Mouse Mammary Fat Pad Research Articles

The role of peritumoral electroacupuncture in regulating cuproptosis for sensitization of chemotherapy efficacy in mice with triple-negative breast cancer

To explore the enhanced sensitization effect of peritumoral electroacupuncture (PEA) on doxorubicin (DOX) chemotherapy in mice with triple-negative breast cancer (TNBC). Eighteen female Balb/c mice were randomly divided into the model, DOX, and EA+DOX groups, with 6 mice in each group. TNBC cells were injected into the mammary fat pad of mice to establish the breast cancer-bearing mice model. Mice of the DOX and EA+DOX groups were injected intraperitoneally with DOX solution at 4 mg/kg once a week for 4 weeks. For mice of the EA+DOX group, 4 filiform needles were inserted surrounding tumor tissues, followed by giving the mice with EA (1 mA, 2 Hz/100 Hz) stimulation for 3 min, once a week for 4 weeks. During the intervention, the tumor volume was measured every two days, and at the end of intervention, the weight of the tumor tissue was measured. The expression of Ki67 and proliferating cell nuclear antigen (PCNA) in tumor tissues was detected by immunohistochemistry. The protein expression levels of iron redox protein 1 (FDX1), lipoic acid synthase (LIAS), aconitase 2 (ACO2) and NADH：ubiquinone oxidoreductase core subunit V1 (NDUFV1), dihydrolipoamide S-acetyltransferase(DLAT), dihydrolipoyl succinyltransferase(DLST) in tumor tissues were detected by Western blot. The content of copper ions, pyruvic acid and α-ketoglutaric acid, succinic acid in tumor tissues was detected by copper ion kit, and the content of reactive oxygen species (ROS) in tumor tissues of mice was detected by fluorescence method. Compared with the model group, the tumor volume and weight, the expression levels of Ki67 and PCNA in tumor tissues were decreased (P<0.05, P<0.01) in the DOX and EA+DOX groups. The improvement of the above indicators was more significant in the EA+DOX group than that in the DOX group (P<0.05, P<0.01). Compared with the model and DOX groups, the contents of ROS, copper ions, pyruvic acid and α-ketoglutaric acid were increased (P<0.05, P<0.01), while the contents of succinic acid, and the expressions of FDX1, LIAS, ACO2 and NDUFV1, DLAT, DLST proteins were decreased (P<0.01) in the EA+DOX group. The combination of PEA and DOX can effectively control the growth rate of tumors in mice with TNBC, which may contribute to its function in enhancing the chemotherapy efficacy of DOX on TNBC by promoting cuproptosis.

Obesity Induces Temporally Regulated Alterations in the Extracellular Matrix That Drive Breast Tumor Invasion and Metastasis.

Obesity is associated with increased incidence and metastasis of triple-negative breast cancer, an aggressive breast cancer subtype. The extracellular matrix (ECM) is a major component of the tumor microenvironment that drives metastasis. To characterize the temporal effects of age and high-fat diet (HFD)-driven weight gain on the ECM, we injected allograft tumor cells at 4-week intervals into mammary fat pads of mice fed a control or HFD, assessing tumor growth and metastasis and evaluating the ECM composition of the mammary fat pads, lungs, and livers. Tumor growth was increased in obese mice after 12 weeks on HFD. Liver metastasis increased in obese mice only at 4 weeks, and elevated body weight correlated with increased metastasis to the lungs but not the liver. Whole decellularized ECM coupled with proteomics indicated that early stages of obesity were sufficient to induce changes in the ECM composition. Obesity led to an increased abundance of the proinvasive ECM proteins collagen IV and collagen VI in the mammary glands and enhanced the invasive capacity of cancer cells. Cells of stromal vascular fraction and adipose stem and progenitor cells were primarily responsible for secreting collagen IV and collagen VI, not adipocytes. Longer exposure to HFD increased the invasive potential of ECM isolated from the lungs and liver, with significant changes in ECM composition found in the liver with short-term HFD exposure. Together, these data suggest that changes in the breast, lungs, and liver ECM underlie some of the effects of obesity on triple-negative breast cancer incidence and metastasis. Significance: Organ-specific extracellular matrix changes in the primary tumor and metastatic microenvironment are mechanisms by which obesity contributes to breast cancer progression.

A YAP-centered mechanotransduction loop drives collective breast cancer cell invasion

Dense and aligned Collagen I fibers are associated with collective cancer invasion led by protrusive tumor cells, leader cells. In some breast tumors, a population of cancer cells (basal-like cells) maintain several epithelial characteristics and express the myoepithelial/basal cell marker Keratin 14 (K14). Emergence of leader cells and K14 expression are regarded as interconnected events triggered by Collagen I, however the underlying mechanisms remain unknown. Using breast carcinoma organoids, we show that Collagen I drives a force-dependent loop, specifically in basal-like cancer cells. The feed-forward loop is centered around the mechanotransducer Yap and independent of K14 expression. Yap promotes a transcriptional program that enhances Collagen I alignment and tension, which further activates Yap. Active Yap is detected in invading breast cancer cells in patients and required for collective invasion in 3D Collagen I and in the mammary fat pad of mice. Our work uncovers an essential function for Yap in leader cell selection during collective cancer invasion.

