Tamoxifen-resistant Breast Cancer Research Articles

Involvement of Long Non-Coding RNA HOTAIR in the Regulation of ERα36-Mediated Epithelial Mesenchymal Transition in Tamoxifen-Resistant Human Breast Cancer

Involvement of Long Non-Coding RNA HOTAIR in the Regulation of ERα36-Mediated Epithelial Mesenchymal Transition in Tamoxifen-Resistant Human Breast Cancer

The SMAC mimetic GDC-0152 is a direct ABCB1-ATPase activity modulator and BIRC5 expression suppressor in cancer cells

Upregulation of the multidrug efflux pump ABCB1/MDR1 (P-gp) and the anti-apoptotic protein BIRC5/Survivin promotes multidrug resistance in various human cancers. GDC-0152 is a DIABLO/SMAC mimetic currently being tested in patients with solid tumors. However, it is still unclear whether GDC-0152 is therapeutically applicable for patients with ABCB1-overexpressing multidrug-resistant tumors, and the molecular mechanism of action of GDC-0152 in cancer cells is still incompletely understood. In this study, we found that the potency of GDC-0152 is unaffected by the expression of ABCB1 in cancer cells. Interestingly, through in silico and in vitro analysis, we discovered that GDC-0152 directly modulates the ABCB1-ATPase activity and inhibits ABCB1 multidrug efflux activity at sub-cytotoxic concentrations (i.e., 0.25×IC50 or less). Further investigation revealed that GDC-0152 also decreases BIRC5 expression, induces mitophagy, and lowers intracellular ATP levels in cancer cells at low cytotoxic concentrations (i.e., 0.5×IC50). Co-treatment with GDC-0152 restored the sensitivity to the known ABCB1 substrates, including paclitaxel, vincristine, and YM155 in ABCB1-expressing multidrug-resistant cancer cells, and it also restored the sensitivity to tamoxifen in BIRC5-overexpressing tamoxifen-resistant breast cancer cells in vitro. Moreover, co-treatment with GDC-0152 restored and potentiated the anticancer effects of paclitaxel in ABCB1 and BIRC5 co-expressing xenograft tumors in vivo. In conclusion, GDC-0152 has the potential for use in the management of cancer patients with ABCB1 and BIRC5-related drug resistance. The findings of our study provide essential information to physicians for designing a more patient-specific GDC-0152 clinical trial program in the future.

Small molecule inhibitor targeting the Hsp70-Bim protein–protein interaction in estrogen receptor-positive breast cancer overcomes tamoxifen resistance

IntroductionEstrogen receptor (ER) positive patients compromise about 70% of breast cancers. Tamoxifen, an antagonist of ERα66 (the classic ER), is the most effective and the standard first-line drug. However, its efficacy is limited by the development of acquired resistance.MethodsA specific inhibitor of Hsp70-Bim protein–protein interaction (PPI), S1g-2, together with an inhibitor of Hsp70-Bag3 PPI, MKT-077 and an ATP-competitive inhibitor VER155008, were used as chemical tools. Cell viability assays, co-immunoprecipitation and gene knockdown were used to investigate the role of Hsp70 in tamoxifen resistance. A xenograft model was established in which tamoxifen-resistant breast cancer (MCF-7/TAM-R) cells maintained in the presence of 5 μM tamoxifen were subcutaneously inoculated. The anti-tumor efficiency of S1g-2 was measured after a daily injection of 0.8 mg/kg for 14 days.ResultsIt was revealed that Hsp70-Bim PPI protects ERα-positive breast cancer from tamoxifen-induced apoptosis through binding and stabilizing ERα36, rather than ERα66, resulting in sustained EGFR mRNA and protein expression. Disruption of Hsp70-Bim PPI and downregulation of ERα36 expression in tumor samples are consistent with the in vitro functions of S1g-2, resulting in about a three-fold reduction in tumor volume.ConclusionsThe in vivo activity and safety of S1g-2 illustrated that it is a potential strategy for Hsp70-Bim disruption to overcome tamoxifen-resistant ER-positive breast cancer.

