Combination of bazedoxifene with chemotherapy and SMAC-mimetics for the treatment of colorectal cancer

Excessive STAT3 signalling via gp130, the shared receptor subunit for IL-6 and IL-11, contributes to disease progression and poor survival outcomes in patients with colorectal cancer. Here, we provide evidence that bazedoxifene inhibits tumour growth via direct interaction with the gp130 receptor to suppress IL-6 and IL-11-mediated STAT3 signalling. Additionally, bazedoxifene combined with chemotherapy synergistically reduced cell proliferation and induced apoptosis in patient-derived colon cancer organoids. We elucidated that the primary mechanism of anti-tumour activity conferred by bazedoxifene treatment occurs via pro-apoptotic responses in tumour cells. Co-treatment with bazedoxifene and the SMAC-mimetics, LCL161 or Birinapant, that target the IAP family of proteins, demonstrated increased apoptosis and reduced proliferation in colorectal cancer cells. Our findings provide evidence that bazedoxifene treatment could be combined with SMAC-mimetics and chemotherapy to enhance tumour cell apoptosis in colorectal cancer, where gp130 receptor signalling promotes tumour growth and progression.

Mechanisms of cellular crosstalk in the gastric tumor microenvironment are mediated by YAP1 and STAT3

Deregulation of the Hippo pathway is a driver for cancer progression and treatment resistance. In the context of gastric cancer, YAP1 is a biomarker for poor patient prognosis. Although genomic tumor profiling provides information of Hippo pathway activation, the present study demonstrates that inhibition of Yap1 activity has anti-tumor effects in gastric tumors driven by oncogenic mutations and inflammatory cytokines. We show that Yap1 is a key regulator of cell metabolism, proliferation, and immune responses in normal and neoplastic gastric epithelium. We propose that the Hippo pathway is targetable across gastric cancer subtypes and its therapeutic benefits are likely to be mediated by both cancer cell-intrinsic and -extrinsic mechanisms.

Therapeutic inhibition of the SRC-kinase HCK facilitates T cell tumor infiltration and improves response to immunotherapy

Although immunotherapy has revolutionized cancer treatment, many immunogenic tumors remain refractory to treatment. This can be largely attributed to an immunologically "cold" tumor microenvironment characterized by an accumulation of immunosuppressive myeloid cells and exclusion of activated T cells. Here, we demonstrate that genetic ablation or therapeutic inhibition of the myeloid-specific hematopoietic cell kinase (HCK) enables activity of antagonistic anti-programmed cell death protein 1 (anti-PD1), anti-CTLA4, or agonistic anti-CD40 immunotherapies in otherwise refractory tumors and augments response in treatment-susceptible tumors. Mechanistically, HCK ablation reprograms tumor-associated macrophages and dendritic cells toward an inflammatory endotype and enhances CD8⁺ T cell recruitment and activation when combined with immunotherapy in mice. Meanwhile, therapeutic inhibition of HCK in humanized mice engrafted with patient-derived xenografts counteracts tumor immunosuppression, improves T cell recruitment, and impairs tumor growth. Collectively, our results suggest that therapeutic targeting of HCK activity enhances response to immunotherapy by simultaneously stimulating immune cell activation and inhibiting the immunosuppressive tumor microenvironment.

Host IL11 Signaling Suppresses CD4+ T cell-Mediated Antitumor Responses to Colon Cancer in Mice

IL11 is a member of the IL6 family of cytokines and signals through its cognate receptor subunits, IL11RA and glycoprotein 130 (GP130), to elicit biological responses via the JAK/STAT signaling pathway. IL11 contributes to cancer progression by promoting the survival and proliferation of cancer cells, but the potential immunomodulatory properties of IL11 signaling during tumor development have thus far remained unexplored. Here, we have characterized a role for IL11 in regulating CD4⁺ T cell-mediated antitumor responses. Absence of IL11 signaling impaired tumor growth in a sporadic mouse model of colon cancer and syngeneic allograft models of colon cancer. Adoptive bone marrow transfer experiments and in vivo depletion studies demonstrated that the tumor-promoting activity of IL11 was mediated through its suppressive effect on host CD4⁺ T cells in the tumor microenvironment. Indeed, when compared with Il11ra-proficient CD4⁺ T cells associated with MC38 tumors, their Il11ra-deficient counterparts displayed elevated expression of mRNA encoding the antitumor mediators IFNγ and TNFα. Likewise, IL11 potently suppressed the production of proinflammatory cytokines (IFNγ, TNFα, IL6, and IL12p70) by CD4⁺ T cells in vitro, which we corroborated by RNAscope analysis of human colorectal cancers, where IL11RA^high tumors showed less IFNG and CD4 expression than IL11RA^low tumors. Therefore, our results ascribe a tumor cell-extrinsic immunomodulatory role to IL11 during colon cancer development that could be amenable to an anticytokine-based therapy.See related Spotlight by van der Burg, p. 724.

