Objective: To assess the expression pattern of X-linked inhibitor of apoptosis protein (XIAP), a cellular stress sensor, and delineate the associated changes in the tumor immune microenvironment (TiME) for prognostic value and new therapeutic targets in inflammatory breast cancer (IBC). Methods: Immunohistochemistry was conducted to assess the spatial localization of immune subsets, XIAP, and PDL1 expression in IBC and non-inflammatory breast cancer (nIBC) pretreatment tumors (n = 142). Validation and further exploration were performed by gene expression analysis of patient tumors along with signaling studies in a co-culture model. Results: High XIAP in 37/81 IBC patients correlated significantly with high PD-L1, increased infiltration of FOXP3+ Tregs, CD163+ tumor-associated macrophages (TAMs), low CD8/CD163 ratio in both tumor stroma (TS) and invasive margins (IM), and higher CD8+ T cells and CD79α+ B cells in the IM. Gene set enrichment analysis identified cellular stress response- and inflammation-related genes along with tumor necrosis factor receptor 1 (TNFR1) expression in high-XIAP IBC tumors. Induction of TNFR1 and XIAP was observed when patient-derived SUM149 IBC cells were co-cultured with human macrophage-conditioned media simulating TAMs, further demonstrating that the TNF-α signaling pathway is a likely candidate governing TAM-induced XIAP overexpression in IBC cells. Finally, addition of Birinapant, a pan IAP antagonist, induced cell death in the pro-survival cytokine-enriched conditions. Conclusion: Using immunophenotyping and gene expression analysis in patient biospecimens along with in silico modeling and a preclinical model with a pan-IAP antagonist, this study revealed an interplay between increased TAMs, TNF-α signaling, and XIAP activation during (immune) stress in IBC. These data demonstrate the potential of IAP antagonists as immunomodulators for improving IBC therapeutic regimens.

Background: Inflammatory Breast Cancer (IBC) is a rare, but highly aggressive variant responsible for 10% of breast cancer related mortality. X-linked inhibitor of apoptosis protein (XIAP) can suppress immune-mediated tumor cell death by its ability to inhibit caspase activity, granzyme release, and activate NFkB and MAPK inflammatory crosstalk signaling. In this study we wanted to assess the pattern of expression of XIAP and to delineate the associated changes in the tumor immune microenvironment (TiME) for prognostic value in invasive breast cancers including inflammatory breast cancer (IBC).

Background XIAP is the most potent inhibitor of both the extrinsic and intrinsic cell death pathways, which is linked to chemotherapy resistance and tumor aggressiveness. We analyzed the correlations between XIAP expression in invasive breast cancers and clinicopathological parameters including metastasis-free survival (MFS) and pathological complete response (pCR) to chemotherapy. Methods Breast cancer databases comprising gene expression profiles with clinicopathological annotations from 8,636 non-redundant non-metastatic, non-inflammatory, primary, invasive patients were analyzed for XIAPexpression (binary variable, ”high” vs.“low” by using median as cut-off). XIAP immunohistochemistry was conducted in a cohort of post-chemotherapy mastectomy samples. Results High XIAP mRNA expression was associated with pathological ductal type, pT1 tumor size, ER-positive, PR-positive, HR+/HER2-, luminal A and B PAM50 subtypes. Analysis of MFS (3,454 non-stage 4) revealed shorter MFS (p = 8.1E-03, log-rank test) associated with “XIAP-high” group. The hazard ratio for metastatic relapse was 1.20 (95%CI 1.05-1.38, p = 8.17E-03, Wald test) in “XIAP-high” vs.“XIAP-low” group.In multivariate analysis, two variables (GGI and pT) remained significant, whereas the TN subtype and XIAPexpression tended to be (p = 0.059). The prognostic value of XIAPwas significant in the multivariate analysis including two major signatures (70-gene signature, Recurrence Score), suggesting independent prognostic value. The same analysis, but in each molecular subtype separately, showed significant difference in the TN subtype (p = 1.0E-03).Univariate analysis of pCR to anthracycline-based neoadjuvant chemotherapy (1,203 patients) identified 20% pCR in the “XIAP-high” group vs.26% in the “XIAP-low” group (p = 0.015, logit function). Immunohistochemistry revealed high XIAP cytoplasmic staining only in invasive tumors and identified correlates with variables like grade, T, N, M and subtype status. Conclusions XIAP-high” tumors are more prone to metastatic relapse and resistance to chemotherapy, suggesting the therapeutic benefit of targeting XIAP in the neoadjuvant setting. Legal entity responsible for the study The authors. Funding Department of Defense W81XWH-17-1-0297 (to G.R. Devi) and Duke School of Medicine Bridge Fund (to G.R.Devi). Disclosure All authors have declared no conflicts of interest.