Inflammatory Breast Cancer Cell Lines Research Articles

Abstract PO2-24-03: Soluble E-cadherin promotes inflammatory breast cancer tumorigenesis via PDIA4-mediated suppression of ferroptosis

Abstract Background: Inflammatory breast cancer (IBC) is an aggressive form of breast cancer known for its rapid progression and high metastatic potential without known distinctive drivers. Currently, there are no FDA-approved targeted therapies specifically for IBC patients, highlighting the urgent need for novel and effective treatments. Through our investigation of metastatic xenograft IBC sublines, we have identified soluble E-cadherin (sEcad), an extracellular proteolytic fragment of full-length E-cadherin, as a protein associated with IBC tumor progression. We hypothesize that sEcad promotes IBC tumorigenesis by suppressing ferroptosis. Methods: MDA-IBC3 (ER–/HER2+) and SUM149 (ER–/HER2–) IBC cell lines were used in this study. Stable overexpression of sEcad in IBC cell lines was achieved using lentiviral vectors. Cell death for ferroptosis was measured by propidium iodide staining using flow cytometry. Mass spectrometry and Bio-ID-based proteomics assays were used to identify sEcad-interacting proteins and potential mechanisms. For in vivo studies, control and sEcad -overexpressing SUM149 and MDA-IBC3 cells were injected into the cleared mammary fat pads of SCID/Beige mice and tumor growth was monitored via caliper measurements. Serum sEcad levels from IBC patients (n=301) were analyzed by ELISA. Results: High serum sEcad levels in IBC patients correlated with poorer OS (p=0.02) and earlier development of metastasis (p=0.006). Overexpression of sEcad in IBC cell lines enhanced cell proliferation and colony formation in vitro. Mice injected with sEcad-overexpressing SUM149 and MDA-IBC3 cells had significantly higher tumor growth rates compared to controls (SUM149: p=0.007; MDA-IBC3: p=0.006). Mechanistically, mass spectrometry and Bio-ID assays identified Protein Disulfide Isomerase Family A Member 4 (PDIA4) as a novel binding partner of sEcad, which was validated through co-immunoprecipitation. Additionally, sEcad increased the expression of PDIA4, an enzyme that plays a role in cellular redox regulation and protein folding. PDIA4 has been shown to regulate key players of ferroptosis such as ATF4, SLC7A11. Our results showed that, compared to controls, sEcad-overexpressing IBC cells displayed significant resistance to ferroptosis inducers, including RSL3, FIN56, and sulfasalazine. Knockdown of PDIA4 in sEcad high-expressing cells significantly increased their sensitivity to ferroptosis-promoting drugs. Moreover, we found that PDIA4 regulates ATF4 to impact ferroptosis-mediated cell death in IBC cells. Conclusions: Our study shows that sEcad affects ferroptosis through PDIA4, impacting tumorigenesis in IBC. These findings uncover a novel and pivotal role for sEcad in IBC tumor growth and progression, providing new insights and potential therapeutic targets for IBC patients. Citation Format: Xiaoding Hu, Yun Xiong, Emilly Villodre, Juhee Song, Debu Tripathy, Wendy Woodward, Savitri Krishnamurthy, Junjie Chen, Bisrat Debeb. Soluble E-cadherin promotes inflammatory breast cancer tumorigenesis via PDIA4-mediated suppression of ferroptosis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-24-03.

Abstract PO2-14-10: A selective MCL-1 inhibitor AZD5991 showed tumor regression in a triple-negative inflammatory breast cancer xenograft model

Abstract Background Triple-negative breast cancer (TNBC) accounts for 15-20% of all breast cancer diagnoses but up to 30% of breast cancer-related deaths. Similarly, Inflammatory breast cancer (IBC) accounts for 2-4% of breast cancer diagnosis but causes 8%–10% of all breast cancer-related deaths. The myeloid cell leukemia-1 (MCL-1) is a member of the BCL-2 family of proteins, which is highly amplified in numerous human cancers and associated with cell immortalization, transformation, and chemoresistance. In fact, MCL-1 is amplified in 55% of TNBC after preoperative chemotherapy. Amongst the MCL-1 inhibitors that have been developed, AZD5991 showed high selectivity and affinity for MCL-1. In myeloma and acute myeloid leukemia cells AZD5991 induces apoptosis and showed anti-tumor effects in in vivo models. In the present study, we evaluated the biological role of the MCL-1 inhibitor AZD5991 in IBC and TNBC in vitro and in vivo models. Materials and methods The expression of the MCL-1 gene was analyzed in the World Consortium IBC patient dataset. Next, we screened a panel of TNBC and IBC cell lines for MCL-1 expression by western blot analysis. The effect of AZD5991 on TNBC and IBC cells was analyzed via cell titer-blue proliferation, clonogenic assays and soft agar assay. To further validate these findings, we used siRNA to knockdown MCL-1 and performed cell proliferation, clonogenic and migration assays. To identify signaling pathways involved in MCL-1 Inhibitor’s effects we performed a proteome profiler human apoptosis array in TNBC cells in the presence of AZD5991. The anti-tumor effect of the MCL-1 inhibitor was evaluated using a SUM-149 (TN-IBC) orthotopic xenograft mouse model. The mice were treated with AZD5991 at doses of 15 and 30mg/kg once weekly via tail vein injection for a duration of 4 weeks. Results The mean expression level of MCL-1 was higher in patients with TNBC than in those with non-TNBC. Further, compared to the patients with ER positive, HER-2 negative tumors those with TNBC showed an increased in the mean expression of MCL-1 gene (p value= 0.05). We screened a panel of TNBC and IBC cell lines in which most of the cell lines showed high levels of MCL-1. The cell proliferation assay showed IC50 ranging from 0.27 – 19.6 μM. The SUM149, SUM190, FCIBC02, MDA-IBC3 and MDA-MB-468 cells showed high sensitivity and showed significant decrease in the proliferation rate while BCX010, KPL4, MDA-MB-231, 4T1.2 and E0771 cells as well as the normal breast cells MCF10A exhibited resistance with no significant decrease in proliferation. The clonogenic and soft agar assays with these sensitive and resistant cell lines showed similar results. Further, these findings were validated via genetic knockdown of MCL-1 which resulted in a significant decrease in cell proliferation, colony formation and migration capability of the TNBC cells. To identify signaling pathways involved in MCL-1 Inhibitor’s phenotypic changes, we performed a proteome profiler human apoptosis array which showed a decreased in BCLx expression, and an increase in expression of BAX and phospho-Rad17 proteins in the AZD5991 treated TN-IBC cells. Finally, in a SUM-149 (TN-IBC) orthotopic xenograft mouse model, mice injected with 30mg/kg showed a significant tumor regression compared to the vehicle-treated mice (vehicle vs 30 mg/kg, p value=0.0006). Conclusions and Future directions Our data demonstrates that AZD5991 inhibits tumorigenesis in an inflammatory breast cancer xenograft model. We are currently validating several significant targets to understand the biological mechanisms related to our candidate drug. Our long-term goal is to develop MCL-1 targeted therapy in combination with standard-of-care treatment for inflammatory and triple-negative breast cancers. Citation Format: Mohd Mughees, Moises Tacam, Alex Tan, Michael White, Bisrat Debeb, Emilly Villodre, Xiaoding Hu, Debu Tripathy, Wendy Woodward, Rachel Layman, Geoffrey Bartholomeusz, Chandra Bartholomeusz. A selective MCL-1 inhibitor AZD5991 showed tumor regression in a triple-negative inflammatory breast cancer xenograft model [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-14-10.

