Abstract 32: BCL11A is necessary for the expression of extracellular matrix genes and metastatic progression of triple-negative breast cancer

Cancer stem cells (CSC) contribute to the high incidence of metastatic recurrence in triple-negative breast cancer (TNBC) and elucidating the mechanisms controlling CSC properties should provide novel targets for therapeutic development that improves patient outcomes. The transcription factor BCL11A is highly differentially expressed in TNBC versus all other subtypes and controls breast CSC phenotypes such as marker expression and tumor initiation. However, the genes that BCL11A targets to control CSC biology and whether BCL11A promotes metastatic progression are unknown. To address these questions, we assessed the impact of transiently silencing the expression of BCL11A in TNBC cells using siRNA transfections. Reducing BCL11A expression did not impact TNBC cell viability or in vitro migratory capacity. However, silencing BCL11A significantly decreased invasion of TNBC cell lines, in vitro. Furthermore, stable shRNA-mediated silencing of BCL11A in the highly metastatic MDA-MB-231 cell line reduced metastatic outgrowth when xenografted into immunocompromised mice, suggesting that BCL11A is critical for metastatic progression of TNBC. To identify the BCL11A-regulated transcriptome in TNBC, we performed RNA-seq analysis of cells transiently transfected with non-targeting or BCL11A-targeted siRNAs in the MDA-MB-231 cell line. Consistent with the impact of BCL11A on invasion, numerous genes involved in adhesion and extracellular matrix were reduced with BCL11A silencing. The gene encoding the matrix metalloproteinase, MMP1, was the most significantly differentially expressed gene, with a 10-fold decrease in RNA expression following BCL11A suppression. We confirmed this down-regulation by both qRT-PCR and western blots of independent samples, as well as in the HCC1143 TNBC cell line. Current studies are assessing the functional impact of MMP1 regulation by BCL11A on invasion and metastatic progression of TNBC.

Citation Format: Darcie D. Seachrist, Natasha N. Ingles, Molly M. Hannigan, Donny D. Licatalosi, Ruth A. Keri. BCL11A is necessary for the expression of extracellular matrix genes and metastatic progression of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 32.

Targeting bromodomain and extraterminal proteins in breast cancer

Breast cancer is a collection of distinct tumor subtypes that are driven by unique gene expression profiles. These transcriptomes are controlled by various epigenetic marks that dictate which genes are expressed and suppressed. During carcinogenesis, extensive restructuring of the epigenome occurs, including aberrant acetylation, alteration of methylation patterns, and accumulation of epigenetic readers at oncogenes. As epigenetic alterations are reversible, epigenome-modulating drugs could provide a mechanism to silence numerous oncogenes simultaneously. Here, we review the impact of inhibitors of the Bromodomain and Extraterminal (BET) family of epigenetic readers in breast cancer. These agents, including the prototypical BET inhibitor JQ1, have been shown to suppress a variety of oncogenic pathways while inducing minimal, if any, toxicity in models of several subtypes of breast cancer. BET inhibitors also synergize with multiple approved anti-cancer drugs, providing a greater response in breast cancer cell lines and mouse models than either single agent. The combined findings of the studies discussed here provide an excellent rationale for the continued investigation of the utility of BET inhibitors in breast cancer.

c-Abl inhibits breast cancer tumorigenesis through reactivation of p53-mediated p21 expression

We previously reported that constitutive c-Abl activity (CST-Abl) abrogates the tumorigenicity of triple-negative breast cancer cells through the combined actions of two cellular events: downregulated matrix metalloproteinase (MMP) and upregulated p21^Waf1/Cip1 expression. We now find decreased c-Abl expression to be significantly associated with diminished relapse-fee survival in breast cancer patients, particularly those exhibiting invasive and basal phenotypes. Moreover, CST-Abl expression enabled 4T1 cells to persist innocuously in the mammary glands of mice, doing so by exhausting their supply of cancer stem cells. Restoring MMP-9 expression and activity in CST-Abl-expressing 4T1 cells failed to rescue their malignant phenotypes; however, rendering these same cells deficient in p21 expression not only delayed their acquisition of senescent phenotypes, but also partially restored their tumorigenicity in mice. Although 4T1 cells lacked detectable expression of p53, those engineered to express CST-Abl exhibited robust production and secretion of TGF-β1 that engendered the reactivated expression of p53. Mechanistically, TGF-β-mediated p53 expression transpired through the combined actions of Smad1/5/8 and Smad2, leading to the dramatic upregulation of p21 and its stimulation of TNBC senescence. Collectively, we identified a novel c-Abl:p53:p21 signaling axis that functions as a powerful suppressor of mammary tumorigenesis and metastatic progression.

