Cancer therapy using natural ligands that target estrogen receptor beta

Estrogen receptor beta (ERβ) is one of the two key receptors (ERα, ERβ) that facilitate biological actions of 17β-estradiol (E2). ERβ is widely expressed in many tissues, and its expression is reduced or lost during progression of many tumors. ERβ facilitates estrogen signaling by both genomic (classical and non-classical) and extra-nuclear signaling. Emerging evidence suggests that ERβ functions as a tissue-specific tumor suppressor with anti-proliferative actions. Recent studies have identified a number of naturally available selective ERβ agonists. Targeting ERβ using its naturally available ligands is an attractive approach for treating and preventing cancers. This review presents the beneficial actions of ERβ signaling and clinical utility of several natural ERβ ligands as potential cancer therapy.

Significantly increased PELP1 protein expression in primary and metastatic triple-negative breast carcinoma: comparison with GATA3 expression and PELP1's potential role in triple-negative breast carcinoma

PELP1 is a novel coregulator of nuclear hormone receptors and is implicated in playing a role in driving breast cancer and enhancing metastatic potential. The PELP1 protein expression and potential role of PELP1 in triple-negative breast carcinoma (TNBC) have not been well characterized. We investigated PELP1 expression by immunohistochemistry in primary and metastatic triple-negative tumors in human tissues and compared its expression with GATA-binding protein 3 (GATA3), a novel diagnostic marker for TNBC. We examined the expression of PELP1 and GATA3 in 70 primary TNBC cases and found that PELP1 had a significantly higher frequency of expression compared to GATA3 (96% versus 46%; P < .0001). The mean extent score of expression of PELP1 was also significantly higher than GATA3's expression (3.87 ± 0.07 versus 0.91 ± 0.15; P < .0001). PELP1 had stronger staining intensity than GATA3. Furthermore, PELP1 immunoreactivity was consistently maintained in paired primary and metastatic TNBC cases (100%). The frequency of PELP1 expression (100%) in metastatic triple-negative tumors was higher than that of GATA3 (40%) in the same tumors (P < .0001). These findings indicate that PELP1 is a much more sensitive marker than GATA3 for TNBCs. PELP1 may have diagnostic utility for metastatic TNBC in appropriate settings, such as history of primary TNBC in cases where the primary is negative for GATA3, mammaglobin, and GCDFP-15. The diffuse and strong nuclear immunoreactivity of PELP1 in most cases suggests that PELP1 may be a molecular target for the treatment of TNBC. We hope that this study will provide insights into the role of PELP1 in TNBC.

Abstract 2854: Targeting error-prone alternative nonhomologous end joining (A-NHEJ) DNA repair pathway to treat ESR1-mediated therapy resistance

Endocrine therapies for estrogen receptor (ESR1) positive breast cancer involve modulation of ESR1 signaling using either antiestrogens (AE) or aromatase inhibitors (AI). Despite initial positive response, most patients develop resistance to these drugs and therapy resistance is a major clinical problem. Emerging findings suggest that during the progression of ESR1 positive breast cancer, the cancer cell increasingly becomes dependent on the error-prone alternative-non-homologous end joining (A-NHEJ) DNA repair pathway for double strand break (DSB) repair leading to an increase in chromosomal abnormalities contributing to hormonal therapy resistance. The mechanism by which ESR1 pathway regulates A-NHEJ remains unknown. Recent studies from our lab discovered that ESR1 coregulator Proline-, Glutamic acid-, and Leucine-rich Protein-1 (PELP1) is phosphorylated by the DNA damage response kinases and plays a key role in the A-NHEJ pathway. In this study, we dissected the mechanism by which PELP1 regulates the A-NHEJ pathway and developed a novel inhibitor of PELP1-A-NHEJ axis. Using plasmid based repair assay, we provided evidence that PELP1 regulates degree of end-resection that is essential for A-NHEJ pathway mediated DNA repair. Immunoprecipitation assays revealed that PELP1 interacts with exonuclease protein, Mre11 that plays an essential role in A-NHEJ pathway. Using PELP1 domain deletions and GST pull down assays, we identified C-terminus of PELP1 as the region that interacts with key components of the A-NHEJ pathway. We have rationally screened a random peptide library composed of 10 million peptides, and identified a tight-binding peptide to the C-terminus of PELP1 that interferes with PELP1- Mre11 interaction. Using emerging stapled peptide technology, we converted this peptide to a stable cell permeable Peptide Inhibitor of PELP1 (sPIP3). sPIP3 bound to PELP1 with high affinity, interfered PELP1-Mre11 interaction, reduced A-NHEJ repair frequency in reporter based assays and significantly reduced frequency of chromosomal translocation. In MTT based assays, sPIP3 demonstrated significant cytotoxic effect on breast cancer cells with minimal effect on normal cells. Further, sPIP3 significantly reduced survival and promoted apoptosis of hormonal therapy resistant breast cancer model cells. Collectively, these findings demonstrate the therapeutic potential of sPIP3 which represents a novel drug for the treatment of therapy resistant breast cancer by inhibiting error prone A-NHEJ pathway.

Citation Format: Samaya Krishnan, Binoj Nair, Gangadhara Sareddy, Monica Mann, Ratna K. Vadlamudi. Targeting error-prone alternative nonhomologous end joining (A-NHEJ) DNA repair pathway to treat ESR1-mediated therapy resistance. [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 2854. doi:10.1158/1538-7445.AM2015-2854

Abstract 951: LY500307 as a novel therapeutic agent for treatment of glioblastoma

Glioblastoma (GBM) is the most common type of primary brain tumor with poor prognosis. A gender bias exists in the development of GBM with incidence of developing GBM is greater in males compared to females. Epidemiological studies and several lines of evidence suggest tumor suppressive role of female sexual hormone estrogen on brain tumors. However, estrogen as potential therapy for GBM has limited therapeutic application due to safety concerns including breast cancer, uterine cancer, heart disease, and feminization in men. Therefore alternative agents that mimic estrogen effects will have potent utility in treating GBM. Estrogen effects are mediated though its cognate receptors ERα and ERβ and ERβ functions as a tissue-specific tumor suppressor. Recent studies identified a synthetic LY500307 as a selective ERβ agonist (developed by Eli Lilly and Company) with an excellent preclinical profile and is currently in clinical trials for treating Schizophrenia. We recently showed that ERβ is the major ER subtype expressed in GBM. The objective of this study is to determine the therapeutic effects of novel ERβ agonist LY500307 using both in vitro and orthotopic preclinical models and to determine its mechanism(s) of action. In this study, we have tested the therapeutic efficacy of LY500307 using several established as well as patient derived GBM cells. Treatment of LY500307 significantly reduced the proliferation of GBM cells with no activity on normal astrocytes suggesting its tumor specific effects. Overexpression of ERβ reduced proliferation of GBM cells and knockdown of ERβ compromised the treatment effect of LY500307 further suggesting the specificity. RNA sequencing analysis of LY500307 treated and untreated GBM cells revealed several novel pathways related to apoptosis, cell cycle, stem cells and differentiation that were significantly modulated by LY500307. Mechanistic studies revealed that LY500307 mediated apoptosis of GBM involve genes activated by both ERβ- classical as well as AP1 mediated non-classical pathways and also involve p38MAPK and JNK pathways. Since Glioma Stem Cells (GSCs) are implicated in tumor initiation, invasion and therapy resistance of GBM, we also tested the effect of LY500307 on GSCs. LY500307 treatment significantly inhibited the proliferation, neurosphere formation and self-renewal of GSCs and also resulted in the loss of stemness of GSCs and induction of differentiation and apoptosis. Further, LY500307 treatment significantly reduced the tumor growth in in vivo orthotopic GBM models and promoted apoptosis of tumors. Together, our results demonstrate that LY500307 as a potential therapeutic agent for treatment of GBM. Since LY500307 has good blood-brain barrier permeability and less neuronal toxicity, it can be readily transferred to clinical use with current radiation and chemotherapies, thereby providing an additional tool for enhancing survival in GBM patients.

Citation Format: Gangadhara R. Sareddy, Aleksandra Gruslova, David A. Cavazos, Rajeshwar R. Tekmal, Andrew J. Brenner, Ratna K. Vadlamudi. LY500307 as a novel therapeutic agent for treatment of glioblastoma. [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 951. doi:10.1158/1538-7445.AM2015-951

Abstract LB-079: Specific epigenetic reader role for cyclin D1

Amplification of the CCND1 gene occurs in approximately 30% of human breast cancer and is sufficient when overexpressed for the induction of mammary tumorigenesis. A DNA-associated form of cyclin D1 governs gene expression and chromosomal instability. Herein, the mechanisms governing gene activation by cyclin D1 were defined. Cyclin D1 was recruited to activate gene regulatory regions associated with enrichment of p300, HP1α and reduced HDAC3 and SUV39H1. The recruitment of cyclin D1 into local chromatin was dissociable from its kinase function and required an intrinsically disordered carboxyl-terminus flanked by a glutamine-rich motif. The cyclin D1 epigenetic interaction motif bound acetylated or methylated H3 on specific residues (H3K36me2, H3K9me3). Cyclin D1 bound to the Top2A gene promoter induced Top2A transcription, abundance and sensitivity to Top2A inhibitors. The direct recognition of an epigenetic code by a motif within cyclin D1 and the induction of Top2A may facilitate communication of genome wide expression changes during cell-cycle progression and tumorigenesis.

Citation Format: Gabriele Di Sante, Mathew Craig Casimiro, Chenguang Wang, Zuoren Yu, Marco Crosariol, Ratna K. Vadlamudi, Monica Mann, Peter Tompa, Agnes Tantos, Richard G. Pestell. Specific epigenetic reader role for cyclin D1. [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 LB-079. doi:10.1158/1538-7445.AM2015-LB-079

Synthesis of a novel, sequentially active-targeted drug delivery nanoplatform for breast cancer therapy

Breast cancer is the leading cause of cancer deaths among women. Paclitaxel (PTX), an important breast cancer medicine, exhibits reduced bioavailability and therapeutic index due to high hydrophobicity and indiscriminate cytotoxicity. PTX encapsulation in one-level active targeting overcomes such barriers, but enhances toxicity to normal tissues with cancer-similar expression profiles. This research attempted to overcome this challenge by increasing selectivity of cancer cell targeting while maintaining an ability to overcome traditional pharmacological barriers. Thus, a multi-core, multi-targeting construct for tumor specific delivery of PTX was fabricated with (i) an inner-core prodrug targeting the cancer-overexpressed cathepsin B through a cathepsin B-cleavable tetrapeptide that conjugates PTX to a poly(amidoamine) dendrimer, and (ii) the encapsulation of this prodrug (PGD) in an outer core of a RES-evading, folate receptor (FR)-targeting liposome. Compared to traditional FR-targeting PTX liposomes, this sequentially active-targeted dendrosome demonstrated better prodrug retention, an increased cytotoxicity to cancer cells (latter being true when FR and cathepsin B activities were both at moderate-to-high levels) and higher tumor reduction. This research may eventually evolve a product platform with reduced systemic toxicity inherent with traditional chemotherapy and localized toxicity inherent to single-target nanoplatforms, thereby allowing for better tolerance of higher therapeutic load in advanced disease states.

Abstract P3-04-16: Estrogen receptor β agonists reduce breast cancer tumor growth in syngeneic mouse models

The estrogen receptors (ER) play a significant role in breast cancer, with the majority of breast cancers expressing estrogen receptor alpha (ERα) and depending on its signaling. ERα has proliferative function, however, estrogen receptor beta (ERβ) has anti-proliferative functions. Recently, several selective ERβ agonists have been identified. The objective of this study was to determine the effectiveness of ERβ agonists in inhibiting the growth of distinct breast cancer cells both in-vitro and in-vivo, and to determine the mechanisms involved. The mouse mammary tumor cell lines, D2A1 and MM51, express both ERα and ERβ. Specifically D2A1 cells are dependent on estrogen for growth and have increased expression of aromatase. Additionally, D2A1 cells are very aggressive and highly metastatic; representing a good model of breast cancer progression. MM51 cells are Her2/neu positive and are an adequate model to study the crosstalk between growth factors and ER signaling. Syngeneic mouse tumor models were used to incorporate an intact immune system which plays a role in the tumor’s microenvironment. Our in-vitro studies demonstrate that ERβ agonists significantly inhibit cell growth in a dose dependent manner. Our syngeneic studies show that, in-vivo, ERβ agonists effectively reduce tumor volume and inhibit tumor progression. This study reveals that in addition to acting on ERβ, these agonists reduce the expression of ERα at both the mRNA and protein level, therefore modulating the ratio of ERα to ERβ. Additionally, treatment with ERβ agonists results in increases apoptosis through increased p53 expression, and cell cycle arrest through p27 and cyclin D1. Together, these studies demonstrate the therapeutic potential of ERβ agonists for the treatment of breast cancer.

