Josefine Bostner

Amplification of CCND1 and PAK1 as predictors of recurrence and tamoxifen resistance in postmenopausal breast cancer

The 11q13 region is amplified in approximately 15% of all breast tumors. Situated in this region are the cyclin D1 gene (CCND1) and the p-21-activated kinase 1 (PAK1) gene. Both genes encode proteins shown to activate the estrogen receptor (ER), leading to transcription of CCND1 and other ER-responsive genes. Here, we investigate the prognostic and treatment predictive role of CCND1 and PAK1 gene amplification in postmenopausal breast cancer patients randomized to tamoxifen treatment or no adjuvant treatment. Amplification of CCND1 and PAK1, assessed by real-time PCR, was observed in 12.5 and 9.3%, respectively. Amplification of PAK1 was seen in 37% of the CCND1-amplified tumors, indicating coamplification (P<0.001). In ER-positive patients, amplification of at least one of the genes indicated a reduced recurrence-free survival (P=0.025). When response to tamoxifen treatment was analysed, patients with PAK1 amplification showed decreased benefit from the drug (ER+; relative risk ratio (RR)=1.62; 95% confidence interval (CI), 0.47–5.55) compared to patients without amplification (ER+; RR=0.53; 95% CI, 0.32–0.88). This was not evident for CCND1 amplification. We show that PAK1 may be a predictor of tamoxifen resistance and furthermore, we do not discard PAK1 as a potential candidate oncogene in the 11q13 amplicon. In addition, we show that high pak1 protein levels may predict tamoxifen insensitivity.

Estrogen Receptor-alpha Phosphorylation at Serine 305, Nuclear p21-Activated Kinase 1 Expression, and Response to Tamoxifen in Postmenopausal Breast Cancer

Purpose: In vitro, p21-activated kinase 1 (Pak1) phosphorylates the serine 305 residue of the estrogen receptor α (ERα) and influences the response of breast cancer cells to tamoxifen. We investigated the influence of Pak1 and pERαser305 on breast cancer prognosis and results of tamoxifen therapy. Experimental Design: We examined Pak1 and pERαser305 protein by immunohistochemistry in a series of 912 tumors from node-negative breast cancer patients randomized to tamoxifen or no adjuvant endocrine treatment. Results: Cytoplasmic Pak1 correlated to large tumors and ER negativity, whereas nuclear Pak1 and pERαser305 correlated to small tumors and ER positivity. Nuclear expression of Pak1 and pERαser305 predicted reduced response to tamoxifen in patients with ERα-positive tumors (tamoxifen versus no tamoxifen: hazard ratio (HR), 1.33; 95% confidence interval (95% CI), 0.42-4.2; P = 0.63), whereas patients lacking this combination benefitted significantly from tamoxifen (HR, 0.43; 95% CI, 0.30-0.62; P < 0.0001). Similar nonsignificant trends were detected in analyses of the proteins separately. Pak1 in the cytoplasm was an independent prognostic marker, indicating increased recurrence rate (HR, 1.79; 95% CI, 1.17-2.74; P = 0.0068) and breast cancer mortality (HR, 1.98; 95% CI, 1.14-3.46; P = 0.016) for patients randomized to no adjuvant treatment. Conclusion: Our results suggest that patients with tumors expressing Pak1 and pERαser305 in combination are a group in which tamoxifen treatment is insufficient. In addition, the pathway may be of interest as a drug target in breast cancer. Furthermore, the findings support previous studies showing that Pak1 has differential roles in the cytoplasm and the nucleus. Clin Cancer Res; 16(5); 1624–33

High-Resolution Genomic Analysis of the 11q13 Amplicon in Breast Cancers Identifies Synergy with 8p12 Amplification, Involving the mTOR Targets S6K2 and 4EBP1

