Hormone Receptor-positive Breast Cancer Cells Research Articles

Tumor stromal topography promotes chemoresistance in migrating breast cancer cell clusters

Multicellular clustering provides cancer cells with survival advantages and facilitates metastasis. At the tumor migration front, cancer cell clusters are surrounded by an aligned stromal topography. It remains unknown whether aligned stromal topography regulates the resistance of migrating cancer cell clusters to therapeutics. Using a hybrid nanopatterned model to characterize breast cancer cell clusters at the migration front with aligned stromal topography, we demonstrate that topography-induced migrating cancer cell clusters exhibit upregulated cytochrome P450 family 1 (CYP1) drug metabolism and downregulated glycolysis gene signatures, which correlates with unfavorable prognosis. Screening on approved oncology drugs shows that cancer cell clusters on aligned stromal topography are more resistant to diverse chemotherapeutics. Full-dose drug testings further indicate that topography induces drug resistance of hormone receptor-positive breast cancer cell clusters to doxorubicin and tamoxifen and triple-negative breast cancer cell clusters to doxorubicin by activating the aryl hydrocarbon receptor (AhR)/CYP1 pathways. Inhibiting the AhR/CYP1 pathway restores reactive oxygen species-mediated drug sensitivity to migrating cancer cell clusters, suggesting a plausible therapeutic direction for preventing metastatic recurrence.

Abstract P2-26-09: Synergistic activity of PI3K inhibitor in combination with AZD6738, ATR inhibitor in breast cancer preclinical model via DNA damage response pathway

Abstract Background: The PI3K inhibition has been an appealing approach for anticancer therapy due to its crucial role in cell growth, proliferation, and survival in various cancers. Emerging data suggest the PI3K pathway is also involved in DNA replication and genome stability, making DNA damage response (DDR) inhibitors as an attractive combination treatment for PI3K pathway blockades. Here, to enhance the efficacy of PI3K inhibitors, we investigated the novel approach combining PI3K inhibitors (alpelisib, AZD8835, AZD8186, NVP-BKM120) with DDR blockade using ATR inhibitor (AZD6738) in breast cancer preclinical models. Methods: Hormone receptor-positive breast cancer cells, MCF7 (PIK3CA E545K mutation) and T47D (PIK3CA H1047R mutation) were used. First, cell viability and the synergistic effect of combination drug was carried out by MTT assy. Next, western blot, cell cycle analysis, apoptosis assay, and immunocytochemistry were conducted to validate the hypothesis. Finally, tumor xenograft experiments were conducted using BALB/c nude mice to validate the in vitro data. Results: A synergistic antiproliferative effect was observed over a wide range of combination (PI3K inhibitor + ATR inhibitor) concentrations (even in a lower concentration as 1/10 x IC50) in vitro, suggesting that when alpelisib is combined with an ATR inhibitor, there may be possibility of lowering the effective dosage of alpelisib. After confirmation of the strong synergistic effect in sub-G1/G0-G1 arrest-mediated apoptosis by the combination treatment, we demonstrated that expressions of phospho ATR, ATM, and CHK1 were suppressed but -H2AX markedly increased by combination treatment as compared to PI3K inhibitors and ATR inhibitor alone. This suggests that combination treatment activates apoptotic pathway through enhanced DNA double strand breaks. Finally, the in vivo study showed that the combination treatment group tended to show a greater tumor growth inhibition compared with PI3K inhibitor or ATR inhibitor alone. Conclusion: The combined inhibition of PI3K and ATR showed a synergistic anticancer effect in vitro and in vivo. ATR inhibitor in combination with PI3K inhibitor merits further clinical investigation to enhance the activity of PI3K inhibitor for the treatment of PIK3CA mutated breast cancer patients. Citation Format: Yong Wha Moon, Mithun Gosh, Nahee Park, Kamal Pandey, Nar Bahadur Katwal, Sa Deok Hong. Synergistic activity of PI3K inhibitor in combination with AZD6738, ATR inhibitor in breast cancer preclinical model via DNA damage response pathway [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 P2-26-09.

Palbociclib regulates intracellular lipids in mammary tumor cells by secreting lipoprotein lipase.

