Triple-negative Breast Cancer Cell Models Research Articles

Small Non-Coding RNA Profiling Identifies miR-181a-5p as a Mediator of Estrogen Receptor Beta-Induced Inhibition of Cholesterol Biosynthesis in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is a highly heterogeneous disease, representing the most aggressive breast cancer (BC) subtype with limited treatment options due to a lack of estrogen receptor alpha (ERα), progesterone receptor (PR), and Erb-B2 receptor tyrosine kinase 2 (HER2/neu) expression. Estrogen receptor beta (ERβ) is present in a fraction of TNBC patients, where its expression correlates with improved patient outcomes, supported by the fact that it exerts oncosuppressive effects in TNBC cell models in vitro. ERβ is involved in microRNA-mediated regulation of gene expression in hormone-responsive BC cells and could mediate its actions through small noncoding RNAs (sncRNAs) in TNBCs also. To verify this possibility, smallRNA sequencing was performed on three ERβ-expressing cell lines from different TNBC molecular subtypes. Several sncRNAs resulted modulated by ERβ, with a subset being regulated in a tumor subtype-independent manner. Interestingly, sncRNA profiling of 12 ERβ+and 32 ERβ− primary TNBC biopsies identified 7 microRNAs, 1 PIWI-interacting RNA (piRNA), and 1 transfer RNA (tRNA) differentially expressed in ERβ+ compared to ERβ− tumors and cell lines. Among them, miR-181a-5p was found to be overexpressed in ERβ+ tumors and predicted target key components of the cholesterol biosynthesis pathway previously found to be inhibited by ERβ in TNBC cells.

Pre-treatment with the CDK4/6 inhibitor palbociclib improves the efficacy of paclitaxel in TNBC cells

Triple Negative Breast Cancer (TNBC) is a challenging disease due to the lack of druggable targets; therefore, chemotherapy remains the standard of care and the identification of new targets is a high clinical priority. Alterations in the components of the cell cycle machinery have been frequently reported in cancer; given the success obtained with the CDK4/6 inhibitor palbocicib in ER-positive BC, we explored the potential of combining this drug with chemotherapy in Rb-positive TNBC cell models. The simultaneous combination of palbociclib with paclitaxel exerted an antagonistic effect; by contrast, the sequential treatment inhibited cell proliferation and increased cell death more efficaciously than single treatments. By down-regulating the E2F target c-myc, palbociclib reduced HIF-1α and GLUT-1 expression, and hence glucose uptake and consumption both under normoxic and hypoxic conditions. Importantly, these inhibitory effects on glucose metabolism were enhanced by palbociclib/paclitaxel sequential combination; the superior efficacy of such combination was ascribed to the ability of paclitaxel to inhibit palbociclib-mediated induction of AKT and to further down-regulate the Rb/E2F/c-myc signaling. Our results suggest that the efficacy of standard chemotherapy can be significantly improved by a pre-treatment with palbociclib, thus offering a better therapeutic option for Rb-proficient TNBC.

Mutant p53 improves cancer cells' resistance to endoplasmic reticulum stress by sustaining activation of the UPR regulator ATF6.

Missense mutations in the TP53 gene are frequent in human cancers, giving rise to mutant p53 proteins that can acquire oncogenic properties. Gain of function mutant p53 proteins can enhance tumour aggressiveness by promoting cell invasion, metastasis and chemoresistance. Accumulating evidences indicate that mutant p53 proteins can also modulate cell homeostatic processes, suggesting that missense p53 mutation may increase resistance of tumour cells to intrinsic and extrinsic cancer-related stress conditions, thus offering a selective advantage. Here we provide evidence that mutant p53 proteins can modulate the Unfolded Protein Response (UPR) to increase cell survival upon Endoplasmic Reticulum (ER) stress, a condition to which cancer cells are exposed during tumour formation and progression, as well as during therapy. Mechanistically, this action of mutant p53 is due to enhanced activation of the pro-survival UPR effector ATF6, coordinated with inhibition of the pro-apoptotic UPR effectors JNK and CHOP. In a triple-negative breast cancer cell model with missense TP53 mutation, we found that ATF6 activity is necessary for viability and invasion phenotypes. Together, these findings suggest that ATF6 inhibitors might be combined with mutant p53-targeting drugs to specifically sensitise cancer cells to endogenous or chemotherapy-induced ER stress.