The long noncoding RNA MANCR to promote and stabilize triple negative breast cancer.

e13150 Background: Cancer remains a leading cause of death worldwide, despite many advances in cancer treatment over the past decade. Triple Negative Breast Cancer (TNBC) is among the highest with a poor prognosis. Early diagnosis and modern treatment regimens for breast cancer (BC) have led to a high disease-free survival rate. Still, survival decreases significantly for patients with metastatic disease. Long non-coding RNAs are among a recent class of epigenetic regulators that function in the nucleus to support the stability of the cells and maintain the fidelity of chromatin interactions. Our laboratory discovered the long noncoding RNA MANCR (LINC00704) as being upregulated in human BC tumors and this is indicative of a worse survival rate than in patients with low MANCR-expressing tumors. MANCR is aberrantly expressed in TNBC cells, and these cells are highly dependent on MANCR to retain their tumorigenic characteristics. Methods: Our functional in vitro studies in MDA-MB-231 TNBC cells used GapmerRs to knockdown MANCR. For in vivo studies, TNBC cells were injected into the 4th mammary fat pad of mice, allowed initial tumor formation, and then treated the animals with 2 nmol/g of a negative control or MANCR targeting GapmeR. We also identified genome interaction sites at single nucleotide resolution by chromatin isolation by RNA purification (ChIRP)-seq to determine the mechanism of MANCR activity in TNBC cells. Results: We found that MANCR knockdown promotes DNA damage and decreases cell proliferation, migration, anchorage-independent colony formation, transwell invasion, and overall survival. Additionally, targeting MANCR in animals with existing tumors drastically inhibited tumor growth and the end-point tumor mass over time. The MANCR GapmeR treatment also inhibited the ability of TNBC cells to circulate and disseminate to distant organs. After performing ChIRP-seq in the MDA-MB-231 cells, we identified 988 genome-wide binding sites that exhibit MANCR interactions, of which 79% are intergenic and 21% are genic regions. Furthermore, 127 MANCR ChIRP peaks were found to overlap with fragile sites in the genome, indicating MANCR provides stability to these sites. Conclusions: These data suggest that targeting MANCR has therapeutic potential for patients with “MANCR-high” TNBC tumors by disrupting genome stability. Indeed, our in vivo studies demonstrate that “MANCR-high” TNBC tumors require MANCR to rapidly grow and promote disease progression. Lastly, many of the MANCR-chromatin interactions identified were found in intergenic regions and overlap with fragile sites within the genome. Collectively these data strongly indicate that MANCR stabilizes the TNBC genome, and disrupting genome stability by targeting MANCR has therapeutic potential.

Abstract LB213: NF1 loss promotes bone metastasis in estrogen receptor positive breast cancer

Abstract Up to 80% of breast cancer (BCa) expresses estrogen receptor-α (ER). Over 60% ER+ BCa metastasizes to the bone and are challenging to treat. This study investigates what drives bone metastasis by focusing on a key tumor suppressor neurofibromin (NF1), a GTPase-activating protein that represses RAS signaling. Earlier, we reported that NF1 acts as a transcriptional corepressor for ER in BCa. Our group established that combination fulvestrant (selective ER degrader) and binimetinib (MEK-inhibitor) induces tumor regression in NF1lowER+ models. This combination is now in clinical trial, NCT05554354 (NCI ComboMATCH). Numerous studies indicate that the NF1 loss may impact bone health by altering the equilibrium between bone formation and resorption. Since, bone is the primary site of metastasis in 50-70% of ER+ BCa, understanding the role of NF1 loss in bone metastases becomes imperative. An osteolytic vicious cycle may drive bone metastasis, where cancer cells in the bone stimulate the bone-destructing osteoclasts (OC); leading to subsequent bone deterioration, which in turn, releases growth factors to further promote tumor growth. OCs and many cells in the bone are ER+. We thus hypothesize that deregulated RAS and ER signaling by NF1 loss can drive ER+ bone metastasis by promoting an osteolytic vicious cycle. To assess the clinical impact of NF1 loss on bone metastasis, we analyzed metastatic BCa patient data from cBioPortal and the MSK-EMC cohort. To define how NF1 loss affect bone metastasis, NF1 knockout (KO) ER+ BCa cells were tested in vitro and in vivo for bone tropism, growth in bone and effect on the vicious cycle. Analyses of clinical data suggest that NF1 copy number (CN) loss in ER+ tumors associates with accelerated metastasis to the bone. Additionally, NF1 CN loss and mutations are more prevalent in bone metastasis BCa patients. Lower levels of NF1 mRNA are correlated with shorter duration of bone metastasis-free survival.Our preclinical studies further supported the driver role of NF1 in bone metastasis. NF1KO ER+ BCa cells migrate more efficiently toward the bone in vitro compared to their NF1+ counterparts. When injected into the mammary fat pads of mice, NF1KO cells more frequently metastasized to the bone compared to NF1+ cells. When NF1KO cells were delivered to the mouse femur by intra-iliac injection, they grew more efficiently and induced more bone degradation. This is consistent with our in vitro results, which show that NF1KO ER+ BCa cells can more efficiently promote OC formation from progenitor cells. For this experiment, Mass-spectrometry based unbiased profiling of the conditioned medium showed that osteolytic factors, such as ICAM1 and OSTF1, were enriched in the NF1KO medium. Hence, we conclude that the loss of NF1 deregulates RAS and ER, leading to increased osteolytic factors, that drive bone metastasis. Co-targeting RAS and ER can be a potential treatment for NF1 loss-induced bone metastasis in ER+ BCa. Citation Format: Zifan Zhao, Ze-Yi Zheng, Jonathan Lei, Matthew J. Baik, Yi-Hsuan Wu, Junkai Wang, Igor Bado, Meenakshi Anurag, Bing Zhang, Xiang Zhang, Eric Chang. NF1 loss promotes bone metastasis in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB213.