The chromosomal region 11q13 is amplified in 15–20% of breast cancers; an event not only associated with estrogen receptor (ER) expression but also implicated in resistance to endocrine therapy. Coamplifications of the 11q13 and 8p12 regions are common, suggesting synergy between the amplicons. The aim was to identify candidate oncogenes in the 11q13 region based on recurrent amplification patterns and correlations to mRNA expression levels. Furthermore, the 11q13/8p12 coamplification and its prognostic value, was evaluated at the DNA and the mRNA levels. Affymetrix 250K NspI arrays were used for whole‐genome screening of DNA copy number changes in 29 breast tumors. To identify amplicon cores at 11q13 and 8p12, genomic identification of significant targets in cancer (GISTIC) was applied. The mRNA expression levels of candidate oncogenes in the amplicons [RAD9A, RPS6KB2 (S6K2), CCND1, FGF19, FGF4, FGF3, PAK1, GAB2 (11q13); EIF4EBP1 (4EBP1), PPAPDC1B, and FGFR1 (8p12)] were evaluated using real‐time PCR. Resulting data revealed three main amplification cores at 11q13. ER expression was associated with the central 11q13 amplification core, encompassing CCND1, whereas 8p12 amplification/gene expression correlated to S6K2 in a proximal 11q13 core. Amplification of 8p12 and high expression of 4EBP1 or FGFR1 was associated with a poor outcome in the group. In conclusion, single nucleotide polymorphism arrays have enabled mapping of the 11q13 amplicon in breast tumors with high resolution. A proximal 11q13 core including S6K2 was identified as involved in the coamplification/coexpression with 8p12, suggesting synergy between the mTOR targets S6K2 and 4EBP1 in breast cancer development and progression.

The mTOR effectors 4EBP1 and S6K2 are frequently coexpressed, and associated with a poor prognosis and endocrine resistance in breast cancer: a retrospective study including patients from the randomised Stockholm tamoxifen trials

IntroductionmTOR and its downstream effectors the 4E-binding protein 1 (4EBP1) and the p70 ribosomal S6 kinases (S6K1 and S6K2) are frequently upregulated in breast cancer, and assumed to be driving forces in tumourigenesis, in close connection with oestrogen receptor (ER) networks. Here, we investigated these factors as clinical markers in five different cohorts of breast cancer patients.MethodsThe prognostic significance of 4EBP1, S6K1 and S6K2 mRNA expression was assessed with real-time PCR in 93 tumours from the treatment randomised Stockholm trials, encompassing postmenopausal patients enrolled between 1976 and 1990. Three publicly available breast cancer cohorts were used to confirm the results. Furthermore, the predictive values of 4EBP1 and p4EBP1_S65 protein expression for both prognosis and endocrine treatment benefit were assessed by immunohistochemical analysis of 912 node-negative breast cancers from the Stockholm trials.ResultsS6K2 and 4EBP1 mRNA expression levels showed significant correlation and were associated with a poor outcome in all cohorts investigated. 4EBP1 protein was confirmed as an independent prognostic factor, especially in progesterone receptor (PgR)-expressing cancers. 4EBP1 protein expression was also associated with a poor response to endocrine treatment in the ER/PgR positive group. Cross-talk to genomic as well as non-genomic ER/PgR signalling may be involved and the results further support a combination of ER and mTOR signalling targeted therapies.ConclusionThis study suggests S6K2 and 4EBP1 as important factors for breast tumourigenesis, interplaying with hormone receptor signalling. We propose S6K2 and 4EBP1 as new potential clinical markers for prognosis and endocrine therapy response in breast cancer.

