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Metastasis is the cause of over 90% of all deaths associated with breast cancer, yet the strategies to predict cancer spreading based on primary tumor profiles and therefore prevent metastasis are egregiously limited. As rare precursor cells to metastasis, circulating tumor cells (CTCs) in multicellular clusters in the blood are 20-50 times more likely to produce viable metastasis than single CTCs. However, the molecular mechanisms underlying various CTC clusters, such as homotypic tumor cell clusters and heterotypic tumor-immune cell clusters, are yet to be fully elucidated. Combining machine learning-assisted computational ranking with experimental demonstration to assess cell adhesion candidates, we identified a transmembrane protein Plexin- B2 (PB2) as a new therapeutic target that drives the formation of both homotypic and heterotypic CTC clusters. High PB2 expression in human primary tumors predicts an unfavorable distant metastasis-free survival and is enriched in CTC clusters compared to single CTCs in advanced breast cancers. Loss of PB2 reduces formation of homotypic tumor cell clusters as well as heterotypic tumor-myeloid cell clusters in triple-negative breast cancer. Interactions between PB2 and its ligand Sema4C on tumor cells promote homotypic cluster formation, and PB2 binding with Sema4A on myeloid cells (monocytes) drives heterotypic CTC cluster formation, suggesting that metastasizing tumor cells hijack the PB2/Sema family axis to promote lung metastasis in breast cancer. Additionally, using a global proteomic analysis, we identified novel downstream effectors of the PB2 pathway associated with cancer stemness, cell cycling, and tumor cell clustering in breast cancer. Thus, PB2 is a novel therapeutic target for preventing new metastasis.

This file contains significantly enriched MSigDB gene sets from pathway analysis of the six gene regulatory patterns found in figure 6.

A growing body of evidence suggests that the inflammatory NFκB pathway is associated with the progression of ER+ tumors to more aggressive stages. However, it is unknown whether NFκB is a driver or a consequence of aggressive ER+ disease. To investigate this question, we developed breast cancer cell lines expressing an inducible, constitutively active form of IκB kinase β (CA-IKKβ), a key kinase in the canonical NFκB pathway. We found that CA-IKKβ blocked E2-dependent cell proliferation in vitro and tumor growth in vivo in a reversible manner, suggesting that IKKβ may contribute to tumor dormancy and recurrence of ER+ disease. Moreover, coactivation of ER and IKKβ promoted cell migration and invasion in vitro and drove experimental metastasis in vivo. Gene expression profiling revealed a strong association between ER and CA-IKKβ–driven gene expression and clinically relevant invasion and metastasis gene signatures. Mechanistically, the invasive phenotype appeared to be driven by an expansion of a basal/stem-like cell population rather than EMT. Taken together, our findings suggest that coactivation of ER and the canonical NFκB pathway promotes a dormant, metastatic phenotype in ER+ breast cancer and implicates IKKβ as a driver of certain features of aggressive ER+ breast cancer.Significance: The canonical NFκB pathway promotes expansion of stem/basal-like cells and a dormant, metastatic phenotype in ER+ breast cancer cells. Cancer Res; 78(4); 974–84. ©2017 AACR.

This file contains supplemental data related to T47D-CA-IKKβ and control cell lines, estrogen receptor expression, phosphorylation, and activity, cell morphology and EMT. Additional analysis of metastases and stem cell phenotypes are included.

This file contains gene expression profiling data for MCF-7-CA-IKKβ cells treated with E2, DOX, E2+DOX.

Circulating tumor cell (CTC) clusters mediate metastasis at a higher efficiency and are associated with lower overall survival in breast cancer compared to single cells. Combining single-cell RNA sequencing and protein analyses, here we report the profiles of primary tumor cells and lung metastases of triple-negative breast cancer (TNBC). ICAM1 expression increases by 200-fold in the lung metastases of three TNBC patient-derived xenografts (PDXs). Depletion of ICAM1 abrogates lung colonization of TNBC cells by inhibiting homotypic tumor cell-tumor cell cluster formation. Machine learning-based algorithms and mutagenesis analyses identify ICAM1 regions responsible for homophilic ICAM1-ICAM1 interactions, thereby directing homotypic tumor cell clustering, as well as heterotypic tumor-endothelial adhesion for trans-endothelial migration. Moreover, ICAM1 promotes metastasis by activating cellular pathways related to cell cycle and stemness. Finally, blocking ICAM1 interactions significantly inhibits CTC cluster formation, tumor cell transendothelial migration, and lung metastasis. Therefore, ICAM1 can serve as a novel therapeutic target for metastasis initiation of TNBC., Circulating tumor cell (CTC) clusters are more efficient at mediating metastasis as compared to single cells and are associated with poor prognosis in breast cancer. Here, the authors show that ICAM1 is enriched in CTC clusters and its loss suppresses cell-cell interaction and CTC cluster formation, and propose ICAM1 as a therapeutic target for treating breast cancer metastasis.

