Mesothelioma ranks among oncology's most intractable diagnoses, with median survival measured in months and few second-line options after platinum-based chemotherapy fails. A new therapeutic strategy that exploits a fundamental metabolic vulnerability in cancer cells — their dependence on mitochondrial antioxidant machinery — has now moved from bench to bedside with early clinical results that warrant serious attention.
The work centers on peroxiredoxin 3 (PRX3), a mitochondrial enzyme that neutralizes reactive oxygen species (ROS) and enables tumor cells to survive the oxidative stress inherent to rapid proliferation. The natural compound thiostrepton (TS) covalently binds and inactivates PRX3, tipping the intracellular redox balance toward lethal ROS accumulation. Genetic knockout of PRX3 in mesothelioma models impaired mitochondrial bioenergetics and suppressed tumor growth, validating the target independently of the drug. In patient-derived mesothelioma explants, TS triggered apoptosis. In the NCT05278975 phase 1 trial, RSO-021 — a formulated TS product — was delivered intrapleurally once weekly to patients with relapsed pleural mesothelioma and malignant pleural effusion. At 90 mg, the regimen was well tolerated; 67% of evaluable patients achieved disease control at 12 weeks, and tumor reductions were observed. Genomic screening further identified SLC7A11, a cystine transporter that feeds glutathione synthesis, as a resistance mediator, pointing toward rational combination strategies.
The pro-oxidant therapeutic concept is not new — ascorbate, arsenic trioxide, and APR-246 have all exploited redox dysregulation — but targeting a mitochondria-specific peroxiredoxin with intrapleural delivery represents a mechanistically distinct and anatomically focused approach that limits systemic exposure. The phase 1 design is inherently small and non-randomized, so the 67% disease control figure must be interpreted cautiously; historical benchmarks in this setting are low, making the signal encouraging but far from definitive. The identification of SLC7A11 as a resistance node is a meaningful translational advance, since xCT inhibitors are already in clinical development. Whether this approach extends beyond mesothelioma to other solid tumors with high PRX3 expression remains an open and scientifically compelling question.