Dulcitol Selectively Inhibits Proliferation and Metastasis Related Markers in Triple-Negative Breast Cancer: Uncovering an Unforeseen Activity.

<p>Supplementary Figure 1. AXL, MER and TYRO-3 expression in Triple Negative Breast Cancer (TNBC) cell lines and PDXs by Western blot analysis. Supplementary Figure 2. AXL mRNA expression in a large dataset of breast cancer tumors. Supplementary Figure 3. The 100 genes most correlated with AXL expression in 254 basal-like breast cancers. Supplementary Figure 4. Effect of the anti-AXL monoclonal antibody 20G7-D9 on matrix degradation by breast cancer cell lines. Supplementary Figure 5. GAS6 regulates expression of EMT markers in TNBC - Western Blot quantifications. Supplementary Figure 6. E-cadherin expression in TNBC cell lines</p>

<p>Supplementary Figure 1. AXL, MER and TYRO-3 expression in Triple Negative Breast Cancer (TNBC) cell lines and PDXs by Western blot analysis. Supplementary Figure 2. AXL mRNA expression in a large dataset of breast cancer tumors. Supplementary Figure 3. The 100 genes most correlated with AXL expression in 254 basal-like breast cancers. Supplementary Figure 4. Effect of the anti-AXL monoclonal antibody 20G7-D9 on matrix degradation by breast cancer cell lines. Supplementary Figure 5. GAS6 regulates expression of EMT markers in TNBC - Western Blot quantifications. Supplementary Figure 6. E-cadherin expression in TNBC cell lines</p>

TRIM29 Functions as a Tumor Suppressor in Nontumorigenic Breast Cells and Invasive ER+ Breast Cancer

Background: Increased rates of locoregional recurrence (LR) have been observed in TNBC despite chemotherapy and radiation (RT). A novel radiosensitizer screen nominated the AR as a promising target for treatment of radioresistant breast cancer, including TNBC. We assessed the activity of seviteronel (Sevi), a selective CYP17 lyase and AR inhibitor in Phase 2 clinical development for advanced breast and prostate cancer, as a potential radiosensitizer in AR+ TNBC model. Methods: Clonogenic survival assays were used to determine the intrinsic RT sensitivity of 21 breast cancer cell (BCC) lines. IC50 values were determined for 130 clinically available compounds and correlation coefficients were calculated using IC50 values and SF-2Gy. Gene expression was measured using RNA Seq or qRT-PCR and protein expression was measured using RPPA arrays. AR function was assessed using functional inhibition with Sevi in MDA-MB-453, ACC-422, ACC-460, SUM-185 (all four AR+ TNBC), MDA-MB-231 (AR- TNBC), and T47D (AR- ER+) BCC lines. Double-stranded DNA (dsDNA) break repair was assessed with γH2AX foci counting. In vivo tumor growth was measured with varying control and treatment groups (16-20 tumors/group). Kaplan-Meier analysis was performed to estimate local control. A Cox proportional hazards model and multi-variate analysis (MVA) were used to determine variables associated with LRF survival. Results: Our novel radiosensitizer screen identified the activity of anti-androgen therapy as a potentially effective strategy for radiosensitization in RT-resistant BCC lines (R2 =0.46, p-value < 0.01) (Speers et al, J Clin Oncol 35, 2017 (suppl; abstr e12102). Heterogeneity in AR expression was identified in human BCC lines and TNBC samples from patients (N=2098). There was a strong correlation between AR RNA expression and protein expression across all BC intrinsic subtypes. AR inhibition using Sevi induced radiation sensitivity in vitro with an enhancement ratio (ER) of 1.24-1.69 in four different AR+ TNBC lines. No such radiosensitization was seen in AR(-) TNBC or ER+, AR(-) BCC lines. Radiosensitization was at least partially dependent on impaired dsDNA break repair with significant delays in dsDNA break repair at 16 and 24 hours in all AR+ TNBC lines examined (p-value < 0.01). AR inhibition with Sevi significantly radiosensitized AR+ TNBC xenografts in mouse models and markedly delayed tumor-volume tripling time (TTT) and tumor growth (MDA-MB-453: median TTT 16.1 days for RT alone vs. not reached after 45 days for Sevi+RT, p-value <0.001). Similar delays were seen in tumor growth, weight, and tumor doubling. Clinically, TNBC patients whose tumors had higher than median expression of AR had higher rates of LR after RT (HR for LR ˜3, p-value <0.01, 2 independent datasets). In MVA, high AR expression was the variable most significantly associated with worse LR survival after RT in TNBC patients, outperforming all other variables (HR of 3.42; p-value < 0.01). Conclusions: Our results implicate the AR as a mediator of radioresistance in breast cancer and support the rationale for developing Sevi as a novel radiosensitizing agent in AR+ TNBC. Citation Format: Speers CW, Chandler B, Olsen E, Wilder-Romans K, Moubadder L, Nyati S, Rae J, Hayes DF, Spratt DE, Wahl DR, Eisner J, Feng FY, Pierce LJ. Radiosensitization of androgen receptor (AR)-positive triple-negative breast cancer (TNBC) cells using seviteronel (INO-464), a selective CYP17 lyase and AR inhibitor [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 P1-09-05.