Mitotic Vulnerability in Triple-Negative Breast Cancer Associated with LIN9 Is Targetable with BET Inhibitors

Triple-negative breast cancers (TNBC) are highly aggressive, lack FDA-approved targeted therapies, and frequently recur, making the discovery of novel therapeutic targets for this disease imperative. Our previous analysis of the molecular mechanisms of action of bromodomain and extraterminal protein inhibitors (BETi) in TNBC revealed these drugs cause multinucleation, indicating BET proteins are essential for efficient mitosis and cytokinesis. Here, using live cell imaging, we show that BET inhibition prolonged mitotic progression and induced mitotic cell death, both of which are indicative of mitotic catastrophe. Mechanistically, the mitosis regulator LIN9 was a direct target of BET proteins that mediated the effects of BET proteins on mitosis in TNBC. Although BETi have been proposed to function by dismantling super-enhancers (SE), the LIN9 gene lacks an SE but was amplified or overexpressed in the majority of TNBCs. In addition, its mRNA expression predicted poor outcome across breast cancer subtypes. Together, these results provide a mechanism for cancer selectivity of BETi that extends beyond modulation of SE-associated genes and suggest that cancers dependent upon LIN9 overexpression may be particularly vulnerable to BETi. Cancer Res; 77(19); 5395-408. ©2017 AACR.

Mutant p53 dictates the oncogenic activity of c-Abl in triple-negative breast cancers

We recently established c-Abl as a potent suppressor of triple-negative breast cancer (TNBC) progression through its reactivation of a p53:p21 signaling axis coupled to senescence. Moreover, we observed co-expression of p53 and c-Abl to be essential for normal mammary epithelial cell physiology, as this relationship is lost upon breast cancer progression. Cytoplasmic c-Abl activity is markedly increased in some TNBCs and contributes to disease progression; however, the mechanisms underlying these events remain largely unknown. In addressing this question, we show here that c-Abl is predominantly restricted to the cytoplasm of human MDA-MB-231 TNBC cells, and to the nucleus of human MCF-7 luminal A cells. TTK is a mitotic protein kinase that phosphorylates c-Abl on Thr735, thereby creating a recognition binding motif for 14-3-3 adaptor proteins in response to oxidative stress. By interrogating the METABRIC database, we observed a significant correlation between p53 expression and that of c-Abl and TTK in basal-like breast cancers. Moreover, heterologous expression of TTK in MCF-7 cells significantly stimulated their growth in part via a c-Abl-dependent mechanism. Conversely, depleting TTK expression in MDA-MB-231 cells not only inhibited their organoid growth in 3D-cultures, but also sensitized them to the tumor suppressing activities of c-Abl independent of its subcellular localization. Moreover, we show that mutant p53 forms cytoplasmic complexes with c-Abl, thereby dictating the subcellular localization of c-Abl and the sensitivity of MDA-MB-231 cells to Imatinib. In response to nutrient deprivation, c-Abl:p53 complexes readily accumulate in the nucleus, resulting in the hyperactivation of c-Abl and initiation of its anti-tumor activities. Collectively, we identified a novel mutant p53:c-Abl cytoplasmic signaling complex that promotes MDA-MB-231 cell growth and highlights the contextual cues that confer oncogenic activity to c-Abl in breast cancer.

