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This study aims to explore the effect and mechanism of a mitochondrion-targeted derivative of ergosterol peroxide(Mito-EP) on breast cancer. The methyl thiazolyl tetrazolium(MTT) assay was employed to examine the proliferation of MDA-MB-231 cells treated with different concentrations(0, 0.075, 0.15, 0.3, 0.6, 1.2, and 2.4 μmol·L~(-1)) of Mito-EP. Cells were grouped for treatment with water(blank control), low, medium, and high concentrations(0.15, 0.3, and 0.6 μmol·L~(-1)) of Mito-EP, and ergosterol peroxide(EP)(0.6 μmol·L~(-1)). After the cells were treated for 48 h, flow cytometry was employed to examine the apoptosis rate, reactive oxygen species(ROS) level, mitochondrial membrane potential, and cell cycle distribution, and the apoptosis, ROS, and mitochondrial membrane potential were observed by laser confocal microscopy. A mouse model bearing subcutaneous xenograft tumor was established by injecting 4T1 cell suspension and used to study the inhibitory effect of Mito-EP on breast cancer. Western blot was employed to determine the protein levels of B-cell lymphoma 2(Bcl-2), Bcl-2-associated X protein(Bax), cytochrome C(Cyt C), cleaved caspase-7, and cleaved caspase-9 in cells and the tumor tissue. The results showed that Mito-EP reduced the proliferation rate of MDA-MB-231 cells in a concentration-dependent manner. Compared with the blank control group, EP(0.6 μmol·L~(-1)) caused slight changes in the apoptosis rate, ROS level, and mitochondrial membrane potential. However, Mito-EP increased the apoptosis rate, elevated the ROS level, decreased mitochondrial membrane potential, up-regulated the protein levels of Bax, Cyt C, cleaved caspase-7, and cleaved caspase-9, and down-regulated the protein level of Bcl-2(all P<0.05). Moreover, Mito-EP reduced the tumor volume and weight. In summary, Mito-EP may promote apoptosis in breast cancer cells by activating the mitochondrial apoptosis pathway.

Metastatic breast-cancer is a major cause of death in women worldwide, yet the relationship between oncogenic drivers that promote metastatic versus primary cancer is still contentious. To elucidate this relationship in treatment-naive animals, we hereby describe mammary-specific transposon-mutagenesis screens in female mice together with loss-of-function Rb, which is frequently inactivated in breast-cancer. We report gene-centric common insertion-sites (gCIS) that are enriched in primary-tumors, in metastases or shared by both compartments. Shared-gCIS comprise a major MET-RAS network, whereas metastasis-gCIS form three additional hubs: Rho-signaling, Ubiquitination and RNA-processing. Pathway analysis of four clinical cohorts with paired primary-tumors and metastases reveals similar organization in human breast-cancer with subtype-specific shared-drivers (e.g. RB1-loss, TP53-loss, high MET, RAS, ER), primary-enriched (EGFR, TGFβ and STAT3) and metastasis-enriched (RHO, PI3K) oncogenic signaling. Inhibitors of RB1-deficiency or MET plus RHO-signaling cooperate to block cell migration and drive tumor cell-death. Thus, targeting shared- and metastasis- but not primary-enriched derivers offers a rational avenue to prevent metastatic breast-cancer., (© 2023. The Author(s).)

Systematically investigating the scores of genes mutated in cancer and discerning disease drivers from inconsequential bystanders is a prerequisite for precision medicine but remains challenging. Here, we developed a somatic CRISPR/Cas9 mutagenesis screen to study 215 recurrent "long-tail" breast cancer genes, which revealed epigenetic regulation as a major tumor-suppressive mechanism. We report that components of the BAP1 and COMPASS-like complexes, including KMT2C/D, KDM6A, BAP1, and ASXL1/2 ("EpiDrivers"), cooperate with PIK3CAH1047R to transform mouse and human breast epithelial cells. Mechanistically, we find that activation of PIK3CAH1047R and concomitant EpiDriver loss triggered an alveolar-like lineage conversion of basal mammary epithelial cells and accelerated formation of luminal-like tumors, suggesting a basal origin for luminal tumors. EpiDriver mutations are found in ∼39% of human breast cancers, and ∼50% of ductal carcinoma in situ express casein, suggesting that lineage infidelity and alveogenic mimicry may significantly contribute to early steps of breast cancer etiology., Significance: Infrequently mutated genes comprise most of the mutational burden in breast tumors but are poorly understood. In vivo CRISPR screening identified functional tumor suppressors that converged on epigenetic regulation. Loss of epigenetic regulators accelerated tumorigenesis and revealed lineage infidelity and aberrant expression of alveogenesis genes as potential early events in tumorigenesis. This article is highlighted in the In This Issue feature, p. 2711., (©2022 American Association for Cancer Research.)

