Triple-negative Breast Cancer Phenotype Research Articles

Discovery of novel small molecules targeting the USP21/JAK2/STAT3 axis for the treatment of triple-negative breast cancer

The deficiency in available targeted agents and frequency of chemoresistance are primary challenges in clinical management of triple-negative breast cancer (TNBC). The aberrant expression of USP21 and JAK2 represents a characterized mechanism of TNBC progression and resistance to paclitaxel (PTX). Despite its clear that high expression of USP21-mediated de-ubiquitination leads to increased levels of JAK2 protein, we lack regulator molecules to dissect the mechanisms that the interaction between USP21 and JAK2 contributes to the phenotype and resistance of TNBC. Here, we report a USP21/JAK2/STAT3 axis-targeting regulator 13c featuring a N-anthraniloyl tryptamine scaffold that showed excellent anti-TNBC potency and promising safety profile. Importantly, the therapeutic potential of using 13c in combination with PTX in PTX-resistant TNBC was demonstrated. This study showcases N-anthraniloyl tryptamine derivatives as a novel anti-TNBC chemotype with a pharmacological mode of action targeting the USP21/JAK2/STAT3 axis and provides a potential therapeutic target for the treatment of TNBC.

MiRNA-200c-3p deficiency promotes epithelial-mesenchymal transition in triple-negative breast cancer by activating CRKL expression

Epithelial-mesenchymal transition (EMT) plays an important role in malignant progression of Triple-negative breast cancer (TNBC). Many studies have confirmed that miRNA-200c-3p is related to EMT. And we found that it is involved in the regulation of EMT, but the exact mechanism is unclear. CRKL is highly expressed in a variety of tumors and plays a role in EMT. In this study, the potential targets of miRNA-200c-3p were searched in miRPathDB, Targetscan and PicTar. And there are 68 potential targets at the intersection of the three databases. Then, bioinformatics and text mining performed by Coremine Medica, and found that among 68 potential targets, CRKL has the strongest correlation with EMT in TNBC. Therefore, we speculated that miRNA-200c-3p involvement in EMT might be related to CRKL. To verify miRNA-200c-3p inhibits the malignant phenotype of TNBC by regulating CRKL, RT‒PCR, western blotting, Clonal formation assays,CCK-8 proliferation assays, transwell invasion assays, Luciferase reporter assay and nude mouse transplantation tumor assay were performed. In this study, we found that miRNA-200c-3p is under-expressed and EMT-related genes are up-regulated in TNBC, and miRNA-200c-3p can inhibit cancer cell proliferation, invasion and the expression of EMT-related genes and proteins in TNBC. Further research confirmed that miRNA-200c-3p could inhibit EMT by inhibiting the expression of CRKL that directly combining CRKL gene.

Serine/Threonine kinase 16 phosphorylates STAT3 and confers a JAK2-Inhibition resistance phenotype in triple-negative breast cancer

Although Janus kinase 2 (JAK2) plays a critical role in the progression of triple-negative breast cancer (TNBC), its inhibitors are incapable of eradicating these tumor cells, implicating drug resistance mechanisms exist. Our evidences show that TNBC cells express high level of Serine/Threonine Kinase 16 (STK16) when JAK2 signaling is blocked. Pharmacological inhibition or silencing of STK16 significantly enhances the sensitivity of TNBC cells to JAK2 inhibition, while over-expression of STK16 alleviates the anti-tumor effect of JAK2-inhibitor. Mechanistically, elevated STK16 expression rescues the phosphorylation status and transcriptional activity of STAT3, as STK16 is able to directly catalyze the phosphorylation of STAT3 at ser-727 residue. Our data indicate that upon JAK2 inhibition, TNBC cells express STK16 to maintain STAT3 transcriptional activity, dual-inhibition of JAK2/STK16 offers a potential way to treat TNBC patients.

Abstract PO5-09-06: Outcomes of breast cancer in a minority-enriched population treated at a large safety-net system: Is site of care a predictor of poor outcomes?

