NDRG1 in Aggressive Breast Cancer Progression and Brain Metastasis

BACKGROUND

N-Myc downstream regulated gene 1 (NDRG1) suppresses metastasis in many human malignancies, including breast cancer, yet has been associated with worse survival in patients with inflammatory breast cancer. The role of NDRG1 in the pathobiology of aggressive breast cancers remains elusive.

METHODS

To study the role of NDRG1 in tumor growth and brain metastasis in vivo, we transplanted cells into cleared mammary fat pads or injected them in tail veins of SCID/Beige mice (n = 7-10 per group). NDRG1 protein expression in patient breast tumors (n = 216) was assessed by immunohistochemical staining. Kaplan-Meier method with 2-sided log-rank test was used to analyze the associations between NDRG1 and time-to-event outcomes. A multivariable Cox regression model was used to determine independent prognostic factors. All statistical tests were 2-sided.

RESULTS

We generated new sublines that exhibited a distinct propensity to metastasize to the brain. NDRG1-high-expressing cells produced more prevalent brain metastases (100% vs 44.4% for NDRG1-low sublines, P = .01, Fisher's exact test), greater tumor burden, and reduced survival in mice. In aggressive breast cancer cell lines, silencing NDRG1 led to reduced migration, invasion, and tumor-initiating cell subpopulations. In xenograft models, depleting NDRG1 inhibited primary tumor growth and brain metastasis. In patient breast tumors, NDRG1 was associated with aggressiveness: NDRG1-high expression was also associated with shorter overall survival (hazard ratio [HR] = 2.27, 95% confidence interval [95% CI] = 1.20 to 4.29, P = .009) and breast cancer-specific survival (HR = 2.19, 95% CI = 1.07 to 4.48, P = .03). Multivariable analysis showed NDRG1 to be an independent predictor of overall survival (HR = 2.17, 95% CI = 1.10 to 4.30, P = .03) and breast cancer-specific survival rates (HR = 2.27, 95% CI = 1.05 to 4.92, P = .04).

CONCLUSIONS

We demonstrated that NDRG1 drives tumor progression and brain metastasis in aggressive breast cancers and that NDRG1-high expression correlates with worse clinical outcomes, suggesting that NDRG1 may serve as a therapeutic target and prognostic biomarker in aggressive breast cancers.

Identification of triple-negative breast cancer cell lines classified under the same molecular subtype using different molecular characterization techniques: Implications for translational research

The original algorithm that classified triple-negative breast cancer (TNBC) into six subtypes has recently been revised. The revised algorithm (TNBCtype-IM) classifies TNBC into five subtypes and a modifier based on immunological (IM) signatures. The molecular signature may differ between cancer cells in vitro and their respective tumor xenografts. We identified cell lines with concordant molecular subtypes regardless of classification algorithm or analysis of cells in vitro or in vivo, to establish a panel of clinically relevant molecularly stable TNBC models for translational research. Gene expression data were used to classify TNBC cell lines using the original and the revised algorithms. Tumor xenografts were established from 17 cell lines and subjected to gene expression profiling with the original 2188-gene algorithm TNBCtype and the revised 101-gene algorithm TNBCtype-IM. A total of six cell lines (SUM149PT (BL2), HCC1806 (BL2), SUM149PT (BL2), BT549 (M), MDA-MB-453 (LAR), and HCC2157 (BL1)) maintained their subtype classification between in vitro and tumor xenograft analyses across both algorithms. For TNBC molecular classification-guided translational research, we recommend using these TNBC cell lines with stable molecular subtypes.

The CD151-midkine pathway regulates the immune microenvironment in inflammatory breast cancer

The immune microenvironment in inflammatory breast cancer (IBC) is poorly characterised, and molecular and cellular pathways that control accumulation of various immune cells in IBC tissues remain largely unknown. Here, we discovered a novel pathway linking the expression of the tetraspanin protein CD151 in tumour cells with increased accumulation of macrophages in cancerous tissues. It is notable that elevated expression of CD151 and a higher number of tumour-infiltrating macrophages correlated with better patient responses to chemotherapy. Accordingly, CD151-expressing IBC xenografts were characterised by the increased infiltration of macrophages. In vitro migration experiments demonstrated that CD151 stimulates the chemoattractive potential of IBC cells for monocytes via mechanisms involving midkine (a heparin-binding growth factor), integrin α6β1, and production of extracellular vesicles (EVs). Profiling of chemokines secreted by IBC cells demonstrated that CD151 increases production of midkine. Purified midkine specifically stimulated migration of monocytes, but not other immune cells. Further experiments demonstrated that the chemoattractive potential of IBC-derived EVs is blocked by anti-midkine antibodies. These results demonstrate for the first time that changes in the expression of a tetraspanin protein by tumour cells can affect the formation of the immune microenvironment by modulating recruitment of effector cells to cancerous tissues. Therefore, a CD151-midkine pathway can be considered as a novel target for controlled changes of the immune landscape in IBC. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract P3-01-10: Ndrg1-egfr axis in inflammatory breast cancer tumorigenesis and brain metastasis

Background: Inflammatory breast cancer (IBC) is a rare (1-2%) but lethal form of primary breast cancer responsible for 10% of breast cancer-related deaths in the United States. IBC tumors grow aggressively and have a high risk of metastasis, particularly to the brain. Unraveling the pathways involved in IBC aggressiveness and metastasis could reveal new therapeutic targets. We recently identified NDRG1 (N-Myc downstream regulated gene1) in a newly isolated subline of MDA-IBC3 cells as a top candidate protein associated with enhanced propensity for brain metastasis. Although the metastasis suppressor properties of NDRG1 are widely described, its function in the pathobiology of IBC is unknown. Here we investigated the function of NDRG1 in tumorigenesis and metastatic progression to brain in IBC.

Methods: NDRG1 gene expression was analyzed in large publically available breast cancer clinical datasets and the IBC Consortium dataset, and median expression level was used to stratify patients into NDRG1-high and NDRG1-low groups. Tissue microarrays of IBC patient samples were immunostained with anti-NDRG1 antibody. Stable knockdown (KD) of NDRG1 in IBC cell lines (HER2+: MDA-IBC3; TNBC: SUM149, BCX010) was obtained by lentiviral gene transfer. For in vivo studies, control and NDRG1 KD IBC cell lines were transplanted into cleared mammary fat pads of SCID/Beige mice and tumor growth monitored via caliper measurements. Reverse phase protein array analysis was used for proteomic profiling.

