Activity-Based Near-Infrared Fluorogenic Probe for Enabling in Vitro and in Vivo Profiling of Neutrophil Elastase

Neutrophil elastase (NE), a typical hematopoietic serine protease, has significant roles in inflammatory and immune responses, and thus is highly associated with various diseases such as acute lung injury (ALI) and lung cancer. Rapid and accurate measurement of NE activity in biological systems is particularly important for understanding the role of NE in inflammatory diseases, as well as clinical diagnosis. However, the specific detection and noninvasive imaging of NE in vivo remains a challenge. To address this issue, a small-molecule substrate based near-infrared fluorogenic probe (NEP) for NE was constructed via incorporating pentafluoroethyl as the recognition group with a hemicyanine dye-based fluorophore. This initially quenched probe possesses more than 25-fold red fluorescence enhancement upon the catalysis of human NE, and the detection limit is about 29.6 ng/mL. In addition, the high specificity and the long emission wavelength (λ_emmax = 700 nm) of NEP allowed the direct monitoring of NE-trafficking, exogenous NE uptake, and endogenous NE upregulation at the cellular level. Moreover, the successful spatiotemporal imaging of NE in ALI model mice also made it a promising new tool in clinical diagnosis for ALI and other lung diseases.