The nuclear enzyme topoisomerase IIα (TopoIIα) is able to cleave DNA in a reversible manner, making it a valuable target for agents such as etoposide that trap the enzyme in a covalent bond with the 5' DNA end to which it cleaves. This prevents DNA religation and triggers cell death in cancer cells. However, development of resistance to these agents limits their therapeutic use. In this study, we examined the therapeutic targeting of geminin for improving the therapeutic potential of TopoIIα agents.
Human mammary epithelial (HME) cells and several breast cancer cell lines were used in this study. Geminin, TopoIIα and cell division cycle 7 (Cdc7) silencing were done using specific small interfering RNA. Transit or stable inducible overexpression of these proteins and casein kinase Iε (CKIε) were also used, as well as several pharmacological inhibitors that target TopoIIα, Cdc7 or CKIε. We manipulated HME cells that expressed H2B-GFP, or did not, to detect chromosome bridges. Immunoprecipitation and direct Western blot analysis were used to detect interactions between these proteins and their total expression, respectively, whereas interactions on chromosomal arms were detected using a trapped in agarose DNA immunostaining assay. TopoIIα phosphorylation by Cdc7 or CKIε was done using an in vitro kinase assay. The TopoGen decatenation kit was used to measure TopoIIα decatenation activity. Finally, a comet assay and metaphase chromosome spread were used to detect chromosome breakage and changes in chromosome condensation or numbers, respectively.
We found that geminin and TopoIIα interact primarily in G2/M/early G1 cells on chromosomes, that geminin recruits TopoIIα to chromosomal decatenation sites or vice versa and that geminin silencing in HME cells triggers the formation of chromosome bridges by suppressing TopoIIα access to chromosomal arms. CKIε kinase phosphorylates and positively regulates TopoIIα chromosome localization and function. CKIε kinase overexpression or Cdc7 kinase silencing, which we show phosphorylates TopoIIα in vitro, restored DNA decatenation and chromosome segregation in geminin-silenced cells before triggering cell death. In vivo, at normal concentration, geminin recruits the deSUMOylating sentrin-specific proteases SENP1 and SENP2 enzymes to deSUMOylate chromosome-bound TopoIIα and promote its release from chromosomes following completion of DNA decatenation. In cells overexpressing geminin, premature departure of TopoIIα from chromosomes is thought to be due to the fact that geminin recruits more of these deSUMOylating enzymes, or recruits them earlier, to bound TopoIIα. This triggers premature release of TopoIIα from chromosomes, which we propose induces aneuploidy in HME cells, since chromosome breakage generated through this mechanism were not sensed and/or repaired and the cell cycle was not arrested. Expression of mitosis-inducing proteins such as cyclin A and cell division kinase 1 was also increased in these cells because of the overexpression of geminin.
TopoIIα recruitment and its chromosome decatenation function require a normal level of geminin. Geminin silencing induces a cytokinetic checkpoint in which Cdc7 phosphorylates TopoIIα and inhibits its chromosomal recruitment and decatenation and/or segregation function. Geminin overexpression prematurely deSUMOylates TopoIIα, triggering its premature departure from chromosomes and leading to chromosomal abnormalities and the formation of aneuploid, drug-resistant cancer cells. On the basis of our findings, we propose that therapeutic targeting of geminin is essential for improving the therapeutic potential of TopoIIα agents.
The PACS01 trial has demonstrated that a docetaxel addition to adjuvant anthracycline-based chemotherapy improves disease-free survival (DFS) and overall survival of node-positive early breast cancer (EBC). We searched for prognostic and predictive markers for docetaxel's benefit.
Tumor samples from 1,099 recruited women were analyzed for the expression of 34 selected proteins using immunohistochemistry. The prognostic and predictive values of each marker and four molecular subtypes (luminal A, luminal B, HER2-overexpressing, and triple-negative) were tested.
Progesterone receptor-negativity (HR = 0.66; 95% CI 0.47 to 0.92, P = 0.013), and Ki67-positivity (HR = 1.53; 95% CI 1.12 to 2.08, P = 0.007) were independent adverse prognostic factors. Out of the 34 proteins, only Ki67-positivity was associated with DFS improvement with docetaxel addition (adjusted HR = 0.51, 95% CI 0.33 to 0.79 for Ki67-positive versus HR = 1.10, 95% CI 0.75 to 1.61 for Ki67-negative tumors, P for interaction = 0.012). Molecular subtyping predicted the docetaxel benefit, but without providing additional information to Ki67 status. The luminal A subtype did not benefit from docetaxel (HR = 1.16, 95% CI 0.73 to 1.84); the reduction in the relapse risk was 53% (HR = 0.47, 95% CI 0.22 to 1.01), 34% (HR = 0.66, 95% CI 0.37 to 1.19), and 12% (HR = 0.88, 95% CI 0.49 to 1.57) in the luminal B, HER2-overexpressing, and triple-negative subtypes, respectively.
