Scientists have found a clever way to attack mesothelioma, one of the deadliest cancers: instead of shielding healthy cells, they strip the tumor of its own defenses and let it poison itself. The experimental drug, RSO-021, showed promising early results in a Phase 1 trial.

The disease

Mesothelioma is a rare, aggressive cancer of the lining of the lungs and other organs, strongly linked to asbestos exposure. It disproportionately strikes men who worked in shipbuilding, oil refining and manufacturing, with about 30,000 people diagnosed worldwide each year. The prognosis is grim: median survival is roughly 12 months, and only about 10% of patients survive five years. New options are badly needed.

The counterintuitive strategy

Here’s the twist. Cancer cells generate a lot of reactive oxygen species — damaging molecular byproducts like hydrogen peroxide — as they grow fast. To survive their own metabolism, they rely on antioxidant enzymes to mop up that damage. Conventional thinking often tries to boost antioxidants. The researchers did the opposite: RSO-021 uses thiostrepton (a naturally occurring antibiotic) to disable an antioxidant enzyme called PRX3 inside the tumor’s mitochondria. With its cleanup crew knocked out, hydrogen peroxide accumulates inside the cancer cells until they die. In effect, the drug turns the tumor’s own high-output metabolism into a self-destruct mechanism, while healthy cells — which produce far less oxidative stress — are less affected.

The trial results

The Phase 1 human trial, run in the UK in 2022–2023 and sponsored by RS Oncology, tested the drug’s safety and early activity. The results were encouraging for such an early study: disease progression was controlled in 67% of participants, tumors shrank in some patients, and average progression-free survival was 4.2 months, with overall survival exceeding what is typical for existing treatments. Importantly, there were no drug-related deaths and it was generally well tolerated. The work, from University of Vermont researchers, was published in Nature Communications.

Why it matters

Beyond mesothelioma specifically, the approach is scientifically interesting because exploiting cancer’s oxidative stress is a strategy that could, in principle, extend to other tumors that depend on the same defenses. For a cancer with so few options, even modest gains in progression-free and overall survival matter. “Our overall survival data is very promising and will hopefully persist with additional patients,” said researcher Brian Cunniff, calling it a potential “game changer.”

The caveats

Enthusiasm should be measured. This is a Phase 1 trial — small, designed mainly to assess safety, and without a randomized comparison group. Percentages like “67% disease control” are promising but preliminary, and a 4.2-month progression-free survival, while better than the baseline, is an incremental gain, not a cure. Larger, controlled trials are needed to confirm the benefit and define which patients respond. This summarizes early research and is not medical advice.