Regulatory cross-talk determines the cellular levels of 53BP1 protein, a critical factor in DNA repair

DNA double strand breaks (DSBs) severely disrupt DNA integrity. 53BP1 plays critical roles in determining DSB repair. Whereas the recruitment of 53BP1 to the DSB site is key for its function, recent evidence suggests that 53BP1's abundance also plays an important role in DSB repair because recruitment to damage sites will be influenced by protein availability. Initial evidence has pointed to three proteins, the ubiquitin-conjugating enzyme UbcH7, the cysteine protease cathepsin L (CTSL), and the nuclear structure protein lamin A/C, that may impact 53BP1 levels, but the roles of each protein and any interplay between them were unclear. Here we report that UbcH7-dependent degradation plays a major role in controlling 53BP1 levels both under normal growth conditions and during DNA damage. CTSL influenced 53BP1 degradation during DNA damage while having little effect under normal growth conditions. Interestingly, both the protein and the mRNA levels of CTSL were reduced in UbcH7-depleted cells. Lamin A/C interacted with 53BP1 under normal conditions. DNA damage disrupted the lamin A/C-53BP1 interaction, which preceded the degradation of 53BP1 in soluble, but not chromatin-enriched, cellular fractions. Inhibition of 53BP1 degradation by a proteasome inhibitor or by UbcH7 depletion restored the 53BP1-lamin A/C interaction. Depletion of lamin A/C, but not CTSL, caused a similar enhancement in cell sensitivity to DNA damage as UbcH7 depletion. These data suggest that multiple pathways collectively fine-tune the cellular levels of 53BP1 protein to ensure proper DSB repair and cell survival.

Hotspots of aberrant enhancer activity punctuate the colorectal cancer epigenome

In addition to mutations in genes, aberrant enhancer element activity at non-coding regions of the genome is a key driver of tumorigenesis. Here, we perform epigenomic enhancer profiling of a cohort of more than forty genetically diverse human colorectal cancer (CRC) specimens. Using normal colonic crypt epithelium as a comparator, we identify enhancers with recurrently gained or lost activity across CRC specimens. Of the enhancers highly recurrently activated in CRC, most are constituents of super enhancers, are occupied by AP-1 and cohesin complex members, and originate from primed chromatin. Many activate known oncogenes, and CRC growth can be mitigated through pharmacologic inhibition or genome editing of these loci. Nearly half of all GWAS CRC risk loci co-localize to recurrently activated enhancers. These findings indicate that the CRC epigenome is defined by highly recurrent epigenetic alterations at enhancers which activate a common, aberrant transcriptional programme critical for CRC growth and survival.

Bromodomain and Extraterminal Protein Inhibition Blocks Growth of Triple-negative Breast Cancers through the Suppression of Aurora Kinases

Bromodomain and extraterminal (BET) proteins are epigenetic "readers" that recognize acetylated histones and mark areas of the genome for transcription. BRD4, a BET family member protein, has been implicated in a number of types of cancer, and BET protein inhibitors (BETi) are efficacious in many preclinical cancer models. However, the drivers of response to BETi vary depending on tumor type, and little is known regarding the target genes conveying BETi activity in triple-negative breast cancer (TNBC). Here, we show that BETi repress growth of multiple in vitro and in vivo models of TNBC by inducing two terminal responses: apoptosis and senescence. Unlike in other cancers, response to BETi in TNBC is not dependent upon suppression of MYC Instead, both end points are preceded by the appearance of polyploid cells caused by the suppression of Aurora kinases A and B (AURKA/B), which are critical mediators of mitosis. In addition, AURKA/B inhibitors phenocopy the effects of BETi. These results indicate that Aurora kinases play an important role in the growth suppressive activity of BETi in TNBC. Elucidating the mechanism of response to BETi in TNBC should 1) facilitate the prediction of how distinct TNBC tumors will respond to BETi and 2) inform the rational design of drug combination therapies.

Bioengineering of Tobacco Mosaic Virus to Create a Non-Infectious Positive Control for Ebola Diagnostic Assays

The 2014 Ebola epidemic is the largest to date. There is no cure or treatment for this deadly disease; therefore there is an urgent need to develop new diagnostics to accurately detect Ebola. Current RT-PCR assays lack sensitive and reliable positive controls. To address this critical need, we devised a bio-inspired positive control for use in RT-PCR diagnostics: we encapsulated scrambled Ebola RNA sequences inside of tobacco mosaic virus to create a biomimicry that is non-infectious, but stable, and could therefore serve as a positive control in Ebola diagnostic assays. Here, we report the bioengineering and validation of this probe.

