Pharmacological manipulation of Ezh2 with salvianolic acid B results in tumor vascular normalization and synergizes with cisplatin and T cell-mediated immunotherapy

Tumor vasculature is characterized by aberrant structure and function, resulting in immune suppressive profiles of tumor microenvironment (TME) through limiting immune cell infiltration into tumors. The defective vascular perfusion in tumors also impairs the delivery and efficacy of chemotherapeutic agents. Targeting abnormal tumor blood vessels has emerged as an effective therapeutic strategy to improve the outcome of chemotherapy and immunotherapy. In this study, we demonstrated that Salvianolic acid B (SalB), one of the major ingredients of Salvia miltiorriza elicited vascular normalization in the mouse models of breast cancer, contributing to improved delivery and response of chemotherapeutic agent cisplatin as well as attenuated metastasis. Moreover, SalB in combination with anti-PD-L1 blockade retarded tumor growth, which was mainly due to elevated infiltration of immune effector cells and boosted delivery of anti-PD-L1 into tumors. Mechanistically, tumor cell enhancer of zeste homolog 2 (Ezh2)-driven cytokines disrupted the endothelial junctions with diminished VE-cadherin expression, which could be rescued in the presence of SalB. The restored vascular integrity by SalB via modulating the interactions between tumor cells and endothelial cells (ECs) offered a principal route for achieving vascular normalization. Taken together, our data elucidated that SalB enhanced sensitivity of tumor cells to chemotherapy and immunotherapy through triggering tumor vascular normalization, providing a potential therapeutic strategy of combining SalB and chemotherapy or immunotherapy for patients with breast cancer.