PET-leveraged ALDH probe toward cancer stem cells

Developing novel aldehyde dehydrogenase (ALDH) probes is essential for enhancing the localization and visualization of cancer stem cells (CSCs) by improving specificity and signal-to-noise ratios. This study introduces four new ALDH fluorescent probes (AldeCou1–4), designed using a coumarin-linker-benzaldehyde scaffold. Among them, AldeCou-1 exhibits a significant Stokes shift of 125 nm (λ_ex/λ_em = 380/505 nm), which enhances the signal-to-noise ratio and minimizes inner-filter effects. AldeCou-1 demonstrated superior green fluorescence imaging in A549 and MDA-MB-231 cells, enabling differentiation between these cell lines based on ALDH activity. Compared to conventional ALDH activity assay kits, such as ALDEFLUOR, which require additional buffers and inhibitors that complicate imaging protocols, AldeCou-1 enables simplified assay conditions by eliminating the need for ATP-binding cassette (ABC) transporter inhibitors and specialized buffers. Computational analysis suggests that the fluorescence turn-on mechanism of AldeCou-1 is driven by ALDH-mediated photoinduced electron transfer (PET). These findings provide valuable mechanistic insights and pave the way for developing next-generation ALDH probes for improved CSC screening and characterization.