Estrogen Receptor-positive Breast Cancer Cells Research Articles

All-trans-retinoic acid modulates glycolysis via H19 and telomerase: the role of mir-let-7a in estrogen receptor-positive breast cancer cells

BackgroundBreast cancer (BC) is the most commonly diagnosed cancer in women. Treatment approaches that differ between estrogen-positive (ER+) and triple-negative BC cells (TNBCs) and may subsequently affect cancer biomarkers, such as H19 and telomerase, are an emanating delight in BC research. For instance, all-trans-Retinoic acid (ATRA) could represent a potent regulator of these oncogenes, regulating microRNAs, mostly let-7a microRNA (miR-let-7a), which targets the glycolysis pathway, mainly pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA) enzymes. Here, we investigated the potential role of ATRA in H19, telomerase, miR-let-7a, and glycolytic enzymes modulation in ER + and TNBC cells.MethodsMCF-7 and MDA-MB-231 cells were treated with 5 µM ATRA and/or 100 nM fulvestrant. Then, ATRA-treated or control MCF-7 cells were transfected with either H19 or hTERT siRNA. Afterward, ATRA-treated or untreated MDA-MB-231 cells were transfected with estrogen receptor alpha ER(α) or beta ER(β) expression plasmids. RNA expression was evaluated by RT‒qPCR, and proteins were assessed by Western blot. PKM2 activity was measured using an NADH/LDH coupled enzymatic assay, and telomerase activity was evaluated with a quantitative telomeric repeat amplification protocol assay. Student’s t-test or one-way ANOVA was used to analyze data from replicates.ResultsOur results showed that MCF-7 cells were more responsive to ATRA than MDA-MB-231 cells. In MCF-7 cells, ATRA and/or fulvestrant decreased ER(α), H19, telomerase, PKM2, and LDHA, whereas ER(β) and miR-let-7a increased. H19 or hTERT knockdown with or without ATRA treatment showed similar results to those obtained after ATRA treatment, and a potential interconnection between H19 and hTERT was found. However, in MDA-MB-231 cells, RNA expression of the aforementioned genes was modulated after ATRA and/or fulvestrant, with no significant effect on protein and activity levels. Overexpression of ER(α) or ER(β) in MDA-MB-231 cells induced telomerase activity, PKM2 and LDHA expression, in which ATRA treatment combined with plasmid transfection decreased glycolytic enzyme expression.ConclusionsTo the best of our knowledge, our study is the first to elucidate a new potential interaction between the estrogen receptor and glycolytic enzymes in ER + BC cells through miR-let-7a.

TRPV1-Dependent Antiproliferative Activity of Dioecious Maclura pomifera Extracts in Estrogen Receptor-Positive Breast Cancer Cell Lines Involves Multiple Apoptotic Pathways.

Globally, breast cancer is a significant cause of mortality. Recent research focused on identifying compounds regulating the transient receptor potential vanilloid 1 (TRPV1) ion channel activity for the possibility of developing cancer therapeutics. In this study, the antiproliferative properties and mechanisms of action through TRPV1 of Maclura pomifera, a dioecious tree native to the south-central USA, have been investigated. Male and female extracts of spring branch tissues and leaves (500 µg/mL) significantly reduced the viability of MCF-7 and T47D cells by 75-80%. M. pomifera extracts induced apoptosis by triggering intracellular calcium overload via TRPV1. Blocking TRPV1 with the capsazepine antagonist and pretreating cells with the BAPTA-AM chelator boosted cell viability, revealing that M. pomifera phytochemicals activate TRPV1. Both male and female M. pomifera extracts initiated apoptosis through multiple pathways, the mitochondrial, ERK-induced, and endoplasmic reticulum-stress-mediated apoptotic pathways, demonstrated by the expression of activated caspase 3, caspase 9, caspase 8, FADD, FAS, ATF4, and CHOP, the overexpression of phosphorylated PERK and ERK proteins, and the reduction of BCL-2 levels. In addition, AKT and pAKT protein expressions were reduced in female M. pomifera-treated cells, revealing that female plant extract also inhibits PI3K/Akt signaling pathways. These results suggest that phytochemicals in M. pomifera extracts could be promising for developing breast cancer therapeutics.

Discovery of Terminal Oxazole-Bearing Natural Products by a Targeted Metabologenomic Approach.