New docetaxel-peptide conjugate for the treatment of sortilin-positive triple-negative breast cancer.

e12556 Background: Triple-negative breast cancer (TNBC) is a heterogeneous disease which still lacks defined molecular biomarkers. In the last decade, targeting of specific gene/protein molecular signature of tumors emerged among the best anticancer strategies. Recently, increased expression of the Sortilin (SORT1) receptor has been reported in TNBC patients. Given SORT1 functions in protein internalization, sorting and trafficking, we developed a new peptide-anticancer drug conjugation platform to target SORT1-positive breast cancer by linking Docetaxel to a peptide (KA-peptide) that specifically targets SORT1. Methods: MDA-MB-231 cells were used as a TNBC cell model for in vitro and in vivo xenograft (CD1 nude mice) assays. Cell migration was assessed using the xCELLigence real-time system, whereas MTT assay was used for cell proliferation analysis. Apoptosis biomarkers expression was assessed by immunoblotting. Results: In MDA-MB-231, the Docetaxel-KA-peptide conjugate (DoceKA) exerted potent anti-proliferative and anti-migratory activities in vitro. DoceKA triggered faster and higher cell death mechanisms than did free Docetaxel alone. The apoptotic and anti-migratory effects were reversed by the SORT1 ligands Neurotensin and Progranulin, and upon siRNA-mediated silencing of SORT1. DoceKA altered microtubules polymerization and triggered the down-regulation of IL-6, Survivin, Bcl-xL and mutant p53 pro-survival biomarkers. In vivo, DoceKA exhibited a greater tumor regression capacity with a prolonged survival in a murine MDA-MB-231 xenograft tumor model than did Docetaxel. Conclusions: Collectively, we demonstrate that DoceKA is specifically internalized through a receptor-mediated mechanism. Such property allows for targeting SORT1-positive breast cancers, and makes DoceKA a promising novel therapy for the treatment of TNBC.

SiRNA Library Screening to Identify Complementary Therapeutic Pairs in Triple-Negative Breast Cancer Cells.

The existence of tightly integrated cross talk through multiple signaling and effector pathways has been appreciated in malignant cells. The realization of the plasticity of such networks is stimulating the development of combinational therapy to overcome the limitations of one-dimensional therapies. Synergistic pairs of siRNAs or siRNA and drug combinations are the new frontiers in identifying effective therapeutic combinations. To elucidate effective combinations, we developed a versatile protocol to screen siRNA libraries in triple-negative breast cancer cell models. This protocol outlines the steps to identify synergistic combinations of siRNA-siRNA or siRNA-drug combinations using siRNA libraries via a robotic screen. By focusing on smaller functional siRNA libraries, we present methodologies to identify synergistic siRNA pairings against cancerous cell growth and molecular targets to augment the activity of pro-apoptotic TRAIL protein. Here, we summarize the critical steps to undertake such combinational target identification, emphasizing critical factors that affect the outcome of the screens. Our experience suggests that siRNA library screening is an efficient protocol to identify complementary therapeutic pairs of new or already-existing drugs. This protocol is simple, robust and can be completed within a 1-week working period.

Genomewide binding of transcription factor Snail1 in triple-negative breast cancer cells.

Transcriptional regulation mediated by the zinc finger protein Snail1 controls early embryogenesis. By binding to the epithelial tumor suppressor CDH1 gene, Snail1 initiates the epithelial–mesenchymal transition (EMT). The EMT generates stem‐like cells and promotes invasiveness during cancer progression. Accordingly, Snail1 mRNA and protein is abundantly expressed in triple‐negative breast cancers with enhanced metastatic potential and phenotypic signs of the EMT. Such high endogenous Snail1 protein levels permit quantitative chromatin immunoprecipitation‐sequencing (ChIP‐seq) analysis. Snail1 associated with 185 genes at cis regulatory regions in the Hs578T triple‐negative breast cancer cell model. These genes include morphogenetic regulators and signaling components that control polarized differentiation. Using the CRISPR/Cas9 system in Hs578T cells, a double deletion of 10 bp each was engineered into the first exon and into the second exon–intron junction of Snail1, suppressing Snail1 expression and causing misregulation of several hundred genes. Specific attention to regulators of chromatin organization provides a possible link to new phenotypes uncovered by the Snail1 loss‐of‐function mutation. On the other hand, genetic inactivation of Snail1 was not sufficient to establish a full epithelial transition to these tumor cells. Thus, Snail1 contributes to the malignant phenotype of breast cancer cells via diverse new mechanisms.

