Regulatory Mechanisms of XBP1 in Tumorigenesis and Cancer Progression: Challenges and Therapeutic Strategies

Endoplasmic reticulum (ER) stress is a common state of cellular adversity experienced by tumor cells under unfavorable conditions such as hypoxia, nutrient deprivation, and oncogene activation. As the most conserved signaling branch of the unfolded protein response (UPR), the inositol-requiring enzyme 1α (IRE1α)- X-box-binding protein 1 (XBP1) pathway plays a central role in sustaining tumor cell survival, driving malignant progression, and remodeling the tumor microenvironment (TME). XBP1, the terminal transcription factor of this pathway, finely orchestrates tumor cell fate through both its canonical and non-canonical functions. This review systematically summarizes the dual mechanisms of XBP1 in cancer: within cancer cells, XBP1 promotes proliferation, metastasis, and chemoresistance via metabolic reprogramming, anti-apoptotic proteins, and DNA repair; within immune cells (macrophages, dendritic cells, T cells), XBP1 fosters an immunosuppressive microenvironment, while also modulating cancer-associated fibroblasts, endothelial cells, and osteoclasts. Despite its therapeutic promise, several major unresolved questions remain, including the precise molecular switch governing XBP1's pro-tumorigenic versus anti-tumorigenic functions, the functional divergence between XBP1u and XBP1s isoforms in different cellular contexts, and the lack of reliable predictive biomarkers for patient stratification. Key translational challenges involve the on-target toxicity of systemic XBP1/IRE1α inhibition due to its essential roles in normal tissues, the cell-type-specific and context-dependent effects that complicate therapeutic outcomes, and the limited selectivity and off-target effects of current inhibitors, as well as compensatory activation of other UPR branches that may drive adaptive resistance. Finally, this review discusses XBP1-targeted therapeutic strategies, including small-molecule inhibitors, nucleic acid-based drugs, immunotherapeutic combination approaches, and XBP1-based tumor vaccines, and provides perspectives on future research directions, aiming to establish a theoretical foundation for the development of more effective and precise XBP1-targeted therapies for tumorigenesis and cancer progression.