Esculin induces endoplasmic reticulum stress and drives apoptosis and ferroptosis in colorectal cancer via PERK regulating eIF2α/CHOP and Nrf2/HO-1 cascades

Cortex fraxini (also known as Qinpi), the bark of Fraxinus rhynchophylla Hance and Fraxinus stylosa Lingelsh, constitutes a crucial component in several traditional Chinese formulas (e.g., Baitouweng Tang, Jinxiao Formula, etc.) and has demonstrated efficacy in alleviating intestinal carbuncle and managing diarrhea. Cortex fraxini has demonstrated commendable anticancer activity in the realm of Chinese ethnopharmacology; nevertheless, the underlying mechanisms against colorectal cancer (CRC) remain elusive. Esculin, an essential bioactive compound derived from cortex fraxini, has recently garnered attention for its ability to impede viability and induce apoptosis in cancer cells. This investigation aims to assess the therapeutic potential of esculin in treating CRC and elucidate the underlying mechanisms. The impact of esculin on CRC cell viability was assessed using CCK-8 assay, Annexin V/PI staining, and Western blotting. Various cell death inhibitors, along with DCFH-DA, ELISA, biochemical analysis, and Western blotting, were employed to delineate the modes through which esculin induces HCT116 cells death. Inhibitors and siRNA knockdown were utilized to analyze the signaling pathways influenced by esculin. Additionally, an azomethane/dextran sulfate sodium (AOM/DSS)-induced in vivo CRC mouse model was employed to validate esculin's potential in inhibiting tumorigenesis and to elucidate its underlying mechanisms. Esculin significantly suppressed the viability of various CRC cell lines, particularly HCT116 cells. Investigation with diverse cell death inhibitors revealed that esculin-induced cell death was associated with both apoptosis and ferroptosis. Furthermore, esculin treatment triggered cellular lipid peroxidation, as evidenced by elevated levels of malondialdehyde (MDA) and decreased levels of glutathione (GSH), indicative of its propensity to induce ferroptosis in HCT116 cells. Enhanced protein levels of protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) and p-eIF2α suggested that esculin induced cellular endoplasmic reticulum (ER) stress, subsequently activating the Nrf2/ARE signaling pathway and initiating the transcriptional expression of heme oxygenase (HO)-1. Esculin-induced excessive expression of HO-1 could potentially lead to iron overload in HCT116 cells. Knockdown of Ho-1 significantly attenuated esculin-induced ferroptosis, underscoring HO-1 as a critical mediator of esculin-induced ferroptosis in HCT116 cells. Furthermore, utilizing an AOM/DSS-induced colorectal cancer mouse model, we validated that esculin potentially inhibits the onset and progression of colon cancer by inducing apoptosis and ferroptosis in vivo. These findings provide comprehensive insights into the dual induction of apoptosis and ferroptosis in HCT116 cells by esculin. The activation of the PERK signaling pathway, along with modulation of downstream eIF2α/CHOP and Nrf2/HO-1 cascades, underscores the mechanistic basis supporting the clinical application of esculin on CRC treatment.