Therapeutic Targeting of the Tumour Microenvironment in Metastatic Colorectal Cancer

Liver metastasis is the primary contributor to the death of patients with colorectal cancer. Despite the overall success of current treatments including targeted therapy, chemotherapy, and immunotherapy combinations in colorectal cancer patients, the prognosis of patients with liver metastasis remains poor. Recent studies have highlighted the importance of the tumour microenvironment and the crosstalk within that determines the fate of circulating tumour cells in distant organs. Understanding the interactions between liver resident cells and tumour cells colonising the liver opens new therapeutic windows for the successful treatment of metastatic colorectal cancer. Here we discuss critical cellular interactions within the tumour microenvironment in primary tumours and in liver metastases that highlight potential therapeutic targets. We also discuss recent therapeutic advances for the treatment of metastatic colorectal cancer.

STAT3 Signalling via the IL-6ST/gp130 Cytokine Receptor Promotes Epithelial Integrity and Intestinal Barrier Function during DSS-Induced Colitis

The intestinal epithelium provides a barrier against commensal and pathogenic microorganisms. Barrier dysfunction promotes chronic inflammation, which can drive the pathogenesis of inflammatory bowel disease (IBD) and colorectal cancer (CRC). Although the Signal Transducer and Activator of Transcription-3 (STAT3) is overexpressed in both intestinal epithelial cells and immune cells in IBD patients, the role of the interleukin (IL)-6 family of cytokines through the shared IL-6ST/gp130 receptor and its associated STAT3 signalling in intestinal barrier integrity is unclear. We therefore investigated the role of STAT3 in retaining epithelial barrier integrity using dextran sulfate sodium (DSS)-induced colitis in two genetically modified mouse models, to either reduce STAT1/3 activation in response to IL-6 family cytokines with a truncated gp130^∆STAT allele (GP130^∆STAT/+), or by inducing short hairpin-mediated knockdown of Stat3 (shStat3). Here, we show that mice with reduced STAT3 activity are highly susceptible to DSS-induced colitis. Mechanistically, the IL-6/gp130/STAT3 signalling cascade orchestrates intestinal barrier function by modulating cytokine secretion and promoting epithelial integrity to maintain a defence against bacteria. Our study also identifies a crucial role of STAT3 in controlling intestinal permeability through tight junction proteins. Thus, therapeutically targeting the IL-6/gp130/STAT3 signalling axis to promote barrier function may serve as a treatment strategy for IBD patients.

Repurposing the selective estrogen receptor modulator bazedoxifene to suppress gastrointestinal cancer growth

Excessive signaling through gp130, the shared receptor for the interleukin (IL)6 family of cytokines, is a common hallmark in solid malignancies and promotes their progression. Here, we established the in vivo utility of bazedoxifene, a steroid analog clinically approved for the treatment of osteoporosis, to suppress gp130‐dependent tumor growth of the gastrointestinal epithelium. Bazedoxifene administration reduced gastric tumor burden in gp130^Y757F mice, where tumors arise exclusively through excessive gp130/STAT3 signaling in response to the IL6 family cytokine IL11. Likewise, in mouse models of sporadic colon and intestinal cancers, which arise from oncogenic mutations in the tumor suppressor gene Apc and the associated β‐catenin/canonical WNT pathway, bazedoxifene treatment reduces tumor burden. Consistent with the proposed orthogonal tumor‐promoting activity of IL11‐dependent gp130/STAT3 signaling, tumors of bazedoxifene‐treated Apc‐mutant mice retain excessive nuclear accumulation of β‐catenin and aberrant WNT pathway activation. Likewise, bazedoxifene treatment of human colon cancer cells harboring mutant APC did not reduce aberrant canonical WNT signaling, but suppressed IL11‐dependent STAT3 signaling. Our findings provide compelling proof of concept to support the repurposing of bazedoxifene for the treatment of gastrointestinal cancers in which IL11 plays a tumor‐promoting role.

Inhibition of the SRC Kinase HCK Impairs STAT3-Dependent Gastric Tumor Growth in Mice

Persistent activation of the latent transcription factor STAT3 is observed in gastric tumor epithelial and immune cells and is associated with a poor patient prognosis. Although targeting STAT3-activating upstream kinases offers therapeutically viable targets with limited specificity, direct inhibition of STAT3 remains challenging. Here we provide functional evidence that myeloid-specific hematopoietic cell kinase (HCK) activity can drive STAT3-dependent epithelial tumor growth in mice and is associated with alternative macrophage activation alongside matrix remodeling and tumor cell invasion. Accordingly, genetic reduction of HCK expression in bone marrow-derived cells or systemic pharmacologic inhibition of HCK activity suppresses alternative macrophage polarization and epithelial STAT3 activation, and impairs tumor growth. These data validate HCK as a molecular target for the treatment of human solid tumors harboring excessive STAT3 activity.