A targeted metabologenomic method was developed to selectively discover terminal oxazole-bearing natural products from bacteria. For this, genes encoding oxazole cyclase, a key enzyme in terminal oxazole biosynthesis, were chosen as the genomic signature to screen bacterial strains that may produce oxazole-bearing compounds. Sixteen strains were identified from the screening of a bacterial DNA library (1,000 strains) using oxazole cyclase gene-targeting polymerase chain reaction (PCR) primers. The PCR amplicon sequences were subjected to phylogenetic analysis and classified into nine clades. 1H-13C coupled-HSQC NMR spectra obtained from the culture extracts of the hit strains enabled the unequivocal detection of the target compounds, including five new oxazole compounds, based on the unique 1JCH values and chemical shifts of oxazole: lenzioxazole (1) possessing an unprecedented cyclopentane, permafroxazole (2) bearing a tetraene conjugated with carboxylic acid, tenebriazine (3) incorporating two modified amino acids, and methyl-oxazolomycins A and B (4 and 5). Tenebriazine displayed inhibitory activity against pathogenic fungi, whereas methyl-oxazolomycins A and B (4 and 5) selectively showed anti-proliferative activity against estrogen receptor-positive breast cancer cells. This metabologenomic method enables the logical and efficient discovery of new microbial natural products with a target structural motif without the need for isotopic labeling.

Abstract SY19-03: Mechanisms of sensitivity and resistance to CDK2 inhibitors

Abstract CDK2 is a core cell-cycle kinase that phosphorylates many substrates to drive progression through the cell cycle. We used several CDK2 inhibitors in clinical development to interrogate CDK2 substrate phosphorylation, cell-cycle progression, and drug adaptation in preclinical models. In normal mammary cells and estrogen receptor-positive breast cancer cells, CDK2 inhibition causes a rapid loss of substrate phosphorylation that is rapidly restored by a hard-wired cell-cycle buffering mechanism. In this mechanism, CDK4/6 backstops Rb1 hyper-phosphorylation to maintain Cyclin A2 expression, enabling re-activation of CDK2 in the presence of CDK2 inhibitor. By contrast, CCNE1-amplified ovarian cancers do not exhibit this rapid rebound. Our results augment our understanding of CDK plasticity and CDK dependencies, delineate the genetic backgrounds in which this adaptive rebound upon CDK2 inhibition can occur, and suggest contexts in which CDK2 inhibition will be most effective as a cancer therapy. Citation Format: Sabrina L. Spencer. Mechanisms of sensitivity and resistance to CDK2 inhibitors [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 SY19-03.

Long-term Multimodal Recording Reveals Epigenetic Adaptation Routes in Dormant Breast Cancer Cells.

This study advances the understanding of therapy-induced dormancy with potential clinical implications for breast cancer. Estrogen receptor-positive breast cancer cells adapt to endocrine treatment by entering a dormant state characterized by strong heterochromatinization with no recurrent genetic changes. Targeting the epigenetic rewiring impairs the adaptation of cancer cells to ETs. See related commentary by Llinas-Bertran et al., p. 704. This article is featured in Selected Articles from This Issue, p. 695.

Synthesis, biological evaluation and in-silico ADMET studies of novel chalcones and dihydro pyrazoles of 2H-Chromene as anticancer agents

2H-chromenes and chalcones are biologically important scaffolds with applications in drug discovery. Their ease of synthesis and biological importance have attracted the attention of medicinal chemists worldwide. Inspired by this, we synthesized various substituted chalcones and dihydropyrazole derivatives bearing various aryl and hetero-aryl 2H-chromene moieties. The resulting compounds were evaluated for cytotoxicity in vitro against doxorubicin in triple-negative breast cancer cell lines (MDA-MB-231), estrogen receptor-positive breast cancer cell lines (MCF-7), and human brain glioblastoma (U-87 MG) cell lines. Compounds 6b and 6j exhibited anticancer activity against triple-negative breast cancer cell line (MDA-MB-231), with IC50 values of 4.02 µM and 3.35 µM, respectively. Further investigation involving in silico pharmacokinetic (ADME) and toxicity studies also revealed pivotal features for the favourable bioavailability of these derivatives.

