Human Triple-negative Breast Cancer Research Articles

Influence of chromatin remodeling molecule ARID1A on metastatic heterogeneity in triple negative breast cancer: Binding of YAP.

1085 Background: Heterogeneity is the prominent character of TNBC and one predominant cause of treatment failure. As a key nuclear SWI/SNF protein complex subunit, ARID1A plays a critical role in tumor identity determining by manipulating gene expression. The present study aimed to investigate whether and how ARID1A determined the metastatic heterogeneity of triple-negative breast cancer. Methods: This study retrospectively collected and analysed clinical and pathological data from 258 patients diagnosed with triple-negative breast cancer at Fudan University Cancer Hospital from August 2015 to June 2016 to define the prognostic ability of ARID1A.CRISPR/Cas9 or plasmids-mediated ARID1A were used to determine the ARID1A function in regulating the metastatic character in TNBC. Cell morphology, tumor invasion, and metastasis were analyzed in terms of ARID1A status both in vitro and in vivo experiments. The molecular mechanism of ARID1A determining metastasis potential of TNBC was explored by RNA-Seq and nuclear positioning. Results: ARID1A low expression was found to have independent prognostic value for poor OS (43.9 vs 53.6 months, P=0.0001) and RFS (31.0 vs 45.5 months, P=0.0029) in TNBC patients. Both nuclear and cytoplasmic protein analysis and Immunofluorescent localization assay confirm that ARID1A recruits the Hippo pathway effector YAP into nucleus in human triple negative breast cancer cells. Next we designed the YAP truncator plasmid and confirmed by Co-Immunoprecipitation that ARID1A could competitively bind to the WW domain of YAP to form the ARID1A/YAP complex. Furthermore, down-regulation of ARID1A promoted migration and invasion both in human triple negative breast cancer cells and xenograft model through Hippo/YAP signaling axis. Conclusions: Our study provides new insights into the previously unrecognized role of ARID1A in TNBC metastasis, which might provide new therapeutic options for patients with TNBC.

A Tetramethylpyrazine Releasing Hydrogel can Potentiate CAR-T Cell Therapy against Triple Negative Breast Cancer by Reprogramming Tumor Vasculatures

Irregular vasculature of solid tumors has proven to be a pivotal factor restricting their response to chimeric antigen receptor-T (CAR-T) cell therapy because it is tightly associated with hypoxia and other biological barriers. Herein, an injectable hydrogel composed of poly (ethylene glycol) dimethacrylate (PEGDMA) and ferrous chloride (FeCl2) responding to endogenous hydrogen peroxides (H2O2) is developed to enable sustained intratumoral release of Chinese herbal extracts tetramethylpyrazine (TMP). TMP is selected due to its potency in activating vascular endothelial growth factor (VEGF) expression and the endothelial nitric oxide synthase/nitric oxide (eNOS/NO) axis inside vascular endothelial cells. Upon being fixed inside tumors with the PEGDMA based hydrogel, TMP can remodel tumor vasculature by simultaneously promoting angiogenesis and dilating tumor vasculature and thus attenuate tumor hypoxia in two murine xenografts bearing human triple negative breast cancer (TNBC). Resultantly, treatment with TMP fixation potentiates the tumor suppression effect of intravenously injected epidermal growth factor receptor expressing CAR-T (HER-1-CAR-T) cells toward two TNBC tumor xenografts by promoting their tumor infiltration, survival, and effector function. This study highlights a concise yet effective approach to reinforce the therapeutic potency of CAR-T cells towards targeted solid tumors by simply remodeling tumor vasculature.

Effect of microRNA-21 blockade in human triple negative breast cancer allografts on progression and immune checkpoint proteins.