The anticancer activity of bile acids in drug discovery and development.

Bile acids (BAs) constitute essential components of cholesterol metabolites that are synthesized in the liver, stored in the gallbladder, and excreted into the intestine through the biliary system. They play a crucial role in nutrient absorption, lipid and glucose regulation, and the maintenance of metabolic homeostasis. In additional, BAs have demonstrated the ability to attenuate disease progression such as diabetes, metabolic disorders, heart disease, and respiratory ailments. Intriguingly, recent research has offered exciting evidence to unveil their potential antitumor properties against various cancer cell types including tamoxifen-resistant breast cancer, oral squamous cell carcinoma, cholangiocarcinoma, gastric cancer, colon cancer, hepatocellular carcinoma, prostate cancer, gallbladder cancer, neuroblastoma, and others. Up to date, multiple laboratories have synthesized novel BA derivatives to develop potential drug candidates. These derivatives have exhibited the capacity to induce cell death in individual cancer cell types and display promising anti-tumor activities. This review extensively elucidates the anticancer activity of natural BAs and synthetic derivatives in cancer cells, their associated signaling pathways, and therapeutic strategies. Understanding of BAs and their derivatives activities and action mechanisms will evidently assist anticancer drug discovery and devise novel treatment.

Favipiravir, an antiviral drug, in combination with tamoxifen exerts synergistic effect in tamoxifen-resistant breast cancer cells via hTERT inhibition

Tamoxifen (TAM) is one of the most successful treatments for breast cancer; however, TAM resistance continues to be a significant barrier. TAM resistance has been reported to be associated with increased expression of human telomerase reverse transcriptase (hTERT). This enzyme shares structural similarity with RNA-dependent RNA polymerase (RdRp) enzyme of RNA viruses, suggesting that RdRp inhibitors may also inhibit hTERT. Favipiravir (FAV) is an antiviral drug that inhibits RdRp of RNA viruses. Thus, we propose that FAV may also elicit an antitumor effect by suppressing hTERT. This study aimed to investigate the effect of FAV and TAM on TAM-resistant breast cancer (TAMR-1). The cell viabilities were determined. The levels of CDK1/ hTERT, in addition to regulators of hTERT-targeted signaling pathways were measured. Apoptosis, migration, and cell cycle distribution were also determined. Our data revealed that the combination of TAM and FAV suppressed cell proliferation synergistically (CI < 1) and resulted in a significant change in cell migration and apoptosis. Indeed, this was associated with reduced levels of hTERT and CDK1 and shift in the cell cycle distribution. Our findings suggest that the TAM/FAV combination exhibits synergistic effects against TAMR-1 human breast cancer cells by targeting hTERT.

USP46 enhances tamoxifen resistance in breast cancer cells by stabilizing PTBP1 to facilitate glycolysis

Tamoxifen (TAM) is the primary drug for treating estrogen receptor alpha-positive (ER+) breast cancer (BC). However, resistance to TAM can develop in some patients, limiting its therapeutic efficacy. The ubiquitin-specific protease (USP) family has been associated with the development, progression, and drug resistance of various cancers. To explore the role of USPs in TAM resistance in BC, we used qRT-PCR to compare USP expression between TAM-sensitive (MCF-7 and T47D) and TAM-resistant cells (MCF-7R and T47DR). We then modulated USP46 expression and examined its impact on cell proliferation, drug resistance (via CCK-8 and EdU experiments), glycolysis levels (using a glycolysis detection assay), protein interactions (confirmed by co-IP), and protein changes (analyzed through Western blotting). Our findings revealed that USP46 was significantly overexpressed in TAM-resistant BC cells, leading to the inhibition of the ubiquitin degradation of polypyrimidine tract-binding protein 1 (PTBP1). Overexpression of PTBP1 increased the PKM2/PKM1 ratio, promoted glycolysis, and intensified TAM resistance in BC cells. Knockdown of USP46 induced downregulation of PTBP1 protein by promoting its K48-linked ubiquitination, resulting in a decreased PKM2/PKM1 ratio, reduced glycolysis, and heightened TAM sensitivity in BC cells. In conclusion, this study highlights the critical role of the USP46/PTBP1/PKM2 axis in TAM resistance in BC. Targeted therapy against USP46 may represent a promising strategy to improve the prognosis of TAM-resistant patients.