Citation Format: Cathy Samayoa, Naveen K Krishnegowda, Ratna K Vadlamudi, Rajeshwar R Tekmal. Estrogen receptor β agonists reduce breast cancer tumor growth in syngeneic mouse models [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-04-16.

Novel role of PELP1 in regulating chemotherapy response in mutant p53-expressing triple negative breast cancer cells

Triple-negative breast cancer (TNBC), the most aggressive breast cancer subtype, occurs in younger women and is associated with poor prognosis. Gain-of-function mutations in TP53 are a frequent occurrence in TNBC and have been demonstrated to repress apoptosis and up-regulate cell cycle progression. Even though TNBC responds to initial chemotherapy, resistance to chemotherapy develops and is a major clinical problem. Tumor recurrence eventually occurs and most patients die from their disease. An urgent need exists to identify molecular-targeted therapies that can enhance chemotherapy response. In the present study, we report that targeting PELP1, an oncogenic co-regulator molecule, could enhance the chemotherapeutic response of TNBC through the inhibition of cell cycle progression and activation of apoptosis. We demonstrate that PELP1 interacts with MTp53, regulates its recruitment, and alters epigenetic marks at the target gene promoters. PELP1 knockdown reduced MTp53 target gene expression, resulting in decreased cell survival and increased apoptosis upon genotoxic stress. Mechanistic studies revealed that PELP1 depletion contributes to increased stability of E2F1, a transcription factor that regulates both cell cycle and apoptosis in a context-dependent manner. Further, PELP1 regulates E2F1 stability in a KDM1A-dependent manner, and PELP1 phosphorylation at the S1033 residue plays an important role in mediating its oncogenic functions in TNBC cells. Accordingly, depletion of PELP1 increased the expression of E2F1 target genes and reduced TNBC cell survival in response to genotoxic agents. PELP1 phosphorylation was significantly greater in the TNBC tumors than in the other subtypes of breast cancer and in the normal tissues. These findings suggest that PELP1 is an important molecular target in TNBC, and that PELP1-targeted therapies may enhance response to chemotherapies.

PELP1 overexpression in the mouse mammary gland results in the development of hyperplasia and carcinoma

Estrogen receptor (ER) coregulator overexpression promotes carcinogenesis and/or progression of endocrine related-cancers in which steroid hormones are powerful mitogenic agents. Recent studies in our laboratory, as well as others, demonstrated that the estrogen receptor coregulator PELP1 is a proto-oncogene. PELP1 interactions with histone demethylase KDM1 play a critical role in its oncogenic functions and PELP1 is a prognostic indicator of decreased survival in patients with breast cancer. However, the in vivo significance of PELP1 deregulation during initiation and progression of breast cancer remains unknown. We generated an inducible, mammary gland-specific PELP1-expressing transgenic (Tg) mouse (MMTVrtTA-TetOPELP1). We found more proliferation, extensive side branching, and precocious differentiation in PELP1-overexpressing mammary glands than in control glands. Aged MMTVrtTA-TetOPELP1 Tg mice had hyperplasia and preneoplastic changes as early as 12 weeks, and ER-positive mammary tumors occurred at a latency of 14 to 16 months. Mechanistic studies revealed that PELP1 deregulation altered expression of a number of known ER target genes involved in cellular proliferation (cyclin D1, CDKs) and morphogenesis (EGFR, MMPs) and such changes facilitated altered mammary gland morphogenesis and tumor progression. Furthermore, PELP1 was hyper-phosphorylated at its CDK phosphorylation site, suggesting an autocrine loop involving the CDK-cyclin D1-PELP1 axis in promoting mammary tumorigenesis. Treatment of PELP1 Tg mice with a KDM1 inhibitor significantly reduced PELP1-driven hyperbranching, reversed alterations in cyclin D1 expression levels, and reduced CDK-driven PELP1 phosphorylation. These results further support the hypothesis that PELP1 deregulation has the potential to promote breast tumorigenesis in vivo and represent a novel model for future investigation into molecular mechanisms of PELP1-mediated tumorigenesis.

Abstract 2731: PELP1 promotes DNA double-strand break repair via alternative-NHEJ: Implications in therapy resistance

Estrogen Receptor positive breast cancer is commonly treated with hormonal therapy; however, many patients acquire therapy resistance, a major clinical problem. Recent evidence suggests that the accumulation of chromosomal abnormalities via increased error-prone Alternative-Non-Homologous End Joining (A-NHEJ) DNA repair pathway could contribute to breast cancer therapy resistance. Proline, Glutamic acid, Leucine rich Protein-1 (PELP1), an oncogenic co-regulator for transcription factors, is commonly overexpressed in breast cancer, and its deregulation has been implicated in therapy resistance. Our recent studies identified PELP1 as a novel substrate of the DNA damage response (DDR) kinases. In this study, we discovered that PELP1 regulates the A-NHEJ pathway, and we developed a novel peptide drug that targets PELP1-A-NHEJ axis for the treatment of therapy resistance. Our results suggest that PELP1 is phosphorylated at Ser1033 by DDR kinases and phosphorylated PELP1 co-localizes with the gamma-H2AX foci. Using Homologous Recombination (HR) and NHEJ pathway specific reporter assays, we found that PELP1 knockdown decreases NHEJ, with no apparent effect on the HR pathway. Further, using A-NHEJ specific reporter cell line, we found that PELP1 knockdown decreased the frequency of A-NHEJ, while PELP1 overexpression increased the repair frequency. PELP1's ability to regulate A-NHEJ pathway was further confirmed by sequencing repaired plasmids and by quantitating the degree of end resection. More importantly, metaphase chromosome spreads revealed gross chromosomal abnormalities in PELP1 deregulated breast cancer cells. Mechanistic studies revealed that PELP1 interacts with Mre11, and modulates the degree of end resection at the DNA double strand breaks. Mapping studies identified the C-terminus of PELP1 as the binding site for Mre11. Using yeast based genetic screen composed of 10 million peptides, we identified a unique peptide, PIP3 that binds the C-terminus of PELP1. We developed a stapled peptide of PIP3 (sPIP3), which functioned as a potent cytotoxic agent for breast cancer cells with little activity on normal cells. Further, sPIP3 efficiently inhibited the A-NHEJ pathway and significantly, reduced survival and promoted apoptosis of therapy resistant model cells. Collectively, these findings suggest that PELP1 plays a critical role in the A-NHEJ pathway and sPIP3 represents a novel drug for the treatment of therapy resistant breast cancer.

Citation Format: Samaya R. Krishnan, Binoj C. Nair, Gangadhara R. Sareddy, Monica Mann, Ratna K. Vadlamudi. PELP1 promotes DNA double-strand break repair via alternative-NHEJ: Implications in therapy resistance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2731. doi:10.1158/1538-7445.AM2014-2731

Abstract 622: S-equol, an estrogen receptor β agonist, inhibits tumor growth and progression of breast cancer

Breast cancer is the primary cause of cancer-associated mortality in women worldwide. Estrogen and the Estrogen Receptors (ER) play a significant role in breast cancer, with over two-thirds of breast cancers expressing ERα. Current endocrine therapy, such as aromatase inhibitors, target estrogen biosynthesis and anti-estrogens target ERα. However, therapeutic resistance frequently arises. In addition to the importance of ERα, ERβ has also been shown to play a critical, but opposing role in breast cancer. ERβ has been shown to inhibit the growth of ERα-positive breast cancer cells. The ratio of ERα to ERβ, in addition to the cross talk between ER's and growth factor signaling, has been implicated in the development of therapeutic resistance. Recently, several plant-derived compounds that exhibit ERβ agonist activity have been identified. S-equol is a potent ERβ agonist and a metabolite from the soy isoflavone daidzein, and has been previously shown to alleviate menopausal symptoms in a clinical trial. Activation of ERβ, or its over expression, shifts the balance of ER's from the oncogenic action of ERα to the tumor suppressor activity of ERβ, and therefore may be a valuable therapeutic approach in the treatment of breast cancer. In this study we sought out to determine the efficacy of the ERβ agonist, S-equol, in inhibiting the growth and progression of breast tumors using a syngeneic mouse model. We used mouse mammary tumor cells expressing endogenous ERβ, and to determine the contribution of ERβ, cells with knockdown of ERβ were generated using shRNA. ERβ mRNA and protein expression was analyzed using qRT-PCR and western blot respectively. Syngeneic tumors were established and mice were treated with either a vehicle control or S-equol. Treatment with S-equol reduces tumor volume and inhibits the progression of mouse mammary tumor cells in tumors expressing ERβ. Our mechanistic studies show that S-equol reduces the expression of ERα, and increases the expression of p53 and p27 in an ERβ dependent manner. Additionally, S-equol modulates the expression of inflammatory molecules involved in aromatase expression and promotes the differentiation of cancer stem cells. In conclusion, this study suggests that targeting ERβ may be a valuable strategy in treatment of breast cancer.

Citation Format: Cathy Samayoa, Naveen K. Krishnegowda, Samaya R. Krishnan, Ratna K. Vadlamudi, Rajeshwar R. Tekmal. S-equol, an estrogen receptor β agonist, inhibits tumor growth and progression of breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 622. doi:10.1158/1538-7445.AM2014-622

Premature menopause and risk of neurological disease: basic mechanisms and clinical implications

Since basic scientific studies in the 1990s revealed dramatic gender differences in neurological damage from cerebral ischemia, significant evidence has accumulated for a neuroprotective role of ovarian-derived 17β-Estradiol (E2). Intriguingly, observational studies have further suggested that early and prolonged loss of ovarian E2 (premature menopause) leads to a doubled lifetime risk for dementia and a fivefold increased risk of mortality from neurological disorders, but some controversy remains. Here, we briefly summarize and analyze clinical cohort studies assessing the detrimental neurological outcomes of premature menopause. Furthermore, we discuss current basic science studies elucidating the molecular mechanisms underlying the enhanced risk of neurological disease in prematurely menopausal women and the "window of opportunity" for estrogen benefit. Finally, we highlight four critical issues in the field that require collaboration between basic scientists and clinicians for successful resolution, with the ultimate goal of maintaining optimal neurological health in prematurely menopausal women.

Brain-derived estrogen exerts anti-inflammatory and neuroprotective actions in the rat hippocampus

17β-estradiol (E2) has been implicated to play a critical role in neuroprotection, synaptic plasticity, and cognitive function. Classically, the role of gonadal-derived E2 in these events is well established, but the role of brain-derived E2 is less clear. To address this issue, we investigated the expression, localization, and modulation of aromatase and local E2 levels in the hippocampus following global cerebral ischemia (GCI) in adult ovariectomized rats. Immunohistochemistry (IHC) revealed that the hippocampal regions CA1, CA3 and dentate gyrus (DG) exhibited high levels of immunoreactive aromatase staining, with aromatase being co-localized primarily in neurons in non-ischemic animals. Following GCI, aromatase became highly expressed in GFAP-positive astrocytes in the hippocampal CA1 region at 2-3 days post GCI reperfusion. An ELISA for E2 and IHC for E2 confirmed the GCI-induced elevation of local E2 in the CA1 region and that the increase in local E2 occurred in astrocytes. Furthermore, central administration of aromatase antisense (AS) oligonucleotides, but not missense (MS) oligonucleotides, blocked the increase in aromatase and local E2 in astrocytes after GCI, and resulted in a significant increase in GCI-induced hippocampal CA1 region neuronal cell death and neuroinflammation. As a whole, these results suggest that brain-derived E2 exerts important neuroprotective and anti-inflammatory actions in the hippocampal CA1 region following GCI.

Design of a paclitaxel prodrug conjugate for active targeting of an enzyme upregulated in breast cancer cells

Breast cancer is the second most common cause of cancer-related deaths in women. Chemotherapy is an important treatment modality, and paclitaxel (PTX) is often the first-line therapy for its metastatic form. The two most notable limitations related to PTX-based treatment are the poor hydrophilicity of the drug and the systemic toxicity due to the drug's nonspecific and indiscriminate distribution among the tissues. The present work describes an approach to counter both challenges by designing a conjugate of PTX with a hydrophilic macromolecule that is coupled through a biocleavable linker, thereby allowing for active targeting to an enzyme significantly upregulated in cancer cells. The resultant strategy would allow for the release of the active ingredient preferentially at the site of action in related cancer cells and spare normal tissue. Thus, PTX was conjugated to the hydrophilic poly(amdioamine) [PAMAM] dendrimer through the cathepsin B-cleavable tetrapeptide Gly-Phe-Leu-Gly. The PTX prodrug conjugate (PGD) was compared to unbound PTX through in vitro evaluations against breast cancer cells and normal kidney cells as well as through in vivo evaluations using xenograft mice models. As compared to PTX, PGD demonstrated a higher cytotoxicity specific to cell lines with moderate-to-high cathepsin B activity; cells with comparatively lower cathepsin B activity demonstrated an inverse of this relationship. Regression analysis between the magnitude of PGD-induced cytotoxic increase over PTX and cathepsin B expression showed a strong, statistically significant correlation (r(2) = 0.652, p < 0.05). The PGD conjugate also demonstrated a markedly higher tumor reduction as compared to PTX treatment alone in MDA-MB-231 tumor xenograft models, with PGD-treated tumor volumes being 48% and 34% smaller than PTX-treated volumes at weeks 2 and 3 after treatment initiation.