In patients with node-positive EBC receiving adjuvant anthracycline-based chemotherapy, the most powerful predictor of docetaxel benefit is Ki67-positivity.
The presence of circulating tumor cells (CTC) in breast cancer might be associated with stem cell-like tumor cells which have been suggested to be the active source of metastatic spread in primary tumors. Furthermore, to be able to disseminate and metastasize, CTC must be able to perform epithelial-mesenchymal transition (EMT). We studied the expression of three EMT markers and the stem cell marker ALDH1 in CTC from 502 primary breast cancer patients. Data were correlated with the presence of disseminated tumor cells (DTC) in the bone marrow (BM) and with clinicopathological data of the patients.
A total of 2 × 5 ml of blood was analyzed for CTC with the AdnaTest BreastCancer (AdnaGen AG) for the detection of EpCAM, MUC-1, HER2 and beta-Actin transcripts. The recovered c-DNA was additionally multiplex tested for three EMT markers [TWIST1, Akt2, phosphoinositide kinase-3 (PI3Kα)] and separately for the tumor stem cell marker ALDH1. The identification of EMT markers was considered positive if at least one marker was detected in the sample. Two BM aspirates from all patients were analyzed for DTC by immunocytochemistry using the pan-cytokeratin antibody A45-B/B3.
Ninety-seven percent of 30 healthy donor samples investigated were negative for EMT and 95% for ALDH1 transcripts, respectively. CTC were detected in 97/502 (19%) patients. At least one of the EMT markers was expressed in 29% and ALDH1 was present in 14% of the samples, respectively. Interestingly, 5% of the ALDH1-positive and 18% of the EMT-positive patients were CTC-negative based on the cut-off level determined for CTC-positivity applying the AdnaTest BreastCancer. DTC in the BM were detected in 107/502 (21%) patients and no correlation was found between BM status and CTC positivity (P = 0.41). The presence of CTC, EMT and ALDH1 expression was not correlated to any of the prognostic clinical markers.
Our data indicate that (1) a subset of primary breast cancer patients shows EMT and stem cell characteristics and (2) the currently used detection methods for CTC are not efficient to identify a subtype of CTC which underwent EMT. (3) The clinical relevance on prognosis and therapy response has to be further evaluated in a prospective trial.
Pre-clinical data suggest p53-dependent anthracycline-induced apoptosis and p53-independent taxane activity. However, dedicated clinical research has not defined a predictive role for TP53 gene mutations. The aim of the current study was to retrospectively explore the prognosis and predictive values of TP53 somatic mutations in the BIG 02-98 randomized phase III trial in which women with node-positive breast cancer were treated with adjuvant doxorubicin-based chemotherapy with or without docetaxel.
The prognostic and predictive values of TP53 were analyzed in tumor samples by gene sequencing within exons 5 to 8. Patients were classified according to p53 protein status predicted from TP53 gene sequence, as wild-type (no TP53 variation or TP53 variations which are predicted not to modify p53 protein sequence) or mutant (p53 nonsynonymous mutations). Mutations were subcategorized according to missense or truncating mutations. Survival analyses were performed using the Kaplan-Meier method and log-rank test. Cox-regression analysis was used to identify independent predictors of outcome.
TP53 gene status was determined for 18% (520 of 2887) of the women enrolled in BIG 02-98. TP53 gene variations were found in 17% (90 of 520). Nonsynonymous p53 mutations, found in 16.3% (85 of 520), were associated with older age, ductal morphology, higher grade and hormone-receptor negativity. Of the nonsynonymous mutations, 12.3% (64 of 520) were missense and 3.6% were truncating (19 of 520). Only truncating mutations showed significant independent prognostic value, with an increased recurrence risk compared to patients with non-modified p53 protein (hazard ratio = 3.21, 95% confidence interval = 1.740 to 5.935, P = 0.0002). p53 status had no significant predictive value for response to docetaxel.
p53 truncating mutations were uncommon but associated with poor prognosis. No significant predictive role for p53 status was detected.
BACKGROUND: Activation of the PI3K/MAPK pathways results in anti-estrogen resistance in vitro, however a biomarker that can predict clinical resistance has not yet been identified. Common drivers of these pathways are PIK3CA mutations, loss of PTEN and over-expression of HER2 and IGF-1R. We aimed to test the prognostic and predictive value of PI3K/MAPK pathway drivers as well as downstream activated proteins in postmenopausal breast cancer patients.
METHODS: We collected primary tumor tissue from 563 ERα positive breast cancer patients who were randomized between tamoxifen (1–3 years) versus no adjuvant systemic therapy. PIK3CA hotspot mutations were assessed by Sequenom Mass Spectrometry. Immunohistochemistry was performed for expression of PTEN, IGF-1R and the downstream markers p-AKT(Thr308), p-AKT(Ser473), p-mTOR, p-p706SK and p-ERK1/2. Cox proportional hazard models for recurrence free interval were used to assess hazard ratios and interaction between these markers and treatment.
