Polymer-based nanodrugs enhance sonodynamic therapy through epigenetic reprogramming of the immunosuppressive tumor microenvironment.

While sonodynamic therapy (SDT) has shown promise in treating triple-negative breast cancer (TNBC) due to its non-invasive nature, deep tissue penetration, and induction of immunogenic cell death (ICD), its efficacy remains limited by the complex immunosuppressive tumor microenvironment (TME). In this study, we developed tumor microenvironment-responsive nanoparticles (GdNPs) to enhance SDT effectiveness through epigenetic reprogramming of the TME by encapsulating the sonosensitizer chlorin e6 (Ce6) and the histone deacetylase 6 (HDAC6) inhibitor Ricolinostat (Ric) (GdNPs/Ce6-Ric). GdNPs/Ce6-Ric effectively accumulate at tumor sites via the enhanced permeability and retention (EPR) effect and release Ce6 and Ric in response to the acidic TME. Upon ultrasound stimulation, GdNPs/Ce6-Ric induce cancer cell apoptosis and trigger ICD by generating reactive oxygen species (ROS), which activate cytotoxic T cells and promote tumor cell elimination. Notably, the epigenetic modulation by Ric within the immunosuppressive TME increased the proportion of natural killer (NK) cells and cytotoxic T cells while decreasing the population of immunosuppressive regulatory T (Treg) cells. This modulation synergistically enhanced the anti-tumor effects of SDT by downregulating the HDAC6/p-STAT3/PD-L1 pathway. Furthermore, GdNPs/Ce6-Ric minimized lung metastases by not only improving systemic immune responses but also inhibiting TGFβ-induced epithelial-mesenchymal transition (EMT) of tumor cells through the blockade of α-tubulin deacetylation. Thus, GdNPs/Ce6-Ric-based epigenetic modulation of the immunosuppressive TME offers a promising approach to enhance the efficacy of SDT in treating TNBC.