Proline, glutamic acid and leucine-rich protein-1 is essential for optimal p53-mediated DNA damage response

Proline-, glutamic acid- and leucine-rich protein-1 (PELP1) is a scaffolding oncogenic protein that functions as a coregulator for a number of nuclear receptors. p53 is an important transcription factor and tumor suppressor that has a critical role in DNA damage response (DDR) including cell cycle arrest, repair or apoptosis. In this study, we found an unexpected role for PELP1 in modulating p53-mediated DDR. PELP1 is phosphorylated at Serine1033 by various DDR kinases like ataxia-telangiectasia mutated, ataxia telangiectasia and Rad3-related or DNAPKc and this phosphorylation of PELP1 is important for p53 coactivation functions. PELP1-depleted p53 (wild-type) breast cancer cells were less sensitive to various genotoxic agents including etoposide, camptothecin or γ-radiation. PELP1 interacts with p53, functions as p53-coactivator and is required for optimal activation of p53 target genes under genomic stress. Overall, these studies established a new role of PELP1 in DDRs and these findings will have future implications in our understanding of PELP1's role in cancer progression.

Inhibition of mTOR signaling reduces PELP1-mediated tumor growth and therapy resistance

Proline, Glutamic acid-, and Leucine-rich Protein 1 (PELP1) is a proto-oncogene that modulates estrogen receptor (ER) signaling. PELP1 expression is upregulated in breast cancer, contributes to therapy resistance, and is a prognostic marker of poor survival. In a subset of breast tumors, PELP1 is predominantly localized in the cytoplasm and PELP1 participates in extranuclear signaling by facilitating ER interactions with Src and phosphoinositide 3-kinase (PI3K). However, the mechanism by which PELP1 extranuclear actions contributes to cancer progression and therapy resistance remains unclear. In this study, we discovered that PELP1 cross-talked with the serine/threonine protein kinase mTOR and modulated mTOR signaling. PELP1 knockdown significantly reduced the activation of mTOR downstream signaling components. Conversely, PELP1 overexpression excessively activated mTOR signaling components. We detected the presence of the mTOR signaling complex proteins in PELP1 immunoprecipitates. mTOR-targeting drugs (rapamycin and AZD8055) significantly reduced proliferation of PELP1-overexpressed breast cancer cells in both in vitro and in vivo xenograft tumor models. MCF7 cells that uniquely retain PELP1 in the cytoplasm showed resistance to hormonal therapy and mTOR inhibitors sensitized PELP1cyto cells to hormonal therapy in xenograft assays. Notably, immunohistochemical studies using xenograft tumors derived from PELP1 overexpression model cells showed increased mTOR signaling and inhibition of mTOR rendered PELP1-driven tumors to be highly sensitive to therapeutic inhibition. Collectively, our data identified the PELP1-mTOR axis as a novel component of PELP1 oncogenic functions and suggest that mTOR inhibitor(s) will be effective chemotherapeutic agents for downregulating PELP1 oncogenic functions.

Abstract P5-09-14: Plant-derived estrogen receptorb agonists alone or in combination with aromatase inhibitors restore sensitivity in endocrine therapy resistant breast tumors

Estrogen receptors (ER) play an important role in breast cancer. Over two-thirds of all breast cancers express ERa, and current endocrine therapies target its signaling. Antiestrogens (AE) block the binding of estrogen to ERα, while aromatase inhibitors (AI) inhibit local and systemic estrogen production. Both treatments improve outcomes for about 50% of patients with early or advanced ERα positive breast cancer. Unfortunately, therapeutic resistance frequently arises. There is a critical need to develop effective alternate strategies to prevent or delay the development of resistance to endocrine therapy and the resulting tumor progression. Both normal and tumor tissue express ERβ which has anti-proliferative activity and recent studies have identified several natural compounds that have the potential to function as ERβ agonists. Plant-derived ERβ-agonists, Liquiritigenin (Liq), from the plant Glycyrrhizae uralensis and S-equol, from the soy isoflavone daidzein, are currently in clinical trials for the treatment of vasomotor hot flashes associated with menopause. In this study we sought to determine if ERβ agonists alone or in combination with AI could resensitize Letrozole-resistant breast cancer cells in vivo. Xenografts were established using cells which model post-menopausal breast cancer. Endocrine therapy sensitive (MCF-7aro) and Letrozole resistant (LTLT-Ca) tumors were treated with either ERβ agonists or in combination with AI and progression was measured. In MCF-7aro tumors, ERβ agonist treatment reduced tumor volume and prolonged sensitivity to AI. In the therapy resistant tumors (LTLT-Ca), ERβ agonist treatment blocked tumor growth and restored sensitivity to AI therapy. To determine the molecular mechanism by which ERβ agonists inhibit tumor growth and prolong and restore sensitivity, qRT-PCR and western blot analysis was performed. Our results show changes in the levels of p53, NFkB, cyclin D1, and KLF5 in addition to other genes. To determine the role of ERβ agonists on the activation of these genes specific gene promoter-luciferase reporter constructs were used and the specificity of ERβ-mediated actions was confirmed using a siRNA approach. This study suggests that ERβ acts as a tumor suppressor by suppressing cell growth through the inhibition of cell cycle genes and by inducing apoptosis through the regulation of p53. In conclusion, this study demonstrates the potential role for ERβ agonists to improve adjuvant endocrine therapy to treat both hormone-responsive and hormone-resistant breast cancers.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-09-14.

Abstract P5-07-05: Oncogene PELP1 regulates alternative splicing in breast cancer through PRMT6

Background: Alternative splicing (AS) is essential in regulating gene expression and protein diversity; however, dysregulation leads to cancer development with tumor-specific splice variants that act by disrupting a tumor suppressor function. Protein arginine methylation is a modification involved in signal transduction, pre-RNA metabolism and transcriptional activation and deregulation of arginine methylase expression or functions can contribute to cancer progression via alternate splicing. PELP1 is a proto-oncogene, whose expression is associated with higher histological grade and shorter breast cancer specific survival, and PELP1 localization is a determinant of hormone sensitivity. This study focuses on examining the role of PELP1 in regulating gene expression and its possible role in alternative splicing.

Methods: ZR75 and MCF7 cells stably expressing PELP1-shRNA or overexpressing PELP1 were used in RNASeq and ChipSeq analysis. Gene differential expression lists were generated using DEseq and PELP1 regulated pathways were analyzed using Ingenuity Pathway Analysis (IPA). Cell proliferation, migration and ERE reporter gene assays were used to test the role of PRMT6 in PELP1's oncogenic functions. Immunoprecipitation, confocal microscopy, ChIP, and GST pull down assays were used to demonstrate PELP1-PRMT6 interactions. Exon specific RTqPCR assays and CD44 minigene reporter assays were used to demonstrate PELP1's role in splicing.

Results: RNA- and ChIP-sequencing results showed that the ERa coregulator PELP1 is a novel regulator of alternative splicing in breast cancer through the modulation of several genes involved in splicing including protein arginine methyltransferase 6 (PRMT6). PRMT6 plays a key role in coupling of transcription and alternative splicing by functioning as a transcriptional coactivator that can also regulate alternative splicing in a hormone independent manner. We discovered the novel complex of PELP1 and PRMT6 by co-immunoprecipitation. Biochemical assays revealed that PELP1 binds RNA, colocalizes with the splicing factor SC35 and promotes alternative splicing in reporter gene assays. PELP1 regulates the exon inclusion:skipping ratio of alternatively spliced exons in endogenous vascular endothelial growth factor (VEGF). PELP1's regulation of VEGF splicing is affected by the status of PRMT6. Interestingly, PRMT6 is needed for optimal oncogenic functions of PELP1. Further PELP1 has the potential to regulate the histone methyltransferase activity of PRMT6 and chromatin immunoprecipitation showed that PELP1 affects the enzyme recruitment and enrichment of the histone modification H3R2me2 at estrogen responsive genes.

Conclusions: Our findings show a role of PELP1-PRMT6 axis in ERα-mediated RNA splicing and their deregulation has implications for targeted therapeutics in ERα-driven breast cancer. This work was supported by the NIH grant CA095681 and NIH F31 Fellowship 1F31CA173909-01A1.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-07-05.

Abstract P5-09-12: Novel role of proto-oncogene PELP1 in A-NHEJ pathway of double strand break repair: Implications for treatment of hormonal therapy resistance

Background: DNA damage response (DDR) is critical for the maintenance of genome stability and serves as an anti-cancer barrier. Deregulation of key components of the DDR pathway such as p53 and ATM is associated with breast cancer progression. Recent studies implicated Alternative Non-homologous End-Joining (A-NHEJ) pathway in hormonal therapy resistance. Expression of proline, glutamic acid, leucine rich protein 1 (PELP1), a proto-oncogene, is an indicator of poor prognosis and therapy resistance in ER+ breast cancer. PELP1 was recently identified as a novel substrate of DNA damage kinases such as ATM. The objective of this study is to determine the role of PELP1 in the regulation of DNA repair and to study its effects on therapy resistance

Methods: We have used ER+ therapy sensitive MCF7, MCF7-Aro, ZR75 and therapy resistant MCF7-Tam, MCF7-LTLT, MCF7-HER2 model cells in our assays. UV-laser micro-irradiation, immunofluorescence staining and confocal microscopy were used to examine Ser-1033 phospho-PELP1 localization upon DNA damage. Homologous recombination (HR) reporter cell lines and NHEJ pathway reporter plasmids were used to determine the role of PELP1 in DNA repair pathways. U2OS-EJ2-GFP reporter cell line was used to evaluate the role of PELP1 in A-NHEJ pathway. MEFs lacking PELP1 and PELP1 specific siRNA were used to determine the role of PELP1 in DNA repair. Immunoprecipitation and western blotting were used to determine PELP1 interacting proteins. Yeast based peptide library screen was performed to identify PELP1 binding inhibitory peptides. MTT and clonogenic assays were used to determine the therapeutic effect of PELP1 inhibitor on therapy resistant breast cancer model cells.

Results: Results from this study showed that Ser-1033 phospho PELP1 was recruited to the site of DSB and co-localize with γ-H2A.X in breast cancer cells. Using reporter plasmid assays that distinguish various DNA repair pathways, we found that PELP1 regulates the NHEJ pathway and not the HR pathway. Further, using U2OS-EJ2-GFP reporter cell lines, we demonstrated that PELP1 is important for A-NHEJ mediated double strand break repair. Mechanistic studies revealed PELP1 interacts with E3ubiquitin ligase, SNF2 Histone Linker PHD RING Helicase (SHPRH, a yeast homolog of Rad5p). We have developed cell permeable peptide inhibitor (PIP3) that bind PELP1 and interferes with its interactions with SHPRH. Accordingly, treatment of U2OS-EJ2-GFP reporter cell lines with the (PIP3) peptide reduced the A-NHEJ repair frequency. Further, therapy resistant breast cancer cells which are addicted to A-NHEJ pathway were highly sensitive to PIP3 treatment.

Conclusions: These data provide novel insights into role of PELP1 in DNA repair, underscore the importance of PELP1 in the A-NHEJ pathway of DNA repair and demonstrates the significance of targeting PELP1 to sensitize therapy resistant breast cancer cells.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-09-12.

Abstract P2-05-01: Induction of PELP1 expression in mammary gland promotes tumorigenesis by enhancing CDK-CyclinD1 signaling

Introduction: Estrogen receptor coregulator over-expression promotes carcinogenesis and/or progression of endocrine related-cancers where steroid hormones are powerful mitogenic agents. Recent studies in our laboratory as well as others demonstrated that PELP1 is a proto-oncogene and a prognostic indicator of decreased survival in breast cancer patients. Recent studies indicated that PELP1 is needed for optimal epigenetic modifications at ER target genes and PELP1 interactions with KDM1 play a key role in PELP1 mediated oncogenic functions. However, the in vivo significance of PELP1 deregulation during initiation and progression of breast cancer remains unknown. The objective of this study is determine the molecular mechanisms by which PELP1 regulate breast cancer progression in vivo.

Method: To determine the significance of PELP1 over-expression in mammary tumorigenesis, we used an inducible, tissue-specific PELP1 expressing transgenic mouse. Mammary epithelial-specific expression of PELP1 was validated by immunohistochemistry and Western blot analysis. PELP1-mediated morphological and histological changes were analyzed by examining carmine-stained whole mounts and H&E-stained paraffin embedded mammary glands sections. Differential expression of breast cancer-focused genes between wild type and PELP1 transgenic mammary glands was determined using real-time RT2 Profiler PCR array. Proliferation was analyzed using Ki-67 immuno staining. RTqPCR, Western and IHC analysis were used to confirm the changes in the expression of PELP1 regulated genes.