Many 3D in vitro models induce breast cancer spheroid formation; however, this alone does not recapitulate the complex in vivo phenotype. To effectively screen therapeutics, it is urgently needed to validate in vitro cancer spheroid models against the gold standard of xenografts. A new oxime-crosslinked hyaluronan (HA) hydrogel is designed, manipulating gelation rate and mechanical properties to grow breast cancer spheroids in 3D. This HA-oxime breast cancer model maintains the gene expression profile most similar to that of tumor xenografts based on a pan-cancer gene expression profile (comprising 730 genes) of three different human breast cancer subtypes compared to Matrigel or conventional 2D culture. Differences in gene expression between breast cancer cultures in HA-oxime versus Matrigel or 2D are confirmed for 12 canonical pathways by gene set variation analysis. Importantly, drug response is dependent on the culture method. Breast cancer cells respond better to the Rac inhibitor (EHT-1864) and the PI3K inhibitor (AZD6482) when cultured in HA-oxime versus Matrigel. This study demonstrates the superiority of an HA-based hydrogel as a platform for in vitro breast cancer culture of both primary, patient-derived cells and cell lines, and provides a hydrogel culture model that closely matches that in vivo., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

BRCA1-deficient tumor cells have defects in homologous-recombination repair and replication fork stability, resulting in PARP inhibitor sensitivity. Here, we demonstrate that a deubiquitinase, USP1, is upregulated in tumors with mutations in BRCA1. Knockdown or inhibition of USP1 resulted in replication fork destabilization and decreased viability of BRCA1-deficient cells, revealing a synthetic lethal relationship. USP1 binds to and is stimulated by fork DNA. A truncated form of USP1, lacking its DNA-binding region, was not stimulated by DNA and failed to localize and protect replication forks. Persistence of monoubiquitinated PCNA at the replication fork was the mechanism of cell death in the absence of USP1. Taken together, USP1 exhibits DNA-mediated activation at the replication fork, protects the fork, and promotes survival in BRCA1-deficient cells. Inhibition of USP1 may be a useful treatment for a subset of PARP-inhibitor-resistant BRCA1-deficient tumors with acquired replication fork stabilization., (Copyright © 2018 Elsevier Inc. All rights reserved.)

A novel heterometallic metal-porphyrinic framework (MPFs) built from Y and K ions as nods and meso-tetra(4-carboxyphenyl)porphyrin as linkers has been successfully synthesized and characterized. The single crystal X-ray diffraction indicated that this complex 1 exhibited a bilayered architecture of the porphyrins, which is seldom seen in MPFs. In addition, in vitro anticancer activity of complex 1 on three human breast cancer cells (BT474, SKBr-3 and ZR-75-30) was further determined.

A switch from catabolic to anabolic metabolism, a major hallmark of cancer, enables rapid cell duplication, and is driven by multiple oncogenic alterations, including PIK3CA mutation, MYC amplification, and TP53 loss. However, tumor growth requires active mitochondrial function and oxidative phosphorylation (OXPHOS). Recently, loss of the retinoblastoma (RB1) tumor suppressor in breast cancer was shown to induce mitochondrial protein translation (MPT) and OXPHOS. Here, we discuss how increased OXPHOS can enhance anabolic metabolism and cell proliferation, as well as cancer stemness and metastasis. Mitochondrial STAT3, FER/FER-T, and CHCHD2 are also implicated in OXPHOS. We propose that RB1 loss represents a prototypic oncogenic alteration that promotes OXPHOS, that aggressive tumors acquire lethal combinations of oncogenes and tumor suppressors that stimulate anabolism versus OXPHOS, and that targeting both metabolic pathways would be therapeutic., (Crown Copyright © 2017. Published by Elsevier Inc. All rights reserved.)

In response to stresses, cells often halt normal cellular processes, yet stress-specific pathways must bypass such inhibition to generate effective responses. We investigated how cells redistribute global transcriptional activity in response to DNA damage. We show that an oscillatory increase of p53 levels in response to double-strand breaks drives a counter-oscillatory decrease of MYC levels. Using RNA sequencing (RNA-seq) of newly synthesized transcripts, we found that p53-mediated reduction of MYC suppressed general transcription, with the most highly expressed transcripts reduced to a greater extent. In contrast, upregulation of p53 targets was relatively unaffected by MYC suppression. Reducing MYC during the DNA damage response was important for cell-fate regulation, as counteracting MYC repression reduced cell-cycle arrest and elevated apoptosis. Our study shows that global inhibition with specific activation of transcriptional pathways is important for the proper response to DNA damage; this mechanism may be a general principle used in many stress responses., (Published by Elsevier Inc.)