A review of the carcinogenic potential of bisphenol A

The estrogenic properties of bisphenol A (BPA), a ubiquitous synthetic monomer that can leach into the food and water supply, have prompted considerable research into exposure-associated health risks in humans. Endocrine-disrupting properties of BPA suggest it may impact developmental plasticity during early life, predisposing individuals to disease at doses below the oral reference dose (RfD) established by the Environmental Protection Agency in 1982. Herein, we review the current in vivo literature evaluating the carcinogenic properties of BPA. We conclude that there is substantial evidence from rodent studies indicating that early-life BPA exposures below the RfD lead to increased susceptibility to mammary and prostate cancer. Based on the definitions of "carcinogen" put forth by the International Agency for Research on Cancer and the National Toxicology Program, we propose that BPA may be reasonably anticipated to be a human carcinogen in the breast and prostate due to its tumor promoting properties.

Combined SFK/mTOR inhibition prevents rapamycin-induced feedback activation of AKT and elicits efficient tumor regression

Resistance to receptor tyrosine kinase (RTK) blockade in breast cancer is often mediated by activation of bypass pathways that sustain growth. Src and mammalian target of rapamycin (mTOR) are two intrinsic targets that are downstream of most RTKs. To date, limited clinical efficacy has been observed with either Src or mTOR inhibitors when used as single agents. Resistance to mTOR inhibitors is associated with loss of negative feedback regulation, resulting in phosphorylation and activation of AKT. Herein, we describe a novel role for Src in contributing to rapalog-induced AKT activation. We found that dual activation of Src and the mTOR pathway occurs in nearly half of all breast cancers, suggesting potential cross-talk. As expected, rapamycin inhibition of mTOR results in feedback activation of AKT in breast cancer cell lines. Addition of the Src/c-Abl inhibitor, dasatinib, completely blocks this feedback activation, confirming convergence between Src and the mTOR pathway. Analysis in vivo revealed that dual Src and mTOR inhibition is highly effective in two mouse models of breast cancer. In a luminal disease model, combined dasatinib and rapamycin is more effective at inducing regression than either single agent. Furthermore, the combination of dasatinib and rapamycin delays tumor recurrence following the cessation of treatment. In a model of human EGFR-2-positive (HER2(+)) disease, dasatinib alone is ineffective, but potentiates the efficacy of rapamycin. These data suggest that combining mTOR and Src inhibitors may provide a new approach for treating multiple breast cancer subtypes that may circumvent resistance to targeted RTK therapies.

GABA(A) receptor pi (GABRP) stimulates basal-like breast cancer cell migration through activation of extracellular-regulated kinase 1/2 (ERK1/2)

Breast cancer is a heterogeneous disease comprised of distinct subtypes predictive of patient outcome. Tumors of the basal-like subtype have a poor prognosis due to inherent aggressiveness and the lack of targeted therapeutics. Basal-like tumors typically lack estrogen receptor-α, progesterone receptor and HER2/ERBB2, or in other words they are triple negative (TN). Continued evaluation of basal-like breast cancer (BLBC) biology is essential to identify novel therapeutic targets. Expression of the pi subunit of the GABA(A) receptor (GABRP) is associated with the BLBC/TN subtype, and herein, we reveal its expression also correlates with metastases to the brain and poorer patient outcome. GABRP expression in breast cancer cell lines also demonstrates a significant correlation with the basal-like subtype suggesting that GABRP functions in the initiation and/or progression of basal-like tumors. To address this postulate, we stably silenced GABRP in two BLBC cell lines, HCC1187 and HCC70 cells. Decreased GABRP reduces in vitro tumorigenic potential and migration concurrent with alterations in the cytoskeleton, specifically diminished cellular protrusions and expression of the BLBC-associated cytokeratins, KRT5, KRT6B, KRT14, and KRT17. Silencing GABRP also decreases phosphorylation of extracellular regulated kinase 1/2 (ERK1/2) in both cell lines and selective inhibition of ERK1/2 similarly decreases the basal-like cytokeratins as well as migration. Combined, these data reveal a GABRP-ERK1/2-cytokeratin axis that maintains the migratory phenotype of basal-like breast cancer. GABRP is a component of a cell surface receptor, thus, these findings suggest that targeting this new signaling axis may have therapeutic potential in BLBC.

