Conditionally Activated ROS Generation by MMP2/9-Specific C₆₀-Based Fluorescence Probes

A C₆₀-coumarin conjugate, covalently connected via a matrix metalloproteinase (MMP2/9)-cleavable peptide linker (Pro-Leu-Gly-Val-Arg-Gly), is developed as a probe for both imaging and photodynamic treatment of MMP2/9-expressing malignant cells. In the synthesized probe, the coumarin fluorescence is completely suppressed intramolecularly by the C₆₀ moiety, while an intensive fluorescence increase is observed in the presence of MMP2/9 dependent on cleavage of the peptide linker. The specificity of the probe to detect MMP2 is confirmed by control experiments resulting in no emission 1) with a control probe bearing a shuffled peptide (Val-Arg-Leu-Gly-Pro-Gly) or 2) in the presence of an MMP2 inhibitor (1,10-phenantheoline). The probe is added to three types of tumor cell lines with different MMP2/9-expression levels to perform in vitro cellular imaging. MMP2/9 is successfully detected by the probe in DAOY cells with the highest expression level of MMP2/9. Upon cleavage of the probe by MMP2/9, photoinduced ¹O₂ generation is much enhanced, resulting in the MMP-dependent induction of higher photocytotoxicity of the probe in DAOY compared to HCT116 with much lower expression. The results suggest that the probe can serve as (I) a fluorescent reporter for MMP2/9 and (II) a photosensitizer for selective photodynamic treatment of malignant cells with MMP2/9 overexpression.