NADPH-Independent Fluorescent Probe for Live-Cell Imaging of Heme Oxygenase-1

Heme oxygenase-1 (HO-1) catalyzes heme degradation on the consumption of NADPH and molecular oxygen. As an inducible enzyme, HO-1 is highly induced in various disease states, including cancer. Currently, two fluorescent probes for HO-1 have been designed based on the catalytic activity of HO-1, in which the probes serve as a substrate, so NADPH is required to enable the detection. Probes functioning in a NADPH-dependent way may influence other NADPH-consuming pathways, as all these pathways share a common NADPH pool. Here, we report the peptide-based fluorescent probe NBD-P₅ as a simple alternative approach for HO-1 sensing. The designed probe NBD-P₅ functions independently of the catalytic activity of HO-1, therefore enabling fast and sensitive detection of HO-1 with no requirements of other substances, including NADPH and biliverdin reductase. Moreover, it overcomes the need for a large substrate amount and long incubation time during the detection. NBD-P₅ can be quickly taken up by cells, demonstrates an excellent colocalization with the endoplasmic reticulum (where HO-1 is mainly located), and is shown to be reliable in reporting changes in HO-1 levels in live cells. This work provides a simple alternative approach for designing HO-1 fluorescent probes, and we expect it will act as a practical tool for further studying HO-1 biology.