Nitroreductase Detection and Hypoxic Tumor Cell Imaging by a Designed Sensitive and Selective Fluorescent Probe, 7-[(5-Nitrofuran-2-yl)methoxy]-3H-phenoxazin-3-one

Abstract

A highly selective and sensitive fluorescence probe, 7-[(5-nitrofuran-2-yl)methoxy]-3H-phenoxazin-3-one (1), is developed for imaging the hypoxic status of tumor cells via the indirect detection of nitroreductase. The detection mechanism is based on the fact that nitroreductase can selectively catalyze the reduction of the nitro group in 1 to a hydroxylamine or amino group in the presence of reduced nicotinamide adenine dinucleotide as an electron donor that is indispensable, followed by the 1,6-rearrangement-elimination and the release of resorufin. As a result, the reaction produces a distinct color and fluorescence change from almost colorless and nonfluorescent to pink and strong red fluorescence. The fluorescence increase of probe 1 at λ(550/585 nm) is directly proportional to the concentration of nitroreductase in the range of 15-300 ng/mL, with a detection limit of 0.27 ng/mL. The ready reduction of the nitro group in 1 under hypoxic conditions leads to the establishment of a sensitive and selective fluorescence method for imaging the hypoxic status of tumor cells, and with this method Hela and A549 cells under normoxic and hypoxic conditions (even for different extents of hypoxia) can be differentiated successfully. This method is simple and may be useful for the imaging of disease-relevant hypoxia.

Highly sensitive and fast responsive ratiometric fluorescent probe for Cu2+ based on a naphthalimide-rhodamine dyad and its application in living cell imaging

“…The fluorescence intensity ratio was found to increase linearly with the Cu 2+ concentration in the range of 0-16 μM (Fig. 8) and the detection limit of Cu 2+ was measured to be 18.6 nM [38,39], which were far lower than the WHO recommended value for Cu 2+ (2.0 mg/L) and the U.S. Environment Protection Agency (EPA) set the maximum allowable level of copper (~20 μM) in drinking water [40,41].…”

A rapid response “Turn-On” fluorescent probe for nitroreductase detection and its application in hypoxic tumor cell imaging

“…A549 cells (human epithelial lung carcinoma cells) were selected because they are known to express nitroreductase. 17,19,39 In our experiments, A549 cells were rst grown at 37 C under normoxic (20% O 2 ) for 8 h and hypoxic (2% O 2 ) conditions for different times (2, 4, 6 and 8 h) and then incubated with probe 1 for 30 min under the respective conditions. As shown in Fig.…”

Spring‐Loaded Iron(II) Complexes as Magnetogenic Probes Reporting on a Chemical Analyte in Water

“…However, true aqueous robustness for this line of iron(II) complexes can only be found with a nitro substituent as the trigger group; the drastic inductive reversion associated with the reduction of the nitro group to an amino group is the principal reason for the observation of an initially stable probe that suffers swift fragmentation when reacted with a reductive analyte. Although catalytic hydrogenation served as a model analyte, other analytes such as dithionite [27,28] or nitroreductase/NADH [26,[29][30][31][32] convert similar probes just as well. The latter analyte is habitually the target in the identification of hypoxia as a biomarker of cancer metastasis.…”

“…By analogy with the previously reported probe 7, the amine derivative of 3 loses a pyrazole unit to afford a characteristic 5-methylenefuran-2-(5H)-imine intermediate ( Figure S25), which is hydrolyzed to 10 (Scheme 3). [26] The final value of 2.79 μ B can be explained by the accumulation of one full equivalent of free pyrazole in the sample, which partially coordinates to the iron center at the newly established free coordination site and, thus, effectively renders a limited proportion of complex 10 lowspin. This phenomenon can be expected to be much less pronounced in a real-world setting, as concentrations should remain significantly below the 6 mm that were used for the present measurements.…”