A study of antibody conjugates for the treatment of inflammatory breast cancer.

e15016 Background: Inflammatory breast cancer (inflammatory carcinoma) is a rare metastatic malignant tumor, it accounts for about 2% of all breast cancer cases. Despite its low incidence, inflammatory breast cancer is highly invasive, its five-year survival rate is less than 41%, making its prognosis the worst of all breast cancer subtypes, and effective drugs are urgently needed in clinical practice. Therefore, our study develops novel antibody conjugate drugs that can target overexpressed-ICAM-1 in inflammatory breast cancer cells as an original molecular target precisely. Methods: In this study, flow cytometry was used to perform precise and quantitative target screening of inflammatory breast cancer cell lines (SUM-149, KPL4), the endocytosis efficiency of ADC drugs was verified by flow cytometry efficiency analysis and single-photon confocal analysis, and the cytotoxicity of different drugs and cell lines was explored by CCK8 experiment. A nude mouse model of orthotopic xenograft inflammatory breast cancer was constructed, and the in vivo therapeutic effect of inflammatory breast cancer was observed by intravenous injection of two ICAM-1 antibody conjugates (ICAM-1-MMAE and ICAM-1-DXD), also the ADC drug structure with the best therapeutic effect for inflammatory breast cancer was screened. Results: ICAM-1 molecule in a variety of inflammatory breast cancer cell lines were highly over-expressed, and the antibody internalization rate was 51% at 4h, and after the peak the endocytosis efficiency slowed down into the plateau stage; ICAM1-MMAE and ICAM1-DXD are safer than first-line chemotherapy agents for breast cancer; The tumor volume was significantly reduced after administration into the orthotopic breast cancer xenograft model, which further verified the obvious effect of ADC drugs in vivo. Conclusions: Both ICAM-1-MMAE and ICAM-1-DXD have shown significant anti-inflammatory breast cancer effects in vitro and in vivo, and this study provides potential antibody conjugate drugs for targeted therapy of inflammatory breast cancer, which is expected to help improve the poor prognosis of inflammatory breast cancer.

Abstract 1580: LCN2 is a therapeutic target against inflammatory breast cancer

Abstract Breast cancer (BC) is the most common cancer type accounting for 12% of annual cancer cases worldwide. In the United States, 30% of the newly diagnosed cancer cases in woman are BC. Inflammatory breast cancer (IBC) is a rare and aggressive subtype of BC that accounts for 1 to 5% of all types of BC. Due to its inflammatory characteristics and the absence of a palpable mass, IBC is usually confounded with a mastitis. Once properly diagnosed, IBC has already metastasized. A high portion of IBC tumors overexpress human epidermal growth factor receptor 2 (HER2). These IBC patients (HER2+) are treated with Trastuzumab, a monoclonal antibody. However, many IBCs become resistant to this therapy. Thus, there is not an optimal treatment against this horrendous disease. One potential target against IBC is Lipocalin-2 (LCN2), a secreted protein involved in iron homeostasis, immune responses, transport of siderophores, and epithelial cell differentiation. In many aggressive tumors, high levels of LCN2 have been associated with increased cancer cell motility, proliferation, angiogenesis, invasion, and metastasis. Our research team published that LCN2 is aberrantly abundant in IBCs compared with non-IBC patients and cell lines and showed that small interference RNAs (siRNAs) targeting LCN2 effectively reduced the cell proliferation and invasion ability of IBC cells. Therefore, to understand the mechanisms involved after LCN2 knockdown, we did a RNA-sequencing using IBC3 cells transfected with LCN2-siRNA or with a negative control siRNA, where we identified 138 dysregulated genes. Genes as SOX18, which correlates to distant metastasis and poor clinical prognosis in cancer, and as LRP4, which correlates to proliferating clinical features by activating the PI3K/AKT pathway were identified. We used the Ingenuity Pathway Analysis software to identify the pathways regulated after LCN2 knockdown and found 25 canonical pathways altered. These results will be further validated by qPCR and Western Blot analysis. Also, after the identification of LCN2 as a plausible target for therapy against IBC, we worked on the preparation of a Herceptin-conjugated liposome loaded with siRNA against LCN2, to improve internalization in HER2+ IBC cells. We developed a three step reaction to obtain trastuzumab DSPE-PEG(2000) maleimide conjugates used to prepare the liposomal formulation. Trastuzumab conjugated liposomes were prepared and characterized using dynamic light scattering to measure their size distribution. Our formulation displayed sizes of 18.3 and 73.7 nm which could correspond to free DSPE-PEG(2000) trastuzumab and the trastuzumab-liposome, respectively. There is ongoing work to determine the optimal timepoint for internalization of liposomes into IBC cell lines and further treatment with liposomes charged with siRNA LCN2 to treat cell lines and determine the biological effect with the aim of developing a targeted treatment for inflammatory breast cancer. Citation Format: Marienid Flores-Colon, Pablo E. Vivas-Mejia. LCN2 is a therapeutic target against inflammatory breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1580.