Repurposing of drugs as STAT3 inhibitors for cancer therapy

Drug repurposing is a valuable approach in delivering new cancer therapeutics rapidly into the clinic. Existing safety and patient tolerability data for drugs already in clinical use represent an untapped resource in terms of identifying therapeutic agents for off-label protein targets. The multicellular effects of STAT3 mediated by a range of various upstream signaling pathways make it an attractive therapeutic target with utility in a range of diseases including cancer, and has led to the development of a variety of STAT3 inhibitors. Moreover, heightened STAT3 transcriptional activation in tumor cells and within the cells of the tumor microenvironment contribute to disease progression. Consequently, there are many STAT3 inhibitors in preclinical development or under evaluation in clinical trials for their therapeutic efficacy predominantly in inflammatory diseases and cancer. Despite these advances, many challenges remain in ultimately providing STAT3 inhibitors to patients as cancer treatments, highlighting the need not only for a better understanding of the mechanisms associated with STAT3 activation, but also how various pharmaceutical agents suppress STAT3 activity in various cancers. In this review we discuss the importance of STAT3-dependent functions in cancer, review the status of compounds designed as direct-acting STAT3 inhibitors, and describe some of the strategies for repurposing of drugs as STAT3 inhibitors for cancer therapy.

Abstract 4962: Repurposing bazedoxifene to suppress gastrointestinal cancer growth

The interleukin (IL)6 family of inflammatory cytokines, characterized by the shared use of the gp130 receptor, supports the progression of solid cancers. Specifically, gp130 signaling becomes rate limiting for the growth of gastrointestinal tumors arising from oncogenic driver mutations in Apc, but remains dispensable for the homeostatic renewal of the gastrointestinal mucosa. In the present study we investigate the effects of the selective estrogen receptor modulator bazedoxifene, clinically approved for the treatment of osteoporosis, as a putative small molecule inhibitor of gp130 receptor oligomerization and activation. We assessed the effects of bazedoxifene on IL6 and IL11-dependent STAT3 activation and cell proliferation in gastric and colon cancer cell lines. In patient-derived colon cancer organoid cultures, we assessed bazedoxifene effects on IL11-dependent growth. The gp130Y757F, Lgr5CreERT2- or Cdx2CreERT2-driven Apc flox mouse models of gastrointestinal cancer, were used to examine the effects of bazedoxifene on tumour growth. In silico modeling suggests that the inhibitory activity of bazedoxifene is due to its ability to mimic the interaction between the Site III interface of gp130 receptor and the tryptophan-157 in IL6, or tryptophan-168 in IL11 cytokine. We show that bazedoxifene interferes with IL6 and IL11-dependent proliferation of BAF/03 cells. Bazedoxifene suppresses gastric tumor growth in gp130Y757F mice irrespective of their gender, in which tumors arise through excessive IL11-dependent STAT3 signaling. Strikingly, in sporadic colon cancer models based on aberrant activation of the β-catenin/canonical WNT pathway, bazedoxifene treatment also reduces tumor burden in mice following conditional ablation of the Apc suppressor gene using the Lgr5CreERT2- or Cdx2CreERT2-driver alleles. Consistent with our observation that nuclear accumulation of β-catenin remains unaffected in colonic tumors of bazedoxifene-treated mice, bazedoxifenetreatment of human SW480 colon cancer cells harboring mutant APC did not affect canonical WNT signaling, but suppressed IL11-dependent STAT3 signaling. Our findings provide compelling proof-of-concept for the repurposing of bazedoxifene for the treatment of gastrointestinal cancers that arise from bona fide oncogenic driver mutations.

Note: This abstract was not presented at the meeting.

Citation Format: Pathum Thilakasiri, Tracy Nero, Michael W. Parker, Matthias Ernst, Ashwini L. Chand. Repurposing bazedoxifene to suppress gastrointestinal cancer growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4962.

ADAM17 is required for EGF-R-induced intestinal tumors via IL-6 trans-signaling

Schmidt et al. show that loss of the membrane-bound metalloprotease ADAM17 led to impaired intestinal cancer development in the murine APC^min/+ model, which also depended on IL-6 trans-signaling via the soluble IL-6R and could be blocked by the specific IL-6 trans-signaling inhibitor sgp130Fc.

Colorectal cancer is treated with antibodies blocking epidermal growth factor receptor (EGF-R), but therapeutic success is limited. EGF-R is stimulated by soluble ligands, which are derived from transmembrane precursors by ADAM17-mediated proteolytic cleavage. In mouse intestinal cancer models in the absence of ADAM17, tumorigenesis was almost completely inhibited, and the few remaining tumors were of low-grade dysplasia. RNA sequencing analysis demonstrated down-regulation of STAT3 and Wnt pathway components. Because EGF-R on myeloid cells, but not on intestinal epithelial cells, is required for intestinal cancer and because IL-6 is induced via EGF-R stimulation, we analyzed the role of IL-6 signaling. Tumor formation was equally impaired in IL-6^−/− mice and sgp130Fc transgenic mice, in which only trans-signaling via soluble IL-6R is abrogated. ADAM17 is needed for EGF-R–mediated induction of IL-6 synthesis, which via IL-6 trans-signaling induces β-catenin–dependent tumorigenesis. Our data reveal the possibility of a novel strategy for treatment of colorectal cancer that could circumvent intrinsic and acquired resistance to EGF-R blockade.