VAV3 mediates resistance to breast cancer endocrine therapy

IntroductionEndocrine therapies targeting cell proliferation and survival mediated by estrogen receptor α (ERα) are among the most effective systemic treatments for ERα-positive breast cancer. However, most tumors initially responsive to these therapies acquire resistance through mechanisms that involve ERα transcriptional regulatory plasticity. Herein we identify VAV3 as a critical component in this process.MethodsA cell-based chemical compound screen was carried out to identify therapeutic strategies against resistance to endocrine therapy. Binding to ERα was evaluated by molecular docking analyses, an agonist fluoligand assay and short hairpin (sh)RNA–mediated protein depletion. Microarray analyses were performed to identify altered gene expression. Western blot analysis of signaling and proliferation markers, and shRNA-mediated protein depletion in viability and clonogenic assays, were performed to delineate the role of VAV3. Genetic variation in VAV3 was assessed for association with the response to tamoxifen. Immunohistochemical analyses of VAV3 were carried out to determine its association with therapeutic response and different tumor markers. An analysis of gene expression association with drug sensitivity was carried out to identify a potential therapeutic approach based on differential VAV3 expression.ResultsThe compound YC-1 was found to comparatively reduce the viability of cell models of acquired resistance. This effect was probably not due to activation of its canonical target (soluble guanylyl cyclase), but instead was likely a result of binding to ERα. VAV3 was selectively reduced upon exposure to YC-1 or ERα depletion, and, accordingly, VAV3 depletion comparatively reduced the viability of cell models of acquired resistance. In the clinical scenario, germline variation in VAV3 was associated with the response to tamoxifen in Japanese breast cancer patients (rs10494071 combined P value = 8.4 × 10−4). The allele association combined with gene expression analyses indicated that low VAV3 expression predicts better clinical outcome. Conversely, high nuclear VAV3 expression in tumor cells was associated with poorer endocrine therapy response. Based on VAV3 expression levels and the response to erlotinib in cancer cell lines, targeting EGFR signaling may be a promising therapeutic strategy.ConclusionsThis study proposes VAV3 as a biomarker and a rationale for its use as a signaling target to prevent and/or overcome resistance to endocrine therapy in breast cancer.

ERRα is a marker of tamoxifen response and survival in triple-negative breast cancer.

Purpose: Estrogen-related receptor alpha (ERRα) signaling has recently been implicated in breast cancer. We investigated the clinical value of ERRα in randomized cohorts of tamoxifen-treated and adjuvant-untreated patients. Experimental Design: Cox proportional hazards regression was used to evaluate the significance of associations between ERRα gene expression levels and patient DMFS in a previously published microarray dataset representing 2,000 breast tumor cases derived from multiple medical centers worldwide. The 912 tumors used for immunostaining were from a tamoxifen-randomized primary breast cancer trial conducted in Stockholm, Sweden, during 1976–1990. Mouse model was used to study the effect of tamoxifen treatment on lung colonization of MDA-MB-231 control cells and MDA-MB-231 cells with stable knockdown of ERRα. The phenotypic effects associated with ERRα modulation were studied using immunoblotting analyses and wound-healing assay. Results: We found that in ER-negative and triple-negative breast cancer (TNBC) adjuvant-untreated patients, ERRα expression indicated worse prognosis and correlated with poor outcome predictors. However, in tamoxifen-treated patients, an improved outcome was observed with high ERRα gene and protein expression. Reduced ERRα expression was oncogenic in the presence of tamoxifen, measured by in vitro proliferation and migration assays and in vivo metastasis studies. Conclusions: Taken together, these data show that ERRα expression predicts response to tamoxifen treatment, and ERRα could be a biomarker of tamoxifen sensitivity and a prognostic factor in TNBC. Clin Cancer Res; 22(6); 1421–31. ©2015 AACR.

S6 kinase signaling: tamoxifen response and prognostic indication in two breast cancer cohorts

Detection of signals in the mammalian target of rapamycin (mTOR) and the estrogen receptor (ER) pathways may be a future clinical tool for the prediction of adjuvant treatment response in primary breast cancer. Using immunohistological staining, we investigated the value of the mTOR targets p70-S6 kinase (S6K) 1 and 2 as biomarkers for tamoxifen benefit in two independent clinical trials comparing adjuvant tamoxifen with no tamoxifen or 5 years versus 2 years of tamoxifen treatment. In addition, the prognostic value of the S6Ks was evaluated. We found that S6K1 correlated with proliferation, HER2 status, and cytoplasmic AKT activity, whereas high protein expression levels of S6K2 and phosphorylated (p) S6K were more common in ER-positive, and low-proliferative tumors with pAKT-s473 localized to the nucelus. Nuclear accumulation of S6K1 was indicative of a reduced tamoxifen effect (hazard ratio (HR): 1.07, 95% CI: 0.53-2.81, P=0.84), compared with a significant benefit from tamoxifen treatment in patients without tumor S6K1 nuclear accumulation (HR: 0.42, 95% CI: 0.29-0.62, P<0.00001). Also S6K1 and S6K2 activation, indicated by pS6K-t389 expression, was associated with low benefit from tamoxifen (HR: 0.97, 95% CI: 0.50-1.87, P=0.92). In addition, high protein expression of S6K1, independent of localization, predicted worse prognosis in a multivariate analysis, P=0.00041 (cytoplasm), P=0.016 (nucleus). In conclusion, the mTOR-activated kinases S6K1 and S6K2 interfere with proliferation and response to tamoxifen. Monitoring their activity and intracellular localization may provide biomarkers for breast cancer treatment, allowing the identification of a group of patients less likely to benefit from tamoxifen and thus in need of an alternative or additional targeted treatment.