Genome-wide binding of transcription factor ZEB1 in triple-negative breast cancer cells.

Zinc finger E‐box binding homeobox 1 (ZEB1) is a transcriptional regulator involved in embryonic development and cancer progression. ZEB1 induces epithelial‐mesenchymal transition (EMT). Triple–negative human breast cancers express high ZEB1 mRNA levels and exhibit features of EMT. In the human triple–negative breast cancer cell model Hs578T, ZEB1 associates with almost 2,000 genes, representing many cellular functions, including cell polarity regulation (DLG2 and FAT3). By introducing a CRISPR‐Cas9‐mediated 30 bp deletion into the ZEB1 second exon, we observed reduced migratory and anchorage‐independent growth capacity of these tumor cells. Transcriptomic analysis of control and ZEB1 knockout cells, revealed 1,372 differentially expressed genes. The TIMP metallopeptidase inhibitor 3 and the teneurin transmembrane protein 2 genes showed increased expression upon loss of ZEB1, possibly mediating pro‐tumorigenic actions of ZEB1. This work provides a resource for regulators of cancer progression that function under the transcriptional control of ZEB1. The data confirm that removing a single EMT transcription factor, such as ZEB1, is not sufficient for reverting the triple–negative mesenchymal breast cancer cells into more differentiated, epithelial‐like clones, but can reduce tumorigenic potential, suggesting that not all pro‐tumorigenic actions of ZEB1 are linked to the EMT.

Crambescidin 800, Isolated from the Marine Sponge Monanchora viridis, Induces Cell Cycle Arrest and Apoptosis in Triple-Negative Breast Cancer Cells.

Triple negative breast cancer (TNBC) is currently the only group of breast cancers without an effective targeted therapy. Marine sponges have historically been a source of compounds with anticancer activity. In this study, we screened extracts from twenty marine sponges collected off the coast of Western Australia for cytotoxic activity against TNBC cells. One very active extract derived from the sponge Monanchora viridis was selected for bioactivity-guided fractionation. Through multiple steps of purification, we isolated a potent cytotoxic compound, which was identified as crambescidin 800 (C800). We found that C800 exhibited cytotoxic potency in a panel of breast cancer cells, of which TNBC and luminal cancer cell models were the most sensitive. In addition, C800 induced cell cycle arrest at the G2/M phase, resulting in a decline in the expression of cyclin D1, CDK4, and CDK6 in TNBC cells. This effect was associated with the inhibition of phosphorylation of Akt, NF-κB, and MAPK pathways, resulting in apoptosis in TNBC cells.

Nanoparticle-Encapsulated Doxorubicin Demonstrates Superior Tumor Cell Kill in Triple Negative Breast Cancer Subtypes Intrinsically Resistant to Doxorubicin.

The effect of size and release kinetics of doxorubicin-nanoparticles on anti-tumor efficacy was evaluated in a panel of human cancer cell lines, including triple-negative breast cancer (TNBC) cells that frequently demonstrate resistance to doxorubicin. Different nano-formulations of sol-gel-based Doxorubicin containing nanoparticles were synthesized. Increased cell kill in chemoreffactory triple-negative breast cancer cells was associated with the smallest size of nanoparticles and the slowest release of Dox. Modeling of dose-response parameters in Dox-sensitive versus Dox-resistant lines demonstrated increased EMax and area under the curve in Dox-resistant mesenchymal TNBC cells, implying potentially favorable activity in this molecular subtype of breast cancer. Mesenchymal TNBC cells demonstrated a high rate of fluorescent bead uptake suggestive of increased endocytosis, which may partially account for the enhanced efficacy of Dox-np in this subtype. Thus, manipulation of size and release kinetics of this nanoparticle platform is associated with enhanced dose-response metrics and tumor cell kill in therapeutically recalcitrant TNBC cell models. This platform is easily customizable and warrants further exploration.

