Challenging a Misnomer? The Role of Inflammatory Pathways in Inflammatory Breast Cancer.

Inflammatory breast cancer is a rare, yet highly aggressive form of breast cancer, which accounts for less than 5% of all locally advanced presentations. The clinical presentation of inflammatory breast cancer often differs significantly from that of noninflammatory breast cancer; however, immunohistochemistry reveals few, if any, distinguishing features. The more aggressive triple-negative and HER2-positive breast cancer subtypes are overrepresented in inflammatory breast cancer compared with noninflammatory breast cancer, with a poorer prognosis in response to conventional therapies. Despite its name, there remains some controversy regarding the role of inflammation in inflammatory breast cancer. This review summarises the current molecular evidence suggesting that inflammatory signaling pathways are upregulated in this disease, including NF-κB activation and excessive IL-6 production among others, which may provide an avenue for novel therapeutics. The role of the tumor microenvironment, through tumor-associated macrophages, infiltrating lymphocytes, and cancer stem cells is also discussed, suggesting that these tumor extrinsic factors may help account for the differences in behavior between inflammatory breast cancer and noninflammatory breast cancer. While there are various novel treatment strategies already underway in clinical trials, the need for further development of preclinical models of this rare but aggressive disease is paramount.

Ehf controls mammary alveolar lineage differentiation and is a putative suppressor of breast tumorigenesis.

The transcription factor EHF is highly expressed in the lactating mammary gland, but its role in mammary development and tumorigenesis is not fully understood. Utilizing a mouse model of Ehf deletion, herein, we demonstrate that loss of Ehf impairs mammary lobuloalveolar differentiation at late pregnancy, indicated by significantly reduced levels of milk genes and milk lipids, fewer differentiated alveolar cells, and an accumulation of alveolar progenitor cells. Further, deletion of Ehf increased proliferative capacity and attenuated prolactin-induced alveolar differentiation in mammary organoids. Ehf deletion also increased tumor incidence in the MMTV-PyMT mammary tumor model and increased the proliferative capacity of mammary tumor organoids, while low EHF expression was associated with higher tumor grade and poorer outcome in luminal A and basal human breast cancers. Collectively, these findings establish EHF as a non-redundant regulator of mammary alveolar differentiation and a putative suppressor of mammary tumorigenesis.

Longitudinal quantification of mouse gastric tumor organoid viability and growth using luminescence and microscopy.

Tumor-derived organoids are valuable for testing anti-cancer drugs in vitro, but existing lysis-based protocols for viability measurement are laborious and restricted at a single time point. Here, we provide a lysis-free protocol for longitudinal and rapid assessment of mouse gastric tumor organoid viability and growth. We describe organoid plating, viability assessment via luminescence measurement, quantification of organoid growth by microscopy imaging, and treatment of organoids with test compounds to evaluate the effects on viability and growth at various time points.

Paracrine IL-6 Signaling Confers Proliferation between Heterogeneous Inflammatory Breast Cancer Sub-Clones.

Inflammatory breast cancer (IBC) describes a highly aggressive form of breast cancer of diverse molecular subtypes and clonal heterogeneity across individual tumors. Accordingly, IBC is recognized by its clinical signs of inflammation, associated with expression of interleukin (IL)-6 and other inflammatory cytokines. Here, we investigate whether sub-clonal differences between expression of components of the IL-6 signaling cascade reveal a novel role for IL-6 to mediate a proliferative response in trans using two prototypical IBC cell lines. We find that SUM149 and SUM 190 cells faithfully replicate differential expression observed in a subset of human IBC specimens between IL-6, the activated form of the key downstream transcription factor STAT3, and of the HER2 receptor. Surprisingly, the high level of IL-6 produced by SUM149 cells activates STAT3 and stimulates proliferation in SUM190 cells, but not in SUM149 cells with low IL-6R expression. Importantly, SUM149 conditioned medium or co-culture with SUM149 cells induced growth of SUM190 cells, and this effect was abrogated by the IL-6R neutralizing antibody Tocilizumab. The results suggest a novel function for inter-clonal IL-6 signaling in IBC, whereby IL-6 promotes in trans proliferation of IL-6R and HER2-expressing responsive sub-clones and, therefore, may provide a vulnerability that can be exploited therapeutically by repurposing of a clinically approved antibody.