Lipoprotein metabolism is essential for the growth and proliferation of cancer cells, and is involved in the supply of energy and cellular components. Lipoprotein lipase (LPL) is a very important enzyme in lipoprotein metabolism; however, the details underlying the mechanism of LPL secretion are unclear. Palbociclib is an antitumor drug that inhibits cell cycle progression and suppresses the growth of cancer cells. The effects of palbociclib on energy metabolism, particularly on lipid metabolism, have not been fully elucidated. We examined the regulation of LPL secretion, which is primarily involved in lipoprotein metabolism. FM3A mouse mammary tumor cells, which are hormone receptor-positive breast cancer cells, were treated with palbociclib, and the activity and protein levels of secreted LPL were measured. Moreover, the changes in intracellular lipid content were measured by fluorescence staining using Nile Red. FM3A cells were treated with palbociclib, the activity and protein content of secreted LPL were increased. The stimulatory secretion of LPL by palbociclib was suppressed by an intracellular Ca2+ chelator (BAPTA-AM) and a Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor (STO-609). Furthermore, the palbociclib-stimulated secretion of LPL was not observed in AMP-activated protein kinase (AMPK)-knockdown cells. An increase in the fluorescence intensity of Nile Red was observed in palbociclib-treated cells; however, no increase was observed in LPL-knockdown cells. Our data suggest that palbociclib causes intracellular lipid accumulation in breast cancer cells by stimulating Ca2+/CaMKK/AMPK-mediated LPL secretion.

Targeting Mutated p53 Dependency in Triple-Negative Breast Cancer Cells Through CDK7 Inhibition.

BackgroundCyclin-dependent kinase 7 (CDK7) is crucial for cell cycle progression and gene expression transcriptional regulation, which are often not assessed in cancer developing process. CDK7 inhibitors have emerged as promising drugs for treating diverse cancers, including breast cancer. However, the mechanism behind its anticancer effect has not been well investigated. Here, the possible mechanism of CDK7 inhibitors for treating human triple-negative breast cancer (TNBC) has been studied.MethodsThe effects of CDK7 inhibitors on breast cancer cells have been identified by measuring cell viability (Cell Counting Kit-8) and cell proliferation and calculating colony formation. The short hairpin RNA and short interfering RNA were used for the construction of knockdown cells. To assess the expression of associated proteins, western blot was used.ResultsThis study confirmed that, compared to hormone receptor-positive breast cancer cells, TNBC cells were more sensitive to THZ1, a novel CDK7 inhibitor. THZ1 treatment specifically downregulated mutated p53 in a dose- and time-dependent manner in TNBC cells with p53 mutation. Another CDK7 inhibitor, LDC4297, also potently interfered with the expression of mutated p53. Furthermore, endogenous CDK7 expression was positively correlated with the levels of mutated p53 in TNBC cells with p53 mutation. Downregulating mutated p53 expression significantly suppressed the proliferation of TNBC cells with p53 mutation.ConclusionOur findings demonstrated that targeting CDK7 was an effective approach for the treatment of TNBC with p53 mutation.

Deregulated Immune Pathway Associated with Palbociclib Resistance in Preclinical Breast Cancer Models: Integrative Genomics and Transcriptomics.

Recently, cyclin-dependent kinase (CDK) 4/6 inhibitors have been widely used to treat advanced hormone receptor-positive breast cancer. Despite promising clinical outcomes, almost all patients eventually acquire resistance to CDK4/6 inhibitors. Here, we screened genes associated with palbociclib resistance through genomics and transcriptomics in preclinical breast cancer models. Palbociclib-resistant cells were generated by exposing hormone receptor-positive breast cancer cell lines to palbociclib. Whole-exome sequencing (WES) and a mRNA microarray were performed to compare the genomic and transcriptomic landscape between both palbociclib-sensitive and resistant cells. Microarray analysis revealed 651 differentially expressed genes (DEGs), while WES revealed 107 clinically significant mutated genes. Furthermore, pathway analysis of both DEGs and mutated genes revealed immune pathway deregulation in palbociclib-resistant cells. Notably, DEG annotation revealed activation of type I interferon pathway, activation of immune checkpoint inhibitory pathway, and suppression of immune checkpoint stimulatory pathway in palbociclib-resistant cells. Moreover, mutations in NCOR1, MUC4, and MUC16 genes found in palbociclib-resistant cells were annotated to be related to the immune pathway. In conclusion, our genomics and transcriptomics analysis using preclinical model, revealed that deregulated immune pathway is an additional mechanism of CDK4/6 inhibitor resistance besides the activation of cyclin E-CDK2 pathway and loss of RB, etc. Further studies are warranted to evaluate whether immune pathways may be a therapeutic target to overcome CDK4/6 inhibitor resistance.