Background: Multi-gene prognostic signatures derived from primary tumor biopsies can guide clinicians in designing an appropriate course of treatment. Identifying genes and pathways most essential to a signature performance may facilitate clinical application, provide insights into cancer progression, and uncover potentially new therapeutic targets. We previously developed a 17-gene prognostic signature (HTICS) for HER2+:ERα- breast cancer patients, using genes that are differentially expressed in tumor initiating cells (TICs) versus non-TICs from MMTV-Her2/neu mammary tumors. Here we probed the pathways and genes that underlie the prognostic power of HTICS., Methods: We used Leave-One Out, Data Combination Test, Gene Set Enrichment Analysis (GSEA), Correlation and Substitution analyses together with Receiver Operating Characteristic (ROC) and Kaplan-Meier survival analysis to identify critical biological pathways within HTICS. Publically available cohorts with gene expression and clinical outcome were used to assess prognosis. NanoString technology was used to detect gene expression in formalin-fixed paraffin embedded (FFPE) tissues., Results: We show that three major biological pathways: cell proliferation, immune response, and cell migration, drive the prognostic power of HTICS, which is further tuned by Homeostatic and Glycan metabolic signalling. A 6-gene minimal Core that retained a significant prognostic power, albeit less than HTICS, also comprised the proliferation/immune/migration pathways. Finally, we developed NanoString probes that could detect expression of HTICS genes and their substitutions in FFPE samples., Conclusion: Our results demonstrate that the prognostic power of a signature is driven by the biological processes it monitors, identify cell proliferation, immune response and cell migration as critical pathways for HER2+:ERα- cancer progression, and defines substitutes and Core genes that should facilitate clinical application of HTICS.

Multiplatform genomic analyses have identified 93 frequently altered genes in breast cancer. Of these, as many as 49 genes are directly or indirectly involved in transcription. These include constitutive and inducible DNA-binding transcription factors (DB-TFs, 13 genes), corepressors/coactivators (14 genes), epigenetic (10), and mediator/splicing/rRNA (3) factors. At least nine additional genes are immediate upstream regulators of transcriptional cofactors. G:profiler analysis reveals that these alterations affect cell cycle, development/differentiation, steroid hormone, and chromatin modification pathways. A notable observation is that DB-TFs that mediate major oncogenic signaling (e.g., WNT, receptor tyrosine kinase (RTK), NOTCH, and HIPPO), which switch from default repression (signal OFF) to transcriptional activation (signal ON), are not altered in breast cancer. Instead, corepressors (e.g., pRb for E2F1 downstream of various proliferation signals) or upstream factors (e.g., APC and AXIN for TCF, downstream of canonical WNT signaling) are lost, or coactivators (e.g., NOTCH1/2 for CSL/RBPJk) are induced. In contrast, constitutive (MYC, TBX3) and signal-induced (TP53, FOXA1) DB-TFs that do not mediate default repression are directly altered in breast cancer. Some of these TFs have been implicated in the establishment of super-enhancers and positive transcriptional elongation. In addition, oncogenic transcription is induced by mutations affecting regulatory elements or chromatin conformation that create new TF-binding sites in promoters and enhancers of oncogenic genes to promote tumorigenesis. Here we review these diverse oncogenic alterations in TFs in BC and discuss implications for therapy., (© 2017 Elsevier Inc. All rights reserved.)

Objective: Cardiovascular events induced in breast cancer patients receiving radiotherapy (RT), chemotherapy (CT), or a combination of both (CRT) can increase the risk of death. This nationwide population-based study aims to estimate the risk of cardiovascular complications with a follow-up period of 5 years., Materials and Methods: The study cohorts consisted of all patients hospitalized with a principal diagnosis of breast cancer who underwent treatment in 2002. The Cox proportional hazard model and Kaplan-Meier plot were analyzed to compare the cardiovascular event-free survival rate among breast cancer patients treated with different modalities., Results: Of the 5514 breast cancer patients identified, 289 patients had cardiovascular disease (CVD): 110 (5.7%) from the surgery-alone group, 24 (4.1%) from the RT group, 79 (4.6) from the CT group, and 76 (5.8%) from the CRT group. Breast cancer patients who undergo CT and CRT at an age less than 55 years had a higher risk of CVD when compared with the surgery-alone group (for both groups, p < 0.001). By contrast, breast cancer patients aged over 55 years had no increased risk of CVD among the different treatment modalities., Conclusion: Breast cancer patients receiving CT and/or CRT have a higher risk of CVD, especially younger patients (aged < 55 years). Therefore, regular examinations of cardiac functions and electrocardiogram should be considered in cases of young breast cancer patients who are receiving CT and/or CRT., (Copyright © 2016. Published by Elsevier B.V.)

