GTN enhances antitumor effects of doxorubicin in TNBC by targeting the immunosuppressive activity of PMN-MDSC

An immunosuppressive tumor microenvironment is one of the major obstacles to the efficacy of standard chemotherapies, such as doxorubicin, used to treat triple negative breast cancer (TNBC). Combination therapy may be a potential way to overcome this barrier. A nitric oxide (NO) donor such as glyceryl trinitrate (GTN) has shown beneficial effects in combination with standard chemotherapy/radiotherapy in patients with cancer. In this study, we investigated the combination of doxorubicin/GTN in a mouse model of TNBC. The results indicated that GTN significantly improved the anti-tumor efficacy of doxorubicin in mouse models of BC. Flow cytometry and immunohistochemistry analysis revealed that the GTN/doxorubicin combination increases the intra-tumor recruitment and activation of CD8+ lymphocytes that is associated with the ability of doxorubicin and doxorubicin/GTN to recruit and dampen the immunosuppressive function of PMN-MDSCs PD-L1low. Mechanistically, in PMN-MDSC, doxorubicin/GTN combination reduced STAT5 phosphorylation, while GTN +/- doxorubicin induced a ROS-dependent cleavage of STAT5 associated with a decrease of FATP2. Our results identify a new combination enhancing the immune-mediated anticancer therapy in a TNBC mouse model through a ROS-dependent reprograming of PMN-MDSCs towards a less immunosuppressive phenotype. These findings open up a new therapeutic perspective by combining GTN to doxorubicin for patients with TNBC. Overall design: RNA pofiles of 4T1-tumor bearing Balb/c mice treated ot not by doxorubicin +/- GTN