Inhibitory effects of iron depletion plus eribulin on the breast cancer microenvironment

BackgroundIron is required for the proliferation of cancer cells, and its depletion suppresses tumor growth. Eribulin mesylate (eribulin), a non-taxane microtubule inhibitor, disrupts the tumor microenvironment via vascular remodeling and obstruction of the epithelial-mesenchymal transition (EMT). Herein, we investigated the effects of the iron chelator on tumor-related properties of breast cancer cells and the effects of iron chelator plus eribulin on tumor growth in vivo.MethodsTwo triple-negative breast cancer (TNBC) cell lines, MDA-MB-231 and BT-549, and one hormone-receptor positive breast cancer cell line, MCF-7, were used in our study. Cell proliferation, cell migration, cell cycle position, and gene expression were analyzed via MTT assays, wound-healing assays, flow cytometry, and quantitative real-time-polymerase chain reaction, respectively. For the in vivo experiments, mice with breast cancer xenografts were treated with the inhibitors, alone or together, and tumor volume was determined.ResultsIron chelator inhibited breast cancer cell proliferation and decreased the proportion of S-phase cells. Conversely, it induced hypoxia, angiogenesis, EMT, and immune checkpoints, as determined by quantifying the expression of marker mRNAs in MDA-MB-231 and MCF-7 cells. Eribulin suppressed the expression of the hypoxia and EMT related marker mRNAs in the presence of iron chelator. Iron chelator plus eribulin inhibited tumor growth in vivo to a greater extent than did either inhibitor alone.ConclusionsAlthough iron chelator induces oncogenic events (hypoxia, angiogenesis, EMT, and immune checkpoints), it may be an effective treatment for breast cancer when administered in combination with eribulin.

Progesterone receptor membrane component 1 regulates lipid homeostasis and drives oncogenic signaling resulting in breast cancer progression

BackgroundPGRMC1 (progesterone receptor membrane component 1) is a highly conserved heme binding protein, which is overexpressed especially in hormone receptor-positive breast cancer and plays an important role in breast carcinogenesis. Nevertheless, little is known about the mechanisms by which PGRMC1 drives tumor progression. The aim of our study was to investigate the involvement of PGRMC1 in cholesterol metabolism to detect new mechanisms by which PGRMC1 can increase lipid metabolism and alter cancer-related signaling pathways leading to breast cancer progression.MethodsThe effect of PGRMC1 overexpression and silencing on cellular proliferation was examined in vitro and in a xenograft mouse model.Next, we investigated the interaction of PGRMC1 with enzymes involved in the cholesterol synthesis pathway such as CYP51, FDFT1, and SCD1. Further, the impact of PGRMC1 expression on lipid levels and expression of enzymes involved in lipid homeostasis was examined. Additionally, we assessed the role of PGRMC1 in key cancer-related signaling pathways including EGFR/HER2 and ERα signaling.ResultsOverexpression of PGRMC1 resulted in significantly enhanced proliferation. PGRMC1 interacted with key enzymes of the cholesterol synthesis pathway, alters the expression of proteins, and results in increased lipid levels. PGRMC1 also influenced lipid raft formation leading to altered expression of growth receptors in membranes of breast cancer cells. Analysis of activation of proteins revealed facilitated ERα and EGFR activation and downstream signaling dependent on PGRMC1 overexpression in hormone receptor-positive breast cancer cells. Depletion of cholesterol and fatty acids induced by statins reversed this growth benefit.ConclusionPGRMC1 may mediate proliferation and progression of breast cancer cells potentially by altering lipid metabolism and by activating key oncogenic signaling pathways, such as ERα expression and activation, as well as EGFR signaling. Our present study underlines the potential of PGRMC1 as a target for anti-cancer therapy.

Abstract P1-10-19: Tyrosine aminoacyl-tRNA synthetase sensitizes breast cancer to chemotherapy througha necroptosis-mediated mechanism: High-throughput proteomics and machine learningalgorithm based feature selection analyses