Breast cancer is associated with alterations in a number of growth factor and hormone-regulated signaling pathways. Mouse models of metastatic breast cancer typically feature mutated oncoproteins that activate PI3K, Stat3, and Ras signaling, but the individual and combined roles of these pathways in breast cancer progression are poorly understood. In this study, we examined the relationship between oncogenic pathway activation and breast cancer subtype by analyzing mouse mammary tumor formation in which each pathway was activated singly or pairwise. All three oncogenes showed cooperation during primary tumor formation, but efficient dissemination was only dependent on Ras. In addition, transcriptional profiling demonstrated that Ras induced adenocarcinomas with molecular characteristics related to human basal-like and HER2(+) tumors. In contrast, Ras combined with PIK3CA(H1047R), an oncogenic mutant linked to ERα(+)/luminal breast cancer in humans, induced metastatic luminal B-like tumors. Consistent with these data, elevated Ras signaling was associated with basal-like and HER2(+) subtype tumors in humans and showed a statistically significant negative association with estrogen receptor (ER) signaling across all breast cancer. Despite this, there are luminal tumors with elevated Ras signaling. Importantly, when considered as a continuous variable, Ras pathway activation was strongly linked to reduced survival of patients with ERα(+) disease independent of PI3K or Stat3 activation. Therefore, our studies suggest that Ras activation is a key determinant for dissemination and poor prognosis of ERα(+)/luminal breast cancer in humans, and hormone therapy supplemented with Ras-targeting agents may be beneficial for treating this aggressive subtype., (©2015 American Association for Cancer Research.)

This study is to investigate the effect of ethyl gallate on invasion capabilities and its mechanism of breast cancer MDA-MB-231 cells. Using cell adhesion and transwell assay, separately, the effects of ethyl gallate on the invasion of MDA-MB-231 cells were measured. The Akt-NF-κB signal pathway protein expressions were analyzed with Western blot. Also, the mRNA levels of MMP-9 and MMP-2 were analyzed by RT-PCR. Ethyl gallate inhibited the abilities of motility, adhesion and invasion of breast cancer MDA-MB-231 cells in vitro (P<0.05), inhibited the mRNA levels of MMP-9, MMP-2, phosphorylation of AKt and protein expression of NF-κB. It is concluded that ethyl gallate can inhibit the abilities of invasion of breast cancer in vitro by inhibiting the mRNA levels of MMP-9/MMP-2, phosphorylation of Akt and protein expression of NF-κB.

HER2(+) breast cancer is currently treated with chemotherapy plus anti-HER2 inhibitors. Many patients do not respond or relapse with aggressive metastatic disease. Therefore, there is an urgent need for new therapeutics that can target HER2(+) breast cancer and potentiate the effect of anti-HER2 inhibitors, in particular those that can target tumor-initiating cells (TIC). Here, we show that MMTV-Her2/Neu mammary tumor cells cultured as nonadherent spheres or as adherent monolayer cells select for stabilizing mutations in p53 that "immortalize" the cultures and that, after serial passages, sphere conditions maintain TICs, whereas monolayer cells gradually lose these tumorigenic cells. Using tumorsphere formation as surrogate for TICs, we screened p53-mutant Her2/Neu(+) tumorsphere versus monolayer cells with a lentivirus short hairpin RNA kinome library. We identified kinases such as the mitogen-activated protein kinase and the TGFβR protein family, previously implicated in HER2(+) breast cancer, as well as autophagy factor ATG1/ULK1 and the noncanonical IκB kinase (IKK), TANK-binding kinase 1 (TBK1), which have not been previously linked to HER2(+) breast cancer. Knockdown of TBK1 or pharmacologic inhibition of TBK1 and the related protein, IKKε, suppressed growth of both mouse and human HER2(+) breast cancer cells. TBK1/IKKε inhibition promoted cellular senescence by suppressing p65-NF-κB and inducing p16(Ink4a). In addition, TBK1/IKKε inhibition cooperated with lapatinib, a HER2/EGFR1-targeted drug, to accelerate apoptosis and kill HER2(+) breast cancer cells both in culture and in xenografts. Our results suggest that patients with HER2(+) breast cancer may benefit from anti-TBK1/IKKε plus anti-HER2 combination therapies and establish conditions that can be used to screen for additional TIC-specific inhibitors of HER2(+) breast cancer., (©2014 AACR.)

The high intra- and inter-tumor heterogeneity of many types of cancers, including breast cancer (BC), poses great challenge to development of subtype-specific prognosis. In BC, the classification of tumors as either ERα+ (Luminal A and Luminal B), HER2+ (ERα+ or ERα-) or triple-negative (TNBC)(Basal-like, claudin-low) guides both prognostication and therapy. Indeed, prognostic signatures for ERα+ BC are being incorporated into clinical use. However, these signatures distinguish between luminal A (low risk) and Luminal B (high risk) BC; signatures that identify low/high risk patients with luminal B BC are yet to be developed. Likewise, no signature is in clinical use for HER2+ or TNBC. The major obstacles to development of robust signatures stem from diversity of BC, clonal evolution and heterogeneity within each subtype. We have recently generated a prognostic signature for HER2+:ERα- BC based on the identification of genes that were differentially expressed in a tumor-initiating cell (TIC)-enriched fraction versus non-TIC fraction from a mouse model of HER2+ BC (MMTV-Hers/Neu). Here we describe the rationale behind development of this prognosticator, and present new features of the signature, including elevated PI3K pathway activity and low TNFalpha and IFNgamma signaling in high-risk tumors. In addition, we address controversies in the field such as whether random gene expression signatures significantly associate with cancer outcome. Finally, we suggest a guideline for development of prognostic signatures and discuss future directions.