e13097 Background: Triple negative breast cancer (TNBC) is an orphan disease that attacks > 46,000 US women every year. TNBC recurs after standard-of-care surgery, chemotherapy and radiation, killing half its victims within 4 years. Poly(ADP-ribose) polymerase (PARP) inhibitors, topoisomerase inhibitors, immune checkpoint inhibitors, and antibody-drug conjugates extend the survival of a fraction of TNBC patients for a few months. Thus, TNBC shows a critical need for molecularly-targeted therapy. Most TNBC cells show high microRNA 21 (miR-21), identical in humans and mice, which decreases tumor suppressor proteins that keep cell growth in check. Hypothesis: Short anti-miR-21 RNA analogs conjugated to a receptor ligand will direct TNBC cell uptake and slow the growth of TNBC orthotopic allografts with immune activation and minimal toxicity. Methods: We designed an anti-miR-21 RNA analog using aminomethyl bridged nucleic acid (BNA), exhibiting low toxicity, and serum stability. We lipofected a concentration ramp of the anti-miR-21 RNA analog into human TNBC cell lines (MDA-MB-231, MDA-MB-157, MDA-MB-436, MDA-MB-468, BT-20, BT-549, HCC1806, HCC1937, HCC1806) representing a spectrum of TNBC subtypes, then measured proliferation and biochemical markers. We also conjugated a peptide analog for endocytosis by the insulin-like growth factor 1 receptor (IGF1R), overexpressed in most TNBC lesions. The peptide ligand for IGF1R provides a unique strategy for delivering the anti-miR-21 RNA analog preferentially into TNBC cells. We administered 5 mg/kg of the anti-miR-21 RNA-peptide analog in sterile saline intraperitoneally twice a week for 14 days into immunocompetent female Balb/c mice bearing syngeneic EMT6 TNBC tumors in their mammary fat pads. Results: The anti-miR-21 RNA analog slowed proliferation, increased apoptosis, elevated tumor suppressor proteins, and suppressed immune checkpoint gene expression in multiple human TNBC lines. IC50 for inhibiting cell proliferation correlated with miR-21 copies/cell in 7 TNBC cell lines, but not in the non-tumorigenic breast epithelial cell line MCF-10A. The anti-miR-21 RNA-peptide analog stopped orthotopic TNBC allograft growth in syngeneic immunocompetent female Balb/c mice during 14 days of therapy, with apparent safety. Conclusions: This strategy optimizes cancer cell-specific delivery to block proliferation and immune checkpoints. The results support further preclinical proof-of-concept studies to enable an eIND submission for the anti-miR-21 RNA-peptide analog.

Glutathione Depleting a Chemoselective Novel Pro-oxidant Nano Metal-Organic Framework Induced G2/M Arrest and ROS-Mediated Apoptotic Cell Death in a Human Triple-Negative Breast Cancer Cell Line.

The progression of a new class of compounds to inhibit the uncontrolled proliferation of carcinoma cells has become one of the most powerful weapons to combat "cancer". To this end, a new Mn(II)-based metal-organic framework, namely, [{Mn(5N3-IPA)(3-pmh)}(H2O)]α (5N3H2-IPA = 5-azidoisophthalic acid and 3-pmh = (3-pyridylmethylene)hydrazone), has been synthesized adopting a mixed ligand approach and exploited as a successful anticancer agent via systematic in vitro and in vivo studies. Single-crystal X-ray diffraction analyses depict that MOF 1 exhibits a 2D pillar-layer structure consisting of water molecules in each 2D void space. Due to the insolubility of the as-synthesized MOF 1, a green hand grinding methodology has been adopted to scale down the particle size to the nanoregime keeping its structural integrity intact. The nanoscale metal-organic framework (NMOF 1) adopts a discrete spherical morphology as affirmed by scanning electron microscopic analysis. The photoluminescence studies revealed that NMOF 1 is highly luminescent, enhancing its biomedical proficiency. Initially, the affinity of the synthesized NMOF 1 for GSH-reduced has been evaluated by various physicochemical techniques. NMOF 1 constrains the proliferation of cancer cells in vitro by inducing G2/M seizure and accordingly leads to apoptotic cell death. More significantly, compared to cancer cells, NMOF 1 exhibits less cytotoxicity against normal cells. It has been demonstrated that NMOF 1 interacts with GSH, causing a drop in cellular GSH levels and the production of intercellular ROS. It is quite intriguing that we discovered that NMOF 1-mediated ROS generation aids in significantly modifying the mitochondrial redox status, which is a crucial factor in apoptosis. According to mechanistic research, NMOF 1 increases the production of proapoptotic proteins and lowers the expression of antiapoptotic proteins, which significantly aids in activating caspase 3 and the subsequent cleavage of PARP1 and cell death via intrinsic apoptotic pathways. Finally, an in vivo investigation using immuno-competent syngeneic mice demonstrates that NMOF 1 can stop tumor growth without causing adverse side effects.

Detection of Treatment Response in Triple-Negative Breast Tumors to Paclitaxel Using MRI Cell Size Imaging.