Abstract Although more than 70% of entire patients are currently receiving the chemotherapy regimen, pathologic complete response (pCR) rate is still low. Therefore, the need for a marker predictive of response to a particular cytotoxic regimen is becoming all the more necessary to optimize therapeutic efficacy and to avoid unnecessary complications. We performed quantitative proteomics in FFPE biopsy breast cancer samples consist of non-responsive and responsive groups to chemotherapy. To define the best classifier to evaluate the predictive power of signatures, we employed four different machine learning algorithms and performed repeated cross-validation on the training set to classify samples between pCR and non-pCR groups. The candidate proteins selected from the machine-learning algorithms were subsequently validated by immunohistochemistry of 123 cases of independent needle biopsy FFPE samples. The further experimental model of breast cancer was performed to identify the molecular mechanism of how the biomarker potentiates sensitivity of multiple breast cancer cells to chemotherapy response and synergistic effect with a combination of necroptotic mimetics. The filtered dataset was subjected to statistical analysis using Student’s t-test (p-value < 0.05), which resulted in 539 proteins with differential abundances. To identify the most meaningful changes in two conditions, the volcano plot was used and 13 proteins were prioritized. We searched for biological process in the Gene Ontology (GO) enrichment analysis in each proteomic cluster. Several immune responses process, apoptotic process, DNA replication process, and aminoacylation for protein translation process primarily were represented in the group with complete remission. On the other hand, cell adhesion process, cytoskeleton organization process, vesicle organization process and Golgi organization process overrepresented in breast cancer which showed poor responses to the therapy. The machine learning approaches demonstrated the highest AUC value, 0.978 (sensitivity 1.0 and specificity 0.714) with a combination of 11 proteins. For the accuracy prediction, four different algorithms demonstrated evenly high accuracy rates from 0.85 to 0.95 with a combination of the selected seven candidates. They were evaluated in the subsequent steps of verification using immunohistochemistry (IHC) in 123 patient cohorts. The predictive relevance of individual proteins, YARS to distinguish CR from nCR was AUC of 0.749 for all cases. The overexpression of YARS induced chemotherapeutic sensitivity in hormone receptor-positive breast cancer cell lines such as T47D, which was confirmed with multiple molecular biology-driven assays. The further experimental model of breast cancer demonstrated that YARS induced tumor necroptosis which enhanced chemotherapy response and was synergized with a combination of SMAC mimetics that is a potent necroptosis inducer. In summary, our discovery data provide a global molecular landscape for determining chemotherapy response in breast cancer at the proteome level. Furthermore, we provided a novel protein candidate to predict chemotherapy response and identify a novel protein YARS in combination with Smac mimetics synergistically induced necroptosis which produces more cell death in response to combined chemotherapy in breast cancer. Citation Format: Han Suk Ryu. Tyrosine aminoacyl-tRNA synthetase sensitizes breast cancer to chemotherapy througha necroptosis-mediated mechanism: High-throughput proteomics and machine learningalgorithm based feature selection analyses [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-10-19.

Di- and tri-substituted s-triazine derivatives: Synthesis, characterization, anticancer activity in human breast-cancer cell lines, and developmental toxicity in zebrafish embryos.

Here we report on a small library based on a 4-aminobenzonitile-s-triazine moiety. We used a straightforward orthogonal synthetic pathway to prepare di- and tri-substituted s-triazine derivatives, whose basic structure was modified. The newly synthesized compounds were fully characterized by 1H NMR, 13C NMR and elemental analysis. They showed strong anticancer activity against two human breast cancer cell lines (MIDA-MB-231 and MCF-7), with IC50 values less than 1 µM. These s-triazine compounds were generally more selective towards hormone receptor-positive breast cancer cell line MCF-7 than the triple negative MDA-MB-231 cell line. Zebrafish embryos were used to test the developmental toxicity of the target compounds in vivo. The phenotype of embryos treated with the derivatives resembled that of those treated with estrogen disruptors. This observation strongly supports the notion that that these compounds induce their anticancer activity in human breast cancer cells via targeting the estrogen and progesterone receptors.

Aberrant fatty acid profile and FFAR4 signaling confer endocrine resistance in breast cancer

BackgroundEvidence suggests that fatty acid receptor FFAR4 plays a tumor-promoting role in adipose tissue-adjacent malignancies, but its clinical relevance remains unexplored. Here, we investigated the clinical significance and underlying mechanisms of FFAR4 in hormone receptor-positive breast cancer (HRPBC).MethodsFFAR4 expression was assessed by immunohistochemistry in an exploration cohort of 307 breast cancer cases collected from two independent institutes. Two public breast cancer microarray datasets served as validation cohorts. Gas chromatography-mass spectrometry was employed to identify FFAR4 ligands in normal and cancerous breast tissues. Survival analyses were performed in all cohorts and designated molecular subgroups. Mechanistic studies were performed in vitro in hormone receptor-positive breast cancer cell lines MCF-7 and T-47D.ResultsAberrant FFAR4 expression and endogenous FFAR4 ligands were identified in breast cancer tissues, five FFAR4 ligands showed significantly elevated proportions in cancerous versus normal tissues. In the exploration cohort, FFAR4 was demonstrated as an independent prognostic factor for recurrences (HR: 2.183, 95% CI: 1.360–3.504, P = 0.001) and breast cancer-specific deaths (HR: 2.102, 95% CI: 1.173–3.766, P = 0.013) in HRPBC cases. In contrast, FFAR4 expression was not associated with prognosis in hormone receptor-negative cases. In the validation cohorts, FFAR4 mRNA levels were also observed to be associated with disease recurrence in estrogen receptor-positive cases, but not so in estrogen receptor-negative cases. FFAR4 activation by endogenous ligands and a synthetic ligand TUG891 significantly dampened tamoxifen’s efficacy on HRPBC cells, whereas FFAR4 knockdown or antagonist AH7614 abrogated this effect. Furthermore, FFAR4-induced tamoxifen resistance was dependent on ERK and AKT pathways in HRPBC.ConclusionsOur results establish a novel role of FFAR4 and its ligands in the complicated interactions between tissue lipid profile and cancer biology. FFAR4 signaling confers tamoxifen resistance in HRPBC cell line and FFAR4 expression can serve as a prognostic biomarker for tamoxifen-treated HRPBC patients. FFAR4 may serve as a potential target for anti-breast cancer therapies, especially in endocrine resistant cases.