Abstract 5111: Norcantharidin impairs tumor growth in vivo and inhibits stemness of triple-negative breast cancer cells

Abstract Triple-negative breast cancer (TNBC) is characterized by an abundance of treatment-resistant cancer stem cells (CSC). The absence of a molecular target, coupled with its highly aggressiveness, leads to the lack of an effective therapy for TNBC. Norcantharidin (NCTD) is a synthetic demethylated small-molecule analog of the naturally occurring cantharidin isolated from blister beetles (Mylabris phalerata Pall). Unlike the conventional chemotherapeutics, NCTD toxicity is higher to cancer cells than normal ones, making this small molecule promising for cancer treatment. The aims of this work were: A) To study the effect of NCTD on 4T1 cell line proliferation in vitro. B) To analyze the effect of NCTD on 4T1 derived CSC on self-renewal and clonogenic capacity. C) To evaluate the effect of NCTD on 4T1 tumor growth in vivo. We employed the well-known 4T1 triple-negative breast cancer cell model, which presents a huge proportion of CSC. We observed that NCTD treatment during 96 h significantly reduced 4T1 cell proliferation in vitro. In addition, the IC50 value of NCTD was 27.35 ± 2.83 μM. Related to CSC, NCTD pre-treatment for 96 h impaired CSC self-renewal (Number of secondary mammospheres: Control: 276±39; NCTD: 163±18; p≤0.05) as well as the clonogenic capacity (Number of colonies: Control: 359±38; NCTD: 122±11; p≤0.05). By q-PCR, we observed that NCTD treatment for 48 h significantly induced an increase of Gli-1 and Smooth in CSC, keys member of Sonic Hedgehog pathway. Finally, we performed an in vivo assay, where 4T1 cells were orthotopically inoculated on mammary gland of BALB/c mice, and NCTD was i.p. inoculated twice a week (5mg/kg). We observed that NCTD treatment significantly reduced tumor growth in vivo. Our data suggest that NCTD treatment reduces tumor growth both in vitro and in vivo, possibly through the direct effect on CSC self-renewal and clonogenic capacity, by modulating Sonic Hedgehog pathway. Citation Format: Damian E. Berardi, Guido Cicuttin, Maria A. Taruselli, Stefano M. Cirigliano, Elisa D. Bal de Kier Joffé, Alejandro J. Urtreger, Laura B. Todaro. Norcantharidin impairs tumor growth in vivo and inhibits stemness of triple-negative breast cancer cells [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 5111. doi:10.1158/1538-7445.AM2017-5111

GTSE1: a novel TEAD4-E2F1 target gene involved in cell protrusions formation in triple-negative breast cancer cell models.

GTSE1 over-expression has been reported as a potential marker for metastasis in various types of malignancies, including breast cancer. Despite this, the transcriptional regulation of this protein and the causes of its misregulation in tumors remain largely unknown. The aims of this work were to elucidate how GTSE1 is regulated at the transcriptional level and to clarify the mechanism underlying GTSE1-dependent cell functions in triple-negative breast cancer (TNBC).Here, we identified GTSE1 as a novel target gene of the TEAD4 transcription factor, highlighting a role for the YAP and TAZ coactivators in the transcriptional regulation of GTSE1.Moreover, we found that TEAD4 controls the formation of cell protrusions required for cell migration through GTSE1, unveiling a relevant effector role for this protein in the TEAD-dependent cellular functions and confirming TEAD4 role in promoting invasion and metastasis in breast cancer.Finally, we highlighted a role for the pRb-E2F1 pathway in the control of GTSE1 transcription and observed that treatment with drugs targeting the pRb-E2F1 or YAP/TAZ-TEAD pathways dramatically downregulated the expression levels of GTSE1 and of other genes involved in the formation of metastasis, suggesting their potential use in the treatment of TNBC.

PML promotes metastasis of triple-negative breast cancer through transcriptional regulation of HIF1A target genes.

Elucidating the molecular basis of tumor metastasis is pivotal for eradicating cancer-related mortality. Triple-negative breast cancer (TNBC) encompasses a class of aggressive tumors characterized by high rates of recurrence and metastasis, as well as poor overall survival. Here, we find that the promyelocytic leukemia protein PML exerts a prometastatic function in TNBC that can be targeted by arsenic trioxide. We found that, in TNBC patients, constitutive HIF1A activity induces high expression of PML, along with a number of HIF1A target genes that promote metastasis at multiple levels. Intriguingly, PML controls the expression of these genes by binding to their regulatory regions along with HIF1A. This mechanism is specific to TNBC cells and does not occur in other subtypes of breast cancer where PML and prometastatic HIF1A target genes are underexpressed. As a consequence, PML promotes cell migration, invasion, and metastasis in TNBC cell and mouse models. Notably, pharmacological inhibition of PML with arsenic trioxide, a PML-degrading agent used to treat promyelocytic leukemia patients, delays tumor growth, impairs TNBC metastasis, and cooperates with chemotherapy by preventing metastatic dissemination. In conclusion, we report identification of a prometastatic pathway in TNBC and suggest clinical development toward the use of arsenic trioxide for TNBC patients.