The angiotensin receptor blocker, Losartan, inhibits mammary tumor development and progression to invasive carcinoma

Drugs that target the Renin-Angiotensin System (RAS) have recently come into focus for their potential utility as cancer treatments. The use of Angiotensin Receptor Blockers (ARBs) and Angiotensin-Converting Enzyme (ACE) Inhibitors (ACEIs) to manage hypertension in cancer patients is correlated with improved survival outcomes for renal, prostate, breast and small cell lung cancer. Previous studies demonstrate that the Angiotensin Receptor Type I (AT₁R) is linked to breast cancer pathogenesis, with unbiased analysis of gene-expression studies identifying significant up-regulation of AGTR1, the gene encoding AT₁R in ER^+ve/HER2^−ve tumors correlating with poor prognosis. However, there is no evidence, so far, of the functional contribution of AT₁R to breast tumorigenesis. We explored the potential therapeutic benefit of ARB in a carcinogen-induced mouse model of breast cancer and clarified the mechanisms associated with its success.

Mammary tumors were induced with 7,12-dimethylbenz[α]antracene (DMBA) and medroxyprogesterone acetate (MPA) in female wild type mice and the effects of the ARB, Losartan treatment assessed in a preventative setting (n = 15 per group). Tumor histopathology was characterised by immunohistochemistry, real-time qPCR to detect gene expression signatures, and tumor cytokine levels measured with quantitative bioplex assays. AT₁R was detected with radiolabelled ligand binding assays in fresh frozen tumor samples.

We showed that therapeutic inhibition of AT₁R, with Losartan, resulted in a significant reduction in tumor burden; and no mammary tumor incidence in 20% of animals. We observed a significant reduction in tumor progression from DCIS to invasive cancer with Losartan treatment. This was associated with reduced tumor cell proliferation and a significant reduction in IL-6, pSTAT3 and TNFα levels. Analysis of tumor immune cell infiltrates, however, demonstrated no significant differences in the recruitment of lymphocytes or tumour-associated macrophages in Losartan or vehicle-treated mammary tumors.

Analysis of AT₁R expression with radiolabelled ligand binding assays in human breast cancer biopsies showed high AT₁R levels in 30% of invasive ductal carcinomas analysed. Furthermore, analysis of the TCGA database identified that high AT₁R expression to be associated with luminal breast cancer subtype.

Our in vivo data and analysis of human invasive ductal carcinoma samples identify the AT₁R is a potential therapeutic target in breast cancer, with the availability of a range of well-tolerated inhibitors currently used in clinics. We describe a novel signalling pathway critical in breast tumorigenesis, that may provide new therapeutic avenues to complement current treatments.

Insights into Orphan Nuclear Receptors as Prognostic Markers and Novel Therapeutic Targets for Breast Cancer

There is emerging evidence asserting the importance of orphan nuclear receptors (ONRs) in cancer initiation and progression. In breast cancer, there is a lot unknown about ONRs in terms of their expression profile and their transcriptional targets in the various stages of tumor progression. With the classification of breast tumors into distinct molecular subtypes, we assess ONR expression in the different breast cancer subtypes and with patient outcomes. Complementing this, we review evidence implicating ONR-dependent molecular pathways in breast cancer progression to identify candidate ONRs as potential prognostic markers and/or as therapeutic targets.

Distinct nuclear receptor expression in stroma adjacent to breast tumors

The interaction between breast tumor epithelial and stromal cells is vital for initial and recurrent tumor growth. While breast cancer-associated stromal cells provide a favorable environment for proliferation and metastasis, the molecular mechanisms contributing to this process are not fully understood. Nuclear receptors (NRs) are intracellular transcription factors that directly regulate gene expression. Little is known about the status of NRs in cancer-associated stroma. Nuclear Receptor Low-Density Taqman Arrays were used to compare the gene expression profiles of all 48 NR family members in a collection of primary cultured cancer-associated fibroblasts (CAFs) obtained from estrogen receptor (ER)α positive breast cancers (n = 9) and normal breast adipose fibroblasts (NAFs) (n = 7). Thirty-three of 48 NRs were expressed in both the groups, while 11 NRs were not detected in either. Three NRs (dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX-1); estrogen-related receptor beta (ERR-β); and RAR-related orphan receptor beta (ROR-β)) were only detected in NAFs, while one NR (liver receptor homolog-1 (LRH-1)) was unique to CAFs. Of the NRs co-expressed, four were significantly down-regulated in CAFs compared with NAFs (RAR-related orphan receptor-α (ROR-α); Thyroid hormone receptor-β (TR-β); vitamin D receptor (VDR); and peroxisome proliferator-activated receptor-γ (PPAR-γ)). Quantitative immunohistochemistry for LRH-1, TR-β, and PPAR-γ proteins in stromal fibroblasts from an independent panel of breast cancers (ER-positive (n = 15), ER-negative (n = 15), normal (n = 14)) positively correlated with mRNA expression profiles. The differentially expressed NRs identified in tumor stroma are key mediators in aromatase regulation and subsequent estrogen production. Our findings reveal a distinct pattern of NR expression that therefore fits with a sustained and increased local estrogen microenvironment in ER-positive tumors. NRs in CAFs may provide a new avenue for the development of intratumoral-targeted therapies in breast cancer.