Revealing Different Roles of the mTOR-Targets S6K1 and S6K2 in Breast Cancer by Expression Profiling and Structural Analysis

Background The AKT/mTORC1/S6K pathway is frequently overstimulated in breast cancer, constituting a promising therapeutic target. The benefit from mTOR inhibitors varies, likely as a consequence of tumour heterogeneity, and upregulation of several compensatory feed-back mechanisms. The mTORC1 downstream effectors S6K1, S6K2, and 4EBP1 are amplified and overexpressed in breast cancer, associated with a poor outcome and divergent endocrine treatment benefit. S6K1 and S6K2 share high sequence homology, but evidence of partly distinct biological functions is emerging. The aim of this work was to explore possible different roles and treatment target potentials of S6K1 and S6K2 in breast cancer. Materials and methods Whole-genome expression profiles were compared for breast tumours expressing high levels of S6K1, S6K2 or 4EBP1, using public datasets, as well as after in vitro siRNA downregulation of S6K1 and/or S6K2 in ZR751 breast cancer cells. In silico homology modelling of the S6K2 kinase domain was used to evaluate its possible structural divergences to S6K1. Results Genome expression profiles were highly different in S6K1 and S6K2 high tumours, whereas S6K2 and 4EBP1 profiles showed significant overlaps, both correlated to genes involved in cell cycle progression, among these the master regulator E2F1. S6K2 and 4EBP1 were inversely associated with IGF1 levels, and their prognostic value was shown to be restricted to tumours positive for IGFR and/or HER2. In vitro, S6K1 and S6K2 silencing resulted in upregulation of genes in the mTORC1 and mTORC2 complexes. Isoform-specific silencing also showed distinct patterns, e.g. S6K2 downregulation lead to upregulation of several cell cycle associated genes. Structural analyses of the S6K2 kinase domain showed unique structure patterns, deviating from those of S6K1, facilitating the development of isoform-specific inhibitors. Our data support emerging proposals of distinct biological features of S6K1 and S6K2, suggesting their importance as separate oncogenes and clinical markers, where specific targeting in different breast cancer subtypes could facilitate further individualised therapies.

Abstract B07: Estrogen-related receptor alpha regulates S6K1 expression and tamoxifen sensitivity in breast cancer

