In Vivo Targeting of Hydrogen Peroxide by Activatable Cell-Penetrating Peptides

A hydrogen peroxide (H₂O₂)-activated cell-penetrating peptide was developed through incorporation of a boronic acid-containing cleavable linker between polycationic cell-penetrating peptide and polyanionic fragments. Fluorescence labeling of the two ends of the molecule enabled monitoring its reaction with H₂O₂ through release of the highly adhesive cell-penetrating peptide and disruption of fluorescence resonance energy transfer. The H₂O₂ sensor selectively reacts with endogenous H₂O₂ in cell culture to monitor the oxidative burst of promyelocytes and in vivo to image lung inflammation. Targeting H₂O₂ has potential applications in imaging and therapy of diseases related to oxidative stress

Fluorescent Ligand for Human Progesterone Receptor Imaging in Live Cells

We employed molecular modeling to design and then synthesize fluorescent ligands for the human progesterone receptor. Boron dipyrromethene (BODIPY) or tetramethylrhodamine were conjugated to the progesterone receptor antagonist RU486 (Mifepristone) through an extended hydrophilic linker. The fluorescent ligands demonstrated comparable bioactivity to the parent antagonist in live cells and triggered nuclear translocation of the receptor in a specific manner. The BODIPY labeled ligand was applied to investigate the dependency of progesterone receptor nuclear translocation on partner proteins and to show that functional heat shock protein 90 but not immunophilin FKBP52 activity is essential. A tissue distribution study indicated that the fluorescent ligand preferentially accumulates in tissues that express high levels of the receptor <i>in vivo</i>. The design and properties of the BODIPY-labeled RU486 make it a potential candidate for <i>in vivo</i> imaging of PR by positron emission tomography through incorporation of ¹⁸F into the BODIPY core

In Search of the Perfect Photocage: Structure–Reactivity Relationships in <i>meso</i>-Methyl BODIPY Photoremovable Protecting Groups

A detailed investigation of the photophysical parameters and photochemical reactivity of <i>meso</i>-methyl BODIPY photoremovable protecting groups was accomplished through systematic variation of the leaving group (LG) and core substituents as well as substitutions at boron. Efficiencies of the LG release were evaluated using both steady-state and transient absorption spectroscopies as well as computational analyses to identify the optimal structural features. We find that the quantum yields for photorelease with this photocage are highly sensitive to substituent effects. In particular, we find that the quantum yields of photorelease are improved with derivatives with higher intersystem crossing quantum yields, which can be promoted by core heavy atoms. Moreover, release quantum yields are dramatically improved by boron alkylation, whereas alkylation in the <i>meso</i>-methyl position has no effect. Better LGs are released considerably more efficiently than poorer LGs. We find that these substituent effects are additive, for example, a 2,6-diiodo-<i>B</i>-dimethyl BODIPY photocage features quantum yields of 28% for the mediocre LG acetate and a 95% quantum yield of release for chloride. The high chemical and quantum yields combined with the outstanding absorption properties of BODIPY dyes lead to photocages with uncaging cross sections over 10 000 M^–1 cm^–1, values that surpass cross sections of related photocages absorbing visible light. These new photocages, which absorb strongly near the second harmonic of an Nd:YAG laser (532 nm), hold promise for manipulating and interrogating biological and material systems with the high spatiotemporal control provided by pulsed laser irradiation, while avoiding the phototoxicity problems encountered with many UV-absorbing photocages. More generally, the insights gained from this structure–reactivity relationship may aid in the development of new highly efficient photoreactions