Abstract B079: Vitamin D metabolism is suppressed postpartum: Implications for targeting the postpartum window for cancer prevention

Abstract Postpartum mammary gland involution is a physiologic inflammatory process that associates with increased risk of postpartum breast cancer (PPBC). Pre-clinical studies provide rationale for targeting this pro-tumor window of involution for PPBC prevention. However, the liver also undergoes physiological remodeling after weaning—consistent with weaning-induced mammary gland involution—which could potentially impact the efficacy of anti-cancer prodrugs administered during the postpartum period. Here, we used mouse models to test the efficacy of vitamin D, a prodrug with known anti-cancer properties, during the postpartum period. Vitamin D supplementation is of particular interest due to its inclusion in dietary guidelines for postpartum women, where vitamin D deficiency is prevalent. Dietary vitamin D is biologically inactive and requires hydroxylation in the liver by Cyp2r1 to produce its circulating form (25(OH)D), which is further hydroxylated in the kidneys to produce the active form (1,25(OH)2D). To understand the impact of liver involution on vitamin D hydroxylation, RNAseq was performed on livers collected from nulliparous or involution mice. Expression of Cyp2r1 was 2-fold lower in involution livers, compared to nulliparous livers (p&amp;lt;0.001). Further, Cyp24a1, which is responsible for degradation of active vitamin D, was increased 5.5-fold in involution livers compared to nulliparous livers (p&amp;lt;0.001). These findings suggest that vitamin D supplementation would be ineffective in the postpartum period. Indeed, nulliparous mice supplemented with vitamin D showed a &amp;gt;2-fold increase in serum 25(OH)D (67.4±8.1nmol/L) compared to nulliparous mice fed a deficient diet (28.7±11.7nmol/L, p&amp;lt;0.01). In contrast, supplementation of involution mice did not increase serum 25(OH)D (supplemented=46.6±8.7nmol/L, deficient=33.7±8.5nmol/L, p&amp;gt;0.05). In the liver, tissue-specific concentrations of 25(OH)D were lower in supplemented involution mice (1.3±0.6ng/g), compared to supplemented nulliparous mice (2.0±0.4ng/g; p=0.02). To assess whether suppression of vitamin D metabolism impacts the anti-cancer activity of dietary vitamin D, mammary cancer cells (D2A1, 2 × 104 cells) were injected into mammary fatpads of mice. In nulliparous mice, vitamin D supplementation associated with a 3-fold reduction in tumor growth (p=0.03); whereas no anti-cancer effects were observed in involution mice. These findings suggest the anti-cancer effects of vitamin D are blocked postpartum due to suppression of vitamin D metabolism in the liver. Understanding how the postpartum liver metabolizes drugs is essential for targeting treatments to this window. A retrospective analysis of our RNAseq data identified 22 additional Cytochrome P450 (CYP450) enzymes—key players in drug metabolism—whose expression was regulated by reproductive stage, suggesting that the effect of liver involution extends beyond suppressed vitamin D metabolism. These findings highlight the importance of considering the postpartum involution period in the design and administration of pharmacological interventions. Citation Format: Sarah M Bernhardt, Pepper Schedin. Vitamin D metabolism is suppressed postpartum: Implications for targeting the postpartum window for cancer prevention [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B079.

Ketamine Promoted Breast Cancer Invasion and Metastasis Through Up-regulating Wnt, BMP, and EGFR Signaling.

In this study, we used an orthotropic breast cancer model combined with ketamine addiction and next-generation sequencing (NGS) to comprehensively investigate molecular alterations in ketamine-mediated metastasis. Ketamine is widely used in anesthesia and drug abuse. Our previous study revealed that ketamine promotes the growth of breast cancer cells; however, the detailed molecular mechanism remains unknown. An orthotropic breast cancer model was established by injecting EO771 breast cancer cells into the mammary fat pad of mice intraperitoneally administered ketamine (30 mg/kg, daily) for 68 days. Tumors collected at day 38 were frozen for future analysis, and their metastasis state was checked at day 68. Tumors were grouped and subjected to NGS analysis, followed by differential gene expression analysis (DEseq) and pathway identification. DEseq analysis showed that ketamine up-regulated metastasis-related signaling, and the key genes were BMP5, FZD6, MMP1B, EGFR, WNT5A, BMP7, and DCN. Ketamine addiction up-regulates the expression of genes involved in the Wnt, EGFR, and BMP signaling cascades, which may be associated with breast cancer progression and metastasis.

