Andrew Stone

Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia

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Publications (9)63.64 Total impact

  • Epigenomics 12/2013; 5(6):595-598. · 2.43 Impact Factor
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    ABSTRACT: Acquired resistance to the anti-estrogen tamoxifen remains a significant challenge in breast cancer management. In this study we used an integrative approach to characterize global protein expression and tyrosine-phosphorylation events in tamoxifen-resistant MCF7 breast cancer cells (TamR) compared with parental controls. Quantitative mass-spectrometry and computational approaches were combined to identify perturbed signalling networks, and candidate regulatory proteins were functionally interrogated by siRNA-mediated knockdown. Network analysis revealed that cellular metabolism was perturbed in TamR cells, together with pathways enriched for proteins associated with growth-factor, cell-cell and cell-matrix-initiated signalling. Consistent with known roles for Ras/MAPK and PI3-kinase signalling in tamoxifen resistance, tyrosine phosphorylated MAPK1, SHC1 and PIK3R2 were elevated in TamR cells. Phosphorylation of the tyrosine kinase Yes and expression of the actin-binding protein MARCKS were elevated 2- and 8-fold in TamR cells respectively, and were selected for further analysis. Knockdown of either protein in TamR cells had no effect on anti-estrogen-sensitivity, but significantly decreased cell motility. MARCKS expression was significantly higher in breast cancer cell lines than normal mammary epithelial cells and in ER-negative versus ER-positive breast cancer cell lines. In primary breast cancers, cytoplasmic MARCKS staining was significantly higher in basal-like and HER2 cancers than in luminal cancers, and was independently predictive of poor survival in multivariate analyses of the whole cohort (p<0.0001) and in ER-positive patients (p=0.0005). These findings provide network-level insights into the molecular alterations associated with the tamoxifen-resistant phenotype and identify MARCKS as a potential biomarker of therapeutic responsiveness that may assist stratification of patients for optimal therapy. This article is protected by copyright. All rights reserved.
    FEBS Journal 07/2013; · 4.25 Impact Factor
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    ABSTRACT: Overexpression of the anti-apoptotic factor, BCL-2, is a frequent feature of malignant disease and is commonly associated with poor prognosis and resistance to conventional chemotherapy. In breast cancer, however, high BCL-2 expression is associated with favourable prognosis, estrogen receptor (ER) positivity and low tumour grade; whilst low expression is included in several molecular signatures associated with resistance to endocrine therapy. In the present study, we correlate BCL-2 expression and DNA methylation profiles in human breast cancer and in multiple cell models of acquired endocrine-resistance to determine whether BCL-2 hypermethylation could provide a useful biomarker of response to cytotoxic therapy. In human disease, diminished expression of BCL-2 was associated with hypermethylation of the second exon, in a region that overlapped a CpG island and an ER-binding site. Hypermethylation of this region, which occurred in 10% of primary tumours, provided a stronger predictor of patient survival (p=0.019) when compared to gene expression (n=522). In multiple cell-models of acquired endocrine-resistance, BCL-2 expression was significantly reduced in parallel with increased DNA methylation of the exon 2 region. The reduction of BCL-2 expression in endocrine-resistant cells lowered their apoptotic threshold to anti-mitotic agents: nocodazole, paclitaxel and the PLK1 inhibitor, BI2536. This phenomenon could be reversed with ectopic expression of BCL-2, and rescued with the BCL-2 inhibitor, ABT-737. Collectively, these data imply that BCL-2 hypermethylation provides a robust biomarker of response to current and next generation cytotoxic agents in endocrine-resistant breast cancer, which may prove beneficial in directing therapeutic strategy for patients with non-resectable, metastatic disease.
