Formaldehyde inflicts cytotoxicity by altering the glutathione redox balance

SCHEIDEGGER, MARCO A.; UMANSKY, CARLA; AGUSTIN MORELLATO; LUCAS PONTEL

Simposio; 22nd EMBL PhD Symposium: The Roaring 20s: A New Decade for Life Sciences; 2020

EMBL

Cell metabolism provides energy and molecules required for cell growth and development. However,some biological reactions such as histone and nucleic acid demethylations or the one carbon cyclecan also generate formaldehyde (FA), which reaches blood concentrations of up to 45 μM. FA is awell-established genotoxic metabolite that might be abundant in highly proliferative cancer cells. Toaddress how cancer cells cope with endogenous FA, we inactivated the FA-metabolizing enzymealcohol dehydrogenase 5 (ADH5) in human colorectal carcinoma cells (HCT116). Despite active DNArepair, these cells presented a significant reduced tolerance to FA in viability assays showing signs ofapoptosis. They also failed to form 3D-tumor spheroids in presence of blood concentrations of FA.Accordingly, human preB lymphoblastic leukaemia cells (Nalm6) lacking ADH5 were significative moresensitive to blood levels of FA than wild type controls. An interrogation of DNA damage markersindicated FA triggered a P53 response in absence of ADH5. However, inactivation of P53 could notrevert FA-induced cell death, suggesting that other cell-death signalling mechanisms take place.Additional experiments revealed that FA induces the accumulation of reactive oxygen species (ROS)in cells lacking ADH5, suggesting an alternative cytotoxic mechanism. By combining glutathione(GSH) potential sensors and ultraperformance liquid chromatography coupled with mass spectrometrywe found that FA reacts with the redox active thiol group present in GSH forming S-hydroxymethyl-GSH and altering the balance between reduced and oxidized GSH. The toxicity of FA can be fullyrescued by thiol-containing antioxidants, indicating that cell antioxidant defences are a target of FA.This novel cytotoxic action of FA might have wide implications for Fanconi Anaemia patients, a cancerpronedisease whose onset has been linked to FA, as well as for cancer development in carriers ofBRCA2 mutations.