Results: In several independent cohorts of patients with breast cancer (including The Cancer Genome Atlas), NDRG1 mRNA expression was significantly higher in ER-negative and high-grade breast tumors (p<0.0001) and was associated with poor overall survival (p=0.0003), relapse-free survival (p<0.0001), and metastasis-free survival (p=0.0012). NDRG1 expression was higher in more aggressive, basal-like and HER2+ subtypes than in hormone receptor-positive subtypes (p<0.0001), and was also higher in IBC vs. non-IBC tumors (p=0.007, IBC consortium dataset). Immunostaining showed NDRG1 was frequently expressed in IBC patient tumors (83%) and was associated with worse overall survival (OS, p=0.0129) and disease-specific survival (DSS, p=0.013). On multivariate analysis, NDRG1 was an independent prognostic factor for poor OS [HR 2.5 (95%CI, 1.3-4.7), p=0.0047] and DSS [HR 2.6 (95%CI 1.3-5.1), p=0.006]. Notably, NDRG1 expression was higher in patients with brain metastasis vs. primary tumors (GSE43837, p=0.018) and correlated with shorter time to development of brain metastasis (GSE2034, p=0.026). NDRG1-high sublines had enhanced propensity for brain metastasis as shown by higher incidence (100% vs. 44% for NDRG1-low sublines, p=0.01) and increased brain metastasis burden (p=0.0008). Invitro, silencing NDRG1 in IBC cell lines significantly reduced colony formation, migration, invasion, and cancer stem-like properties. In vivo, silencing of NDRG1 inhibited primary tumor growth of SUM149 (p<0.0001) and MDA-IBC3 (p=0.0426) xenografts. Proteomics analysis showed that NDRG1 correlated positively with activation of the EGFR/STAT3 signaling pathway. Mechanistically, NDRG1 knockdown in IBC cell lines reduced EGFR expression and suppressed phosphorylation of EGFR and STAT3, whereas NDRG1 overexpression increased EGFR expression and enhanced EGFR-STAT3 activation.

Conclusions: We showed that high NDRG1 was associated with worse clinical outcomes in patients with IBC and that NDRG1 drives tumor progression in IBC potentially via activation of the EGFR-STAT3 signaling pathway. Targeting the NDRG1-EGFR axis may be a novel therapeutic approach in IBC and other aggressive breast cancers. Additional investigations are underway to determine the detailed mechanisms of NDRG1-mediated IBC tumorigenesis and brain metastasis

Citation Format: Emilly Schlee Villodre, Xiaoding Hu, Richard Larson, Bedrich L Eckhardt, Yun Gong, Lei Huo, Juhee Song, Savitri Krishnamurthy, Nuhad Ibrahim, Naoto T Ueno, Debu Tripathy, Wendy A Woodward, Bisrat G Debeb. Ndrg1-egfr axis in inflammatory breast cancer tumorigenesis and brain metastasis [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-01-10.

Activation of Canonical BMP4-SMAD7 Signaling Suppresses Breast Cancer Metastasis

Metastasis is the major cause of death in patients with cancer; with no therapeutic cure, treatments remain largely palliative. As such, new targets and therapeutic strategies are urgently required. Here, we show that bone morphogenetic protein-4 (BMP4) blocks metastasis in animal models of breast cancer and predicts improved survival in patients. In preclinical models of spontaneous metastasis, BMP4 acted as an autocrine mediator to modulate a range of known metastasis-regulating genes, including Smad7, via activation of canonical BMP-SMAD signaling. Restored BMP4 expression or therapeutically administered BMP4 protein, blocked metastasis and increased survival by sensitizing cancer cells to anoikis, thereby reducing the number of circulating tumor cells. Gene silencing of Bmp4 or its downstream mediator Smad7, reversed this phenotype. Administration of recombinant BMP4 markedly reduced spontaneous metastasis to lung and bone. Elevated levels of BMP4 and SMAD7 were prognostic for improved recurrence-free survival and overall survival in patients with breast cancer, indicating the importance of canonical BMP4 signaling in the suppression of metastasis and highlighting new avenues for therapy against metastatic disease. SIGNIFICANCE: Targeting the BMP4-SMAD7 signaling axis presents a novel therapeutic strategy to combat metastatic breast cancer, a disease that has had no reduction in patient mortality over 20 years. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/6/1304/F1.large.jpg.

Eicosapentaenoic acid in combination with EPHA2 inhibition shows efficacy in preclinical models of triple-negative breast cancer by disrupting cellular cholesterol efflux

Triple-negative breast cancer (TNBC), the most aggressive breast cancer subtype, currently lacks effective targeted therapy options. Eicosapentaenoic acid (EPA), an omega-3 fatty acid and constituent of fish oil, is a common supplement with anti-inflammatory properties. Although it is not a mainstream treatment, several preclinical studies have demonstrated that EPA exerts anti-tumor activity in breast cancer. However, against solid tumors, EPA as a monotherapy is clinically ineffective; thus, we sought to develop a novel targeted drug combination to bolster its therapeutic action against TNBC. Using a high-throughput functional siRNA screen, we identified Ephrin type-A receptor 2 (EPHA2), an oncogenic cell-surface receptor tyrosine kinase, as a therapeutic target that sensitizes TNBC cells to EPA. EPHA2 expression was uniquely elevated in TNBC cell lines and patient tumors. In independent functional expression studies in TNBC models, EPHA2 gene-silencing combined with EPA significantly reduced cell growth and enhanced apoptosis compared with monotherapies, both in vitro and in vivo. EPHA2 specific inhibitors similarly enhanced the therapeutic action of EPA. Finally, we identified that therapy-mediated apoptosis was attributed to a lethal increase in cancer cell membrane polarity due to ABCA1 inhibition and subsequent dysregulation of cholesterol homeostasis. This study provides new molecular and pre-clinical evidence to support a clinical evaluation of EPA combined with EPHA2 inhibition in patients with TNBC.

Clinically relevant inflammatory breast cancer patient-derived xenograft-derived ex vivo model for evaluation of tumor-specific therapies

Inflammatory breast cancer (IBC) is a rare and aggressive presentation of invasive breast cancer with a 62% to 68% 5-year survival rate. It is the most lethal form of breast cancer, and early recognition and treatment is important for patient survival. Like non-inflammatory breast cancer, IBC comprises multiple subtypes, with the triple-negative subtype being overrepresented. Although the current multimodality treatment regime of anthracycline- and taxane-based neoadjuvant therapy, surgery, and radiotherapy has improved the outcome of patients with triple-negative IBC, overall survival continues to be worse than in patients with non-inflammatory locally advanced breast cancer. Translation of new therapies into the clinics to successfully treat IBC has been poor, in part because of the lack of in vitro preclinical models that can accurately predict the response of the original tumor to therapy. We report the generation of a preclinical IBC patient-derived xenograft (PDX)-derived ex vivo (PDXEx) model and show that it closely replicates the tissue architecture of the original PDX tumor harvested from mice. The gene expression profile of our IBC PDXEx model had a high degree of correlation to that of the original tumor. This suggests that the process of generating the PDXEx model did not significantly alter the molecular signature of the original tumor. We demonstrate a high degree of similarity in drug response profile between a PDX mouse model and our PDXEx model generated from the same original PDX tumor tissue and treated with the same panel of drugs, indicating that our PDXEx model had high predictive value in identifying effective tumor-specific therapies. Finally, we used our PDXEx model as a platform for a robotic-based high-throughput drug screen of a 386-drug anti-cancer compound library. The top candidates identified from this drug screen all demonstrated greater therapeutic efficacy than the standard-of-care drugs used in the clinic to treat triple-negative IBC, doxorubicin and paclitaxel. Our PDXEx model is simple, and we are confident that it can be incorporated into a PDX mouse system for use as a first-pass screening platform. This will permit the identification of effective tumor-specific therapies with high predictive value in a resource-, time-, and cost-efficient manner.

