An integrated experimental and computational study on a COX-2-targeted AIE probe for precise cancer cell imaging via restriction of intramolecular rotation.

BACKGROUND: The overexpression of cyclooxygenase-2 (COX-2) and alterations in microenvironmental viscosity are recognized as pivotal hallmarks for the early diagnosis and progression of malignant tumors. Although fluorescent probes have been developed for tumor imaging, many conventional fluorophores suffer from aggregation-caused quenching (ACQ) in dense biological environments. Furthermore, existing sensors often lack the specificity to simultaneously target COX-2 and dynamically report local viscosity variations within complex cellular environments. Therefore, developing a robust molecular tool that overcomes ACQ limitations while simultaneously achieving precise COX-2 targeting and dynamic viscosity sensing remains a critical challenge.

RESULTS: In this work, we developed a long-wavelength fluorescent probe, S1, featuring a donor-acceptor (D-A) architecture for the targeted visualization of COX-2 expression and microenvironmental viscosity. S1 integrates a 1,8-naphthalimide core with a celecoxib moiety for precise COX-2 targeting and a triphenylamine (TPA) molecular rotor. The probe operates via an aggregation-induced emission (AIE) mechanism, exhibiting a distinct fluorescence turn-on response in high-viscosity environments with a linear correlation between log I610 and log η (R2 = 0.9872). S1 self-assembles into stable nanoparticles in water (diameter = 138.80 nm, PDI = 0.223), with the absolute quantum yield increasing from 10.65% in methanol to 25.36% in water. Confocal imaging demonstrated high-contrast discrimination of COX-2-overexpressing MCF-7 cancer cells from normal human umbilical vein endothelial cells (HUVEC). Furthermore, molecular dynamics simulations revealed a highly stable binding enthalpy (ΔH = -93.96 kcal/mol) within the COX-2 active site, confirming target-induced restriction of intramolecular rotation (RIR).

SIGNIFICANCE AND NOVELTY: This study presents a novel, synergistic "target-and-lock" strategy to visualize COX-2 expression and viscosity variations. We conclude that the rigid binding pocket of COX-2 successfully restricts the molecular rotation of S1 to activate high-contrast emission in cancer cells. Significantly, this integrated experimental and computational paradigm provides a reliable and general design principle for next-generation, organelle-specific AIE sensors to dynamically track complex pathological microenvironments.