Dual-miRNA-Propelled Three-Dimensional DNA Walker for Highly Specific and Rapid Discrimination of Breast Cancer Cell Subtypes in Clinical Tissue Samples

TrkA overexpression occurs in over 20% of breast cancers, including triple-negative breast cancers (TNBC), and has recently been recognized as a potential driver of carcinogenesis. Recent clinical trials of pan-Trk inhibitors have demonstrated targeted activity against tumors harboring NTRK fusions, a relatively rare alteration across human cancers. Despite this success, current clinical trials have not investigated TrkA overexpression as an additional therapeutic target for pan-Trk inhibitors. Here, we evaluate the cancerous phenotypes of TrkA overexpression relative to NTRK1 fusions in human cells and assess response to pharmacologic Trk inhibition. To evaluate the clinical utility of TrkA overexpression, a panel of TrkA overexpressing cells were developed via stable transfection of an NTRK1 vector into the non-tumorigenic breast cell lines, MCF10A and hTERT-IMEC. A panel of positive controls was generated via stable transfection with a CD74-NTRK1 fusion vector into MCF10A cells. Cells were assessed via various in vitro and in vivo analyses to determine the transformative potential and targetability of TrkA overexpression. TrkA overexpressing cells demonstrated transformative phenotypes similar to Trk fusions, indicating increased oncogenic potential. TrkA overexpressing cells demonstrated growth factor-independent proliferation, increased PI3Kinase and MAPKinase pathway activation, anchorage-independent growth, and increased migratory capacity. These phenotypes were abrogated by the addition of the pan-Trk inhibitor, larotrectinib. In vivo analysis demonstrated increased tumorgenicity and metastatic potential of TrkA overexpressing breast cancer cells. Herein, we demonstrate TrkA overexpressing cells show increased tumorgenicity and are sensitive to pan-Trk inhibitors. These data suggest that TrkA overexpression may be an additional target for pan-Trk inhibitors and provide a targeted therapy for breast cancer patients.