    Molecular Cancer Therapeutics 07/2013; · 5.60 Impact Factor
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    ABSTRACT: We have previously shown that during pregnancy the E-twenty-six (ETS) transcription factor ELF5 directs the differentiation of mammary progenitor cells toward the estrogen receptor (ER)-negative and milk producing cell lineage, raising the possibility that ELF5 may suppress the estrogen sensitivity of breast cancers. To test this we constructed inducible models of ELF5 expression in ER positive luminal breast cancer cells and interrogated them using transcript profiling and chromatin immunoprecipitation of DNA followed by DNA sequencing (ChIP-Seq). ELF5 suppressed ER and FOXA1 expression and broadly suppressed ER-driven patterns of gene expression including sets of genes distinguishing the luminal molecular subtype. Direct transcriptional targets of ELF5, which included FOXA1, EGFR, and MYC, accurately classified a large cohort of breast cancers into their intrinsic molecular subtypes, predicted ER status with high precision, and defined groups with differential prognosis. Knockdown of ELF5 in basal breast cancer cell lines suppressed basal patterns of gene expression and produced a shift in molecular subtype toward the claudin-low and normal-like groups. Luminal breast cancer cells that acquired resistance to the antiestrogen Tamoxifen showed greatly elevated levels of ELF5 and its transcriptional signature, and became dependent on ELF5 for proliferation, compared to the parental cells. Thus ELF5 provides a key transcriptional determinant of breast cancer molecular subtype by suppression of estrogen sensitivity in luminal breast cancer cells and promotion of basal characteristics in basal breast cancer cells, an action that may be utilised to acquire antiestrogen resistance.
    PLoS Biology 12/2012; 10(12):e1001461. · 12.69 Impact Factor
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    ABSTRACT: Cyclin E2, but not cyclin E1, is included in several gene signatures that predict disease progression in either tamoxifen-resistant or metastatic breast cancer. We therefore examined the role of cyclin E2 in antiestrogen resistance in vitro and its potential for therapeutic targeting through cyclin-dependent kinase (CDK) inhibition. High expression of CCNE2, but not CCNE1, was characteristic of the luminal B and HER2 subtypes of breast cancer and was strongly predictive of shorter distant metastasis-free survival following endocrine therapy. After antiestrogen treatment of MCF-7 breast cancer cells, cyclin E2 mRNA and protein were downregulated and cyclin E2-CDK2 activity decreased. However, this regulation was lost in tamoxifen-resistant (MCF-7 TAMR) cells, which overexpressed cyclin E2. Expression of either cyclin E1 or E2 in T-47D breast cancer cells conferred acute antiestrogen resistance, suggesting that cyclin E overexpression contributes to the antiestrogen resistance of tamoxifen-resistant cells. Ectopic expression of cyclin E1 or E2 also reduced sensitivity to CDK4, but not CDK2, inhibition. Proliferation of tamoxifen-resistant cells was inhibited by RNAi-mediated knockdown of cyclin E1, cyclin E2, or CDK2. Furthermore, CDK2 inhibition of E-cyclin overexpressing cells and tamoxifen-resistant cells restored sensitivity to tamoxifen or CDK4 inhibition. Cyclin E2 overexpression is therefore a potential mechanism of resistance to both endocrine therapy and CDK4 inhibition. CDK2 inhibitors hold promise as a component of combination therapies in endocrine-resistant disease as they effectively inhibit cyclin E1 and E2 overexpressing cells and enhance the efficacy of other therapeutics.
    Molecular Cancer Therapeutics 05/2012; 11(7):1488-99. · 5.60 Impact Factor
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    ABSTRACT: The cell cycle is a tightly regulated series of events that governs cell replication and division. Deregulation of cell cycle kinases, e.g., cyclin-dependent kinases (CDKs), can initiate a hyper-proliferative cell phenotype and cause genomic instability, thus facilitating malignant transformation. Pharmacological agents targeting CDKs have been developed as potential anti-cancer agents for over 20 years, evolving from early pan-CDK inhibitors to second-generation inhibitors with much greater specificity and selectivity. Despite these advances in drug design and highly successful preclinical investigations, CDK inhibitors have yet to achieve their expected efficacy in clinical trials. In addition, inhibitors of other cell cycle kinases are currently progressing through clinical trials. Recent biochemical and genetic studies might be used to improve the effectiveness of cell cycle kinase inhibitors as anti-cancer agents through better drug design, therapeutic combinations, and patient selection.
