometalated iridium(III) complexes with the formula [Ir(C^N)2 L](PF6) (C^N = 2-phenylpyridine (ppy, in Ir-1), 2-(2-thienyl)pyridine (thpy, in Ir-2), 2-(2,4-difluorophenyl)pyridine (dfppy, in Ir-3), L = 2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)quinolin-8-ol) were designed and synthesized, which utilize 8-hydroxyquinoline derivative as N^N ligands to chelate the cofactor Fe2+ of the Jumonji domain-containing protein (JMJD) histone demethylase. As expected, the results of UV/Vis titration analysis confirm the chelating capabilities of Ir-1-3 for Fe2+, and molecular docking studies also show that Ir-1-3 can interact with the active pocket of JMJD protein, and treatment of cells with Ir-1-3 results in significant upregulation of trimethylated histone 3 lysine 9 (H3K9Me3), indicating the inhibition of JMJD activity. Meanwhile, Ir-1-3 exhibit much higher cytotoxicity against the tested tumor cell lines compared with the clinical chemotherapeutic agent cisplatin. And Ir-1-3 can block the cell cycle at G2/M phase and inhibit cell migration and colony formation. Further studies show that Ir-1-3 can specifically accumulate in lysosomes, damage the integrity of lysosomes, and induce apoptosis and autophagy. Reduction of mitochondrial membrane potential (MMP) and elevation of reactive oxygen species (ROS) also contribute to the antitumor effects of Ir-1-3. Finally, Ir-1 can inhibit tumor growth effectively in vivo and increase the expression of H3K9Me3 in tumor tissues. Our study demonstrates that these iridium(III) complexes are promising anticancer agents with multiple functions, including the inhibition of JMJD and induction of apoptosis and autophagy.

Two simple but effective turn-on benzothiazole-based fluorescent probes for detecting hydrogen sulfide in real water samples and HeLa cells

Two simple turn-on fluorescent probes, containing a benzothiazole and the 2,4-dinitrobenzenesulfonyl group, were designed for detecting H₂S. Two probes exhibited good selectivity and high sensitivity, which were applied to detect the H₂S in real water samples. Probe P2 with a positive charge had better solubility than probe P1 in water; therefore, probe P2 was successfully applied to detect both the endogenous and exogenous H₂S in lysosomes of living HeLa cells.

Synthesis and biological evaluation of zwitterionic half-sandwich Rhodium(III) and Ruthenium(II) organometallic complexes

Herein we present the synthesis and characterization of a panel of structurally related zwitterionic piano-stool rhodium(III) and ruthenium(II) complexes. The identities of these novel complexes have been determined by NMR spectroscopy, mass spectrometry, elemental analysis and single-crystal X-ray crystallography. The stability and fluorescence property of these zwitterionic complexes were also confirmed. Zwitterionic rhodium(III) complexes Rh1-Rh4 displayed potent cytotoxic activity against A549 and HeLa human cancer cells. On the contrary, zwitterionic ruthenium(II) complexes Ru1-Ru4 presented no obvious cytotoxic activity to the test cell lines. Moreover, the trend that the introduction of fluorinated substituent and phenyl ring in the η⁵-Cp^R ring and N,N-chelating ligand, respectively, could enhance the cytotoxicity of these zwitterionic rhodium(III) complexes, were observed. The exploration of mechanism using flow cytometry displayed that the cytotoxicity of these rhodium(III) complexes was associated with the perturbation of the cell cycle and the induction of cell apoptosis. Furthermore, microscopic analysis using confocal microscopy indicated that the representative rhodium(III) complex Rh4 entered A549 cells via energy-dependent pathway and predominantly accumulated in lysosomes, thus leading to the disruption of lysosomal integrity.

A lysosome-targeted fluorescent probe for the specific detection and imaging of formaldehyde in living cells

We presented herien the rational design, synthesis, and photophysical property studies of the lysosome-targeted fluorescence FA probe NP-Lyso, an isopropyl group modified ortho-diaminonaphthalimide derivative. After the reaction of FA and ortho-phenylenediamine modified with the isopropyl group in NP-Lyso, the probe exhibited favorable features such as a large fluorescence enhancement, specific selectivity and high sensitivity for the detection of FA. More importantly, NP-Lyso could be used to detect and image endogenous FA in lysosomes. In light of these prominent properties, we envision that NP-Lyso will be an efficient optical imaging approach for investigating the biofunctions of FA in living systems.

A fluorescent probe for specific detection of cysteine in lysosomes via dual-color mode imaging

Biothiols, as part of the reactive sulfur species (RSS), are a class of bioactive molecules that play important physiological roles in human body. However, due to the similarity in structure and reaction sites of biothiols, it is difficult to differentiated detection them at the same time. In this work, a fluorescent probe CM-NBD combined coumarin derivative and 7-nitrobenzofurazan has been developed, which can effectively detect biothiols through simple ether cleavage. Because of a specific location group, CM-NBD can well localize in lysosomes with a high co-localization coefficient. Interesting, due to the weakly acidic environment of lysosomes, Cys can be distinguished from Hcy/GSH and H₂S via dual-color mode. The probe is able not only to image exogenous biothiols but also to discriminate Cys from Hcy/GSH and H₂S in cells and zebrafish model.

