Histone Deacetylases as Epigenetic Regulators of EMT in Hypoxia-driven Tumor Metastasis: Mechanistic Insights and Therapeutic Implications

INTRODUCTION: The hypoxic microenvironment is a hallmark of solid tumors, driving metastasis through Hypoxia-Inducible Factor-1α (HIF-1α)-mediated Epithelial-Mesenchymal Transition (EMT). Histone deacetylases (HDACs) critically enhance HIF-1α signaling by deacetylation, making them a potential therapeutic target for metastasis inhibition. METHODS: We conducted a systematic review of literature from PubMed, Web of Science, and Embase databases; patent data from WIPO PATENTSCOPE, USPTO, and CNIPA (January 2015 to July 2024); and clinical trial data from ClinicalTrials.gov and the Synapse database. Search terms included MeSH keywords: "Histone Deacetylase Inhibitors," "hypoxia," "Epithelial- Mesenchymal Transition," and "Neoplasm Metastasis." RESULTS: Recent patents demonstrate improved HDAC inhibitor delivery systems and isoformselective compounds, particularly targeting HDAC1/3/6. Clinical data show that HDAC inhibitors reverse EMT markers, such as E-cadherin, in solid tumors, though efficacy varies by cancer type. Mechanistically, HDAC4/6 stabilize HIF-1α through direct deacetylation and Hsp90-P300 regulation, driving hypoxia-induced EMT across multiple cancers. Combination therapies with immunotherapy show promising synergistic effects. DISCUSSION: HDACs regulate hypoxia-induced EMT through HIF-1α stabilization, with isoform- selective inhibitors showing improved tumor specificity. While effective at reversing EMT markers, responses vary by cancer type, necessitating biomarker-guided approaches. Combination therapies show promise but require monitoring for potential risks of EMT induction. CONCLUSION: HDAC inhibition represents a viable strategy against hypoxia-driven metastasis. Future work should optimize selective inhibitors, develop predictive biomarkers, and explore natural compound derivatives to enhance efficacy and reduce toxicity.