Cancer stem cells as the source of tumor associated myoepithelial cells in the tumor microenvironment developing ductal carcinoma in situ

The heterogeneous cell population in the stromal microenvironment is considered to be attributed to the multiple sources from which the cells originate. Tumor associated myoepithelial cells (TAMEs) are one of the most important populations in the tumor microenvironment (TME) especially in breast cancer. On the other hand, cancer stem cells (CSCs) have previously been described to be the origin of tumor-associated cellular components in the TME. We prepared a cancer stem cell model converting mouse-induced pluripotent stem cells (miPSCs) in the presence of conditioned medium of breast cancer cell line MDA-MB-231 cells. The converted cells developed tumors progressing into invasive carcinoma with ductal carcinoma in situ (DCIS) like structure when transplanted into mouse mammary fat pads. The primary cultured cells from the tumor further exhibited markers of CSC such as Sox2, Oct3/4, - CD133 and EpCAM, and mammary gland-related TAME markers such as α-smooth muscle actin, cytokeratin 8, whey acidic protein, prolactin receptor and progesterone receptor as well. These results indicated that the CSCs could be an origin of TAMEs contributing to mammary gland epithelial cell differentiation and the progression to invasive carcinoma during tumor development. The gene expression profiles confirmed the enhanced signaling pathways of PI3K/AKT and MAPK, which have been demonstrated to be enriched in the CSC models, together with the estrogen receptor signaling which was peculiar to mammary gland-derived character.

MAP3K1 expression is associated with progression and poor prognosis of hormone receptor-positive, HER2-negative early-stage breast cancer.

In this study, we assessed whether the overexpression of MAP3K1 promotes the proliferation, migration, and invasion of breast cancer cells, which affect the prognosis of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative early stage breast cancer. Two HR-positive, HER2-negative breast cancer cell lines (MCF7 and T-47D) overexpressing MAP3K1 were transfected with two MAP3K1 short hairpin RNA plasmids (shMAP3K1 [#3] and shMAP3K1 [#5]). The proliferation, migration, and invasion of these cells were then examined. We assessed whether shMAP3K1 affects the cell cycle, levels of downstream signaling molecules (ERK, JNK, p38 MAPK, and NF-κB), and sensitivity to chemotherapeutic and hormonal agents. To assess the anti-tumor effect of MAP3K1 knockdown in the breast cancer orthotopic model, MCF7 and T-47D cells treated with or without shMAP3K1 (#3) and shMAP3K1 (#5) were inoculated into the mammary fat pads of mice. In total, 182 patients with HR-positive, HER2-negative T1 and T2 breast cancer and 0-3 nodal metastases were included. Additionally, 73 patients with T1 and T2 breast cancer and negative nodes who received adjuvant endocrine therapy alone were selected as an independent validation cohort. In both cell lines, shMAP3K1 (#3) and shMAP3K1 (#5) significantly reduced cell growth, migration, and invasion by downregulating MMP-9 and by blocking the G2/M phase of the cell cycle and its regulatory molecule cyclin B1. Moreover, both shMAP3K1 (#3) and shMAP3K1 (#5) downregulated ERK-, JNK-, p38 MAPK-, and NF-κB-dependent gene transcription and enhanced the sensitivity of both cell lines to doxorubicin, docetaxel, and tamoxifen. We observed that both shMAP3K1 (#3) and shMAP3K1 (#5) inhibited tumor growth compared with that in the scrambled group of MCF7 and T-47D cell orthotopic tumors. Patients with MAP3K1 overexpression exhibited significantly poorer 10-year disease-free survival (DFS) (70.4% vs. 88.6%, p = 0.003) and overall survival (OS) (81.9% vs. 96.3%, p = 0.001) than those without MAP3K1 overexpression. Furthermore, phospho-ERK (p < 0.001) and phospho-JNK (p < 0.001) expressions were significantly associated with MAP3K1 expression, and both phospho-ERK and phospho-JNK expressions were significantly correlated with poor 10-year DFS and OS. These biological findings, including a significant association between DFS and OS, and the expressions of MAP3K1, phospho-ERK, and phospho-JNK were further validated in an independent cohort. Multivariate analysis identified MAP3K1 expression as an independent poor prognostic factor for DFS and OS. Our results indicate that the overexpression of MAP3K1 plays a major role in the poor prognosis of HR-positive, HER2-negative early stage breast cancer.