The identification of markers targetable by specific mAbs represents a high medical need in cancer therapy. Our objective is to discover novel tumor-associated proteins showing promise as targets for monoclonal antibody (mAb) therapy, and to generate and validate highly specific mAbs for therapeutic applications. The approach we used to discover novel tumor markers is based on a high through-put immune-histochemical (IHC) screening of tumor and normal tissues using collections of murine polyclonal and mAbs raised against recombinant human proteins. In the course of such analysis, we discovered and validated different surface exposed proteins over-expressed in one or more cancers. Here, we report a surface exposed protein mainly over-expressed in ovary and breast cancers. Interestingly, the protein is highly expressed in high grade breast cancers. Approximately 40% of cancers in which the protein is over-expressed belong to the triple negative subtype. In line with IHC data, an expression profile analysis in different cells lines showed that this protein is expressed in ovarian and breast cancer cell lines. In breast cell lines, high expression was found in triple negative cells positive to the androgen receptor. Gene silencing experiments combined to phenotypic analysis, showed that loss of protein expression significantly reduces cell proliferation and invasiveness. Several mAbs able to recognize the target protein on the surface of breast and ovary cancer cell lines have been selected and validated in a number of immunoassays. The specificity of the mAb binding was confirmed by gene silencing and competition assays with peptides encompassing the mAb epitopes. Specific mAbs able to detect the protein in cancer cells in IHC are under validation. These antibodies show limited reactivity on normal human tissues and are negative on PBMC from normal donors. Moreover, these mAbs are efficiently internalized by cancer cells, suggesting that they are amenable to the development of Antibody-Drug-Conjugate. Finally, they efficiently recognize the macaca protein ortholog, thus facilitating future safety studies in non-human primates. Overall, results so far accumulated highlight the potential of this novel tumor-associated protein and available mAbs for the development of targeted therapy against ovarian cancer and triple negative breast cancer. Other promising targets and related monoclonal antibodies will be described during the meeting. Citation Format: Matteo Parri, Susanna Campagnoli, Alberto Grandi, Elisa De Camilli, Aurelien Lacombe, Boquan Jin, Serenella Eppenberger-Castori, Giuseppe Viale, Luigi Terracciano, Piero Pileri, Renata Maria Grifantini. Novel targets and monoclonal antibodies for cancer therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3800.

p53 mutations occur in 80% of triple-negative breast cancer (TNBC) cases. Several types of p53 mutations have been reported, among which gain of function mutations have been associated with increased cancer stem cells, chemotherapy resistance, and disease relapse in several malignancies. Particularly, hotspot p53 mutations (mutations at amino acid location 157, 175, 248, 249, 273 predict worse overall survival in some cancer types. We have previously reported that Ganglioside GD2, a cell surface glycosphingolipid, identifies breast cancer stem cells and promotes tumorigenesis. We have also reported that GD3 synthase, a key enzyme which catalyzes the rate-limiting step of the GD2 biosynthesis pathway, is significantly upregulated in breast tumors with p53 mutations. Here, we hypothesize that mutant p53 promotes stemness in TNBC cells by regulating GD3 synthase and GD2 expression. To identify specific p53 mutations that contribute to TNBC stemness, we stratified TNBC cell lines (N=18) based on p53 mutation status including mutation type, location, and domain affected. We measured GD2 and GD3 synthase expression in the available TNBC cell lines by flow cytometry and RT-PCR, respectively. We found that GD3 synthase expression is significantly upregulated in TNBC cell lines with p53 hotspot mutations compared to cell lines with other p53 mutations (Median relative expression 0.0114 compared to 0.0003, p=0.005). Similarly, we found that GD2 expression is significantly higher in TNBC cell lines with hotspot mutations compared to non-hotspot counterparts (Median GD2+ cells 15.2% compared to 0.97%, p= 0.013) Additionally, GD2 and GD3 synthase are upregulated in basal-type TNBC cell lines and TCGA patient samples compared to other TNBC molecular subtypes. Interestingly, we also found that GD2 expression is not always directly correlated with GD3S expression, suggesting that GD2 synthase expression is also a key factor in the regulation of GD2 expression. To examine the effect of mutant p53 protein levels on TNBC stemness, we measured p53 expression in all the available TNBC cell lines by western blot, and found that p53 protein levels do not correlate with GD2 or GD3S expression. To validate these findings, we analyzed RPPA data from the MD Anderson Cancer Cell Lines Project and found similar results. These data suggest that it is the type of p53 mutation, but not the amount of p53 protein in the cells that determines GD2 and GD3 synthase expression in TNBC cells. For instance, p53 hotspot mutations involving amino acid position 248 have been shown to be strongly associated with increased cancer stemness. We found that cell lines with p53 mutations at this specific location have significantly higher GD3 synthase expression compared to other mutant p53 forms. We are currently examining the direct role of mutant p53 in the regulation of GD3S expression by stabilizing mutant p53 using MDM2 inhibitors as well as stable knockdown of p53 gene in multiple TNBC cell lines to establish a clear link between mutant p53 and stem cell marker expression in TNBC cell lines. In conclusion, stem cell markers are highly expressed in p53 mutant TNBC cell lines compared to wild type p53 counterparts. Specifically, cell lines with hotspot p53 mutations significantly correlate with increased TNBC stemness. The type of p53 mutation, rather than level of its expression correlates with stem cell marker expression in TNBC cells. Citation Format: Fouad El-Dana, Bin Yuan, Stanley Ly, Vivek Anand, Venkata Lokesh Battula. Hotspot p53 mutations correlate with increased expression of stem cell markers in triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS16-19.