Nephronectin is Correlated with Poor Prognosis in Breast Cancer and Promotes Metastasis via its Integrin-Binding Motifs

Most cancer patients with solid tumors who succumb to their illness die of metastatic disease. While early detection and improved treatment have led to reduced mortality, even for those with metastatic cancer, some patients still respond poorly to treatment. Understanding the mechanisms of metastasis is important to improve prognostication, to stratify patients for treatment, and to identify new targets for therapy. We have shown previously that expression of nephronectin (NPNT) is correlated with metastatic propensity in breast cancer cell lines. In the present study, we provide a comprehensive analysis of the expression pattern and distribution of NPNT in breast cancer tissue from 842 patients by immunohistochemical staining of tissue microarrays from a historic cohort. Several patterns of NPNT staining were observed. An association between granular cytoplasmic staining (in <10% of tumor cells) and poor prognosis was found. We suggest that granular cytoplasmic staining may represent NPNT-positive exosomes. We found that NPNT promotes adhesion and anchorage-independent growth via its integrin-binding and enhancer motifs and that enforced expression in breast tumor cells promotes their colonization of the lungs. We propose that NPNT may be a novel prognostic marker in a subgroup of breast cancer patients.

Abstract P1-01-09: BMP4 suppresses the progression of breast cancer through altered expression of metastasis regulating genes

Metastasis is a lethal manifestation of cancer, the development of which is the major cause of death in cancer patients. During a search for metastasis-regulating elements, an inverse correlation was identified between the in vivo tumor expression of bone morphogenetic protein-4 (BMP4) and spontaneous metastasis in a panel of isogenic mammary tumors of varying metastatic capacity. BMP4 is an essential morphogen in development, regulating cellular mechanisms akin to those in metastasis, including cellular differentiation, pluripotency and apoptosis. We therefore initiated an investigation of the impact of BMP4 expression on the metastatic process.

We studied the effect of enforced expression of BMP4 in a highly metastatic mammary tumour model called 4T1.2, comparing in vitro properties and tumour progression in mice. There were no differences in proliferation in vitro or when implanted into the mammary gland of immunocompetent mice. In contrast, mice bearing equivalent-sized 4T1.2-BMP4 tumors revealed dramatically reduced metastasis to lung, lymph node and bone. In a parallel study where the established orthotopic primary tumor was resected, survival was significantly extended in mice bearing 4T1.2-BMP4 tumors. Enforced BMP4 expression in tumor cells introduced intravenously resulted in a 2.5-fold decrease in lung metastatic burden, consistent with the impaired capacity of tumor cells to survive in circulation and colonize the lung. Conversely, silencing BMP4 expression in separate weakly metastatic tumours enhanced their ability to colonize the lung and shortened the survival of the mice. No changes were found in the ability of tumor cells expressing BMP4 or treated with recombinant BMP4 to migrate or invade through Matrigel in chemotactic assays but BMP4 enhanced anoikis in both mouse and human breast cancer cells, indicating that BMP4 sensitizes disseminated cells to anoikic stresses induced by cell-substrate detachment and shear flow during systemic transit. BMP4 activated canonical BMP-SMAD signaling in our mammary tumours, leading to altered expression of known metastasis-regulating genes, including SMAD7. SMAD7 depletion in metastasis-deficient 4T1.2-BMP4 tumors accelerated the onset of metastatic disease.

In a meta-analysis of 3,587 breast cancer patients in publically available datasets, low BMP4 mRNA expression was significantly associated with reduced relapse-free survival (RFS) (HR = 0.85, P = 0.01). In an independent analysis using the BreastMark algorithm, low levels of BMP4 mRNA were associated with reduced RFS (HR = 0.88, P = 0.035), distant metastasis-free survival (HR = 0.83, P = 0.035) and overall survival (HR = 0.78, P = 0.006). At the protein level, in a tissue microarray from 415 treatment naïve patients, improved overall survival was observed in multivariate analysis for both BMP4 (HR = 0.66, P = 0.037) and SMAD7 expression (HR = 0.64, P = 0.035) individually. Expression of both proteins compared to neither further improved OS (HR = 0.55, P = 0.005).

In summary, we found strong evidence that BMP4 is a metastasis suppressor correlating inversely with metastatic potential in preclinical breast cancer models and predicting improved relapse-free and overall survival in breast cancer patients.

Citation Format: Redfern AD, Eckhardt BL, Cao Y, Sloan EK, Parker BS, Loi S, Ueno NT, Lau PK, Latham B, Anderson RL. BMP4 suppresses the progression of breast cancer through altered expression of metastasis regulating genes [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-01-09.

Abstract P1-10-09: EPHA2-targeting enhances eicosapentaenoic acid cytotoxicity against triple-negative inflammatory breast cancer via ABCA1 inhibition–mediated membrane rigidity

Background: Effective treatment options for triple-negative inflammatory breast cancer (TN-IBC), the most aggressive form of breast cancer, are currently lacking. We previously reported that mediators of inflammation promote the growth of TN-IBC xenografts. Eicosapentaenoic acid (EPA), an omega-3 fatty acid (fish oil) with anti-inflammatory properties, is an emerging FDA-approved therapeutic with a favorable toxicology profile. Here we aimed to develop a novel approach to enhance EPA efficacy against TN-IBC by identifying a kinase inhibitor that synergizes with EPA's antitumor activity.

Methods and Results: Using a high-throughput siRNA screen in the TN-IBC cell line SUM149PT, we identified inhibition of ephrin type-A receptor 2 (EPHA2), an oncogenic receptor tyrosine kinase, as a target that sensitizes TN-IBC cells to EPA therapy. To determine the clinical relevance of EPHA2, we investigated a meta-analysis of breast cancer mRNA expression data sets and found that high EPHA2 tumor expression, compared with low expressing, correlated significantly with poor overall survival in TN-IBC patients (P = 0.01), while not with other subtypes. Similar findings were observed in vitro, were EPHA2 protein and mRNA overexpression occurred predominantly in the TN subtypes among 49 and 51 breast cancer cell lines (63% and 47%, respectively), highlighting EPHA2 translational potential. Functional expression studies using proliferation and apoptosis assays in vitro, and xenografts in vivo, were performed in two EPHA2-expressing TN-IBC cell lines, SUM149PT and BCX010, to validate EPHA2 as a synergistic combinational target with EPA. EPHA2 gene silencing in combination with EPA significantly reduced cell growth, and enhanced apoptosis, compared with untreated and monotherapy in vitro (P &lt; 0.05), and in vivo (P &lt; 0.001). To translate our findings to the clinic, we validated dasatinib, an FDA-approved small molecule inhibitor of EPHA2, in combination to EPA to significantly enhance apoptosis of TN-IBC cells in vitro (P &lt; 0.05) and in vivo (P &lt; 0.05), compared with untreated and monotherapies. Using membrane fluidity assessment and cholesterol quantification we determined that apoptosis induction after combination therapy was due to increased membrane rigidity and cholesterol concentrations in the plasma membrane of TN-IBC cells (P &lt; 0.05, compared with monotherapies). Finally, we discovered by western blot and gain/loss-of-expression studies that combination therapy inhibited the cholesterol efflux protein ATP-binding cassette sub-family A member 1 (ABCA1), which plays a significant role mediating increased cellular cholesterol (P &lt; 0.05), cell membrane rigidity (P &lt; 0.05), and induction of apoptosis (P &lt; 0.05) in TN-IBC after EPA and EPHA2-targeting combination therapy.