Abstract 1970: The mRNA-destabilizing protein tristetraprolin suppresses tumorigenic phenotypes in a triple-negative breast cancer cell model via a non-canonical mechanism

Abstract The purpose of this study was to define mechanisms by which the mRNA-destabilizing factor tristetraprolin (TTP) impacts tumorigenic phenotypes in an aggressive model of metastatic breast cancer. Widespread repression of TTP levels in human tumors and cancer cell lines relative to non-transformed tissues suggests that TTP may function as a tumor suppressor in diverse neoplastic contexts, and low TTP expression is a negative prognostic indicator in breast cancer. TTP is a tandem zinc finger protein that binds to AU-rich elements (AREs) and targets their associated mRNAs for degradation. AREs are potent cis-acting determinants of cytoplasmic mRNA turnover in mammalian cells, and are essential for limiting cellular production of many clinically important gene products including regulators of inflammation, cell proliferation, and apoptosis. In this study, we show that restoration of TTP levels attenuates several tumorigenic phenotypes in the aggressively metastatic breast cancer line MDA-MB-231. Notably, TTP-expressing cell lines replicate approximately 70% slower than non-transfected controls. Inhibition of cell proliferation did not result from apoptosis but rather by a delay at the G1/S checkpoint. TTP expression also significantly reduced the formation of cultured mammospheres based on both sphere-forming efficiency frequency and extreme limiting dilution analyses, indicating that this protein reduces stemness and non-adherent growth potential. Finally, cell motility was suppressed by TTP, demonstrated using wound healing assays. These findings are consistent with a tumor suppressor role for TTP. To identify potential mechanisms linking TTP to diminution of tumorigenic phenotypes, we surveyed the expression of genes encoding select pro-tumorigenic factors, including several known to encode TTP-targeted mRNAs. Expression of cyclin D1, cyclin E and c-Myc proteins were significantly reduced in TTP-expressing MDA-MB-231 cells, however, this was not mediated by accelerated mRNA decay. Interestingly, we observed that the mRNA-destabilizing function of TTP is abrogated by the constitutively active ERK signaling pathway in MDA-MB-231 cells, suggesting that TTP suppresses tumorigenic properties in this cell model independently of its canonical mRNA-destabilizing function. Consistent with this model, expressing a non-RNA-binding mutant form of TTP (C147R) robustly attenuated the same tumorigenic properties suppressed by the wild type protein. Together, these findings show that the mRNA-destabilizing activity of TTP is dispensable for its tumor suppressive properties in MDA-MB-231 cells, and by extension that TTP must limit diverse tumorigenic properties in these cells via an as yet uncharacterized non-canonical mechanism. Citation Format: Christina R. Ross, Gerald M. Wilson. The mRNA-destabilizing protein tristetraprolin suppresses tumorigenic phenotypes in a triple-negative breast cancer cell model via a non-canonical mechanism. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1970. doi:10.1158/1538-7445.AM2015-1970

Abstract 2260: Defining molecular mechanisms linking Endophilin A2 to metastasis in human breast cancer models

Abstract Breast cancers in the human epidermal growth factor receptor 2 (HER2) and triple-negative breast cancer (TNBC) subtypes have high rates of tumor metastasis. Tumor metastasis is driven by formation of invadopodia that degrade extracellular matrix (ECM) in basement membranes to spread locally and colonize distant sites. Endophilin A2 (Endo II) is an adaptor protein that coordinates internalization and trafficking of receptors that drive invadopodia formation and breast cancer metastasis. We have recently identified Endo II as a positive regulator of human TNBC metastasis, invadopodia formation, epidermal growth factor receptor (EGFR) internalization and signaling. Here, we extend these studies of Endo II to HER2 breast cancers, and define molecular mechanisms that link Endo II to invadopodia formation and cell invasion. Analysis of Endo II expression in human invasive ductal carcinomas revealed significantly high expression of Endo II in HER2 primary tumors, and significantly higher expression in paired lymph node metastases compared to other subtypes. We also observed that high levels of Endo II mRNA was associated with reduced rates of relapse free survival in patients with lymph node positive, estrogen receptor negative tumors. This correlates with our findings that Endo II promotes invadopodia formation and breast cancer cell invasion. Mechanistically, these defects may be due to reduced EGFR signaling and lowered expression of epithelial-mesenchymal transition (EMT) signature genes observed in Endo II knock-down (KD) cells. We are currently validating these results in mammary orthotopic tumor xenograft models of HER2 and TNBC cell models with stable Endo II KD. Together, these findings identify high levels of Endo II in high risk breast cancer subtypes, with high expression of EMT genes, and a potential link between Endo II levels and poor prognosis in breast cancer patients. Citation Format: Tomas Baldassarre, Kathleen Watt, Peter Truesdell, Mark Schneider, Sandip Sengupta, Andrew WB Craig. Defining molecular mechanisms linking Endophilin A2 to metastasis in human breast cancer models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2260. doi:10.1158/1538-7445.AM2015-2260