Abstract LB202: Obesity-trained C1q+ macrophages compromiseT cell anti-tumor immunity

Abstract Adipose tissue in the mammary gland undergoes dramatic remodeling during obesity and is involved in numerous metabolic diseases. However, how obesity-driven remodeling in adipose tissue regulates anti-tumor immunity remains unclear. Here we provide the detailed cellular atlases of mouse mammary fat pad and tumor at single-cell resolution in lean and obese mice. By leveraging scRNA-seq, we found that high-fat feeding causes a marked increase of macrophage in adipose tissue. Interestingly, a subset of macrophages expressing high levels of C1q complex genes is accumulated in obese subjects. We found that glucocorticoid may as a key regulator of C1q+ macrophage identity. Synthetic glucocorticoid, Dexamethasone, triggers C1q expression in macrophages. We found that C1q+ macrophage derived C1q complex could suppress CD8+ T cell response, thus fueling breast cancer progression. In mouse TNBC tumor, we uncovered a specific inflammatory responsive tumor subset in obese tumors with high CCR2 ligand expression. Obesity-induced TNFα exposure triggers of breast cancer cells reprogramming and CCR2 ligand production. Consequently, CCR2 ligands promote macrophage into tumor. Moreover, depletion of macrophages by anti-CSF1R suppresses tumor growth in obese mice. Our findings define a novel fundamental mechanism of C1q+ macrophage involved in anti-tumor response in obesity. Citation Format: Tao Zhang, Shimeng Liu, Myles Brown. Obesity-trained C1q+ macrophages compromiseT cell anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB202.

Abstract 1147: A novel anti-Galectin-3 antibody therapeutic for the treatment of triple negative breast cancer

Abstract About 43,600 women in the U.S. are expected to die in 2021 from breast cancer. Triple negative breast cancer (TNBC), which accounts for approximately 15% of all breast cancers, is diagnosed by exclusion of expression and/or amplification of three biomarkers (estrogen receptor [ER], progesterone receptor [PR], and human epidermal growth factor receptor 2 [HER2]).Characterized by a high risk of relapse (one half of patients with early stages experience recurrence), short overall survival and progression-free survival (life expectancy of few months after failure of first-line chemotherapy), TNBC represents a high unmet medical need. Galectin-3 plays multiple roles in tumor initiation and development via a variety of cellular processes, spanning from angiogenesis to tumor migration. Galectin-3 (Gal3) expression is induced in TNBC patients and highly correlates with poor survival, as shown by our and others’ bioinformatics analysis from public database. We recently discovered and patented a series of antibodies with high specificity and affinity for Gal3, one of which is currently tested in human volunteers. This clinical candidate has shown superior pharmacokinetic properties and clean toxicity profile in GLP studies on non-human primates. Here, we show that anti-Gal3 inhibit both anchorage dependent and independent growth of TNBC cells, as well as Gal3-induced escape from NK cell killing. Also, anti-Gal3 proved to be efficacious in in vivo studies, where TNBC cells were implanted in mammary fat pads of mice and tumor progression, measured as growth of primary mass and presence of metastatic nodules in the lungs, was followed during the two months of treatment. The results presented herein support the conclusion that our therapeutic modality could offer an alternative promising treatment of TNBC. Citation Format: Li Zhang, Heng Wu, Karyssa Palopo, Jie Hu, Marvin Cadiente, Anh Nguyen, Teodelinda Mirabella, Dongxu Sun. A novel anti-Galectin-3 antibody therapeutic for the treatment of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1147.

Abstract 2436: CIRBP is a functional mediator of leptomeningeal metastasis

Abstract Background: Cold-Inducible RNA Binding Protein (CIRBP) has been implicated in cancer initiation. Moreover, we have previously identified an association of CIRBP with the invasive growth of parenchymal brain metastases. Using a patient-derived xenograft (PDX) model, in which cells implanted in the mouse mammary fat pad spontaneously metastasize to the leptomeninges, we identified CIRBP as being elevated in leptomeningeal metastases (LM) compared to matched primary mammary tumors. LM grow in the subarachnoid space that harbors the cerebral spinal fluid (CSF). The leptomeninges represent an inhospitable environment for disseminated cancer cells since the CSF is mitogen and nutrient poor. To investigate the importance of CIRBP for metastatic breast cancer cells in the leptomeninges, we stably reduced CIRBP expression in MDA-MB-231 cells and performed mammary fat pad and cranial injections. CIRBP knockdown had no influence on primary tumor growth, but diminished growth within the brain. Hypothesis: We hypothesize that CIRBP functions as a stress response protein enabling cancer cells to grow in the harsh environment of the CSF. Results: In response to various cellular stressors, such as hypothermia, hypoxia or UV irradiation, CIRBP can translocate from the nucleus to the cytoplasm. We show that culturing MDA-MB-231 cells in artificial CSF (aCSF) also causes CIRBP relocation from nucleus to cytoplasm. Using RNA-IP approaches, we have identified mRNAs bound by CIRBP in breast cancer cells treated with aCSF. Ultimately, we will determine whether any of the identified CIRBP-regulated targets contribute to the formation of LM. Finally, we have generated CIRBP variants that are confined either to the nucleus or the cytoplasm. We are currently assessing the ability of these compartment-restricted CIRBP proteins to promote the formation of central nervous system metastases. Conclusions: We have identified CIRBP as a promoter of leptomeningeal metastasis. Our results have begun to reveal the mechanisms through which CIRBP mediates this process. Citation Format: Rima Ezzeddine, Matthew Dankner, Paul Savage, Steven Hebert, William Brothers, Matthew G. Annis, Sarah M. Maritan, Marc R. Fabian, Claudia Kleinman, Morag Park, Peter M. Siegel. CIRBP is a functional mediator of leptomeningeal metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2436.

