Flavylium-Based Hypoxia-Responsive Probe for Cancer Cell Imaging.

A hypoxia-responsive probe based on a flavylium dye containing an azo group () was synthesized to detect hypoxic conditions via a reductase-catalyzed reaction in cancer cells. In in vitro enzymatic investigation, the azo group of was reduced by a reductase in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) followed by fragmentation to generate a fluorescent molecule, . The response of to the reductase was as fast as 2 min with a limit of detection (LOD) of 0.4 μM. Moreover, displayed high enzyme specificity even in the presence of high concentrations of biological interferences, such as reducing agents and biothiols. Therefore, was tested to detect hypoxic and normoxic environments in cancer cells (HepG2). Compared to the normal condition, the fluorescence intensity in hypoxic conditions increased about 10-fold after 15 min. Prolonged incubation showed a 26-fold higher fluorescent intensity after 60 min. In addition, the fluorescence signal under hypoxia can be suppressed by an electron transport process inhibitor, diphenyliodonium chloride (DPIC), suggesting that reductases take part in the azo group reduction of in a hypoxic environment. Therefore, this probe showed great potential application toward in vivo hypoxia detection.