Triple-negative breast cancer (TNBC) is one of the most aggressive and metastatic breast cancer subtypes lacking targeted therapy. Our recent work demonstrated that circulating tumor cell (CTC) clusters and polyclonal metastasis of TNBC are driven by aggregation of CD44+ cancer stem cells (CSC) and associated with an unfavorable prognosis, such as low overall survival. However, there is no existing therapeutic that can specifically block CTC or CSC cluster formation. Methods: Using patient-derived xenograft (PDX) models, we established an ex vivo tumor cell clustering assay for a pilot screening of blockade antibodies. After identifying EGFR as a target candidate, we modulated the gene expression and inhibited its kinase activity to determine its functional importance in tumor cell clustering and therapeutic inhibition of lung metastasis. We also examined the molecular regulation network of EGFR and a potential connection to CSC marker CD44 and microRNAs, which regulate CTC clustering. Results: We report here that EGFR inhibition successfully blocks circulating CSC (cCSC) clustering and lung metastasis of TNBC. EGFR enhances CD44-mediated tumor cell aggregation and CD44 stabilizes EGFR. Importantly, blocking EGFR by a novel anti-EGFR monoclonal antibody (clone LA1) effectively blocked cell aggregation in vitro and reduced lung metastasis in vivo. Furthermore, our data demonstrated that the tumor suppressor microRNA-30c serves as another negative regulator of cCSC clustering and lung metastasis by targeting CD44 as well as its downstream effector EGFR. Conclusion: Our studies identify a novel anti-EGFR therapeutic strategy to inhibit cCSC aggregation and therefore abolish cCSC cluster-mediated metastasis of TNBC.

Over two years into the COVID-19 pandemic, the human immune response to SARS-CoV-2 during the active disease phase has been extensively studied. However, the long-term impact after recovery, which is critical to advance our understanding SARS-CoV-2 and COVID-19-associated long-term complications, remains largely unknown. Herein, we characterized multi-omic single-cell profiles of circulating immune cells in the peripheral blood of 100 patients, including covenlesent COVID-19 and sero-negative controls. The reduced frequencies of both short-lived monocytes and long-lived regulatory T (Treg) cells are significantly associated with the patients recovered from severe COVID-19. Consistently, sc-RNA seq analysis reveals seven heterogeneous clusters of monocytes (M0-M6) and ten Treg clusters (T0-T9) featuring distinct molecular signatures and associated with COVID-19 severity. Asymptomatic patients contain the most abundant clusters of monocyte and Treg expressing high CD74 or IFN-responsive genes. In contrast, the patients recovered from a severe disease have shown two dominant inflammatory monocyte clusters with S100 family genes: S100A8 & A9 with high HLA-I whereas S100A4 & A6 with high HLA-II genes, a specific non-classical monocyte cluster with distinct IFITM family genes, and a unique TGF-β high Treg Cluster. The outpatients and seronegative controls share most of the monocyte and Treg clusters patterns with high expression of HLA genes. Surprisingly, while presumably short-ived monocytes appear to have sustained alterations over 4 months, the decreased frequencies of long-lived Tregs (high HLA-DRA and S100A6) in the outpatients restore over the tested convalescent time (>= 4 months). Collectively, our study identifies sustained and dynamically altered monocytes and Treg clusters with distinct molecular signatures after recovery, associated with COVID-19 severity.