Conditional overexpression of liver receptor homolog-1 in female mouse mammary epithelium results in altered mammary morphogenesis via the induction of TGF-β

Liver receptor homolog-1 (LRH-1) is an orphan nuclear receptor that belongs to the NR5A subgroup of nuclear receptors. LRH-1 induces key genes to regulate metabolic process, ovarian function, cancer cell proliferation, and steroidogenesis. In the breast, LRH-1 modulates and synergizes with endogenous estrogen signaling to promote breast cancer cell proliferation. We used small interfering RNA knockdown strategies to deplete LRH-1 in breast cancer cells and followed with microarray analysis to identify LRH-1-dependent mechanisms. We identified key genes involved in TGF-β signaling to be highly responsive to LRH-1 knockdown. This relationship was validated in 2 breast cancer cell lines overexpressing LRH-1 in vitro and in a novel transgenic mouse with targeted LRH-1 overexpression in mammary epithelial cells. Notably, TGF-β signaling was activated in LRH-1-overexpressing breast cancer cells and mouse mammary glands. Further analyses of mammary gross morphology revealed a significant reduction in mammary lateral budding after LRH-1 overexpression. These findings suggest that the altered mammary morphogenesis in LRH-1 transgenic animals is mediated via enhanced TGF-β expression. The regulation of TGF-β isoforms and SMAD2/3-mediated downstream signaling by LRH-1 also implicates a potential contribution of LRH-1 in breast cancer. Collectively, these data demonstrate that LRH-1 regulates TGF-β expression and downstream signaling in mouse mammary glands.

Liver receptor homologue-1 expression in ovarian epithelial and granulosa cell tumours

Granulosa cell tumours of the ovary (GCT) express aromatase and produce oestrogens. The ovarian-specific aromatase promoter (pII) is regulated by members of the group 5A nuclear receptor family, SF-1 and LRH-1. Since both SF-1 and LRH-1 are implicated in proliferation and cancer, we hypothesised that alteration in the expression of either or both receptors may be associated with GCT. We therefore determined the expression of LRH-1, SF-1 and aromatase in a cohort of GCT, mucinous and serous cystadenocarcinomas, and normal ovaries. LRH-1 mRNA was present at low level in normal ovary and serous cystadenocarcinoma, but was elevated approximately 30-fold in GCT, and 8-fold in mucinous cystadenocarcinoma, compared to normal ovary. LRH-1 protein expression was confirmed in GCT by immunohistochemistry. SF-1 mRNA was significantly lower that of LRH-1 in all samples and not significantly altered in GCT, compared to normal ovary. Aromatase mRNA was present at low level in normal ovary and serous and mucinous cystadenocarcinoma, and significantly elevated (18-fold) in GCT compared to normal ovary. Despite the coordinate over-expression of both LRH-1 and aromatase in GCT versus normal ovary, their levels did not correlate in individual patients; rather, aromatase expression correlated with that of SF-1. Finally, although both LRH-1 and SF-1 activated aromatase promoter activity in transient transfection studies, gel-shift and chromatin immunoprecipitation data indicated that SF-1, but not LRH-1, bound to the aromatase promoter. We conclude that SF-1 regulates aromatase expression in GCT; over-expression of LRH-1 suggests that this receptor may be involved in the pathogenesis of GCT by mechanisms other than the regulation of aromatase. Its role in this disease therefore warrants further investigation.

Therapeutic potential of Liver Receptor Homolog-1 modulators

Liver Receptor Homolog-1 (LRH-1; NR5A2) belongs to the orphan nuclear receptor superfamily, and plays vital roles in early development, cholesterol homeostasis, steroidogenesis and certain diseases, including cancer. It is expressed in embryonic stem cells, adult liver, intestine, pancreas and ovary. It binds to DNA as a monomer and is regulated by various ligand-dependent and -independent mechanisms. Recent work identified synthetic ligands for LRH-1; such compounds may yield useful therapeutics for a range of pathologic conditions associated with aberrant expression and activity of LRH-1.