Abstract Background: Breast cancer outcomes in the United States continue to improve, but sociodemographic disparities remain prevalent and impact care delivery and outcomes in vulnerable populations. Safety-net health systems are intended to address inequities by providing access to care for the uninsured/underinsured. Care delivery in a safety-net setting is often inherently complicated by limited resources at these institutions. Here, we present the overall survival (OS) data of breast cancer patients treated at a large safety-net system, compared to the national average. Methods: Parkland Health (PH) is the safety-net system for Dallas County and is affiliated with the University of Texas Southwestern Harold C. Simmons Comprehensive Cancer Center (NCI-CCC). Electronic medical records of patients diagnosed with invasive breast cancer between 2018 to 2020 at PH were reviewed and data on demographics, treatment, and outcomes were collected. Categorical data was summarized with counts and percentages and continuous data was summarized with median and interquartile range. Statistical comparisons used Chi-square test for categorical data and rank sum test for continuous data with a significance level of 0.05. Survival data was analyzed using Cox proportional hazard model. Data from the National Cancer Database (NCDB) for the same period was used for comparison. Results: Of the 657 patients included in the study, the majority (82.5%) belonged to racial and ethnic minorities (Hispanic 50.2%; Black 32.3%). Compared to the NCDB, PH patients were more often uninsured (67% vs 1.6%) or enrolled on Medicaid (14.5% vs 6.9%), and less often on Medicare (8.5% v. 43%) (p< 0.01). Triple negative breast cancer (TNBC) phenotype and late-stage diagnosis (stage III/IV) rates were higher at PH compared to NCDB (TNBC 22.8% vs 10.7%, p< 0.01; late stage 30.6% vs 13.2%, p< 0.01). At a median follow up of 33 (range 24-43) months in PH and 28 (range 21-36) months in NCDB, the unadjusted OS for the PH population was 86.3% vs 92.6% for the NCDB population (p < 0.01). Within the PH population, Black race, higher stage, and TNBC were associated with decreased OS. There was a significant interaction between Black race and TNBC. When combining all patients (PH+NCDB), site of care (PH) was associated with a higher risk of death from breast cancer (HR 1.467, 95% CI 1.192-1.805, p< 0.0005), however, multivariate analysis did not show a significant difference based on site of care. Factors associated with a significantly increased risk of death in this multivariate analysis (corrected for interaction between Black race and TNBC phenotype) included age, late-stage diagnosis, TNBC, Black race, and uninsured status (Table 1). Conclusions: Breast cancer patients treated at PH were more likely to have adverse disease characteristics compared to the NCDB population. When accounting for these risk factors in multivariate analysis, patients treated at PH had similar outcomes compared to the national average. Our findings reinforce the critical role of safety-net systems in promoting health equity and eliminating disparities. Table 1 Citation Format: Sarah Kashanian, Shifa Kanjwal, L. Steven Brown, Andrea Semlow, Mary Hodges, Robyn Cobb, Brad Walsh, Umber Dickerson, Navid Sadeghi. Outcomes of breast cancer in a minority-enriched population treated at a large safety-net system: Is site of care a predictor of poor outcomes? [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 PO5-09-06.

Abstract PO1-27-07: Is HER2-low a biologically distinct breast cancer (BC) subtype? Prognosis and pathological complete response rate after neoadjuvant treatment (NAT) in early breast cancer (BC) HER2 negative

Abstract Background: Overexpression of HER2 is a significant prognostic and predictive factor in early breast cancer. HER2 positive tumors are those scored by immunohistochemistry (IHC) 3+ or 2+ with amplification by in situ hybridization (ISH). These tumors may benefit from HER2-targeted treatment and additionally, in early HER2-positive BC, achieving a complete pathological response after neoadjuvant treatment improves patient survival. In recent years, new anti-HER2 antibody-drug conjugates have proven effective for HER2 low BC (defined as IHC score 1+ or 2+ not amplified) in the metastatic disease setting; however, in HER2-low early BC, studies testing novel anti-HER2 antibody-drug conjugates as neoadjuvant therapy (NAT) are ongoing. Currently, we don´t know exactly whether HER2 expression can influence the pathological response rate after NAT or disease-free survival (DFS) in these patients compared to HER2-zero (IHC 0). The aim of our study is to determine the impact on response rate to NAT and survival outcomes in early HER2-negative BC. Methods: We conducted a retrospective study in two hospitals in Andalucia, Spain. Patients with early HER2 negative BC treated with NAT from January 2015 to June 2022 were included. Patients were divided into HER2 low patients (IHC 1+ or 2+ not amplified) and HER2 0 (IHC 0). We collected clinical and pathological characteristics, pathological response rate using the Residual Cancer Burden (RCB) system where a complete pathological response (pCR) was defined as ypT0/ypTis and ypN0, and survival outcomes. The primary objective of the study was to analyze the pCR rate after NAT according to HER2 score, and secondary objectives were to assess disease-free survival and overall survival (DFS and OS rates). Results: 574 patients were included (100% women). 397 patients had hormone receptors (luminal BC) on these tumors, and 177 did not have them, i.e., triple-negative BC (TNBC). 225 patients were HER2-zero, and 312 patients were HER2-low (253/312 patients had luminal BC and 59/312 patients were TNBC). The pCR in HER2-low patients was 17.3% and 23.1% in HER2-zero patients (p=0.047). For luminal BC patients, the pCR was 16.7% in HER2-low tumors and 13.7% in HER2-zero tumors (p=0.29). Similarly, there was no difference in pCR rates in TNBC patients (45.8% in HER2-low and 53.8% in HER2-zero tumors, respectively, (p=0.958). The overall survival (OS) at 96 months was 88.7% (95% CI 85.6%-92%). Regarding survival outcomes, neither HER2 expression level was associated with higher 8-year DFS: 81.1% in HER2-low patients (95% CI 75.7%-86.8%) and 74.9% in HER2-zero patients (95% CI 62.3%-90.1%) p=0.64. There was no difference between histological subtypes at 8-years regarding DFS rate: 80.5% (95% CI 74.3%-87.2%) in luminal HER2-low patients and 76.3% (95% CI 60.8%-95.7%) in luminal HER2-zero patients, p=0.22; 83.8% in TNBC HER2-low (95% CI 74.5%-94.2%) and 77.5% in TNBC HER2-zero patients (95% CI 69.4%-86.6%) p=0.26. We also didn´t find significant differences in terms of OS. For HER2-low patients, the 8-year OS was 90.9% (95% CI 87%-94.9%) and for HER2-zero patients, it was 86.4% (95% CI 80.8%- 92.5%) p=0.46. There were also no differences in OS for different histological subgroups with an 8-year OS in luminal HER2-low breast cancer patients of 92.5% (95% CI 88%-96.7%) and 87% in HER2-zero (95% CI 78.9%-96.1%) p=0.91. In patients with triple-negative breast cancer phenotype, the OS was 84.2% for HER2-low (95% CI 74.5%-95.2%) and 85.3% for HER2-zero (95% CI 77.9%-93.4%) p=1. Conclusions: We found no difference in survival outcomes and response rate to conventional NAT between HER2-low and HER2-zero expression levels. Therefore, our data do not support the hypothesis of HER2-low as a biologically specific breast cancer subtype. Further research on this approach with HER2 antibody-drug conjugate schemes as an alternative to traditional NAT schemes is warranted. Citation Format: Ana Gil-Torralvo, Yeray Rodriguez, Alejandro Falcon, David Morales, Mónica Cejuela, Isabel Miras, Marta Amérigo, Manuel Ruíz - Borrego, Juan Bayo, Francisco Javier Salvador Bofill. Is HER2-low a biologically distinct breast cancer (BC) subtype? Prognosis and pathological complete response rate after neoadjuvant treatment (NAT) in early breast cancer (BC) HER2 negative [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 PO1-27-07.

