Murine Breast Cancer Cell Line Research Articles

Abstract 7460: Characterizing the role of PCBP1 in the activation of the cGAS-STING/type I Interferon axis to promote anti-tumor immunity

Abstract The emergence of immunotherapies has encouraged the need to better understand the molecular mechanisms that modulate the tumor immune microenvironment to kill cancer cells as well as the strategies used by cancer cells to evade the immune system. In several cancer types, the Poly(rC) Binding Protein 1 (PCBP1) has shown to have tumor suppressive effects, however its function in regulating the tumor immune environment remains unclear. To investigate this in the context of breast cancer, we established a CRISPR-Cas9-medited knock-out of PCBP1 in a Py8119 murine breast cancer cell line. PCBP1−/− cells revealed a decrease in the activation of the cGAS-STING pathway and is associated with lower levels of type I interferons (IFNs) and Interferon Stimulated Genes’ (ISGs) expression. The cGAS-STING pathway plays an important role in innate immunity as it fights pathogenic infections and tumorigenesis through the production of type I IFN and ISGs. It also promotes the priming and infiltration of T cells at the tumor site to fight cancer cells. Our results suggested that PCBP1 is acting on the activation of the cGAS-STING pathway and could further modulate the tumor immune microenvironment. We then confirmed our results in vivo by establishing a tumorigenic C57BL/6 PyMT transgenic mouse model with conditional knockout for PCBP1 in mammary cells. Our data demonstrate that PCBP1−/− PyMT mice have higher tumor burdens compared to PCBP1+/+ PyMT mice and also show a decreased ISGs’ signature by RNA-sequencing, qPCR and western blot, as previously observed in vitro in the Py8119 PCBP1−/− cell line. Additional single nuclei RNA-sequencing analyses confirmed that this downregulation of ISGs is observed in mammary cancer cells where PCBP1 is knocked-out. Strikingly, IHC and flow cytometry analyses of PCBP1−/− tumors isolated from these mice also revealed a decrease in CD8+ T-cells. Therefore, PCBP1 silencing may promote tumor growth by impairing the activation of the cGAS-STING/IFN-I/ISGs axis, which may contribute to the decrease in CD8+ T-cells’ infiltration at the tumor site. Additionally, we are further investigating the molecular mechanisms mediated by PCBP1 that trigger this activation of the cGAS-STING pathway. Citation Format: Cécile Fréreux, Paramita Chakraborty, Annamarie C. Dalton, Breege V. Howley, Bryan Granger, Joseph A. Karam, Silvia G. Vaena, Martin J. Romeo, Philip H. Howe. Characterizing the role of PCBP1 in the activation of the cGAS-STING/type I Interferon axis to promote anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7460.

Abstract 186: Tumor exosome-macrophage interactions: The role of tumor-associated glycans and scavenger receptor class A

Abstract Introduction: Increased macrophage infiltration and polarization towards a breast tumor-supportive phenotype have been linked to therapy resistance, immune suppression, and poor patient prognosis. Despite their importance, the specific interactions that drive tumor-associated macrophage (TAM) polarization remain poorly understood. The class A scavenger receptor (SR-A) is a pattern-recognition receptor expressed by macrophages, and the accumulation of SR-A-expressing TAMs has been correlated with poor patient outcomes. Our preliminary data show that SR-A binds to tumor-associated glycans (TAGs) on the surface of breast cancer cells. However, how macrophages bind tumor cell ligands in the tumor microenvironment (TME) is not clear. Tumor-derived exosomes (TDEs) are secreted extracellular vesicles that resemble the tumor cell membrane, carrying cargo that may mediate an immune response within the TME. In this study, we investigated whether TDE glycans represent tumor cell-surface TAGs and whether TDEs interact with macrophages through SR-A. Methods: TDEs were isolated from the murine breast cancer cell line (E0771) by ultracentrifugation of the cell culture medium and then sized and counted using nanoparticle tracking analysis and electron microscopy. The glycans present on the tumor cell surface and TDEs were characterized using plant lectins in flow cytometry and sandwich ELISAs. The isolated TDEs were then fluorescently labeled, and their binding to the murine macrophage cell line Raw 264.7 was assayed by flow cytometry and fluorescence microscopy. Results: SR-A binds strongly to breast cancer cell lines, and a significant portion of the binding depends on the presence of cell surface N-linked glycans. Lectins reactive with sialylated and fucosylated terminal structures showed differential binding to tumor cells and TDEs. We observed that the glycan profiles of E0771 cells and exosomes isolated from E0771 cultures were similar. Our results indicate that TDEs interact with Raw 264.7 cells, and the interaction is mediated by SR-A. Conclusions: TDEs released in the TME can potentially interact with TAMs through SR-A. The glycan profile of TDEs is representative of host cells and may contribute to SR-A-mediated interaction with TAMs. Citation Format: Fariba Jousheghany, Emily S. Blitz, Samir V. Jenkins, Steven R. Post, Vinay Raj, Rajshekar A. Kore, Azemat Jamshidi-Parsian, Robert J. Griffin, Thomas J. Kelly, Behjatolah Monzavi-Karbassi. Tumor exosome-macrophage interactions: The role of tumor-associated glycans and scavenger receptor class A [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 186.