The scaffolding protein NHERF1 sensitizes EGFR-dependent tumor growth, motility and invadopodia function to gefitinib treatment in breast cancer cells.

Triple negative breast cancer (TNBC) patients cannot be treated with endocrine therapy or targeted therapies due to lack of related receptors. These patients overexpress the epidermal growth factor receptor (EGFR), but are resistant to tyrosine kinase inhibitors (TKIs) and anti-EGFR therapies. Mechanisms suggested for resistance to TKIs include EGFR independence, mutations and alterations in EGFR and in its downstream signalling pathways. Ligand-induced endocytosis and degradation of EGFR play important roles in the downregulation of the EGFR signal suggesting that its activity could be regulated by targeting its trafficking. Evidence in normal cells showing that the scaffolding protein Na+/H+ exchanger regulatory factor 1 (NHERF1) can associate with EGFR to regulate its trafficking, led us to hypothesize that NHERF1 expression levels could regulate EGFR trafficking and functional expression in TNBC cells and, in this way, modulate its role in progression and response to treatment. We investigated the subcellular localization of NHERF1 and its interaction with EGFR in a metastatic basal like TNBC cell model, MDA-MB‑231, and the role of forced NHERF1 overexpression and/or stimulation with EGF on the sensitivity to EGFR specific TKI treatment with gefitinib. Stimulation with EGF induces an interaction of NHERF1 with EGFR to regulate its localization, degradation and function. NHERF1 overexpression is sufficient to drive its interaction with EGFR in non-stimulated conditions, inhibits EGFR degradation and increases its retention time in the plasma membrane. Importantly, NHERF1 overexpression strongly sensitized the cell to the pharmacological inhibition by gefitinib of EGFR-driven growth, motility and invadopodia-dependent ECM proteolysis. The further determination of how the NHERF1‑EGFR interaction is regulated may improve our understanding of TNBC resistance to the action of existing anticancer drugs.

YM155 sensitizes triple-negative breast cancer to membrane-bound TRAIL through p38 MAPK- and CHOP-mediated DR5 upregulation.

Because available treatments have limited efficacy in triple-negative breast cancer (TNBC), the identification of new therapeutic strategies to improve patients' outcome is urgently needed. In our study, we investigated the effects of the administration of the small molecule selective survivin suppressant YM155, alone or in association with CD34+ cells transduced with a replication-deficient adenovirus encoding the human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene (CD34-TRAIL+ cells), in three TNBC cell models. YM155 exposure significantly impaired TNBC cell growth and selectively modulated survivin expression at both mRNA and protein level. In addition, co-culturing YM155-treated TNBC cells with CD34-TRAIL+ cells resulted in markedly increased cytotoxic effect and apoptotic response in comparison with single treatments. Such a chemosensitizing effect was observed only in TNBC cells inherently expressing DR5 and relied on the ability of YM155 to upregulate DR5 expression through a p38 MAPK- and CHOP-dependent mechanism. YM155/CD34-TRAIL+ combination also showed a significant inhibitory effect on the growth of DR5-expressing TNBC cells following xenotransplantation into NOD/SCID mice, in the absence of toxicity. Overall, our data (i) provide, for the first time, evidence that YM155 sensitizes TNBC cells to CD34-TRAIL+ cells-induced apoptosis by a mechanism involving the downregulation of survivin and the simultaneous p38 MAPK- and CHOP-mediated upregulation of DR5, and (ii) suggest the combination of YM155 with TRAIL-armed CD34+ progenitor cells as a promising therapeutic option for patients with TNBC expressing DR5.