Apigenin and its combination with Vorinostat induces apoptotic-mediated cell death in TNBC by modulating the epigenetic and apoptotic regulators and related miRNAs

Triple-negative breast cancer (TNBC) is a metastatic disease and a formidable treatment challenge as it does not respond to existing therapies. Epigenetic regulators play a crucial role in the progression and metastasis by modulating the expression of anti-apoptotic, pro-apoptotic markers and related miRNAs in TNBC cells. We have investigated the anti-TNBC potential of dietary flavonoid ‘Apigenin’ and its combination with Vorinostat on MDA-MB-231 cells. At Apigenin generated ROS, inhibited cell migration, arrested the cell cycle at subG0/G1 phases, and induced apoptotic-mediated cell death. Apigenin reduced the expression of the class-I HDACs at the transcriptomic and proteomic levels. In the immunoblotting study, Apigenin has upregulated pro-apoptotic markers and downregulated anti-apoptotic proteins. Apigenin inhibited the enzymatic activity of HDAC/DNMT and increased HAT activity. Apigenin has manifested its effect on miRNA expression by upregulating the tumor-suppressor miR-200b and downregulation oncomiR-21. Combination study reduced the growth of TNBC cells synergistically by modulating the expression of epigenetic and apoptotic regulators. Molecular docking and MD simulations explored the mechanism of catalytic inhibition of HDAC1 and HDAC3 and supported the in-vitro studies. The overall studies demonstrated an anti-TNBC potential of Apigenin and may help to design an effective strategy to treat metastatic phenotype of TNBC.

PTGER3 knockdown inhibits the vulnerability of triple-negative breast cancer to ferroptosis.

Prostaglandin E receptor 3 (PTGER3) is involved in a variety of biological processes in the human body and is closely associated with the development and progression of a variety of cancer types. However, the role of PTGER3 in triple-negative breast cancer (TNBC) remains unclear. In the present study, low PTGER3 expression was found to be associated with poor prognosis in TNBC patients. PTGER3 plays a crucial role in regulating TNBC cell invasion, migration, and proliferation. Upregulation of PTGER3 weakens the epithelial-mesenchymal phenotype in TNBC and promotes ferroptosis both invitro and invivo by repressing glutathione peroxidase 4 (GPX4) expression. On the other hand, downregulation of PTGER3 inhibits ferroptosis by increasing GPX4 expression and activating the PI3K-AKT pathway. Upregulation of PTGER3 also enhances the sensitivity of TNBC cells to paclitaxel. Overall, this study has elucidated critical pathways in which low PTGER3 expression protects TNBC cells from undergoing ferroptosis, thereby promoting its progression. PTGER3 may thus serve as a novel and promising biomarker and therapeutic target for TNBC.

An insight into immunohistochemical profile of triple negative breast carcinoma in a tertiary care center

Introduction: Triple Negative Breast Cancer (TNBC) is a type of breast cancer that fails to express Estrogen Receptor (ER), Progesterone Receptor (PR) and Human Epidermal Growth Factor Receptor 2 (HER2) in Immunohistochemical analysis. TNBC has a unique molecular profile, aggressive nature and lack of efficient targeted therapies. The aim of the study was to evaluate the expression of basal markers like Epidermal Growth Factor Receptor (EGFR) and Cytokeratin 5/6 (CK 5/6) and to correlate their expression with the clinico-pathological parameters, thus enabling the identification of the aggressive basal like phenotype of TNBC in resource-constrained settings. Methodology: The study was conducted at a South Indian tertiary care centre for 2 years. Data such as age of presentation, tumour measurements, margins and necrosis, numbers, levels and sizes of lymph nodes were collected. Data on histological type and grade, in situ component, lymphovascular and perineural invasion, stromal reaction and lymph node status were recorded. Primary Immunohistochemical studies were performed for the markers ER,PR and HER2.Patients with negative expression for all the three markers were identified. IHC studies for EGFR and Cytokeratin 5/6(CK5/6) were done on tissue blocks and the expression of these two markers were equated with the clinico-pathological parameters. Results: Among the 94 cases, 44 cases (46.8%) expressed CK5/6 and 46 (48.9%) expressed EGFR. A plausible association was noted between the expression of the two markers with age of the patient, tumour size, histological grade and tumour necrosis. Conclusion: Combination of the time honoured gross and histopathological examinations along with the application of basal markers like CK 5/6 and EGFR, helps in identifying the basal-like phenotype with dismal clinical outcome among the triple-negative breast cancers in resource-constrained settings. An insight into such an aggressive tumour, provided by these markers may be critical in designing personalized treatment strategies for such patients.