Conclusions: This is the first study demonstrating that EPA can enhance conventional targeted therapy against breast cancer. Our study provides molecular and preclinical evidence to support the development of an EPA/EPHA2-inhibition–based phase I clinical trial for patients with EPHA2-positive TN-IBC; our study further suggests the use of EPHA2 and ABCA1 protein expression as biomarkers for patient selection and therapeutic response.

Citation Format: Torres-Adorno AM, Vitrac H, Qi Y, Tan L, Levental KR, Fan Y-Y, Yang P, Chapkin RS, Eckhardt BL, Ueno NT. EPHA2-targeting enhances eicosapentaenoic acid cytotoxicity against triple-negative inflammatory breast cancer via ABCA1 inhibition–mediated membrane rigidity [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-10-09.

Abstract P3-07-04: EphA2: An emerging target in triple-negative breast cancer

Purpose: Breast tumors classified as 'triple negative' (TNBC) lack defining markers ER/PR/HER2 and do not have clinically-approved targeted therapy. This heterogeneous classification of breast cancers, while immediately responsive to standard chemotherapy, commonly develop resistance and have a poor five-year survival rate. As such, the identification of new therapeutic targets are warranted. As part of our drug discovery platform, we have identified EphA2, as a synthetic-lethal gene that enhances the therapeutic action of FDA-approved, anti-inflammatory compounds. Thus we sought to ascertain the relevance of EphA2-targeted therapy in TNBC, through the evaluation of the marker in preclinical and clinical specimens.

Methods: Sixty-one human and murine breast cancer cell lines or patient-derived xenografts were collated. Protein lysates were created from cells in vitro or from respective tumors established from cells implanted into NSG mice. Forty-nine tumors established (minimum 500mm3) and were surgically removed, fixed in formalin and paraffin embedded. A TMA was constructed with tumor specimens represented twice on the array and reflected all molecular subtypes including; ER-positive (n=5), PR-positive (n=3), HER2-positive (n=9) and TNBC (n=31). Immunostaining for EphA2 was performed with the rabbit monoclonal antibody EphA2 (D4A2) XP (Cell Signaling, #6997) using manufacturer's instructions. Immunostaining was evaluated using the H-score method (score between 0-300), with positive staining for EphA2 reflecting a score of 100 or greater. Analysis of breast cancer lysates by western blot was analyzed by absolute and relative quantitation methods; gene expression data was assessed through Oncomine or using the BreastMark algorithm (http://glados.ucd.ie/BreastMark/). This algorithm integrates gene expression and survival data from 26 datasets on 12 different microarray platforms corresponding to ˜17,000 genes in up to 4,738 samples.

Results: In an integrated gene expression platform (BreastMark), we observed that elevated EphA2 expression was associated with poor prognosis in a cohort of TNBC patient tumor samples. Western blot analysis of EphA2 protein on breast cancer cell lines, identified a greater percentage of TNBC cells expressing EphA2 compared to non-TNBC cell lines. EphA2 immunostaining was observed in the majority of tumor tissues. When present on cancer cells, EphA2 localized to the cell surface; while displaying ubiquitous localization within stromal populations. Cell surface expression of EphA2 on cancer cells was largely restricted to TNBC tumors (11/31 tumors, 35.5%) compared to other molecular subtypes (1/13 non-TNBC tumors, 7.7%; p = 0.0294). Expression of EphA2 in stromal cell populations was similar between groups (TNBC = 22/31, non-TNBC = 11/13; p = 0.1711).

Conclusions: Our analysis determined that EphA2 was specifically expressed on cancer cells derived from tumors with a 'triple-negative' molecular subtype. Collectively our data suggests that EphA2 is an emerging target in TNBC and that therapies directed against EphA2 may provide a significant benefit for a majority of patients that express this marker.

Citation Format: Eckhardt BL, Torres AM, Woodward WA, Krishnamurthy S, Meric-Bernstam F, Ueno NT. EphA2: An emerging target in triple-negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-07-04.

EGFR signaling promotes inflammation and cancer stem-like activity in inflammatory breast cancer

Inflammatory breast cancer (IBC) is the most lethal and aggressive type of breast cancer, with a strong proclivity to metastasize, and IBC-specific targeted therapies have not yet been developed. Epidermal growth factor receptor (EGFR) has emerged as an important therapeutic target in IBC. However, the mechanism behind the therapeutic effect of EGFR targeted therapy is not well defined. Here, we report that EGFR regulates the IBC cell population that expresses cancer stem-like cell (CSC) markers through COX-2, a key mediator of inflammation whose expression correlates with worse outcome in IBC. The COX-2 pathway promoted IBC cell migration and invasion and the CSC marker-bearing population in vitro, and the inhibition of this pathway reduced IBC tumor growth in vivo. Mechanistically, we identified Nodal, a member of the TGFβ superfamily, as a potential driver of COX-2-regulated invasive capacity and the CSC phenotype of IBC cells. Our data indicate that the EGFR pathway regulates the expression of COX-2, which in turn regulates the expression of Nodal and the activation of Nodal signaling. Together, our findings demonstrate a novel connection between the EGFR/COX-2/Nodal signaling axis and CSC regulation in IBC, which has potential implications for new combination approaches with EGFR targeted therapy for patients with IBC.

Abstract 1235: EPHA2-targeted therapy enhances the cytotoxicity of eicosapentaenoic acid against triple-negative inflammatory breast cancer

Background: Inflammatory breast cancer (IBC) is the most aggressive form of breast cancer. We have previously reported that mediators of inflammation, such as COX-2, promote the growth of Triple-Negative receptor (TN) IBC xenografts; therefore, inflammation in TN-IBC has a unique opportunity as a therapeutic strategy. Eicosapentaenoic acid (EPA), a non-toxic omega-3 fatty acid with anti-inflammatory properties, has partially reduced tumor growth in pre-clinical models of TN-IBC. Therefore, our goal is to develop a novel non-toxic approach that enhances EPA efficacy against TN-IBC in combination with targeted therapy.