Abstract 4158: Non-invasive mapping of acidosis and extracellular lactosis for assessing tumor invasion in vivo

Abstract Tumor cells typically display a hyperglycolytic metabolic phenotype characterized by increased lactate production, known as the Warburg effect. This drift in oxidative metabolism often results in a more acidic microenvironment. This adverse microenvironment represents a unique metabolic signature in cancer cells with more invasive phenotypes. However, to date, there are no effective methods available to evaluate cancer progression and metastatic potential in vivo. To bridge this gap, we have developed a molecular imaging technique (CEST-MRI) that can track extracellular pH (pHe; acidoCEST) and extracellular lactate levels (shiftCEST) simultaneously to discern different cancer phenotypes. In this study we have generated and selected in vivo two PyMT derived murine breast cancer cell lines, a parental and a G6 metastatic. We first characterized the cell’s metabolism by analyzing key biomarkers with qPCR, Western Blot and microscopy, and confirmed their distinct metabolic profiles with Seahorse and RNA Sequencing. Notably, the metastatic PyMT exhibited a more active metabolism, aligning with the invasive phenotype observed by spheroid invasion assay. Herein, we combined the injection of iopamidol and shift reagent (SR) to perform quasi-simultaneous acidoCEST and shiftCEST. First, we assessed the approach in vitro by introducing iopamidol and SR into phantoms containing the individual contrast agents, and the combination in pure water and cells supernatants at different pHe and lactate levels. We performed LDH assays to cross-validate the extracellular concentrations and monitored the pH with a micro pH meter (Mettler-Toledo). In vivo, the cells were injected orthotopically in the 4th mammary fat pad of C57BL/6N mice. Hybrid shift/acidoCEST sequences were optimized and acquired following the injection of the iopamidol+SR solution. Preclinical shift/acidoCEST enabled the simultaneous and accurate determination of extracellular acidosis and lactosis, revealing increased acidification in the metastatic models despite lower lactate secretion. Metastatic tumors exhibited a negative correlation between tumor volume and pHe, indicating the significance of acidity in mutagenesis and invasion. In contrast, no correlation was observed for the parental non-metastatic tumor. Additionally, the metastatic tumors had lower levels of lactate than the parental tumors, which could be attributed to their higher mitochondrial activity, reflecting a diverted metabolic fitness. In summary, our study highlights the efficacy of shift/acidoCEST as a reliable method for non-invasive metabolic imaging, enabling the simultaneous detection of extracellular acidity and lactate production by MRI. This research introduces a unique platform for assessing the metabolic aggressiveness of cancer, emphasizing the significance of acidity and lactate production as crucial biomarkers in cancer invasion. Citation Format: Anais Choffart, Remy Chiaffarelli, Max Zimmermann, Laura Kuebler, André Martins. Non-invasive mapping of acidosis and extracellular lactosis for assessing tumor invasion in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4158.

Abstract 6866: Investigating the role of Epha2 in breast cancer-mediated myeloid cell expansion and function

Abstract Bone metastases are present in over 70% of metastatic breast cancer patients, and current therapy reduces osteolysis in tumor-induced bone disease (TIBD) but does not improve overall survival. Frequently, TIBD is characterized by an increase in osteoclast proliferation and bone-resorbing activity, and patients often experience pain and pathologic fractures. Increased bone resorption releases growth factors that aid in the progression of tumor growth causing the ‘vicious cycle’. Additionally, bone metastatic patients are often resistant to first- and second-line therapies highlighting an importance for research in this area. The receptor tyrosine kinase, Ephrin-type-A 2 receptor (EphA2), participates in both forward and reverse signaling during receptor/ligand engagement and participates in many physiological and pathological processes, including bone homeostasis, immunity, and cancer. Interestingly, EphA2 is highly expressed in bone metastases, and previous evidence suggests that EphA2 can promote TIBD and reduce anti-tumor immunity. We therefore hypothesize that increased expression of EphA2 in breast cancer cells at the site of bone metastasis promotes expansion of myeloid cells, leading to TIBD. Previous data shows a reduction in osteoclast number and bone lesions following EphA2 knockout. However, the mechanism by which EphA2 mediates the expansion of osteoclasts is not well understood. In agreement with previous work, our data shows that EphA2 deletion in murine breast cancer (BC) cell line, 4T1, reduces bone lesion area and number and the presence of bone metastasis-associated macrophages. Additionally, we observed a significant reduction in Ly6Chi cells. To assess the effects of EphA2 deletion on the behavior of 4T1 cells, we conducted a wound healing assay and observed a decrease in wound healing capacity in 4T1 cells following EphA2 deletion. This suggests that EphA2 expression in 4T1 cells may increase their metastatic potential. We will repeat these studies and incorporate factors from the bone marrow. Our future studies will investigate the role of EphA2 signaling and reverse signaling in BC cell lines, myeloid progenitor cells, osteoclasts, and bone metastasis-associated macrophages. We will utilize murine and human BC cell lines to elucidate the effects of EphA2 deletion in BC on immune cell populations, bone metastasis, and tumor progression. Additionally, we will investigate how EphA2 reverse signaling impacts osteoclasts’ ability to modulate immune cells. We aim to reduce TIBD and tumor burden by reducing the expansion of osteoclasts and shifting the immune cells to an anti-tumorigenic phenotype. Our studies will provide additional insight into the underlying mechanisms of the vicious cycle which will offer new treatment strategies for patients with osteolytic breast cancer. Citation Format: Dominique Parker, Verra Ngwa, Jin Chen, Julie Rhoades. Investigating the role of Epha2 in breast cancer-mediated myeloid cell expansion and function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6866.