RESULTS: No significant interaction between any of the tested PI3K/MAPK pathways drivers and tamoxifen was found. [/bold]However, interactions were identified between tamoxifen and the downstream activated proteins (p-AKT(Thr308), p- mTOR, p-p70S6K and p-ERK1/2). After correcting for multiple testing, p-p70S6K remained significantly associated with tamoxifen resistance. Patients whose tumor did not express p-p70S6K did derive significant benefit from tamoxifen (HR 0.24, 95 % CI= 0.12–0.47, p < 0.0001), while patients whose tumor did express p-p70S6K did not (multivariate HR=1.02, 95% CI=0.48–2.21, p = 0.95), p for interaction 0.003.
CONCLUSION: We conclude that the downstream marker of PI3K/MAPK activation p-p70S6K predicts tamoxifen resistance in ERα positive postmenopausal breast cancer patients.
Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD01-03.
Molecular characterization of the normal epithelial cell types that reside in the mammary gland is an important step toward understanding pathways that regulate self-renewal, lineage commitment, and differentiation along the hierarchy. Here we determined the gene expression signatures of four distinct subpopulations isolated from the mouse mammary gland. The epithelial cell signatures were used to interrogate mouse models of mammary tumorigenesis and to compare with their normal human counterpart subsets to identify conserved genes and networks.
RNA was prepared from freshly sorted mouse mammary cell subpopulations (mammary stem cell (MaSC)-enriched, committed luminal progenitor, mature luminal and stromal cell) and used for gene expression profiling analysis on the Illumina platform. Gene signatures were derived and compared with those previously reported for the analogous normal human mammary cell subpopulations. The mouse and human epithelial subset signatures were then subjected to Ingenuity Pathway Analysis (IPA) to identify conserved pathways.
The four mouse mammary cell subpopulations exhibited distinct gene signatures. Comparison of these signatures with the molecular profiles of different mouse models of mammary tumorigenesis revealed that tumors arising in MMTV-Wnt-1 and p53-/- mice were enriched for MaSC-subset genes, whereas the gene profiles of MMTV-Neu and MMTV-PyMT tumors were most concordant with the luminal progenitor cell signature. Comparison of the mouse mammary epithelial cell signatures with their human counterparts revealed substantial conservation of genes, whereas IPA highlighted a number of conserved pathways in the three epithelial subsets.
The conservation of genes and pathways across species further validates the use of the mouse as a model to study mammary gland development and highlights pathways that are likely to govern cell-fate decisions and differentiation. It is noteworthy that many of the conserved genes in the MaSC population have been considered as epithelial-mesenchymal transition (EMT) signature genes. Therefore, the expression of these genes in tumor cells may reflect basal epithelial cell characteristics and not necessarily cells that have undergone an EMT. Comparative analyses of normal mouse epithelial subsets with murine tumor models have implicated distinct cell types in contributing to tumorigenesis in the different models.
Alterations in cell cycle regulators have been implicated in human malignancies including breast cancer. PD 0332991 is an orally active, highly selective inhibitor of the cyclin D kinases (CDK)4 and CDK6 with ability to block retinoblastoma (Rb) phosphorylation in the low nanomolar range. To identify predictors of response, we determined the in vitro sensitivity to PD 0332991 across a panel of molecularly characterized human breast cancer cell lines.
Forty-seven human breast cancer and immortalized cell lines representing the known molecular subgroups of breast cancer were treated with PD 0332991 to determine IC50 values. These data were analyzed against baseline gene expression data to identify genes associated with PD 0332991 response.
Cell lines representing luminal estrogen receptor-positive (ER+) subtype (including those that are HER2 amplified) were most sensitive to growth inhibition by PD 0332991 while nonluminal/basal subtypes were most resistant. Analysis of variance identified 450 differentially expressed genes between sensitive and resistant cells. pRb and cyclin D1 were elevated and CDKN2A (p16) was decreased in the most sensitive lines. Cell cycle analysis showed G0/G1 arrest in sensitive cell lines and Western blot analysis demonstrated that Rb phosphorylation is blocked in sensitive lines but not resistant lines. PD 0332991 was synergistic with tamoxifen and trastuzumab in ER+ and HER2-amplified cell lines, respectively. PD 0332991 enhanced sensitivity to tamoxifen in cell lines with conditioned resistance to ER blockade.
These studies suggest a role for CDK4/6 inhibition in some breast cancers and identify criteria for patient selection in clinical studies of PD 0332991
The detection of cytokeratin-19 (CK-19) mRNA-positive circulating tumor cells (CTC) before and/or after adjuvant chemotherapy in patients with operable breast cancer is associated with poor clinical outcome. Reliable prognostic markers for late disease relapse are not available. In this study we investigated the value of CTC detection during the first five years of follow-up in predicting late disease relapse.