    Critical reviews in oncogenesis 01/2012; 17(2):175-98.
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    ABSTRACT: In the present study, we have taken the novel approach of using an in vitro model representative of tamoxifen-withdrawal subsequent to clinical relapse to achieve a greater understanding of the mechanisms that serve to maintain the resistant-cell phenotype, independent of any agonistic impact of tamoxifen, to identify potential novel therapeutic approaches for this disease state. Following tamoxifen withdrawal, tamoxifen-resistant MCF-7 cells conserved both drug resistance and an increased basal rate of proliferation in an oestrogen deprived environment, despite reduced epidermal growth-factor receptor expression and reduced sensitivity to gefitinib challenge. Although tamoxifen-withdrawn cells retained ER expression, a sub-set of ER-responsive genes, including pS2 and progesterone receptor (PgR), were down-regulated by promoter DNA methylation, as confirmed by clonal bisulphite sequencing experiments. Following promoter demethylation with 5-Azacytidine (5-Aza), the co-addition of oestradiol (E2) restored gene expression in these cells. In addition, 5-Aza/E2 co-treatment induced a significant anti-proliferative effect in the tamoxifen-withdrawn cells, in-contrast to either agent used alone. Microarray analysis was undertaken to identify genes specifically up regulated by this co-treatment. Several anti-proliferative gene candidates were identified and their promoters were confirmed as more heavily methylated in the tamoxifen resistant vs sensitive cells. One such gene candidate, growth differentiation factor 15 (GDF15), was carried forward for functional analysis. The addition of 5-Aza/E2 was sufficient to de-methylate and activate GDF15 expression in the tamoxifen resistant cell-lines, whilst in parallel, treatment with recombinant GDF15 protein decreased cell survival. These data provide evidence to support a novel concept that long-term tamoxifen exposure induces epigenetic silencing of a cohort of oestrogen-responsive genes whose function is associated with negative proliferation control. Furthermore, reactivation of such genes using epigenetic drugs could provide a potential therapeutic avenue for the management of tamoxifen-resistant breast cancer.
    PLoS ONE 01/2012; 7(7):e40466. · 3.53 Impact Factor
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    ABSTRACT: Cyclin D1, and to a lesser extent the other D-type cyclins, is frequently deregulated in cancer and is a biomarker of cancer phenotype and disease progression. The ability of these cyclins to activate the cyclin-dependent kinases (CDKs) CDK4 and CDK6 is the most extensively documented mechanism for their oncogenic actions and provides an attractive therapeutic target. Is this an effective means of targeting the cyclin D oncogenes, and how might the patient subgroups that are most likely to benefit be identified?
    Nature Reviews Cancer 01/2011; 11(8):558-72. · 29.54 Impact Factor
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    ABSTRACT: Antihormones are of substantial benefit in treating oestrogen receptor-α positive (ER+) breast cancer. However, their anti-tumour effect is limited by emergence of resistance. Our in vitro studies are highlighting a new underlying concept: that antihormones are not passive bystanders but alongside growth inhibitory effects promote adverse compensatory mechanisms within tumour cells. These mechanisms involve drug-induction of signalling elements normally suppressed by oestrogen (E2)-occupied E R˜ While best exemplified by the tyrosine kinases epidermal growth factor receptor and HER2, microarrays reveal the true diversity of the induced signalling kinases, where their potential to promote resistance is exacerbated under paracrine conditions. Such drug-induced events permit initial ER+ breast cancer cell survival, allow development and maintenance of resistance, and also promote gain of invasiveness under conditions of poor intercellular contact. In addition, prolonged antihormonal exposure is associated with epigenetic silencing of classical E2-induced tumour suppressors, an event which further contributes to resistance. Based on proof of principle experiments targeting induced signalling events alongside antihormones or restoring E2-induced suppressor genes through DNA methylation inhibitor-containing strategies, it is our belief that continued deciphering of these mechanisms will reveal improved treatments for breast cancer.
    01/2009: pages 63-84;