Mucin-1-Targeted Chimeric Antigen Receptor T Cells Are Effective and Safe in Controlling Solid Tumors in Immunocompetent Host.

The chimeric antigen receptor (CAR) T-cell therapy in solid epithelial tumors has been explored, however, with limited success. As much of the preclinical work has relied on xenograft models in immunocompromised animals, the immune-related efficacies and toxicities may have been missed. In this study, we engineered syngeneic murine CAR T cells targeting the tumor form of human mucin-1 (tMUC1) and tested the MUC1 CAR T cells' efficacy and toxicity in the immunocompetent human MUC1-expressing mouse models. The MUC1 CAR T cells significantly eliminated murine pancreatic and breast cancer cell lines in vitro. In vivo, MUC1 CAR T cells significantly slowed the mammary gland tumor progression in the spontaneous PyVMT×MUC1.Tg (MMT) mice, prevented lung metastasis, and prolonged survival. Most importantly, there was minimal short or long-term toxicity with acceptable levels of transient liver toxicity but no kidney toxicity. In addition, the mice did not show any signs of weight loss or other behavioral changes with the treatment. We also report that a single dose of MUC1 CAR T-cell treatment modestly reduced the pancreatic tumor burden in a syngeneic orthotopic model of pancreatic ductal adenocarcinoma given at late stage of an established tumor. Taken together, these findings suggested the further development of tMUC1-targeted CAR T cells as an effective and relatively safe treatment modality for various tMUC1-expressing solid tumors.

Inhibition of tumor migration and invasion by fenofibrate via suppressing epithelial-mesenchymal transition in breast cancers

The recurrence and metastasis in breast cancer within 3 years after the chemotherapies or surgery leads to poor prognosis with approximately 1-year overall survival. Large-scale scanning research studies have shown that taking lipid-lowering drugs may assist to reduce the risk of death from many cancers, since cholesterol in lipid rafts are essential for maintain integral membrane structure and functional signaling regulation. In this study, we examined five lipid-lowering drugs: swertiamarin, gemfibrozil, clofibrate, bezafibrate, and fenofibrate in triple-negative breast cancer, which is the most migration-prone subtype. Using human and murine triple-negative breast cancer cell lines (Hs 578 t and 4 T1), we found that fenofibrate displays the highest potential in inhibiting the colony formation, wound healing, and transwell migration. We further discovered that fenofibrate reduces the activity of pro-metastatic enzymes, matrix metalloproteinases (MMP)-9 and MMP-2. In addition, epithelial markers including E-cadherin and Zonula occludens-1 are increased, whereas mesenchymal markers including Snail, Twist and α-smooth muscle actin are attenuated. Furthermore, we found that fenofibrate downregulates ubiquitin-dependent GDF-15 degradation, which leads to enhanced GDF-15 expression that inhibits cell migration. Besides, nuclear translocation of FOXO1 is also upregulated by fenofibrate, which may responsible for GDF-15 expression. In summary, fenofibrate with anti-cancer ability hinders TNBC from migration and invasion, and may be beneficial to repurposing use of fenofibrate.

Unsymmetrical Low-Generation Cationic Phosphorus Dendrimers as a Nonviral Vector to Deliver MicroRNA for Breast Cancer Therapy.