Methods and Results: Using a high-throughput, siRNA screen (939 genes) in the TN-IBC cell line SUM149PT, we identified Ephrin type-A receptor 2 (EPHA2), an oncogenic cell-surface receptor tyrosine kinase, as a target that modulates the sensitivity of TN-IBC cells to EPA treatment. To determine the clinical relevance of EPHA2, we interrogated a meta-analysis of breast cancer mRNA expression data sets, and found that high EPHA2 tumor expression was significantly correlated with poor overall survival in TN-IBC patients, compared to low EPHA2 expressing tumors (P = 0.01). We observed no significant correlations to other breast cancer subtypes. Similar findings were observed in vitro were EPHA2 expression predominantly occurred in the TN-IBC subtypes (19 of 30) among 49 breast cancer cell lines. Gain/loss-of-expression studies were performed to functionally validate EPHA2 as a synergistic combinational target with EPA in two EPHA2-expressing TN-IBC models, SUM149PT and BCX010, using proliferation and apoptosis assays in vitro and established tumor xenografts in vivo. EPHA2 gene silencing significantly reduced cell growth and induced apoptosis in combination with EPA when compared with untreated control and monotherapy in vitro (P &lt; 0.05) and in vivo (P &lt; 0.001), while vector-induced EPHA2 expression reversed cell growth reduction and apoptosis induction following combination treatment with EPA in vitro (P &lt; 0.05). To translate our findings to the clinic, we validated that dasatinib, a small molecule inhibitor of EPHA2, in combination with EPA significantly enhanced cell death of SUM149PT and BCX010 cells in vitro when compared to non-treated and monotherapy (P &lt; 0.05). Finally, using membrane fluidity assessment and reverse-phase protein array (300 antibodies), we determined that combination treatment efficacy depended on EPA/EPHA2 inhibition-mediated increase in cell membrane rigidity (P &lt; 0.001, compared to monotherapy), which subsequently inhibited receptor tyrosine kinase signaling activity, potentially resulting in induction of apoptosis.

Conclusions: Our preclinical findings provide a rationale for the development of a phase 1 clinical trial investigating combination EPA and EPHA2-inhibitors in patients with EPHA2-positive TN-IBC.

Citation Format: Angie M. Torres-Adorno, Heidi Vitrac, Yuan Qi, Yiwen Yang, Peiying Yang, Bedrich L. Eckhardt, Naoto T. Ueno. EPHA2-targeted therapy enhances the cytotoxicity of eicosapentaenoic acid against triple-negative inflammatory breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1235. doi:10.1158/1538-7445.AM2017-1235

Poor prognosis of patients with triple-negative breast cancer can be stratified by RANK and RANKL dual expression

PURPOSE

As clinical studies have correlated RANK expression levels with survival in breast cancer, and that RANK signaling is dependent on its cognate ligand RANKL, we hypothesized that dual protein expression further stratifies the poor outcome in TNBC.

METHODS

RANK mRNA and protein expression was evaluated in TNBC using genomic databases, cell lines and in a tissue microarray of curated primary tumor samples derived from 87 patients with TNBC. RANK expression was evaluated either by Mann-Whitney U test on log-normalized gene expression data or by Student's t test on FACS data. Analysis of RANK and RANKL immunostaining was calculated by H-score, and correlations to clinical factors performed using χ ² or Fisher's exact test. Associations with RFS and OS were assessed using univariate and multivariate Cox proportional hazard models. Survival estimates were generated using the Kaplan-Meier method.

RESULTS

In three distinct datasets spanning 684 samples, RANK mRNA expression was higher in primary tumors derived from TNBC patients than from those with other molecular subtypes (P < 0.01). Cell surface-localized RANK protein was consistently higher in TNBC cell lines (P = 0.037). In clinical samples, TNBC patients that expressed both RANK and RANKL proteins had significantly worse RFS (P = 0.0032) and OS (P = 0.004) than patients with RANK-positive, RANKL-negative tumors. RANKL was an independent, poor prognostic factor for RFS (P = 0.04) and OS (P = 0.01) in multivariate analysis in samples that expressed both RANK and RANKL.

CONCLUSIONS

RANK and RANKL co-expression is associated with poor RFS and OS in patients with TNBC.

Abstract 3543: Ligand-directed and transcription-based molecular imaging and treatment of cancer

Inflammatory breast cancer (IBC) is a rare and aggressive disease that progresses rapidly, often in a matter of weeks or months. In the United States, IBC accounts for 1 to 5 percent of all breast cancers diagnosed per year. Due to the lack of reliable and effective detection methods, IBC can be difficult to diagnose and thus, it is more likely to have metastasized by the time it is identified. Specific delivery of drugs and/or imaging agents to tumors takes advantage of dynamic molecular addresses on the surface of tumor cells and the tumor vasculature through inherent receptor/ligand interactions. By using a combinatorial phage display library in vivo (consisting of more than 1×109unique CX(7/8)C amino acid residues) we identified an unique peptide sequence - WIFPWIQL - that mediates targeting to breast cancer metastasis. We further validated that the WIFPWIQL peptide specifically binds to the stress-response 78 kDa glucose-regulated protein (GRP78), expressed at the cell surface of IBC tumors. GRP78 expression is elevated with breast cancer progression, and correlates with metastatic disease in IBC. Using near infrared (NIR) fluorescent-tagged phage variants and/or antibody fragments, we demonstrate WIFPIWIQL specifically targets breast tumors in vivo. As a therapeutic approach, we coupled a toxic apoptotic moiety D(KLAKLAK)2 - to the WIFPWIQL peptide to create BMTP-78. BMTP-78 is cytotoxic to cultured IBC cells in vitro. Furthermore, BMTP-78 prevents the growth of IBC tumor xenografts, reduces tumor burden and mitigates metastasis in breast cancer pre-clinical models. Taking into consideration that phage particles can be adapted to transduce mammalian cells by targeting a specific receptor, we developed a unique phage-based targeted vector by combining genomic elements from adeno-associated virus (AAV) and an M13-derived phage (P) - termed AAVP. AAVP chimeras are able to deliver reporter genes that can be used to image, diagnose and treat pre-clinical breast cancer. In our initial in vivo assessment, AAVP particles harboring the tumor targeting peptide, WIFPWIQL, delivered the Herpes Simplex Virus thymidine kinase gene (HSVtk) driven by the CMV promoter, to EF43.fgf-4 mouse mammary tumors after a single intravenous injection. Positron emission tomography (PET) studies demonstrated WIFPIWIQL-targeted AAVP-HSKtk tumors could be non-invasively imaged. More importantly, transcriptional targeting of AAVP vectors was achieved by replacing the CMV promoter with a human GRP78 promoter that selectively controls transgene expression and allows molecular imaging of breast tumors in real time. Taken together, our data presents a GRP78 receptor/ligand system that can be used to specifically image and target breast tumors. Our findings infer potential clinical applications of AAVP for targeted detection and eradication of IBC tumors via a GRP78-targeted mechanism in a disease for which no effective treatment currently exists.

Citation Format: Andrey S. Dobroff, Bedrich L. Eckhardt, Carolina C. Salmeron, Daniel F. Cimino, Wadih Arap, Renata Pasqualini. Ligand-directed and transcription-based molecular imaging and treatment of cancer. [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 3543. doi:10.1158/1538-7445.AM2015-3543

Is the future of personalized therapy in triple-negative breast cancer based on molecular subtype?