Protein pathway activation mapping guided biomarker development to identify optimal combinations of MEK inhibitor with PI3K/mTOR pathway inhibitors for the treatment of triple-negative breast cancer.

2612 Background: Activated MAPK and PI3K pathway signaling are associated with poor prognosis in triple negative breast cancer (TNBC). Although some TNBC cell models are sensitive to MEK inhibition, feedback activation of the PI3K pathway mediates resistance. Thus, suppression of both arms of the MAPK/PI3K/mTOR network is a rational approach to targeting TNBC. Here we explore the anti-tumor efficacy of combinations of MEK inhibitor with PI3K, AKT, or mTOR inhibitors with a focus on biomarker development. Methods: Combinations of the MEK inhibitor PD-0325901 with the PI3K inhibitor GDC-0941, AKT inhibitor MK-2206, dual mTORC 1/2 inhibitor Torin 1, or the rapalog temsirolimus were evaluated in TNBC cell lines. Synergy was assessed using the combination index method of Chou and Talalay. We utilized reverse-phase protein array to map the signaling architecture of the treated lines to verify target suppression and identify pharmacodynamic biomarkers. Results: All combinations demonstrated synergy that was mediated by both suppression of proliferation and cell death in a dose-dependent manner. Cell death was delayed, peaking at least 96 hours post-dosing, and was associated with sustained suppression of target proteins in both pathways, including pERKT202/Y204, pS6rpS235/236, p4EBP-1S65, and pPRAS40T246. However, suppression of pAKT (at T308 or S473) was variable and not consistently required for cell death. Pathway mapping identified a protein network ‘signature’ specific to all combination therapies that emerged at 72 hours and was associated with cell death. Thus, all combinations appear to share common downstream effectors. All combinations showed promising efficacy and will be evaluated in a human-in-mouse model of TNBC. Conclusions: These data support therapeutic strategies for TNBC that simultaneously inhibit both arms of the MAPK/PI3K/mTOR signaling network. For continued biomarker development, we stress the importance of studying the delayed effects of combination therapy. This strategy coupled with a protein network based approach uncovered a unique functional signaling ‘signature’.

Abstract 4502: Eribulin alters vascular function in human triple-negative (TN) breast MX-1 and MDA-MB-231 tumor xenograft models as measured by DCE-MRI.

Abstract Objective: Eribulin mesylate (ERI) is a simplified synthetic macrocyclic ketone analog of the marine sponge natural product halichondrin B and an inhibitor of microtubule dynamics. Literature reports have increasingly shown tubulin binding agents have vascular disruptive activity. In this study, we evaluated the effect of eribulin on tumor vasculature using DCE-MRI of TN human breast MX-1 xenografts in nude rats. Methods: The effects of ERI on human TN breast MX-1 and MDA-MB-231 tumor are examined in nude rats and nude mice. ERI was administered at MTD dose (0.3 mg/kg at Q4D4 in nude rats and 3.0 mg/kg at D1 in nude mice). In nude rats, DCE-MRI was conducted on a Bruker 4.7 T scanner with Magnevist contrast. Imaging was conducted on day -1, 6 hrs, day 2, day 5-6 and day 10. In nude mice, morphology of tumor vasculature was analyzed with immunohistochemistry (IHC) staining with anti-mouse endothelial marker CD31 antibody. Microvessel density (MVD) and vessel perimeter were analyzed using Aperio Image Scope. Results and discussion: ERI inhibited tumor growth of MX-1 (day 5; 290 +/- 169 vs 1195 +/- 36 mm3, N=5, p<0.01) and MDA-MB-231 (day 6; 295 +/- 113 vs 570 +/- 56 mm3, N=5, p<0.05) in nude rats compared to vehicle (VEH). DCE-MRI analysis demonstrated that, at 6 hrs, Ktrans (1/s) in the tumor rim was decreased in the ERI group (MX-1; 0.471 +/- 0.061 vs 0.611 +/- 0.082, p<0.05 vs VEH and MDA-MB-231; 0.290 +/- 0.130 vs 0.537 +/- 0.132, p<0.05 vs VEH). Interestingly, Ktrans in the tumor core was increased in the ERI group at later time points (MX-1 day 5; 0.723 +/- 0.155 vs 0.097 +/- 0.073, p<0.05 vs VEH and MDA-MB-231 day 10; 0.612 +/- 0.187 vs 0.103 +/- 0.090, p<0.01 vs VEH). The effects of ERI on tumor vasculature function were reproduced in a mouse MX-1 xenograft model. The trend towards a decrease in Ktrans at 6hrs (confirmed by Hoechst dye perfusion of mouse tumor samples taken at 6 hrs showing a 70% reduction compared to VEH. N=5, p<0.05) suggests ERI may cause an acute shutdown of vascular function. In endothelial cells, lack of significant change by IHC at 6hrs and no increased apoptosis at 24hrs in vitro indicate the acute activity may be different from vascular disrupting agents. IHC analysis of tumor vasculature morphology was performed to investigate the increase in the tumor core Ktrans at day 5. Results demonstrated that ERI treated tumors had higher MVD compared to VEH along with decreased vessel perimeter in mice, indicating ERI affected tumor vascular morphology, suggestive of vascular normalization. Conclusions: ERI altered tumor vasculature acutely in the tumor rim and increase vascular perfusion in the tumor core 5 days after treatment. In addition to regulation of mitosis, ERI may have induced normalization of tumor vasculature in preclinical TN breast cancer cell models. Further analysis of the mechanism of ERI on vascular normalization will be warranted. Citation Format: Paul J. McCracken, Ken Ito, Mamoru Yanagimachi, Xavier Tizon, Peggy Provent, Shanqin Xu, Namita Kumar, Denice Welsh, Tyler J. Teceno, Galina Kuznetsov, Yasuhiro Funahashi. Eribulin alters vascular function in human triple-negative (TN) breast MX-1 and MDA-MB-231 tumor xenograft models as measured by DCE-MRI. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4502. doi:10.1158/1538-7445.AM2013-4502