Blood was analyzed from 312 women with operable breast cancer who had not experienced disease relapse during the first two years of follow-up. A real-time reverse transcriptase polymerase chain reaction (RT-PCR) for CK-19 mRNA was used to detect CTC three months after the completion of adjuvant chemotherapy and every six months thereafter for a follow-up period of five years.
Eighty patients (25.6% of the study population) remained CTC free throughout the five-year period. A change in CTC status was observed in 133 patients (42.6%); 64 patients (20.5%) with initially CK-19 mRNA-positive CTC during the first 24 months turned CTC-negative afterwards while 69 (22.1%) who were initially CTC-negative became CTC-positive. Ninety-nine patients (31.7%) remained persistently CK-19 mRNA-positive. After a median follow-up period of 107 months (range: 38 to 161 months), the persistently CTC-positive patients with either hormonal receptor positive or negative tumors, had a higher risk of late-disease relapse compared to the persistently CTC-negative patients (36.4% versus 11.2%, P <0.001). Multivariate analysis revealed that persistently CTC-positive patients also had a shorter disease-free (P = 0.001) and overall survival (P = 0.001).
Persistent detection of CK-19 mRNA-positive CTC during the first five years of follow-up is associated with an increased risk of late relapse and death in patients with operable breast cancer and indicates the presence of chemo-and hormonotherapy-resistant residual disease. This prognostic evaluation may be useful when deciding on subsequent adjuvant systemic therapy.
Epigenetic silencing of tumor suppressing genes by promoter-specific DNA methylation is common in many types of cancer. As an early event, this process has been well shown to promote tumor initiation and progression; however little is known how such epigenetic silencing can contribute to tumor metastasis. The PRKD1 gene encodes Protein Kinase D1 (PKD1), a serine/threonine kinase expressed in epithelial cells of the normal mammary gland that maintains the epithelial phenotype of normal breast cells and prevents epithelial-to-mesenchymal transition (EMT). PKD1 is also a critical suppressor of tumor cell invasion and is silenced in expression and activity during breast tumor progression. Here, we show that aberrant methylation of PRKD1 promoter region is not only correlated with the silencing of its expression but is also associated with invasiveness of breast cancer cell lines and with aggressiveness of breast tumors. Using the highly invasive MDA-MB-231 cells, we show that the inhibition of PRKD1 promoter methylation with the DNA methyltransferase inhibitor decitabine restores PKD1 expression and significantly decreases their invasive abilities in vitro. More importantly, in a tumor xenograft model it dramatically blocks tumor spread and metastasis to the lung in a PKD1-dependent fashion. Our data suggest that the status of epigenetic regulation of the PRKD1 promoter can provide valid information on the invasiveness of breast tumors, and therefore could serve as an early diagnostic marker. Moreover, targeted upregulation of PKD1 expression may be used as a therapeutic approach to reverse the invasive phenotype of breast cancer cells.
Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-24.
IntroductionThe purpose of this study is to develop a prediction model utilizing tumor hemoglobin parameters measured by ultrasound-guided near-infrared optical tomography (US-NIR), in conjunction with standard pathologic tumor characteristics to predict pathologic response before neoadjuvant chemotherapy (NAC) is given.Methods
Thirty-four patients¿ data were retrospectively analyzed using a multiple logistic regression model to predict response. These patients were split into 30 groups of training (24 tumors) and testing (12 tumors) for cross validation. Tumor vascularity was assessed using US-NIR measurements of total hemoglobin (tHb), oxygenated and deoxygenated hemoglobin concentrations (oxyHb and deoxyHb) acquired before treatment. Tumor pathologic variables of tumor type, Nottingham score, mitotic index, the estrogen and progesterone receptors, and human epidermal growth factor receptor 2 acquired before NAC in biopsy specimens were also used in the prediction model. The patients¿ pathologic response was graded based on the Miller-Payne system. The overall performance of the prediction models was evaluated using Receiver Operating Characteristic (ROC) curves. The quantitative measures were sensitivity, specificity, positive and negative predictive values (PPV and NPV), and the area under the ROC curve (AUC).ResultsUtilizing tumor pathologic variables alone, an average sensitivity of 56.8%, specificity of 88.9%, PPV and NPV of 84.8% and 70.9%, and AUC of 84.0% were obtained from the testing data. Among the hemoglobin predictors with and without tumor pathological variables, the best predictor is tHb combined with tumor pathological variables followed by oxyHb with pathological variables. When tHb was included as an additional predictor to tumor pathological variables, the corresponding measures improved to 79%, 94%, 90%, 86%, and AUC 92.4%, respectively. When oxyHb was included as an additional predictor to tumor variables, these measures improved to 77%, 85%, 83%, 83%, and AUC 90.6%, respectively. The addition of tHb or oxyHb significantly improves the prediction sensitivity, NPV and AUC as compared with using tumor pathological variables alone.Conclusions
These initial findings indicate that combining widely used tumor pathologic variables with hemoglobin parameters determined by US-NIR, may provide a powerful tool for predicting patient pathologic response to NAC before the initiation of the treatment.Trial registrationClincalTrials.gov, NCT00908609, registered 22 May 2009.
