Abstract 4716: First-in-class peroxiredoxin 3 (PRX3) inhibitor RSO-021 triggers mesenchymal-to-epithelial transition in mesothelioma

Abstract Mesothelioma, a lethal cancer associated with asbestos exposure, lacks effective drug therapy particularly in the relapsed treatment setting. Epithelial-to-mesenchymal transition (EMT) confers an aggressive sarcomatoid phenotype capable of invasion, metastasis, and drug resistance. Pharmacological targeting of EMT could favorably alter the progression and treatment of mesothelioma. We identified a geospatial transcriptomic gradient between adjacent epithelioid and sarcomatoid regions in patient-derived biphasic mesotheliomas involving hypoxia tolerance, TGF-β, mitochondrial oxidative phosphorylation, and EMT. Mesothelioma cells rely on buffering of mitochondrial oxidative stress through the expression and activity of mitochondrial peroxiredoxin 3 (PRX3), which is covalently inactivated by the first-in-class inhibitor RSO-021, now under investigation in the phase 1/2 MITOPE clinical trial (NCT05278975). To better understand the pharmacodynamics of RSO-021, transcriptomic profiles of drug sensitive and resistant biphasic mesothelioma cell lines were generated. Differential analysis revealed that RSO-021 induced up-regulation of ROS response and apoptosis signaling, while down-regulating TGF-β and EMT markers, WNT signaling, and TEAD target genes. Additionally, we observed altered expression of the mesothelioma specific EMT genes Col5A2, mesothelin and VISTA. Resistance to RSO-021 conferred significant proliferative defects and was reversible upon RSO-021 removal, however the down-regulation of EMT genes was conserved, suggesting an irreversible mesenchymal-to-epithelial transition. In summary PRX3 is a clinically actionable drug target, inhibition of which correlates with EMT modulation. This activity suggests a mechanism to alter mesothelioma progression and prevent the emergence of the most aggressive mesothelioma phenotype. Citation Format: Terri Messier, Victoria Gibson, David J. Seward, Essa Y. Baitei, Peter Wells Jordan, Charlotte Poile, Joanna Dzialo, Aleksandra Bzura, Kudzayi Kutywayo, Apostolos Nakas, George N. Naumov, Dean A. Fennell, Brian Cunniff. First-in-class peroxiredoxin 3 (PRX3) inhibitor RSO-021 triggers mesenchymal-to-epithelial transition in mesothelioma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4716.