Hypomethylation of the MMP7 promoter and increased expression of MMP7 distinguishes the basal-like breast cancer subtype from other triple-negative tumors

Identification of novel targets for the treatment of basal-like breast cancer is essential for improved outcomes in patients with this disease. This study investigates the association of MMP7 expression and MMP7 promoter methylation with subtype and outcome in breast cancer patient cohorts. Immunohistochemical analysis was performed on a breast cancer tissue microarray and validated in independent histological samples. MMP7 expression significantly correlated with patient age, tumor size, triple-negative (TN) status, and recurrence. Analysis of publically available datasets confirmed MMP7 gene expression as a prognostic marker of breast cancer metastasis, particularly metastasis to the brain and lungs. Methylation of the MMP7 promoter was assessed by methylation-specific PCR in a panel of breast cancer cell lines and patient tumor samples. Hypomethylation of the MMP7 promoter significantly correlated with TN status in DNA from patient tumor samples, and this association was confirmed using The Cancer Genome Atlas (TCGA) dataset. Evaluation of a panel of breast cancer cell lines and data from the Curtis and TCGA breast carcinoma datasets revealed that elevated MMP7 expression and MMP7 promoter hypomethylation are specific biomarkers of the basal-like molecular subtype which shares considerable, but not complete, overlap with the clinical TN subtype. Importantly, MMP7 expression was identified as an independent predictor of pathological complete response in a large breast cancer patient cohort. Combined, these data suggest that MMP7 expression and MMP7 promoter methylation may be useful as prognostic biomarkers. Furthermore, MMP7 expression and promoter methylation analysis may be effective mechanisms to distinguish basal-like breast cancers from other triple-negative subtypes. Finally, these data implicate MMP7 as a potential therapeutic target for the treatment of basal-like breast cancers.

Biodistribution and clearance of a filamentous plant virus in healthy and tumor-bearing mice

Aim: Nanoparticles based on plant viruses are emerging biomaterials for medical applications such as drug delivery and imaging. Their regular structures can undergo genetic and chemical modifications to carry large payloads of cargos, as well as targeting ligands. Of several such platforms under development, only few have been characterized in vivo. We recently introduced the filamentous plant virus, potato virus X (PVX), as a new platform. PVX presents with a unique nanoarchitecture and is difficult to synthesize chemically. Methods: Here, we present a detailed analysis of PVX biodistribution and clearance in healthy mice and mouse tumor xenograft models using a combination of ex vivo whole-organ imaging, quantitative fluorescence assays and immunofluorescence microscopy. Results & conclusion: While up to 30% of the PVX signal was from the colon, mammary and brain tumor tissues, remaining particles were cleared by the reticuloendothelial system organs (the spleen and liver), followed by slower processing and clearance through the kidneys and bile.

Original submitted 7 November 2012; Revised submitted 19 January 2013; Published online 9 July 2013

On-command drug release from nanochains inhibits growth of breast tumors

PURPOSE

To evaluate the ability of radiofrequency (RF)-triggered drug release from a multicomponent chain-shaped nanoparticle to inhibit the growth of an aggressive breast tumor.

METHODS

A two-step solid phase chemistry was employed to synthesize doxorubicin-loaded nanochains, which were composed of three iron oxide nanospheres and one doxorubicin-loaded liposome assembled in a 100-nm-long linear nanochain. The nanochains were tested in the 4T1-LUC-GFP orthotopic mouse model, which is a highly aggressive breast cancer model. The 4T1-LUC-GFP cell line stably expresses firefly luciferase, which allowed the non-invasive in vivo imaging of tumor response to the treatment using bioluminescence imaging (BLI).

RESULTS

Longitudinal BLI imaging showed that a single nanochain treatment followed by application of RF resulted in an at least 100-fold lower BLI signal compared to the groups treated with nanochains (without RF) or free doxorubicin followed by RF. A statistically significant increase in survival time of the nanochain-treated animals followed by RF (64.3 days) was observed when compared to the nanochain-treated group without RF (35.7 days), free doxorubicin-treated group followed by RF (38.5 days), and the untreated group (30.5 days; n=5 animals per group).