Results: We observed an increase in proliferation, extensive side branching and precocious differentiation in PELP1 expressing mammary gland compared to controls. Aged MMTVrtTA-TetOPELP1 bitransgenic mice revealed hyperplasia and preneoplastic changes as early as 12 weeks and mammary tumors occurred at a latency of 10.5 months. Mechanistic studies using tissues from control and PELP1 transgenic mice revealed that PELP1 deregulation modulates expression of a number of known ER target genes involved in cellular proliferation (such as cyclin D1, CDKs) and morphogenesis (EGFR, MMPs) and such changes facilitated altered mammary gland morphogenesis and tumor progression. Western and IHC analysis of mammary glands confirmed upregulation of CDK and Cyclin D1 protein levels in PELP1 Tg mice. Further, PELP1 is hyperphosphorylated at CDK phosphorylation site in PELP1 (Ser 991), suggesting an autocrine loop involving CDk-CyclinD1-PELP1 axis in promoting mammary tumorigenesis. Treatment of PELP1 Tg mice with pargyline, an inhibitor of KDM1 for four months significantly reduced PELP1 driven hyperplasia. Mechanistic studies revealed that pargyline treatment reduced cyclin D1 expression levels and substantially reduced CDK driven PELP1 phosphorylation.

Conclusions: PELP1 deregulation modulates expression of a number of known ER target genes and cancer promoting genes. PELP1 mediated epigenetic changes via KDM1 play role in PELP1 oncogenic functions in vivo. Collectively, these results support that PELP1 deregulation has potential to promote breast tumorigenesis in vivo.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-05-01.

KDM1 is a novel therapeutic target for the treatment of gliomas

Glioma development is a multistep process, involving alterations in genetic and epigenetic mechanisms. Understanding the mechanisms and enzymes that promote epigenetic changes in gliomas are urgently needed to identify novel therapeutic targets. We examined the role of histone demethylase KDM1 in glioma progression. KDM1 was overexpressed in gliomas and its expression positively correlated with histological malignancy. Knockdown of KDM1 expression or its pharmacological inhibition using pargyline or NCL-1 significantly reduced the proliferation of glioma cells. Inhibition of KDM1 promoted up regulation of the p53 target genes p21 and PUMA. Patient-derived primary GBM cells expressed high levels of KDM1 and pharmacological inhibition of KDM1 decreased their proliferation. Further, KDM1 inhibition reduced the expression of stemness markers CD133 and nestin in GBM cells. Mouse xenograft assays revealed that inhibition of KDM1 significantly reduced glioma xenograft tumor growth. Inhibition of KDM1 increased levels of H3K4-me2 and H3K9-Ac histone modifications, reduced H3K9-me2 modification and promoted expression of p53 target genes (p21 and PUMA), leading to apoptosis of glioma xenograft tumors. Our results suggest that KDM1 is overexpressed in gliomas and could be a potential therapeutic target for the treatment of gliomas.

Abstract 674: The lysine demethylase KDM1 is a novel therapeutic target for the treatment of gliomas

Glioma development is a multistep process, involving alterations in genetic and epigenetic mechanisms. Understanding the mechanisms and enzymes that promote epigenetic changes in gliomas are urgently needed to identify novel therapeutic targets. In the present study we explored the significance of histone demethylase KDM1 in glioma progression. In order to know the status of expression of KDM1, we utilized glioma tissue microarrays which consist of different grades of astrocytomas, oligodendrogliomas, ependymomas and normal brain tissues. Immunohistochemical analysis showed that KDM1 expression is overexpressed in the gliomas compared to normal brain, and KDM1 expression levels were positively correlated with histological malignancy. KDM1 expression was also found to be elevated in various established glioma cell lines. To study the functional significance of KDM1 in gliomas, KDM1 expression was silenced using siRNA or its pharmacological inhibition using pargyline or NCL-1. Silencing of KDM1 or inhibition of its enzyme activity significantly reduced the proliferation and colony formation of glioma cells. Mechanistic studies showed that inhibition of KDM1 promoted the acetylation of p53 and up regulation of its target genes p21 and PUMA. Patient-derived primary GBM cells expressed high levels of KDM1 and pharmacological inhibition of KDM1 decreased their proliferation. Further, KDM1 inhibition reduced the expression of stemness markers CD133 and nestin in GBM cells. Mouse xenograft assays revealed that inhibition of KDM1 using pargyline significantly reduced U87 glioma xenograft tumor growth. Inhibition of KDM1 increased levels of H3K4-me2 and H3K9-Ac histone modifications, reduced H3K9-me2 modification and promoted expression of p53 target genes (p21 and PUMA), leading to apoptosis of glioma xenograft tumors. Our results suggest that KDM1 is overexpressed in gliomas and could be a potential therapeutic target for the treatment of gliomas.

Citation Format: Gangadhara R. Sareddy, Sandeep Saran, Binoj C. Nair, Samaya R. Krishnan, Vijay K. Gonugunta, Andrew J. Brenner, Ratna K. Vadlamudi. The lysine demethylase KDM1 is a novel therapeutic target for the treatment of gliomas. [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 674. doi:10.1158/1538-7445.AM2013-674

Abstract 855: Targeting triple negative breast cancer using novel cell permeable inhibitor to block ATM-PELP1-p53 axis

Triple negative breast cancer (TNBC) is clinically aggressive and TNBC patients do not benefit from antiestrogen and herceptin-based therapies; so new therapeutic drugs are urgently needed. DNA damage response (DDR) is critical for the maintenance of genome stability and serves as an anti-cancer barrier. Recent evidence suggests that deregulation of key components of the DDR pathway such as p53 and ATM is associated with TNBC progression and metastasis. Our ongoing studies have identified proline, glutamic acid, leucine rich protein 1 (PELP1), a proto-oncogene overexpressed in breast cancer, as a novel substrate of ATM. PELP1 overexpression in breast cancer is an indicator of poor prognosis. The objective of this study is to determine the mechanism and significance of the ATM-PELP1-p53 pathway in TNBC cells. For this purpose, we used ER-negative mutant (MT) p53 (MDA-MB-231, BT20, MDA-MB-468) and ER-positive wildtype (WT) p53 (ZR-75 and MCF7) breast cancer cell lines. We generated model cells that have stable expression of control or PELP1shRNA. Our results with PELP1 knockdown models indicate that PELP1 functions as a co-regulator of p53. Immunoprecipitation and chromatin immunoprecipitation (ChIP) assays revealed that PELP1 interacts with p53 and is recruited to p53 target genes, respectively. The p53 regulatory role of PELP1 is mediated by the phosphorylation of PELP1 (p-PELP1) by ATM at the conserved SQ motif. Through model cell lines that overexpress WT or MT (S1033A) PELP1 we demonstrated the significance of p-PELP1 in WT p53 co-activation functions. Utilizing the unique sequence surrounding the ATM phosphorylation site in PELP1, we developed a novel cell permeable peptide (TAT-1033PELP1 peptide) as well as a p-PELP1 antibody that uniquely recognizes S1033 p-PELP1. We confirmed ATM mediated phosphorylation of PELP1 in vivo using S1033 p-PELP1 antibody. The TAT-1033PELP1 inhibitor peptide significantly reduced ATM mediated phosphorylation of endogenous PELP1. Interestingly, in TNBC cells that have MTp53, PELP1 knockdown or treatment with TAT-1033PELP1 peptide resulted in a significant loss of cell viability in response to genotoxic stress. However, treatment of ER- positive breast cancer cells with this peptide or PELP1 knockdown resulted in resistance to genotoxic stress, suggesting unique therapeutic activity of TAT-1033PELP1 peptide towards TNBC cells. Mechanistic studies showed that PELP1 functionally interacts with MTp53 and regulates the expression of NF-Y and p63/p73 target genes. The TAT-1033PELP1 peptide also reduces the migratory potential of TNBC cells. IHC analysis of a tumor tissue array revealed increased PELP1 phosphorylation in TNBC tumors. Collectively, our results suggest that a hyperactive ATM-PELP1-p53MT pathway contributes to TNBC progression and that the TAT-1033PELP1 peptide represents a novel therapeutic to block PELP1 oncogenic functions in TNBC.

Citation Format: Samaya Krishnan, Binoj C. Nair, Gangadhara R. Sareddy, Monica Mann, Ratna K. Vadlamudi. Targeting triple negative breast cancer using novel cell permeable inhibitor to block ATM-PELP1-p53 axis. [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 855. doi:10.1158/1538-7445.AM2013-855

Abstract 1312: The estrogen receptor β agonists, Liquiritigenin and S-equol, inhibit breast cancer cell proliferation through the activation of tumor-suppressor and other pathways

Estrogen and estrogen receptors (ERα and ERβ) play an important role in breast cancer. Currently, antiestrogen (AE) targeted to ERα and aromatase inhibitors (AI), which block local and systemic estrogen production, are used in the treatment of breast cancer. Both treatments improve outcomes for about 50% of patients with early or advanced ERα positive breast cancer. Unfortunately, in women with advanced breast cancer, essentially all breast cancers develop resistance to these two classes of agents. Moreover, the side effects associated with currently used AI limit the long-term utility of them as chemopreventative agents. Therefore there is a critical need to develop effective alternate strategies to prevent or delay the development of resistance to endocrine therapy and the resulting tumor progression. Recent studies have identified several natural compounds that have the potential to function as ERβ agonists. Plant-derived ERβ-agonists, Liquiritigenin (LIQ), from the plant Glycyrrhizae uralensis and an active component of MF101, and S-equol, from the soy isoflavone daidzein, are currently being tested to treat vasomotor hot flashes associated with menopause. In addition, S-equol is also being tested as a treatment for BPH in men. However, the exact mechanism of action of these compounds is not clear. In this study we sought to determine the mechanism by which ERβ acts as a tumor suppressor, and whether these ERβ agonists could resensitize Letrozole-resistant breast cancer cells. MCF7aro and LTLT-ca cells were used as models of hormone-responsive and hormone-resistant breast cancer respectively. MTT assay was used to determine the half maximal inhibitory concentrations of the ERβ agonists. Upon treatment, our results show changes in the levels of p53, NFkB, cyclin D1, KLF5 and others using qRT-PCR and western blot analysis. The effects of ERβ agonists on the activation of these genes were confirmed using specific gene promoter-luciferase reporter gene constructs. Specificity of ERβ-mediated actions was confirmed using a siRNA approach in addition to other methods and knockdown efficiency was confirmed through RT-PCR. Interestingly, our results show that the plant-derived ERβ-agonists, LIQ and S-equol, not only affect the growth of breast cancer cells and tumors but treatment increases the expression of p53 and others, and upon ERβ knockdown this effect is ablated. This study suggests that ERβ acts as a tumor suppressor by regulating the expression of p53 and others involved in cell proliferation. In conclusion, this study demonstrates the potential role for ERβ agonists to improve adjuvant endocrine therapy to treat both hormone-responsive and hormone-resistant breast cancers, as well as provides rationale for new preventive approaches to decrease the incidence of breast cancer.

Citation Format: Cathy Samayoa, Anil Kotha, Naveen K. Krishnegowda, Ratna K. Vadlamudi, Rajeshwar Rao Tekmal. The estrogen receptor β agonists, Liquiritigenin and S-equol, inhibit breast cancer cell proliferation through the activation of tumor-suppressor and other pathways. [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 1312. doi:10.1158/1538-7445.AM2013-1312

Hypersensitivity of the hippocampal CA3 region to stress-induced neurodegeneration and amyloidogenesis in a rat model of surgical menopause

Females who enter menopause prematurely via bilateral ovariectomy (surgical menopause) have a significantly increased risk for cognitive decline and dementia. To help elucidate the mechanisms underlying this phenomenon, we used an animal model of surgical menopause, long-term (10-week) bilateral ovariectomy in female rats. Herein, we demonstrate that long-term oestrogen deprivation dramatically increases sensitivity of the normally resistant hippocampal CA3 region to ischaemic stress, an effect that was gender-specific, as it was not observed in long-term orchiectomized males. Furthermore, the enhanced damage to the CA3 region correlated with a worse cognitive outcome after ischaemic stress. Long-term ovariectomized rats also displayed a robust hyperinduction of Alzheimer's disease-related proteins in the CA3 region and a switch in amyloid precursor protein processing from non-amyloidogenic to amyloidogenic following ischaemic stress CA3 hypersensitivity also extended to an Alzheimer's disease-relevant insult, as the CA3 region of long-term ovariectomized rats was profoundly hypersensitive to the neurotoxic effects of amyloid-β1-42, the most amyloidogenic form of the amyloid-β peptide. Additional studies revealed that CA3 region hypersensitivity, Alzheimer's disease-related protein induction, and amyloidogenesis are mediated by a NADPH oxidase/superoxide/c-Jun N-terminal kinase/c-Jun signalling pathway, involving both transcriptional and post-translational mechanisms. In addition, while 17β-oestradiol replacement at the end of the long-term oestrogen deprivation period could not prevent CA3 hypersensitivity and amyloidogenesis, if 17β-oestradiol was initiated at the time of ovariectomy and maintained throughout the 10-week oestrogen deprivation period, it completely prevented these events, providing support for the 'critical window' hypothesis for oestrogen replacement therapy benefit. Collectively, these findings may help explain the increased risk of cognitive decline and dementia observed in women following surgical menopause, and they provide increased support that early 17β-oestradiol replacement is critical in preventing the negative neural effects associated with bilateral ovariectomy.