Everolimus Reverses Palbociclib Resistance in ER+ Human Breast Cancer Cells by Inhibiting Phosphatidylinositol 3-Kinase(PI3K)/Akt/Mammalian Target of Rapamycin (mTOR) Pathway

BackgroundPalbociclib, a specific inhibitor of CDK4/6, has been shown to provide a survival benefit in hormone receptor-positive advanced breast cancer; however, its resistance and related mechanisms are unclear.Material/MethodsIn this study, we constructed palbociclib-resistant hormone receptor-positive breast cancer cells (MCF-7-P) via culturing with palbociclib for at least 6 months. Quantitative real-time PCR (qRT-PCR) and western blot were used to detect the expression of stemness markers in MCF-7-P and MCF-7 cells. Additionally, cell spheroid formation, Transwell migration, ALDH1 activity, and flow cytometry assays were performed to detect stemness and migration ability of MCF-7-P cells, and the effects of everolimus on MCF-7-P cells stemness and migration ability. Growth inhibition assay was used to examine the effect of everolimus on the sensitivity of palbociclib in MCF-7-P and MCF-7 cells.ResultsMCF-7-P cells had stronger stemness and higher expression of ABCG2 and MDR1. Moreover, PI3K/Akt/mTOR signaling was hyper-activated in MCF-7-P cells. Additionally, everolimus, which is a mTOR inhibitor, attenuated MCF-7-P cells stemness and re-sensitized MCF-7-P cells to palbociclib. Importantly, everolimus enhanced the antitumor effect of palbociclib in palbociclib-sensitive hormone receptor-positive cells (MCF-7 cells).ConclusionsThese findings provide a rationale for future clinical trials of palbociclib and everolimus combination-based therapy in hormone receptor-positive breast cancer.

Antitumor properties of Salvianolic acid B against triple-negative and hormone receptor-positive breast cancer cells via ceramide-mediated apoptosis.

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited treatment options. It is urgent to develop new therapeutics against this disease. Salvinolic acid B (Sal-B) is a leading bioactive component of Salvia miltiorrhiza Bunge, a well-known Chinese medicine for treating various diseases without appreciable adverse effects. To understand the antitumor properties of Sal-B against TNBC, we analyzed its effects on the cell viability, cell cycle and apoptosis of triple-negative MDA-MB-231 cells with the hormone receptor-positive MCF-7 cells as the control. The in vitro analysis showed that Sal-B could significantly reduce the cell viability and suppress the proliferation of both MDA-MB-231 and MCF-7 cells with decreased cyclin B1 expression, but with no noticeable cell cycle phase change. In mouse models, Sal-B markedly inhibited the growth, decreased the PCNA expression, and increased the cell apoptosis of MDA-MB-231 tumor xenografts. To understand the antitumor mechanisms, we analyzed the expression levels of ceramides, and anti-apoptotic (Bcl-xL and survivin) and pro-apoptotic (caspase-3 and caspase-8) proteins. We found that Sal-B enhanced the ceramide accumulation and inhibited the anti-apoptotic protein expression. Interestingly, the ceramide accumulation was accompanied by decreased expression of glucosylceramide and GM3 synthases, two key enzymes regulating ceramide metabolism. These findings indicate that Sal-B exerts its antitumor effects at least partially by inducing the ceramide accumulation and ceramide-mediated apoptosis via inhibiting the expression of glucosylceramide and GM3 synthases, which was independent of estrogen receptor α. Sal-B appears to be a promising therapeutic agent against TNBC.

Kaempferol, a natural dietary flavonoid, suppresses 17β-estradiol-induced survivin expression and causes apoptotic cell death in endometrial cancer.