CONCLUSIONS

These studies showed that the combination of RF and nanochains has the potential to effectively treat highly aggressive cancers and prolong survival.

FOXC1 is enriched in the mammary luminal progenitor population, but is not necessary for mouse mammary ductal morphogenesis

Expression of FOXC1, a forkhead box transcription factor, correlates with the human basal-like breast cancer (BLBC) subtype, and functional analyses have revealed its importance for in vitro invasiveness of BLBC cells. Women diagnosed with this breast tumor subtype have a poorer outcome because of the lack of targeted therapies; thus, continued investigation of factors driving these tumors is critical to uncover novel therapeutic targets. Several processes that dictate normal mammary morphogenesis parallel cancer progression, and enforced expression of FOXC1 can induce a progenitor state in more-differentiated mammary epithelial cells. Consequently, evaluating how FOXC1 functions in the normal gland is critical to further understand BLBC biology. Although FOXC1 is well known to control normal development of a number of tissues, its role in the mammary gland has not yet been investigated. Herein, we describe FOXC1 expression patterning in the normal breast, where it is localized to the basal/myoepithelium, suggesting that FOXC1 would be required for normal development. However, mammary glands lacking Foxc1 have no overt defect in ductal outgrowth, alveologenesis, or lineage specification. Of significant interest, we found that expression of FOXC1 is enriched in the normal luminal progenitor population, which is the postulated cell of origin of BLBC. These results indicate that FOXC1 is unnecessary for mammary morphogenesis and that its role in BLBC likely involves processes that are unrelated to cell lineage specification.

Abstract LB-221: Inhibition of rapamycin-induced feedback activation of AKT with dasatinib induces complete tumor regression in a preclinical model of breast cancer

Resistance to receptor tyrosine kinase (RTK) blockade in breast cancer treatment is commonly mediated by activation of bypass pathways that sustain growth. We propose moving away from the individual targeting of RTKs to inhibit multiple commonly activated, overlapping, and essential downstream pathways. The mammalian Target of Rapamycin (mTOR) and the non-receptor tyrosine kinase, Src, are two intrinsic targets that intersect downstream of most RTKs. To date, limited clinical efficacy has been shown with either mTOR or Src inhibitors as single agents. Here we show that dasatinib, a dual Src/c-abl inhibitor, is able to block the well-established de-repression of AKT that occurs with rapamycin inhibition of mTOR. Furthermore, dual inhibition of these distinct, but compensatory arms of RTK signaling results in rapid and complete regression in over 80% of MMTV-PyMT-induced mammary tumors, with only moderate effects on tumor inhibition as single agents. Importantly, Src and mTOR pathway co-activation occurs in nearly half of human breast cancers, independent of tumor sub-type. These studies support the evaluation of combined mTOR and Src inhibitors in breast cancer patients. Such inhibitors are currently FDA approved, expediting the transition to clinical safety and efficacy trials. We expect this approach will prevent molecular evolution of bypass pathways and induce tumor regression.

Citation Format: Jennifer L. Yori, Kristen Lozada, Darcie D. Seachrist, Jonathan Mosley, Fadi W. Abdul-Karim, Christine N. Booth, Chris A. Flask, Ruth A. Keri. Inhibition of rapamycin-induced feedback activation of AKT with dasatinib induces complete tumor regression in a preclinical model of breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-221. doi:10.1158/1538-7445.AM2013-LB-221

The HER2- and heregulin β1 (HRG)-inducible TNFR superfamily member Fn14 promotes HRG-driven breast cancer cell migration, invasion, and MMP9 expression

