Phenazine methosulfate restores ATP synthesis and membrane potential under ETC blockade and exposes vulnerabilities in glioblastoma cells
Researchers in Oslo and Athens have identified a small redox‑active molecule that can bypass blocks in the mitochondrial electron transport chain (ETC) and restore key energy parameters in cells, even when several respiratory complexes are pharmacologically or otherwise blocked. The study reveals a chemical “redox bypass” that revives electron flow, mitochondrial membrane potential and respiratory ATP synthesis, and may help probe metabolic weak spots in aggressive cancers such as glioblastoma.

In work published in Antioxidants, the team shows that phenazine methosulfate (PMS) can, at subtoxic concentrations, reroute electron flow in both cell‑free systems and mammalian cells under ETC blockade. PMS drives NADH–PMS–O₂ redox cycling, which increases oxygen consumption, restores mitochondrial membrane potential, and supports oxidative ATP production when complexes I, III, and IV are inhibited. At the same time, PMS shifts metabolism away from glycolysis‑driven lactate production, indicating a broader rebalancing of cellular bioenergetics.
Mechanistic data suggest that PMS operates as an enzyme‑independent electron shuttle: it directly reduces cytochrome c and likely coenzyme Q₁₀, feeding electrons into distal ETC components and effectively bypassing upstream blocks. Molecular modelling supports close association of reduced PMS with ubiquinone and cytochrome c in the inner mitochondrial membrane, consistent with these alternative electron entry points.

These bypass effects are clearly seen in human glioblastoma (GBM) cells, which often exhibit abnormal mitochondria, high oxidative stress, and a strong dependence on glycolysis. In GBM models, PMS not only restores ETC‑driven ATP synthesis and mitochondrial polarization under complex I, III and IV inhibition, but also alleviates metformin‑induced respiratory suppression and lactate accumulation, metformin‑induced respiratory suppression and lactate accumulation, and appears to outperform existing redox‑bypass candidates in this setting. By pushing GBM cells toward a more respiratory state while modulating reactive oxygen species output, PMS helps expose redox and metabolic vulnerabilities that could be exploited in future therapeutic strategies.

“We found that at low, non‑toxic doses, PMS behaves like a plug‑in bypass cable for the mitochondrial electron transport chain,” says Dr Theodossis Theodossiou of the University of Oslo and Oslo University Hospital. “It can reroute electrons around classical respiratory blocks, revive mitochondrial membrane potential, and restart ATP production”.

“In glioblastoma cells, this metabolic switch may be particularly harmful: Many GBM cells are wired to survive on glycolysis, and when PMS pushes them toward respiration, they may lack sufficient defences to cope with toxic oxygen intermediates”. "This also reveals how dependent these tumours are on a precarious redox balance.”

The authors emphasise that PMS itself is a tool compound rather than a ready‑made therapy, given its strong ROS‑generating capacity at higher, sustained doses. However, they argue that the PMS‑driven redox bypass concept is a useful framework for situations involving acute blockade of cellular respiration, such as cyanide poisoning. The same concept could also prove valuable for drugs that inhibit respiration and cause severe side effects, including lactic acidosis, as seen with the antidiabetic drug metformin. PMS and potential homologous derivatives can transiently support mitochondrial function in stressed cells, while selectively exploiting the redox fragility of cancer cells, such as GBM

Affiliations: Department of Physics, University of Oslo, Norway; Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, Norway;
Institute of Biosciences Applications, National Centre for Scientific Research Demokritos, Athens, Greece.
Funding: This research was supported by the European Innovation Council (EIC) Pathfinder Open programme, grant agreement No. 101130209, Nu‑CapCure.
Contact: Dr Theodossis A. Theodossiou, Department of Physics, University of Oslo / Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital. E-mail: theodoss@uio.no