Melanoma differentiation-associated gene (MDA)-7)/interleukin (IL)-24, a member of the IL-10 family of cytokines, inhibits growth of various human cancer cells, yet the underlying mechanism is largely unknown. Here, we report that mda-7/IL-24 efficiently suppresses the development of rat mammary tumors in vivo. Microarray analysis for genes differentially expressed in rat mammary tumor cells overexpressing MDA-7/IL-24 compared with those that do not express this cytokine identified growth arrest-specific gene-3 (gas3) as a target for mda-7/IL-24. Upregulation of gas3 by mda-7/IL-24 was STAT3 dependent. Induction of gas3 inhibited attachment and proliferation of tumor cells in vitro and in vivo by inhibiting the interaction of β1 integrin with fibronectin. A mutated GAS3, which is unable to bind β1 integrin, was also unable to inhibit fibronectin-mediated attachment and cell growth both in adherent and suspension cultures, suggesting that GAS3 exerts its effects through interaction with and regulation of β1 integrin. Thus, mda-7/IL-24 inhibits breast cancer growth, at least in part, through upregulation of GAS3 and disruption of β1 integrin function. Importantly, the expression of the mda-7/IL-24 receptor, IL-20R1, is highly correlated with GAS3 expression in human breast cancer (P = 1.02 × 10(-9)), and the incidence of metastases is significantly reduced in patients with HER2(+) breast cancer expressing high-levels of IL-20R1. Together, our results identify a novel MDA-7/IL-24-GAS3-β1integrin-fibronectin signaling pathway that suppresses breast cancer growth and can be targeted for therapy., (©2013 AACR.)

The aim of this study was to explore the molecular mechanisms of jolkinolide B (JB), which is extracted from the root of Euphorbia fischeriana Steud. In this study, we found that JB, a diterpenoid from the traditional Chinese medicinal herb, strongly inhibited the PI3K/Akt/mTOR signaling pathway. Furthermore, we evaluated the effects of JB on the proliferation and apoptosis of MCF-7 human breast cancer cells. Our results showed significant induction of apoptosis in MCF-7 cells incubated with JB. The viability of the MCF-7 cells was assessed by MTT assay. Flow cytometry was used to detect apoptosis and cell cycle analysis. Transmission electron microscopy (TEM) analysis was used to observe cell morphology. MCF-7 cells were subcutaneously inoculated into nude mice to study the in vivo antitumor effects of JB. The growth of MCF-7 cells was inhibited and arrested in the S phase by JB. The data showed significantly decreased tumor volume and weight in nude mice inoculated with MCF-7 cells. In addition, treatment with JB was able to induce downregulation of cyclinD1, cyclinE, mTOR, p-PI3K and p-Akt, and upregulation of PTEN and p-eIF4E. Collectively, JB-induced apoptosis of MCF-7 cells occurs through the PI3K/Akt/mTOR signaling pathway. Furthermore, the PI3K/Akt signaling cascade plays a role in the induction of apoptosis in JB-treated cells. These observations suggest that JB may have therapeutic applications in the treatment of cancer.

Human Epidermal Growth Factor Receptor 2-positive (HER2(+)) breast cancer (BC) is a highly aggressive disease commonly treated with chemotherapy and anti-HER2 drugs, including trastuzumab. There is currently no way to predict which HER2(+) BC patients will benefit from these treatments. Previous prognostic signatures for HER2(+) BC were developed irrespective of the subtype or the hierarchical organization of cancer in which only a fraction of cells, tumor-initiating cells (TICs), can sustain tumor growth. Here, we used serial dilution and single-cell transplantation assays to identify MMTV-Her2/Neu mouse mammary TICs as CD24(+):JAG1(-) at a frequency of 2-4.5%. A 17-gene Her2-TIC-enriched signature (HTICS), generated on the basis of differentially expressed genes in TIC versus non-TIC fractions and trained on one HER2(+) BC cohort, predicted clinical outcome on multiple independent HER2(+) cohorts. HTICS included up-regulated genes involved in S/G2/M transition and down-regulated genes involved in immune response. Its prognostic power was independent of other predictors, stratified lymph node(+) HER2(+) BC into low and high-risk subgroups, and was specific for HER2(+):estrogen receptor alpha-negative (ERα(-)) patients (10-y overall survival of 83.6% for HTICS(-) and 24.0% for HTICS(+) tumors; hazard ratio = 5.57; P = 0.002). Whereas HTICS was specific to HER2(+):ERα(-) tumors, a previously reported stroma-derived signature was predictive for HER2(+):ERα(+) BC. Retrospective analyses revealed that patients with HTICS(+) HER2(+):ERα(-) tumors resisted chemotherapy but responded to chemotherapy plus trastuzumab. HTICS is, therefore, a powerful prognostic signature for HER2(+):ERα(-) BC that can be used to identify high risk patients that would benefit from anti-HER2 therapy.