Abstract P1-05-10: Targeting breast cancer metastasis through disruption of novel PELP1-G9a complex

Although there are several therapies available for the treatment of breast cancer, many patients have tumor recurrences that ultimately metastasize. There are several oncogenic estrogen receptor alpha (ERα) coregulators that promote breast cancer metastasis and targeting these coregulators could be a promising cancer therapeutic. One coactivator of ERα that is known to be upregulated in breast cancer and promote metastasis is proline-, glutamic acid-, and leucine-rich protein 1 (PELP1). PELP1 affects the migratory and invasive potential of breast cancer cells both in vitro and in vivo and modulates the expression of several genes involved in the epithelial to mesenchymal transition (EMT) including Snail, Twist and Zeb1. To elucidate the mechanism by which PELP1 promotes metastasis, we studied the proteins that interact with PELP1 and promote cancer metastasis. We identified a novel PELP1-interacting protein G9a (Bat8/KMT1C/EHMT2), a histone lysine methyltransferase known to overexpressed in aggressive breast cancer and promote invasion and metastasis. G9a contributes to the epigenetic silencing of tumor suppressor genes, interacts with Snail to promote EMT and its knockdown inhibits cell migration and invasion as well as lung metastasis. The objective of this study is to characterize the interaction of PELP1 and G9a in the promotion of breast cancer metastasis. The complex formation of PELP1 and G9a was confirmed by an in vivo immunoprecipitation and an in vitro binding assay. The region of PELP1 that binds to G9a was mapped further by PELP-GST deletions. To determine whether formation of the complex is necessary for PELP1's oncogenic functions including the promotion of metastasis, we developed a peptide to disrupt the complex formation. The sequence of the peptide has homology to both PELP1 and G9a with a TAT-sequence to enable cellular uptake. Cellular uptake was confirmed by fluorescent microscopy while biotin-avidin peptide pull-down assays confirmed PELP1-peptide binding. A peptide competition assay confirmed that the peptide could interrupt PELP1-G9a interaction. Treatment of two ER-positive, PELP1-overexpressing breast cancer cells (MCF7-PELP and ZR75-PELP) with the peptide significantly inhibited the PELP-1 mediated proliferation. Peptide treatment also substantially inhibited PELP1-mediated cell migration in Boyden chamber assays as well as decreased anchorage independence as seen by soft agar assay. Interestingly, disrupting PELP1-G9a interaction with the peptide also sensitized tamoxifen and letrozole resistant cells to the respective hormonal therapy. Mechanistic studies revealed that PELP1-G9a interactions play a critical role in epigenetic changes in therapy resistant cells. In conclusion, our studies identified a novel complex involved in breast cancer metastasis. The interaction of PELP1 and G9a is required for PELP1-mediated oncogenic properties and disruption of the complex by peptide treatment results in decreased metastatic potential and changes in epigenetic modifications. The novel peptide could be used for therapeutic targeting of breast cancer metastasis and therapy resistance. This work was supported by the NIH grant CA095681 and CPRIT pre-doctoral fellowship RP101491.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-10.

Abstract PD09-07: Therapeutic potential of targeting ATM-PELP1-p53 axis in triple negative breast cancer

Triple negative breast cancer (TNBC) comprises approximately 15% of all breast cancers, lacks expression of ER, PR, and HER2 and is clinically aggressive with shorter disease free survival. TNBC patients do not benefit from antiestrogen and herceptin-based therapies. Evolving evidence suggests that overexpression of mutant p53 is significantly associated with TNBC progression. DNA damage response (DDR) is critical for the maintenance of genome stability and serves as an anti-cancer barrier during tumorigenesis. However, the role of DDR in tumor progression and metastasis is less known. Recent studies suggest that the ATM kinase is hyperactive in late stage breast tumor tissues with lymph node metastasis. Our ongoing studies have identified proline, glutamic acid, leucine rich protein 1 (PELP1), a proto-oncogene overexpressed in breast cancer, as a novel substrate of ATM. The objective of this study is to determine the mechanism and significance of ATM mediated phosphorylation of PELP1 and its crosstalk with the p53 pathway in TNBC cells. To test this we have used three ER-negative mutant p53 breast cancer cell lines (MDA-MB-231, MDA-MB-468, BT20), with ER-positive (ZR-75 and MCF7) cell lines as controls. Using PELP1 specific shRNAs, we generated model cells that have stable expression of either control or PELP1 shRNA. Our results with PELP1 knockdown models indicate that PELP1 promotes stability of p53 and functions as a co-regulator of p53. PELP1 has the potential to modulate CBP/p300 mediated acetylation of the Lysine 382 residue of p53. Immunoprecipitation and chromatin immunoprecipitation (ChIP) assays were performed to examine PELP1 interaction with p53 and its recruitment to p53 target genes respectively. ChIP assays revealed that PELP1 knockdown significantly reduces the recruitment of p53 to the target genes. The p53 regulatory role of PELP1 is mediated by the phosphorylation of PELP1 at the conserved SQ motif by ATM. We generated model cells that overexpress WT or mutant (S1033A) PELP1 and demonstrated the significance of ATM mediated phosphorylation in PELP1 mediated p53 co-activation functions. Based on the sequence of the site of phosphorylation, we have developed a novel cell permeable peptide (TAT-1033PELP1 inhibitor) as well as a phospho-PELP1 antibody that uniquely recognizes S1033 phosphorylated PELP1. We confirmed ATM mediated phosphorylation of PELP1 in vivo using phospho PELP1 antibody (1033p-PELP1). The TAT 1033 inhibitor peptide significantly reduced ATM mediated phosphorylation of endogenous PELP1. Treatment of ER− positive breast cancer cells with this peptide resulted in resistance to genotoxic stress compared to cells that are treated with control TAT peptide. However, in TNBC cells that has a mutant p53, PELP1 knockdown or treatment with TAT-PELP1 inhibitor resulted in significant loss of cell viability and increase in apoptosis in response to genotoxic stress. IHC analysis of tumor tissue array (n = 100) revealed increased PELP1 phosphorylation in advanced ER-negative tumors and its status correlated with ATM. Collectively, our results suggest that hyperactive ATM-PELP1-p53 pathway contributes to TNBC progression and that the TAT-1033PELP1 inhibitor represents a novel therapeutic to block PELP1 oncogenic functions in TNBC.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD09-07.

Abstract P5-04-04: Significance of PELP1/HDAC2/microRNA-200 regulatory network in EMT and metastasis of breast cancer

Tumor metastasis remains a significant clinical problem and is the leading cause of death among breast cancer patients. Estrogen receptor (ER)-coregulators play an essential role in cancer progression and metastatic tumors express increased levels of coregulators. Proline glutamic acid rich protein (PELP1) is an ER coregulator, its expression is upregulated during breast cancer progression to metastasis and is an independent prognostic predictor of shorter survival of breast cancer patients. MicroRNA (miR) mediated regulation of tumorigenesis is emerging as a new paradigm in cancer biology and widespread misexpression of miRs has been reported in breast cancer. The objective of this study is to examine the mechanism and therapeutic significance of PELP1 regulation of miRs leading to breast cancer metastasis. We have used both ER+ve (ZR75, MCF7) and ER-ve (MDAMB231, MDAMB468) models that either stably overexpress PELP1 or PELP1shRNA. Boyden chamber, and invasion assays demonstrated that PELP1 down regulation significantly affect migration of both ER+ve and ER-ve cells. Epithelial to Mesenchymal Transition (EMT) real time qPCR Array studies identified PELP1 modulate expression of EMT genes Snail, Twist, ZEB1, ZEB2, Vimentin and MMPs. Importantly, whole genome microRNA array analysis using PELP1 model cells revealed that miR200a and miR141 were significantly upregulated in cells expressing PELP1-shRNA compared to control cells. Accordingly, over expression of PELP1 in low metastatic model cells decreased expression of miR200a and miR141. PELP1 regulation of miRs was further confirmed by ZEB1 and ZEB2 3′ UTR luciferase reporter assays. ChIP analysis revealed recruitment of PELP1 to the proximal promoter region of miR-200a and miR141 and promoter reporter assays further confirmed PELP1 regulation of miRs. Interestingly, PELP1 down regulated expression of miR200a and miR141 by promoting repressive chromatin modifications via HDAC2. Supporting this, HDAC inhibitors reversed PELP1 driven repressive effects. Further, ectopic expression of miR200a and miR141 mimetic decreased PELP1 mediated invasion/metastatic functions. Prognostic significance of PELP1-miRNA axis was determined using Tissue micro-array (TMA) and in situ hybridization (ISH assays) of Locked Nucleic Acid (LNA™)-based microarray approach in 102 human breast tumors. To test therapeutic potential in vivo, we have generated ZR-PELP1- and MCF7-PELP1-shMIMIC of miR200a and miR141 stable cells. In vitro gene expression and Boyden chamber assays using these model cells revealed that shMIMIC of miR200a and miR141 reversed PELP1 mediated alterations in gene expression and reduced PELP1 driven migration/invasion. Proof of principle studies using IVIS imaging of nude mice based assays of GFP-Luc labeled cells demonstrated therapeutic efficacy of miRIDIAN shMIMIC of miR200a and miR141 on PELP1 driven in vivo metastasis. Collectively, these novel findings demonstrate for the first time a previously unknown role for PELP1 in epigenetically controlling the functions of tumor metastasis suppressor miR-200a and miR141. These results suggest that PELP1-miR axis may be crucial stimulus for promoting EMT and breast cancer metastasis. This study is funded by NIH T32CA148724 Postdoc Fellowship Grant.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-04-04.

Abstract P6-04-07: Significance and therapeutic potential of PELP1-mTOR axis in breast cancer progression and therapy resistance

Proline, Glutamic-acid and Leucine-rich Protein 1 (PELP1) is a proto-oncogene that modulates ER signaling by functioning as an ER-coregulator. Emerging studies demonstrated that in a subset of breast tumors, PELP1 is predominantly localized in the cytoplasm and that PELP1 participates in extranuclear signaling by facilitating ER interactions with Src, PI3K, and AKT. PELP1 expression is upregulated in breast cancer, its deregulation contributes to therapy resistance, and PELP1 is a prognostic marker of poor survival. However, the mechanism by which PELP1 extranuclear actions contributes to cancer progression and therapy resistance remains unknown. We have recently discovered that PELP1 has the potential to interact with mammalian target of rapamycin (mTOR), a serine/threonine kinase that forms two distinct complexes called mTORC1 (containing Raptor and PRAS40) and mTORC2 (containing Rictor and Protor). The objective of this application is to test whether crosstalk occurs between mTOR and PELP1 signaling axis and to test whether mTOR targeting drugs can be used to target PELP1 oncogenic functions. We have used breast cancer cells with PELP1 overexpression (MCF7-PELP1, ZR75-PELP1, T47D-PELP1) or PELP1 down regulation (MCF7-PELP1shRNA, ZR75-PELP1shRNA) along with controls to study the role of PELP1 in the regulation of mTOR axis. PELP1 knockdown significantly reduced downstream mTOR signaling components as analyzed by Western analysis using phospho-S6K, -4EBP1, -mTOR and -Akt, antibodies. Overexpression of PELP1 activated mTOR signaling components. Using immunoprecipitation, we have demonstrated that PELP1 interacts with mTOR. Further immunopreciptation analysis using Rictor and Raptor specific antibodies revealed that PELP1 associates with both TORC1 and TORC2 complexes. Using PELP1WT and PELP1cyto (that predominantly localizes in the cytoplasm), we have demonstrated the differential activation of mTOR signaling components: PELP1WT activated both TORC1 and TORC2 pathways, while PELP1cyto uniquely activated TORC2. mTOR targeting drugs (Rapamycin or AZD8055) showed a significant effect on the in vitro proliferation of PELP1 model cells. AZD8055 is more potent in reducing PELP1 driven tumor growth in vivo compared to rapamycin. Immunohistochemical studies on xenografts derived from MCF7, MCF7-PELP1WT and MCF7-PELP1cyto models demonstrated that PELP1 signaling modulates mTOR signaling in vivo and inhibition of mTOR signaling rendered PELP1 driven tumors to be highly sensitive to therapeutic inhibition. Further, mTOR inhibitors sensitized tamoxifen therapy resistant PELP1cyto model cells to hormonal therapy. IHC analysis of mammary glands and mammary tumors from PELP1Tg mice revealed deregulation of mTOR signaling components with excessive activation of S6K and 4EBP1. Using breast tumor tissue arrays (n = 100), we found significant correlation of PELP1 cytosolic localization with mTOR signaling. Collectively, the experimental results from these studies identified PELP1-mTOR axis as a novel component of PELP1 oncogenic functions and suggests, mTOR inhibitor(s) will be effective chemotherapeutic agents for down regulating PELP1 oncogenic functions and for blocking PELP1-mediated therapy resistance.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-07.