Abstract 4424: Differential metabolic response of triple-negative and estrogen receptor-positive breast cancer cells to abemaciclib, a CDK4/6 inhibitor

Abstract Background: Inhibition of the cell cycle kinases CDK4/6 is the standard-of-care for advanced hormone receptor-positive breast cancer. The clinical efficacy of CDK4/6 inhibitors in triple-negative breast cancer remains uncertain. Mechanisms of sensitivity and resistance are not fully understood. This study comprehensively investigated the metabolic response of triple-negative and estrogen receptor-positive breast cancer cells to abemaciclib (Abe), with the aim of providing metabolic insights for resistance mechanisms. Methods: MCF-7 (MCF) and MDA-MB-231 (MDA) cells were treated with Abe (0, 100, and 500 nM) for 1, 2, or 7 days. Cell cycle and cell senescence analyses were performed to assess drug effects. Cellular metabolism was investigated using the Seahorse assay, LC-MS/MS based targeted metabolomics, and stable isotope-assisted metabolic flux analyses with [U-13C]glutamine, [1,2-13C]glucose, and [U-13C]glucose as the tracers. Results: Abe induced cell cycle arrest at G0/G1 in both cell lines, more pronounced in MCF. Dose- and time-dependent cell senescence occurred in both treated cell lines, more pronounced in MDA. The Seahorse assay indicated that energy metabolism (assessed by oxygen consumption rate and extracellular acidification rate) was reduced in both treated cell lines. Targeted metabolomics revealed that post Abe treatment, intracellular lactate significantly decreased in both cell lines; intracellular TCA intermediates significantly decreased in MCF while being unchanged in MDA; intracellular deoxynucleotides decreased in both cell lines, to a lesser extent in MDA; cellular energy levels (assessed as the ratios of ATP/AMP, ATP/ADP, CTP/CMP, CTP/CDP) were significantly lower in MCF while remaining unchanged or increased in MDA; intracellular levels of many amino acids significantly increased in MDA while decreasing in MCF. [U-13C]glutamine flux revealed a significant decrease of intracellular glutamine-derived TCA intermediates in both treated cell lines. [1,2-13C]glucose flux indicated an enhanced oxidate pentose phosphate pathway (PPP) activity and increased de novo syntheses of purine nucleotides (ATP and GTP) in treated MDA (but not MCF). [U-13C]glucose flux suggested that while both cell lines responded to Abe with decreased anaerobic glycolysis (pyruvate converting to lactate), MDA (but not MCF) showed an enhanced capability of utilizing glucose-derived carbon to replenish TCA intermediates and increased amino acid synthesis. Conclusion: Adaptive cellular metabolism, characterized by enhanced utilization of glucose-derived carbon to replenish TCA intermediates and increased PPP activity, thus promoting biosynthesis of amino acids and purine nucleotides to maintain cellular energy and redox balance, may contribute to the intrinsic resistance of triple-negative breast cancer to CDK4/6 inhibitors. Citation Format: Jun Jiang, Xun Bao, Yuanyuan Jiang, Yang Yue, Maik Huettemann, Jing Li. Differential metabolic response of triple-negative and estrogen receptor-positive breast cancer cells to abemaciclib, a CDK4/6 inhibitor [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 4424.

Abstract 5534: Needle biopsy induces pro-metastatic progression and systemic dissemination of estrogen receptor-positive breast cancer cells through the COX-2/PGE2 cascade

Abstract Breast cancer is the most commonly diagnosed malignancy in the U.S. and over two-thirds of invasive breast cancer cases are diagnosed early stage. However, 15-year survival rates for early-stage breast cancer remain in the range of 70-77%. Mounting evidence showed an increased risk of disease progression and mortality among early-stage breast cancer patients whose surgery was delayed over 60 days after the diagnostic biopsy. Yet, the mechanism(s) underlying the rapidly increased mortality due to delay of surgery after diagnosis remains unknown. Our cohort analyses of early-stage breast cancer patients reveal the emergence of a significantly rising mortality risk when the biopsy-to-surgery interval was extended beyond 53 days. Additionally, histology of post-biopsy tumors shows prolonged retention of a metastasis-permissive wound stroma dominated by M2-like macrophages capable of promoting cancer cell epithelial-to-mesenchymal transition and angiogenesis by secretion of transforming growth factor beta 1 (TGF-β1) and vascular endothelial growth factor (VEGF). We show that needle biopsy promotes systemic dissemination of cancer cells through a mechanism of sustained activation of the cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) cascade, which favors M2-polarization and its associated pro-metastatic changes, but are abrogated by oral treatment with COX-2 inhibitors in estrogen receptor-positive (ER+) syngeneic mouse tumor models. Therefore, we conclude that needle biopsy of ER+ breast cancer provokes progressive pro-metastatic changes, which may explain the mortality risk posed by surgery delay after diagnosis. Also, our data may provide a rationale for a pharmacologic strategy to inhibit the COX-2/PGE2 cascade in cases when delay of surgery is unavoidable. Citation Format: Hiroyasu Kameyama, Macall Leslie, Reese Simmons, Yunguang Sun, Misung Yi, Priya Dondapati, John F. Langenheim, Kar-Ming Fung, Inna Chervoneva, Hallgeir Rui, Takemi Tanaka. Needle biopsy induces pro-metastatic progression and systemic dissemination of estrogen receptor-positive breast cancer cells through the COX-2/PGE2 cascade [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 5534.