Breast cancer treatment response evaluation using the response evaluation criteria in solid tumors (RECIST) guidelines, based on tumor volume changes, has limitations, prompting interest in novel imaging markers for accurate therapeutic effect determination. To use MRI-measured cell size as a new imaging biomarker for assessing chemotherapy response in breast cancer. Longitudinal; animal model. Triple-negative human breast cancer cell (MDA-MB-231) pellets (4 groups, n = 7) treated with dimethyl sulfoxide (DMSO) or 10 nM of paclitaxel for 24, 48, and 96 hours, and 29 mice with MDA-MB-231 tumors in right hind limbs treated with paclitaxel (n = 16) or DMSO (n = 13) twice weekly for 3 weeks. Oscillating gradient spin echo and pulsed gradient spin echo sequences at 4.7 T. MDA-MB-231 cells were analyzed using flowcytometry and light microscopy to assess cell cycle phases and cell size distribution. MDA-MB-231 cell pellets were MR imaged. Mice were imaged weekly, with 9, 6, and 14 being sacrificed for histology after MRI at weeks 1, 2, and 3, respectively. Microstructural parameters of tumors/cell pellets were derived by fitting diffusion MRI data to a biophysical model. One-way ANOVA compared cell sizes and MR-derived parameters between treated and control samples. Repeated measures 2-way ANOVA with Bonferroni post-tests compared temporal changes in MR-derived parameters. A P-value <0.05 was considered statistically significant. In vitro experiments showed that the mean MR-derived cell sizes of paclitaxel-treated cells increased significantly with a 24-hours treatment and decreased (P = 0.06) with a 96-hour treatment. For in vivo xenograft experiments, the paclitaxel-treated tumors showed significant decreases in cell size at later weeks. MRI observations were supported by flowcytometry, light microscopy, and histology. MR-derived cell size may characterize the cell shrinkage during treatment-induced apoptosis, and may potentially provide new insights into the assessment of therapeutic response. 2 TECHNICAL EFFICACY STAGE: 4.

Effects of adipocyte-conditioned cell culture media on S1P treatment of human triple-negative breast cancer cells.

Sphingosine-1-phosphate (S1P) is a potent sphingolipid metabolite that regulates a wide range of biological functions such as cell proliferation, cell apoptosis and angiogenesis. Its cellular level is elevated in breast cancer, which, in turn, would promote cancer cell proliferation, survival, growth and metastasis. However, the cellular concentration of S1P is normally in the low nanomolar range, and our previous studies showed that S1P selectively induced apoptosis of breast cancer cells at high concentrations (high nanomolar to low micromolar). Thus, local administration of high-concentration S1P alone or in combination of chemotherapy agents could be used to treat breast cancer. The breast mainly consists of mammary gland and connective tissue stroma (adipose), which are dynamically interacting each other. Thus, in the current study, we evaluated how normal adipocyte-conditioned cell culture media (AD-CM) and cancer-associated adipocyte-conditioned cell culture media (CAA-CM) would affect high-concentration S1P treatment of triple-negative breast cancer (TNBC) cells. Both AD-CM and CAA-CM may suppress the anti-proliferative effect and reduce nuclear alteration/apoptosis caused by high-concentration S1P. This implicates that adipose tissue is likely to be detrimental to local high-concentration S1P treatment of TNBC. Because the interstitial concentration of S1P is about 10 times higher than its cellular level, we undertook a secretome analysis to understand how S1P would affect the secreted protein profile of differentiated SGBS adipocytes. At 100 nM S1P treatment, we identified 36 upregulated and 21 downregulated secretome genes. Most of these genes are involved in multiple biological processes. Further studies are warranted to identify the most important secretome targets of S1P in adipocytes and illustrate the mechanism on how these target proteins affect S1P treatment of TNBC.

Assessment of the sensitivity of 2 H MR spectroscopy measurements of [2,3-2 H2 ]fumarate metabolism for detecting tumor cell death.

Imaging the metabolism of [2,3-2 H2 ]fumarate to produce malate can be used to detect tumor cell death post-treatment. Here, we assess the sensitivity of the technique for detecting cell death by lowering the concentration of injected [2,3-2 H2 ]fumarate and by varying the extent of tumor cell death through changes in drug concentration. Mice were implanted subcutaneously with human triple negative breast cancer cells (MDA-MB-231) and injected with 0.1, 0.3, and 0.5 g/kg [2,3-2 H2 ]fumarate before and after treatment with a multivalent TRAlL-R2 agonist (MEDI3039) at 0.1, 0.4, and 0.8 mg/kg. Tumor conversion of [2,3-2 H2 ]fumarate to [2,3-2 H2 ]malate was assessed from a series of 13 spatially localized 2 H MR spectra acquired over 65 min using a pulse-acquire sequence with a 2-ms BIR4 adiabatic excitation pulse. Tumors were then excised and stained for histopathological markers of cell death: cleaved caspase 3 (CC3) and DNA damage (terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL]). The rate of malate production and the malate/fumarate ratio plateaued at tumor fumarate concentrations of 2 mM, which were obtained with injected [2,3-2 H2 ]fumarate concentrations of 0.3 g/kg and above. Tumor malate concentration and the malate/fumarate ratio increased linearly with the extent of cell death determined histologically. At an injected [2,3-2 H2 ]fumarate concentration of 0.3 g/kg, 20% CC3 staining corresponded to a malate concentration of 0.62 mM and a malate/fumarate ratio of 0.21. Extrapolation indicated that there would be no detectable malate at 0% CC3 staining. The use of low and nontoxic fumarate concentrations and the production of [2,3-2 H2 ]malate at concentrations that are within the range that can be detected clinically suggest this technique could translate to the clinic.