STING agonist enhances the efficacy of programmed death-ligand 1 monoclonal antibody in breast cancer immunotherapy by activating the interferon-β signalling pathway

ABSTRACT This study aimed to explore the role of a stimulator of interferon (IFN) gene (STING) agonist in breast cancer (BCa) immunotherapy. Clinical samples were collected from 37 patients with BCa. A tumor-bearing mouse model was established by injecting 4T1 cells into the mammary fat pad of mice. STING agonist and atezolizumab were injected in the mice twice a week for 2 weeks. Peripheral blood, tumor mass, lung, liver, brain cortex and kidney samples of the tumor-bearing mice were collected. Anti-IFN alpha receptor subunit 1 (IFNAR1) was used to treat 4T1 cells. Tumor tissues of patients with BCa exhibited lower STING and high programmed cell death protein 1 and programmed death-ligand 1 protein expressions. The STING agonist inhibited 4T1 cell growth in mice (P < 0.001) and increased the IFN-β level and phosphorylation of STING, TBK1, IRF3 and STAT1 in tumor mass of tumor-bearing mice (P < 0.001). It synergized with atezolizumab to inhibit 4T1 cell growth in mice and increased tumor necrosis factor-α, IFN-β, interleukin-10 and IFN-γ levels in the peripheral blood and tumor mass (P < 0.01). It synergized with atezolizumab to increase CD8+ cytotoxic T cells and decrease FOXP3+ Treg cells in the tumor-bearing mouse model. The STING agonist was nontoxic to the lung, liver, brain cortex and kidney. Anti-IFNAR1 reversed the STING agonist promotion on TBK1, IRF3 and STAT1 phosphorylation in 4T1 cells (P < 0.01). STING agonists enhance the efficacy of atezolizumab in BCa immunotherapy by activating the IFN-β signaling pathway.

KRT13 promotes stemness and drives metastasis in breast cancer through a plakoglobin/c-Myc signaling pathway

BackgroundKeratins (KRTs) are intermediate filament proteins that interact with multiple regulatory proteins to initiate signaling cascades. Keratin 13 (KRT13) plays an important role in breast cancer progression and metastasis. The objective of this study is to elucidate the mechanism by which KRT13 promotes breast cancer growth and metastasis.MethodsThe function and mechanisms of KRT13 in breast cancer progression and metastasis were assessed by overexpression and knockdown followed by examination of altered behaviors in breast cancer cells and in xenograft tumor formation in mouse mammary fat pad. Human breast cancer specimens were examined by immunohistochemistry and multiplexed quantum dot labeling analysis to correlate KRT13 expression to breast cancer progression and metastasis.ResultsKRT13-overexpressing MCF7 cells displayed increased proliferation, invasion, migration and in vivo tumor growth and metastasis to bone and lung. Conversely, KRT13 knockdown inhibited the aggressive behaviors of HCC1954 cells. At the molecular level, KRT13 directly interacted with plakoglobin (PG, γ-catenin) to form complexes with desmoplakin (DSP). This complex interfered with PG expression and nuclear translocation and abrogated PG-mediated suppression of c-Myc expression, while the KRT13/PG/c-Myc signaling pathway increased epithelial to mesenchymal transition and stem cell-like phenotype. KRT13 expression in 58 human breast cancer tissues was up-regulated especially at the invasive front and in metastatic specimens (12/18) (p < 0.05). KRT13 up-regulation in primary breast cancer was associated with decreased overall patient survival.ConclusionsThis study reveals that KRT13 promotes breast cancer cell growth and metastasis via a plakoglobin/c-Myc pathway. Our findings reveal a potential novel pathway for therapeutic targeting of breast cancer progression and metastasis.

Baicalein resensitizes tamoxifen-resistant breast cancer cells by reducing aerobic glycolysis and reversing mitochondrial dysfunction via inhibition of hypoxia-inducible factor-1α.