Endometrioid endometrial carcinoma, commonly known as type 1 endometrial cancer, accounts for >80% of endometrial carcinomas and is dependent on estrogen. We recently reported on the prognostic significance of the BIRC5 survivin gene in endometrial cancer. Estradiol induces survivin expression in estrogen receptor-positive, but not in estrogen receptor-negative, cancer cells. Kaempferol, a bioflavonoid, reportedly inhibits estrogen receptor-α (ERα) in hormone receptor-positive breast cancer cells. However, whether kaempferol-mediated inhibition of ERα suppresses survivin and induces cell death in endometrial cancer remains unclarified. The present study evaluated the antitumor effects of kaempferol on endometrial cancer cells. Cell viability assays, flow cytometry analysis, western blotting and annexin V analyses were used to analyze the antitumor effects of kaempferol. The results demonstrated that kaempferol successfully suppressed the viability of two ER-positive endometrial cancer cell lines, with IC50 values of 83 and 65 µM. In addition, kaempferol induced sub-G1 cell accumulation and apoptotic cell death (P<0.01) in a dose-dependent manner. Treatment of cells with estradiol significantly induced co-expression of nuclear ERα and survivin proteins (P<0.001). Further evaluation revealed that kaempferol causes apoptotic cell death largely by suppressing ERα, survivin and Bcl-2 protein. Therefore, the results of the present study suggested that targeting ERα and survivin with kaempferol may be a novel therapeutic option against endometrial carcinoma.

PO-059 IBTK promotes B cell lymphomagenesis in Eμ-MYC transgenic mice conferring resistance to apoptosis

IntroductionAlbeit the advancement in breast cancer (BC) treatment, BC remains as the second leading cause of cancer death worldwide. Unlike the other BC subtypes, the lack of hormone receptor (HR) rendering the aggressive triple negative BC (TNBC) towards chemotherapy which is destructive to one’s quality of life. Tumour necrosis factor related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic agent due to its selective killing of malignant cells leaving the normal cells unharmed. Despite being TRAIL-sensitive, the TNBC MDA-MB-231 cells develop resistance to TRAIL after repeated treatment. The epigenetic drugs zebularine (Zeb) and trichostatin A (TSA) were reported to increase the TRAIL-induced apoptosis. Therefore, we aim to study the combinational anti-cancer effect of Zeb and TSA followed by TRAIL (TZT treatment) and compare its effect with the standard chemotherapy drug doxorubicin (DOX).Material and methodsMDA-MB-231, MCF-7 (HR positive breast cancer cells) and MCF-10A (normal breast epithelial cells) were treated with TZT and DOX respectively and subjected to cell proliferation, cell cycle arrest and apoptosis analyses.Results and discussionsBased on the results obtained, TZT treatment hampered the cell proliferation in MDA-MB-231 and MCF-7 as compared to TRAIL treatment alone but not in MCF-10A. Nevertheless, the cell proliferation of both breast cancer and normal cells treated with DOX was significant reduced. Subsequently, the cell cycle distribution was evaluated via flow cytometry analysis. Higher induction of G1 cell cycle arrest was observed in the MDA-MB-231 treated with TZT (57.5%) as compared to TRAIL alone (52.2%) at 24 hours. In MCF-7, there is the minimal induction of G1 arrest with TZT treatment (71.2%) as compared to TRAIL alone (69.7%) at 24 hours. However, DOX treatment induced G2/M arrest in breast cancer and normal cells. Furthermore, the morphological features of apoptosis were determined by haematoxylin and eosin staining. Intriguingly, the hallmark of apoptosis was clearly observed in breast cancer treated with TZT compared to MCF-10A. The results suggest the significance of Zeb and TSA to foster the TRAIL-induced apoptosis in TNBC but not in normal breast epithelial cells, despite further molecular analyses are requisite to validate the enhancement of apoptosis induction.ConclusionThis research provides an insight of potential alternative of TZT in treating the TNBC to improve the patients’ prognosis in the near future.

PO-056 The epigenetic drugs zebularine and trichostatin a enhanced the TRAIL-induced apoptosis in the aggressive triple negative breast cancer

Introduction Albeit the advancement in breast cancer (BC) treatment, BC remains as the second leading cause of cancer death worldwide. Unlike the other BC subtypes, the lack of hormone receptor (HR) rendering the aggressive triple negative BC (TNBC) towards chemotherapy which is destructive to one’s quality of life. Tumour necrosis factor related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic agent due to its selective killing of malignant cells leaving the normal cells unharmed. Despite being TRAIL-sensitive, the TNBC MDA-MB-231 cells develop resistance to TRAIL after repeated treatment. The epigenetic drugs zebularine (Zeb) and trichostatin A (TSA) were reported to increase the TRAIL-induced apoptosis. Therefore, we aim to study the combinational anti-cancer effect of Zeb and TSA followed by TRAIL (TZT treatment) and compare its effect with the standard chemotherapy drug doxorubicin (DOX). Material and methods MDA-MB-231, MCF-7 (HR positive breast cancer cells) and MCF-10A (normal breast epithelial cells) were treated with TZT and DOX respectively and subjected to cell proliferation, cell cycle arrest and apoptosis analyses. Results and discussions Based on the results obtained, TZT treatment hampered the cell proliferation in MDA-MB-231 and MCF-7 as compared to TRAIL treatment alone but not in MCF-10A. Nevertheless, the cell proliferation of both breast cancer and normal cells treated with DOX was significant reduced. Subsequently, the cell cycle distribution was evaluated via flow cytometry analysis. Higher induction of G1 cell cycle arrest was observed in the MDA-MB-231 treated with TZT (57.5%) as compared to TRAIL alone (52.2%) at 24 hours. In MCF-7, there is the minimal induction of G1 arrest with TZT treatment (71.2%) as compared to TRAIL alone (69.7%) at 24 hours. However, DOX treatment induced G2/M arrest in breast cancer and normal cells. Furthermore, the morphological features of apoptosis were determined by haematoxylin and eosin staining. Intriguingly, the hallmark of apoptosis was clearly observed in breast cancer treated with TZT compared to MCF-10A. The results suggest the significance of Zeb and TSA to foster the TRAIL-induced apoptosis in TNBC but not in normal breast epithelial cells, despite further molecular analyses are requisite to validate the enhancement of apoptosis induction. Conclusion This research provides an insight of potential alternative of TZT in treating the TNBC to improve the patients’ prognosis in the near future.