FoxO3a Drives the Metabolic Reprogramming in Tamoxifen-Resistant Breast Cancer Cells Restoring Tamoxifen Sensitivity.

Tamoxifen-resistant breast cancer cells (TamR-BCCs) are characterized by an enhanced metabolic phenotype compared to tamoxifen-sensitive cells. FoxO3a is an important modulator of cell metabolism, and its deregulation has been involved in the acquisition of tamoxifen resistance. Therefore, tetracycline-inducible FoxO3a was overexpressed in TamR-BCCs (TamR/TetOn-AAA), which, together with their control cell line (TamR/TetOn-V), were subjected to seahorse metabolic assays and proteomic analysis. FoxO3a was able to counteract the increased oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) observed in TamR by reducing their energetic activity and glycolytic rate. FoxO3a caused glucose accumulation, very likely by reducing LDH activity and mitigated TamR biosynthetic needs by reducing G6PDH activity and hindering NADPH production via the pentose phosphate pathway (PPP). Proteomic analysis revealed a FoxO3a-dependent marked decrease in the expression of LDH as well as of several enzymes involved in carbohydrate metabolism (e.g., Aldolase A, LDHA and phosphofructokinase) and the analysis of cBioPortal datasets of BC patients evidenced a significant inverse correlation of these proteins and FoxO3a. Interestingly, FoxO3a also increased mitochondrial biogenesis despite reducing mitochondrial functionality by triggering ROS production. Based on these findings, FoxO3a inducing/activating drugs could represent promising tools to be exploited in the management of patients who are refractory to antiestrogen therapy.

Role of monocarboxylate transporter I/lactate dehydrogenase B-mediated lactate recycling in tamoxifen-resistant breast cancer cells.

Although tamoxifen (TAM) is widely used in patients with estrogen receptor-positive breast cancer, the development of tamoxifen resistance is common. The previous finding suggests that the development of tamoxifen resistance is driven by epiregulin or hypoxia-inducible factor-1α-dependent glycolysis activation. Nonetheless, the mechanisms responsible for cancer cell survival and growth in a lactic acid-rich environment remain elusive. We found that the growth and survival of tamoxifen-resistant MCF-7 cells (TAMR-MCF-7) depend on glycolysis rather than oxidative phosphorylation. The levels of the glycolytic enzymes were higher in TAMR-MCF-7 cells than in parental MCF-7 cells, whereas the mitochondrial number and complex I level were decreased. Importantly, TAMR-MCF-7 cells were more resistant to low glucose and high lactate growth conditions. Isotope tracing analysis using 13C-lactate confirmed that lactate conversion to pyruvate was enhanced in TAMR-MCF-7 cells. We identified monocarboxylate transporter1 (MCT1) and lactate dehydrogenase B (LDHB) as important mediators of lactate influx and its conversion to pyruvate, respectively. Consistently, AR-C155858 (MCT1 inhibitor) inhibited the proliferation, migration, spheroid formation, and in vivo tumor growth of TAMR-MCF-7 cells. Our findings suggest that TAMR-MCF-7 cells depend on glycolysis and glutaminolysis for energy and support that targeting MCT1- and LDHB-dependent lactate recycling may be a promising strategy to treat patients with TAM-resistant breast cancer.