Abstract GS5-08: Soluble E-cadherin: a novel prognostic biomarker and driver of brain metastasis in inflammatory breast cancer

Abstract Background: Inflammatory breast cancer (IBC) is a highly aggressive form of breast cancer with rapid onset and a strong propensity to spread to distant organs. Five-year overall survival (OS) rates remain poor, in part because of the high risk of brain metastasis: 19% of patients with IBC have brain metastases within the first 2 years after diagnosis. Our hypothesis for this study was that soluble E-cadherin (sEcad), an 80-kDa extracellular proteolytic fragment of full-length E-cadherin - a tumor promoter in IBC, is crucial for driving brain metastasis in IBC. Methods: We analyzed serum sEcad levels in from 348 IBC patients by ELISA. Four IBC cell lines [ER–/HER2+ (MDA-IBC3; SUM190) and ER–/HER2– (SUM149; BCX010)], human brain microvascular endothelial cells, and immortalized human astrocytes were used in this study. Stable overexpression of sEcad in IBC cell lines was achieved using lentiviral vectors. Mass spectrometry and Bio-ID-based proteomics assays, and RNA sequencing were used to identify sEcad-interacting proteins and potential mechanisms. In vivo, we studied tumor growth and brain metastasis in mice by injecting IBC cells into the mammary fatpad or tail vein, respectively, of SCID/Beige mice. Results: In IBC patients, higher serum sEcad levels correlated with poorer OS (p=0.02), earlier development of metastasis (p=0.006), and development of brain metastasis (p=0.04). On multivariable analysis, sEcad independently predicted OS (hazard ratio [HR]=2.07 [95% CI 1.19-3.60], p=0.01). In vitro, sEcad overexpression in IBC cell lines promoted anchorage-independent growth, migration, invasion, and resistance to anoikis. In vivo, sEcad-overexpressing SUM149 cells promoted primary tumor growth (p=0.007). Mice injected with sEcad-overexpressing MDA-IBC3 cells also had higher incidence of brain metastasis (100% vs 50%, p=0.03), metastatic burden (p=0.02) and number of metastases per mouse (p=0.0009), and had worse OS (p=0.0016), and brain metastasis-free survival (p=0.04), relative to controls. We further found that sEcad increased cancer cell adhesion to brain endothelial cells (p=0.01) and promoted induction of reactive astrocytes (as identified by high glial fibrillary acidic protein levels) in vitro and in vivo. Mechanistically, mass spectrometry and Bio-ID assays identified X-linked inhibitor of apoptosis protein (XIAP), a potent inhibitor of apoptotic cell death, as a novel binding partner of sEcad, which was validated through co-immunoprecipitation. Further analysis showed that sEcad bound to the BIR2 domain of XIAP. XIAP is the most potent and best-defined anti-apoptotic IAP family member, and it could induce NF-κB activation to inhibit tumor cell apoptosis Gene set enrichment analysis of RNA-seq profiling data showed activation of NF-kB signaling and downregulation of apoptotic pathways in the sEcad-overexpressing SUM149 cells compared with controls. Immunoblotting revealed that sEcad enhanced XIAP expression, activated NF-κB signaling, and inhibited cleavage of caspase-3 in IBC cells. Conclusions: We found that higher serum sEcad correlates with development of brain metastases and independently predicts poor OS in patients with IBC. We further found that sEcad promotes tumor growth and brain metastasis, perhaps via activation of XIAP/NF-κB signaling in breast cancer cells and promotion of endothelial cell adhesion and reactive astrocytosis in the brain microenvironment. These findings uncover a novel and crucial role for sEcad in brain metastasis and provide new insights and potential therapeutic targets for patients with metastatic IBC. Citation Format: Xiaoding Hu, Yun Xiong, Emilly S. Villodre, Juhee Song, Ganiraju C Manyam, Moises J Tacam, Jing Wang, Chandra Bartholomeusz, Debu Tripathy, Naoto T. Ueno, Wendy Woodward, Savitri Krishnamurthy, Junjie Chen, Bisrat Debeb. Soluble E-cadherin: a novel prognostic biomarker and driver of brain metastasis in inflammatory breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr GS5-08.

Abstract P6-10-08: Evaluation of potent novel second-generation MELK-selective inhibitor in aggressive breast cancers

