ER-Targeted NIR Probe Enables High-Throughput Discovery of hCES2A Inhibitors
- PA-HDCI, a near-infrared fluorogenic probe built on the HDCI fluorophore scaffold, localizes to the endoplasmic reticulum and reports on human carboxylesterase 2A (hCES2A) activity in living cells and animals.
- The probe combines a large Stokes shift, high metabolic stability, and reliable ER targeting, enabling in situ, real-time imaging of hCES2A function across multiple biological systems.
- Using PA-HDCI in a high-throughput screening assay, the team identified compound A4, a highly potent covalent inhibitor of hCES2A.
- hCES2A is the intestinal enzyme that converts the chemotherapy drug irinotecan into its toxic active metabolite, driving irinotecan-induced intestinal toxicity (IIT).
- In tumor-bearing mouse models, A4 showed a favorable safety profile and reduced irinotecan-associated intestinal toxicity while therapeutic efficacy was maintained.
- Together, the work delivers both a new imaging tool and a validated drug-discovery platform for hCES2A-targeted therapeutics.
Solid probe engineering, not just a screening reagent: coaxing ER-selective localization and a large Stokes shift out of the HDCI scaffold gives clean signal separation in situ — photophysics that holds up in cells, not just a cuvette. The real value-add is methodological. A mechanistic imaging tool doubling as an HTS readout turns hCES2A activity into a screenable phenotype in living systems, closing the usual gap between biochemical assays and cellular reality. Target-wise, nothing novel here — hCES2A is a known off-target liability that bioactivates irinotecan into its gut-toxic metabolite, so this is a 'fix the side effect' play, not a new mechanism. A4 is an HTS-derived covalent hit with encouraging mouse data, but still needs the standard covalent-hit workup: reactivity profiling, esterase-family selectivity, and SAR.