Phase separation of Nur77 mediates XS561-induced apoptosis by promoting the formation of Nur77/Bcl-2 condensates

The orphan nuclear receptor Nur77 is a critical regulator of the survival and death of tumor cells. The pro-death effect of Nur77 can be regulated by its interaction with Bcl-2, resulting in conversion of Bcl-2 from a survival to killer. As Bcl-2 is overexpressed in various cancers preventing them from apoptosis and promoting their resistance to chemotherapy, targeting the apoptotic pathway of Nur77/Bcl-2 may lead to new cancer therapeutics. Here, we report our identification of XS561 as a novel Nur77 ligand that induces apoptosis of tumor cells by activating the Nur77/Bcl-2 pathway. In vitro and animal studies revealed an apoptotic effect of XS561 in a range of tumor cell lines including MDA-MB-231 triple-negative breast cancer (TNBC) and MCF-7/LCC2 tamoxifen-resistant breast cancer (TAMR) in a Nur77-dependent manner. Mechanistic studies showed XS561 potently induced the translocation of Nur77 from the nucleus to mitochondria, resulting in mitochondria-related apoptosis. Interestingly, XS561-induced accumulation of Nur77 at mitochondria was associated with XS561 induction of Nur77 phase separation and the formation of Nur77/Bcl-2 condensates. Together, our studies identify XS561 as a new activator of the Nur77/Bcl-2 apoptotic pathway and reveal a role of phase separation in mediating the apoptotic effect of Nur77 at mitochondria.

RelB-activated GPX4 inhibits ferroptosis and confers tamoxifen resistance in breast cancer

Tamoxifen (TAM) resistance remains a major obstacle in the treatment of advanced breast cancer (BCa). In addition to the competitive inhibition of the estrogen receptor (ER) signaling pathway, damping of mitochondrial function by increasing reactive oxygen species (ROS) is critical for enhancing TAM pharmacodynamics. Here, we showed that RelB contributes to TAM resistance by inhibiting TAM-provoked ferroptosis. TAM-induced ROS level promoted ferroptosis in TAM-sensitive cells, but the effect was alleviated in TAM-resistant cells with high constitutive levels of RelB. Mechanistically, RelB inhibited ferroptosis by transcriptional upregulating glutathione peroxidase 4 (GPX4). Consequently, elevating RelB and GPX4 in sensitive cells increased TAM resistance, and conversely, depriving RelB and GPX4 in resistant cells decreased TAM resistance. Furthermore, suppression of RelB transcriptional activation resensitized TAM-resistant cells by enhancing ferroptosis in vitro and in vivo. The inactivation of GPX4 in TAM-resistant cells consistently resensitized TAM by increasing ferroptosis-mediated cell death. Together, this study uncovered that inhibition of ferroptosis contributes to TAM resistance of BCa via RelB-upregulated GPX4.

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

Inhibiting MEK1 R189 citrullination enhances the chemosensitivity of docetaxel to multiple tumour cells.

Drug resistance is still a big challenge for cancer patients. We previously demonstrated that inhibiting peptidylarginine deiminase 2 (PADI2) enzyme activity with Cl-amine increases the efficacy of docetaxel (Doc) on tamoxifen-resistant breast cancer cells with PADI2 expression. However, it is not clear whether this effect applies to other tumour cells. Here, we collected four types of tumour cells with different PADIs expression and fully evaluated the inhibitory effect of the combination of PADIs inhibitor (BB-Cla) and Doc in vitro and in vivo on tumour cell growth. Results show that inhibiting PADIs combined with Doc additively inhibits tumour cell growth across the four tumour cells. PADI2-catalysed citrullination of MEK1 Arg 189 exists in the four tumour cells, and blocking the function of MEK1 Cit189 promotes the anti-tumour effect of Doc in these tumour cells. Further analysis shows that inhibiting MEK1 Cit189 decreases the expression of cancer cell stemness factors and helps prevent cancer cell stemness maintenance. Importantly, this combined treatment can partially restore the sensitivity of chemotherapy-resistant cells to docetaxel or cisplatin in tumour cells. Thus, our study provides an experimental basis for the combined therapeutic approaches using docetaxel- and PADIs inhibitors-based strategies in tumour treatment. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

Monopolar spindle 1 contributes to tamoxifen resistance in breast cancer through phosphorylation of estrogen receptor α.