Abstract Background Inflammatory breast cancer (IBC) and triple-negative breast cancer (TNBC) are aggressive breast cancer subtypes with poor clinical outcomes due to the lack of well-validated and actionable targets and the onset of chemo-resistant metastasis. TNBC and IBC account for 15-20% and 2-4% of all breast cancer diagnoses but result in 30% and 8%–10% of breast cancer-related deaths, respectively. MELK (maternal embryonic leucine zipper kinase) is a potential therapeutic target in both TNBC and triple-negative IBC (TN-IBC). We have shown that 1) MELK expression is higher in basal tumors (mostly TNBC) and in IBC than in non-IBC, 2) high MELK expression is an independent prognostic factor for poor overall survival (P=0.0002) and poor distant metastasis-free survival (P=0.008) in breast cancer, and 3) MELK knockout leads to significantly lower metastatic burden and prolonged survival in a xenograft model of TNBC (unpublished data). MELK inhibitor (MELKi) OTS167 is in clinical trials but it lacks specificity and cross-reacts with other essential kinases. It is critical to discover novel, selective inhibitors with good bioavailability that target MELK and minimize adverse effects. We have developed a second-generation small-molecule MELK inhibitor 30e that is a highly potent and slow-binding ATP-competitive inhibitor of MELK. 30e exhibits potent cellular inhibition of MELK (IC50< 10 nM), as assessed using a live cell NanoBRET assay, and is highly selective as assessed by live-cell KiNativ profiling experiments in MDA-MB-231 TNBC cells. Methods We screened a panel of TNBC and IBC cell lines for MELK expression by western blot and qPCR analysis. We assessed the effects of MELK inhibition with the 30e on migration and invasion. The role of MELK in regulating cancer stem cell phenotypes was assessed using the mammosphere assay and flow cytometry (CD44+/CD24-/low surface marker). MELK’s protumorigenic role was determined in vitro using a soft agar assay, and the anti-tumor activity of 30e was assessed in vivo using a TN-IBC orthotopic xenograft mouse model. Results We found that TNBC had high mRNA levels of MELK (62%) compared to non-TNBC cell lines (25%), which correlated with MELK protein levels. 30e inhibited cell viability in TNBC and IBC cells in a dose-dependent manner and with IC50s ranging from 0.45 to 1.76 μM (P≤0.05). However, no significant effect was observed when normal MCF-10A breast cells were treated with 30e (IC50>20 μM). 30e also significantly reduced colony formation ability. Further, we observed that 30e reduced mammosphere formation efficiency and the CD44+/CD24-/low subpopulation in both TNBC and IBC cells in a dose-dependent manner (P≤0.05), suggesting the potential of 30e to inhibit the stem cell population in vitro. The soft agar assay also showed a significant decrease in colony formation in the TNBC and IBC cells after treatment with 30e, an indirect indicator of in vivo tumorigenicity. To assess the efficacy of 30e treatment on tumor growth, we evaluated this inhibitor as a single agent in a SUM-149 (TN-IBC) orthotopic mouse model. The mice were treated with intraperitoneal injections daily with 3 doses (2.5, 5, and 10 mg/kg) of 30e. Our data show that 30e suppressed tumor growth in a dose-dependent manner (P< 0.007). Conclusions and Future Directions Our data demonstrate that a novel, potent and specific MELK inhibitor inhibits tumor growth by suppressing the cancer stem cell phenotype. MELK is a promising target for aggressive cancers such as TNBC and IBC. We are evaluating how MELK inhibition modulates the tumor microenvironment, which is a critical component of breast cancer response to treatment. We performed a cytokine antibody array and are validating the top targets. Further, we will evaluate 30e in combination with standard-of-care treatment for toxicity and inhibition of metastasis. Citation Format: Mohd Mughees, Moises Tacam, Alex Tan, Hector Gonzalez, Emilly S. Villodre, Bisrat Debeb, Debu Tripathy, Geoffrey Bartholomeusz, Juhyeon Lee, Kevin Dalby, Chandra Bartholomeusz. Evaluation of potent novel second-generation MELK-selective inhibitor in aggressive breast cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-08.

MARCKS as a Potential Therapeutic Target in Inflammatory Breast Cancer.

Inflammatory breast cancer (IBC) is the most pro-metastatic form of breast cancer (BC). We previously demonstrated that protein overexpression of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) protein was associated with shorter survival in IBC patients. MARCKS has been associated with the PI3K/AKT pathway. MARCKS inhibitors are in development. Our objective was to investigate MARCKS, expressed preferentially in IBC that non-IBC (nIBC), as a novel potential therapeutic target for IBC. The biologic activity of MPS, a MARCKS peptide inhibitor, on cell proliferation, migration, invasion, and mammosphere formation was evaluated in IBC (SUM149 and SUM190) and nIBC (MDA-MB-231 and MCF7) cell lines, as well as its effects on protein expression in the PTEN/AKT and MAPK pathways. The prognostic relevance of MARCKS and phosphatase and tensin homolog (PTEN) protein expression as a surrogate marker of metastasis-free survival (MFS) was evaluated by immunohistochemistry (IHC) in a retrospective series of archival tumor samples derived from 180 IBC patients and 355 nIBC patients. In vitro MPS impaired cell proliferation, migration and invasion, and mammosphere formation in IBC cells. MARCKS inhibition upregulated PTEN and downregulated pAKT and pMAPK expression in IBC cells, but not in nIBC cells. By IHC, MARCKS expression and PTEN expression were negatively correlated in IBC samples and were associated with shorter MFS and longer MFS, respectively, in multivariate analysis. The combination of MARCKS-/PTEN+ protein status was associated with longer MFS in IBC patient only (p = 8.7 × 10−3), and mirrored the molecular profile (MARCKS-downregulated/PTEN-upregulated) of MPS-treated IBC cell lines. In conclusion, our results uncover a functional role of MARCKS implicated in IBC aggressiveness. Associated with the good-prognosis value of the MARCKS-/PTEN+ protein status that mirrors the molecular profile of MPS-treated IBC cell lines, our results suggest that MARCKS could be a potential therapeutic target in patients with MARCKS-positive IBC. Future preclinical studies using a larger panel of IBC cell lines, animal models and analysis of a larger series of clinical samples are warranted in order to validate our results.

Inflammatory Breast Cancer: The Secretome of HCMV+ Tumor-Associated Macrophages Enhances Proliferation, Invasion, Colony Formation, and Expression of Cancer Stem Cell Markers.

Inflammatory breast cancer (IBC) is a highly aggressive phenotype of breast cancer that is characterized by a high incidence early metastasis. We previously reported a significant association of human cytomegalovirus (HCMV) DNA in the carcinoma tissues of IBC patients but not in the adjacent normal tissues. HCMV-infected macrophages serve as “mobile vectors” for spreading and disseminating virus to different organs, and IBC cancer tissues are highly infiltrated by tumor-associated macrophages (TAMs) that enhance IBC progression and promote breast cancer stem cell (BCSC)-like properties. Therefore, there is a need to understand the role of HCMV-infected TAMs in IBC progression. The present study aimed to test the effect of the secretome (cytokines and secreted factors) of TAMs derived from HCMV+ monocytes isolated from IBC specimens on the proliferation, invasion, and BCSC abundance when tested on the IBC cell line SUM149. HCMV+ monocytes were isolated from IBC patients during modified radical mastectomy surgery and tested in vitro for polarization into TAMs using the secretome of SUM149 cells. MTT, clonogenic, invasion, real-time PCR arrays, PathScan Intracellular Signaling array, and cytokine arrays were used to characterize the secretome of HCMV+ TAMs for their effect on the progression of SUM149 cells. The results showed that the secretome of HCMV+ TAMs expressed high levels of IL-6, IL-8, and MCP-1 cytokines compared to HCMV- TAMs. In addition, the secretome of HCMV+ TAMs induced the proliferation, invasion, colony formation, and expression of BCSC-related genes in SUM149 cells compared to mock untreated cells. In addition, the secretome of HCMV+ TAMs activated the phosphorylation of intracellular signaling molecules p-STAT3, p-AMPKα, p-PRAS40, and p-SAPK/JNK in SUM149 cells. In conclusion, this study shows that the secretome of HCMV+ TAMs enhances the proliferation, invasion, colony formation, and BCSC properties by activating the phosphorylation of p-STAT3, p-AMPKα, p-PRAS40, and p-SAPK/JNK intracellular signaling molecules in IBC cells.