1,1-Bis (3'-indolyl)-1-(p-biphenyl) methane (CDIM9) has been identified as a new peroxisome proliferator-activated receptor (PPAR)-gamma agonist that exhibits both receptor dependent and independent antitumor activities. CDIM9 has not previously been studied with respect to its effects against basal-like breast cancer. Our goal in the present study was to investigate the anti-basal-like breast tumor activity of CDIM9 in vitro and in vivo.
The effects of CDIM9 on cell protein and DNA syntheses were determined in basal-like breast cancer MDA-MB231 and BT549 cells in vitro. Maximum tolerated dose and dose-limited toxicity were determined in BalB/c mice, and antitumor growth activities were assessed in MDA-MB231 basal-like breast tumor xenografts in athymic nude mice.
CDIM9 exhibited selective cell cytotoxicity and anti-proliferation effects on basal-like breast cancer lines. In MDA-MB231 cell, CDIM9 induced caveolin-1 and p27 expression, which was significantly downregulated by co-treatment with the PPAR-gamma antagonist GW9662. Nonsteroidal anti-inflammatory drug-activated gene-1 and activating transcription factor-3 were upregulated by CDIM9 through a PPAR-gamma independent pathway. CDIM9 (40 mg/kg daily, intraperitoneally, for 35 days) inhibited the growth of subcutaneous MDA-MB231 tumor xenografts by 87%, and produced a corresponding decrease in proliferation index. Nearly half of the treated mice (46%) had complete durable remissions, confirmed by histology. The growth of an established tumor was inhibited by CDIM9 treatment (64 mg/kg daily, intraperitoneally, for 10 days), with a mean tumor growth inhibition of 67% as compared with controls. CDIM9 induced increases in tumor caveolin-1 and p27 in vivo, which may contribute to its antitumor activity in basal-like breast cancer.
CDIM9 showed potent antiproliferative effects on basal-like breast cancer cell in tissue culture and dramatic growth inhibition in animal models at safe doses. These findings justify further development of this drug for treatment of basal-like breast cancer.
Estrogen and androgen signalling pathways exert opposing influences on the proliferation of mammary epithelial and hormone-dependent breast cancer cells. We previously reported that plasma concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), the main metabolite of the insecticide DDT (1,1,1-trichloro-2,2-bis [p-chlorophenyl]ethane) and a potent androgen antagonist, were associated with tumor aggressiveness in women diagnosed with breast cancer. We sought to examine the biological plausibility of this association by testing the effect of p,p'-DDE on the proliferation of CAMA-1 cells, a human breast cancer cell line that expresses the estrogen receptor alpha (ERalpha) and the androgen receptor (AR), in the presence of physiological concentrations of estrogens and androgens in the cell culture medium.
The proliferation of CAMA-1 cells was determined in 96-well plates following a 9-day treatment with p,p'-DDE alone (0.1 to 10 muM) or in combination with 17beta-estradiol (E2) (100 pM) and dihydrotestosterone (DHT) (100, 500, or 1,000 pM). We also assessed p,p'-DDE-induced modifications in cell cycle entry and the expression of the sex-steroid-dependent genes ESR1, AR, CCND1, and TFF1 (pS2) (mRNA and/or protein).
We found that treatment with p,p'-DDE induced a dose-response increase in the proliferation of CAMA-1 cells when cultivated in the presence of physiological concentrations of estrogens and androgens, but not in the absence of sex steroids in the cell culture medium. A similar effect of p,p'-DDE was noted on the proliferation of MCF7-AR1 cells, an estrogen-responsive cell line that was genetically engineered to overexpress the AR. DHT added together with E2 to the cell culture medium decreased the recruitment of CAMA-1 cells in the S phase and the expression of ESR1 and CCND1 by comparison with cells treated with E2 alone. These androgen-mediated effects were blocked with similar efficacy by p,p'-DDE and the potent antiandrogen hydroxyflutamide.
Our results suggest that p,p'-DDE could increase breast cancer progression by opposing the androgen signalling pathway that inhibits growth in hormone-responsive breast cancer cells. The potential role of environmental antiandrogens in breast carcinogenesis deserves further investigation.
Estimates of the proportion of estrogen receptor (ER) negative (-) and triple-negative (TRN) breast cancer from sub-Saharan Africa are variable and include high values. Large studies of receptor status conducted on non-archival tissue are lacking from this region.
We identified 1218 consecutive women (91% black) diagnosed with invasive breast cancer from 2006--2012 at a public hospital in Soweto, South Africa. Immunohistochemistry based ER, progesterone receptor (PR) and human epidermal factor 2 (HER2) receptors were assessed at diagnosis on pre-treatment biopsy specimens. Mutually-adjusted associations of receptor status with stage, age, race and grade were examined using risk ratios (RRs). ER status was compared with age-stratified US Surveillance Epidemiology and End Results program (SEER) data.