The overexpression of mitotic kinase monopolar spindle 1 (Mps1) has been identified in many tumor types, and targeting Mps1 for tumor therapy has shown great promise in multiple preclinical cancer models. However, the role played by Mps1 in tamoxifen (TAM) resistance in breast cancer has never been reported. The sensitivity of breast cancer cells to tamoxifen was analysed in colony formation assays and wound healing assays. Enhanced transactivational activity of estrogen receptor α (ERα) led by Mps1 overexpression was determined by luciferase assays. The interaction between Mps1 and ERα was verified by co-immunoprecipitation and proximity ligation assay. Phosphorylation of ERα by Mps1 was detected by in vitro kinase assay and such phosphorylation process in vivo was proven by co-immunoprecipitation. The potential phosphorylation site(s) of ERα were analyzed by mass spectrometry. Mps1 determines the sensitivity of breast cancer cells to tamoxifen treatment. Mps1 overexpression rendered breast cancer cells more resistant to tamoxifen, while an Mps1 inhibitor or siMps1 oligos enabled cancer cells to overcome tamoxifen resistance. Mechanistically, Mps1 interacted with estrogen receptor α and stimulated its transactivational activity in a kinase activity-dependent manner. Mps1 was critical for ERα phosphorylation at Thr224 amino acid site. Importantly, Mps1 failed to enhance the transactivational activity of the ERα-T224A mutant. Mps1 contributes to tamoxifen resistance in breast cancer and is a potential therapeutic that can overcome tamoxifen resistance in breast cancer.

Candidate Oligo Therapeutic Target, miR-330-3p, Induces Tamoxifen Resistance in Estrogen Receptor-Positive Breast Cancer Cells via HDAC4.

Tamoxifen is a drug used for treating breast cancer (BC), especially for individuals diagnosed with estrogen receptor-positive (ER+) BC. Its prolonged use could reduce the risk of recurrence and significantly lengthen the survival rate of BC patients. However, an increasing number of patients developed resistance to tamoxifen treatment, which reduced therapeutic efficiency and caused substandard prognosis. Therefore, the exploration of the molecular processes involved in tamoxifen resistance (TR) is urgently required. This investigation aimed to elucidate the relationship of microRNA-330 (miR-330-3p) with the TR of BC. There is little information on miR-330-3p's link with drug-resistant BC, although it is well known to regulate cell proliferation and apoptosis. Primarily, miR-330-3p expression in parental BC (MCF7/T47D), TR (MCF7-TR), and T47D/TR cell lines was detected by qRT-PCR. Then, the impact of miR-330-3p on the TR of BC cells was assessed by a cell proliferation assay. Lastly, dual-luciferase reporter, qRT-PCR, and western blot assessments were carried out to identify histone deacetylase 4 (HDAC4) as the potential miR-330-3p target gene. The data indicated that miRNA-330 was overexpressed in TR ER+ BC cells and its overexpression could induce TR. Furthermore, miRNA-330 could also reduce the expression of HDAC4, which is closely linked to TR, and overexpression of HDAC4 could reverse miRNA-330-induced drug resistance. In summary, miR-330-3p could induce TR of ER+ BC cells by downregulating HDAC4 expression, which might be a novel marker of TR and a possible treatment target against BC patients who are tamoxifen-resistant.