Most human breast tumors have mutations that elevate signaling through a key metabolic pathway that is induced by insulin and a number of growth factors. This pathway serves to activate an enzyme known as phosphatidylinositol 3' kinase (PI3K) as well as to regulate proteins that signal in response to lipid products of PI3K. The specific mutations that activate this pathway in breast cancer can occur in genes coding for tyrosine kinase receptors, adaptor proteins linked to PI3K, catalytic and regulatory subunits of PI3K, serine/threonine kinases that function downstream of PI3K, and also phosphatidylinositol 3' phosphatase tumor suppressors that function to antagonize this pathway. While each genetic change results in net elevation of PI3K pathway signaling, and all major breast cancer subtypes show pathway activation, the specific mutation(s) involved in any one tumor may play an important role in defining tumor subtype, prognosis and even sensitivity to therapy. Here, we describe mouse models of breast cancer with elevated PI3K signaling, and how they may be used to guide development of novel therapeutics.

Triple-negative breast cancer (TNBC) is a heterogeneous disease that includes Basal-like and Claudin-low tumors. The Claudin-low tumors are enriched for features associated with epithelial-to-mesenchymal transition (EMT) and possibly for tumor initiating cells. Primary TNBCs respond relatively well to conventional chemotherapy; however, metastatic disease is virtually incurable. Thus, there is a great interest in identifying specific therapeutic targets for TNBC. The tumor suppressor RB1 is frequently lost in Basal-like breast cancer. To test for a causative role of RB1 gene loss in BC and for its effect on specific subtypes, we deleted mouse Rb in mammary stem/bipotent progenitor cells. This led to diverse mammary tumors including TNBC, with a subset of the latter containing p53 mutations and exhibiting features of Basal-like BC or EMT. Combined mutation of Rb and p53 in mammary stem/bipotent progenitors induced EMT type tumors. Here, we review our findings and those of others, which connect Rb and p53 to EMT in TNBC. Furthermore, we discuss how by understanding this circuit and its vulnerabilities, we may identify novel therapy for TNBC.

Purpose: The incidence of bone metastasis in advanced breast cancer (BrCa) exceeds 70%. Bortezomib, a proteasome inhibitor used for the treatment of multiple myeloma, also promotes bone formation. We tested the hypothesis that proteasome inhibitors can ameliorate BrCa osteolytic disease., Experimental Design: To address the potentially beneficial effect of bortezomib in reducing tumor growth in the skeleton and counteracting bone osteolysis, human MDA-MB-231 BrCa cells were injected into the tibia of mice to model bone tumor growth for in vivo assessment of treatment regimens before and after tumor growth., Results: Controls exhibited tumor growth, destroying trabecular and cortical bone and invading muscle. Bortezomib treatment initiated following inoculation of tumor cells strikingly reduced tumor growth, restricted tumor cells mainly to the marrow cavity, and almost completely inhibited osteolysis in the bone microenvironment over a 3- to 4-week period as shown by [(18)F]fluorodeoxyglucose positron emission tomography, micro-computed tomography scanning, radiography, and histology. Thus, proteasome inhibition is effective in killing tumor cells within the bone. Pretreatment with bortezomib for 3 weeks before inoculation of tumor cells was also effective in reducing osteolysis. Our in vitro and in vivo studies indicate that mechanisms by which bortezomib inhibits tumor growth and reduces osteolysis result from inhibited cell proliferation, necrosis, and decreased expression of factors that promote BrCa tumor progression in bone., Conclusion: These findings provide a basis for a novel strategy to treat patients with BrCa osteolytic lesions, and represent an approach for protecting the entire skeleton from metastatic bone disease., (©2010 AACR.)