CC-671 is a potent and selective TTK1 (Mps1) and CLK2 inhibitor. In support of a phase I proof of concept, we used an image-based, multiplex cell assay to evaluate the antiproliferative impact of CC-671 across a broad panel of cancer cell lines representing tumors from various anatomic origins. CC-671 potently and selectively inhibited proliferation and induced apoptosis. Cell lines representing leukemia, lymphoma, colorectal cancer (CRC), head and neck (H&N), and bladder cancers were uniformly sensitive to CC-671 while the cell lines from other tumor types, such as breast and lung cancers, were differentially sensitive to CC-671. Cell cycle analysis using phospho-histone H3 (pHH3) as a mitosis biomarker suggested that CC-671 had cell line-specific mitotic effects. CC-671 accelerated mitotic exit in 120 cell lines while causing mitotic block in 37 cell lines at concentrations < 1 μM. Custom gene expression signatures correlating with sensitivity or resistance were generated. Mapping these signatures to a gene expression database of clinical tumor samples identified additional CC-671 sensitive tumor types including Wilms tumor, superficial bladder cancer, triple-negative, and luminal Btype breast cancer, and several squamous cell carcinomas (lung, esophageal, cervical, H&N). To identify a breast cancer patient selection profile, the CC-671 antiproliferative activity was assessed in a panel of 49 breast cancer cell lines. CC-671 potently inhibited the growth of breast cancer cell lines with 50% inhibitory concentrations (IC50 values) < 100 nM in 14 lines and > 10 μM in 21 lines. Triple-negative breast cancer (TNBC) cell lines were significantly more sensitive to CC-671 than non-TNBC (ER+/PR+ and/or HER2+) lines. Within TNBC, the mesenchymal (M) and basal-like 1 (BL1) subtypes were more sensitive to CC-671. In addition, TNBC lines with cancer stem cell (CSC)-like properties were also sensitive, indicating a potential role of TTK1 and CLK2 in cancer stem cells. Interestingly, mutations in several genes (phosphatidylinositol-4,5-bisphosphate 3kinase 110 kDa catalytic subunit alpha [PIK3CA], serine/threonine kinase 11 [STK11], and phosphatase and tensin homolog [PTEN]) in the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway tend to associate with CC-671 TNBC sensitivity. These mutational correlates are being confirmed in additional TNBC lines. Citation Format: Shuichan Xu, Tam Tran, Tao Shi, Ning Jiang, Dan Zhu, Jennifer R. Riggs, John Boylan. Identification of a patient enrichment strategy supporting development of a potent and selective dual TTK/CLK2 inhibitor CC-671 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A043.

