A highly sensitive and selective two-photon fluorescent probe for real-time sensing of cytochrome P450 1A1 in living systems

Cytochrome P450 1A1 (CYP1A1), a heme-containing monooxygenase, is of particular importance for human health because of its vital role in the metabolic activation of pro-carcinogenic compounds to their ultimate carcinogens. However, CYP1A1 protein levels are extraordinarily low in normal and cancer tissues. Thus, a practical method for ultra-sensitive and real-time monitoring of CYP1A1 activity in complex biological systems is highly sought after. In the present study, we developed a highly specific and sensitive two-photon fluorescent probe for monitoring CYP1A1 activity on the basis of the substrate preferences of this key enzyme. A panel of O-alkylated derivatives was designed and synthesized using HBN as the basic fluorophore. After screening and optimization, the derivative iPrBN was selected for further study as it displayed excellent specificity, high sensitivity and fast turn-on response to CYP1A1 relative to other human CYP isoforms. The detection limit of iPrBN for CYP1A1 was 0.036 nM, suggesting that it would be sensitive and versatile enough to detect endogenous CYP1A1 activity. Indeed, we successfully applied iPrBN to the real-time monitoring of CYP1A1 activity in human cancer cell lines and performed high-throughput screening of CYP1A1 modulators. iPrBN was also applied for the first time to the two-photon imaging of intracellular CYP1A1 in living cancer tissues and zebrafish, and our results showed that iPrBN exhibited high imaging resolution and fast response towards CYP1A1. These findings suggest that this probe is capable of accurately sensing CYP1A1 activity in complex biological systems, which will facilitate further investigations of CYP1A1-associated physiological and pathological processes.