Effect of doxorubicin on efficacy of immune checkpoint inhibitors through increasing infiltration of CD8-positive T cells and activating STAT1-IRF1-CXCL10 axis.

e13095 Background: Immune checkpoint inhibitors (ICIs) generate an enduring clinical remission in metastatic cancers. However, the efficacy of ICIs monotherapy for triple negative breast cancer (TNBC) is limited. Strategies are urgently needed to enhance anticancer immune responses in TNBC to prolong survival of patients. Methods: BALB/c mice subcutaneous tumor experiments were done to evaluate the efficacy of doxorubicin combined with PD-1 inhibitor, compared with other chemotherapy including cisplatin and paclitaxel. RNA-seq and single-sample gene set enrichment analysis (ssGSEA) were done with our collected mice tumor tissue to observe changes of tumor immune environment in TNBC after chemotherapy combined with immunotherapy. Then, we performed coculture, Transwell assay and FACs in TNBC cell lines, including MDA-MB-231, BT549 and 4T1, and primary CD8+T cells, to assess effects of doxorubicin on CD8+T cell migration in vitro. Gene Ontology (GO) and Kyoto Encyclopedia of Genes, Genomes (KEGG) analysis were enriched from RNA-seq data to seek for a pathway. We analyzed the difference of CD8+T cell infiltration related gene expression, including CCL2, CCL3, CCL4, CCL5, CXCL9, CXCL10, CXCL11. Western blot, qPCR and ELISA were utilized to explore possible mechanism in stronger migration of CD8+T cells by doxorubicin. Rescue assays were used to confirm the involved mechanisms. Results: Subcutaneous tumor experiment showed that doxorubicin could enhance the efficacy of immune checkpoint inhibitors (p＜0.05),andthe immune microenvironment in TNBC transferred from "anti-inflammatory" to "proinflammatory" status after doxorubicin combined with immunotherapy, compared with other chemotherapy drugs combined with immunotherapy. Higher CD8+T cells infiltration occurred in TNBC treated with doxorubicin in vivo (p＜0.05). The CD8+T cells migration assay demonstrated a higher CD8+T cell migration with doxorubicin in vitro (p＜0.05). KEGG analysis revealed that the chemokine-related pathway was significantly activated after doxorubicin treatment, in which CXCL10 chemokine was most likely to be responsible for CD8+T cell infiltration based on its expression and secretion (both p<0.01). Further experiments demonstrated that the expression of the whole STAT1-IRF1-CXCL10 axis was up-regulated in TNBC mice treated with doxorubicin (p＜0.01), and the STAT1-IRF1-CXCL10 axis was also activated in doxorubicin-treated TNBC cell lines (p＜0.0001). Conclusions: This research demonstrated that doxorubicin can enhance efficacy of immune checkpoint inhibitors through increasing infiltration of CD8+T cells in triple-negative breast cancer via activating STAT1-IRF1-CXCL10 axis. These results provide rationales of doxorubicin combined with PD-1 inhibitor for extending survival of TNBC patients.