Drug resistance is a major hurdle for the effectiveness of tamoxifen (TAM) to provide clinical benefit. Therefore, it is essential to identify a sensitizer that could be used to improve TAM efficacy in treating TAM‐resistant breast cancer. Here, we investigated the ability of baicalein to reverse TAM resistance. We found that baicalein increased the efficacy of TAM in inhibiting proliferation and inducing apoptosis of TAM‐resistant cells. It also enhanced the TAM‐induced growth reduction of resistant cells from NOD/SCID mouse mammary fat pads, without causing obvious systemic toxicity. Analyses using the CellMiner tool and the Kaplan–Meier plotter database showed that HIF‐1α expression was inversely correlated with TAM therapeutic response in NCI‐60 cancer cells and breast cancer patients. HIF‐1α expression was increased in TAM‐resistant cells due to an increase in mRNA levels and reduced ubiquitin‐mediated degradation. Baicalein reduced HIF‐1α expression by promoting its interaction with PHD2 and pVHL, thus facilitating ubiquitin ligase‐mediated proteasomal degradation and thereby suppressing the nuclear translocation, binding to the hypoxia‐response element, and transcriptional activity of HIF‐1α. As a result, baicalein downregulated aerobic glycolysis by restricting glucose uptake, lactate production, ATP generation, lactate/pyruvate ratio and expression of HIF‐1α‐targeted glycolytic genes, thereby enhancing the antiproliferative efficacy of TAM. Furthermore, baicalein interfered with HIF‐1α inhibition of mitochondrial biosynthesis, which increased mitochondrial DNA content and mitochondrial numbers, restored the generation of reactive oxygen species in mitochondria, and thus enhanced the TAM‐induced mitochondrial apoptotic pathway. The HIF‐1α stabilizer dimethyloxallyl glycine prevented the baicalein‐induced downregulation of glycolysis and mitochondrial biosynthesis and reduced the effects of baicalein on reversing TAM resistance. Our results indicate that baicalein is a promising candidate to help overcome TAM resistance by sensitizing resistant cells to TAM‐induced growth inhibition and apoptosis. The mechanism underlying the effects of baicalein consists of inhibition of HIF‐1α–mediated aerobic glycolysis and mitochondrial dysfunction.

Molecular Imaging Reveals a High Degree of Cross-Seeding of Spontaneous Metastases in a Novel Mouse Model of Synchronous Bilateral Breast Cancer

PurposeSynchronous bilateral breast cancer (SBBC) patients present with cancer in both breasts at the time of diagnosis or within a short time interval. They show higher rates of metastasis and lower overall survival compared to women with unilateral breast cancer. Here we established the first preclinical SBBC model and used molecular imaging to visualize the patterns of metastasis from each primary tumor.ProceduresWe engineered human breast cancer cells to express either Akaluc or Antares2 for bioluminescence imaging (BLI) and tdTomato or zsGreen for ex vivo fluorescence microscopy. Both cell populations were implanted into contralateral mammary fat pads of mice (n=10), and dual-BLI was performed weekly for up to day 29 (n=3), 38 (n=4), or 42 (n=3). Primary tumors and lungs were fixed, and ex vivo fluorescence microscopy was used to analyze the cellular makeup of micrometastases.ResultsSignal from both Antares2 and Akaluc was first detected in the lungs on day 28 and was present in 9 of 10 mice at endpoint. Ex vivo fluorescence microscopy of the lungs revealed that for mice sacrificed on day 38, a significant percentage of micrometastases were composed of cancer cells from both primary tumors (mean 37%; range 27 to 45%), while two mice sacrificed on day 42 showed percentages of 51% and 70%.ConclusionsA high degree of metastatic cross-seeding of cancer cells derived from bilateral tumors may contribute to faster metastatic growth and intratumoral heterogeneity. We posit that our work will help understand treatment resistance and optimal planning of SBBC treatment.

Abstract 2575: Intermittent calorie restriction reverses the adverse effects of obesity and advanced age on tumor growth in a mouse model of breast cancer

Abstract Advanced age and obesity are two major risk factors for breast cancer (BC) mortality. This presents a significant public health concern as the number of older individuals and incidence of obesity are increasing worldwide. In our mouse models of BC, we have demonstrated that, similar to obesity, advanced age accelerates mammary tumor growth. Mechanistically, obesity and advanced age suppress tumor gene expression relating to antitumor immunity and reduce tumoral abundance of cytotoxic CD8+ T cells. Thus, advanced age- and obesity-related enhancement of mammary tumor growth is explained, in part, through the development of an immunosuppressive tumor microenvironment. Given the aging of our populations and the increasing prevalence of obesity, interventions capable of reversing the tumor-promoting effects of advanced age and obesity are needed. We have previously demonstrated that weight loss by intermittent calorie restriction (ICR), in which mice are placed on a 5:2 calorie restriction (CR) regimen (5 days 14% CR, 2 nonconsecutive days 70% CR per week), attenuates tumor growth and immunosuppression in formerly obese mice. This project tests if ICR will provide similar benefit to aged and aged obese mice. Cohorts of young control (5 mos), young diet-induced obese (DIO; 5 mos), aged control (15 mos), and aged DIO (15 mos) mice were generated and subsequently randomized to either remain on their baseline diet or switch to the ICR intervention. Following 9 weeks on ICR or baseline diet, serum samples were collected and then tumor development induced by orthotopic transplantation of E0771 cancer cells into the 4th mammary fat pad of mice. At tumor endpoint mammary tumors were collected and weighed. To determine if ICR alters systemic inflammation in each experimental group, cytokine levels were measured in serum samples collected prior to tumor inoculation. Multiple inflammatory cytokines were downregulated following ICR intervention in young DIO, aged control, and aged DIO mice, including CCL7, CCL10, and CCL24. Downregulation of inflammatory cytokines was correlated with decreased tumor burden in young DIO, aged control, and aged DIO mice placed on ICR, compared with their respective non-intervention controls. Ongoing analyses are investigating if ICR increases the abundance of cytotoxic CD8+ T cells within the tumor microenvironment of young DIO, aged control, and aged DIO mice. These findings demonstrate that ICR may be effective in reversing obesity- and advanced age-related enhancement of mammary tumor growth in mouse models of breast cancer. More research is needed to test if these preclinical findings translate to obese and aged humans with BC. Identifying dietary interventions that may attenuate obesity- and age-related tumor growth has the potential to improve both patient outcomes and quality of life. This research was supported by R35CA197627 to S. Hursting. Citation Format: Dalton M. Craven, Laura A. Smith, Michael F. Coleman, Elaine M. Glenny, Stephen D. Hursting. Intermittent calorie restriction reverses the adverse effects of obesity and advanced age on tumor growth in a mouse model of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2575.