Five friends of methylated chromatin target of protein-arginine-methyltransferase[prmt]-1 (chtop), a complex linking arginine methylation to desumoylation

Chromatin target of Prmt1 (Chtop) is a vertebrate-specific chromatin-bound protein that plays an important role in transcriptional regulation. As its mechanism of action remains unclear, we identified Chtop-interacting proteins using a biotinylation-proteomics approach. Here we describe the identification and initial characterization of Five Friends of Methylated Chtop (5FMC). 5FMC is a nuclear complex that can only be recruited by Chtop when the latter is arginine-methylated by Prmt1. It consists of the co-activator Pelp1, the Sumo-specific protease Senp3, Wdr18, Tex10, and Las1L. Pelp1 functions as the core of 5FMC, as the other components become unstable in the absence of Pelp1. We show that recruitment of 5FMC to Zbp-89, a zinc-finger transcription factor, affects its sumoylation status and transactivation potential. Collectively, our data provide a mechanistic link between arginine methylation and (de)sumoylation in the control of transcriptional activity.

Targeting the PELP1-KDM1 axis as a potential therapeutic strategy for breast cancer

INTRODUCTION

The estrogen receptor (ER) co-regulator proline glutamic acid and leucine-rich protein 1 (PELP1) is a proto-oncogene that modulates epigenetic changes on ER target gene promoters via interactions with lysine-specific histone demethylase 1 (KDM1). In this study, we assessed the therapeutic potential of targeting the PELP1-KDM1 axis in vivo using liposomal (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine; DOPC) siRNA to downregulate PELP1 expression and KDM1 inhibitors, pargyline and N-((1S)-3-(3-(trans-2-aminocyclopropyl)phenoxy)-1-(benzylcarbamoyl)propyl)benzamide using preclinical models.

METHODS

Preclinical xenograft models were used to test the efficacy of drugs in vivo. Ki-67 and terminal deoxynucleotidyl transferase dUTP nick end-labeling immunohistochemical analysis of epigenetic markers was performed on tumor tissues. The in vitro effect of PELP1-KDM axis blockers was tested using proliferation, reporter gene, chromatin immunoprecipitation and real-time RT-PCR assays. The efficacy of the KDM1 targeting drugs alone or in combination with letrozole and tamoxifen was tested using therapy-resistant model cells.

RESULTS

Treatment of ER-positive xenograft-based breast tumors with PELP1-siRNA-DOPC or pargyline reduced tumor volume by 58.6% and 62%, respectively. In a postmenopausal model, in which tumor growth is stimulated solely by local estrogen synthesis, daily pargyline treatment reduced tumor volume by 78%. Immunohistochemical analysis of excised tumors revealed a combined decrease in cellular proliferation, induction of apoptosis and upregulation of inhibitory epigenetic modifications. Pharmacological inhibition of KDM1 in vitro increased inhibitory histone mark dimethylation of histone H3 at lysine 9 (H3K9me2) and decreased histone activation mark acetylation of H3K9 (H3K9Ac) on ER target gene promoters. Combining KDM1 targeting drugs with current endocrine therapies substantially impeded growth and restored sensitivity of therapy-resistant breast cancer cells to treatment.

CONCLUSION

Our results suggest inhibition of PELP1-KDM1-mediated histone modifications as a potential therapeutic strategy for blocking breast cancer progression and therapy resistance.

Abstract 3294: A novel, inducible, mammary gland-specific PELP1 murine breast cancer model

Despite treatment advances, breast cancer remains the second most lethal malignant disease for women worldwide. Although pharmacologic agents that modulate estrogen receptor-alpha (ER) functions or reduce circulating estrogens levels significantly reduced mortality in patients with estrogen sensitive (ER positive) tumors, both de novo and acquired resistance limits efficacy. A critical need for identifying more precise diagnostic/prognostic biomarkers and novel therapeutic targets prompted deeper investigation into ER-coregulatory protein function and regulation. ER-coactivator PELP1, mediates both nuclear and extra-nuclear estrogen signaling and crosstalk with growth factors. Deregulated PELP1 expression occurs in hormone-driven cancers, associates with undifferentiated invasive breast adenocarcinomas and an independent prognostic biomarker in assessing clinical outcome of luminal-like breast cancer patients. Collectively, several studies suggest PELP1 is an ER coregulator with tumorigenic potential. However, the in vivo significance of PELP1 deregulation during initiation and progression of breast cancer remains unknown. To determine the role of PELP1 over-expression in mammary tumorigenesis, we generated an inducible transgenic murine model. Transgene construct (pTetOPELP1) consists of a full-length human PELP1 cDNA linked to luciferase gene reporter through an internal ribosomal entry site (IRES). pTetOPELP1 mice crossed with mammary gland-specific rtTA mice (MMTVrtTA) to establish two independent MMTVrtTA-TetOPELP1 transgenic lines. Transgene induction in adult nulliparous bitransgenic females was achieved with doxycycline administered in drinking water. Concurrent expression and activity of the luciferase gene reporter was detected specifically in the mammary gland by in vivo bioluminescence imaging, luciferase assay and RT-PCR. Mammary epithelial-specific expression of PELP1 was validated by immunohistochemistry and Western blot analysis. PELP1-mediated morphological and histological changes were analyzed by examining carmine-stained whole mounts and H&E-stained paraffin embedded mammary glands sections. We observed an increase in proliferation, extensive side branching and precocious differentiation in PELP1 expressing mammary gland compared to controls. Aged MMTVrtTA-TetOPELP1 bitransgenic mice (n=42) revealed hyperplasia and preneoplastic changes as early as 12 weeks with ER-positive mammary gland tumors developing by 8 months following PELP1 induction. Taken together, we established PELP1 as an oncogenic in vivo. Our inducible mammary-specific PELP1 transgenic model will serve as a valuable tool for future in vivo investigation into molecular mechanisms of PELP1-mediated tumorigenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3294. doi:1538-7445.AM2012-3294

Abstract 5753: Potential therapeutic use of ER beta modulators in treating endocrine therapy resistant breast cancers

Although systemic hormone therapies that either block local estrogen production by aromatase inhibitors (AI) such as letrozole or block actions of estrogen/ER actions by anti-estrogens (AEs) like tamoxifen are well tolerated, unfortunately, essentially all breast cancers in women with advanced breast cancer develop resistance to these agents, and the benefit of adjuvant therapy is also limited by the development of resistance. In addition, side effects associated with the systemic inhibition of aromatase with current compounds limits their long-term utility of them as chemopreventative agents. Using in vitro and preclinical postmenopausal breast cancer models, we have investigated whether treatment of endocrine therapy resistant (AI or AE) breast cancer cells with selective plant-derived ER beta agonists (Liquiritigenin; LIQ or Nyasol; NYA) alone or in combination with AE or AI affects the growth of resistant breast cancer cells, thereby restores sensitivity to AE or AI. To test whether combination therapy restores sensitivity to letrozole or tamoxifen, we have treated resistant breast cancer cells with either letrozole or tamoxifen alone or with a combination of AE or AI and LIQ/NYA, active ingredient of MF101 used for treatment hot flashes in postmenopausal women. In addition, an effect of these compounds on cell growth was also tested using different breast cancer cells with and without ERα including triple negative breast cancer cells. Efficacy of these drugs was also tested in these model cells with or without ERβ expression. Compared to single agents, combination treatment not only restored sensitivity to letrozole but also resulted in decreased cell proliferation and increased apoptosis as well as increased ERβ and decreased ERα levels in resistant cells. Combination of LIQ or NYA not only diminished cell growth various breast cancer cells (that express endogenous aromatase) but also affected the expression of aromatase. Detailed investigations indicated that LIQ/NYA affects the induction of aromatase by specifically inhibiting breast cancer specific aromatase promoter 1.3 as well as its activity through inflammatory cytokine-mediated actions. ERβ-mediated inhibition of tumor cell growth appears to be regulated by different molecular mechanisms. Some of these molecular pathways are different than that are known to be responsible for resistance to hormonal therapeutic agents. These studies suggest the therapeutic benefit of LIQ or NYA ERβ agonist to resensitize breast cancer cells that are resistant to AEs or AI and their ability to selectively inhibit tumor induction of aromatase. Our study suggests a novel role of natural ER beta agonists as valuable therapeutic modulators to treat endocrine sensitive as well as resistant tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5753. doi:1538-7445.AM2012-5753

Abstract 5628: Novel cell permeable peptide inhibitors of PELP1 oncogenic functions

Estrogen receptor (ERα) is the fundamental transcription factor in breast cancer progression and a majority of breast cancers start as ERα positive. Therapies targeting ERα are effective; however, many eventually develop resistance and recur as metastases. ERα signaling is mediated by coregulator proteins that can have altered expression and/or function that promotes therapy resistance and metastasis by enhancing hormone-independent ERα signaling and by epigenetic changes. An alternative strategy for inhibiting ERα signaling in therapy resistant and metastatic tumors is to inhibit the function of ERα coregulators. PELP1 is an ERα coactivator and proto-oncogene which is overexpressed in breast cancer, promotes breast cancer progression by epigenetic changes at ERα target genes and is an independent marker of poor prognosis and breast cancer survival. The objective of this study is to develop an inhibitor of PELP1-mediated ERα coactivator functions. Since PELP1 lacks any known enzymatic activities, we targeted PELP1 protein-protein interactions to inhibit its oncogenic functions. We used a yeast two-hybrid system to screen a library of random peptides (∼10-7) fused to a transcriptional activation domain and identified 23 peptides with high affinity for PELP1. Two of these PELP1-inhibiting peptides (PIP-1 and PIP-2) significantly block PELP1 coactivator functions and we used a TAT-peptide fusion of PIPs to deliver the peptides into cells. Cellular uptake of the TAT- PIP was confirmed by fluorescent microscopy and biotin-avidin peptide pull-down assays confirmed PELP1-PIP binding. Both PIP- 1 and -2 significantly inhibited PELP1-mediated proliferation in two ERα-positive breast cancer cells (MCF7 and ZR75). A GenBank search revealed homology of PIPs with the methyltransferase G9a (Bat8/KMT1C/EHMT2) that is commonly overexpressed in aggressive breast cancer, contributes to epigenetic silencing of tumor suppressors and promotes cancer invasion and metastasis. In vivo co-immunoprecipitation analysis and an in vitro binding assay confirmed PELP1 interaction with G9a. Peptide competition assays indicated that the TAT-fused peptides could interrupt PELP1-G9a interaction. Both PIP-1 and -2 substantially inhibited PELP1-mediated cell invasion/migration in Boyden chamber assays. Interestingly, disrupting PELP1-G9a interaction with PIPs sensitized resistant cells to hormonal therapy. Mechanistic studies revealed that PELP1-G9a interactions play a critical role in epigenetic changes in therapy resistant cells. In conclusion, our studies identified a novel inhibitor of PELP1 that can be used for therapeutic targeting of ERα-coregulator driven cancer progression and therapy resistance. This work was supported by the NIH grant CA095681 and CPRIT pre-doctoral fellowship.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5628. doi:1538-7445.AM2012-5628

Abstract 958: PELP1 regulation of mTOR Axis: Role in breast cancer progression and resistance

Hormonal therapy resistance is a major clinical problem. Emerging evidence suggests that estrogen (ER) participates in extra-nuclear signaling events in the cytoplasm / membrane and such actions may play a role in therapy resistance. Recent studies suggested that mTOR pathway play a critical role in ER-mediated cell proliferation and growth factor signaling crosstalk. Proline, Glutamic-acid and Leucine-rich Protein 1 (PELP1) participates in ER extra-nuclear actions. PELP1 is a prognostic indicator of shorter breast cancer specific survival and PELP1 expression is predominantly in the cytoplasm in a subset of breast tumors. The objective of this application is to test whether cross talk occurs between mTOR-PELP1 signaling axis and whether mTOR targeting drugs can be used to target PELP1 oncogenic functions leading to therapy resistance. We have tested this hypothesis using ER-positive breast cancer cells that over express PELP1 (MCF7-PELP1, ZR75-PELP1) and models cells lacking PELP1 (MCF7-PELP1 shRNA, ZR-75-PELP1 shRNA). Vector transfected ZR75 and MCF7 cells were used as controls. Rapamycin and AZD8055 were used as pharmacological inhibitors to block mTOR pathway. Over expression of PELP1 enhanced the estrogen and Heregulin mediated cell proliferation in breast cancer cells. Rapamycin (10−7M) or AZD8055 (10−8M) treatment significantly reduced PELP1 driven growth in both MCF7 and ZR75 cells that are treated with estrogen. Similarly, Rapamycin and AZD8055 treatment of MCF7 and ZR75 cells significantly reduced PELP1 mediated increase in cell growth of Heregulin stimulated cells. Mechanistic studies using yeast two hybrid screen and reciprocal immunoprecipitations demonstrated that PELP1 directly interacts with mTOR and PP2A. PELP1cyto model cells that uniquely express PELP1 in the cytoplasm, exhibit excessive activation of mTOR signaling pathway upon estrogen and growth factor stimulation. Over expression of PELP1 in the breast cancer model cells increased phosphorylation of mTOR axis components (phos-mTOR, -S6K, -4EBP1,-AKT). Further, Knock down of PELP1 with siRNA significantly reduced the activation of mTOR signaling components upon estrogen and Heregulin stimulation. Immunohistochenistry studies using xenograft tumor tissues with PELP1 overexpression and PELP1cyto driven tumors with PELP1 deregulation showed correlation of PELP1 expression with the activation of mTOR signaling components and that PELP1cyto driven tumors have excessive activation of mTOR signaling components. Combination therapy of Tamoxifen and Rapamycin or AZD8055, sensitized PELP1 deregulated cells to hormonal therapy. Our results suggest that PELP1 driven oncogenic functions involve PELP1 modulation of mTOR signaling and blockade of mTOR signaling render PELP1 driven tumors highly sensitive to therapeutic inhibition.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 958. doi:1538-7445.AM2012-958

