Sculponeatin A induces mitochondrial dysfunction in non‐small cell lung cancer through WWP2‐mediated degradation of mitochondrial STAT3

Abstract Background and Purpose The phosphorylation of signal transducer and activator of transcription 3 (STAT3) monomer at S727 promotes its mitochondrial localisation and regulates mitochondrial function, thus exerting a protective effect on tumour cells. However, no inhibitor drugs targeting mitochondrial STAT3 (mitoSTAT3) or S727‐STAT3 phosphorylation have been identified. Here, we report a novel diterpenoid extracted from Isodon sculponeatus , sculponeatin A (sptA), induces mitochondrial dysfunction in non‐small cell lung cancer (NSCLC) by targeting mitoSTAT3 degradation. Experimental Approach xCELLigence real‐time cell analysis assay and high‐content analysis were performed to measure cytotoxicity. Mitochondrial function was assessed by transmission electron microscopy, mitochondrial permeability transition pore opening and Seahorse cellular flux assays. The effects of sptA on the upstream signalling pathway of mitochondrial dysfunction were measured by Western blot, gene alterations and other approaches. Immunofluorescence and live cell imaging were performed to visualise the expression and position of mitoSTAT3. Nude mice and zebrafish were modelled with subcutaneous xenografts. Pharmacokinetics of sptA were examined in rats. Drug toxicity was evaluated in zebrafish. Key Results sptA inhibited mitochondrial respiration in NSCLC cells. sptA induced mitochondrial dysfunction by promoting the degradation of mitoSTAT3. sptA promoted WW domain containing E3 ubiquitin protein ligase 2 (WWP2)‐mediated ubiquitination and degradation of mitoSTAT3 through direct binding. sptA inhibited tumour growth in vivo. Evaluation of drug toxicity in zebrafish showed that overdose of sptA may cause heart damage. Conclusions and Implications These findings suggest that pharmacological targeting the degradation of mitoSTAT3 by sptA may provide therapeutic benefits against NSCLC.