Antiproliferative and Apoptotic Effects of pH-Responsive Veratric Acid-Loaded Polydopamine Nanoparticles in Human Triple Negative Breast Cancer Cells.

Veratric acid (VA) is plant-derived phenolic acid known for its therapeutic potential, but its anticancer effect on highly invasive triple-negative breast cancer (TNBC) is yet to be evaluated. Polydopamine nanoparticles (nPDAs) were chosen as the drug carrier to overcome VA's hydrophobic nature and ensure a sustained release of VA. We prepared pH-sensitive nano-formulations of VA-loaded nPDAs and subjected them to physicochemical characterization and in vitro drug release studies, followed by cell viability and apoptotic assays on TNBC cells (MDA-MB-231 cells). The SEM and zeta analysis revealed spherical nPDAs were uniform size distribution and good colloidal stability. In vitro drug release from VA-nPDAs was sustained, prolonged and pH-sensitive, which could benefit tumor cell targeting. MTT and cell viability assays showed that VA-nPDAs (IC50=17.6 μM) are more antiproliferative towards MDA-MB-231 cells than free VA (IC50=437.89 μM). The induction of early and late apoptosis by VA-nPDAs in the cancer cells was identified using annexin V and dead cell assay. Thus, the pH response and sustained release of VA from nPDAs showed the potential to enter the cell, inhibit cell proliferation, and induce apoptosis in human breast cancer cells, indicating the anticancer potential of VA.

Targeting of microRNA-22 Suppresses Tumor Spread in a Mouse Model of Triple-Negative Breast Cancer.

microRNA-22 (miR-22) is an oncogenic miRNA whose up-regulation promotes epithelial-mesenchymal transition (EMT), tumor invasion, and metastasis in hormone-responsive breast cancer. Here we show that miR-22 plays a key role in triple negative breast cancer (TNBC) by promoting EMT and aggressiveness in 2D and 3D cell models and a mouse xenograft model of human TNBC, respectively. Furthermore, we report that miR-22 inhibition using an LNA-modified antimiR-22 compound is effective in reducing EMT both in vitro and in vivo. Importantly, pharmacologic inhibition of miR-22 suppressed metastatic spread and markedly prolonged survival in mouse xenograft models of metastatic TNBC highlighting the potential of miR-22 silencing as a new therapeutic strategy for the treatment of TNBC.

Room-Temperature, Copper-Free, and Amine-Free Sonogashira Reaction in a Green Solvent: Synthesis of Tetraalkynylated Anthracenes and In Vitro Assessment of Their Cytotoxic Potentials.

The multifold Sonogashira coupling of a class of aryl halides with arylacetylene in the presence of an equivalent of Cs2CO3 has been accomplished using a combination of Pd(CH3CN)2Cl2 (0.5 mol %) and cataCXium A (1 mol %) under copper-free and amine-free conditions in a readily available green solvent at room temperature. The protocol was used to transform several aryl halides and alkynes to the corresponding coupled products in good to excellent yields. The rate-determining step is likely to involve the oxidative addition of Ar-X. The green protocol provides access to various valuable polycyclic aromatic hydrocarbons (PAHs) with exciting photophysical properties. Among them, six tetraalkynylated anthracenes have been tested for their anticancer properties on the human triple-negative breast cancer (TNBC) cell line MDA-MB-231 and human dermal fibroblasts (HDFs). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to find out the IC50 concentration and lethal dose. The compounds being intrinsically fluorescent, their cellular localization was checked by live cell fluorescence imaging. 4',6-Diamidino-2-phenylindole (DAPI) and propidium iodide (PI) staining was performed to check apoptosis and necrosis, respectively. All of these studies have shown that anthracene and its derivatives can induce cell death via DNA damage and apoptosis.