Inflammatory Breast Cancer: The Cytokinome of Post-Mastectomy Wound Fluid Augments Proliferation, Invasion, and Stem Cell Markers.

Inflammatory breast cancer (IBC) is an aggressive phenotype with a high recurrence and low survival rate. Approximately 90% of local breast cancer recurrences occur adjacent to the same quadrant as the initial cancer, implying that tumor recurrence may be caused by residual cancer cells and/or quiescent cancer stem cells (CSCs) in the tumor. We hypothesized that wound fluid (WF) collected after modified radical mastectomy (MRM) may activate cancer cells and CSCs, promoting epithelial mesenchymal transition (EMT) and invasion. Therefore, we characterized the cytokinome of WF drained from post-MRM cavities of non-IBC and IBC patients. The WF of IBC patients showed a significantly higher expression of various cytokines than in non-IBC patients. In vitro cell culture models of non-IBC and IBC cell lines were grown in media conditioned with and/without WF for 48 h. Afterwards, we assessed cell viability, the expression of CSCs and EMT-specific genes, and tumor invasion. Genes associated with CSCs properties and EMT markers were regulated in cells seeded in media conditioned by WF. IBC-WF exhibited a greater potential for inducing IBC cell invasion than non-IBC cells. The present study demonstrates the role of the post-surgical tumor cavity in IBC recurrence and metastasis.

Abstract 5673: The role of NMDA receptors subunits in the progression of inflammatory breast cancer (IBC)

Abstract Inflammatory Breast Cancer (IBC) has a 73% incidence of metastasis to the brain as compared to other cancer types like breast, lung, and bone cancer. Previous research showed that tumor cells from different breast cancer subtypes (-HR/-HER2) and (-HR/+ HER2) have a high incidence of crossing the blood-brain barrier and inducing increased expression of glutamate receptors NMDA subunits (NMDAR1 and NMDR2) in the brain. IBC is the most aggressive and rare type of breast cancer. The absence of a solid tumor is replaced by swelling, redness, and skin changes, resulting in many cases in misdiagnosis of an infection in the invasion and migration phase; this type of cancer blocks blood and lymphatic vessels in the breast's skin, causing local inflammation and rapid metastasis. However, little is known of the role that these glutamatergic receptors have in the development and/or progression of IBC. The present work provides a new understanding of the cellular and molecular effects NMDA receptors (NMDAR) have on oncogenic phenotypes in IBC. The detection and quantification of the NMDAR were evaluated by RT-qPCR, Western blot, and immunofluorescence (IF) techniques in deferments breast cancer cell lines (MCF7, MDA-MB-231) and IBC cell lines (SUM149, and SUM190). Also, NMDAR antagonists (memantine and dizocilpine "MK-801") were used in 2D and 3D cell cultures to see the pro-oncogenic effects of migration and proliferation in cell models. In addition to this, the autocrine regulation of Glutamate in IBC cell lines is verified. Results showed a significant increase in the expression of NMDARs in IBC cell lines. In the functional cell culture assays with NMDAR antagonists, a decrease in migration and proliferation in IBC cell lines was found. These findings may be related to the high aggressiveness and the high rate of metastasis by IBC within the brain. Our results have high clinical relevance since having extensive knowledge of the role of NMDARs in IBC progression could complement therapeutic approaches for patients with IBC. Citation Format: Laura L. Mendez Santacruz, Xavier S. Bittman-Soto, Keishla M. Rodriguez-Martir, Jesus M. Padilla Escalona, Esther Peterson, Carmen Maldonado-Vlaar. The role of NMDA receptors subunits in the progression of inflammatory breast cancer (IBC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5673.

Abstract 6200: MANGO: pipeline for identifying genomic translocations with key biological significance in inflammatory breast cancer

Abstract Genomic instability in cancer is essential for aberrant gene expression and translocation events that potentiate oncogenesis. Thus gene fusions, nonsense mutations and gene deregulation are key contributors to oncogenic phenotypes. Certain genomic translocations have been linked to cancer subtypes, such BCR—ABL1 for chronic myeloid leukemia (CML) serving as potential onco-biomarkers. Inflammatory breast cancer (IBC) is the rarest and most lethal subtype of breast cancer with a 5-year survival rate below 50%. Ethnic disparities for breast cancer exist; negative estrogen (ER) and progesterone (PR) hormone receptor status is more frequent in Hispanic and African American women. In addition, inflammatory breast cancer lacks defined molecular markers limiting its early onset detection which leads to poorer overall prognosis. Thus, we hypothesized that profiling IBC translocations, including its subtypes, show valuable insights to better understand this complex disease. We developed MANGO, a pipeline that leverages STAR, STAR-Fusion, FusionInspector, and Trinity to identify, visualize and assemble gene fusions from IBC sequencing data. Using the SUM149PT cell line as a model for IBC, we identified and experimentally validated a model fusion gene ZDHHC5—EPB41L5. Fusion unaware sequence assemblies cross-validated the fusion and its multiple splice sites, one of which encodes a fusion peptide. Differential gene expression between SUM149PT and SUM190PT, an IBC cell line without evidence for the identified translocation, showed loss of expression of ZDHHC5 but no change in EPB41L5, suggesting the latter retained its expression in its new genomic localization. Furthermore, in-silico functional predictions for experimental results reveals an in-frame fusion peptide with transmembrane signals in EPB41L5. Genomic translocation mapping reveals triple-negative IBC diverges from traditional breast cancer translocation patterns. In short, MANGO serves as a powerful tool to identify biologically significant translocations involved in IBC and other cancer classifications. Citation Format: Carlos S. Morales-Rivera, Emilia R. Driscoll, Esther A. Peterson-Peguero. MANGO: pipeline for identifying genomic translocations with key biological significance in inflammatory breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6200.