The orphan nuclear receptor LRH-1 and ERα activate GREB1 expression to induce breast cancer cell proliferation

Background

Liver Receptor Homolog 1 (LRH-1, NR5A2) is an orphan nuclear receptor that is over-expressed in cancers in tissues such as the breast, colon and pancreas. LRH-1 plays important roles in embryonic development, steroidogenesis and cholesterol homeostasis. In tumor cells, LRH-1 induces proliferation and cell cycle progression. High LRH-1 expression is demonstrated in breast cancers, positively correlating with ERα status and aromatase activity. LRH-1 dependent cellular mechanisms in breast cancer epithelial cells are poorly defined. Hence in the present study we investigated the actions of LRH-1 in estrogen receptor α (ERα) positive breast cancer cells.

Results

The study aimed to investigate LRH-1 dependent mechanisms that promote breast cancer proliferation. We identified that LRH-1 regulated the expression of Growth Regulation by Estrogen in Breast Cancer 1 (GREB1) in MCF-7 and MDA-MB-231 cells. Over-expression of LRH-1 increased GREB1 mRNA levels while knockdown of LRH-1 reduced its expression. GREB1 is a well characterised ERα target gene, with three estrogen response elements (ERE) located on its promoter. Chromatin immunoprecipitation studies provided evidence of the co-localisation of LRH-1 and ERα at all three EREs. With electrophoretic mobility shift assays, we demonstrated direct binding of LRH-1 to EREs located on GREB1 and Trefoil Factor 1 (TFF1, pS2) promoters. LRH-1 and ERα co-operatively activated transcription of ERE luciferase reporter constructs suggesting an overlap in regulation of target genes in breast cancer cells. Over-expression of LRH-1 resulted in an increase in cell proliferation. This effect was more pronounced with estradiol treatment. In the presence of ICI 182,780, an ERα antagonist, LRH-1 still induced proliferation.

Conclusions

We conclude that in ER-positive breast cancer cells, LRH-1 promotes cell proliferation by enhancing ERα mediated transcription of target genes such as GREB-1. Collectively these findings indicate the importance of LRH-1 in the progression of hormone-dependent breast cancer and implicate LRH-1 as a potential avenue for drug development.

Amino acid transport system L activity in developing mouse ovarian follicles

BACKGROUND

Little is known about metabolic processes in the developing ovarian follicle. Using mouse ovarian follicles, we investigated uptake of L-leucine by follicles at varying stages of maturity in the presence of insulin-like growth factor (IGF)-1. METHODS Mouse ovarian follicles were cultured in vitro for 5 days in increasing concentrations of IGF-1, and follicle diameter and atresia measured as endpoints for growth. Uptake of (3)H-leucine was measured in follicles at different stages of development. In optimal IGF-1-mediated growth conditions, competitive inhibition of (3)H-leucine uptake by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), a non-metabolizable substrate analogue of L-leucine, was performed to demonstrate specificity of influx, via system L transporters. To test whether uptake rates were dependent on intracellular amino acid availability, follicles from in vitro cultures were pre-treated with L-phenylalanine prior to (3)H-leucine uptake.

RESULTS

Follicle development (P< 0.001) and survival (P< 0.001) increased with IGF-1 treatment. As pre-antral follicles progressed to late antral stage, we observed an increase in L-leucine uptake, which was reduced in pre-ovulatory follicles. BCH decreased L-leucine uptake rates in early antral (P< 0.05), antral (P< 0.001) and pre-ovulatory follicles (P< 0.01). L-leucine influx increased in follicles preloaded with phenylalanine (trans-stimulation). In follicles lacking free intracellular amino acids (zero-trans suppression), uptake rate was reduced (P< 0.05).

CONCLUSIONS

These results demonstrate, for the first time, evidence of specific system L amino acid transport in intact, mouse ovarian follicles and profile L-leucine uptake during folliculogenesis. A better understanding of ovarian follicle metabolic pathways is necessary for improved in vitro maturation as well as determining the impact of altered metabolism on fertility.

Tissue-specific regulation of aromatase promoter II by the orphan nuclear receptor LRH-1 in breast adipose stromal fibroblasts

In postmenopausal breast cancers, the increase in aromatase expression observed in tumour associated adipose stromal cells is mediated via the upregulation of promoter II (PII) transcription. Factors such as PGE₂ which are secreted from breast carcinomas induce PII expression. The orphan nuclear receptor LRH-1/NR5A2 is one of the critical downstream transcriptional mediators of this effect. The aim of the current study was to determine whether LRH-1 could bind directly to PII and whether the suppression of LRH-1 expression could inhibit aromatase expression in human adipose stromal fibroblasts. Chromatin immunoprecipitation demonstrated endogenous LRH-1 occupancy on PII under basal conditions and with treatment with forskolin and phorbol 12-myristate 13-acetate (PMA). To assess the impact of LRH-1 knockdown on FSK/PMA mediated PII expression, cells were transfected with shRNA targeted against LRH-1 (shLRH-1) and treated with forskolin and PMA. A decrease in LRH-1, PII and total aromatase mRNA transcripts was observed in shLRH-1 transfected cells compared to controls under basal and treatment conditions. The results of this study support the hypothesis that suppression of LRH-1 may potentially be beneficial in the tissue specific regulation of aromatase expression in post menopausal breast cancer.