Abstract 2976: The potential use of butyrate and propionate to inhibit oncogenic phenotypes in oral squamous cell carcinoma and triple negative breast cancer

Abstract Background Oral squamous cell carcinoma (OSCC) and triple-negative breast cancer (TNBC) are aggressive cancers with low survival rates, particularly in Hispanics. Since the underpinning mechanisms of oncogenesis for both OSCC and TNBC are multifactorial, the development of novel targeted therapies is limited. The tumor microbiome has been shown to modulate the microenvironment. The microbial product short-chain fatty acids (SCFA) may represent a putative target for treatment as they can potentially inhibit cell growth, proliferation, migration, and induce morphologic changes in cancer cells. We evaluated the impact of the SCFAs butyrate, acetate, and propionate on the oncogenic phenotypes of OECM-1 and MDA-231 cell line models for OSCC and TNBC respectively. Methods OECM-1 and MDA-231 cell lines were cultured in RPMI-1640 medium supplemented with 10% FBS. Cytotoxicity was determined using an alamarBlue assay by treating the cells with SCFA in a series of 7 concentrations starting at 125 mM (1:2 dilution factor) for 24, 48, and 72 hours (h). Proliferation quantification was performed using trypan blue dye after treatment with SCFA for 24h, 48h and 72h. Migration and invasion were measured after treatment for 24h with SCFAs. Comparative analysis of our results was performed using GraphPad Prism v10. Results Higher concentrations of all SCFA decreased cell viability in OSCC and TNBC at all time points. In OECM-1 cells, the average inhibitory concentration of 50% (IC50) was 3mM for butyrate, 382mM for acetate, and 64mM for propionate while in MDA-MB-231 cells, the average IC50 was 4.3mM for butyrate, 462mM for acetate, and 20mM for propionate. Both OECM-1 and MDA-MB-231 cells treated with butyrate and propionate at 5mM resulted in a slower migration after 24h of treatment. Additionally, there was a significant reduction of cell number and proliferation rate after 48h and 72h of butyrate treatment at the concentrations 1mM (p=0.0425) and 5mM (p=0.0007) in OSCC. Conclusions Our results show that butyrate and propionate can reduce oncogenic phenotypes in OSCC and TNBC and may represent a potential target for the development of alternative treatment strategies for both cancers. Future work includes measuring the impact of these SCFA in epithelial-mesenchymal transition, loss of adhesion, and cell death. Citation Format: Angel J. Amaral Maisonet. The potential use of butyrate and propionate to inhibit oncogenic phenotypes in oral squamous cell carcinoma and triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2976.

Scutellaria barbata D.Don extract regulates Ezrin-mediated triple negative breast cancer progress via suppressing the RhoA /ROCK1 signaling.

Triple-negative breast cancer (TNBC) lacks effective therapeutic targets. Scutellaria barbata D.Don (SB) has been revealed to have anti-breast cancer (BC) effect, but the effect of SB extract in TNBC is still unclear. Herein, this research delves into the underlying mechanism. SB was extracted by solvent extraction, and the main components were identified using an Agilent 6,520 HPLC-Chip/Q-TOF (Chip/Q-TOF) MS system. In vitro cell experiments were conducted. The effects of SB extract alone, SB extract plus EGF, GSK alone, GSK plus Ezrin overexpression, or SB extract plus Ezrin overexpression on cell viability, invasion, migration, and apoptosis were examined by cell function experiments. The apoptosis- and RhoA/ROCK1 pathway-related protein levels were analyzed by western blot assay. Mass spectrometry analysis exhibited that SB extract mainly contains long-chain fatty acids and ursolic acid. SB extract mitigated TNBC cell biological phenotypes, apoptosis- and RhoA/ROCK1 pathway-related marker expressions, which were reversed by EGF. The further results found that GSK obviously weakens TNBC cell biological behaviors, apoptosis- and RhoA/ROCK1 signaling-related protein levels, while oe-Ezrin treatment reverses the effect of GSK on TNBC cells. Moreover, SB extract regulated Ezrin-mediated function of TNBC cells by impeding the RhoA/ROCK1 pathway. Our findings demonstrated that SB extract regulated Ezrin-mediated proliferation, migration, invasion, and apoptosis of TNBC cells via suppressing the RhoA /ROCK1 signaling. Our results offer the experimental foundation for further investigation of the anti-cancer role of SB in TNBC cells. SB extract inhibits the biological phenotypes of TNBC cells.SB extract inhibits the biological behaviors of TNBC cells through the RhoA/ROCK1 pathway.SB extract modulates Ezrin-mediated TNBC cell proliferation, migration, invasion, and apoptosis via restraining the RhoA/ROCK1 signaling.

Fractionation and phytochemical composition of an ethanolic extract of Ziziphus nummularia leaves: antioxidant and anticancerous properties in human triple negative breast cancer cells.