P120 catenin is a key effector of a Ras-PKCɛ oncogenic signaling axis

Within the family of protein kinase C (PKC) molecules, the novel isoform PRKCE (PKCɛ) acts as a bona fide oncogene in in vitro and in vivo models of tumorigenesis. Previous studies have reported expression of PKCɛ in breast, prostate and lung tumors above that of normal adjacent tissue. Data from the cancer genome atlas suggest increased copy number of PRKCE in triple negative breast cancer (TNBC). We find that overexpression of PKCɛ in a non-tumorigenic breast epithelial cell line is sufficient to overcome contact inhibition and results in the formation of cellular foci. Correspondingly, inhibition of PKCɛ in a TNBC cell model results in growth defects in two-dimensional (2D) and three-dimensional (3D) culture conditions and orthotopic xenografts. Using stable isotope labeling of amino acids in a cell culture phosphoproteomic approach, we find that CTNND1/p120ctn phosphorylation at serine 268 (P-S268) occurs in a strictly PKCɛ-dependent manner, and that loss of PKCɛ signaling in TNBC cells leads to reversal of mesenchymal morphology and signaling. In a model of Ras activation, inhibition of PKCɛ is sufficient to block mesenchymal cell morphology. Finally, treatment with a PKCɛ ATP mimetic inhibitor, PF-5263555, recapitulates genetic loss of function experiments impairing p120ctn phosphorylation as well as compromising TNBC cell growth in vitro and in vivo. We demonstrate PKCɛ as a tractable therapeutic target for TNBC, where p120ctn phosphorylation may serve as a readout for monitoring patient response.

Metformin Induces a Senescence-associated Gene Signature in Breast Cancer Cells

Diabetic patients taking metformin have lower incidence of breast cancer than those taking other anti-diabetic medications. Additionally, triple negative breast cancer (TNBC), a form of breast cancer disproportionately afflicting premenopausal African American women, shows atypical susceptibility to metformin's antiproliferative effect. The mechanisms involved in metformin's function in TNBC has not yet been fully elucidated. Therefore, we sought to identify pathways regulated by metformin in using the MDA-MB-468 TNBC cell model. Metformin dose-dependently caused apoptosis, decreased cell viability, and induced cell morphology/chromatin condensation consistent with the permanent proliferative arrest. Furthermore, gene expression arrays revealed that metformin caused expression of stress markers DDIT3, CYP1A1,and GDF-15 and a concomitant reduction in PTGS1 expression. Our findings show that metformin may affect the viability and proliferative capacity of TNBC by inducing an antiproliferative gene signature, and that metformin may be effective in the treatment/prevention of TNBC.