Abstract 2301: Epigenetic regulation of microRNA-200a and 141 by proto-oncogene PELP1: Role in breast cancer progression and metastasis

Endocrine therapy is a key component of adjuvant therapy for estrogen receptor (ER)-positive breast cancer. However, initial or acquired resistance frequently occurs and tumor recurs as advanced metastatic disease. Accumulating evidence suggests that ER-coregulators play an essential role in cancer progression. Metastatic tumors exhibit increased expression of coregulators and their deregulation occurs in both ER+ve and ER-ve tumors. Proline glutamic acid rich protein (PELP1) is an ER coregulator, its expression is upregulated during breast cancer progression to metastasis and PELP1 is an independent prognostic predictor of shorter breast cancer specific survival. The objective of this study is to examine the mechanism and significance of PELP1 regulation of microRNAs and its effect on breast cancer metastasis. We have used both ER+ve (ZR75, MCF7) and ER-ve (MDAMB231) models that either stably overexpress PELP1 or PELP1shRNA. Boyden chamber, wound healing, and invasion assays demonstrated that PELP1 down regulation significantly affect migration of both ER+ve and ER-ve cells. Epithelial to Mesenchymal Transition (EMT) real time qPCR Array (Super array) studies identified PELP1 modulate expression of eight genes involved in the EMT (including Snail, Twist, ZEB1, ZEB2, Vimentin and MMPs). In xenograft assays, overexpression of PELP1 in non-metastatic ZR75, MCF7 cells increased their propensity for metastasis in vivo, while PELP1 knockdown in metastatic MDAMB231 model cells decreased in vivo metastasis. Mechanistic studies using whole genome microRNA array analysis using PELP1 model cells revealed that miR200a and miR141 were significantly upregulated in cells expressing PELP1-shRNA compared to control shRNA expressing cells. Accordingly, over expression of PELP1 in low metastatic model cells decreased expression of miR200a and miR141. Chromatin immunoprecipitation (ChIP) analysis revealed recruitment of PELP1 to the proximal promoter region of miR-200a and miR141. Mechanistic studies showed PELP1 down regulate expression of metastasis suppressive microRNAs (miR200a and miR141) by promoting repressive chromatin modifications via its association with HDAC2. Accordingly, HDAC inhibitors reversed PELP1 driven repressive effects. Further, ectopic expression of miR200a and miR141 mimetics decreased PELP1 mediated metastatic functions. Collectively, these findings demonstrate for the first time a previously unknown role for PELP1 in the epigenetic control of miR-200a and miR141. These results reveal that PELP1 play a role in breast cancer metastasis by promoting cell motility / EMT by modulating miRNA expression. Understanding how proto-oncogene PELP1 plays a role in metastasis will be useful in maximizing treatment opportunities for metastatic breast cancer. This study is funded by T32CA148724 NIH Postdoctoral Fellowship Grant.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2301. doi:1538-7445.AM2012-2301

Therapeutic significance of estrogen receptor β agonists in gliomas

Gliomas are the most common and devastating central nervous system neoplasms. A gender bias exists in their development: females are at lower risk than males, implicating estrogen-mediated protective effects. Estrogen functions are mediated by two estrogen receptor (ER) subtypes: ERα, which functions as tumor promoter, and ERβ, which functions as tumor suppressor. We examined the potential use of ERβ agonists as a novel therapeutic to curb the growth of gliomas. Western analysis of six glioma model cells showed detectable expression of ERβ with little or no ERα. Treatment of glioma cells with ERβ agonists resulted in significant decrease in proliferation. Immunohistochemical analysis of tumor tissues revealed that ERβ expression is downregulated in high-grade gliomas. We found that ERβ agonists promote both expression and tumor-suppressive functions of ERβ in glioma cells. Liquiritigenin, a plant-derived ERβ agonist significantly reduced in vivo tumor growth in a xenograft model. Compared with control mice, animals treated with liquiritigenin had greater than 50% reduction in tumor volume and size. Immunohistochemical analysis of tumors revealed a significant increase in the nuclear ERβ expression with a concomitant decrease in cell proliferation in the liquiritigenin-treated group. Our results suggest that ERβ signaling has a tumor-suppressive function in gliomas. Because ERβ agonists are currently in clinical trials and are well tolerated with fewer side effects, identification of an ERβ agonist as a therapeutic agent can be readily extended to clinical use with current chemotherapies, providing an additional tool for enhancing survival in glioma patients.

Emerging significance of estrogen cancer coregulator signaling in breast cancer

Estrogen receptor (ERα) plays an important role in the initiation and progression of breast cancer. Many breast cancer patients respond positively to hormonal therapy; however, initial or acquired resistance to endocrine therapies frequently occurs and tumors recur as metastases. Emerging evidence suggests that ERα action is complex and involves functional interactions with coregulators. The levels of ERα coregulator proteins are tightly regulated under normal conditions and ERα-coregulator proteins have the potential to be differentially expressed in malignant tumors and have altered functions leading to tumor progression and metastases. In this review, we summarize recent findings that relate to ERα coregulators and discuss implications of ERα coregulator deregulation in breast cancer metastasis.

P4-01-08: The Role of Ser991 PELP1 Phosphorylation in Therapy Resistance and Metastasis of Breast Cancer

BACKGROUND: Growth factor induced activation of MAPK pathway is suggested to play a critical role both in invasive and hormone therapy resistant breast cancer via ligand independent activation of ERα. Proline Glutamic acid Leucine Rich Protein (PELP1) is a well established ER-coregulator that plays a critical role in ER's nuclear and extra-nuclear functions. PELP1 functions as a proto-oncogene and deregulation of PELP1 expression is linked to increased proliferation, metastasis and therapy resistance. The objective of this study is to examine, whether growth factor signaling modulates PELP1 mediated ER coactivation functions via MAPK pathway.

METHODS: Bioinformatics and phosphopeptide specific antibodies were employed in this study. In vitro kinase assays and MAPK inhibitors were used to confirm MAPK phosphorylation of PELP1. Site directed mutants and ERE reporter gene assays were used to demonstrate the significance of MAPK site in PELP1. Growth factor and estrogen regulation of PELP1 phosphoryaltion at Ser991 was validated in therapy sensitive (MCF7, ZR75) and resistant (MCF-7 HER2, MCF7-Tam and MCF-7Ca-LTLT cells using PELP1 specific phosphoantibody. Breast cancer model cells stably expressing PELP1 mutant or PELP1 peptides encompassing MAPK phosphorylation was used to test the significance of this MAPK site in PELP1 using proliferation, migration, and invasion assays. IHC analysis using PELP1 phospho antibodies was performed using murine xenograft tumors and human breast tumor arrays (TMA).

RESULTS: Growth factors (EGF, Heregulin) induced Ser991 phosphorylation of PELP1 in murine mammary epithelial cells and also in human breast cancer cell lines. Growth factor mediated Ser991PELP1 phosphorylation was abrogated by ERK1/2 MAPK pathway inhibitors including PD98059 and U0126. In ERE-reporter luciferase assays using ZR75 cells, PELP1 (WT) but not the ser991Ala mutant of PELP1 corroborated growth factor-ER crosstalk. Therapy resistant model cells (MCF-7-Tam, MCF-7-LTLT-ca and MCF-7-HER2) exhibited enhanced Ser991PELP1 phosphoryation compared to parental MCF7. TAT-Peptide encompassing Ser991 inhibited growth factor mediated phosphorylation of PELP1 and revealed a potent ability to inhibit the growth of therapy resistant cells. Xenograft tumors of hormone therapy model cell lines showed increased Ser991PELP1 phosphorylation and enhanced nuclear localization compared to hormonal sensitive xenograft tumors. IHC analysis of human breast invasive TMA revealed enhanced PELP1 ser991 phosphorylation in advanced metastatic tumors with prominent nuclear/nucleolar localization compared to normal and benign tumors. CONCLUSIONS: In this study, we identified that growth factor-MAPK pathway modulate ER coregulator PELP1 functions via phosphorylation and demonstrated that Ser991 phosphorylation of PELP1 has the potential to govern the growth Factor-ER cross talk leading to therapy resistance and metastatic phenotype of breast cancer. Peptides encompassing Ser991PELP1 site and Phosphoantibodies targeting Ser991 represent a novel therapeutic target and diagnostic markers in breast cancer. Supported by DOD Fellowship W81XWH-09-1-0010 (BCN) and DOD W81XWH-08-1-0604 (RKV)

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-01-08.

P4-03-05: Development of an Inducible Estrogen Receptor Co-Activator PELP1 Mammary Tumor Model

Despite treatment advances, breast cancer remains the second most lethal malignant disease for women worldwide. Given the importance of estrogen receptor (ER) and hormone-dependent nature of breast cancer, pharmacologic agents were developed to either modulate ER functions or reduce circulating estrogens levels. Although targeted endocrine therapies significantly reduce mortality in patients with estrogen sensitive (ER+) tumors, both de novo and acquired resistance limits efficacy. A critical need for identifying more precise diagnostic/prognostic biomarkers and novel therapeutic targets prompted deeper investigation into ER-coregulatory protein function and regulation. ER-coactivator PELP1, mediates both nuclear and extra-nuclear estrogen signaling and crosstalk with growth factors. PELP1 is deregulated in hormone-driven cancers, associates with undifferentiated invasive breast adenocarcinomas and an independent prognostic biomarker in assessing clinical outcome of luminal-like breast cancer patients. Collectively, several studies suggest PELP1 is an ERα coregulator with tumorigenic potential. However, the in vivo significance of PELP1 deregulation during initiation and progression of breast cancer is unknown. To determine the role of PELP1 overexpression in mammary tumorigenesis, we generated an inducible transgenic murine model. Transgene construct (pTetOPELP1) consists of a full-length human PELP1 cDNA linked to luciferase gene reporter through an internal ribosomal entry site (IRES). PELP1 transgene was purified and microinjected into mouse zygotes to generate pTetOPELP1 mice. Founder mice were identified by Southern blot analysis, of genomic DNA extracted from tail biopsies, for transgene integration through germline transmission. pTetOPELP1 mice were breed with mammary gland-specific rtTA mice (MMTVrtTA) to produce MMTVrtTA-TetOPELP1 bitransgenic mice. Potential founder mice were identified by polymerase chain reaction and breed to establish two independent transgenic lines. Transgene expression was induced in adult female bitransgenic animals with 200mg/mL of doxycycline administered in drinking water. Concurrent expression and activity of the luciferase gene reporter was detected specifically in the mammary gland by in vivo bioluminescence imaging, luciferase assay and RT-PCR. Mammary epithelial-specific expression of PELP1 was validated by immunohistochemistry and Western blot analysis. PELP1-mediated morphological and histological changes were analyzed by examining carmine-stained whole mounts and H&E-stained mammary glands sections. Our early findings with MMTVrtTA-TetOPELP1 bitransgenic mice (n=30) early preneoplastic changes and hyperplasia were evident as early as 12 weeks and the formation of mammary tumors by 8 months of age following PELP1 induction by doxycycline treatment. By utilizing the tetracycline-regulatory system, we created a novel, inducible and mammary gland-specific PELP1-expressing transgenic model for future in vivo studies into molecular mechanisms of PELP1-mediated mammary tumorigenesis.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-03-05.

