Investigating hypoxia-inducible factor signaling in cancer: Mechanisms, clinical implications, targeted therapeutic strategies, and resistance.

Hypoxia, a hallmark of the tumor microenvironment (TME), drives cancer progression through immune modulation, angiogenesis promotion, metabolic reprogramming, and uncontrolled cell proliferation. This review explores the diverse functions of hypoxia-inducible factor (HIF) signaling in cancer development and progression, providing a comprehensive overview of the molecular pathways. HIFs, particularly HIF-1α and HIF-2α, regulate several genes related to cancer hallmarks such as invasion, metabolic reprogramming, angiogenesis, and therapy resistance, thus mediating a significant portion of the hypoxic response. Hydroxylation of proline and asparagine residues in HIF-α subunits, which occurs in an oxygen-dependent manner, serves as a key regulatory mechanism for both their stability and transcriptional function. Notably, this complex interaction is regulated by multiple signaling pathways, including the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK), phosphoinositide 3-kinase/protein kinase B/mechanistic target of rapamycin (PI3K/Akt/mTOR), and Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways. In cancer, HIF signaling affects several aspects of tumor cell biology that contribute to the cancerous characteristics, including angiogenesis induction through the upregulation of vascular endothelial growth factor (VEGF) expression, metabolic reprogramming through the enhancement of the Warburg effect, facilitation of cancer invasion and metastasis by driving epithelial-to-mesenchymal transition (EMT) and matrix remodeling patterns, and mediation of therapeutic resistance partly due to the effects on drug efflux pumps and DNA damage repair. Direct and indirect HIF inhibitors-including small molecules, peptidomimetics, antibodies, and proteolysis-targeting chimeras (PROTACs)-are under preclinical and clinical evaluation for their therapeutic efficacy. Preclinical and early clinical trials have demonstrated significant synergistic effects in inhibiting tumor development when HIF inhibition is combined with traditional therapies (chemotherapy or radiation) or immunotherapies, emphasizing major clinical implications and the potential for improving patient outcomes. Although challenges exist, particularly regarding drug resistance, further research to improve therapeutic efficacy and prolong survival for patients is warranted.