Natural products have long been utilized in traditional medicine as remedies to improve health and treat illnesses, and have had a key role in modern drug discovery. Recently, there has been a revived interest in the search for bioactives from natural sources as alternative or complementary modalities to synthetic medicines; especially for cancer treatment, which incidence and mortality rates are on the rise worldwide. Ziziphus nummularia has been widely used in traditional medicine for the treatment of various diseases. Its traditional uses and numerous ethnopharmacological properties may be attributed to its richness in bioactive metabolites. However, its phytochemical composition or chemopreventive effects against the aggressive triple-negative breast cancer (TNBC) are still poorly explored. Here, phytochemical composition of an ethanolic extract of Z. nummularia leaves (ZNE) and its chromatographically isolated fractions was identified both qualitatively by spectrophotometric assays and analytically by HPLC-PDA-MS/MS. The anti-proliferative effects of ZNE were tested in several cancer cell lines, but we focused on its anti-TNBC effects since they were not explored yet. The anti-cancerous potential of ZNE and its fractions was tested in vitro in MDA-MB-231, a TNBC cell line. Results showed that ZNE and its Fraction 6 (F6) reduced the viability of MDA-MB-231 cells. F6 decreased MDA-MB-231 viability more than crude ZNE or its other fractions. ZNE and F6 are rich in phytochemicals and HPLC-PDA-MS/MS analysis identified several metabolites that were previously reported to have anti-cancerous effects. Both ZNE and F6 showed potent antioxidant capacity in the DPPH assay, but promoted reactive oxygen species (ROS) production in MDA-MB-231 cells; an effect which was blunted by the antioxidant N-acetyl cysteine (NAC). NAC also blunted ZNE- and F6-induced reduction in TNBC cell viability. We also demonstrated that ZNE and F6 induced an arrest of the cell cycle, and triggered apoptosis- and autophagy-mediated cell death. ZNE and F6 inhibited metastasis-related cellular processes by modifying cell migration, invasion, and adhesion. Taken together, our findings reveal that Z. nummularia is rich in phytochemicals that can attenuate the malignant phenotype of TNBC and may offer innovative avenues for the discovery of new drug leads for treatment of TNBC and other cancers.

Abstract B039: Butyrate and propionate-reduced oncogenic phenotypes in triple-negative breast cancer

Abstract Objectives Triple negative breast cancer (TNBC) is the most aggressive form of breast cancer affecting 5% of all patients with no known treatment. Hispanic women show a higher risk of developing this type of cancer at an early age. Heterogeneity of TNBC between patients makes it challenging to devolop a effective treatment. The compostion of microbiome amongst the patients has a high variablity that could affect the production of the microbial products. The changes in microbial products have not been previously evaluated and could possibly contribute to chronic inflammation in the patients. Short-chain fatty acids (SCFA), i.e. butyrate, acetate, and propionate which are metabolical products of the microbiome that can potentially inhibit cell growth, proliferation and migration of cancer cells, may represent an alternative treatment for TNBC. Here, we measured the impact of SCFAs treament on viability and migration of MDA-231 cell lines. Methods MDA-231 cell line is an aggressive triple-negative breast cancer (TNBC) cell line common for evaluating new therapeutic strategies. MDA-231 cells were cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum and we evaluated oncogenic phenotypes (cell viability and migration) after SCFA treatment. Cells were treated with butyrate, acetate, and propionate in cell culture media at seven concentrations starting at 125mM (1:2 dilution factor) for 24, 48 and 72 hours (h). We determined the cell viability using Alamar blue and determined the half-maximal inhibitory concentration (IC50) after SCFA treatment at all time points. Furthermore, we performed a wound-healing assay for 24h to evaluate the impact of SCFA on cell migration. MDA-231 cells were cultured to a 100% confluency and a scratch was performed in the cell monolayer to create an artificial gap, simulating the wound. Immediately after performing the wound, the cells were treated with SCFA at concentrations of 1mM and 5mM. Results Higher concentrations of butyrate and propionate reduced cell viability for MDA-231 was reduced. Particularly, butyrate showed an IC50 at 24h, 48h and 72h of 4.7mM, 4.34 mM and 3.6mM, respectively. However, propionate showed an IC50 only at 48h and 72h of 21.09 mM and 19.5 mM, respectively. There was no impact in cell viability after acetate treatment. In relation to migration, MDA-231 cell lines treated with butyrate and propionate at 5mM show a slower migration rate at 24h when compared to the untreated cells. Conclusions Our results suggest that butyrate and propionate can reduce oncogenic phenotypes in MDA-231. Future work will measure the impact of SCFA on cell proliferation, motility, and epithelial-mesenchymal transition. SCFAs may represent a promising target for novel treatment strategies for TNCB. Citation Format: Liah M Román-Calderón, Ariana S García-López, Jeannette L Salgado-Montilla, Gabriel Borges-Vélez, Esther A Peterson-Peguero, Josué Pérez-Santiago. Butyrate and propionate-reduced oncogenic phenotypes in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B039.