The development of nonviral dendritic polymers with a simple molecular backbone and great gene delivery efficiency to effectively tackle cancer remains a great challenge. Phosphorus dendrimers or dendrons are promising vectors due to their structural uniformity, rigid molecular backbones, and tunable surface functionalities. Here, we report the development of a new low-generation unsymmetrical cationic phosphorus dendrimer bearing 5 pyrrolidinium groups and one amino group as a nonviral gene delivery vector. The created AB5-type dendrimers with simple molecular backbone can compress microRNA-30d (miR-30d) to form polyplexes with desired hydrodynamic sizes and surface potentials and can effectively transfect miR-30d to cancer cells to suppress the glycolysis-associated SLC2A1 and HK1 expression, thus significantly inhibiting the migration and invasion of a murine breast cancer cell line in vitro and the corresponding subcutaneous tumor mouse model in vivo. Such unsymmetrical low-generation phosphorus dendrimers may be extended to deliver other genetic materials to tackle other diseases.

Magnetic Resonance Imaging of Macrophage Response to Radiation Therapy.

Magnetic resonance imaging (MRI) is a non-invasive imaging modality which, in conjunction with biopsies, provide a qualitative assessment of tumor response to treatment. Intravenous injection of contrast agents such as fluorine (19F) nanoemulsions labels systemic macrophages, which can, then, be tracked in real time with MRI. This method can provide quantifiable insights into the behavior of tumor-associated macrophages (TAMs) in the tumor microenvironment and macrophage recruitment during therapy. Female mice received mammary fat pad injections of murine breast or colon cancer cell lines. The mice then received an intravenous 19F nanoemulsion injection, followed by a baseline 19F MRI. For each cancer model, half of the mice then received 8 Gy of localized radiation therapy (RT), while others remained untreated. The mice were monitored for two weeks for tumor growth and 9F signal using MRI. Across both cohorts, the RT-treated groups presented significant tumor growth reduction or arrest, contrary to the untreated groups. Similarly, the fluorine signal in treated groups increased significantly as early as four days post therapy. The fluorine signal change correlated to tumor volumes irrespective of time. These results demonstrate the potential of 19F MRI to non-invasively track macrophages during radiation therapy and its prognostic value with regard to tumor growth.

Abstract A031: Development of poly lactic acid based biodegradable nanoparticles for co-delivery of pirarubicin and gemcitabine for synergistic anti-tumor efficacy

Abstract Nanoparticles based drug delivery systems have provided a befitted solution for the poor pharmacokinetic properties and systemic toxicity caused by the chemo drugs because of their ability to improve bioavailability of the drugs at the desired site and thereby decreasing extracellular toxicity. The present work investigates the single or dual chemo drugs loaded PLA-based biodegradable polymeric nanoparticles for improved anti-tumor efficacy as compared to free drug formulations. For the study, an amphiphilic block copolymer; mPEG PLA has been synthesized and characterized using Gel permeation chromatography (GPC) for its molecular weight and poly dispersity index as well as with Nuclear magnetic resonance (NMR) and Fourier-transform Infrared (FT-IR) spectroscopies. Thereafter, two different chemo drugs Pirarubicin (PIRA, THP analogue of Doxorubicin) and Gemcitabine (GEM) have been chemically conjugated individually to mPEG PLA block copolymer via a linker molecule, Levulinic acid to give an acid labile polymer-drug conjugate and the % drug conjugation efficiency has been calculated using High performance liquid chromatography (HPLC). The synthesized polymer-drug conjugates have been employed to prepare PIRA/GEM single or dual-loaded nanoparticles via nanoprecipitation technique and the physiochemical properties including size, zeta potential, and stability were analyzed using Dynamic Light Scattering (DLS) and High-resolution transmission electron microscopy (HR-TEM). To carry out toxicity assessment of the mPEG PLA nanoparticles, both cytocompatibility and hemocompatibility were checked using MTT assay and Hemolysis assay respectively. Moreover, the cellular internalization studies of dye-loaded mPEG PLA nanoparticles were done using Confocal microscopy on SUM-149, breast cancer cells.  Besides, the drug release kinetic studies of the free PIRA/GEM from the PIRA/GEM single or dual-loaded nanoparticles were carried out in different pH environments; pH 7.4 and pH 5.0. The in-vitro cell proliferation inhibition studies of PIRA/GEM or dual-loaded nanoparticles were carried out on different human and murine breast cancer cell lines including MCF-7, MDA-MB-468, SUM 149, MDA-MB-231 and 4T1 and half-maximal inhibitory concentrations (IC50 values) were compared to that of respective free drug formulations. The overall results suggested that the prepared sub-nano sized PIRA/GEM single or dual-loaded particles are highly stable, uniformly spherical in size and biocompatible in nature. They were found to possess high cellular uptake, sustained drug release rate and synergistic efficacy and potential against both human and murine breast cancer cells in-vitro conditions. Citation Format: Priya Gupta. Development of poly lactic acid based biodegradable nanoparticles for co-delivery of pirarubicin and gemcitabine for synergistic anti-tumor efficacy [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A031.

