ITPKB suppresses ER calcium release to promote CXCL9 expression and enhance immunotherapy sensitivity in triple-negative breast cancer

Immunotherapeutic strategies for triple-negative breast cancer (TNBC) have yielded only modest response rates, severely limiting patients' clinical outcomes. Clarifying the underlying mechanisms to reverse immunotherapy resistance therefore represents a critical unmet need. In this study, we employed the single-cell RNA sequencing (scRNA-Seq) analysis of human TNBC tissues to identify inositol-trisphosphate 3-kinase B (ITPKB) as a central regulator governing cytotoxic T lymphocyte trafficking into the tumor microenvironment (TME). Ectopic expression of ITPKB robustly enhanced the secretion of C-X-C motif chemokine ligand 9 (CXCL9), a critical chemokine required for effective anti-tumor immune responses. Mechanistically, elevated ITPKB activity accelerated the conversion of inositol 1,4,5-trisphosphate (IP3) to inositol 1,3,4,5-tetrakisphosphate (IP4), thereby dampening IP3-driven endoplasmic reticulum (ER) calcium release. Attenuated intracellular calcium ions (Ca^2 +) flux, in turn, promoted the recruitment of signal transducer and activator of transcription 1 (STAT1) and nuclear factor-kappa B (NF-κB) to CXCL9 promoter, driving robust CXCL9 transcription. In addition, utilizing a stepwise virtual screening strategy of 3677 compounds, we identified amentoflavone (AMF) as a novel ITPKB agonist-like compound. AMF treatment could stabilize ITPKB by preventing Trim25-mediated K48-linked ubiquitination and degradation. Notably, in 4T1 and EMT6 syngeneic TNBC murine models, ITPKB-overexpressing or AMF administration exhibited markedly enhanced sensitivity to anti-programmed cell death protein 1 (αPD-1) immune checkpoint blockade. Collectively, these results position ITPKB as a therapeutically tractable molecular switch that remodels the tumor immune landscape via Ca²⁺-dependent transcriptional rewiring. Targeting ITPKB thus represents a promising strategy to overcome immunotherapy resistance and expand the pool of TNBC patients who may benefit from αPD-1-based immunotherapy.