The current concept of epigenetic repression is based on one repressor unit corresponding to one silent gene. This notion, however, cannot adequately explain concurrent silencing of multiple loci observed in large chromosome regions. The long-range epigenetic silencing (LRES) can be a frequent occurrence throughout the human genome. To comprehensively characterize the influence of estrogen signaling on LRES, we analyzed transcriptome, methylome, and estrogen receptor alpha (ESR1)-binding datasets from normal breast epithelia and breast cancer cells. This "omics" approach uncovered 11 large repressive zones (range, 0.35 approximately 5.98 megabases), including a 14-gene cluster located on 16p11.2. In normal cells, estrogen signaling induced transient formation of multiple DNA loops in the 16p11.2 region by bringing 14 distant loci to focal ESR1-docking sites for coordinate repression. However, the plasticity of this free DNA movement was reduced in breast cancer cells. Together with the acquisition of DNA methylation and repressive chromatin modifications at the 16p11.2 loci, an inflexible DNA scaffold may be a novel determinant used by breast cancer cells to reinforce estrogen-mediated repression.

Purpose: N,N-Diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine (DPPE; tesmilifene) is thought to potentiate the antineoplastic effect of cytotoxic drugs. In a phase III randomized trial for metastatic breast cancer using doxorubicin with or without DPPE, addition of the latter resulted in a significant improvement in overall survival and a trend toward a difference in progression-free survival but, paradoxically, no difference in objective tumor response. Here we tested the hypothesis that DPPE targets breast tumor-initiating cells (TICs)., Experimental Design: Human breast TICs from pleural effusions were identified as CD44(+):CD24(-/low) cells by flow cytometry and functionally by their ability to form nonadherent spheres in culture. Mouse mammary TICs from two different models of breast cancer were identified as cells capable of initiating spheres in culture and secondary tumors following transplantation into the mammary gland of syngeneic mice., Results: We show that at physiologically attainable concentrations, treatment with DPPE alone reduced tumorsphere formation and viability of CD44(+):CD24(-/low) breast cancer cells. The kinetics of killing varied for the different breast tumor cells and required continuous exposure to the drug. Whereas doxorubicin killed CD44(+):CD24(-/low) and CD44(-):CD24(+) cells equally well, DPPE induced apoptosis preferentially in CD44(+):CD24(-/low) cells. Treatment of Her2/Neu(+) mammary tumor cells with DPPE in vitro efficiently killed TICs, as determined by flow cytometry and transplantation assays; DPPE further cooperated with doxorubicin to completely eradicate tumorigenic cells., Conclusions: Our results show that continuous treatment with DPPE alone directly targets breast TICs, and provide rationale to test for cooperation between DPPE and known drugs with efficacy toward breast cancer subtypes.

Myeloid cell leukemia-1 (Mcl-1), an antiapoptotic Bcl-2 family member, is overexpressed in many types of human cancer and associates with cell immortalization, malignant transformation, and chemoresistance. Glycogen synthase kinase-3beta (GSK-3beta), a key component of the Wnt signaling pathway, is involved in multiple physiologic processes such as protein synthesis, tumorigenesis, and apoptosis. Here, we report that expression of Mcl-1 was correlated with phosphorylated GSK-3beta (p-GSK-3beta) at Ser(9) (an inactivated form of GSK-3beta) in multiple cancer cell lines and primary human cancer samples. In addition, Mcl-1 was strikingly linked with poor prognosis of human breast cancer, in which the high level of Mcl-1 was related to high tumor grade and poor survival of breast cancer patients. Furthermore, we found that activation of GSK-3beta could down-regulate Mcl-1 and was required for proteasome-mediated Mcl-1 degradation. Under some physiologic conditions, such as UV irradiation, anticancer drug treatment, and inhibition of growth factor pathways, Mcl-1 was down-regulated through activation of GSK-3beta. Our results indicate that Mcl-1 stabilization by GSK-3beta inactivation could be involved in tumorigenesis and serve as a useful prognostic marker for human breast cancer.

Purpose: Genetic alterations were previously identified in normal epithelia adjacent to invasive cancers. The aim of this study was to determine DNA methylation in histologically normal tissues from multiple geographic zones adjacent to primary breast tumors., Experimental Design: First, methylation status of a 4-kb region of RASSF1A promoter was interrogated using oligonucleotide-based microarray in 144 samples (primary tumors, 47; adjacent normals, 69; reduction mammoplasty tissues, 28). Second, allelic imbalance (AI)/loss of heterozygosity (LOH) surrounding RASSF1A promoter were analyzed in 30 samples (tumors, 8; adjacent normals, 22). Third, global methylation screening of 49 samples (tumors, 12; adjacent normals, 25; reduction mammoplasty, 12) was done by differential methylation hybridization. Real-time quantitative methylation-specific PCR was used to validate the microarray findings., Results: DNA methylation in the core RASSF1A promoter was low in reduction mammoplasty tissues (P=0.0001) when compared with primary tumors. The adjacent normals had an intermediate level of methylation. The regions surrounding the core were highly methylated in all sample types. Microsatellite markers showed AI/LOH in tumors and some of the adjacent normals. Concurrent AI/LOH and DNA methylation in RASSF1A promoter occurred in two of six tumors. Global methylation screening uncovered genes more methylated in adjacent normals than in reduction mammoplasty tissues. The methylation status of four genes was confirmed by quantitative methylation-specific PCR., Conclusions: Our findings suggest a field of methylation changes extending as far as 4 cm from primary tumors. These frequent alterations may explain why normal tissues are at risk for local recurrence and are useful in disease prognostication.