Evaluating differences in optical properties of indolent and aggressive murine breast tumors using quantitative diffuse reflectance spectroscopy.

We used diffuse reflectance spectroscopy to quantify tissue absorption and scattering-based parameters in similarly sized tumors derived from a panel of four isogenic murine breast cancer cell lines (4T1, 4T07, 168FARN, 67NR) that are each capable of accomplishing different steps of the invasion-metastasis cascade. We found lower tissue scattering, increased hemoglobin concentration, and lower vascular oxygenation in indolent 67NR tumors incapable of metastasis compared with aggressive 4T1 tumors capable of metastasis. Supervised learning statistical approaches were able to accurately differentiate between tumor groups and classify tumors according to their ability to accomplish each step of the invasion-metastasis cascade. We investigated whether the inhibition of metastasis-promoting genes in the highly metastatic 4T1 tumors resulted in measurable optical changes that made these tumors similar to the indolent 67NR tumors. These results demonstrate the potential of diffuse reflectance spectroscopy to noninvasively evaluate tumor biology and discriminate between indolent and aggressive tumors.

Differential DNA damage repair and PARP inhibitor vulnerability of the mammary epithelial lineages

It is widely assumed that all normal somatic cells can equally perform homologous recombination (HR) and non-homologous end joining in the DNA damage response (DDR). Here, we show that the DDR in normal mammary gland inherently depends on the epithelial cell lineage identity. Bioinformatics, post-irradiation DNA damage repair kinetics, and clonogenic assays demonstrated luminal lineage exhibiting a more pronounced DDR and HR repair compared to the basal lineage. Consequently, basal progenitors were far more sensitive to poly(ADP-ribose) polymerase inhibitors (PARPis) in both mouse and human mammary epithelium. Furthermore, PARPi sensitivity of murine and human breast cancer cell lines as well as patient-derived xenografts correlated with their molecular resemblance to the mammary progenitor lineages. Thus, mammary epithelial cells are intrinsically divergent in their DNA damage repair capacity and PARPi vulnerability, potentially influencing the clinical utility of this targeted therapy.

Tumor cell-expressed lipolysis-stimulated lipoprotein receptor negatively regulates T-cell function.

Lipolysis-stimulated lipoprotein receptor (LSR) is known as a lipoprotein receptor. LSR is expressed in various solid tumors, including epithelial ovarian, gastric, and colon cancers. High LSR expression is significantly associated with poor prognosis, but its role in cancer has not been fully elucidated. LSR belongs to the Ig protein superfamily, which is conserved in B7 family. Here, we assessed LSR as a novel immune checkpoint molecule. We developed a novel anti-LSR antibody (#27-6 mF-18) that defects antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity activity. The #27-6 mF-18 cross-reacts with both human and mouse LSR. We found that LSR was expressed on 4T1 murine breast cancer cell line. The #27-6 mF-18 exhibited antitumor effects against the 4T1 syngeneic tumor model, a poor immunogenic model refractory to treatment with anti-PD-1 or anti-CTLA-4 antibodies. Compared with control antibody-treated mice, mice treated with #27-6 mF-18 showed significantly increased numbers of CD8+ T cells and a ratio of activated CD8+ T cells infiltrated in the tumor tissue. This antitumor effect was abrogated by CD8+ T-cell depletion through anti-CD8 antibody treatment, indicating that LSR negatively regulates tumor immunity by repressing CD8+ T cells. These findings show that LSR negatively regulates T-cell immune activity. LSR targeting could provide immune checkpoint inhibitors for cancer immunotherapy.

Evaluating [18F]FDG and [18F]FLT Radiotracers as Biomarkers of Response for Combined Therapy Outcome in Triple-Negative and Estrogen-Receptor-Positive Breast Cancer Models.

Breast cancer (BC) is the most frequent cancer and the second leading cause of death in women. A typical feature of BC cells is the metabolic shift toward increased glycolysis, which has become an interesting therapeutic target for metabolic drugs such as metformin (MET). Recently, the administration of the antihypertensive syrosingopine (SYRO) in combination with MET has shown a synergistic effect toward a variety of cancers. However, a fundamental need remains, which is the development of in vivo biomarkers that are able to detect early clinical response. In this study, we exploited a triple-negative murine BC cell line (4T1) and a metastatic ER+ murine BC cell line (TS/A) in order to investigate, in vivo, the early response to treatment, based on MET and/or SYRO administration, evaluating [18F]FDG and [18F]FLT as potential biomarkers via PET/CT. The study provides evidence that SYRO plus MET has a synergistic effect on tumor growth inhibition in both 4T1 and TS/A experimental models and has showed the highest efficacy on the TNBC xenograft mice (4T1) via the expression reduction in the lactate transporter MCT4 and in the epithelial-mesenchymal transition biomarker Snail, promoting its potential application in therapy settings. In addition, the selective reduction in the [18F]FLT tumor uptake (at 7 dd), observed in the SYRO plus MET treated mice in comparison with the vehicle group, suggests that this radiotracer could be potentially used as a biomarker for the early detection of therapy response, in both evaluated xenografts models.

