A near infrared fluorescent probe for hypoxia based on dicyanoisophorone and its application in Hela cells imaging

Hypoxia will accelerate tumors metastasis and deterioration, thereby limiting the effects of chemotherapy or radiotherapy. Thus, developing efficient techniques for detecting hypoxia in tumor cells is extremely important for cancer diagnosis and therapy. In this work, we reported a dicyanoisophorone-based probe (DCI-Azo) that specifically switched on its near infrared emission with hypoxia up-regulated azo-reductase (AzoR). In order to reduce the difficulty of synthesis and simplify the post-processing process, we adopted a one-pot-synthesis method to synthesized NIR fluorophore (DCI-Am) with yield 97 %. Based on the fluorophore, DCI-Azo was designed and synthesized. The sensitivity of DCI-Azo for hypoxia in vitro was evaluated with Na₂S₂O₄ and rat liver microsomes. It exhibited near-infrared emission (λ_em = 650 nm), large Stokes Shift (>160 nm), high sensitivity (LOD 0.53 μg mL^-1 rat liver microsomes), high selectivity, and low cytotoxicity (cell viability > 80 % after incubation for 24 h). Moreover, the probe was successfully used for detecting hypoxia (1% O₂) in Hela cells and tumor tissue in mouse model. The fluorescence intensity in Hela cells has increased ∼ 26-fold when the oxygen level is reduced to 1 % from 21 % O₂. The fluorescence intensity of the tumor area enhanced ∼ 5 folds compared to the normal area nearby. All these features demonstrated that the probe DCI-Azo was a versatile tool for in vivo assay and imaging for cancer diagnosis studies.