Development of Rofecoxib-Based Fluorescent Probes and Investigations on Their Solvatochromism, AIE Activity, Mechanochromism, and COX-2-Targeted Bioimaging

Abstract

Cyclooxygenase-2 (COX-2) fluorescent probes are promising tools for early cancer diagnosis. Traditionally, COX-2 probes were designed by connecting two parts, a fluorophore and a COX-2 binding unit, via a flexible linker. Herein, a new class of COX-2-specific fluorescent probes have been developed by one-step modification from rofecoxib by an integrative approach to combining the fluorophore and binding units into one. Among them, several new rofecoxib analogues not only retained their COX-2 binding ability but also exhibited attractive fluorescent properties, such as tunable Blue-Red emission, solvatochromism, AIE behavior and mechanochromism. Notably, the emission of 2a16 can be switched between greenish-yellow in the crystalline state to red-orange in the amorphous state by grinding and fuming treatments. Furthermore, the highly fluorescent compound 2a16 (Фf = 0.94 in powder) displayed much stronger fluorescent imaging of COX-2 in HeLa cancer cells overexpressing COX-2 than RAW264.7 normal cells with minimal expressing of COX-2. Most importantly, 2a16 can light up human cancer tissues from adjacent normal tissues with much brighter fluorescence by targeting COX-2 enzyme. These results illustrate the potential of 2a16 as a new red fluorescent probe for human cancer imaging in clinical applications.

Development of Rofecoxib‐Based Fluorophores from ACQ to AIE by Positional Regioisomerization

“…To gain insight into the mechanism of these photophysical properties from regioisomerization, density functional theory (DFT) calculations were carried out for the frontier molecular orbitals, including the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of PYR2 and PYR4 at the B3LYP/6‐311++G(d,p) level in DMSO (Figure 1c, d) [42,49] . Both compounds had similar frontier molecular orbitals.…”

“…It was shown that similar pattens for both PYR2 and PYR4 were observed for absorption and emission spectra in different solvents, although the magnitudes in intensity varied. The absorption bands at about 350 nm may be attributed to the π‐π* transition, and the weak ones at around 400 nm were ascribed to ICT transition [42] . When the solvent polarity was increased gradually from low polarity in chloroform (λ em =628 nm) to high polarity in DMSO (λ em =704 nm), the emission of PYR2 exhibited a red shift and the intensity gradually weakened, which was mainly due to the non‐radiative decay in polar solvents [52,53] .…”

“…The absorption bands at about 350 nm may be attributed to the π-π* transition, and the weak ones at around 400 nm were ascribed to ICT transition. [42] When the solvent polarity was increased gradually from low polarity in chloroform (λ em = 628 nm) to high polarity in DMSO (λ em = 704 nm), the emission of PYR2 exhibited a red shift and the intensity gradually weakened, which was mainly due to the non-radiative decay in polar solvents. [52,53] Such behaviors are consistent with those of other fluorophores such as 4-(N,Ndimethylamino)benzonitrile (DMABN) and could be explained by the twisted intramolecular charge transfer (TICT) mechanism.…”

“…[28,40,41] Our research group has been interested in developing rofecoxib-based fluorescent materials. [42][43][44] Herein, we report our latest development on a facile ACQ-to-AIE conversion by migrating a small piperidine group from the para-position (PYR4) to the ortho-position (PYR2) based on the rofecoxib scaffold. Compound PYR4 was identified to be a ACQ molecule while PYR2 was shown to be AIE-active.…”

Biosensors for the Detection of Enzymes Based on Aggregation-Induced Emission

“…Additionally, AIEgen probes have been synthesized for the detection and imaging of other enzymes such as lipase [ 106 , 107 ], fucosidase [ 108 ], cyclooxygenase-2 (COX-2) [ 109 ] and β-N-acetylhexosaminidase (Hex) [ 110 ]. For example, lipase plays an important role in industrial catalysis, drug discovery and disease diagnosis; two AIEgens have been designed and used for the detection of lipase, including TPE and benzophenone derivatives [ 106 , 107 ].…”