BRD4 Inhibition Enhances the Antitumor Effects of Radiation Therapy in a Murine Breast Cancer Model.

Bromodomain-containing protein 4 (BRD4) is an intracellular protein that regulates expression of various cellular functions. This study investigated whether BRD4 inhibition can alter the immunomodulatory and antitumor effects of radiation therapy (RT). A murine breast cancer cell line was implanted into BALB/c mice. The dual-tumor model was used to evaluate the abscopal effects of RT. A total of 24 Gy was delivered and BRD4 inhibitor was injected intravenously. Tumor size was measured, and in vivo imaging was performed to evaluate tumor growth. Flow cytometry and immunohistochemistry were performed to examine immunologic changes upon treatment. The combination of BRD4 inhibitor and RT significantly suppressed tumor growth compared to RT alone. BRD4 inhibitor reduced the size of the unirradiated tumor, indicating that it may induce systemic immune responses. The expression of HIF-1α and PD-L1 in the tumor was significantly downregulated by the BRD4 inhibitor. The proportion of M1 tumor-associated macrophages (TAMs) increased, and the proportion of M2 TAMs decreased upon BRD4 inhibition. BRD4 inhibitor expanded CD4+ and CD8+ T cell populations in the tumor microenvironment. Additionally, splenic monocytic myeloid derived suppressor cells, which were increased by RT, were reduced upon the addition of BRD4 inhibitor. Therefore, the addition of BRD4 inhibitor significantly enhanced the systemic antitumor responses of local RT.

Evaluation of the anti-tumor effects of an anti-Human Epidermal growth factor receptor 2 (HER2) monoclonal antibody in combination with CD11b+/Gr-1+ myeloid cells depletion using a recombinant peptibody in 4T1-HER2 tumor model.

Clinical efficacy of Human Epidermal growth factor Receptor 2 (HER2) targeted strategies is limited due to impaired anti-tumor responses negatively regulated by immunosuppressive cells. We thus, investigated the inhibitory effects of an anti-HER2 monoclonal antibody (1T0 mAb) in combination with CD11b+/Gr-1+ myeloid cells depletion in 4T1-HER2 tumor model. BALB/c mice were challenged with human HER2-expressing 4T1 murine breast cancer cell line. A week post tumor challenge, each mouse received 50µg of a myeloid cells specific peptibody every other day, or 10mg/kg of 1T0 mAb two times a week, and their combination for two weeks. The treatments effect on tumor growth was measured by calculating tumor size. Also, the frequencies of CD11b+/Gr-1+ cells and T lymphocytes were measured by flow cytometry. Peptibody treated mice indicated tumor regression and 40% of the mice eradicated their primary tumors. The peptibody was capable to deplete notably splenic CD11b+/Gr-1+ cells as well as intratumoral CD11b+/Gr-1+ cells (P<0.0001) and led to an increased number of tumor infiltrating CD8+ T cells (3.3 folds) and also that of resident tumor draining lymph nodes (TDLNs) (3 folds). Combination of peptibody and 1T0 mAb resulted in enhanced expansion of tumor infiltrating CD4+and CD8+ T cells which was associated with tumor eradication in 60% of the mice. Peptibody is able to deplete CD11b+/Gr-1+ cells and increase anti-tumoral effects of the 1T0 mAb in tumor eradication. Thus, this myeloid population have critical roles in development of tumors and their depletion is associated with induction of anti-tumoral responses.

Abstract 6427: Selective-HDAC inhibitor relieves the suppressive immune microenvironment in the brain to impede breast cancer brain metastasis