The synthetic food preservative sodium benzoate (SB) is widely used in both food and pharmaceutical industries. A growing body of evidence highlights the adverse effects of SB on human health; however, effect of the prolonged intake of SB on the reproductive system is not fully elucidated. The current study investigates the effect of different doses of SB (0-1000 mg/kg BW) on the reproductive system of male rats administered oral SB for 90 consecutive days. Results revealed that increasing doses of SB significantly altered the weight of reproductive organs, decreased sperm count and motility and enhanced the percentage of abnormal sperms. This was concomitant with significant decline in plasma testosterone and FSH levels, increase in plasma LH and decrease in the activities of 17β-HSD and 17-KSR enzymes in the testes. Inflammation and oxidative stress were induced as indicated by the significant increase in TNF-α and IL-6 levels, inhibition of antioxidant enzymes activity and levels of GSH, increase in the levels of NO and TBARS and enhanced protein expression of mtTFA and UCP2 in the testes. Interestingly, p53 expression and caspase-3 activity were upregulated in the testes suggesting induction of apoptosis. Histopathological examination of the testes confirmed apoptosis and revealed degenerative alterations of the testes' architecture and perturbation of spermatogenesis. Based upon these findings, the no-observed-adverse-effect level of SB on the reproductive system was determined to be less than 1 mg/kg BW/day, highlighting the risks of long-term exposure to low as well as high doses of SB on male reproductive health.

Tumor-initiating cells with reprogramming plasticity are thought to be essential for cancer development and metastatic regeneration in many cancers; however, the molecular mechanisms are not fully understood. This study reports that CD81, a tetraspanin protein marker of small extracellular vesicles (exosomes), functions as a binding partner of CD44 and facilitates self-renewal of tumor initiating cells. Using machine learning-assisted protein structure modeling, co-immunoprecipitation, and mutagenesis approaches, we further demonstrate that CD81 interacts with CD44 on the cellular membrane through their extracellular regions. In-depth global and phosphoproteomic analyses of clustering tumor cells unveils endocytosis-related signature pathways of proteins and phosphorylation patterns regulated by CD81 and CD44 specifically or shared between two. Notably, CRISPR Cas9-mediated depletion of either CD44 or CD81 results in loss of both proteins in cancer cell-secreted exosomes, a state which abolishes exosome-induced self-renewal of recipient cells for mammosphere formation. CD81 is expressed in >80% of human circulating tumor cells (CTCs) and specifically enriched in clustered CTCs along with CD44 isolated from breast cancer patients. Mimicking the phenotypes of CD44 deficiency, loss of CD81 also inhibits tumor cluster aggregation, tumorigenesis, and lung metastasis of triple negative breast cancer (TNBC), supporting the clinical significance of CD81 in association with patient outcomes. Our study highlights the novel role of CD81 and its partnership with CD44 in cancer exosomes, self-renewal, CTC clustering, and metastasis initiation of TNBC.

Tumor-initiating cells with reprogramming plasticity and/or de-differentiation attributes have been thought to initiate primary tumor development as well as to regenerate secondary tumors in metastatic organs; however, the molecular mechanisms are not fully understood. We previously found that breast tumor-initiating cell marker, CD44, directs multicellular aggregation and cluster formation of circulating tumor cells (CTCs), which further enhance stemness and survival of such cells, enabling metastatic colonization to the lungs. To further elucidate the molecular network underlying CTC cluster formation, we performed global proteomic profiling and discovered that the tetraspanin protein CD81, which is normally enriched in exosomes (small extracellular vesicles), is a new driver of cancer initiation and metastasis as a facilitator and target of CD44. Loss of CD81 compromises tumorigenicity and mammosphere formation of triple negative breast cancer (TNBC) cells. Assisted by machine learning-based algorithms and mutagenesis approach, we found that CD81 interacts with CD44 on the cellular membrane through their extracellular regions. Notably, genetic knockout of CD44 or CD81 results in loss of both CD81 and CD44 in secreted exosomes, a state which abolishes exosome-induced self-renewal of recipient cells, such as mammosphere formation. In addition, RNA sequencing analysis showed that CD81 knockdown up-regulates expression of a cell differentiation marker, SEMA7a, whose down-regulation partially rescues mammosphere formation inhibition by CD81 depletion. Clinically, CD81 expression was observed in >80% of CTCs and specifically enriched and co-expressed along with CD44 in clustered CTCs of breast cancer patients. Mimicing the phenotypes of CD44 deficiency, loss of CD81 also inhibited tumor cell aggregation and lung metastasis of TNBC in both human and mouse tumor models, supporting the clinical significance of CD81 in association with patient outcomes. Our study highlights a new driving role of CD81 in cancer exosome-induced stemness, clustered CTCs, and metastasis initiation of TNBC, reported for the first time to our knowledge.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the coronavirus disease 2019 (COVID-19) with innate and adaptive immune response triggered in such patients by viral antigens. Both convalescent plasma and engineered high affinity human monoclonal antibodies have shown therapeutic potential to treat COVID-19. Whether additional antiviral soluble factors exist in peripheral blood remain understudied. Herein, we detected circulating exosomes that express the SARS-CoV-2 viral entry receptor angiotensin-converting enzyme 2 (ACE2) in plasma of both healthy donors and convalescent COVID-19 patients. We demonstrated that exosomal ACE2 competes with cellular ACE2 for neutralization of SARS-CoV-2 infection. ACE2-expressing (ACE2+) exosomes, but not the ACE2-negative controls, blocked the binding of the viral spike (S) protein RBD to ACE2+ cells in a dose dependent manner, which was 400- to 700-fold more potent than that of vesicle-free recombinant human ACE2 extracellular domain protein (rhACE2). As a consequence, exosomal ACE2 prevented SARS-CoV-2 pseudotype virus tethering and infection of human host cells at a 50–150 fold higher efficacy than rhACE2. A similar antiviral activity of exosomal ACE2 was further demonstrated to block wild-type live SARS-CoV-2 infection. Of note, depletion of ACE2+ exosomes from COVID-19 patient plasma impaired the ability to block SARS-CoV-2 RBD binding to host cells. Furthermore, a dramatic increase in plasma ACE2+ exosome levels were detected in patients with severe COVID-19 pathogenesis. Our data demonstrate that ACE2+ exosomes can serve as a decoy therapeutic and a possible innate antiviral mechanism to block SARS-CoV-2 infection.