HER2 overexpression occurs in 15% to 20% of all breast cancers and is associated with increased metastatic potential and poor patient survival. Abnormal HER2 activation, either through HER2 overexpression or heregulin (HRG):HER3 binding, elicits the formation of potent HER2-HER3 heterodimers and drives breast cancer cell growth and metastasis. In a previous study, we found that fibroblast growth factor-inducible 14 (Fn14), a member of the TNF receptor superfamily, was frequently overexpressed in human HER2+ breast tumors. We report here that HER2 and Fn14 are also coexpressed in mammary tumors that develop in two different transgenic mouse models of breast cancer. In consideration of these findings, we investigated whether HER2 activation in breast cancer cells could directly induce Fn14 gene expression. We found that transient or stable transfection of MCF7 cells with a HER2 expression plasmid increased Fn14 protein levels. Also, HRG1-β1 treatment of MCF7 cells transiently induced Fn14 mRNA and protein expression. Both the HER2- and HRG1-β1-induced increase in Fn14 expression in MCF7 cells as well as basal Fn14 expression in HER2 gene-amplified AU565 cells could be reduced by HER2 kinase inhibition with lapatinib or combined HER2 and HER3 depletion using siRNA. We also report that Fn14-depleted, HER2-overexpressing MCF7 cells have reduced basal cell migration capacity and reduced HRG1-β1-stimulated cell migration, invasion, and matrix metalloproteinase (MMP)-9 expression. Together, these results indicate that Fn14 may be an important downstream regulator of HER2/HER3-driven breast cancer cell migration and invasion.

FOXA1 represses the molecular phenotype of basal breast cancer cells

Breast cancer is a heterogeneous disease that comprises multiple subtypes. Luminal subtype tumors confer a more favorable patient prognosis, which is, in part, attributed to estrogen receptor (ER)-α positivity and antihormone responsiveness. Expression of the forkhead box transcription factor, FOXA1, similarly correlates with the luminal subtype and patient survival, but is also present in a subset of ER-negative tumors. FOXA1 is also consistently expressed in luminal breast cancer cell lines even in the absence of ER. In contrast, breast cancer cell lines representing the basal subtype do not express FOXA1. To delineate an ER-independent role for FOXA1 in maintaining the luminal phenotype, and hence a more favorable prognosis, we performed expression microarray analyses on FOXA1-positive and ER-positive (MCF7, T47D), or FOXA1-positive and ER-negative (MDA-MB-453, SKBR3) luminal cell lines in the presence or absence of transient FOXA1 silencing. This resulted in three FOXA1 transcriptomes: (1) a luminal signature (consistent across cell lines), (2) an ER-positive signature (restricted to MCF7 and T47D) and (3) an ER-negative signature (restricted to MDA-MB-453 and SKBR3). Gene set enrichment analyses revealed FOXA1 silencing causes a partial transcriptome shift from luminal to basal gene expression signatures. FOXA1 binds to a subset of both luminal and basal genes within luminal breast cancer cells, and loss of FOXA1 increases enhancer RNA transcription for a representative basal gene (CD58). These data suggest FOXA1 directly represses a subset of basal signature genes. Functionally, FOXA1 silencing increases migration and invasion of luminal cancer cells, both of which are characteristics of basal subtype cells. We conclude FOXA1 controls plasticity between basal and luminal breast cancer cells, not only by inducing luminal genes but also by repressing the basal phenotype, and thus aggressiveness. Although it has been proposed that FOXA1-targeting agents may be useful for treating luminal tumors, these data suggest that this approach may promote transitions toward more aggressive cancers.

Imaging metastasis using an integrin-targeting chain-shaped nanoparticle

While the enhanced permeability and retention effect may promote the preferential accumulation of nanoparticles into well-vascularized primary tumors, it is ineffective in the case of metastases hidden within a large population of normal cells. Due to their small size, high dispersion to organs, and low vascularization, metastatic tumors are less accessible to targeted nanoparticles. To tackle these challenges, we designed a nanoparticle for vascular targeting based on an α(v)β(3) integrin-targeted nanochain particle composed of four iron oxide nanospheres chemically linked in a linear assembly. The chain-shaped nanoparticles enabled enhanced "sensing" of the tumor-associated remodeling of the vascular bed, offering increased likelihood of specific recognition of metastatic tumors. Compared to spherical nanoparticles, the chain-shaped nanoparticles resulted in superior targeting of α(v)β(3) integrin due to geometrically enhanced multivalent docking. We performed multimodal in vivo imaging (fluorescence molecular tomography and magnetic resonance imaging) in a non-invasive and quantitative manner, which showed that the nanoparticles targeted metastases in the liver and lungs with high specificity in a highly aggressive breast tumor model in mice.