Abstract 7653: Role of ITGB2 in patients with luminal B1 breast cancer

Abstract Purpose: Luminal-type breast cancers are the most commonly diagnosed in women. Among them, the luminal B1 subtype exhibits higher proliferation rates and a worse prognosis compared to the luminal A subtype. Despite significant advancements in detection and therapies, recurrence still occurs after primary treatment. In this study, our aim is to identify genomic alterations in early recurrent luminal B1 breast cancer. Experimental Design: In this VGHTPE cohort, we recruited a total of 42 patients diagnosed with stage I-III luminal B1 breast cancer, comprising 15 subjects who experienced recurrence within five years and 27 subjects who did not. Genomic DNA was extracted from formalin-fixed paraffin-embedded samples and subjected to targeted next-generation sequencing. We assessed cell aggressiveness through in vitro transwell migration, invasion, and sphere assays. Results: Luminal B1 breast cancer patients with advanced stage and poorly differentiated tumors were associated with recurrence within five years. Driver gene mutation analysis revealed that TP53 mutations were present in 46.7% of patients who experienced recurrence within five years, compared to 29.6% in the non-recurrence group. In the analysis of copy number variations, the most common amplifications/gains observed in luminal B1 breast cancer patients were in MCL1, MYC, and KLF6. Remarkably, patients who experienced recurrence within five years showed a higher occurrence of gain in ITGB2, the gene encoding the integrin β chain, compared to those who remained recurrence-free. Patients with ITGB2 amplifications/gains had a shorter 5-year recurrence-free survival compared to those with a neutral status. In vitro studies revealed that the knockdown of ITGB2 suppressed cell migration, invasion, and sphere formation in estrogen receptor-positive HER2-negative breast cancer cells. Conclusion: Our study has identified ITGB2 amplifications/gains as a potential biomarker for early recurrence in luminal B1 breast cancer. Citation Format: Chun-Yu Liu, Ji-Lin Chen, Yi-Fang Tsai, Ta-Chung Chao, Wan-Lun Wang, Pei-Ju Lien, Chih-Yi Hsu, Jiun-I Lai, Chi-Cheng Huang, Jen-Hwey Chiu, Ling-Ming Tseng. Role of ITGB2 in patients with luminal B1 breast cancer [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 7653.

HNRNPC promotes estrogen receptor-positive breast cancer cell cycle by stabilizing WDR77 mRNA in an m6A-dependent manner.

Breast cancer has become the most commonly diagnosed cancer. Heterogeneous nuclear ribonucleoprotein C (HNRNPC), a reader of N6-methyladenosine (m6A), has been observed to be upregulated in various types of cancer. Nevertheless, the role of HNRNPC in breast cancer and whether it is regulated by m6A modification deserve further investigation. The expression of HNRNPC in breast cancer was examined by quantitative real-time polymerase chain reaction and western blot analysis. RNAimmunoprecipitation was performed to validate the binding relationships between HNRNPC and WD repeat domain 77 (WDR77). The effects of HNRNPC and m6A regulators on WDR77 were investigated by actinomycin D assay. The experiments in vivo were conducted in xenograft models. In this research, we found that HNRNPC was highly expressed in breast cancer, and played a crucial role in cell growth, especially in the luminal subtype. HNRNPC could combine and stabilize WDR77 mRNA. WDR77 successively drove the G1/S phase transition in the cell cycle and promoted cell proliferation. Notably, this regulation axis was closely tied to the m6A modification status of WDR77 mRNA. Overall, a critical regulatory mechanism was identified, as well as promising targets for potential treatment strategies for luminal breast cancer.