Tumor Growth Remains Refractory to Myc Ablation in Host Macrophages.

Aberrant expression of the oncoprotein c-Myc (Myc) is frequently observed in solid tumors and is associated with reduced overall survival. In addition to well-recognized cancer cell-intrinsic roles of Myc, studies have also suggested tumor-promoting roles for Myc in cells of the tumor microenvironment, including macrophages and other myeloid cells. Here, we benchmark Myc inactivation in tumor cells against the contribution of its expression in myeloid cells of murine hosts that harbor endogenous or allograft tumors. Surprisingly, we observe that LysMCre-mediated Myc ablation in host macrophages does not attenuate tumor growth regardless of immunogenicity, the cellular origin of the tumor, the site it develops, or the stage along the tumor progression cascade. Likewise, we find no evidence for Myc ablation to revert or antagonize the polarization of alternatively activated immunosuppressive macrophages. Thus, we surmise that systemic targeting of Myc activity may confer therapeutic benefits primarily through limiting Myc activity in tumor cells rather than reinvigorating the anti-tumor activity of macrophages.

The angiotensin receptor blocker, Losartan, inhibits mammary tumor development and progression to invasive carcinoma.

Drugs that target the Renin-Angiotensin System (RAS) have recently come into focus for their potential utility as cancer treatments. The use of Angiotensin Receptor Blockers (ARBs) and Angiotensin-Converting Enzyme (ACE) Inhibitors (ACEIs) to manage hypertension in cancer patients is correlated with improved survival outcomes for renal, prostate, breast and small cell lung cancer. Previous studies demonstrate that the Angiotensin Receptor Type I (AT1R) is linked to breast cancer pathogenesis, with unbiased analysis of gene-expression studies identifying significant up-regulation of AGTR1, the gene encoding AT1R in ER+ve/HER2-ve tumors correlating with poor prognosis. However, there is no evidence, so far, of the functional contribution of AT1R to breast tumorigenesis. We explored the potential therapeutic benefit of ARB in a carcinogen-induced mouse model of breast cancer and clarified the mechanisms associated with its success.Mammary tumors were induced with 7,12-dimethylbenz[α]antracene (DMBA) and medroxyprogesterone acetate (MPA) in female wild type mice and the effects of the ARB, Losartan treatment assessed in a preventative setting (n = 15 per group). Tumor histopathology was characterised by immunohistochemistry, real-time qPCR to detect gene expression signatures, and tumor cytokine levels measured with quantitative bioplex assays. AT1R was detected with radiolabelled ligand binding assays in fresh frozen tumor samples.We showed that therapeutic inhibition of AT1R, with Losartan, resulted in a significant reduction in tumor burden; and no mammary tumor incidence in 20% of animals. We observed a significant reduction in tumor progression from DCIS to invasive cancer with Losartan treatment. This was associated with reduced tumor cell proliferation and a significant reduction in IL-6, pSTAT3 and TNFα levels. Analysis of tumor immune cell infiltrates, however, demonstrated no significant differences in the recruitment of lymphocytes or tumour-associated macrophages in Losartan or vehicle-treated mammary tumors.Analysis of AT1R expression with radiolabelled ligand binding assays in human breast cancer biopsies showed high AT1R levels in 30% of invasive ductal carcinomas analysed. Furthermore, analysis of the TCGA database identified that high AT1R expression to be associated with luminal breast cancer subtype.Our in vivo data and analysis of human invasive ductal carcinoma samples identify the AT1R is a potential therapeutic target in breast cancer, with the availability of a range of well-tolerated inhibitors currently used in clinics. We describe a novel signalling pathway critical in breast tumorigenesis, that may provide new therapeutic avenues to complement current treatments.