Mathematical modelling has been used to study tumor-immune cell interaction. Some models were proposed to examine the effect of circulating lymphocytes, natural killer cells, and CD8+T cells, but they neglected the role of CD4+T cells. Other models were constructed to study the role of CD4+T cells but did not consider the role of other immune cells. In this study, we propose a mathematical model, in the form of a system of nonlinear ordinary differential equations, that predicts the interaction between tumor cells and natural killer cells, CD4+T cells, CD8+T cells, and circulating lymphocytes with or without immunotherapy and/or chemotherapy. This system is stiff, and the Runge–Kutta method failed to solve it. Consequently, the “Adams predictor-corrector” method is used. The results reveal that the patient’s immune system can overcome small tumors; however, if the tumor is large, adoptive therapy with CD4+T cells can be an alternative to both CD8+T cell therapy and cytokines in some cases. Moreover, CD4+T cell therapy could replace chemotherapy depending upon tumor size. Even if a combination of chemotherapy and immunotherapy is necessary, using CD4+T cell therapy can better reduce the dose of the associated chemotherapy compared to using combined CD8+T cells and cytokine therapy. Stability analysis is performed for the studied patients. It has been found that all equilibrium points are unstable, and a condition for preventing tumor recurrence after treatment has been deduced. Finally, a bifurcation analysis is performed to study the effect of varying system parameters on the stability, and bifurcation points are specified. New equilibrium points are created or demolished at some bifurcation points, and stability is changed at some others. Hence, for systems turning to be stable, tumors can be eradicated without the possibility of recurrence. The proposed mathematical model provides a valuable tool for designing patients’ treatment intervention strategies.

A growing body of evidence suggests that the inflammatory NFκB pathway is associated with the progression of ER+ tumors to more aggressive stages. However, it is unknown whether NFκB is a driver or a consequence of aggressive ER+ disease. To investigate this question, we developed breast cancer cell lines expressing an inducible, constitutively active form of IκB kinase β (CA-IKKβ), a key kinase in the canonical NFκB pathway. We found that CA-IKKβ blocked E2-dependent cell proliferation in vitro and tumor growth in vivo in a reversible manner, suggesting that IKKβ may contribute to tumor dormancy and recurrence of ER+ disease. Moreover, coactivation of ER and IKKβ promoted cell migration and invasion in vitro and drove experimental metastasis in vivo. Gene expression profiling revealed a strong association between ER and CA-IKKβ–driven gene expression and clinically relevant invasion and metastasis gene signatures. Mechanistically, the invasive phenotype appeared to be driven by an expansion of a basal/stem-like cell population rather than EMT. Taken together, our findings suggest that coactivation of ER and the canonical NFκB pathway promotes a dormant, metastatic phenotype in ER+ breast cancer and implicates IKKβ as a driver of certain features of aggressive ER+ breast cancer. Significance: The canonical NFκB pathway promotes expansion of stem/basal-like cells and a dormant, metastatic phenotype in ER+ breast cancer cells. Cancer Res; 78(4); 974–84. ©2017 AACR.