Estrogen related receptor alpha (ERRα) is an orphan nuclear receptor that plays important role in the metabolic activities and proliferation of cancer cells. We investigated the role of ERRα in regulating the expression of S6K1 in breast cancer cells. First, using RT-qPCR and immunoblotting we found that ERRα overexpression in estrogen receptor (ER) positive MCF7 cells results in decreased S6K1 expression and activity. Conversely, downregulation of ERRα expression resulted in increased S6K1 expression and activity in ER-negative MDA-MB-231 cells. Second, overexpression of ERRα in MCF7 cells also resulted in decreased transcriptional activity of the RPS6KB1 gene promoter as revealed by luciferase reporter assay. On the other hand, ERRα knockdown in MDA-MB-231 cells resulted in increased promoter activity. Third, because the proximal 1 kilobase (Kb) promoter region of S6K1 contains several putative estrogen receptor DNA binding elements (EREs), we investigated whether ERRα modulates S6K1 expression by direct promoter binding using chromatin immunoprecipitation (ChIP) technique. We detected two binding peaks approximately 300 and 600 kb away from the transcription start site (TSS). In addition, we showed that downregulation of ERRα caused increased cell proliferation and sensitivity to the mTOR inhibitor rapamycin. Suprisingly, tamoxifen treatment increased the proliferative capacity of these cells. Interestingly, cytoplasmic and nuclear staining of ERRα in tumor specimens derived from patients in the Stockholm breast cancer trial of adjuvant tamoxifen revealed that (1) in triple-negative tumors, the low-expressing cytoplasmic ERRα group had a worse prognosis, whereas a clear improvement in recurrence-free survival was found in the group with high ERRα-expressing tumors; and (2) in the ERα-negative subgroup, high ERRα rendered a clear tamoxifen benefit, which is very interesting, as this group is not receiving tamoxifen today and may constitute a subgroup which could gain from tamoxifen. Overall, our data indicate that ERRα regulates S6K1 expression and affects the sensitivity to rapamycin tamoxifen. Our long-term goal is to establish ERRα as a marker for endocrine and rapamycin therapy response, as well as a novel target in combination therapy approaches. Citation Format: Subrata Manna, Josefine Bostner, Anya Alayev, Olle Stal, Marina K. Holz. Estrogen-related receptor alpha regulates S6K1 expression and tamoxifen sensitivity in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B07.

Comprehensive Genomic and Transcriptomic Analysis of the 11q13 Amplicon in Breast Cancer.

Background: The chromosomal region 11q13 is amplified in 15-20% of breast cancers; an event associated with ER positive status but also implicated in resistance to endocrine therapies. Coamplifications of the 11q13 and 8p12 regions are commonly occurring, suggesting a synergy between genes in the amplicons. The present aim was to perform a comprehensive analysis of breast tumours harbouring amplification in the 11q13 region, and identify candidate oncogenes in the amplicon based on recurrent amplification patterns and correlations to mRNA expression levels. Furthermore, the 11q13/8p12 connection was evaluated at the mRNA level, as well as its prognostic significance.Methods/materials: Affymetrix 250K Nsp SNP arrays were used for whole genome screening of DNA copy number changes in 29 breast tumours, assumed to be representative for the majority of 11q13 amplified cases in a patient material consisting of 200 postmenopausal women with stage II breast tumours. To identify regions of significant aberrations at 11q13 and 8p12 across all tumours, the principles of a statistical approach called Genomic Identification of Significant Targets in Cancer (GISTIC) was applied. mRNA expression levels of candidate oncogenes in respective amplicon (RAD9A, RPS6KB2, CCND1, FGF19, PAK1, GAB2 (11q13); EIF4EBP1, PPAPDC1B and FGFR1 (8p12) were evaluated using quantitative real-time PCR.Results: Resulting data revealed three main amplification cores at 11q13, centred on 66.9Mb, 69.1Mb and 77.0Mb. Loss of the distal part of 11q occurred in 97% (28/29) of the cases. With the exception for FGF19, a correlation between mRNA level and gene copy number was seen for all genes included in the study. ER expression was associated with the central 11q13 core, though no significant correlation to mRNA expression of included genes could be stated. Regarding the 8p12/11q13 connection, it was shown that DNA copy number, as well as mRNA-expression levels, significantly correlated between RPS6KB2 (core 66.9Mb, 11q13) and EIF4EBP1/PPAPDC1B (8p12). Amplification at 8p12 was significantly inversely correlated to 17q (HER2) amplification, whereas HER2 protein was significantly negatively correlated to PPAPDC1B mRNA-levels. High expression of RPS6KB2, EIF4EBP1 and FGFR1 was associated with a significant increased risk of distant recurrence in the patient group. Coexpression of RPS6KB2 and EIF4EBP1 was shown to predict a worse patient outcome compared to overexpression of only one of the genes, supporting earlier suggestions of a synergy between the 11q13 and 8p12 amplicons.Conclusions: The present study identifies three main amplification cores at 11q13 in breast tumours, with the most proximal correlated to 8p12 at both the genomic and the transcriptomic level. A clinical significance of RPS6KB2(11q13)/EIF4EBP1(8p12) coexpression/coamplification was indicated, but needs to be evaluated in larger patient cohorts. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5166.