Abstract 1144: Dual inhibition of MEK1/2 and PLK1 specifically targets aggressive breast cancer cell population with CEP55 elevated expression

Abstract Triple negative breast cancers (TNBCs), lacking the expression of ER, PR and HER2 amplification, are the most aggressive form of breast cancer (BC). Due to their heterogeneity influenced by high level of genomic instability and aneuploidy, treatment of TNBC patients is one of the biggest challenges faced in the clinics. CEP55, discovered first by our laboratory, is a key regulator of cytokinesis malfunction of which has been shown to cause multinucleation. Furthermore, ERK2/PLK1 critically regulates the functional role of CEP55 via phosphorylation of CEP55 at particular stages of mitosis, allowing it to localize to the midbody for accurate cytokinesis. Research has demonstrated association of CEP55 with various cancers especially BC as over-expression of CEP55 mRNA is associated with worse BC prognosis and poor survival. We hypothesized that, CEP55 regulates the fate of aneuploid cell population, which are highly dependent on mitotic genes for tumor progression among aggressive BC, thus can be targeted for therapy development. We have performed a series of in vitro studies demonstrating that depletion of CEP55 sensitizes cells to anti-mitotic drugs like PLK1 inhibitor (BI2536) and leads to unscheduled CDK1/Cyclin B activation and favor CDK1-Caspase 3-dependent mitotic catastrophe. We also demonstrate that ERK1/2 transcriptionally controls CEP55 mRNA and due to lack of a specific small molecule inhibitor against CEP55, inhibition of MEK1/2 using the small molecule inhibitor Selumetinib, can mimic depletion of CEP55 in vivo. Thus, we rationalized the usage of a MEK1/2 inhibitor in combination with a PLK1 inhibitor across a series of BC cell lines. We observed synthetic lethality among the aggressive hormone receptor negative cell lines, which expressed higher expression of CEP55 compared to normal like and hormone receptor positive BC cell lines with lower CEP55 level. The combination synergistically increased apoptosis of aneuploid population via premature entry of these cells into mitosis in the presence of antimitotic drugs due to exhaustion of CEP55. We have also validated this synergistic effect of MEK1/2 and PLK1 inhibition using xenograft models, results of which imitated the in vitro findings. Therefore, we propose a novel treatment strategy of MEK1/2-PLK1 dual combination for selectively targeting CEP55 over-expressing BC in the clinics. Citation Format: Debottam Sinha, Murugan Kalimutho, J. Alejandro Lopez, Kum Kum Khanna. Dual inhibition of MEK1/2 and PLK1 specifically targets aggressive breast cancer cell population with CEP55 elevated expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1144. doi:10.1158/1538-7445.AM2017-1144

Characterization of the release and biological significance of cell-free DNA from breast cancer cell lines.

In breast cancer, cell-free DNA (cfDNA) has been proven to be a diagnostic and prognostic biomarker. However, there have been few studies on the origin and biological significance of cfDNA. In this study, we assessed the release pattern of cfDNA from breast cancer cell lines under different culture conditions and investigated the biological significance of cfDNA. The cfDNA concentration increased rapidly (6 h) after passage, decreased gradually, and was then maintained at a relatively stable level after 24 h. In addition, the cfDNA concentration did not correlate with the amount of apoptotic and necrotic cells. Interestingly, if more cells were in the G1 phase, more cfDNA was detected (p < 0.01) and the cfDNA concentration correlated positively with the percent of cells in the G1 phase (p < 0.05). We observed that cells could release cfDNA actively, but not exclusively, via exosomes. Furthermore, we showed that cfDNA could stimulate hormone receptor-positive breast cancer cell proliferation by activating the TLR9-NF-κB-cyclin D1 pathway. In conclusion, cfDNA is released from breast cancer mainly by active secretion, and cfDNA could stimulate proliferation of breast cancer cells.