Development of effective immunotherapy for triple negative breast cancer by WEE1 kinase inhibition

Abstract Treatment options for triple negative breast cancer (TNBC) are limited because they are usually insensitive to most available hormonal or targeted therapeutic agents owing to their triple negative nature. Exciting clinical results using immune checkpoint inhibitors (ICI) directed against PD-1/PD-L1 have been reported. However, only a subset of patients (~20%) respond to ICI. Therefore, identifying rational combinations is needed to enhance the efficacy of immunotherapy in TNBC. We demonstrated there that inhibition of WEE1, a G2/M cell cycle checkpoint regulator induced by DNA damage, increased expression levels of MHC-I, and pro-inflammatory chemokines (CXCL9 and CXCL10) together with PD-L1 in human and mouse TNBC cells. Consequently, WEE1 inhibition enhanced cytotoxic T-lymphocyte (CTL)-mediated killing of tumor cells, and CTL infiltration into the tumor, making tumors susceptible to anti-PD-1 mAb immune checkpoint blockade in mouse TNBC models in a CD8+ T cell–dependent manner. Mechanistically, WEE1 inhibition triggered the cellular damage stress and interferon response through the double-stranded DNA/RNA (dsDNA/RNA) by activating the TLR9/IRF7 pathway. Furthermore, combining WEE1 inhibition and TLR9 agonist CpG DNA resulted in tumor regression, facilitating an effective antitumor T cell response. Our findings have rapid translational implications for the exploration of WEE1 inhibitors alongside agents that stimulate CD8+ T cell activity, including ICI and TLR9 agonists, which are both clinically available to treat TNBC patients. We acknowledge the funding support from NCI R01CA222963 and DoD W81XWH-19-1-0106.

Synthesis and biological evaluation of atropisomeric tetrahydroisoquinolines overcoming docetaxel resistance in triple-negative human breast cancer cells

Herein, atropisomeric 8-aryltetrahydroisoquinolines have been synthesized and biologically evaluated. Based on our structure–activity relationship study, a highly bioactive racemic compound has been produced, and it exhibited high antiproliferative activities against various cancer cell lines, including docetaxel-resistant breast cancer cell lines. Each enantiomer can be synthesized in an enantioselective manner by employing the chiral phosphoric acid-catalyzed atroposelective Pictet–Spengler cyclization. An axially (R)-configured enantiomer showed a higher biological activity compared with the axially (S)-configured enantiomer. Further biological studies suggested that the (R)-enantiomer overcomes docetaxel resistance via the downregulation of signal transducer and activator of transcription 3 activation and consequently induces cellular apoptosis in docetaxel-resistant triple-negative breast cancer cell lines.

Chromatin Remodelling Molecule ARID1A Determines Metastatic Heterogeneity in Triple-Negative Breast Cancer by Competitively Binding to YAP.

Heterogeneity represents a pivotal factor in the therapeutic failure of triple-negative breast cancer (TNBC). In this study, we retrospectively collected and analysed clinical and pathological data from 258 patients diagnosed with TNBC at the Fudan University Cancer Hospital. Our findings show that low ARID1A expression is an independent prognostic indicator for poor overall survival (OS) and recurrence-free survival (RFS) in TNBC patients. Mechanistically, both nuclear and cytoplasmic protein analyses and immunofluorescent localisation assays confirm that ARID1A recruits the Hippo pathway effector YAP into the nucleus in human triple-negative breast cancer cells. Subsequently, we designed a YAP truncator plasmid and confirmed through co-immunoprecipitation that ARID1A can competitively bind to the WW domain of YAP, forming an ARID1A/YAP complex. Moreover, the downregulation of ARID1A promoted migration and invasion in both human triple-negative breast cancer cells and xenograft models through the Hippo/YAP signalling axis. Collectively, these findings demonstrate that ARID1A orchestrates the molecular network of YAP/EMT pathways to affect the heterogeneity in TNBC.

TMEM25 inhibits monomeric EGFR-mediated STAT3 activation in basal state to suppress triple-negative breast cancer progression

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with poor outcome and lacks of approved targeted therapy. Overexpression of epidermal growth factor receptor (EGFR) is found in more than 50% TNBC and is suggested as a driving force in progression of TNBC; however, targeting EGFR using antibodies to prevent its dimerization and activation shows no significant benefits for TNBC patients. Here we report that EGFR monomer may activate signal transducer activator of transcription-3 (STAT3) in the absence of transmembrane protein TMEM25, whose expression is frequently decreased in human TNBC. Deficiency of TMEM25 allows EGFR monomer to phosphorylate STAT3 independent of ligand binding, and thus enhances basal STAT3 activation to promote TNBC progression in female mice. Moreover, supplying TMEM25 by adeno-associated virus strongly suppresses STAT3 activation and TNBC progression. Hence, our study reveals a role of monomeric-EGFR/STAT3 signaling pathway in TNBC progression and points out a potential targeted therapy for TNBC.