Abstract A065: Single cell transcriptomics reveals putative tumor promoting subpopulation in Brca1 mutant breast cancer mouse model

Abstract Women with BRCA1 (B1) mutations have an exceptionally high risk of developing breast cancer. The only effective preventive strategy currently offered to these women is the life altering prophylactic mastectomy. Considering the limited treatment options available, it is critical that new preventive strategies be identified. Design of such strategies requires an understanding of early events in the breast cells that drive tumorigenesis. B1 heterozygous mouse models can help us identify these early changes however, despite the well-established association between B1 heterozygosity and cancer predisposition in humans, there are currently no such B1 mouse models that faithfully recapitulate this high risk of tumor formation. We have now established a mouse model that induces mammary tumors in B1 heterozygous (Brca1wt/flx,Trp53flx/flx,K14cre) mice upon replication stress (RS). Our approach is based on our published work that reveals haploinsufficiency for RS suppression in B1 heterozygous cells. We find that increasing RS in B1 heterozygous mice results in accelerated mammary tumorigenesis. RS in this mouse model was delivered by injecting DNA-adduct forming 4-nitroquinoline-1-oxide (4NQO) via mammary intraductal injections over a course of 4 weeks. RS served as an efficient and abnormally rapid driver of tumor formation (30 days post completion of injection regimen) in B1 heterozygous mice. B1 heterozygous mice formed mammary adenocarcinoma. These tumors exhibit a triple negative breast cancer phenotype similar to that found in human BRCA1 mutant breast cancer. Our scRNAseq-based analysis of 42,000 cells from mouse mammary tissue collected at different time points during tumorigenesis has identified early transcriptomic changes that occur in different mammary cell types (e.g., luminal and basal) as they respond to RS. We find that in response to RS, a population of trans-differentiated cells accumulates in the mammary tissue. This population is bi-potent (expresses both luminal progenitor and basal epithelial markers), is specifically enriched in Brca1 heterozygous mammary tissue and expresses certain prognostic markers with a strong correlation to poor outcome in human breast cancer. This population is also enriched for proliferation markers. We suspect that this transdifferentiated population, which is primarily enriched in B1 heterozygous mammary tissue undergoing RS, marks the earliest cancer promoting cell population. Finally, pseudotime reconstruction-based lineage analysis reveals that alveolar luminal progenitor cells are the most likely cell of origin for this putative tumor promoting cell population in the breast. Altogether, our integrative approach reveals that B1 heterozygosity in combination with RS leads to accumulation and proliferation of a specific mammary cell population with a unique transcriptomic profile, that contributes to breast tumorigenesis. Identification of such early drivers is critical for the design of effective preventive and therapeutic strategies for women with BRCA1 mutation. Citation Format: Shailja Pathania, Joshua Rivera, Stevension Tran, Carman Man Chung Li, Joan Brugge, Kourosh Zarringhalam. Single cell transcriptomics reveals putative tumor promoting subpopulation in Brca1 mutant breast cancer mouse model [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A065.

Abstract B070: Myc synthetic lethality as a therapeutic strategy for resistance: Insights into the targetability of mitochondrial complex I in Myc-high TNBC

Abstract Patients with advanced triple-negative breast cancer (TNBC) frequently develop chemoresistance, emphasizing an urgent need for novel therapeutic strategies able to eradicate treatment resistant tumor cells. Recent studies have highlighted MYC as a common oncogenic alteration and a driver of stem-like TNBC phenotype, which commonly features high mitochondrial respiratory activity instated through OXPHOS system and chemoresistance. Interestingly, emerging evidence suggests that residual tumors from chemo treatment remain susceptible to OXPHOS inhibition through inhibition of respiratory complex I. Our previous studies have revealed a specific MYC-dependent and tumor suppressive synthetic lethal action for combination of metformin and BH3 mimetics in cells, ex vivo and in vivo models of aggressive breast cancer (PMID: 30728358). Metformin is a systemic and local metabolic modulator, which acts as a weak complex I inhibitor and promoter of AMPK activation. Here, we have explored the role of MYC in OXPHOS regulation, to address the question if metformin specifically and lethally targets MYC-modulated OXPHOS in MYC-high TNBC. We found that a selective c-MYC inhibitor (EN4) leads to a significant decrease in complex I activity despite only a modest drop in complex I mass in endogenously MYC-high TNBC cell lines. Conversely, engineered MYC overexpression in these cells upregulated complex I activity. Our current work explores transcriptomic, proteomic, and functional approaches to the mechanisms through which MYC regulates complex I activity, structure, and dynamics, ultimately hoping to define a biological rationale for therapeutic targeting of OXPHOS in Myc-high TNBC. Citation Format: Antti O Hiltunen, Linda J Id, Juha Klefström. Myc synthetic lethality as a therapeutic strategy for resistance: Insights into the targetability of mitochondrial complex I in Myc-high TNBC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B070.

Dysregulated Ribosome Biogenesis Is a Targetable Vulnerability in Triple-Negative Breast Cancer: MRPS27 as a Key Mediator of the Stemness-inhibitory Effect of Lovastatin.

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with limited effective therapeutic options readily available. We have previously demonstrated that lovastatin, an FDA-approved lipid-lowering drug, selectively inhibits the stemness properties of TNBC. However, the intracellular targets of lovastatin in TNBC remain largely unknown. Here, we unexpectedly uncovered ribosome biogenesis as the predominant pathway targeted by lovastatin in TNBC. Lovastatin induced the translocation of ribosome biogenesis-related proteins including nucleophosmin (NPM), nucleolar and coiled-body phosphoprotein 1 (NOLC1), and the ribosomal protein RPL3. Lovastatin also suppressed the transcript levels of rRNAs and increased the nuclear protein level and transcriptional activity of p53, a master mediator of nucleolar stress. A prognostic model generated from 10 ribosome biogenesis-related genes showed outstanding performance in predicting the survival of TNBC patients. Mitochondrial ribosomal protein S27 (MRPS27), the top-ranked risky model gene, was highly expressed and correlated with tumor stage and lymph node involvement in TNBC. Mechanistically, MRPS27 knockdown inhibited the stemness properties and the malignant phenotypes of TNBC. Overexpression of MRPS27 attenuated the stemness-inhibitory effect of lovastatin in TNBC cells. Our findings reveal that dysregulated ribosome biogenesis is a targetable vulnerability and targeting MRPS27 could be a novel therapeutic strategy for TNBC patients.