Sensitization of Resistant Breast Cancer Cells with a Jumonji Family Histone Demethylase Inhibitor.

Simple SummaryUsing a cell culture model of resistant breast cancer cells with the phenotype that is often responsible for the early relapse of triple-negative breast cancer, namely, the persistence of these cells in reversible quiescence under a variety of challenges, we found that reprogramming the epigenome by treatment with JIB-04, a small-molecule inhibitor of Jumonji-family histone demethylases, sensitized resistant cells. We used this model of deep intrinsic resistance featuring many molecular mechanisms of achieving this phenotype to perform lengthy evaluations of less cytotoxic doses of JIB-04. We found that resistant cells derived from triple-negative inflammatory breast cancer cell lines were either much more sensitive to JIB-04 than the parental cell line or altered by the treatment such that they became sensitive to the chemotherapeutic drugs paclitaxel and doxorubicin. Notably, JIB-04 exposure increased PD-L1 expression in cancer cells, which means that JIB-04 may have clinical applications in improving the responses of triple-negative breast cancer to anti-PD-L1 therapy.In the present study, we evaluated JIB-04, a small-molecule epigenetic inhibitor initially discovered to inhibit cancer growth, to determine its ability to affect deep intrinsic resistance in a breast cancer model. The model was based on a function-based approach to the selection of cancer cells in a cell culture that can survive a variety of challenges in prolonged, but reversible, quiescence. These resistant cancer cells possessed a variety of mechanisms, including modifications of the epigenome and transcriptome, for generating a high degree of cellular heterogeneity. We found that long pretreatment with JIB-04 sensitized resistant triple-negative inflammatory breast cancer cells and their parental cell line SUM149 to the chemotherapeutic drugs doxorubicin and paclitaxel. Resistant cancer cells derived from another inflammatory breast cancer cell line, FC-IBC02, were considerably more sensitive to JIB-04 than the parental cell line. Investigating a mechanism of sensitization, we found that JIB-04 exposure increased the expression of PD-L1 in resistant cells, suggesting that JIB-04 may also sensitize resistant breast cancer cells to anti-PD-L1 immune therapy. Finally, these results support the usefulness of a cell culture-based experimental strategy for evaluating anticancer agents, such as JIB-04, that may halt cancer evolution and prevent the development of cancer resistance to currently used therapies.

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

Simple SummaryThis study provides novel mechanistic insights into the capacity of the inflammatory cytokine IL-6 and its associated STAT3-dependent signaling pathway to stimulate proliferation in trans between individual sub-clones in a model of heterogeneity in inflammatory breast cancer. The clinical relevance of this discovery is provided by our observation that proliferation of the IL-6 responsive subclone is sensitive to inhibition with the clinically approved anti-IL-6 receptor humanized monoclonal antibody Tocilizumab. These findings therefore provide a rationale for potentially repurposing Tocilizumab for the treatment of a subset of inflammatory breast cancer patients.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.

The role of NMDA receptors subunits in the progression of inflammatory breast cancer (IBC)

Inflammatory Breast Cancer (IBC) has a 73% incidence of metastasis to the brain as compared to other cancer types like breast, lung, and bone cancer. Previous research showed that tumor cells from different breast cancer subtypes (‐HR / ‐HER2) and (‐HR / + HER2) have a high incidence of crossing the blood‐brain barrier and inducing increased expression of glutamate receptors NMDA subunits (NMDAR1 and NMDR2) in the brain. IBC is the most aggressive and rare type of breast cancer. The absence of a solid tumor is replaced by swelling, redness, and skin changes, resulting in many cases in misdiagnosis of an infection in the invasion and migration phase; this type of cancer blocks blood and lymphatic vessels in the breast's skin, causing local inflammation and rapid metastasis. However, little is known of the role that these glutamatergic receptors have in the development and/or progression of IBC. The present work provides a new understanding of the cellular and molecular effects NMDA receptors (NMDAR) have on oncogenic phenotypes in IBC. The detection and quantification of the NMDAR were evaluated by RT‐qPCR, Western blot, and immunofluorescence (IF) techniques in deferments breast cancer cell lines (MCF7, MDA‐MB‐231) and IBC cell lines (SUM149, and SUM190). Also, NMDAR antagonists (memantine and dizocilpine “MK‐801”) were used in 2D and 3D cell cultures to see the pro‐oncogenic effects of migration and proliferation in cell models. In addition to this, the autocrine regulation of Glutamate in IBC cell lines is verified. Results showed a significant increase in the expression of NMDARs in IBC cell lines. In the functional cell culture assays with NMDAR antagonists, a decrease in migration and proliferation in IBC cell lines was found. These findings may be related to the high aggressiveness and the high rate of metastasis by IBC within the brain. Our results have high clinical relevance since having extensive knowledge of the role of NMDARs in IBC progression could complement therapeutic approaches for patients with IBC.