Abstract 2397: An advanced approach technique for tracking point between immune check point inhibitor and cancer cell mechanism in immune response motility by infiltration a breast cancer cell

Abstract In Breast Cancer, Tumor-infiltrating lymphocyte (TIL) motility has been reported that it is reflecting tumor microenvironment response by adoptive cell therapy (ACT). ACT is well-known to be best applied for suppressing cancer cell growth with immune response and it also was well-known the immunotherapy. However, ACT response tracking by general analysis method included immunohistochemistry and flow cytometry was provided limited information for cancer therapy in recent years. Therefore, by assessing relationship immunotherapy marker, PD-L1, known as immune check point inhibitor and TIL using intravital microscopy in breast cancer model, we also imaged whether TIL response was related to immunotherapy following dependent on time point in a various breast cancer cell implanted mouse model such as 4T1 (mouse breast cancer cell), MDA-MB-231 (human triple negative breast cancer cell) and MCF7 (human breast cancer cell). These images result in PD-L1 expression was decreased in cancer cell implanted until 10days, whereas TIL expression increased in a various breast cancer cell when it is measuring displacement length, track mean velocity and confinement ratio called tumor microenvironment. These results indicated that we can imaged immune response related to TIL response in breast cancer cell line by intravital microscopy instead of general microscopy. It means that intravital microscope was an advanced approach technique to understand cancer mechanism accompanied by the immune response and established the method of high-resolution intravital cellular visualization compared to a general histopathological method for evaluating immune response in cancer tissue Citation Format: Hyunseok Kim, Soyeon Ahn, Hyungjin Kwon, Hsuan-Ju Chen, Inwon Park, Pilhan Kim, Akyildiz Kubra. An advanced approach technique for tracking point between immune check point inhibitor and cancer cell mechanism in immune response motility by infiltration a breast cancer cell [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2397.

Abstract SY17-03: Age-related changes in the tumor microenvironment drive tumor progression

Abstract Cancer is a disease of the aged. While the accumulation of cell autonomous mutations contributes to tumorigenesis, the central role age-related changes in the tumor microenvironment play in the transformation process is becoming more fully appreciated. Underscoring the importance of an aged microenvironment in cancer development are findings that senescent fibroblasts, which accumulate with age, directly stimulate preneoplastic and neoplastic cell growth and tumor progression. Investigations into how senescent fibroblasts promote tumorigenesis revealed that they express a plethora of growth factors, extracellular matrix remodeling enzymes, chemokines, and cytokines collectively referred to as the senescence associated secretory phenotype (SASP). To identify a role for senescent stromal cells in a spontaneous model of breast cancer, we used single cell RNA-Sequencing (scRNA-Seq) to interrogate the cell types and their functional status in the MMTV-PyMT breast tumor model. This analysis revealed the presence of senescent cancer associated fibroblasts (senCAFs) that we also identified in a human triple negative breast cancer scRNA-Seq database. To establish a role for senCAFs in breast cancer, we mated the PyMT model to the INKATTAC (INK) mouse that allowed us to inducibly eliminate senescent cells. We found that the elimination of senCAFs reduced tumor growth and unleashed the killing power of NK cells. We will discuss the mechanism by which senCAFs impact NK cell killing. Citation Format: Sheila A. Stewart. Age-related changes in the tumor microenvironment drive tumor progression. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr SY17-03.

Abstract 2680: Combination of the Rac/Cdc42 inhibitor MBQ-167 with paclitaxel reduces metastasis in triple negative breast cancer

Abstract Metastasis represents a therapeutic challenge, especially in the case of triple negative breast cancer (TNBC), where patients often show recurrence and metastasis due to resistance to chemotherapy. The frontline therapy in TNBC is Paclitaxel, which targets actively dividing cells inducing subsequent apoptosis. Since dormant cells or metastatic cancer cells are not targeted by Paclitaxel, this strategy selects for non-dividing stem cells or more motile metastatic cells. Therefore, targeted treatment options are needed to overcome the recurrence and spreading of metastatic cells. We recently reported on MBQ-167, a Rac/Cdc42 inhibitor, which is highly effective in reducing tumor growth and metastasis in mouse models of TNBC (Cruz-Collazo et al., 2021, Molecular Cancer Therapeutics). Unpublished data show that in the MDA-MB-231 human TNBC model, MBQ-167 is as effective as Paclitaxel in reducing tumor growth and is more effective in metastasis prevention. Therefore, we hypothesize that MBQ-167 is a viable candidate for combined therapy with Paclitaxel and will reduce metastasis in TNBC. The purpose of this study is to test MBQ-167 in combination with Paclitaxel in the EGFR overexpressing MDA-MB-468 human TNBC cell line, which is highly malignant and also expresses the Rac1.B oncogenic splice variant. We found that MBQ-167 inhibits Rac, Rac1.B, and Cdc42 activation in this cell line. Next, we tested individual or combined MBQ-167 (50 mg/kg 5X a week) via oral administration and Paclitaxel (10 mg/kg 1X a week) via intraperitoneal administration in SCID mice bearing luciferase-tagged MDA-MB-468 tumors. Tumor growth and metastases were analyzed by chemiluminescence imaging followed by H&amp;E staining of extracted lungs at necropsy. Similar to our studies with the syngeneic 4T-1/Balb/C model, in this MDA-MB-468 model, Paclitaxel increased metastasis while single agent MBQ-167 significantly reduced metastasis. MBQ-167 in combination with Paclitaxel reduced the enhanced lung metastasis in response to Paclitaxel. In conclusion, this study validates the clinical testing of MBQ-167 in combination with Paclitaxel as a potential combination therapy for TNBC. Citation Format: Ailed M. Cruz-Collazo, Nilmary Grafals, Luis D. Borrero, Suranganie Dharmawardhane. Combination of the Rac/Cdc42 inhibitor MBQ-167 with paclitaxel reduces metastasis in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2680.