Background: Although Del-1 was recently proposed as a new biomarker for early breast cancer in our previous studies, the mechanisms of Del-1 expression are barely understood. In the current study, we selected two microRNAs (miR-137 and - 496), potentially affecting Del-1 expression in breast cancer and examined their impact on Del-1 expression in a variety of breast cancer cell lines to identify their potential role in Del-1 expression and thereby breast cancer development or progression. Methods: Del-1 mRNA and miR-137/- 496 levels were measured by qRT-PCR among breast epithelial (MCF10A) and cancer cells (MDA-MB-231, MCF7, SK-BR3 and T-47D). The effects of miR-137/- 496 on cell proliferation and invasion were detected using MTT, wound healing and Transwell assays. Furthermore, luciferase reporter assay was used to identify the direct regulation of Del-1 by miR-137 or - 496 in MDA-MB-231 cells. Plus, we analyzed the expressions of miR-137 or - 496 and Del-1 mRNA from 20 patients with triple negative early breast cancer. Results: miR-137 and - 496 levels were low in all breast cancer cell lines. As Del-1 mRNA expression was remarkably higher in MDA-MB-231 compared to the other breast cancer cell lines, further functional analyses were done with MDA-MB-231 representing triple negative breast cancer subtype. Both miR-137 and miR-496 were revealed to directly bind at the 3’-UTR of Del-1. Del-1 by Luciferase reporter assay and Del-1 expression was upregulated by inhibitors and reversed by both mimics of both miR-137 and miR-496. Furthermore, both miR-137 and miR-496 were also demonstrated to inhibit cell proliferation, migration and invasion of MDA-MB-231, suggesting that these miRNAs affect cancer progression via Del-1. MiR-137 and miR-496 were remarkably down-regulated in 7 out of 12 triple negative breast cancer tissues, in particular with high Ki67 and high histologic grade. Conclusion: Although Del-1 was recently introduced as a new biomarker for triple negative breast cancer, the mechanisms of Del-1 expression were barely identified. The current study firstly demonstrated that microRNA 137 and 496 are involved in Del-1 regulation by binding at Del-1 gene, affecting cancer progression by altering Del-1 expression. Citation Format: Jeeyeon Lee, Yee Soo Chae, Soo Jung Lee, Jin Hyang Jung, Ho Yong Park, Moon-Chang Baek. MiR-137 and MiR-496 target Del-1 and affect triple negative breast cancer progression [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 2797. doi:10.1158/1538-7445.AM2017-2797

e23058 Background: Although Del-1 was recently proposed as a new biomarker for early breast cancer in our previous studies, the mechanisms of Del-1 expression are barely understood. In the current study, we selected two microRNAs (miR-137 and - 496), potentially affecting Del-1 expression in breast cancer and examined their impact on Del-1 expression in a variety of breast cancer cell lines to identify their potential role in Del-1 expression and thereby breast cancer development or progression. . Methods: Del-1 mRNA and miR-137/– 496 levels were measured by qRT-PCR among breast epithelial (MCF10A) and cancer cells (MDA-MB-231, MCF7, SK-BR3 and T-47D). The effects of miR-137/– 496 on cell proliferation and invasion were detected using MTT, wound healing and Transwell assays. Furthermore, luciferase reporter assay was used to identify the direct regulation of Del-1 by miR-137 or – 496 in MDA-MB-231 cells. Plus, we analyzed the expressions of miR-137 or – 496 and Del-1 mRNA from 20 patients with triple negative early breast cancer. Results: miR-137 and – 496 levels were low in all breast cancer cell lines. As Del-1 mRNA expression was remarkably higher in MDA-MB-231 compared to the other breast cancer cell lines, further functional analyses were done with MDA-MB-231 representing triple negative breast cancer subtype. Both miR-137 and miR-496 were revealed to directly bind at the 3’-UTR of Del-1. Del-1 by Luciferase reporter assay and Del-1 expression was upregulated by inhibitors and reversed by both mimics of both miR-137 and miR-496. Furthermore, both miR-137 and miR-496 were also demonstrated to inhibit cell proliferation, migration and invasion of MDA-MB-231, suggesting that these miRNAs affect cancer progression via Del-1. MiR-137 and miR-496 were remarkably down-regulated in 7 out of 12 triple negative breast cancer tissues, in particular with high Ki67 and high histologic grade. Conclusions: Although Del-1 was recently introduced as a new biomarker for triple negative breast cancer, the mechanisms of Del-1 expression were barely identified. The current study firstly demonstrated that microRNA 137 and 496 are involved in Del-1 regulation by binding at Del-1 gene, affecting cancer progression by altering Del-1 expression.