Spinosyn A exerts anti-tumorigenic effects on progesterone-sensitive ERα-positive breast cancer cells by modulating multiple signaling pathways

Breast cancer is one of the most common and deadly cancers in women worldwide. Current treatments for breast cancer have limitations, such as toxicity, resistance, and side effects. Therefore, there is a need to develop new and effective anti-cancer agents from natural sources. Spinosyn A (SPA) is a natural product derived from soil bacteria. SPA has been reported to have anti-parasitic, insecticidal, and anti-bacterial activities. However, its anti-cancer effects and mechanisms are not well understood. In this study, we investigated the effects of SPA on T47-D, estrogen receptor-positive breast cancer cells. We found that SPA inhibited cell proliferation and migration and induced apoptosis and cell cycle arrest. Flow cytometry and holographic imaging microscopy revealed that SPA activated MAPK and PI3K signaling pathways and altered cellular morphology. Finally, RNA-Seq analysis revealed that SPA treatment altered the expression of 1380 genes in T47-D cells, which were enriched in various biological processes and signaling pathways related to cell proliferation, cholesterol metabolism, growth factor activity, amino acid transport activity, extracellular matrix, PI3K-Akt signaling pathway, neuroactive ligand-receptor interaction, and PPAR signaling pathway. Our results suggest that SPA exerts multiple anti-cancer effects on T47-D cells by modulating multiple pathways and cellular processes involved in cell growth, survival, and motility. Our findings provide new insights into the molecular mechanisms of SPA action on breast cancer cells and its potential applications as a novel anti-cancer agent.

Amino acid derivative of probenecid potentiates apoptosis-inducing effects of vinblastine by increasing oxidative stress in a cancer cell-specific manner

Many chemotherapeutic drugs suffer from multidrug resistance (MDR). Efflux transporters, namely ATP-binding cassettes (ABCs), that pump the drugs out of the cancer cells comprise one major reason behind MDR. Therefore, ABC inhibitors have been under development for ages, but unfortunately, without clinical success. In the present study, an l-type amino acid transporter 1 (LAT1)-utilizing derivative of probenecid (PRB) was developed as a cancer cell-targeted efflux inhibitor for P-glycoprotein (P-gp), breast cancer resistant protein (BCRP) and/or several multidrug resistant proteins (MRPs), and its ability to increase vinblastine (VBL) cellular accumulation and apoptosis-inducing effects were explored. The novel amino acid derivative of PRB (2) increased the VBL exposure in triple-negative human breast cancer cells (MDA-MB-231) and human glioma cells (U-87MG) by 10–68 -times and 2-5-times, respectively, but not in estrogen receptor-positive human breast cancer cells (MCF-7). However, the combination therapy had greater cytotoxic effects in MCF-7 compared to MDA-MB-231 cells due to the increased oxidative stress recorded in MCF-7 cells. The metabolomic study also revealed that compound 2, together with VBL, decreased the transport of those amino acids essential for the biosynthesis of endogenous anti-oxidant glutathione (GSH). Moreover, the metabolic differences between the outcomes of the studied breast cancer cell lines were explained by the distinct expression profiles of solute carriers (SLCs) that can be concomitantly inhibited. Therefore, attacking several SLCs simultaneously to change the nutrient environment of cancer cells can serve as an adjuvant therapy to other chemotherapeutics, offering an alternative to ABC inhibitors.

Nuclear isoform of RAPH1 interacts with FOXQ1 to promote aggressiveness and radioresistance in breast cancer

Radioresistance limits the efficacy of radiotherapy against breast cancer, especially the most lethal subtype of breast cancer, triple-negative breast cancer (TNBC). Epithelial-to-mesenchymal transition (EMT) is closely related to tumor radioresistance. In this work, we attempted to identify the key EMT-related transcription factor(s) that can induce radioresistance in breast cancer cells. A set of 44 EMT transcription factors were analyzed in parental and radioresistant TNBC cell lines. The function of FOXQ1, a differentially expressed transcription factor, was determined in TNBC radioresistance. FOXQ1-interacting proteins were identified by co-immunoprecipitation and mass spectrometry. Compared with parental cells, FOXQ1 was significantly upregulated in radioresistant TNBC cells. Silencing of FOXQ1 increased the radiosensitiviy of radioresistant TNBC cells both in vitro and in vivo. FOXQ1 associated with a nuclear isoform of RAPH1 (named RAPH1-i3) in radioresistant TNBC cells. Overexpression of RAPH1-i3 enhanced TNBC cell proliferation and migration, and most interestingly, induced radioresistance in parental TNBC cells when co-expressed with FOXQ1. Similar findings were observed in estrogen receptor-positive breast cancer cell lines that had co-expression of RAPH1-i3 and FOXQ1. Mechanistically, co-expression of RAPH1-i3 and FOXQ1 activated STAT3 signaling and increased the expression of CCND1, MCL1, Bcl-XL, and MMP2. Depletion of RAPH1-i3 impaired the radioresistance of radioresistant TNBC cells. Additionally, RAPH1-i3 upregulation was associated with advanced tumor stage and reduced disease-free survival in TNBC patients. These results collectively show that RAPH1-i3 interacts with FOXQ1 to promote breast cancer progression and radioresistance. RAPH1-i3 and FOXQ1 represent therapeutic targets for the treatment of breast cancer including TNBC.