Significance of PELP1 in ER-negative breast cancer metastasis

Breast cancer metastasis is a major clinical problem. The molecular basis of breast cancer progression to metastasis remains poorly understood. PELP1 is an estrogen receptor (ER) coregulator that has been implicated as a proto-oncogene whose expression is deregulated in metastatic breast tumors and whose expression is retained in ER-negative tumors. We examined the mechanism and significance of PELP1-mediated signaling in ER-negative breast cancer progression using two ER-negative model cells (MDA-MB-231 and 4T1 cells) that stably express PELP1-shRNA. These model cells had reduced PELP1 expression (75% of endogenous levels) and exhibited less propensity to proliferate in growth assays in vitro. PELP1 downregulation substantially affected migration of ER-negative cells in Boyden chamber and invasion assays. Using mechanistic studies, we found that PELP1 modulated expression of several genes involved in the epithelial mesenchymal transition (EMT), including MMPs, SNAIL, TWIST, and ZEB. In addition, PELP1 knockdown reduced the in vivo metastatic potential of ER-negative breast cancer cells and significantly reduced lung metastatic nodules in a xenograft assay. These results implicate PELP1 as having a role in ER-negative breast cancer metastasis, reveal novel mechanism of coregulator regulation of metastasis via promoting cell motility/EMT by modulating expression of genes, and suggest PELP1 may be a potential therapeutic target for metastatic ER-negative breast cancer.

Roscovitine confers tumor suppressive effect on therapy-resistant breast tumor cells

Introduction

Current clinical strategies for treating hormonal breast cancer involve the use of anti-estrogens that block estrogen receptor (ER)α functions and aromatase inhibitors that decrease local and systemic estrogen production. Both of these strategies improve outcomes for ERα-positive breast cancer patients, however, development of therapy resistance remains a major clinical problem. Divergent molecular pathways have been described for this resistant phenotype and interestingly, the majority of downstream events in these resistance pathways converge upon the modulation of cell cycle regulatory proteins including aberrant activation of cyclin dependent kinase 2 (CDK2). In this study, we examined whether the CDK inhibitor roscovitine confers a tumor suppressive effect on therapy-resistant breast epithelial cells.

Methods

Using various in vitro and in vivo assays, we tested the effect of roscovitine on three hormonal therapy-resistant model cells: (a) MCF-7-TamR (acquired tamoxifen resistance model); (b) MCF-7-LTLTca (acquired letrozole resistance model); and (c) MCF-7-HER2 that exhibit tamoxifen resistance (ER-growth factor signaling cross talk model).

Results

Hormonal therapy-resistant cells exhibited aberrant activation of the CDK2 pathway. Roscovitine at a dose of 20 μM significantly inhibited the cell proliferation rate and foci formation potential of all three therapy-resistant cells. The drug treatment substantially increased the proportion of cells in G2/M cell cycle phase with decreased CDK2 activity and promoted low cyclin D1 levels. Interestingly, roscovitine also preferentially down regulated the ERα isoform and ER-coregulators including AIB1 and PELP1. Results from xenograft studies further showed that roscovitine can attenuate growth of therapy-resistant tumors in vivo.

Conclusions

Roscovitine can reduce cell proliferation and survival of hormone therapy-resistant breast cancer cells. Our results support the emerging concept that inhibition of CDK2 activity has the potential to abrogate growth of hormonal therapy-resistant cells.

Estrogen receptor-β activation in combination with letrozole blocks the growth of breast cancer tumors resistant to letrozole therapy

Treatment with anti-estrogens or aromatase inhibitors (AI) is the main therapeutic strategy used against estrogen receptor ERα-positive breast cancer. Resistance to these therapies presents a major challenge in the management of breast cancer. Little is known about ERβ in breast carcinogenesis. Our aim in this study is to examine potential novel strategies utilizing ERβ activity to overcome AI resistance. We provide evidence that ERβ agonist can reduce the growth of AI-resistant breast cancer cells. Our data further confirm that therapeutic activation of ERβ by DPN, an ERβ agonist, blocks letrozole-resistant tumor growth in a xenograft model. Interestingly, DPN exerted tumor growth inhibition only in the presence of the AI letrozole, suggesting that combination therapy including ERβ activators and AI may be used in the clinical setting treating AI resistant breast cancer. An increase in ERβ levels, with diminished ERα/ERβ ratio, was observed in the tumors from mice treated with DPN/letrozole combination compared to single agents and control. Decreased Cyclin D1 and increased CyclinD1/CDK inhibitors p21 and p27 levels in DPN/letrozole treated tumors were observed, suggesting that the combination treatment may inhibit tumor growth by blocking G1/S phase cell cycle progression. Our data show a decrease in MAPK phosphorylation levels without affecting total levels. In addition to providing evidence suggesting the potential use of ERβ agonists in combination with letrozole in treating AI resistant breast cancer and prolonging sensitivity to AI, we also provide mechanistic evidence supporting the role of ERβ in altering the expression profile associated with resistance.

Abstract 1733: Therapeutic significance of ERα—PELP1 axis in blocking endocrine therapy resistance

Breast cancer therapies target the estrogen receptor-alpha (ERα) with letrozol an aromatase inhibitor or anti-estrogens such tamoxifen to limit circulating estrogen levels and alter ERα functions. Many women suffering from recurrent or advanced disease develop resistance to current targeted endocrine treatments. Emerging data suggests therapeutic resistance is precipitated through dysfunction of ERα coregulatory proteins and crosstalk between ERα and growth factor signaling. Deregulated expression of proline-, glutamic acid- and leucine-rich protein 1 (PELP1), an ERα coregulator, was observed in a subset of human breast tumors. Recently, PELP1 was identified as an independent prognostic biomarker of shorter survival in ERα positive/luminal-like breast cancer patients. Epigenetic changes of target gene promoters are modulated by PELP1 via an interaction with lysine specific demethylase 1 (KDM1). Additionally, PELP1 promotes crosstalk between ERα and Src kinase leading to enhanced activation of extranuclear signaling pathways. Therapeutic potential of targeting the ERα-PELP1 axis in vivo was examined using a pharmacological approach in well-established preclinical models of endocrine therapy resistant breast cancer. We utilized (1) siRNA liposomes to down regulate PELP1 expression; (2) pargyline and NCL-1, KDM1 inhibitors, to block PELP1-mediated epigenetic modifications and (3) dasatinib, a Src kinase inhibitor, to prevent PELP1-mediated extranuclear actions in both pre- and post-menopausal conditions. In xenograft-based assays, treatment of ERα positive breast cancer cells with liposomes containing PELP1-siRNA, dasatinib or KDM1 inhibitors significantly reduced proliferation and tumor growth. Combinatorial therapies of letrozol or tamoxifen with PELP1 axis blockers substantially impeded xenograft tumor growth by blocking both ERα nuclear and extranuclear signaling and promoting apoptosis in therapy resistant cells. Taken together, our results suggest targeting the ERα-PELP1 axis in combination with current endocrine therapies will enhance therapeutic efficacy and may inhibit or delay development of endocrine therapy resistance.

This study is funded by Komen grant KG090447 and NIH grant CA095681.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1733. doi:10.1158/1538-7445.AM2011-1733

Abstract 73: PELP1 is a novel reader of chromatin modifications: Implications in cancer progression

Cancer is caused by abnormalities of the genome and epigenome including the frequently occurring epigenetic changes of histone modifications. Specifically, estrogen-induced breast carcinogenesis is characterized by alterations in histone modifications. Reader proteins that recognize these modifications facilitate modulation of genes and their resulting biological actions. In addition to regulation by several coregulators, estrogen receptor alpha (ERα) transcriptional activation or repression depends on the modulation of histone methylation at target promoters. The ERα coregulator PELP1 plays an important role in ERα signaling, is a proto-oncogene with aberrant expression in hormone-related cancers and a prognostic indicator of decreased survival in breast cancer patients. The molecular mechanisms by which PEPL1 promotes oncogenesis remain unknown; however, previous studies from our lab have shown that PELP1 interacts with histones and is a novel reader of chromatin modifications. To explore the PELP1 epigenetic interactome, we used a histone peptide array containing 384 unique combinations of histone modifications including methylation, phosphorylation, acetylation and citrullination. Our results show that PELP1 uniquely recognizes histones modified by arginine dimethylation, arginine citrullination and lysine dimethylation. Phosphorylation of residues adjacent to a methyl modification affects the ability of PELP1 to recognize histone methylation. Using various deletions of PELP1 peptides, we have found that PELP1 acts as a module for recognition of a specific histone modification through the carboxyl-terminal glutamic acid rich region. Reporter gene assays showed that PELP1 functionally interacts with arginine methyltransferases including CARM1 and PRMT6, both shown to be dysregulated in human cancers, and synergistically enhances ERα-transactivation. Chromatin immunoprecipitation assays revealed that PELP1 has the potential to alter histone H3 arginine methylation status at ERα target gene promoters. The critical role of PELP1 status in modulating arginine methylation status was also observed through in vivo studies which show PELP1 knockdown results in decreased tumorigenesis and arginine dimethylation. Our findings suggest that PELP1 is a reader of histone methyl modifications and deregulation may have implications on tumor proliferation via epigenetic alterations at ERα target promoters. Targeting these epigenetic alterations through inhibition of PELP1 and the arginine methyltransferases could be a promising cancer therapeutic. This study was funded by NIH grant CA095681.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 73. doi:10.1158/1538-7445.AM2011-73

Abstract 1464: Significance and therapeutic potential of PELP1 axis in ER-negative breast cancer

The molecular basis of breast cancer progression to metastasis remains poorly understood. Even though ER and PR explain the biology of ER-positive tumors; it remains unknown as to what drives ER-negative metastatic tumors. PELP1 is an ER coregulator that functions as a proto-oncogene, its expression is deregulated in metastatic breast tumors and its expression is retained in ER-negative tumors. In this study, we examined the mechanism and significance of PELP1 mediated signaling in ER-negative breast cancer progression. We have established ER-negative model cells (MDA-MB231 and 4T1 cells) that stably express PELP1-shRNA. These model cells showed decreased PELP1 expression (75% of endogenous levels) and exhibited decreased propensity to proliferate in in vitro growth assays. Boyden chamber and wound healing assays showed PELP1 down regulation substantially affect migration of ER-negative cells and showed alterations in the expression of the EMT markers. Focused microarray studies identified PELP1 modulate expression of eight genes involved in the EMT (including MMPs, E-cadherin, MTA1). Overexpression of PELP1 in nonmetastatic cells increases their propensity for metastasis in vivo xenograft assays, while, PELP1 knockdown in metastatic model cells decreased in vivo metastatic potential of ER negative breast cancer cells. Whole genome microRNA array analysis revealed that miR 200a and miR141 were upregulated in MDA-MB231 and 4T1 cells expressing PELP1-shRNA compared to control shRNA expressing cells. Over expression of PELP1 in low metastatic model cells decreased expression of miR 200a and miR141. Mechanistic studies showed PELP1 down regulate expression of metastasis suppressive microRNAs (miR 200a and miR141) by promoting chromatin modifications. Ectopic expression of miR 200a and miR141 mimetics decreased PELP1 oncogenic function in ER-negative cells. These results suggest that PELP1 play a role in ER-negative breast cancer metastasis by promoting cell motility / EMT by modulating microRNA expression and blockage of PELP1 axis has potential to reduce metastasis potential of ER-negative breast cancer cells. Understanding how NR coregulator PELP1 plays a role in metastasis will be useful in maximizing treatment opportunities for metastatic breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1464. doi:10.1158/1538-7445.AM2011-1464

Therapeutic targeting of PELP1 prevents ovarian cancer growth and metastasis

PURPOSE

Ovarian cancer remains a major threat to women's health, partly due to difficulty in early diagnosis and development of metastases. A critical need exists to identify novel targets that curb the progression and metastasis of ovarian cancer. In this study, we examined whether the nuclear receptor coregulator PELP1 (proline-, glutamic acid-, leucine-rich protein-1) contributes to progression and metastatic potential of ovarian cancer cells and determined whether blocking of the PELP1 signaling axis had a therapeutic effect.

EXPERIMENTAL DESIGN

Ovarian cancer cells stably expressing PELP1-shRNA (short hairpin RNA) were established. Fluorescent microscopy, Boyden chamber, invasion assays, wound healing, and zymography assays were performed to examine the role of PELP1 in metastasis. Expression analysis of the model cells was conducted using tumor metastasis microarray to identify PELP1 Target genes. Therapeutic potential of PELP1-siRNA in vivo was determined using a nanoliposomal formulation of PELP1-siRNA-DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) administered systemically in a xenograft model.

RESULTS

PELP1 knockdown caused cytoskeletal defects and significantly affected the migratory potential of ovarian cancer cells. Microarray analysis revealed that PELP1 affected the expression of selective genes involved in metastasis including Myc, MTA1, MMP2, and MMP9. Zymography analysis confirmed that PELP1 knockdown caused a decrease in the activation of matrix metalloproteases (MMP) 2 and MMP9. Compared with control siRNA-DOPC-treated mice, animals injected with PELP1-siRNA-DOPC had 54% fewer metastatic tumor nodules, exhibited a 51% reduction in tumor growth and an 84% reduction in ascites volume.

CONCLUSION

The results suggest that PELP1 signaling axis is a potential druggable target and liposomal PELP1-siRNA-DOPC could be used as a novel drug to prevent or treat ovarian metastasis.