35% (95% confidence interval (CI): 32--38) of tumors were ER-, 47% (45--52) PR-, 26% (23--29) HER2+ and 21% (18--23) TRN. Later stage tumors were more likely to be ER- and PR- (RRs 1.9 (1.1-2.9) and 2.0 (1.3-3.1) for stage III vs. I) but were not strongly associated with HER2 status. Age was not strongly associated with ER or PR status, but older women were less likely to have HER2+ tumors (RR 0.95 (0.92-0.99) per 5 years). During the study, stage III + IV tumors decreased from 66% to 46%. In black women the percentage of ER- (37% (34--40)) and PR- tumors (48% (45--52)) was significantly higher than in non-black patients (22% (14--31) and 34% (25--44), respectively with P = 0.004 and P = 0.02), which remained after age and stage adjustment. Age-specific ER- proportions in black South African women were similar to those of US black women, especially for women diagnosed over age 50.
Although a greater proportion of black than non-black South African women had ER- or TRN breast cancer, in all racial groups in this study breast cancer was predominantly ER + and was being diagnosed at earlier stages over time. These observations provide initial indications that late-stage aggressive breast cancers may not be an inherent feature of the breast cancer burden across Africa.
Statement of findings
Serial plasma samples from 1006 patients with breast cancer revealed: (i) no correlation of p53 autoantibody status with disease status at the time of sample collection, or with menopausal status at time of primary diagnosis of breast cancer; (ii) 155 out of 1006 (15%) of patients were positive for p53 autoantibodies, and these patients tended to have a persistent autoantibody status throughout follow up, irrespective of disease behaviour; and (iii) where a negative autoantibody status was found at primary diagnosis of breast cancer, this negative status persisted throughout follow up, irrespective of later disease behaviour. We conclude that screening for p53 autoantibody status is not informative on residual tumour activity nor on therapeutic responsiveness.
Early-stage cancers have long been considered to be less aggressive than late-stage cancers because it is assumed that they have accumulated fewer of the mutations that are required for full metastatic potential. For breast cancer, recent gene expression profiling data have challenged this paradigm by identifying early-stage cancers with similar gene expression profiles to fully metastatic cancers. In this review, multistep carcinogenesis is reconsidered in light of these new data. The concept that the tumor stroma plays a key role in determining whether a metastatic tumor cell will remain dormant or become invasive is discussed. Recent studies demonstrating the feasibility of targeting tumor stroma for cancer prevention and treatment are presented.
Basal-like breast cancers (BLBC) frequently overexpress the epidermal growth factor receptor (EGFR) and subsequently have high levels of signaling through the MAP kinase pathway, which is thought to contribute to their aggressive behavior. While we have previously reported the expression of Y-box binding protein-1 (YB-1) in 73% of BLBC, it is unclear whether it can be regulated by a component of the MAP kinase signaling pathway. Phosphorylation of YB-1 at the serine 102 residue is required for transcriptional activation of growth-enhancing genes, such as EGFR. Using Motifscan we identified p90 ribosomal S6 kinase (RSK) as a potential candidate for activating YB-1.
Inhibition of RSK1 and RSK2 was achieved using siRNA and the small molecule SL0101. RSK1, RSK2, activated RSK and kinase-dead RSK were expressed in HCC1937 cells. Kinase assays were performed to illustrate direct phosphorylation of YB-1 by RSK. The impact of inhibiting RSK on YB-1 function was measured by luciferase assays and chromatin immunoprecipitation.
Using an in vitro kinase assay, RSK1 and RSK2 were shown to directly phosphorylate YB-1. Interestingly, they were more effective activators of YB-1 than AKT or another novel YB-1 kinase, PKC alpha. Phosphorylation of YB-1 (serine 102 residue) is blocked by inhibition of the MAP kinase pathway or by perturbing RSK1/RSK2 with siRNA or SL0101. In immortalized breast epithelial cells where RSK is active yet AKT is not, YB-1 is phosphorylated. Supporting this observation, RSK2-/- mouse embryo fibroblasts lose the ability to phosphorylate YB-1 in response to epidermal growth factor. This subsequently interfered with the ability of YB-1 to regulate the expression of EGFR. The RSK inhibitor SL0101 decreased the ability of YB-1 to bind the promoter, transactivate and ultimately reduce EGFR expression. In concordance with these results the expression of constitutively active RSK1 increased YB-1 phosphorylation, yet the kinase-dead RSK did not.
We therefore conclude that RSK1/RSK2 are novel activators of YB-1, able to phosphorylate the serine 102 residue. This provides a newly described mechanism whereby YB-1 is activated in breast cancer. This implicates the EGFR/RSK/YB-1 pathway as an important component of BLBC, providing an important opportunity for therapeutic intervention.
