Ultrasound-Activated Nanoinhibitors Blocking the Chemo-Immune Checkpoint to Overcome Chemotherapy-Induced Immune Resistance.

Breast cancer features an immunosuppressive tumor microenvironment following chemotherapy and develops resistance to conventional immune checkpoint inhibitors. Through single-cell database mining and in vitro analysis, we demonstrate that chemotherapy upregulates Xkr8 expression and promotes phosphatidylserine (PS) externalization, which mediates macrophage- and dendritic cell (DC)-intrinsic immunosuppression. To address this, we fabricate an ultrasound-activated nanoinhibitor (Sono-TT8) that co-delivers tirapazamine (TPZ) and siXkr8 using a TiO2-derived sonosensitizer functionalized with the tLyP-1 peptide for active targeting of neuropilin-1 (NRP-1)-overexpressing tumor cells. Upon ultrasound irradiation, Sono-TT8 induces mitochondrial dysfunction and exacerbates local hypoxia to activate TPZ, while concurrently delivering siXkr8 to silence the Xkr8-PS axis during chemotherapy-induced apoptosis. This nanoinhibitor reprograms the tumor immunosuppressive microenvironment and reduces tumor growth. Furthermore, Sono-TT8 exhibits superior tumor suppression and synergizes with αPD-L1 to inhibit metastatic progression. Our work establishes a chemo-immune checkpoint blockade strategy to overcome immune resistance in breast cancer, offering a nanosensitization approach compatible with multiple clinical treatment modalities.