Significant research has been conducted to better understand the extensive, heterogeneous molecular features of triple-negative breast cancer (TNBC). We reviewed published TNBC molecular classifications to identify major groupings that have potential for clinical trial development. With the ultimate aim to streamline translational medicine, we linked these categories of TNBC according to their gene-expression signatures, biological function, and clinical outcome. To this end, we define five potential clinically actionable groupings of TNBC: 1) basal-like TNBC with DNA-repair deficiency or growth factor pathways; 2) mesenchymal-like TNBC with epithelial-to-mesenchymal transition and cancer stem cell features; 3) immune-associated TNBC; 4) luminal/apocrine TNBC with androgen-receptor overexpression; and 5) HER2-enriched TNBC. For each defined subtype, we highlight the major biological pathways and discuss potential targeted therapies in TNBC that might abrogate disease progression. However, many of these potential targets need clinical validation by clinical trials. We have yet to know how we can enrich the targets by molecular classifications.

Functional and molecular characterisation of EO771.LMB tumours, a new C57BL/6-mouse-derived model of spontaneously metastatic mammary cancer

The translation of basic research into improved therapies for breast cancer patients requires relevant preclinical models that incorporate spontaneous metastasis. We have completed a functional and molecular characterisation of a new isogenic C57BL/6 mouse model of breast cancer metastasis, comparing and contrasting it with the established BALB/c 4T1 model. Metastatic EO771.LMB tumours were derived from poorly metastatic parental EO771 mammary tumours. Functional differences were evaluated using both in vitro assays and spontaneous metastasis assays in mice. Results were compared to non-metastatic 67NR and metastatic 4T1.2 tumours of the 4T1 model. Protein and transcript levels of markers of human breast cancer molecular subtypes were measured in the four tumour lines, as well as p53 (Tp53) tumour-suppressor gene status and responses to tamoxifen in vivo and in vitro. Array-based expression profiling of whole tumours identified genes and pathways that were deregulated in metastatic tumours. EO771.LMB cells metastasised spontaneously to lung in C57BL/6 mice and displayed increased invasive capacity compared with parental EO771. By immunohistochemical assessment, EO771 and EO771.LMB were basal-like, as was the 4T1.2 tumour, whereas 67NR had a luminal phenotype. Primary tumours from all lines were negative for progesterone receptor, Erb-b2/Neu and cytokeratin 5/6, but positive for epidermal growth factor receptor (EGFR). Only 67NR displayed nuclear estrogen receptor alpha (ERα) positivity. EO771 and EO771.LMB expressed mutant p53, whereas 67NR and 4T1.2 were p53-null. Integrated molecular analysis of both the EO771/EO771.LMB and 67NR/4T1.2 pairs indicated that upregulation of matrix metalloproteinase-3 (MMP-3), parathyroid hormone-like hormone (Pthlh) and S100 calcium binding protein A8 (S100a8) and downregulation of the thrombospondin receptor (Cd36) might be causally involved in metastatic dissemination of breast cancer.

BMP4 inhibits breast cancer metastasis by blocking myeloid-derived suppressor cell activity

The TGFβ growth factor family member BMP4 is a potent suppressor of breast cancer metastasis. In the mouse, the development of highly metastatic mammary tumors is associated with an accumulation of myeloid-derived suppressor cells (MDSC), the numbers of which are reduced by exogenous BMP4 expression. MDSCs are undetectable in naïve mice but can be induced by treatment with granulocyte colony-stimulating factor (G-CSF/Csf3) or by secretion of G-CSF from the tumor. Both tumor-induced and G-CSF-induced MDSCs effectively suppress T-cell activation and proliferation, leading to metastatic enhancement. BMP4 reduces the expression and secretion of G-CSF by inhibiting NF-κB (Nfkb1) activity in human and mouse tumor lines. Because MDSCs correlate with poor prognosis in patients with breast cancer, therapies based on activation of BMP4 signaling may offer a novel treatment strategy for breast cancer. Cancer Res; 74(18); 5091-102. ©2014 AACR.

Abstract P5-04-03: Bone morphogenic protein-4: A novel metastasis suppressor gene in breast cancer

Background: The combination of large-scale screening platforms and animal models of cancer, have provided much insight into the genetic mechanisms that control metastatic progression. Indeed, several studies have unraveled an essential role for genes that encode growth factors and extracellular matrix proteins in the progression of breast cancer. We have found that one such growth factor, bone morphogenic protein-4 (BMP4), to be significantly reduced in tumors with a high proclivity to metastasize. BMP4 is known to regulate tissue polarity and differentiation during embryogenesis, however it is not known whether BMP4 can functionally affect tumor progression.

Methods and results: In a panel of mammary tumor lines, we demonstrate an inverse correlation between metastatic propensity and the expression of BMP4 through a combination of RT-PCR, immunohistochemistry (IHC) and ELISA. These findings were extended to publicly available gene expression data sets, where low BMP4 expression was found to be associated with ER-negative breast tumors and in those tumors with high histologic grade. Low BMP4 expression also correlated with poorer survival from distant metastases (HR 0.82, p = 0.013). IHC analysis on a tissue microarray consisting of tumor specimens from 535 patients with invasive breast cancer demonstrated that, compared to normal breast epithelium, BMP4 positivity was significantly less common in both DCIS (HR 0.59, p = 0.00046) and invasive carcinoma (HR = 0.56, p&lt;0.0000001), and was inversely associated with axillary lymph node-positivity (HR = 1.53, p = 0.055). Using surrogate in vitro assays of metastasis, we determined that BMP4 can suppress the ability of highly metastatic 4T1.2 tumor cells to resist anoikis. When BMP4 was overexpressed in 4T1.2 cells (4T1.2-BMP4) and orthotopically implanted in mice, we did not observe an effect on primary tumor growth, however elevated BMP4 expression did block the ability of these tumors to metastasize to the lymph node, lung and bone. In a reverse-complimentary approach, we confirmed that silencing of BMP4 expression by RNAi in weakly metastatic 4T07 and 168FARN cells, can enhance lung colonization. Mechanistically, we establish that BMP4 can induce canonical BMP-SMAD signaling in multiple breast cancer cells, leading to an up-regulation of genes known to suppress metastasis, and a down-regulation of metastasis promoting genes. Specifically, we link the anti-metastatic function of BMP4 to its ability to induce the expression of the known metastasis suppressor, Smad7. Through RNAi-mediated suppression of Smad7 in 4T1.2-BMP4 tumors, we were able to restore the metastatic phenotype of this tumor line. Finally, we demonstrate that administration of recombinant BMP4 protein in 4T1.2 tumor challenged mice elevates Smad7 expression within the primary tumor, and leads to a pronounced decrease in spontaneous bone and lung metastasis.

Conclusion: Utilizing animal models of cancer, and clinically sourced tissues, we provide correlative and functional data to prove that BMP4 is a bona fide metastasis suppressor gene in breast cancer. Furthermore, we demonstrate that BMP4 may be therapeutically viable, and can prevent breast tumor progression through the modulation of known ‘metastasis virulence’ genes.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-04-03.