The cancer stem cell hypothesis proposes that tumors arise in stem or progenitor cells generating in tumors driven by a subcomponent that retains cancer stem cell properties. Recent evidence supports the hypothesis that the BRCA1 gene involved in hereditary breast cancer plays a role in breast stem cell function. Furthermore, studies using mouse BRCA1 knockout models provide evidence for the existence of heterogeneous cancer stem cell populations in tumors generated in these mice. Although these populations may arise from different stem/progenitor cells, they share the expression of a common set of stem cell regulatory genes and show similar characteristics in in vitro mammosphere assays and xenograft models. Furthermore, these 'cancer stem cells' display resistance to chemotherapeutic agents. These studies suggest that breast tumors may display intertumor stem cell heterogeneity. Despite this heterogeneity, cancer stem cells may share common characteristics that can be used for their identification and for therapeutic targeting.
The article by Korfage and colleagues in this issue of Breast Cancer Research highlights the importance of enabling women to make informed choices about breast cancer chemoprevention. Decision aids have the potential to improve knowledge and decision-making in this context, but they do not guarantee increased uptake of chemoprevention amongst high-risk women if this option is inconsistent with women's values. Important avenues for further research in this area include evaluating: decision aids with explicit values clarification exercises and with comparison between chemoprevention and nonpharmacological options to reduce breast cancer risk, the influence of mediating factors such as anxiety and risk perception, and the role of clinicians and family members in decision-making.
The 'cancer stem cell hypothesis' posits that cancers, including breast cancer, arise in tissue stem or progenitor cells. If this is the case, then it follows that the risk for developing breast cancer may be determined in part by the number of breast stem/progenitor cells that can serve as targets for transformation. Stem cell number may be set during critical windows of development, including in utero, adolescence, and pregnancy. The growth hormone/insulin-like growth factor-1 axis may play an important role in regulating breast stem cell number during these developmental windows, suggesting an important link between this signaling pathway and breast cancer risk.
Ninety percent of cancer-related mortality is caused by metastasis. Current cancer treatments can control many primary tumors but rarely stop the metastatic spread. Accumulating evidence demonstrates that miRNAs are involved in cancer initiation and progression. Furthermore, several miRNAs have been found to regulate metastasis. In particular, recent studies provide the first functional evidence that overexpression of a specific miRNA, miR-10b, can contribute to the development of metastasis, which can be exploited therapeutically in treating breast cancer metastasis in mice. Further in-depth analysis should provide more precise evaluation of the roles, mechanisms, and therapeutic utility of this miRNA in breast cancer.
Hes-6 is a member of the basic helix-loop-helix (bHLH) family of transcription factors, and its overexpression has been reported in metastatic cancers of different origins. Hes-6 has been described as an inhibitor of Hes-1 during neuronal development, although its function in cancer is not known. In this study, we investigated the function of Hes-6 in breast cancer and tested the hypothesis that Hes-6 enhances breast cancer cell proliferation and is regulated by estrogen.
To investigate the function of Hes-6, T47D cells stably expressing Hes-6 were generated by lentiviral transduction, and conversely, siRNA also was used to knock down Hes-6 expression in breast cancer cells. The Hes-6-expressing T47D cells were transplanted into immunodeficient mice to study effects on tumor growth.
We found that Hes-6 expression was significantly higher in the high-grade, estrogen receptor (ER)alpha-negative SKBR3 and MDA-MB-231 cells compared with the ERalpha-positive, non-metastasizing T47D and MCF-7 breast carcinoma cells. Moreover, the level of Hes-6 mRNA was 28 times higher in breast cancer samples compared with normal breast samples. In Hes-6-expressing T47D cells, Hes-6 ectopic expression was shown to stimulate cell proliferation in vitro as well as breast tumor growth in xenografts. Moreover, expression of Hes-6 resulted in induction of E2F-1, a crucial target gene for the transcriptional repressor Hes-1. Consistently, silencing of Hes-6 by siRNA resulted in downregulation of E2F-1 expression, whereas estrogen treatment caused induction of Hes-6 and downstream targets hASH-1 and E2F-1 in MCF-7 cells.
Together, the data suggest that Hes-6 is a potential oncogene overexpressed in breast cancer, with a tumor-promoting and proliferative function. Furthermore, Hes-6 is a novel estrogen-regulated gene in breast cancer cells. An understanding of the role and regulation of Hes-6 could provide insights into estrogen signaling and endocrine resistance in breast cancer and, hence, could be important for the development of novel anticancer drugs.
The persistence of circulating tumor cells (CTC) in breast cancer patients might be associated with stem cell like tumor cells which have been suggested to be the active source of metastatic spread in primary tumors. Furthermore, these cells also may undergo phenotypic changes, known as epithelial-mesenchymal transition (EMT), which allows them to travel to the site of metastasis formation without getting affected by conventional treatment. Here we evaluated 226 blood samples of 39 metastatic breast cancer patients during a follow-up of palliative chemo-, antibody - or hormonal therapy for the expression of the stem cell marker ALDH1 and markers for EMT and correlated these findings with the presence of CTC and response to therapy.
