Experimental drug disables tumor antioxidant enzyme, halting mesothelioma in two-thirds of patients

The University of Vermont team repurposed the natural antibiotic thiostrepton to inhibit peroxiredoxin 3 (PRX3), a key antioxidant that mesothelioma cells rely on to survive oxidative stress. Their formulation, RSO-021, was tested in a phase-one trial overseen by the UK regulator MHRA, where it was delivered directly into the chest cavity of 15 relapsed patients. The drug achieved its safety targets at a 90 mg dose, showed clear engagement of the intended target, and halted disease progression in 67% of the cohort, with several tumors regressing.

Overall survival exceeded expectations for existing treatments, and investigators noted possible immunomodulatory effects. Phase-two results are pending, and the researchers are developing next-generation PRX3 inhibitors that could be taken orally and applied to other cancers.