MANGO: pipeline for identifying genomic translocations with key biological significance in inflammatory breast cancer

Genomic instability in cancer is essential for aberrant gene expression and translocation events that potentiate oncogenesis. Thus gene fusions, nonsense mutations and gene deregulation are key contributors to oncogenic phenotypes. Certain genomic translocations have been linked to cancer subtypes, such BCR—ABL1 for chronic myeloid leukemia (CML) serving as potential onco‐biomarkers. Inflammatory breast cancer (IBC) is the rarest and most lethal subtype of breast cancer with a 5‐year survival rate below 50%. Ethnic disparities for breast cancer exist; negative estrogen (ER) and progesterone (PR) hormone receptor status is more frequent in Hispanic and African American women. In addition, inflammatory breast cancer lacks defined molecular markers limiting its early onset detection which leads to poorer overall prognosis. Thus, we hypothesized that profiling IBC translocations, including its subtypes, show valuable insights to better understand this complex disease. We developed MANGO, a pipeline that leverages STAR, STAR‐Fusion, FusionInspector, and Trinity to identify, visualize and assemble gene fusions from IBC sequencing data. Using the SUM149PT cell line as a model for IBC, we identified and experimentally validated a model fusion gene ZDHHC5—EPB41L5. Fusion unaware sequence assemblies cross‐validated the fusion and its multiple splice sites, one of which encodes a fusion peptide. Differential gene expression between SUM149PT and SUM190PT, an IBC cell line without evidence for the identified translocation, showed loss of expression of ZDHHC5 but no change in EPB41L5, suggesting the latter retained its expression in its new genomic localization. Furthermore, in‐silico functional predictions for experimental results reveals an in‐frame fusion peptide with transmembrane signals in EPB41L5. Genomic translocation mapping reveals triple‐negative IBC diverges from traditional breast cancer translocation patterns. In short, MANGO serves as a powerful tool to identify biologically significant translocations involved in IBC and other cancer classifications.

445 Inhibition of GPR30 Reveals Putative Genes Involved in the Pathogenesis of Inflammatory Breast Cancer

OBJECTIVES/GOALS: Inflammatory Breast Cancer (IBC) is the most aggressive form of breast cancer and does not have targeted therapy. GPR30, a 7-transmembrane estrogen receptor, may play a role in regulating cell growth and proliferation of cancerous cells. Here, we evaluated changes in gene expression while inhibiting GPR30 to determine putative targets to treat IBC. METHODS/STUDY POPULATION: IBC cell lines (SUM149PT) were cultured in medium with serum stripped from growth factor and hormones for 48 hours. Cells were then exposed to either G15 (GPR30 inhibitor) at a concentration of 1µM or ETOH (vehicle negative control) 3 hours in triplicates. After exposure, total RNA was extracted using the Qiagen RNAeasy Mini kit and RNA was sequenced using the Illumina NextSeq (2 X 75bp). The higher-quality reads were aligned, annotated, and quantified to the human genome (HG38) using STAR and RSEM softwares. Gene expression analysis was performed in R statistical software (packages tximport and DESeq2). Functional and enrichment analyses were performed using Metascape and STRING database, respectively. RESULTS/ANTICIPATED RESULTS: There were 656 significantly expressed genes (p < 0.05) between groups (G15 vs. ETOH). The top 5 significant genes include: SMIM7, FANCG, ARID1A, MAML2, and ATF3. Significantly impacted biological processes and pathways include: electron transport chain, mitotic cell cycle process, microtubule cytoskeleton organization, cellular component morphogenesis and DNA-dependent DNA replication (adj p < 0.05). Additionally, physical and functional interaction networks showed 3 major clusters (≥ 12 genes), which contained several gene hubs including BRCA1, BRCA2, FOS (proto-oncogene), PLK1 and PAK1 (both serine/threonine-protein kinases), among others. Interestingly, the network analysis showed the previously known interaction between FANCG and BRCA2, which were both dysregulated by GPR30 inhibition. DISCUSSION/SIGNIFICANCE: Through gene expression, functional and enrichment analyses we found several targets genes that could be associated with the pathogenesis of IBC. Validation of candidates genes (qRT-PCR and Western blot), and functional assays (cell proliferation, motility, and invasion) will be performed to understand the potential of these genes in treating IBC.

Abstract P5-08-04: LMP7-specific inhibitor M3258 modulates the tumor microenvironment of aggressive breast cancer

Abstract Background: LMP7 (beta5i/PSMB8) is a proteolytic subunit of the immunoproteasome that is predominantly expressed in leukocytes and inflamed tissues. The immunoproteasome degrades ubiquitinated proteins for maintenance of cell homeostasis and generation of peptides for MHC class I presentation. LMP7 has been implicated in multiple myeloma, autoimmune and inflammatory diseases, and inflammation-related cancers. Here, we evaluated the effect of M3258, an orally bioavailable, highly-selective, and reversible inhibitor of LMP7, on the tumor microenvironment (TME) using in vitro and in vivo models of triple-negative breast cancer (TNBC) and inflammatory breast cancer (IBC). Methods: The proteolytic activity of M3258 was determined using the fluorogenic LMP7-specific peptidic substrate (Ac-ANW)2R110. Its anti-proliferation activity was determined using the CellTiter-Blue cell viability and sulforhodamine B staining assays. Expression of immunoproteasome subunits under different conditions was examined by Western blotting. All in vitro assessments were done with or without IFNγ, which is known to increase immunoproteasome expression. The in vivo anti-tumor efficacy of M3258 was evaluated using a SUM-149 PT TN-IBC xenograft mouse model implanted in humanized mice. Single-cell RNA sequencing (scRNA-seq) was used in this same study to examine the impact of M3258 on the TME. Results: M3258 inhibited LMP7 activity (IC50 = 6.5-212.8 nM) and had no effects on LMP7 protein expression in a panel of TNBC cells (DU4475, HCC1187), IBC cells (SUM190, IBC3, KPL4), and TN-IBC cells (SUM-149 PT, BCX-010, FC-IBC02). M3258 inhibited proliferation of TNBC and IBC cell lines in vitro (IC50 = 1-20 µM). In keeping with previous reports, IFNγ treatment strongly induced LMP7 expression and enhanced its proteolytic activity in these cell lines in vitro and increased M3258 sensitivity (2- to 5-fold). In the humanized SUM-149 PT xenograft mouse model, M3258 orally administered at 10 mg/kg significantly inhibited tumor growth versus vehicle (31.4%, P < 0.01) and was tolerated. ScRNA-seq analysis of the terminal tumor samples from this study revealed that M3258 reduced the abundance of CD4+ and CD8+ T cells, Tregs, M1 and M2 macrophages, and dendritic cells. Gene expression profiling indicated a particularly pronounced inhibitory effect of M3258 on M1 and M2 macrophages. Furthermore, M3258 treatment activated CD8+ T cells and suppressed expression of genes involved in inflammatory response, IFNα signaling, IFNγ signaling, and TNFα signaling in immune cells. In light of the scRNA-seq findings, we assessed the impact of M1 and M2 macrophages on the invasiveness of TN-IBC cells in vitro. Co-cultures with M1 or M2 macrophages enhanced invasiveness of SUM-149 PT cells (4.6-fold by M1, P < 0.001; 6.3-fold by M2, P < 0.01) and BCX-010 cells (2.1-fold by M1, P < 0.05; 4.0-fold by M2, P < 0.01). Since M2 macrophages showed a superior effect than M1 macrophages on TN-IBC cell invasiveness, we further assessed M3258’s ability to inhibit such activity. M3258 at 500 nM significantly inhibited M2 macrophage-induced invasion of SUM-149 PT cells (29.6%, P < 0.05) and BCX-010 (49.5%, P < 0.01). Conclusion: Using the exquisitely selective LMP7 inhibitor M3258, we were able to demonstrate for the first time that LMP7 plays an important role in the inflammatory microenvironment, proliferation and invasiveness of TNBC and IBC cells, in particular by modulating the pathogenic role of M2 macrophages. These data warrant future in vivo studies into the antitumor efficacy of M3258 when used with immunotherapy agents. Citation Format: Xuemei Xie, Jangsoon Lee, Ganiraju C Manyam, Troy Pearson, Gina Walter-Bausch, Manja Friese-Hamim, Samantha M Goodstal, Debu Tripathy, Wang Jing, Michael Sanderson, Naoto T Ueno. LMP7-specific inhibitor M3258 modulates the tumor microenvironment of aggressive breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-08-04.