Downregulation of MALAT1 in triple-negative breast cancer cells

Cancer cell lines (CCLs) serve as models to study the functional consequences of the genomic lesions in patients and as screening platforms for prediction of drug response. While genomic and transcriptomic data have proven to be useful predictors, the ability of these omics platforms to predict protein level and function is limited. Furthermore, since proteins are the targets of the majority of the targeted therapies, protein levels and importantly protein function would be expected to provide more powerful predictions than DNA or RNA data. While large scale genomic and transcriptomic data linked to drug sensitivity are available for over a thousand CCLs, proteomic data is available for only a small subset of lines. Here we performed proteomic profiling of 736 cell lines using reverse-phase protein arrays (RPPAs) with approximately 300 antibodies providing an unbiased sparse representation of the majority of signaling pathways. The functional proteomic analysis revealed 10 protein-based clusters across all cell lines. Similar to human tumors, the breast cell lines fell into three major clusters representing basal-like, luminal/Her2-amplified and claudin-low breast cancer subtypes. The basal-like and claudin-low clusters contained all of the representative breast cancer cell lines as well as a much larger number of other CCLs. For example, the 6 claudin-low breast cancers analyzed reside in an EMT cluster, in which only 8/126 are breast cell lines. However, the complete cluster including multiple non-breast cancer cell lines recapitulated mRNA and protein features of claudin-low breast tumors, including a high EMT signature and low level of hormone receptor pathway activity. We thus explored whether we could gain power for linking the limited number of basal and claudin-low breast cancer cell lines to therapeutic sensitivity by assessing patterns of drug sensitivity in each cluster for both the breast and non-breast cancer cell lines in the cluster. We explored drug sensitivity of 481 therapeutic compounds from the Cancer Therapeutic Response Portal (CTRP v2) and demonstrated that the non- breast cancer and breast cancer cell lines in each cluster provided similar patterns of drug sensitivity. For example, Claudin-low/EMT cell lines of both breast cancer and non-breast cancer origin showed decreased sensitivity to PI3K/mTOR inhibitors compared to luminal breast cancers (p<0.05 for 4 mTOR inhibitors) and drugs targeting EGFR family compared to basal cell lines (p<0.05 for 7 EGFR/ERBB2 inhibitors). Thus it is possible to gain information by characterizing cell lines with similar patterns of protein expression and provide important information related to drug sensitivity of uncommon breast cancer lineages. The functional proteomic analysis provides a wealth of information that complements the genomic and transciptomic studies of cancer cell lines, and demonstrates the opportunity to leverage cell line 'pan-cancer' proteomic patterns to improve characterization of specific breast cancer subtypes. To facilitate broad access to these data, we developed a user-friendly data portal, the MD Anderson Cell Lines Project (MCLP), that provides both data analysis and download (http://ibl.mdanderson.org/mclp/). Citation Format: Zhao W, Li J, Lu Y, Akbani R, Liang H, Mills GB. A pan-cancer perspective of functional proteomics provides novel information content for uncommon breast cancer subtypes [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-07-01.

Rationale: NOTCH4 receptor has been implicated in triple-negative breast cancer (TNBC) development and breast cancer stem cell (BCSC) regulation. However, the potential of NOTCH4 as a BCSC marker and the underlying mechanisms remain unclear.Methods: In this study, we determined the expression and activation of NOTCH4 in breast cancer cell lines and tumor samples by qRT-PCR, western blotting and immunohistochemistry. Subsequently, in vitro and in vivo serial dilution experiments were performed to demonstrate the application of NOTCH4 as an efficient mesenchymal-like (ML)-BCSC marker in TNBC. Stable overexpression of activated NOTCH4 and knockdown cell lines were established using lentivirus. RNA-seq and qRT-PCR were employed to reveal the downstream effectors of NOTCH4, followed by dual-luciferase reporter and chromatin immunoprecipitation assays to identify the genuine binding sites of NOTCH4 on SLUG and GAS1 promoters. Transwell assay, mammosphere formation and chemoresistance experiments were performed to determine the effects of SLUG, GAS1 and NOTCH4 on the mesenchymal-like characteristics of TNBC cells. Survival analysis was used to study the relation of NOTCH4, SLUG and GAS1 with prognosis of breast cancer.Results: NOTCH4 is aberrantly highly expressed and activated in TNBC, which contributes to the maintenance of ML-BCSCs. Furthermore, NOTCH4 shows significantly higher efficiency in labeling ML-BCSCs than the currently commonly used CD24-CD44+ marker. Mechanistically, NOTCH4 transcriptionally upregulates SLUG and GAS1 to promote EMT and quiescence in TNBC, respectively. The effects of NOTCH4 can be mimicked by simultaneous overexpression of SLUG and GAS1. Moreover, SLUG is also involved in harnessing GAS1, a known tumor suppressor gene, via its anti-apoptotic function.Conclusions: Our findings reveal that the NOTCH4-SLUG-GAS1 circuit serves as a potential target for tumor intervention by overcoming stemness of ML-BCSCs and by conquering the lethal chemoresistance and metastasis of TNBC.

