Hyperglycaemia-Induced Metabolic Stress Promotes EMT-Driven Therapeutic Resistance in Cancer: Evidence of a Deleterious Feed-Forward Cycle

The phenotypic plasticity of epithelial cells along the epithelial–mesenchymal (E-M) axis, or epithelial–mesenchymal transition (EMT), is a critical aspect of tumour progression and therapeutic resistance. During EMT, epithelial cells gradually acquire mesenchymal traits, facilitating vital functions in embryogenesis, wound healing, fibrosis, and tumour metastasis. This review article investigates the potential interplay between hyperglycaemia-induced metabolic stress and EMT in the context of therapeutic resistance. The study examines a complex, multifaceted network of molecular mechanisms regulating EMT, including specialised transcription factors and signalling pathways as well as growth factors, integrins, and matrix metalloproteinases in various epithelial carcinomas. Emerging findings have demonstrated the existence of EMT hybrid states along the continuum, possessing heightened metastatic potential and distinctive metabolic signatures that play critical roles in the development of therapeutic resistance in cancer cells. Hyperglycaemia has been particularly highlighted for its potential to promote EMT-driven therapeutic resistance through various interconnected mechanisms. Elevated glucose levels induce the increased production of reactive oxygen species (ROS), activation of EMT-promoting transcription factors, and a metabolic shift towards glycolysis. This hyperglycaemic stress involves upregulation of glucose transporters and glycolytic enzymes, creating feed-forward loops that support drug efflux mechanisms and help maintain the mesenchymal phenotype. Clinical data also indicate that hyperglycaemia in OSCC patients is associated with more advanced tumour stages, more extended hospital stays, less effective treatments, and higher rates of local recurrence and distant metastasis. Overall, these insights reveal a deleterious feed-forward loop in which hyperglycaemia promotes EMT-driven therapeutic resistance, with the strongest clinical evidence in oral squamous cell carcinoma (OSCC) and supportive data from pancreatic and breast cancers. Although glycaemic control represents a promising low-risk adjunctive approach, its clinical benefit remains to be validated in prospective interventional studies.