The surface topography of silicone breast implants mediates the foreign body response in mice, rabbits and humans.

Silicone is widely used in chronic implants and is generally perceived to be safe. However, textured breast implants have been associated with immune-related complications, including malignancies. Here, by examining for up to one year the foreign body response and capsular fibrosis triggered by miniaturized or full-scale clinically approved breast implants with different surface topography (average roughness, 0-90 μm) placed in the mammary fat pads of mice or rabbits, respectively, we show that surface topography mediates immune responses to the implants. We also show that the surface surrounding human breast implants collected during revision surgeries also differentially alters the individual's immune responses to the implant. Moreover, miniaturized implants with an average roughness of 4 μm can largely suppress the foreign body response and fibrosis (but not in T-cell-deficient mice), and that tissue surrounding these implants displayed higher levels of immunosuppressive FOXP3+ regulatory T cells. Our findings suggest that, amongst the topographies investigated, implants with an average roughness of 4 μm provoke the least amount of inflammation and foreign body response.

Delivering Two Tumour Antigens Survivin and Mucin-1 on Virus-Like Particles Enhances Anti-Tumour Immune Responses.

Breast cancer (BC) is the most frequently diagnosed cancer in women, with many patients experiencing recurrence following treatment. Antigens delivered on virus-like particles (VLPs) induce a targeted immune response and here we investigated whether the co-delivery of multiple antigens could induce a superior anti-cancer response for BC immunotherapy. VLPs were designed to recombinantly express murine survivin and conjugated with an aberrantly glycosylated mucin-1 (MUC1) peptide using an intracellular cleavable bis-arylhydrazone linker. Western blotting, electron microscopy and UV absorption confirmed survivin-VLP expression and MUC1 conjugation. To assess the therapeutic efficacy of VLPs, orthotopic BC tumours were established by injecting C57mg.MUC1 cells into the mammary fat pad of mice, which were then vaccinated with surv.VLP-SS-MUC1 or VLP controls. While wild-type mice vaccinated with surv.VLP-SS-MUC1 showed enhanced survival compared to VLPs delivering either antigen alone, MUC1 transgenic mice vaccinated with surv.VLP-SS-MUC1 showed no enhanced survival compared to controls. Hence, while co-delivery of two tumour antigens on VLPs can induce a superior anti-tumour immune response compared to the delivery of single antigens, additional strategies must be employed to break tolerance when targeted tumour antigens are expressed as endogenous self-proteins. Using VLPs for the delivery of multiple antigens represents a promising approach to improving BC immunotherapy, and has the potential to be an integral part of combination therapy in the future.

New monoclonal antibodies that recognize an unglycosylated, conserved, extracellular region of CD44 in vitro and in vivo, and can block tumorigenesis.

CD44 is a transmembrane glycoprotein that binds to hyaluronic acid, plays roles in a number of cellular processes and is expressed in a variety of cell types. It is up-regulated in stem cells and cancer. Anti-CD44 monoclonal antibodies affect cell motility and aggregation, and repress tumorigenesis and metastasis. Here we describe four new anti-CD44 monoclonal antibodies originating from B cells of a mouse injected with a plasmid expressing CD44 isoform 12. The four monoclonal antibodies bind to the terminal, extracellular, conserved domain of CD44 isoforms. Based on differences in western blot patterns of cancer cell lysates, the four anti-CD44 mAbs separated into three distinct categories that include P4G9, P3D2, and P3A7, and P3G4. Spot assay analysis with peptides generated in Escherichia coli support the conclusion that the monoclonal antibodies recognize unglycosylated sequences in the N-terminal conserved region between amino acid 21–220, and analyses with a peptide generated in human embryonic kidney 293 cells, demonstrate that these monoclonal antibodies bind to these peptides only after deglycosylation. Western blots with lysates from three cancer cell lines demonstrate that several CD44 isoforms are unglycosylated in the anti-CD44 target regions. The potential utility of the monoclonal antibodies in blocking tumorigenesis was tested by co-injection of cells of the breast cancer-derived tumorigenic cell line MDA-MB-231 with the anti-CD44 monoclonal antibody P3D2 into the mammary fat pads of mice. All five control mice injected with MDA-MB-231 cells plus anti-IgG formed palpable tumors, while only one of the six test mice injected with MDA-MB-231 cells plus P3D2 formed a tiny tumor, while the remaining five were tumor-free, indicating that the four anti-CD44 mAbs may be useful therapeutically.