Abstract 5811: Epigenetic regulation of chromosomal instability in triple-negative breast cancer

Abstract Metastasis is the leading cause of cancer-related death among women with breast cancer. Chromosomal instability (CIN) has emerged as a hallmark of triple-negative breast cancer (TNBC) as it has recently been shown to promote metastasis. However, the underlying molecular mechanisms by which CIN drives metastasis are not completely understood. We have identified a discrete population of highly metastatic SOX2/OCT4+ cells expressing elevated levels of epigenetic regulator EZH2 associated with increased CIN in both human and mouse TNBC. EZH2 histone methyl transferase (HMT) is the catalytic subunit of the Polycomb repressive complex 2 (PRC2), represses target genes through trimethylation of Histone 3 at lysine 27 (H3K27me3). Importantly, genetic and pharmacologic inhibition of EZH2 lead to reduction of CIN and impaired metastasis. These findings led to the hypothesis that EZH2-mediated CIN constitutes a novel mechanism of metastasis regulation. To directly demonstrate epigenetic regulation of CIN, we used genome wide-Cleavage Under Targets and Release Using Nuclease (CUT&amp;RUN) in parallel with RNA-seq. Gene set enrichment of EZH2-repressed target genes directly implicated the spindle formation pathway network. The central core of this network comprised of tankyrase (TNKS), a multifunctional poly (ADP-ribose) polymerase (PARP) previously implicated in DNA repair, telomere function and centrosome maturation. ChIP-PCR confirmed that EZH2 directly binds to the TNKS promoter, and CRISPR knockout of TNKS abrogated the ability of EZH2 inhibition in suppressing CIN, consistent with pharmacological inhibition of TNKS. More specifically, dysregulation of TNKS by EZH2 in OCT4/SOX2+ cells lead to increased numbers of centrosomes and multipolar mitosis. To directly demonstrate the role of aberrant H3K27me3 in regulating chromosomal segregation during mitosis, we used dCas9-EZH2 or dCas9-EZH2 catalytically dead mutant together with chromosome-specific CRISPR guides to ectopically enhance H3K27 trimethylation at the pericentromeric region of specific chromosomes. Ectopic deposition of EZH2 at pericentromeric regions lead to increased CIN. Conceptually, our work provides an unappreciated link between epigenetic regulation and CIN which have been hitherto studied in isolation. From a clinical perspective, demonstrating epigenetic regulation of CIN has opened the possibility for the development of first CIN suppressive therapeutic strategies targeting TNBC metastasis. Citation Format: Yang Bai, Albert Agustinus, Cem Meydan, Dylan R. McNally, Shira Yomtoubian, Liron Yoffe, Ari M. Melnick, Samuel Bakhoum, Vivek Mittal. Epigenetic regulation of chromosomal instability in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5811.

Abstract 1339: Targeting specific extracellular matrix proteins to reactivate T cell trafficking in triple-negative breast cancer