The orphan nuclear receptor LRH-1 promotes breast cancer motility and invasion

The orphan nuclear receptor liver receptor homologue-1 (LRH-1) has roles in the development, cholesterol and bile acid homeostasis, and steroidogenesis. It also enhances proliferation and cell cycle progression of cancer cells. In breast cancer, LRH-1 expression is associated with invasive breast cancer; positively correlates with ERα status and aromatase activity; and promotes oestrogen-dependent cell proliferation. However, the mechanism of action of LRH-1 in breast cancer epithelial cells is still not clear. By silencing or over-expressing LRH-1 in ER-positive MCF-7 and ER-negative MDA-MB-231 breast cancer cells, we have demonstrated that LRH-1 promotes motility and cell invasiveness. Similar effects were observed in the non-tumourigenic mammary epithelial cell line, MCF-10A. Remodelling of the actin cytoskeleton and E-cadherin cleavage was observed with LRH-1 over-expression, contributing to increased migratory and invasive properties. Additionally, in LRH-1 over-expressing cells, the truncation of the 120 kDa E-cadherin to the inactive 97 kDa form was observed. These post-translational modifications in E-cadherin may be associated with LRH-1-dependent changes to matrix metalloproteinase 9 expression. These findings suggest a new role of LRH-1 in promoting migration and invasion in breast cancer, independent of oestrogen sensitivity. Therefore, LRH-1 may represent a new target for breast cancer therapeutics.

Inhibin and premature ovarian failure

BACKGROUND

Elucidation of the causes of premature ovarian failure (POF) is difficult due to the heterogeneity of the condition. Inhibin is a potential candidate gene for POF based on its dual actions on FSH secretion by the pituitary and gametogenesis in the gonads. A missense mutation in the inhibin alpha subunit gene (INHA G769A) is associated with POF in several populations. However, there is phenotypic heterogeneity in INHA G769A mutation carriers.

METHODS

Relevant studies were identified by searching PubMed and mutational frequencies combined for meta-analysis.

RESULTS

Meta-analysis of published studies revealed a risk difference of 0.04 (-0.030 to 0.11). The occurrence of asymptomatic carriers in populations suggests incomplete penetrance and/or a multi-genetic cause of POF. We propose that a decline in inhibin bioactivity caused by the mutation could increase FSH levels; and in a susceptible individual, the heightened sensitivity to gonadotrophins causes POF. Impaired paracrine effects of inhibin could impact folliculogenesis due to reduced antagonism of activin, bone morphogenetic protein 15 and growth differentiation factor 9. Functional studies of this mutation indicate normal production of dimeric inhibin A and B and impaired bioactivity of inhibin B.

CONCLUSIONS

The identification of an autosomal mutation in the inhibin alpha subunit gene that is significantly linked to POF in certain ethnic populations highlights the role of inhibin in the regulation of ovarian biology and fertility. Although the reduction of inhibin B bioactivity by the INHA G769A mutation is clearly not the only cause, evidence suggests that this change may serve as a susceptibility factor, increasing the likelihood of POF.

Aromatase expression is increased in BRCA1 mutation carriers

BACKGROUND

Until recently, the molecular mechanisms explaining increased incidence of ovarian and breast cancers in carriers of BRCA1 gene mutations had not been clearly understood. Of significance is the finding that BRCA1 negatively regulates aromatase expression in vitro. Our objective was to characterise aromatase gene (CYP19A1) and its promoter expression in breast adipose and ovarian tissue in BRCA1 mutation carriers and unaffected controls.

METHODS

We measured aromatase transcripts, total and promoter-specific (PII, PI.3, PI.4) in prophylactic oophorectomy or mastectomy, therapeutic mastectomy, ovarian and breast tissue from unaffected women.

RESULTS

We demonstrate that the lack of functional BRCA1 protein correlates to higher aromatase levels in 85% of BRCA1 mutation carriers. This increase is mediated by aberrant transcriptional regulation of aromatase; in breast adipose by increases in promoter II/I.3 and I.4-specific transcripts; and in the ovary with elevation in promoter I.3 and II-specific transcripts.

CONCLUSION

Understanding the link between BRCA1 and aromatase is significant in terms of understanding why carcinogenesis is restricted to estrogen-producing tissues in BRCA1 mutation carriers.

Laser capture microdissection and cDNA array analysis of endometrium identify CCL16 and CCL21 as epithelial-derived inflammatory mediators associated with endometriosis

BACKGROUND

Understanding the pathophysiology of chemokine secretion in endometriosis may offer a novel area of therapeutic intervention. This study aimed to identify chemokines differentially expressed in epithelial glands in eutopic endometrium from normal women and those with endometriosis, and to establish the expression profiles of key chemokines in endometriotic lesions.