The current study highlights for the first time cloning, overexpression, purification, and assessing the cytotxcity of the novel interferon epsilon (IFNε), from the Arabian camelCamelus dromedarius, against two human breast cancer cell lines MDA-MB-231 and MCF-7. Full-length cDNA encoding interferon epsilon (IFNε) was isolated and cloned from the liver of the Arabian camel,C. dromedariususing reverse transcription-polymerase chain reaction. The sequence analysis of the camel IFNε cDNA showed a 582-bp open reading frame encoding a protein of 193 amino acids with an estimated molecular weight of 22.953 kDa. A BLAST search analysis revealed that theC. dromedariusIFNε shared high sequence identity with the IFN genes of other species, such asCamelus ferus,Vicugna pacos, andHomo sapiens. Expression of the camel IFNε cDNA inEscherichia coligave a fusion protein band of 22.73 kDa after induction with either isopropyl β-D-1-thiogalactopyranoside or lactose for 5 h. Recombinant IFNε protein was overexpressed in the form of inclusion bodies that were easily solubilized and refolded using SDS and KCl. The solubilized inclusion bodies were purified to apparent homogeneity using nickel affinity chromatography. We examined the effect of IFNε on two breast cancer cell lines MDA-MB-231 and MCF-7. In both cell lines, IFNε inhibited cell survival in a dose dependent manner as observed by MTT assay, morphological changes and apoptosis assay. Caspase-3 expression level was found to be increased in MDA-MB-231 treated cells as compared to untreated cells.

Estrogen action in mammary gland development and breast cancer progression is tightly linked to the GH/IGF-I axis. Although many of the effects of GH on mammary gland growth and development require IGF-I, the extent to which GH action in breast cancer depends on IGF-I is not known. We examined GH action in a panel of estrogen receptor-positive breast cancer cell lines and found that T47D cells express significant levels of GH receptor and that GH significantly enhances 17β-estradiol (E2)-stimulated proliferation in these cells. GH action in the T47D cells was independent of changes in IGF-I and IGF-I receptor (IGF-IR) expression and IGF-IR signaling, suggesting that GH can exert direct effects on breast cancer cells. Although E2-dependent proliferation required IGF-IR signaling, the combination of GH+E2 overcame inhibition of IGF-IR activity to restore proliferation. In contrast, GH required both Janus kinase 2 and epidermal growth factor receptor signaling for subsequent ERK activation and potentiation of E2-dependent proliferation. Downstream of these pathways, we identified a number of immediate early-response genes associated with proliferation that are rapidly and robustly up-regulated by GH. These findings demonstrate that GH can have important effects in breast cancer cells that are distinct from IGF-IR activity, suggesting that novel drugs or improved combination therapies targeting estrogen receptor and the GH/IGF axis may be beneficial for breast cancer patients.

In breast tumors, activation of the nuclear factor κB (NFκB) pathway promotes survival, migration, invasion, angiogenesis, stem cell-like properties, and resistance to therapy--all phenotypes of aggressive disease where therapy options remain limited. Adding an anti-inflammatory/anti-NFκB agent to breast cancer treatment would be beneficial, but no such drug is approved as either a monotherapy or adjuvant therapy. To address this need, we examined whether dimethyl fumarate (DMF), an anti-inflammatory drug already in clinical use for multiple sclerosis, can inhibit the NFκB pathway. We found that DMF effectively blocks NFκB activity in multiple breast cancer cell lines and abrogates NFκB-dependent mammosphere formation, indicating that DMF has anti-cancer stem cell properties. In addition, DMF inhibits cell proliferation and significantly impairs xenograft tumor growth. Mechanistically, DMF prevents p65 nuclear translocation and attenuates its DNA binding activity but has no effect on upstream proteins in the NFκB pathway. Dimethyl succinate, the inactive analog of DMF that lacks the electrophilic double bond of fumarate, is unable to inhibit NFκB activity. Also, the cell-permeable thiol N-acetyl l-cysteine, reverses DMF inhibition of the NFκB pathway, supporting the notion that the electrophile, DMF, acts via covalent modification. To determine whether DMF interacts directly with p65, we synthesized and used a novel chemical probe of DMF by incorporating an alkyne functionality and found that DMF covalently modifies p65, with cysteine 38 being essential for the activity of DMF. These results establish DMF as an NFκB inhibitor with anti-tumor activity that may add therapeutic value in the treatment of aggressive breast cancers.