Inhibition of established micrometastases by targeted drug delivery via cell surface-associated GRP78

PURPOSE

The major cause of morbidity in breast cancer is development of metastatic disease, for which few effective therapies exist. Because tumor cell dissemination is often an early event in breast cancer progression and can occur before diagnosis, new therapies need to focus on targeting established metastatic disease in secondary organs. We report an effective therapy based on targeting cell surface-localized glucose-regulated protein 78 (GRP78). GRP78 is expressed normally in the endoplasmic reticulum, but many tumors and disseminated tumor cells are subjected to environmental stresses and exhibit elevated levels of GRP78, some of which are localized at the plasma membrane.

EXPERIMENTAL DESIGN AND RESULTS

Here, we show that matched primary tumors and metastases from patients who died from advanced breast cancer also express high levels of GRP78. We used a peptidomimetic targeting strategy that uses a known GRP78-binding peptide fused to a proapoptotic moiety [designated bone metastasis targeting peptide 78 (BMTP78)] and show that it can selectively kill breast cancer cells that express surface-localized GRP78. Furthermore, in preclinical metastasis models, we show that administration of BMTP78 can inhibit primary tumor growth as well as prolong overall survival by reducing the extent of outgrowth of established lung and bone micrometastases.

CONCLUSIONS

The data presented here provide strong evidence that it is possible to induce cell death in established micrometastases by peptide-mediated targeting of cell surface-localized GRP in advanced breast cancers. The significance to patients with advanced breast cancer of a therapy that can reduce established metastatic disease should not be underestimated.

Abstract P3-10-09: Peptide-based molecular targeting of inflammatory breast cancer

Inflammatory breast cancer (IBC) is a subtype of breast cancer that has a frequent association with metastatic disease and a poorer prognosis than comparative non-inflammatory breast cancers. While IBC is now considered a distinct subclass of breast cancer, the lack of molecular characterization, both at the genomic and proteomic levels, has hampered the development of rationalized and targeted therapies. Inherent receptor/ligand interactions that can occur on the surface of tumor cells can act as a dynamic molecular address that can enable targeted delivery of drugs and imaging agents to tumors. We hypothesize that such molecular addresses within IBC can be exploited for ligand-based imaging and early detection of disease sites. To this end, it is our goal to generate targeted imaging and therapeutic agents by combining ligand-directed targeting with efficient transduction of IBC cells by hybrid gene delivery vectors. Our strategy utilizes a hybrid vector with genomic elements from adeno-associated virus (AAV) and an M13-derived phage. Ligand-targeted, AAV/phage (AAVP) chimeras can display tumor-homing peptides that mediate selective internalization of viral particles through specific ligand-receptor interactions in vitro and in vivo. Such targeted vehicles are suited for the delivery of different reporter genes that can be used for imaging, diagnosis and therapy of breast cancer

As a part of our ongoing studies we have identified, characterized and evaluated a peptide (WIFPWIQL, amino acid sequence) that can target GRP78, a stress-response protein that is expressed in IBC tumors and elevated during metastatic progression. Indeed, we found that this GRP78-targeting peptide can bind to, and internalize within IBC cells. As a result, we sought to characterize the ability of this peptide to mediate the delivery of fluorescent-based compounds and toxic moieties in preclinical models of IBC and breast cancer metastasis. Using amine-based chemical coupling, we conjugated near-infrared dyes on both WIFPWIQL-phage and on a WIFPWIQL-peptide engrafted antibody. When these fluorescent construct were administered into mice bearing IBC or IBC-like tumors, we could visualize tumor-specific targeting of the vectors in vivo. To demonstrate efficacy of GRP78-targeted therapeutics, we conjugated the tumor-homing, GRP78 ligand to a cell-death inducing domain (creating a compound called BMTP-78, βone metastasis targeting peptide-78), which can selectively kill cells upon internalization. We show here that BMTP78 therapy in mice with established GRP78-positive tumors, but not matched GRP78-negative tumors, could effectively reduce tumor growth and metastatic burden. Finally, we demonstrate a WIFPWIQL-AAVP construct that expresses a suicide gene (HSVtk) under the control of either CMV or GRP78 promoter, could sensitize IBC tumor xenografts to the pro-drug ganciclovir. Collectively, our results demonstrate an in vivo receptor/ligand system that has the potential for imaging and therapeutic targeting of IBC and aggressive breast tumors.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-10-09.

Strategies for the discovery and development of therapies for metastatic breast cancer

Nearly all deaths caused by solid cancers occur as a result of metastasis--the formation of secondary tumours in distant organs such as the lungs, liver, brain and bone. A major obstruction to the development of drugs with anti-metastatic efficacy is our fragmented understanding of how tumours 'evolve' and metastasize, at both the biological and genetic levels. Furthermore, although there is significant overlap in the metastatic process among different types of cancer, there are also marked differences in the propensity to metastasize, the extent of metastasis, the sites to which the tumour metastasizes, the kinetics of the process and the mechanisms involved. Here, we consider the case of breast cancer, which has some marked distinguishing features compared with other types of cancer. Considerable progress has been made in the development of preclinical models and in the identification of relevant signalling pathways and genetic regulators of metastatic breast cancer, and we discuss how these might facilitate the development of novel targeted anti-metastatic drugs.

Abstract 2903: Therapeutic targeting of leukemia and lymphoma with a neuropilin-1 binding pro-apoptotic peptide

Targeted drug delivery offers an opportunity for the development of safer and more effective therapies for the treatment of cancer. In this study, we sought to identify short cell-internalizing peptide ligands that bind to specific cell surface receptors on malignant hematopoietic cells. Such targeting motifs could also serve as vehicles for preferential delivery of cytotoxic agents to leukemias and lymphomas. By screening of human leukemia cells with a combinatorial phage display peptide library, we isolated a peptide motif, sequence FF/YXLRS, which bound to human leukemia and lymphoma cell lines as well as to primary human acute myelogenous leukemia (AML) and acute lymphoblastic leukemia (ALL) bone marrow specimens obtained from patients. The motif was internalized through a receptor-mediated pathway, and we next identified the corresponding receptor as the transmembrane glycoprotein neuropilin-1 (NRP-1). Moreover, the functional relevance of this internalizing receptor was evaluated in the context of disease progression via the targeted delivery of a pro-apoptotic peptidomimetic to leukemia and lymphoma cells, and a potent anti-leukemia cell effect was observed both with cell lines and patient samples when the targeting motif was synthesized in tandem to the pro-apoptotic sequence D(KLAKLAK)2. Markedly, the pro-apoptotic peptide did not have an effect on purified mononuclear cells from normal bone marrow cells. Finally, our results confirmed increased expression of NRP-1 in representative human leukemia and lymphoma cell lines and in a panel of bone marrow specimens obtained from patients with ALL or AML compared to normal bone marrow specimens. Taken together, our results indicate that NRP-1 could, potentially, be used as a target for ligand-directed therapy in human leukemias and lymphomas - as well as in many human solid tumors, which are also know to over-express NRP-1 - and that the prototype CGFYWLRSC-GG-D(KLAKLAK)2 is a promising drug candidate in this setting.