High endogenous CCL2 expression promotes the aggressive phenotype of human inflammatory breast cancer

Inflammatory Breast Cancer (IBC) is a highly aggressive malignancy with distinct clinical and histopathological features whose molecular basis is unresolved. Here we describe a human IBC cell line, A3250, that recapitulates key IBC features in a mouse xenograft model, including skin erythema, diffuse tumor growth, dermal lymphatic invasion, and extensive metastases. A3250 cells express very high levels of the CCL2 chemokine and induce tumors enriched in macrophages. CCL2 knockdown leads to a striking reduction in macrophage densities, tumor proliferation, skin erythema, and metastasis. These results establish IBC-derived CCL2 as a key factor driving macrophage expansion, and indirectly tumor growth, with transcriptomic analysis demonstrating the activation of multiple inflammatory pathways. Finally, primary human IBCs exhibit macrophage infiltration and an enriched macrophage RNA signature. Thus, this human IBC model provides insight into the distinctive biology of IBC, and highlights potential therapeutic approaches to this deadly disease.

Blocking Estrogen Synthesis Leads to Different Hormonal Responses in Canine and Human Triple Negative Inflammatory Breast Cancer.

Simple SummaryEstrogen is responsible for tumor progression, and blocking its synthesis is effective in certain breast cancers. Therefore, the aim of this study is to determine the effect of letrozole (anti-aromatase) and STX-64 (anti-sulfatase) in canine and human inflammatory breast cancer cell lines and xenografts. The results reveal that letrozole blocks estrogen synthesis, reducing tumor progression. However, STX-64 increases estradiol synthesis, increasing tumor progression. In summary, letrozole may be an effective treatment for canine and human inflammatory breast cancer.Blocking estrogen synthesis by inhibitors of estrogen synthesis is a widely used therapy against estrogen receptor-positive tumors. However, these therapies are less effective in negative expression tumors. Therefore, this study determined the effectiveness of anti-aromatase and anti-sulfatase therapies in canine and human inflammatory breast cancer. Cell cultures and xenografts from IPC-366 and SUM149 were treated with different doses of letrozole (anti-aromatase) and STX-64 (anti-sulfatase), in order to observe their effectiveness in terms of cell proliferation, tumor progression, and the appearance of metastases and hormonal profiles. The results revealed that both treatments are effective in vitro since they reduce cell proliferation and decrease the secreted estrogen levels. In xenograft mice, while treatment with letrozole reduces tumor progression by 30–40%, STX-64 increases tumor progression by 20%. The hormonal results obtained determined that STX-64 produced an increase in circulating and intratumoral levels of estradiol, which led to an increase in tumor progression. However, letrozole was able to block estrogen synthesis by decreasing the levels of circulating and intratumoral estrogen and thus slowing down tumor progression. In conclusion, letrozole can be an effective treatment for canine and human inflammatory breast cancer. The knowledge of the hormonal profile of breast tumors reflects useful information on the effectiveness of different endocrine treatments.

Tumor Growth Progression in Ectopic and Orthotopic Xenografts from Inflammatory Breast Cancer Cell Lines.

Xenografts can grow in immunosuppressed hosts, such as SCID mice, and tumor material can be injected into hosts either ectopically or orthotopically. Choosing the correct model to use is a crucial step in animal research. The aim of this study was to report the differences between ectopic and orthotopic xenografts in tumor progression, metastasis capacity, histological features, and steroid hormone profiles in xenografts from the cIMC (canine inflammatory mammary cancer) cell line IPC-366 and hIBC (human inflammatory breast cancer) cell line SUM149. To achieve this purpose, 40 female mice 6–8 weeks old were inoculated with IPC-366 and SUM149 cells subcutaneously (ectopic models) or into mammary fat pad (orthotopic models). Mice were monitored for tumor progression and appearance of metastases, and generated tumors were analyzed in terms of histological examination and steroid hormone production. The results revealed differences in tumor appearance and percentage of metastasis between ectopic and orthotopic models, which were higher in the ectopic xenografts from both cell lines. However, both models had similar characteristics of tumor progression, histological features, and steroid hormone secretion profiles. We show that the ectopic model can be validated as a good and useful model of tumor development in addition to, not contrary to, the orthotopic model in breast cancer research.