Persistent Chemiluminescent Glow of Phenoxy-dioxetane Luminophore Enables Unique CRET-Based Detection of Proteases

Chemiluminescence is being considered an effective imaging modality as it offers low background and high sensitivity. Recent discovery by our group has led to development of new phenoxy-dioxetane chemiluminescence luminophores, which are highly bright under physiological conditions. However, the current scope of probes based on these luminophores is limited, as they can only be turned on by phenol protecting group removal. Here we present a new chemiluminescence resonance energy transfer (CRET) system, Glow-CRET, in which light emission is triggered by proteolytic cleavage of a peptide substrate that links a dioxetane luminophore and a quencher. In order to compose such system, a new phenoxy-dioxetane luminophore, 7-HC-CL, was developed. This luminophore exhibits intense and persistent glow chemiluminescence; it undergoes very slow chemiexcitation, and it has the highest chemiluminescence quantum yield ever reported under physiological conditions. Based on 7-HC-CL, a Glow-CRET probe for matrix metalloproteinases, MMP-CL, was synthesized. Incubation of MMP-CL with its cognate protease resulted in 160-fold increase in chemiluminescence signal. MMP-CL was also able to detect matrix metalloproteinase activity in cancer cells with significantly higher signal-to-background ratio than an analogous fluorescence resonance energy transfer (FRET)-based probe. This work is expected to open new horizons in chemiluminescence imaging, as it enables to use the dioxetanes in ways that had not been possible. We anticipate that 7-HC-CL and future derivatives will be utilized not only for the construction of further Glow-CRET probes, but also for other applications, such as chemiluminescence tagging of proteins.