<i>In situ</i> imaging of aminopeptidase N activity in hepatocellular carcinoma: a migration model for tumour using an activatable two-photon NIR fluorescent probe

Abstract

CD13/aminopeptidase N (APN), which is a zinc-dependent metalloproteinase, plays a vital role in the growth, migration, angiogenesis, and metastasis of tumours. Thus, <i>in situ</i> molecular imaging of endogenous APN levels is considerably significant for investigating APN and its different functions. In this study, a novel two-photon near-infrared (NIR) fluorescence probe <b>DCM-APN</b> was prepared to perform <i>in vitro</i> and <i>in vivo</i> tracking of APN. The <i>N</i>-terminal alanyl site of probe <b>DCM-APN</b> was accurately hydrolysed to the amino group, thereby liberating strong fluorescence owing to the recovery of the Intramolecular Charge Transfer (ICT) effect. By considering its outstanding selectivity, ultra-sensitivity (DL 0.25 ng mL^-1) and favourable biocompatibility, the probe <b>DCM-APN</b> was used to distinguish between normal cells (LO2 cells) and cancer cells (HepG-2 and B16/BL6 cells). Furthermore, migration of hepatocellular carcinoma cells was apparently inhibited by ensuring that the APN catalytic cavity was occupied by bestatin. The identification of three-dimensional (3D) fluorescence in cancer tissues was completed under two-photon excitation coupled with lighting up hepatocellular carcinoma tumours <i>in situ</i>; this revealed that probe <b>DCM-APN</b> is an effective tool for detecting APN, thereby assisting in the early diagnosis of tumour in clinical medicine.