Abstract C047: Multiomics approaches to identify African-ancestry specific phenotypes of triple negative breast cancer

Abstract Despite recent convergence of breast cancer (BC) incidence among African American (AA) and European American (EA) women, BC mortality remains 40% higher among AA women. This disparity is driven partly by BC heterogeneity, where distinct subtypes have differing prognosis and treatment modalities, defined by presence of estrogen and/or progesterone receptor (HR+), overexpression of HER2, or lack of all three biomarkers (triple negative BC (TNBC)). TNBC is the most aggressive subtype, diagnosed as late-stage disease and lacking targeted therapeutic options. TNBC represents ~10% of annual diagnoses, however prevalence is significantly higher among AA women. Our work in the International Center for the Study of Breast Cancer Subtypes (ICSBCS) revealed significant association of west African (AFR) ancestry and TNBC, where we report that Ghanaian and AA women have increased frequency of TNBC, compared to Ethiopian and EA women, and that TNBC patients have higher percentages of quantified AFR ancestry. To characterize AFR ancestry-specific TNBC phenotypes, we have employed transcriptomics and whole genome sequencing (WGS) methods. Our recent publication from an AFR ancestry enriched TNBC transcriptomics cohort (n = 26) leveraged genetic ancestry to identify 600+ AFR and 2000+ AFR sub-continental ancestry associated genes. Pathway analysis showed enrichment of immune cell trafficking and indicates distinct AFR ancestry phenotypes that can be leveraged for future therapeutic opportunities. Recently, we have completed WGS on 80+ AFR ancestry patients with TNBC disease (n = 59) and HR+ disease (n = 23); representing AA (n = 71), Ethiopian (n = 8) and Ghanaian patients (n = 3). TP53 was the most mutated gene, more commonly mutated among TNBC cases (83%) compared to HR+ cases (35%) (p < 0.0001). HR+ had significantly more GATA3 (26%) and PIK3CA (30%) mutations compared to TNBC (0% and 9%, p < 0.05). Prevalence of COSMIC mutational signatures shows higher Signature 1 among HR+ cases, and higher Signature 3 among TNBC cases (both p < 0.05). Signature 3 is associated with DNA double-strand break repair and germline BRCA1/2 mutation status, where 9 TNBC cases have elevated homologous repair deficiency status. Our genomic work utilizes the reference genome, which is primarily sequenced from a single individual. With the African Pan Genome (APG), a set of 125,000+ contigs distinct from the reference genome, we have aligned RNAseq reads to the APG that failed to map to the reference genome. Successful APG alignment of a subset of reads indicates that genes are expressed from these distinct AFR sequences. We also identified CpG sites in contigs with gene expression, showing AFR ancestry specific regulatory regions in the previously unmapped genome. We are working to determine the significance of these in the tumor microenvironment. This work represents a comprehensive, AFR ancestry enriched cohort with multiple genomic data approaches that will allow us to further characterize TNBC disease and define actionable biomarkers and targets for women of African ancestry. Citation Format: Rachel Martini, Max Chao, Timothy Chu, Brian Stonaker, Ishmael Kyei, Ernest Adjei, Mahteme Bekele, Kofi Gyan, Olivier Elemento, Nicolas Robine, John Carpten, Lisa Newman, Melissa Davis. Multiomics approaches to identify African-ancestry specific phenotypes of triple negative breast cancer [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr C047.

SCFβTrCP-mediated degradation of SHARP1 in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a subtype of breast cancer associated with metastasis, high recurrence rate, and poor survival. The basic helix-loop-helix transcription factor SHARP1 (Split and Hairy-related Protein 1) has been identified as a suppressor of the metastatic behavior of TNBC. SHARP1 blocks the invasive phenotype of TNBC by inhibiting hypoxia-inducible factors and its loss correlates with poor survival of breast cancer patients. Here, we show that SHARP1 is an unstable protein that is targeted for proteasomal degradation by the E3 ubiquitin ligase complex SCFβTrCP. SHARP1 recruits βTrCP via a phosphodegron encompassing Ser240 and Glu245 which are required for SHARP1 ubiquitylation and degradation. Furthermore, mice injected with TNBC cells expressing the non-degradable SHARP1(S240A/E245A) mutant display reduced tumor growth and increased tumor-free survival. Our study suggests that targeting the βTrCP-dependent degradation of SHARP1 represents a therapeutic strategy in TNBC.

Contribution of constitutional BRCA1 promoter methylation to early-onset and familial breast cancer patients from Pakistan.