Overexpression of follistatin in the mouse epididymis disrupts fluid resorption and sperm transit in testicular excurrent ducts

Activin is a well-established modulator of male and female reproduction that stimulates the synthesis and secretion of follicle-stimulating hormone. Nonpituitary effects of activin have also been reported, although the paracrine actions of this growth factor in several reproductive tissues are not well understood. To identify the paracrine functions of activin during mammary gland morphogenesis and tumor progression, we produced transgenic mice that overexpress follistatin (FST), an intrinsic inhibitor of activin, under control of the mouse mammary tumor virus (MMTV) promoter. Although the MMTV-Fst mice were constructed to assess the role of activin in females, expression of the transgene was also observed in the testes and epididymides of males. While all 17 transgenic founder males exhibited copulatory behavior and produced vaginal plugs in females, only one produced live offspring. In contrast, transgenic females were fertile, permitting expansion of transgenic mouse lines. Light and transmission electron microscopic examination of the transgenic testes and epididymides revealed impairment of fluid resorption and sperm transit in the efferent ducts and initial segment of the epididymis, as indicated by accumulation of fluid and sperm stasis. Consequently, a variety of degenerative lesions were observed in the seminiferous epithelium, such as vacuolation and early stages of mineralization and fibrosis. Sperm collected from the caudae epididymidis of MMTV-Fst males had detached heads and were immotile. Together, these data reveal that activin signaling is essential for normal testicular excurrent duct function and that its blockade impairs fertility. These results also suggest that selective inhibitors of activin signaling may provide a useful approach for the development of male contraceptives without compromising androgen synthesis and actions.

The forkhead box transcription factor FOXC1 promotes breast cancer invasion by inducing matrix metalloprotease 7 (MMP7) expression

Therapeutic options for treatment of basal-like breast cancers are limited and identification of molecular targets for novel therapies to treat this aggressive cancer is urgently needed. Recently, FOXC1, a forkhead box transcription factor, was identified as a functionally important biomarker of breast cancer aggressiveness and the basal-like breast cancer subtype. However, the mechanism through which FOXC1 controls aggressiveness of basal-like breast cancer remains to be elucidated. Here, we identify matrix metalloprotease 7 (MMP7) as a key downstream effector of FOXC1-mediated invasiveness. Expression of FOXC1 and MMP7 is significantly correlated in breast cancer samples and cell lines at both the mRNA and protein levels. Transient expression of FOXC1 in nontransformed mammary epithelial cell lines resulted in significantly increased expression of MMP7 and an MMP7-dependent increase in invasiveness. In reciprocal experiments, silencing endogenous FOXC1 in basal-like breast cancer cell lines resulted in decreased expression of MMP7 without decreased expression of other matrix metalloproteinases. We also demonstrate that elevated co-expression of FOXC1 and MMP7 is an independent predictor of patient outcome in multivariate analyses of two breast cancer patient cohorts. Together, our findings identify MMP7 as a novel mechanism through which FOXC1 may regulate the basal-like breast cancer invasive phenotype and the propensity of these cancers to metastasize. Furthermore, our findings demonstrate for the first time a correlation between MMP7 expression and basal-like breast cancers, suggesting that MMP7 may be a useful therapeutic target for treatment of this disease.

Enhanced delivery of chemotherapy to tumors using a multicomponent nanochain with radio-frequency-tunable drug release

While nanoparticles maximize the amount of chemotherapeutic drug in tumors relative to normal tissues, nanoparticle-based drugs are not accessible to the majority of cancer cells because nanoparticles display patchy, near-perivascular accumulation in tumors. To overcome the limitations of current drugs in their molecular or nanoparticle form, we developed a nanoparticle based on multicomponent nanochains to deliver drug to the majority of cancer cells throughout a tumor while reducing off-target delivery. The nanoparticle is composed of three magnetic nanospheres and one doxorubicin-loaded liposome assembled in a 100 nm long chain. These nanoparticles display prolonged blood circulation and significant intratumoral deposition in tumor models in rodents. Furthermore, the magnetic particles of the chains serve as a mechanical transducer to transfer radio frequency energy to the drug-loaded liposome. The defects on the liposomal walls trigger the release of free drug capable of spreading throughout the entire tumor, which results in a widespread anticancer effect.