METHODS

Laser capture microdissection isolated epithelial glands from endometrial eutopic tissue from women with and without endometriosis in the mid-secretory phase of their menstrual cycles. Gene profiling of the excised glands used a human chemokine and receptor cDNA array. Selected chemokines were further examined using real-time PCR and immunohistochemistry.

RESULTS

22 chemokine/receptor genes were upregulated and two downregulated in pooled endometrial epithelium of women with endometriosis compared with controls. CCL16 and CCL21 mRNA was confirmed as elevated in some women with endometriosis compared to controls on individual samples. Immunoreactive CCL16 and CCL21 were predominantly confined to glands in eutopic and ectopic endometrium: leukocytes also stained. Immunoreactive CCL16 was overall higher in glands in ectopic vs. eutopic endometrium from the same woman (P < 0.05). Staining for CCL16 and CCL21 was highly correlated in individual tissues.

CONCLUSION

This study provides novel candidate molecules and suggests a potential local role for CCL16 and CCL21 as mediators contributing to the inflammatory events associated with endometriosis.

Mutational analysis of BMP15 and GDF9 as candidate genes for premature ovarian failure

Mutational screening of the bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) genes in a population with premature ovarian failure (POF) identified no new mutations. However, three single nucleotide polymorphisms in the BMP15 gene, two in the 5' untranslated region (31T>G and 71C>G) and another in exon 1 (387G>A), were found to be common in both POF and control groups.

INHA promoter polymorphisms are associated with premature ovarian failure

Inhibin is an important glycoprotein that is involved in folliculogenesis. INHA, the gene encoding the inhibin alpha subunit, was recently proposed as a candidate for premature ovarian failure (POF), a syndrome that leads to the cessation of ovarian function under the age of 40 years. 70 POF patients and 70 controls were screened for the previously identified INHA -16C>T transition mutation. The T allele was found in 31/70 (44.3%) of controls, but only 18/70 (25.7%) of POF patients. This result indicates that the T allele is significantly underrepresented in the POF patient population (Fisher's exact test, two-tail: P = 0.033). Sequence analysis of the INHA promoter in 50 POF patients and 50 controls identified a highly polymorphic imperfect TG repeat at approximately -300 bp, that consisted of four common haplotypes (A, B, C and D). The -16T allele is linked to the shortest repeat haplotype (haplotype C). Despite the association between haplotype C and POF, no significant difference was found between the promoter activity of a luciferase reporter construct containing haplotype C, and most of the other haplotypes tested. Interestingly, haplotype B failed to show any promoter activity. We conclude that the inheritance of specific INHA promoter haplotypes predispose to the development of premature ovarian failure.

Identification of novel mutations in FOXL2 associated with premature ovarian failure

Premature ovarian failure (POF) affects approximately 1% of women and is known to be caused by sex chromosome abnormalities, iatrogenic agents and autoimmune diseases, but in the majority of cases the cause is unknown. However, several families have been identified as having an inherited predisposition to POF, suggesting a genetic component to the condition in these cases. The FOXL2 gene of 70 POF patients from New Zealand and Slovenia was screened for mutations. In a Slovenian POF patient, a novel 30 bp deletion was identified that was predicted to remove 10 out of 14 alanines (A221_A230del), from the polyalanine tract downstream of the winged helix/forkhead domain of the FOXL2 protein. A novel single nucleotide substitution, 772(1009)T>A, which is predicted to change amino acid 258 from tyrosine to asparagine (Y258N), was identified in a New Zealand POF patient. Neither mutation was identified in 200 normal control chromosomes from 100 control samples. Three previously unreported single nucleotide substitutions, considered to be non-functional polymorphisms, were also identified.

Inhibin: a candidate gene for premature ovarian failure

Premature ovarian failure (POF) occurs in 1% of all women, and in 0.1% of women under the age of 30 years. The mechanisms that give rise to POF are largely unknown. Inhibin has a role in regulating the pituitary secretion of FSH, and is therefore a potential candidate gene for ovarian failure. Using single-stranded conformation polymorphism (SSCP) and DNA sequencing, DNA samples were screened from 43 women with POF for mutations in the three inhibin genes. Two variants were found: a 1032C-->T transition in the INHssA gene in one patient, and a 769G-->A transition in the INHalpha gene in three patients. The INHssA variant appears to be a polymorphism, as there was no change in the amino acid sequence of the gene product. The INHalpha variant resulted in a non-conservative amino acid change, with a substitution from alanine to threonine. This alanine is highly conserved across species, and has the potential to affect receptor binding. The INHalpha variant is significantly associated with POF (3/43 patients; 7%) compared with control samples (1/150 normal controls; 0.7%) (Fisher's exact test, P < 0.035). Further analysis of the inhibin gene in POF patients and matched controls will determine its role in the aetiology of POF.