Abstract Brain metastasis (BrM) incidence is rising due to longer survival resulted from better systemic control of cancer, counting for approximately 20% of patients with cancers. Major cancer types, including lung, breast, and skin cancers, have a high rate to develop BrM with a 1-year survival rate of less than 20% for symptomatic patients. The overall response rate for immune checkpoint inhibitors (ICI) is merely 10-30% in patients with neurological symptoms. Developing novel combinatorial therapeutic strategies based on mechanistic understanding is urgently needed to further improve the efficacy of current immunotherapies in BrM patients. We recently found that BrMs in patients frequently have severe MHC-I loss. BrM patients' scRNA-seq data from available datasets show that MHC-I expression level is negatively correlated with HDAC level in breast cancer brain metastasis. On the other hand, HDAC inhibitors (HDACi) are epigenetic modulators which have been indicated to recover MHC-I expression loss that contributes to immune invasion. HDACi has been indicated to enhance ICI efficacy in primary tumors by reprogramming the tumor microenvironment (TME). However, the immunomodulatory effect of HDACi is unclear in the unique brain immune microenvironment (BrIME), which is characterized as immunosuppressive. Here, we report that although the selective-HDACi Entinostat has a relatively poor blood-brain barrier (BBB) penetration compared to pan-HDACi Panobinostat, Entinostat induced a comparable level of histone acetylation in the brain to that of Panobinostat. Furthermore, combinatorial treatment consisting of HDACi Entinostat/Panobinostat and anti-PD1 reduced BrM outgrowth of EO771 mammary tumor cell-induced BrM in synergetic mouse model. We explored the impact of HDACi on cell surface MHC-I expression by flow cytometry. Entinostat restored MHC-I expression levels on both brain-seeking human and murine breast and lung cancer cell lines, indicating a general epigenetic regulation on MHC-I expression by inhibition of HDACs. To dissect the impact of HDACi on the BrIME, immune profiling of BrM was performed by mass cytometry (CyTOF). Notably, Entinostat induced a dramatic increment of a specific antigen-presenting cell (APC) cluster in BrM-bearing BrIME with increased ratio of M1 proinflammatory macrophages: M2 tumor-associated macrophages (TAMs) and decreased Tregs. Our results suggest that Entinostat can upregulate MHC-I for more effective antigen presentation and enhance anti-tumor immunity in BrIME. Citation Format: Shao-Ping Yang, Yimin Duan, Xiangliang Yuan, Lin Zhang, Patrick Zhang, Dihua Yu. Selective-HDAC inhibitor relieves the suppressive immune microenvironment in the brain to impede breast cancer brain metastasis. [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 6427.

Macrophages Promote Tumor Cell Extravasation across an Endothelial Barrier through Thin Membranous Connections.

Macrophages are important players involved in the progression of breast cancer, including in seeding the metastatic niche. However, the mechanism by which macrophages in the lung parenchyma interact with tumor cells in the vasculature to promote tumor cell extravasation at metastatic sites is not clear. To mimic macrophage-driven tumor cell extravasation, we used an in vitro assay (eTEM) in which an endothelial monolayer and a matrigel-coated filter separated tumor cells and macrophages from each other. The presence of macrophages promoted tumor cell extravasation, while macrophage conditioned media was insufficient to stimulate tumor cell extravasation in vitro. This finding is consistent with a requirement for direct contact between macrophages and tumor cells. We observed the presence of Thin Membranous Connections (TMCs) resembling similar structures formed between macrophages and tumor cells called tunneling nanotubes, which we previously demonstrated to be important in tumor cell invasion in vitro and in vivo. To determine if TMCs are important for tumor cell extravasation, we used macrophages with reduced levels of endogenous M-Sec (TNFAIP2), which causes a defect in tunneling nanotube formation. As predicted, these macrophages showed reduced macrophage-tumor cell TMCs. In both, human and murine breast cancer cell lines, there was also a concomitant reduction in tumor cell extravasation in vitro when co-cultured with M-Sec deficient macrophages compared to control macrophages. We also detected TMCs formed between macrophages and tumor cells through the endothelial layer in the eTEM assay. Furthermore, tumor cells were more frequently found in pores under the endothelium that contain macrophage protrusions. To determine the role of macrophage-tumor cell TMCs in vivo, we generated an M-Sec deficient mouse. Using an in vivo model of experimental metastasis, we detected a significant reduction in the number of metastatic lesions in M-Sec deficient mice compared to wild type mice. There was no difference in the size of the metastases, consistent with a defect specific to tumor cell extravasation and not metastatic outgrowth. Additionally, with an examination of time-lapse intravital-imaging (IVI) data sets of breast cancer cell extravasation in the lungs, we could detect the presence of TMCs between extravascular macrophages and vascular tumor cells. Overall, our data indicate that macrophage TMCs play an important role in promoting the extravasation of circulating tumor cells in the lungs.

Role of Cystathionine β-Synthase and 3-Mercaptopyruvate Sulfurtransferase in the Regulation of Proliferation, Migration, and Bioenergetics of Murine Breast Cancer Cells