Abstract It is now widely recognised that the tumour microenvironment (TME) is playing a crucial role in promoting tumour immune evasion by modulating the local immune infiltration. A growing body of evidence highlights the crucial role of the tumour extracellular matrix (ECM) in limiting trafficking of newly activated T cells in solid cancers, thus restricting their access to tumour and preventing the success of cancer immunotherapies. Accordingly, we are investigating whether targeting specific tumour ECM components may enhance T cell infiltration in triple-negative breast cancer (TNBC). Matrisome profiling of patient-derived fibroblasts and patient tumour tissues allowed us to identify two matrix proteins overexpressed in tumours and associated with T cell signatures, the matrix proteoglycan, versican (VCAN) and the glycoprotein, fibronectin (FN1). As there are currently no specific inhibitors of matrix proteins, we have modelled their loss-of-function using the clustered, regularly interspaced, short palindromic repeats-associated nuclease Cas9 (CRISPR-Cas9) technology with the goal of engineering cell-editable matrisomes which are enriched, reduced, or absent for specific matrix proteins. First, we constituted a panel of human and murine mammary fibroblast and TNBC cancer cell lines, which we have introduced with an inducible Cas9 protein expression. We measured VCAN and FN1 expression in the panel which showed distinct VCAN levels. Therefore, depending on VCAN basal levels, we have generated cell lines with VCAN overexpression, transient knockdown or stable knockout. Proteomic matrisome profiling of transient VCAN knockdown cells revealed that reducing VCAN may impact ECM abundance by decreasing VCAN direct binding partners. Finally, we used the edited cells to build 2D and 3D in vitro TME models to evaluate the impact of modulating VCAN expression on chimeric antigen receptor (CAR) T cell cytotoxicity and location. In parallel, we built in vivo mouse models of TNBC with controlled ECM deposition. Specifically, we have targeted mVcan and mFn1 in tumours and investigated the impact of their removal on tumour growth and immune cell infiltration. Overall, this work aims to identify immunomodulating features of the ECM which could be targeted to boost response to immunotherapies in solid cancers. Citation Format: Valentine Gauthier, Elly Tyler, Ying Liu, Tyson V. Sharp, Oliver MT Pearce. Targeting specific extracellular matrix proteins to reactivate T cell trafficking in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1339.

Abstract 1318: Potential mechanism of re-dissemination from lung metastases to tertiary sites in breast carcinoma: Tumor microenvironment of metastasis doorways and related pro-metastatic tumor phenotypes

Abstract Background: The five-year relative survival rate of female breast cancer patients with distant metastases is only 29%, compared to 99% for localized disease. Among all subtypes, triple negative breast cancer (TNBC) has the poorest outcome due to a high risk of early relapse with visceral organ metastases, and a lack of targeted therapies. Targeting metastatic burden could improve patient survival. Recent mouse and human genomic profiling studies show that metastasis is a complex and multidirectional process. Cancer cells can re-disseminate from one metastasis to tertiary sites. But the mechanism of re-dissemination is unknown. Breast cancer cells disseminate from primary tumors via Tumor MicroEnvironment of Metastasis (TMEM) doorways, composed of three cells: a tumor cell, a perivascular macrophage, and an endothelial cell. The direct and stable interaction of these cells cause transient and local vascular opening through which metastasis-competent tumor cells co-expressing invasive, stem, and dormant phenotypes that preferentially reside around TMEM doorways disseminate to distant sites. We hypothesize that TMEM doorways also form in lung metastases, enabling cancer cell re-dissemination to tertiary sites, which increases overall cancer burden and risk of death. Methods: We used MDA-MB-231 and MDA-MB-468 human TNBC cells to generate tumors in the 4th mammary fat pad of 6-8 weeks old NOD/SCID mice. Primary tumors were resected when 5-6 mm and fixed with 10% formalin. When lung metastases were visible via micro-Computed Tomography (microCT) fluorescent dextran was injected intravascularly, and lungs collected and fixed with 10% formalin. Triple immunohistochemistry was used to visualize TMEM doorways. To test TMEM doorway-mediated vascular opening, sequential slides were stained for extravascular dextran. Cells co-expressing stem (SOX9), invasive (MenaINV), and dormant (NR2F1) markers were visualized by immunofluorescent staining. The density of TMEM doorways, CSCs, invasive, and dormant cells was determined by automated image analysis. Results: We demonstrated the presence and activity of TMEM doorways in lung metastases. Within lung metastases, we also documented the presence of cancer cells with a pro-metastatic phenotype indicated by their co-expression of invasive (MenaINV), stemness (SOX9), and dormancy (NR2F1) markers. We will report how the expression of pro-metastatic markers relates to TMEM doorway niches. Conclusion: We documented functional TMEM doorways in lung metastases of TNBC, which could explain the occurrence of an early overall metastatic burden in patients with TNBC. Thus, targeting TMEM doorways after the removal of the primary tumor in patients with TNBC could block cancer cell re-dissemination, decrease metastases, and improve survival. Citation Format: Burcu Karadal-Ferrena, Camille L. Duran, Madeline Friedman-DeLuca, Nicole Barth, Prachiben Patel, John S. Condeelis, David Entenberg, Maja H. Oktay. Potential mechanism of re-dissemination from lung metastases to tertiary sites in breast carcinoma: Tumor microenvironment of metastasis doorways and related pro-metastatic tumor phenotypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1318.