Targeting ER stress in adrenocortical carcinoma: Celastrol as a novel therapeutic candidate

Background: Adrenocortical carcinoma (ACC) is a rare, aggressive malignancy with limited treatment options. Mitotane, the only approved drug, has modest efficacy and frequent adverse effects, underscoring the urgent need for new therapeutic approaches. Celastrol, a triterpene compound derived from traditional Chinese medicine, exhibits anti-inflammatory activity and broad anti-tumor effects, including sensitization of cancer cells to chemo- and radiotherapy. Purpose: In this study, we investigated for the first time the anti-cancer potential of celastrol in the ACC H295R cell line. Methods: Using different in vitro biomolecular technologies and biochemical/biophysical experiments, we evaluated celastrol's effect on ACC cells. Results: Celastrol induced apoptosis in ACC cells and demonstrated efficacy not only in 2D monolayer cultures but also in 3D spheroid models. Importantly, it inhibited spheroid growth and disrupted pre-formed spheroids, highlighting its activity in tumor-like structures. Mechanistic analyses suggested that celastrol triggers apoptosis through induction of endoplasmic reticulum (ER) stress and oxidative stress. These findings parallel our previous observations with mitotane, which also activates the ER stress pathway via the ATF4-ATF3 axis. This partial convergence points to ER stress induction as a potential therapeutic target in ACC. Conclusion: identifying agents capable of complementing or replacing standard therapy remains a central challenge in ACC research. Our findings suggest that celastrol is a potent bioactive compound with activity against both monolayer and 3D ACC models, offering potential translational relevance. By elucidating ER stress as a shared mechanism between celastrol and mitotane, our work supports further exploration of this pathway as a strategy to potentially improve therapeutic outcomes in ACC patients.