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 2903. doi:1538-7445.AM2012-2903

2-methoxyestradiol is an estrogen receptor agonist that supports tumor growth in murine xenograft models of breast cancer

PURPOSE

2-Methoxyestradiol (2MEO) is being developed as a novel antitumor agent based on its antiangiogenic activity, tumor cell cytotoxicity, and apparent lack of toxicity. However, pharmacologic concentrations of 2MEO bind to estrogen receptors (ER). We have therefore examined the ER activity of 2MEO.

EXPERIMENTAL DESIGN

Estrogenic actions of 2MEO were evaluated by changes in gene expression of the ER-positive (MCF7) breast tumor cell line and, in vivo, estrogenicity was assessed in breast tumor xenograft models and by measuring endocrine responses in uterus and liver.

RESULTS

In the ER-positive breast tumor cell line (MCF7), microarray experiments revealed that 269 of 279 changes in gene expression common to 2MEO and estradiol were prevented by the ER antagonist, ICI 182,780. Changes in the expression of selected genes and their sensitivity to inhibition by ICI 182,780 were confirmed by quantitative reverse transcription-PCR measurement. Activation of ER in MCF7 cells by 2MEO was further confirmed by stimulation of an estrogen response element-dependent reporter gene that was blocked by ICI 182,780 (1 micromol/L). Doses of 2MEO (15-150 mg/kg) that had no antitumor efficacy in either nu/nu BALB/c or severe combined immunodeficient mice bearing ER-negative MDA-MB-435 tumors had uterotropic and hepatic estrogen-like actions. In female nu/nu BALB/c mice inoculated with the estrogen-dependent MCF7 tumor cells, 2MEO (50 mg/kg/d) supported tumor growth.

CONCLUSIONS

Tumor growth enhancement by 2MEO at doses generating serum levels (100-500 nmol/L) that have estrogenic activity suggests that a conservative approach to the further clinical evaluation of this agent should be adopted and that its evaluation in breast cancer is inappropriate.

Genomic Analysis of a Spontaneous Model of Breast Cancer Metastasis to Bone Reveals a Role for the Extracellular Matrix

A clinically relevant model of spontaneous breast cancer metastasis to multiple sites, including bone, was characterized and used to identify genes involved in metastatic progression. The metastatic potential of several genetically related tumor lines was assayed using a novel real-time quantitative RT-PCR assay of tumor burden. Based on this assay, the tumor lines were categorized as nonmetastatic (67NR), weakly metastatic to lymph node (168FARN) or lung (66cl4), or highly metastatic to lymph node, lung, and bone (4T1.2 and 4T1.13). In vitro assays that mimic stages of metastasis showed that highly metastatic tumors lines were more adhesive, invasive, and migratory than the less metastatic lines. To identify metastasis-related genes in this model, each metastatic tumor was array profiled against the nonmetastatic 67NR using 15,000 mouse cDNA arrays. A significant proportion of genes relating to the extracellular matrix had elevated expression in highly metastatic tumors. The role of one of these genes, POEM, was further investigated in the model. In situ hybridization showed that POEM expression was specific to the tumor epithelium of highly metastatic tumors. Decreased POEM expression in 4T1.2 tumors significantly inhibited spontaneous metastasis to the lung, bone, and kidney. Taken together, our data support a role for the extracellular matrix in metastatic progression and describe, for the first time, a role for POEM in this process.

Genomic analysis of a spontaneous model of breast cancer metastasis to bone reveals a role for the extracellular matrix

A clinically relevant model of spontaneous breast cancer metastasis to multiple sites, including bone, was characterized and used to identify genes involved in metastatic progression. The metastatic potential of several genetically related tumor lines was assayed using a novel real-time quantitative RT-PCR assay of tumor burden. Based on this assay, the tumor lines were categorized as nonmetastatic (67NR), weakly metastatic to lymph node (168FARN) or lung (66cl4), or highly metastatic to lymph node, lung, and bone (4T1.2 and 4T1.13). In vitro assays that mimic stages of metastasis showed that highly metastatic tumors lines were more adhesive, invasive, and migratory than the less metastatic lines. To identify metastasis-related genes in this model, each metastatic tumor was array profiled against the nonmetastatic 67NR using 15,000 mouse cDNA arrays. A significant proportion of genes relating to the extracellular matrix had elevated expression in highly metastatic tumors. The role of one of these genes, POEM, was further investigated in the model. In situ hybridization showed that POEM expression was specific to the tumor epithelium of highly metastatic tumors. Decreased POEM expression in 4T1.2 tumors significantly inhibited spontaneous metastasis to the lung, bone, and kidney. Taken together, our data support a role for the extracellular matrix in metastatic progression and describe, for the first time, a role for POEM in this process.

Metallothionein-III inhibits initial neurite formation in developing neurons as well as postinjury, regenerative neurite sprouting

Human metallothionein-III (MT-III) is an inhibitory factor deficient in the Alzheimer's disease (AD) brain. MT-III has been identified as an inhibitor of neurite sprouting, and its deficiency has been proposed to be involved in the formation of neurofibrillary tangles (NFT) in the neuropathology of AD. However, there has been limited investigation of the proposed neurite growth inhibitory properties of MT-III. We have applied recombinant human MT-III to both single cell embryonic cortical neurons (to investigate initial neurite formation), as well as mature (21 days postplating) clusters of cortical neurons (to investigate the regenerative sprouting response following injury). We report that MT-III inhibited the initial formation of neurites by rat embryonic (E18) cortical neurons. This was based on both the percentage of neurite positive neurons and the number of neurites per neuron (45 and 30% inhibition, respectively). Neurite inhibition was only observed in the presence of adult rat brain extract, and was also reversible following replacement of MT-III-containing medium. MT-III inhibited the formation and growth of both axons and dendrites. Of more physiological significance, MT-III also inhibited the regenerative neurite sprouting response following axonal transection. The morphology of sprouting neurites was also altered, with the distal tip often ending in bulb-like structures. Based on these results, we propose that MT-III, in the presence of brain extract, is a potent inhibitor of neurite sprouting, and may be involved in abnormal sprouting potentially underlying both AD and epilepsy.

Sheep have an unusual variant of the brain-specific metallothionein, metallothionein-III

Sheep metallothionein-III (MT-III) cDNA was isolated from a brain cDNA library and characterized. In contrast with MT-III from other species, sheep MT-III cDNA is predicted to encode a protein with significantly different metal-binding properties, owing to the loss of three of its cysteine residues. RT-PCR from other sheep confirmed that this aberrant structure is ubiquitous in this species. MT-III was successfully isolated from sheep brain, demonstrating that the cDNA does give rise to a protein product of the predicted structure. Sheep MT-III is similar to other mammalian MT-IIIs in that it retains the Cys-Pro-Cys-Pro motif which is thought to encode growth-inhibitory activity, and we show that it is likewise able to inhibit neuron survival in vitro. This is the first naturally occurring variant of MT-III (or any other major mammalian MT gene) which gives rise to a protein product. These findings are discussed in light of proposed roles of MT in the mammalian brain.