2 x 5 ml blood was analyzed for CTC with the AdnaTest BreastCancer (AdnaGen AG) for the detection of EpCAM, MUC-1 and HER2 transcripts. The recovered c-DNA was additionally multiplex tested for three EMT markers [Twist1, Akt2, PI3Kalpha] and separately for the tumor stem-cell markers ALDH1. The identification of EMT markers was considered positive if at least one marker was detected in the sample.
97% of 30 healthy donor samples investigated were negative for EMT and 95% for ALDH1 transcripts. CTC were detected in 69/226 (31%) cancer samples. In the CTC (+) group, 62% were positive for at least one of the EMT markers and 69% for ALDH1, respectively. In the CTC (-) group the percentages were 7% and 14%, respectively. In non-responders, EMT and ALDH1 expression was found in 62% and 44% of patients, in responders the rates were 10% and 5%, respectively.
Our data indicate that a major proportion of CTC of metastatic breast cancer patients shows EMT and tumor stem cell characteristics. Further studies are needed to prove whether these markers might serve as an indicator for therapy resistant tumor cell populations and, therefore, an inferior prognosis.
PARP-1 (polyADP-ribose polymerase-1) is known to be activated in response to DNA damage, and activated PARP-1 promotes DNA repair. However, a recently disclosed alternative mechanism of PARP-1 activation by phosphorylated externally regulated kinase (ERK) implicates PARP-1 in a vast number of signal-transduction networks in the cell. Here, PARP-1 activation was examined for its possible effects on cell proliferation in both normal and malignant cells.
In vitro (cell cultures) and in vivo (xenotransplants) experiments were performed.
Phenanthridine-derived PARP inhibitors interfered with cell proliferation by causing G2/M arrest in both normal (human epithelial cells MCF10A and mouse embryonic fibroblasts) and human breast cancer cells MCF-7 and MDA231. However, whereas the normal cells were only transiently arrested, G2/M arrest in the malignant breast cancer cells was permanent and was accompanied by a massive cell death. In accordance, treatment with a phenanthridine-derived PARP inhibitor prevented the development of MCF-7 and MDA231 xenotransplants in female nude mice. Quiescent cells (neurons and cardiomyocytes) are not impaired by these PARP inhibitors.
These results outline a new therapeutic approach for a selective eradication of abundant nonhereditary human breast cancers.
Targeted therapies for aggressive breast cancers like triple negative breast cancer (TNBC) are needed. The use of small interfering RNAs (siRNAs) to disable expression of survival genes provides a tool for killing these cancer cells. Cyclin dependent kinase 11 (CDK11) is a survival protein kinase that regulates RNA transcription, splicing and mitosis. Casein kinase 2 (CK2) is a survival protein kinase that suppresses cancer cell death. Eliminating the expression of these genes has potential therapeutic utility for breast cancer.
Expression levels of CDK11 and CK2 mRNAs and associated proteins were examined in breast cancer cell lines and tissue arrays. RNA expression levels of CDC2L1, CDC2L2, CCNL1, CCNL2, CSNK2A1, CSNK2A2, and CSNK2B genes in breast cancer subtypes were analyzed. Effects following transfection of siRNAs against CDK11 and CK2 in cultured cells were examined by viability and clonal survival assays and by RNA and protein measures. Uptake of tenfibgen (TBG) nanocapsules by TNBC cells was analyzed by fluorescence-activated cell sorting. TBG nanocapsules delivered siRNAs targeting CDK11 or CK2 in mice carrying TNBC xenograft tumors. Transcript cleavage and response parameters were evaluated.
We found strong CDK11 and CK2 mRNA and protein expression in most human breast cancer cells. Immunohistochemical analysis of TNBC patient tissues showed 100% of tumors stained positive for CDK11 with high nuclear intensity compared to normal tissue. The Cancer Genome Atlas analysis comparing basal to other breast cancer subtypes and to normal breast revealed statistically significant differences. Down-regulation of CDK11 and/or CK2 in breast cancer cells caused significant loss of cell viability and clonal survival, reduced relevant mRNA and protein expression, and induced cell death changes. TBG nanocapsules were taken up by TNBC cells both in culture and in xenograft tumors. Treatment with TBG- siRNA to CDK11 or TBG- siRNA to CK2αα' nanocapsules induced appropriate cleavage of CDK11 and CK2α transcripts in TNBC tumors, and caused MDA-MB-231 tumor reduction, loss of proliferation, and decreased expression of targeted genes.
CDK11 and CK2 expression are individually essential for breast cancer cell survival, including TNBC. These genes serve as promising new targets for therapeutic development in breast cancer.