IFN-inducible proteins are known to mediate IFN-directed antitumor effects. The human IFN-inducible protein absent in melanoma 2 (AIM2) gene encodes a 39-kDa protein, which contains a 200-amino-acid repeat as a signature of HIN-200 family (hematopoietic IFN-inducible nuclear proteins). Although AIM2 is known to inhibit fibroblast cell growth in vitro, its antitumor activity has not been shown. Here, we showed that AIM2 expression suppressed the proliferation and tumorigenicity of human breast cancer cells, and that AIM2 gene therapy inhibited mammary tumor growth in an orthotopic tumor model. We further showed that AIM2 significantly increased sub-G(1) phase cell population, indicating that AIM2 could induce tumor cell apoptosis. Moreover, AIM2 expression greatly suppressed nuclear factor-kappaB transcriptional activity and desensitized tumor necrosis factor-alpha-mediated nuclear factor-kappaB activation. Together, these results suggest that AIM2 associates with tumor suppression activity and may serve as a potential therapeutic gene for future development of AIM2-based gene therapy for human breast cancer.

Beta-catenin is upregulated in many human cancers and considered to be an oncogene. Hepatocellular carcinoma (HCC) is one of the most prevalent human malignancies, and individuals who are chronic hepatitis B virus (HBV) carriers have a greater than 100-fold increased relative risk of developing HCC. Here we report a mechanism by which HBV-X protein (HBX) upregulates beta-catenin. Erk, which is activated by HBX, associates with GSK-3beta through a docking motif ((291)FKFP) of GSK-3beta and phosphorylates GSK-3beta at the (43)Thr residue, which primes GSK-3beta for its subsequent phosphorylation at Ser9 by p90RSK, resulting in inactivation of GSK-3beta and upregulation of beta-catenin. This pathway is a general signal, as it was also observed in cell lines in which Erk-primed inactivation of GSK-3beta was regulated by IGF-1, TGF-beta, and receptor tyrosine kinase HER2, and is further supported by immunohistochemical staining in different human tumors, including cancers of the liver, breast, kidney, and stomach.

Alterations in histones, chromatin-related proteins, and DNA methylation contribute to transcriptional silencing in cancer, but the sequence of these molecular events is not well understood. Here we demonstrate that on disruption of estrogen receptor (ER) alpha signaling by small interfering RNA, polycomb repressors and histone deacetylases are recruited to initiate stable repression of the progesterone receptor (PR) gene, a known ERalpha target, in breast cancer cells. The event is accompanied by acquired DNA methylation of the PR promoter, leaving a stable mark that can be inherited by cancer cell progeny. Reestablishing ERalpha signaling alone was not sufficient to reactivate the PR gene; reactivation of the PR gene also requires DNA demethylation. Methylation microarray analysis further showed that progressive DNA methylation occurs in multiple ERalpha targets in breast cancer genomes. The results imply, for the first time, the significance of epigenetic regulation on ERalpha target genes, providing new direction for research in this classical signaling pathway.

Aberrant DNA methylation of promoter CpG islands is associated with transcriptionally repressive heterochromatin in neoplasia. The dynamics of this epigenetic process in mediating the transition from an active to an inactive state of transcription remains to be elucidated, however. Here, we used the methylation-specific oligonucleotide microarray to map the methylation patterns of a CpG island, located within the promoter and the first exon regions of RASSF1A, in normal breast tissue controls, primary tumors, and breast cancer cell lines. Oligonucleotide pairs, spaced along the CpG island region, were designed to discriminate between methylated and unmethylated alleles of selected sites. The methylation-specific oligonucleotide data indicate that the majority of test samples show widespread methylation in the first exon of RASSF1A. In contrast, the promoter area was usually undermethylated in normal controls and in 32% of the primary tumors tested, whereas the rest of the primary tumors and breast cancer cell lines showed various degrees of methylation in the region. Methylation profiling of individual tumors further suggest that DNA methylation progressively spreads from the first exon into the promoter area of this gene. Functional analysis indicates that increased density of RASSF1A promoter methylation is associated with altered chromatin, marked by a depletion of acetylated histones and methylated histone 3-lysine 4 and an enrichment of methylated histone 3-lysine 9 in the studied area. The combination of these epigenetic modifications may engender a stable silencing of the gene in breast cancer cells. Thus, this study underscores the importance of detailed mapping of methylation patterns within a CpG island locus that may provide insights into the progressive nature of aberrant DNA methylation and its relationship with transcriptional silencing during the neoplastic process.