Cystathionine β-synthase (CBS), CSE (cystathionine γ-lyase) and 3-mercaptopyruvate sulfurtransferase (3-MST) have emerged as three significant sources of hydrogen sulfide (H2S) in various forms of mammalian cancer. Here, we investigated the functional role of CBS' and 3-MST's catalytic activity in the murine breast cancer cell line EO771. The CBS/CSE inhibitor aminooxyacetic acid (AOAA) and the 3-MST inhibitor 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE) were used to assess the role of endogenous H2S in the modulation of breast cancer cell proliferation, migration, bioenergetics and viability in vitro. Methods included measurements of cell viability (MTT and LDH assays), cell proliferation and in vitro wound healing (IncuCyte) and cellular bioenergetics (Seahorse extracellular flux analysis). CBS and 3-MST, as well as expression were detected by Western blotting; H2S production was measured by the fluorescent dye AzMC. The results show that EO771 cells express CBS, CSE and 3-MST protein, as well as several enzymes involved in H2S degradation (SQR, TST, and ETHE1). Pharmacological inhibition of CBS or 3-MST inhibited H2S production, suppressed cellular bioenergetics and attenuated cell proliferation. Cell migration was only inhibited by the 3-MST inhibitor, but not the CBS/CSE inhibitor. Inhibition of CBS/CSE of 3-MST did not significantly affect basal cell viability; inhibition of 3-MST (but not of CBS/CSE) slightly enhanced the cytotoxic effects of oxidative stress (hydrogen peroxide challenge). From these findings, we conclude that endogenous H2S, generated by 3-MST and to a lower degree by CBS/CSE, significantly contributes to the maintenance of bioenergetics, proliferation and migration in murine breast cancer cells and may also exert a minor role as a cytoprotectant.

Theranostic inorganic-organic hybrid nanoparticles with a cocktail of chemotherapeutic and cytostatic drugs.

Theranostic inorganic-organic hybrid nanoparticles (IOH-NPs) with a cocktail of chemotherapeutic and cytostatic drugs and a composition Gd23+[(PMX)0.5(EMP)0.5]32-, [Gd(OH)]2+[(PMX)0.74(AlPCS4)0.13]2-, or [Gd(OH)]2+[(PMX)0.70(TPPS4)0.15]2- (PMX: pemetrexed, EMP: estramustine phosphate, AlPCS4: aluminum(III) chlorido phthalocyanine tetrasulfonate, TPPS4: tetraphenylporphine sulfonate) are presented for the first time. These IOH-NPs are prepared in water (40-60 nm in size) and have a non-complex composition with outstanding drug loading (71-82% of total nanoparticle mass) of at least two chemotherapeutic or a mixture of cytostatic and photosensitizing agents. All IOH-NPs show red to deep-red emission (650-800 nm) to enable optical imaging. The superior performance of the IOH-NPs with a chemotherapeutic/cytostatic cocktail is validated based on cell-viability assays and angiogenesis studies with human umbilical vein endothelial cells (HUVEC). The synergistic anti-cancer effect of the IOH-NPs with a chemotherapeutic cocktail is shown in a murine breast-cancer cell line (pH8N8) and a human pancreatic cancer cell line (AsPC1), whereas the synergistic cytotoxic and phototoxic efficacy is verified in response to illumination of HeLa-GFP cancer cells, MTT assays with human colon cancer cells (HCT116), and normal human dermal fibroblasts (NHDF). HepG2 spheroids as 3D cell cultures prove the effective uptake of the IOH-NPs with high uniform distribution and the release of the chemotherapeutic drugs with the strong synergistic effect of the cocktail of drugs.

Unregulated LDL cholesterol uptake is detrimental to breast cancer cells.

Tumor uptake of exogenous cholesterol has been associated with the proliferation of various cancers. Previously, we and others have shown that hypercholesterolemia promotes tumor growth and silencing of the LDL receptor (LDLR) in high LDLR-expressing tumors reduces growth. To advance understanding of how LDL uptake promotes tumor growth, LDLR expression was amplified in breast cancer cell lines with endogenously low LDLR expression. Murine (Mvt1) and human (MDA-MB-468) breast cancer cell lines were transduced to overexpress human LDLR (LDLROE). Successful transduction was confirmed by RNA and protein analysis. Fluorescence-labeled LDL uptake was increased in both Mvt1 and MDA-MD-468 LDLROE cells. The expression of the cholesterol-metabolizing genes, ABCA1 and ABCG1, was increased, while HMGCR was decreased in the MDA-MB-468 LDLROE cells. In contrast, Mvt1 LDLROE cells showed no differences in Abca1 and Abcg1 expression and increased Hmgcr expression. Using a Seahorse analyzer, Mvt1 LDLROE cells showed increased respiration (ATP-linked and maximal) relative to controls, while no statistically significant changes in respiration in MDA-MB-468 LDLROE cells were observed. Growth of LDLROE cells was reduced in culture and in hypercholesterolemic mice by two-fold. However, the expression of proliferation-associated markers (Ki67, PCNA and BrdU-label incorporation) was not decreased in the Mvt1 LDLROE tumors and cells. Caspase-3 cleavage, which is associated with apoptosis, was increased in both the Mvt1 and MDA-MB-468 LDLROE cells relative to controls, with the Mvt1 LDLROE cells also showing decreased phosphorylation of p44/42MAPK. Taken together, our work suggests that while additional LDL can promote tumor growth, unregulated and prolonged LDL uptake is detrimental.