Estrogen receptor (ER) and NFκB are two widely expressed, pleiotropic transcription factors that have been shown to interact and affect one another’s activity. While the ability of ER to repress NFκB activity has been extensively studied and is thought to underlie the anti-inflammatory activity of estrogens, how NFκB signaling affects ER activity is less clear. This is a particularly important question in breast cancer since activation of NFκB in ER positive tumors is associated with failure of endocrine and chemotherapies. In this review, we provide an update on the multiple mechanisms by which NFκB can influence ER activity, including down-regulation of ER expression, enhanced ER recruitment to DNA, and increased transcriptional activity of both liganded and unliganded ER. Additionally, a novel example of NFκB potentiation of ER-dependent gene repression is reviewed. Together, these mechanisms can alter response to endocrine therapies and may underlie the poor outcome for women with ER positive tumors that have active NFκB signaling.

Cisplatin is one of the most potent chemotherapeutic antitumor drugs. Oxidative stress has been proven to be involved in cisplatin-induced toxicity. Therefore, the present study was undertaken to examine the antioxidant potential of grape seed proanthocyanidin extract (GSPE) against the toxicity of cisplatin in male rats. Cisplatin treated animals revealed a significant elevation in plasma, heart, kidney and liver thiobarbituric acid reactive substances (TBARS), while the activities of antioxidant enzymes (GST, SOD, CAT and GSH-Px, and the levels of glutathione (GSH) were decreased. Aspartate and alanine transaminases (AST and ALT), creatine kinase and lactate dehydrogenase were significantly increased in plasma, while liver AST and ALT were significantly decreased. Cisplatin significantly increased the levels of plasma total lipid, cholesterol, urea and creatinine, and the relative weight of kidney. On the other hand, plasma total protein and albumin, and body weight were significantly decreased. GSPE reduced cisplatin-induced the levels of TBARS in plasma, heart, kidney and liver, TL, cholesterol, urea and creatinine, and liver AST and ALT. Moreover, it ameliorated cisplatin-induced decrease in the activities of antioxidant enzymes, and GSH, total protein and albumin. Therefore, the present results revealed that GSPE exerts a protective effect by antagonizing cisplatin toxicity.

The clinical use of cisplatin is highly limited, because of its renal toxicity. In this study, the protective effect of grape seed proanthocyanidin extract (GSPE) against cisplatin-induced nephrotoxicity is investigated in rats. Results showed that DNA qualitative analysis indicated an increase in the instability of the DNA purified from the cisplatin exposed kidney cells. Agarose gel electrophoresis revealed DNA damage in the form of smearing as well as ladder like fragmentation of the kidney genomic DNA. Cisplatin produced different RAPD patterns compared to control. Deletion of bands for the amplified DNA extracted from cisplatin treated rats was the most common outcome. Treatment with cisplatin decreased albumin, and increased urea and creatinine. Cisplatin significantly increased the level of kidney free radicals, and decreased the glutathione content and the activities of the antioxidant enzymes. The presence of GSPE with cisplatin significantly alleviated its nephrotoxicity. In conclusion, the present study showed that cisplatin induced damage in the kidney genomic DNA, lipid peroxidation, inhibition of antioxidant enzymes and alterations of biochemical parameters in plasma and kidney of rats. While, GSPE treatment protected against the toxic effects induced by cisplatin. Thus, GSPE may be used to prevent toxicity during chemotherapeutic treatment with cisplatin.