Downregulation of MALAT1 in triple-negative breast cancer cells

BackgroundMALAT1 is one of the most abundant nuclear long non-coding RNAs, which has been found to be elevated in various types of cancers. However, conflicting reports on MALAT1 in breast cancer cell lines challenge understanding of MALAT1's involvement in breast cancer progression. AimMeasurement of normalized relative quantity (NRQ) of MALAT1 transcripts in cell lines representing triple-negative breast cancer (TNBC) and luminal breast cancer. Materials and methodsThe studies were performed using cell lines representing luminal breast cancer (T47D, MCF-7), TNBC (MDA-MB-468, CAL-51, MDA-MB-231), and MCF-10A cell line of normal breast epithelial cells. Total RNA was isolated from six independent cell cultures of each line, treated with DNase I, and used to synthesize complementary DNA, which was used in quantitative real-time PCR (qPCR) assays. Four MALAT1 fragments and reference genes CCSER2, ANKRD17, PUM1, GAPDH were amplified. ResultsGeometric means of the NRQ of MALAT1 in breast cancer cell lines had the shortest 95% confidence intervals when CCSER2 was used for normalization. MALAT1 major transcript levels thus estimated in TNBC cell lines were found to be statistically significantly reduced compared to levels in both MCF-10A cells and luminal breast cancer cell lines, while MALAT1 minority splice variants were found to be increased in almost all breast cancer cell lines. ConclusionCCSER2-normalized qPCR results indicate MALAT1 downregulation in cell lines representing the more aggressive breast cancer subtype compared to both the normal breast epithelial cell line and the estrogen receptor-positive breast cancer cell lines.

OR22-06 Functional Characterization Of X-linked Genes In Regulating Epigenetic Landscape In Endocrine-resistant Breast Cancer

Abstract Disclosure: E.I. Ramos: None. B. Yang: None. M. Sedano: None. V. Reid: None. K. Diwa: None. A. Hidalgo: None. A. Beard: None. J. Patel: None. S.S. Gadad: None. Studies show that genes transcribed from chromosome X play critical roles in several biological processes. X-linked genes are tightly regulated and expressed in tissues protected from immune surveillance. However, several of them get dysregulated in diseases such as cancer. Intriguingly, genome-wide analyses showed their presence in the previously considered gene deserts in the human genome. Their direct role in estrogen transcription in tamoxifen-resistant breast cancer and biological outcomes are still unknown. To this end, we leveraged the power of functional genomics, including RNA with 4-thiouridine (4sU) coupled with RNA-sequencing and CRISPR-based genetic screening, to identify X-linked genes with a potential role in tamoxifen-directed estrogen-regulated transcription. Through a series of phenotypic assays, we selected a poorly studied transcript, “H19X,” with limited protein-coding potential; RNA-In-Situ-Hybridization revealed its localization to the nucleus. In the current study, we have identified the H19X-controlled estrogen-dependent gene regulatory mechanisms in tamoxifen-resistant estrogen receptor-positive (ER+) breast cancer cells. We manipulated the levels of H19X in tamoxifen-resistant ER+ breast cancer cells to generate a comprehensive list of direct transcripts using 4sU-RNA-seq. Interestingly, H19X regulates the expression of estrogen-driven intergenic, divergent, and antisense transcripts whose promoters are bound by ER-alpha (ERα) binding sites. Mechanistically, ‘Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq)’ revealed that H19X modulates chromatin structure at target regions to control gene expression. In addition, ‘chromatin immunoprecipitation (ChIP) with massively parallel DNA sequencing ChIP-seq’ (H3K27ac, H3K27me3) identified a critical role for H19X in controlling the epigenetic landscape in tamoxifen-resistant ER+ breast cancer cells. Collectively, our study sheds light on the molecular functions of X-linked genes and allows us to identify new diagnostic and therapeutic targets in tamoxifen-resistant ER+ breast cancer.S.S.G. is supported by grants from a) The Cancer Prevention and Research Institute of Texas (CPRIT; RR170020); b) Lizanell and Colbert Coldwell foundation; c) The Edward N. and Margaret G. Marsh Foundation; d) The American Cancer Society Presentation: Saturday, June 17, 2023