MicroRNA-455-3p promotes invasion and migration in triple negative breast cancer by targeting tumor suppressor EI24.

Lacking of treatment methods for the patients with triple negative breast cancer (TNBC) underscores the pivotal needs to further understand its biology as well as to find better biomarkers and develop novel therapeutic strategies. Increasing evidences support that aberrantly expressed microRNAs (miRNAs) are involved in tumorigenesis and may serve as biomarkers for diagnostic and prognostic purposes of various cancers. In current study, we found that miR-455-3p and miR-196a-5p were intensively overexpressed in TNBC compared with the hormone receptor (HR) positive breast cancer whereas miR-425-5p was down-regulated by miRNA microarray analysis. qRT-PCR analysis confirmed that the expression of miR-455-3p in TNBC cell lines MDA-MB-231 and MDA-MB-468 was higher than that in HR positive breast cancer cell line MCF-7(p<0.01). Functional experiments in vitro showed that miR-455-3p enhanced cell proliferative, invasive and migrational abilities in TNBC cell lines. miRNA targets prediction showed SMAD2, LTBR and etoposide induced 2.4 (EI24) were potential target genes of miR-455-3p, and then it was confirmed by qRT-PCR assay. Dual luciferase reporter assay showed the specific binding of miR-455-3p to 3′ UTR of EI24 in TNBC. Then we found miR-455-3p inhibited the EI24 expression at the levels of mRNA and protein. Through small interfering RNA (siRNA) targeting EI24 gene, there were strengthened capabilities of invasion and migration of TNBC cells, and increased expression of EI24 had the inverse effects. In conclusion, the data suggest that miRNA455-3p promotes invasion and migration by targeting tumor suppressor EI24 and might be a potential prognostic biomarker and therapeutic target in TNBC.

The Estrogen Receptor Cofactor SPEN Functions as a Tumor Suppressor and Candidate Biomarker of Drug Responsiveness in Hormone-Dependent Breast Cancers.

The treatment of breast cancer has benefitted tremendously from the generation of estrogen receptor-α (ERα)-targeted therapies, but disease relapse continues to pose a challenge due to intrinsic or acquired drug resistance. In an effort to delineate potential predictive biomarkers of therapy responsiveness, multiple groups have identified several uncharacterized cofactors and interacting partners of ERα, including Split Ends (SPEN), a transcriptional corepressor. Here, we demonstrate a role for SPEN in ERα-expressing breast cancers. SPEN nonsense mutations were detectable in the ERα-expressing breast cancer cell line T47D and corresponded to undetectable protein levels. Further analysis of 101 primary breast tumors revealed that 23% displayed loss of heterozygosity at the SPEN locus and that 3% to 4% harbored somatically acquired mutations. A combination of in vitro and in vivo functional assays with microarray-based pathway analyses showed that SPEN functions as a tumor suppressor to regulate cell proliferation, tumor growth, and survival. We also found that SPEN binds ERα in a ligand-independent manner and negatively regulates the transcription of ERα targets. Moreover, we demonstrate that SPEN overexpression sensitizes hormone receptor-positive breast cancer cells to the apoptotic effects of tamoxifen, but has no effect on responsiveness to fulvestrant. Consistent with these findings, two independent datasets revealed that high SPEN protein and RNA expression in ERα-positive breast tumors predicted favorable outcome in patients treated with tamoxifen alone. Together, our data suggest that SPEN is a novel tumor-suppressor gene that may be clinically useful as a predictive biomarker of tamoxifen response in ERα-positive breast cancers.

CDK7-Dependent Transcriptional Addiction in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer that exhibits extremely high levels of genetic complexity and yet a relatively uniform transcriptional program. We postulate that TNBC might be highly dependent on uninterrupted transcription of a key set of genes within this gene expression program and might therefore be exceptionally sensitive to inhibitors of transcription. Utilizing kinase inhibitors and CRISPR/Cas9-mediated gene editing, we show here that triple-negative but not hormone receptor-positive breast cancer cells are exceptionally dependent on CDK7, a transcriptional cyclin-dependent kinase. TNBC cells are unique in their dependence on this transcriptional CDK and suffer apoptotic cell death upon CDK7 inhibition. An "Achilles cluster" of TNBC-specific genes is especially sensitive to CDK7 inhibition and frequently associated with super-enhancers. We conclude that CDK7 mediates transcriptional addiction to a vital cluster of genes in TNBC and CDK7 inhibition may be a useful therapy for this challenging cancer.