Estrogen receptor α (ER) is a good prognostic marker expressed in ≈75% of breast tumors. Women with ER+ tumors will receive endocrine therapy, yet ≈50% will experience relapse, often with more aggressive and metastatic tumors. A growing body of evidence indicates that an inflammatory microenvironment and activation of the NF-κB pathway are highly associated with progression of ER+ tumors to more aggressive stages. However, it is not known whether activation of the canonical arm of the NF-κB pathway is sufficient to drive progression to a more aggressive phenotype. In order to study this, we developed MCF-7 and T47D breast cancer cell lines expressing a DOX-inducible, constitutively active form of IκB kinase β (CA-IKKβ), a key kinase in the canonical arm of the NF-κB pathway. Unexpectedly, we found that DOX induced CA-IKKβ inhibited 17β-estradiol (E2)-dependent proliferation. However, the combination of CA-IKKβ and E2 induced a highly migratory and invasive phenotype. Although this phenotype was accompanied by a change in cell morphology, typical markers of epithelial-mesenchymal transition were not observed. Rather, a decrease in luminal markers (e.g. Gata3, cytokeratin 8 and 18) and an increase in basal markers (e.g. p63, cytokeratin 5 and 14) were observed, suggesting luminal to basal plasticity as an underlying mechanism in the phenotype switch. In addition, we find that the invasive phenotype coincides with significantly lower ER expression, which is similar to that observed in aggressive, Luminal B, ER+ breast tumors. However, ER was still transcriptionally active since the combination of CA-IKKβ and E2 recapitulated the regulation of genes from an ER-NF-κB crosstalk signature, which we have previously reported as enriched in Luminal B tumors. In fact, both transcription factors, ER and NF-κB, proved to be necessary for the observed invasive phenotype. In order to explore the clinical relevance of our finding, we examined primary invasive breast tumors for the presence of phosphorylated IκB kinases α/β (IKKα/β), as an indicator of IKK activity. IKKα/β phosphorylation was observed at the invasive edge of the tumors whereas total IKKβ was observed throughout the tumor, further supporting a role for IKKβ activity in breast tumor invasiveness. Taken together, our findings indicate that activation of the canonical arm of the NF-κB pathway in the presence of E2 switches ER+ breast cancer cells from a highly proliferative to a highly migratory and invasive phenotype, potentially through luminal to basal plasticity. Since the most deadly aspect of breast cancer is metastasis and ≈70% of metastatic tumors are ER+, understanding the effect of the canonical NF-κB pathway can help define new specific drug targets and therapeutic strategies for the treatment of ER+ breast cancers. Citation Format: Lamiaa El-Shennawy, Jonna Frasor. Constitutively active NF-κB signaling switches estrogen receptor positive breast cancer cells from a proliferative to an invasive phenotype through luminal/basal plasticity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1866. doi:10.1158/1538-7445.AM2015-1866

While chemotherapy is the second-line of therapy for the treatment of epithelial ovarian cancer (EOC) after surgery, drug resistance constitutes a significant obstacle to achieving a complete response in many patients. There is a clear unmet need for new treatments for EOC patients. We have shown that PTB is frequently overexpressed and associated with malignancy in EOC (He et al, Clin Cancer Res, 10:4652-60, 2004, He et al, Oncogene 30:356-65, 2011). PTB knockdown via RNA interference significantly impairs EOC cell growth in vitro and in vivo, as well as invasiveness and colony formation in soft agar in vitro (He et al, Oncogene 26:4961-8, 2007). PTB or hnRNP-I is a splicing factor that regulates alternative pre-mRNA splicing, and has been implicated in metabolic, cytoskeletal, and cell membrane changes in cancer cells. In this study, we used A2780 cell lines carrying doxycycline (doxy)-inducible PTB shRNA. We characterized stable transfectants of A2780 cells that carry shRNA against PTB and cells carry a non-targeting control shRNA. In a 48 h MTT cytotoxicity assay, knockdown of PTB inhibited cell growth. When cells with PTB knockdown were treated with carboplatin or paclitaxel, drugs used as current standard of care in EOC, we observed 3- to 6-fold increases in drug sensitivity compared to the vector control. To rule out any drug-drug interaction (e.g., doxy-paclitaxel) (Foroodi et al, Anticancer Drugs 2009 20:115-22) in our assay, we evaluated the kinetics of the inducible knockdown system by western blot. We found that a 120 h doxy treatment was optimal to insure full depletion of PTB, and after doxy removal PTB suppression lasted 48 h more before recovering to its basal level. Based on those data, we performed all the cytotoxicity experiments within 48 h without exposing cells to both doxy and drug at once, and thereby avoiding drug-drug interactions. Findings here support the idea that PTB and other splicing factors may be novel drug targets in the treatment of ovarian cancer. (Support in part by NCI grants R01 CA40570 and R01 CA138762 [to WTB], by OCRF [to XH], and by UIC.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2932. doi:1538-7445.AM2012-2932