Constitutional BRCA1 promoter methylation has been identified as a potential risk factor for breast cancer (BC) in the Caucasian population. However, this data is lacking for BC patients of Asian origin. Therefore, we assessed the contribution of constitutional BRCA1 promoter methylation in Pakistani BC patients. A total of 385 BRCA1/2-negative index BC patients (197 early-onset BC (≤ 30years), 152 familial BC, 17 familial BC and ovarian cancer, 19 male BC) and 107 healthy controls were screened for the constitutional BRCA1 promoter methylation by methylation-sensitive high-resolution melting assay. Overall, 131 patients displayed triple-negative BC (TNBC) and 254 non-TNBC phenotypes. The prevalence of BRCA1 promoter methylation was calculated based on clinicopathological characteristics using univariable and multivariable logistic regression models. Constitutional BRCA1 promoter methylation was identified in 19.5% (75/385) of BC patients and 13.1% (14/107) of controls. The frequency of methylation was higher in early-onset BC (23.4% vs. 13.1%, P = 0.035) and TNBC patients (29.0% vs. 13.1%, P = 0.004) compared to controls. Methylation was also more prevalent in patients with high-grade than low-grade tumors (21.7% vs. 12.2%, P = 0.034) and progesterone receptor (PR)-negative than PR-positive tumors (26.0% vs. 13.9%, P = 0.004). Constitutional BRCA1 promoter methylation remained independently associated with TNBC phenotype (odds ratio 1.99; 95% CI 1.12-3.54; P = 0.02) after adjusting for BC diagnosis age, tumor grade, ER, and PR status. Constitutional BRCA1 promoter methylation is associated with TNBC and can serve as a non-invasive blood-based biomarker for Pakistani TNBC patients.

Histopathological Patterns and Outcomes of Triple-Positive Versus Triple-Negative Breast Cancer: A Retrospective Study at a Tertiary Cancer Center.

Background One of the leading causes of cancer-related deaths in females under 45 years old is breast cancer (BC). The definition of triple-negative breast cancer (TNBC) is the lack of expression of estrogen receptors (ERs) as well as progesterone receptors (PRs) and Erb-B2 receptor tyrosine kinase 2 (HER2) gene amplification. Triple-positive breast cancer (TPBC), on the other hand, is defined as tumors expressing a high level of ER, PR, and HER2 receptors. This study aims to assess the phenotypes of TNBC and TPBC by comparing their individual clinical behavior patterns and prognosis throughout the course of the disease in a tertiary cancer center in the Kingdom of Saudi Arabia (KSA). Methods Our study is a retrospective study using electronic medical records (EMRs) to identify all female patients diagnosed with BCusing the International Classification of Diseases-10 (ICD-10) codes (between C50 and C50.9). About 1209 cases with primary BC female patients were recognized based on histopathology reports. Further subclassification into TPBC and TNBC was performed. Statistical analysis was performed using Rv3.6.2 (R Studio, version 3.5.2, Boston, MA, USA). The descriptive data were presented as means and standard deviations (SD).Survival curves were approximated using the Kaplan-Meier method. The comparison between survival curves between both groups was achieved using the log-rank test. The multivariate model was constructed based on the identified predictors using univariate analysis. Results Univariate analysis of overall survival (OS) showed that mortality was higher in TNBC compared to TPBC (HR = 2.82, P-value <0.05). However, in a multivariate analysis, molecular subtypes did not show a significant effect on OS with a P-value of 0.94. We found that age at diagnosis has been associated with a 4% increase in mortality risk with a yearly rise in age. Conclusion In this limited retrospective cohort study, we found that TNBC may not be associated with a higher risk of death than TPBC. However, other factors, including age at diagnosis, surgical intervention, and lymphovascular invasion (LVI), have been observed to increase the risk of mortality. On the other hand, patients with TNBC were found to have a worse prognosis in terms of local recurrence.This information cannot be generalized to all patients with BC given the limitations of this study. Further, larger cohorts are needed to explore biological and treatment-related outcomes in patients with TNBC and TPBC.

HER3/Akt/mTOR pathway is a key therapeutic target for the reduction of triple‑negative breast cancer metastasis via the inhibition of CXCR4 expression.

Triple‑negative breast cancer (TNBC), a highly metastatic subtype of breast cancer, and it has the worst prognosis among all subtypes of breast cancer. However, no effective systematic therapy is currently available for TNBC metastasis. Therefore, novel therapies targeting the key molecular mechanisms involved in TNBC metastasis are required. The present study examined whether the expression levels of human epidermal growth factor receptor 3 (HER3) were associated with the metastatic phenotype of TNBC, and evaluated the potential of HER3 as a therapeutic target invitro and invivo. A new highly metastatic 4T1 TNBC cell line, termed 4T1‑L8, was established. The protein expression levels in 4T1‑L8 cells were measured using luminex magnetic bead assays and western blot analysis. The HER3 expression levels and distant metastasis‑free survival (DMFS) in TNBC were analyzed using Kaplan‑Meier Plotter. Transwell migration and invasion assays were performed to detect migration and invasion. The anti‑metastatic effects were determined in an experimental mouse model of metastasis. The results revealed that the increased expression of the HER3/Akt/mTOR pathway was associated with a greater level of cell migration, invasion and metastasis of TNBC cells. In addition, it was found that high expression levels of HER3 were associated with a poor DMFS. The inhibition of the HER3/Akt/mammalian target of rapamycin (mTOR) pathway decreased the migration, invasion and metastasis of TNBC cells by decreasing the expression of C‑X‑C chemokine receptor type 4 (CXCR4). Furthermore, treatment of metastatic TNBC cells with everolimus inhibited their migration, invasion and metastasis by decreasing CXCR4 expression. Thus, targeting the HER3/Akt/mTOR pathway opens up a new avenue for the development of therapeutics against TNBC metastasis; in addition, everolimus may prove to be an effective therapeutic agent for the suppression of TNBC metastasis.