A truncated DNA aptamer with high selectivity for estrogen receptor-positive breast cancer cells

The estrogen receptor-positive (ER+) breast cancers constitute more than 50 % of breast cancers, seriously threatening the health of women. Unfortunately, the detection and targeted therapy of ER+ breast cancers remain a challenge. Here, a novel nucleic acid aptamer S1–4 was developed to specifically target ER+ breast cancer MCF-7 cells by using Cell-SELEX and nucleic acid truncation strategies. The affinity dissociation constant of the binding of aptamer S1–4 to MCF-7 cells was 97.6 ± 7.5 nM in vitro. Compared with HER2+ breast cells SK-BR-3 and triple-negative breast cancer cells MDA-MB-231, MCF-7 cells were selectively recognized and targeted by aptamer S1–4. Fluorescence tracing in vivo results also indicated that aptamer S1–4 selectively targeted the cell membrane of tumor tissues in MCF-7- but not in SK-BR3 or MDB-MA-231-bearing mice. This selectively developed novel aptamer probe S1–4 with high affinity could be used for the diagnosis and treatment of ER+ breast cancers.

F-box and leucine-rich repeat protein 16 controls tamoxifen sensitivity via regulation of mitochondrial respiration in estrogen receptor-positive breast cancer cells.

Tamoxifen is one of the most effective therapeutic tools for estrogen receptor-positive (ER +) breast cancer. However, the intrinsic insensitivity and resistance to tamoxifen remains a significant hurdle for achieving optimal responses and curative therapy. In this study, we report that F-box and leucine-rich repeat protein 16 (FBXL16) is located in the mitochondria of ER + breast cancer cells. The mitochondrial FBXL16 plays an essential role in sustaining mitochondrial respiration and thereby regulates the sensitivity of ER + breast cancer cells to tamoxifen treatment. Importantly, high FBXL16 expression is significantly correlated with poor overall survival of ER + breast cancer patients. Moreover, mitochondrial inhibition phenocopies FBXL16 depletion in terms of sensitizing the ER + breast cancer cells to tamoxifen treatment. Together, our study demonstrates that FBXL16 acts as a novel regulator of tamoxifen sensitivity. Thus, targeting FBXL16 may serve as a promising approach for improving the therapeutic efficacy of tamoxifen in ER + breast cancer cells.

High-Affinity Extended Bisphosphonate-Based Coordination Polymers as Promising Candidates for Bone-Targeted Drug Delivery.

Extended bisphosphonate-based coordination polymers (BPCPs) were produced when 1,1'-biphenyl-4,4'-bisphosphonic acid (BPBPA), the analogue of 1,1'-biphenyl-4,4'-dicarboxylic acid (BPDC), reacted with bioactive metals (Ca2+, Zn2+, and Mg2+). BPBPA-Ca (11 Å × 12 Å), BPBPA-Zn (10 Å × 13 Å), and BPBPA-Mg (8 Å × 11 Å) possess channels that allow the encapsulation of letrozole (LET), an antineoplastic drug that combined with BPs treats breast-cancer-induced osteolytic metastases (OM). Dissolution curves obtained in phosphate-buffered saline (PBS) and fasted-state simulated gastric fluid (FaSSGF) demonstrate the pH-dependent degradation of BPCPs. Specifically, the results show that the structure of BPBPA-Ca is preserved in PBS (∼10% release of BPBPA) and collapses in FaSSGF. Moreover, the phase inversion temperature nanoemulsion method yielded nano-Ca@BPBPA (∼160 d. nm), a material with measurably higher (>1.5x) binding to hydroxyapatite than commercial BPs. Furthermore, it was found that the amounts of LET encapsulated and released (∼20 wt %) from BPBPA-Ca and nano-Ca@BPBPA are comparable to those of BPDC-based CPs [i.e., UiO-67-(NH2)2, BPDC-Zr, and bio-MOF-1], where other antineoplastic drugs have been loaded and released under similar conditions. Cell viability assays show that, at 12.5 μM, the drug-loaded nano-Ca@BPBPA exhibits higher cytotoxicity against breast cancer cells MCF-7 and MDA-MB-231 [relative cell viability (%RCV) = 20 ± 1 and 45 ± 4%] compared with LET (%RCV = 70 ± 1 and 99 ± 1%). At this concentration, no significant cytotoxicity was found for the hFOB 1.19 cells treated with drug-loaded nano-Ca@BPBPA and LET (%RCV = 100 ± 1%). Collectively, these results demonstrate the potential of nano-Ca@BPCPs as promising drug-delivery systems to treat OM or other bone-related diseases because these present measurably higher affinity, allowing bone-targeted drug delivery under acidic environments and effecting cytotoxicity on estrogen receptor-positive and triple-negative breast cancer cell lines known to induce bone metastases, without significantly affecting normal osteoblasts at the metastatic site.