Background: Increased rates of locoregional recurrence have been observed in TNBC despite the use of chemotherapy and radiation (RT). Thus, approaches that result in radiosensitizaton of TNBC are critically needed. We have previously characterized the radiation response of 21 breast cancer cell (BCC) lines using clonogenic survival assays. We now pair this data with high-throughput drug screen data available through cancer cell line encyclopedia studies to identify AR as a top target for radiosensitization and assess AR inhibition as a radiosensitization strategy for TNBC. Methods: Clonogenic survival assays were performed to determine the intrinsic RT sensitivity of 21 BCC lines (0-8 Gy RT). IC50 values were determined for 130 clinically available compounds and correlation coefficients were calculated using IC50 values (for drug sensitivity) and SF-2Gy (for radiation sensitivity). Gene expression was measured using Affymetrix microarrays and protein expression was measured using reverse-phase protein lysate arrays (RPPA) of human tumor samples (n=2,061) and BCC lines (n=51). AR function was assessed using siRNA knockdown or inhibition with MDV3100 (enzalutamide). Kaplan-Meier analysis was performed to determine the clinical impact of AR expression on local control and survival. A Cox proportional hazards model was constructed to identify potential factors of survival, and multivariate analysis was used to determine variables most significantly associated with LRF survival. Results: Our radiosensitizer screen nominated bicalutamide as one of the most effective drugs in treating radioresistant BCC lines (R2= 0.46, p-value <0.001). Recognizing that a subgroup of TNBC includes AR expressing tumors, we interrogated the expression of AR in >2000 human breast tumor samples and found signifi[not]cant heterogeneity in AR expression with an increase in TNBC (35% of tumors) compared to non-TNBC (28% of tumors). This same heterogeneity was also identified in human BCC lines. There was a strong correlation between AR RNA expression and protein expression (R2= 0.72, p <0.0001). Inhibition of AR using both siRNA and MDV3100 induced radiation sensitivity in vitro with an enhancement ratio (ER) of 1.35-1.42 in AR-positive TNBC lines. No such radiosensitization was seen in AR-negative TNBC or ER-positive, AR-negative BCC lines. Radiosensitization was at least partially dependent on impaired dsDNA break repair mediated by DNAPKcs. In vivo assessment of tumor growth inhibition with RT and anti-AR strategies are currently underway. Clinically, analyses of patients with TNBC showed that patients whose tumors had high expression of AR had markedly higher rates of LR after RT than patients with low expression of AR (HR for LR 2.9-3.2, p-value <0.01, 2 independent datasets). There was no difference in LR in TNBC patients not treated with RT when stratified by AR expression status. In multivariate analysis, AR expression was the variable most significantly associated with worse LRF survival after RT with a HR of 3.58 (p-value < 0.01). Conclusion: Our results implicate AR as a mediator of radioresistance in breast cancer and support the rationale for developing clinical strategies to inhibit AR as a novel radiosensitizing target in TNBC. Citation Format: Corey Speers, Shuang G Zhao, Meilan Liu, Joseph Evans, Prasanna Alluri, Daniel F Hayes, Felix Y Feng, Lori J Pierce. Androgen receptor (AR): A novel target for radiosensitization and treatment in triple-negative breast cancers (TNBC) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-03-08.