Near-infrared fluorescence probes for enzymes based on binding affinity modulation of squarylium dye scaffold.

We present a novel design strategy for near-infrared (NIR) fluorescence probes utilizing dye-protein interaction as a trigger for fluorescence enhancement. The design principle involves modification of a polymethine dye with cleavable functional groups that reduce the dye's protein-binding affinity. When these functional groups are removed by specific interaction with the target enzymes, the dye's protein affinity is restored, protein binding occurs, and the dye's fluorescence is strongly enhanced. To validate this strategy, we first designed and synthesized an alkaline phosphatase (ALP) sensor by introducing phosphate into the squarylium dye scaffold; this sensor was able to detect ALP-labeled secondary antibodies in Western blotting analysis. Second, we synthesized a probe for ß-galactosidase (widely used as a reporter of gene expression) by means of ß-galactosyl substitution of the squarylium scaffold; this sensor was able to visualize ß-galactosidase activity both in vitro and in vivo. Our strategy should be applicable to obtain NIR fluorescence probes for a wide range of target enzymes.

Rational design of boron dipyrromethene (BODIPY)-based photobleaching-resistant fluorophores applicable to a protein dynamics study.

We studied the photobleaching of a library of boron dipyrromethene (BODIPY) derivatives with a range of electron densities, and found that the photobleaching rate is influenced by the electron-withdrawing capacity of the substituents. Electron-deficient BODIPYs generated less singlet oxygen, were less reactive to singlet oxygen, and were highly resistant to photobleaching. We confirmed the utility of one of these fluorophores, 2,6-diCO(2)R-BDP, for visualizing EGF receptor dynamics in cells expressing an SNAP-tagged EGF receptor.

Positive correlation between the generation of reactive oxygen species and activation/reactivation of transgene expression after hydrodynamic injections into mice.

PURPOSE: Hydrodynamic injection has been shown to reactivate silenced transgene expression in mouse liver. In this study, the roles of inflammatory cytokines and reactive oxygen species (ROS) in the reactivation were examined. METHODS: Production of inflammatory cytokines and ROS by hydrodynamic injection of saline was examined in mice that had received a hydrodynamic injection of a plasmid expressing Gaussia luciferase. The level of reporter gene expression was used as an indicator of the reactivation. The involvement of cytokines and ROS was examined by depleting Kupffer cells or by pre-administration of antioxidants, respectively. RESULTS: A hydrodynamic injection of saline induced a significant production of interleukin (IL)-6. Depleting Kupffer cells using clodronate liposomes markedly reduced the IL-6 production but had no significant effect on the transgene expression. On the other hand, an injection of catalase or N-acetylcysteine significantly inhibited the hydrodynamic injection-induced reactivation of silenced transgene expression. The silenced expression was also reactivated by carbon tetrachloride, an inducer of oxidative stress in the liver, in a dose-dependent manner, and this reactivation was significantly inhibited by catalase. CONCLUSIONS: These findings show a positive correlation between the generation of ROS and the reactivation of silenced transgene expression after hydrodynamic injections.

Hypoxia-sensitive fluorescent probes for in vivo real-time fluorescence imaging of acute ischemia.

Based on the findings that the azo functional group has excellent properties as the hypoxia-sensor moiety, we developed hypoxia-sensitive near-infrared fluorescent probes in which a large fluorescence increase is triggered by the cleavage of an azo bond. The probes were used for fluorescence imaging of hypoxic cells and real-time monitoring of ischemia in the liver and kidney of live mice.

Development and application of a near-infrared fluorescence probe for oxidative stress based on differential reactivity of linked cyanine dyes.

Reactive oxygen species (ROS) operate as signaling molecules under various physiological conditions, and overproduction of ROS is involved in the pathogenesis of many diseases. Therefore, fluorescent probes for visualizing ROS are promising tools with which to uncover the molecular mechanisms of physiological and pathological processes and might also be useful for diagnosis. Here we describe a novel fluorescence probe, FOSCY-1, operating in the physiologically favorable near-infrared region. The probe consists of two differentially ROS-reactive cyanine dyes connected by a linker; reaction of the more susceptible dye with ROS releases intramolecular fluorescence quenching of the less susceptible dye. We successfully applied this probe to detect ROS produced by HL60 cells and porcine neutrophils and for imaging oxidative stress in a mouse model of peritonitis.