A turn-on and lysosome-targeted fluorescent NO releaser in water media and its application in living cells and zebrafishes

Due to the high activity and difficult to transport of nitric oxide, the controlled release of nitric oxide has been a new trend in the research on the biological effect of nitric oxide. In this paper, a water-soluble and turn-on fluorescent NO donor Rh-NO was synthesized. Upon 525 nm irradiation, the fluorescence of the Rh-NO at 568 nm enhanced with the quantum yield (Φ_F) of Rh-NO changing from 5.08% to 35.96%. The mechanism of NO releasing was proved by HRMS and the Dan. The releasing time of 6 min and the releasing yield of 0.61 proved the superiority of Rh-NO. Excellent cell activity above 80% of Rh-NO and Rh guaranteed that nitric oxide was released from Rh-NO in lysosome and zebrafishes successfully, which provided a good platform to understand the biological effects of nitric oxide in lysosomes.

A lysosome-targeted ratiometric fluorescent probe with a large blue shift for monitoring hypochlorous acid in living cells and zebrafish

A new phenothiazine derivative as lysosome-targeted fluorescent probe with a large blue-shift (128 nm) for ClO^- detection in a fine ratiometric manner has been designed and synthesized. Probe Lyso-PTB has remarkable fluorescence ratiometric variations (98-fold), low cytotoxicity, rapid response time (50 s) and a low detection limit (23 nM). In particular, the application of Lyso-PTB for ClO^- detection was successfully demonstrated in lysosome and in zebrafish.

Peptide-capped functionalized Ag/Au bimetal nanoclusters with enhanced red fluorescence for lysosome-targeted imaging of hypochlorite in living cells

Bioimaging probes for monitoring intracellular reactive oxygen species have important implications for cell biology research. Herein, we developed peptide-capped silver/gold nanoclusters (peptide@Ag/Au NCs) for lysosome-targeted imaging of hypochlorite (ClO^-). The peptide@Ag/Au NCs were synthesized via a one-pot method using peptide as both a template and a reducing agent. The fluorescence intensity and absolute quantum yield of peptide@Ag/Au NCs were much higher than those of peptide-capped gold nanoclusters and silver nanoclusters. In the presence of ClO^-, the fluorescence of peptide@Ag/Au NCs was quenched, accompanied by a redshift due to ClO^--induced oxidation of the peptide ligand and decreased Ag content in Ag/Au NCs. The relative fluorescence intensity F₀/F had favourable linearity for ClO^- concentrations in the range 0.1-100 μmol/L (R² = 0.9954), with a detection limit (LOD) of 80 nmol/L. The lysosome-targeted peptide@Ag/Au NCs were applied to detect ClO^- in lysosomes in living cells via fluorescence imaging.

Molecular engineering of a colorimetric two-photon fluorescent probe for visualizing H2S level in lysosome and tumor

As a multifunctional signaling molecule, hydrogen sulfide (H₂S) plays an essential role in diverse physiological and pathological processes. The two-photon fluorescence probes detecting H₂S selectively in vivo could be useful tools to better study the mechanism of diseases. Then, an efficient two-photon lysosome-specific probe 1 has been developed to detect endogenous H₂S in living cells and mice. Probe 1 displays excellent properties with 28-fold fluorescence enhancement, marked color changes in naked-eye and fluorescence, high selectivity and sensitivity, and low detection limit (0.22 μM) to H₂S. These remarkable properties of probe 1 enable its practical applications in detecting H₂S in environment (wastewater) and food (beer). Moreover, as a two-photon probe under near infrared excitation at 790 nm, probe 1 can monitor the level changes of endogenous H₂S of lysosome and tumor in living system with good membrane permeability and high imaging resolution. Specially, the probe detecting H₂S distribution in lysosome could provide more evidences to explain the association of target-organelle and H₂S.

Instantaneous fluorescent probe for the specific detection of H2S

Novel cyanine-based fluorescent probes for the detection of H₂S were developed. The probes developed are stable under physiological conditions. The water soluble fluorescent probe 2 displayed ultrafast and specific response to H₂S displaying NIR fluorescence of 115-fold turn-on with the detection limit of 11 nM without assistance of organic solvent or surfactant. Cell imaging experiments indicated that probe 2 was cell-permeable and was able to detect H₂S sensitively in lysosomes. Moreover, our probe was able to detect H₂S intrinsically produced H₂S through enzymatic/non-enzymatic biosynthetic pathway from Cys/GSH. Moreover, we applied probe 2 to detect H₂S in living mice and demonstrated the fast metabolism of H₂S. Thus, probe 2 shows great promise as a reporter for H₂S.

Lysosome-targeted two-photon fluorescent probe for detection of hypobromous acid in vitro and in vivo

It is found that hypobromous acid (HOBr) can affect the activity of type IV collagen. Herein, we synthesized a lysosome-targeted fluorescence probe NA-lyso based on Suzuki coupling reaction with naphthalimide as a fluorescent group. HOBr can oxidize the amino group and methylthio group, which increased the degree of conjugation of the probe, thereby affecting its optical properties. Accordingly, it can establish a method for the specific detection of HOBr. NA-lyso has the properties including fast response, high fluorescence quantum yield (Φ = 59.17%), high selectivity, low cytotoxicity and good membrane-permeability. The probe can locate to lysosome of cells. The potential of the probe as biosensor for HOBr was demonstrated by imaging of exogenous and endogenous HOBr in living cells and in mice. In consequence, NA-lyso is expected to be a powerful tool to detect HOBr in complex biosystem and provides a means of exploring physiological functions associated with HOBr in living organisms.