NNAT is a novel mediator of oxidative stress that suppresses ER + breast cancer

BackgroundNeuronatin (NNAT) was recently identified as a novel mediator of estrogen receptor-positive (ER+) breast cancer cell proliferation and migration, which correlated with decreased tumorigenic potential and prolonged patient survival. However, despite these observations, the molecular and pathophysiological role(s) of NNAT in ER + breast cancer remains unclear. Based on high protein homology with phospholamban, we hypothesized that NNAT mediates the homeostasis of intracellular calcium [Ca2+]i levels and endoplasmic reticulum (EndoR) function, which is frequently disrupted in ER + breast cancer and other malignancies.MethodsTo evaluate the role of NNAT on [Ca2+]i homeostasis, we used a combination of bioinformatics, gene expression and promoter activity assays, CRISPR gene manipulation, pharmacological tools and confocal imaging to characterize the association between ROS, NNAT and calcium signaling.ResultsOur data indicate that NNAT localizes predominantly to EndoR and lysosome, and genetic manipulation of NNAT levels demonstrated that NNAT modulates [Ca2+]i influx and maintains Ca2+ homeostasis. Pharmacological inhibition of calcium channels revealed that NNAT regulates [Ca2+]i levels in breast cancer cells through the interaction with ORAI but not the TRPC signaling cascade. Furthermore, NNAT is transcriptionally regulated by NRF1, PPARα, and PPARγ and is strongly upregulated by oxidative stress via the ROS and PPAR signaling cascades.ConclusionCollectively, these data suggest that NNAT expression is mediated by oxidative stress and acts as a regulator of Ca2+ homeostasis to impact ER + breast cancer proliferation, thus providing a molecular link between the longstanding observation that is accumulating ROS and altered Ca2+ signaling are key oncogenic drivers of cancer.

Cell facilitation promotes growth and survival under drug pressure in breast cancer

The interplay of positive and negative interactions between drug-sensitive and resistant cells influences the effectiveness of treatment in heterogeneous cancer cell populations. Here, we study interactions between estrogen receptor-positive breast cancer cell lineages that are sensitive and resistant to ribociclib-induced cyclin-dependent kinase 4 and 6 (CDK4/6) inhibition. In mono- and coculture, we find that sensitive cells grow and compete more effectively in the absence of treatment. During treatment with ribociclib, sensitive cells survive and proliferate better when grown together with resistant cells than when grown in monoculture, termed facilitation in ecology. Molecular, protein, and genomic analyses show that resistant cells increase metabolism and production of estradiol, a highly active estrogen metabolite, and increase estrogen signaling in sensitive cells to promote facilitation in coculture. Adding estradiol in monoculture provides sensitive cells with increased resistance to therapy and cancels facilitation in coculture. Under partial inhibition of estrogen signaling through low-dose endocrine therapy, estradiol supplied by resistant cells facilitates sensitive cell growth. However, a more complete blockade of estrogen signaling, through higher-dose endocrine therapy, diminished the facilitative growth of sensitive cells. Mathematical modeling quantifies the strength of competition and facilitation during CDK4/6 inhibition and predicts that blocking facilitation has the potential to control both resistant and sensitive cancer cell populations and inhibit the emergence of a refractory population during cell cycle therapy.