An enzyme-activated two-photon ratiometric fluorescent probe with lysosome targetability for imaging β-glucuronidase in colon cancer cells and tissue

Colon cancer is a malignant neoplasm with high mortality that has seriously threatened human life. Accumulating evidence reveals that the β-glucuronidase (GLU), a lysosomal exoglycosidase enzyme, plays important roles in the pathological progression of colon cancer. Unfortunately, understanding the pathological roles of GLU remains a challenge due to the lack of effective detection methods for visualization the fluctuations of GLU in tissues. In this paper, based on hydrolysis function of GLU, an enzyme-activated ratiometric two-photon (TP) fluorescent probe (RN-GLU) was designed. RN-GLU was synthesized by introducing a glucopyranuronic acid methyl ester as the recognition group and 1, 8-naphthalimide as a TP fluorophore. In the presence of GLU, the trigger group was removed made an ICT process occurred induced enhancement of fluorescence ratio (I553 nm/I441 nm, 214-fold). Probe RN-GLU displayed low detection limit (1.2 × 10-2 μg/L) and rapid detection to GLU in vitro through a ratiometric response mode. Meanwhile, RN-GLU exhibited high selectivity for GLU and showed nearly no response to other relevant biological species. The imaging results demonstrated that RN-GLU could be applied for ratiometric monitoring of endogenous GLU levels in HCT116 cells with good lysosome targetable ability. Due to its two-photon excitation, RN-GLU could monitor GLU in colon cancer tumor tissue with good penetration ability (imaging depth of 200 μm). RN-GLU could be developed as a potential method for evaluating and confirming the functions of GLU in colon cancer diagnosis and complex biosystem.