Diagnostic and differential efficacy of cyclin D1 and CA15-3 in breast cancer and benign breast tumors

Background: Cyclin D1, a key oncoprotein, promotes cancer cell proliferation and is linked to tamoxifen resistance in breast cancer. CA15-3, a carbohydrate-containing protein antigen of the transmembrane glycoprotein MUC-1, initially appeared to inhibit tumor cell lysis and reduce cell-cell interactions. Still, limited clinical reports are available to assess their role in early detection of breast cancer. Thus, the current study sought to investigate the diagnostic and differential efficacy of cyclin D1 and CA15-3 in breast cancer and benign breast tumor. This case-control study was conducted between April 2022 and January 2023. Serum samples were collected from 120 participants, including 30 patients with breast cancer, 30 patients with benign breast tumors (BBT), and 60 control subjects. Cyclin D1 and CA15-3 levels were measured using ELISA, and the diagnostic capabilities of each marker were assessed by analyzing the receiver operating characteristic curves. Results: The mean serum CA15-3 level in BC women (38.89±8.63 U/mL) was significantly higher than in BBT women (32.64±8.47 U/mL) and the control group (21.07±8.49 U/mL). The mean serum CA15-3 level in BBT women was also notably higher than that of the control group. Mean serum Cyclin D1 levels were compared between study groups: 0.85±0.15 ng/mL in BC, 0.97 ± 0.21 ng/mL in BBT, and 0.56 ± 0.14 ng/mL in the control group, with significant differences observed among the three groups. Conclusion: Elevated Cyclin D1 levels were found in both BBT and BC patients at early stages, indicating its potential use as a routine diagnostic test. CA15-3 demonstrated the highest concentration in BC patients compared to BBT and control groups, suggesting its utility in the diagnosis and screening of breast cancer.

Targeting HMG-CoA synthase 2 suppresses tamoxifen-resistant breast cancer growth by augmenting mitochondrial oxidative stress-mediated cell death

AimsIn this study, we aimed to investigate previously unrecognized lipid metabolic perturbations in tamoxifen-resistant breast cancer (BC) by conducting comprehensive metabolomics and transcriptomics analysis. We identified the role of 3-hydroxy-3-methylglutary-coenzyme-A-synthase 2 (HMGCS2), a key enzyme responsible for ketogenesis, in tamoxifen-resistant BC growth. Main methodsComprehensive metabolomics (CE-TOFMS, LC-TOFMS) and transcriptiomics analysis were performed to characterize metabolic pathways in tamoxifen-resistant BC cells. The upregulation of HMGCS2 were verified thorugh immunohistochemistry (IHC) in clinical samples obtained from patients with recurrent BC. HMGCS2 inhibitor was discovered through surface plasmon resonance analysis, enzyme assay, and additional molecular docking studies. The effect of HMGCS2 suppression on tumor growth was studied thorugh BC xenograft model, and intratumoral lipid metabolites were analyzed via MALDI-TOFMS imaging. Key findingsWe revealed that the level of HMGCS2 was highly elevated in both tamoxifen-resistant T47D sublines (T47D/TR) and clinical refractory tumor specimens from patients with ER+ breast cancer, who had been treated with adjuvant tamoxifen. Suppression of HMGCS2 in T47D/TR resulted in the accumulation of mitochondrial reactive oxygen species (mtROS) and apoptotic cell death. Further, we identified alphitolic acid, a triterpenoid natural product, as a novel HMGCS2-specific inhibitor that elevated mtROS levels and drastically retarded the growth of T47D/TR in in vitro and in vivo experiments. SignificanceEnhanced ketogenesis with upregulation of HMGCS2 is a potential metabolic vulnerability of tamoxifen-resistant BC that offers a new therapeutic opportunity for treating patients with ER+ BC that are refractory to tamoxifen treatment.

[The relationship between the expression of amplified in breast cancer 1、androgen receptor and tamoxifen resistance in breast cancer].

Objective: To discuss the value of amplified in breast cancer 1(AIB1) and androgen receptor (AR) for the resistance of adjuvant tamoxifen in estradiol receptor (ER) positive breast cancer. Methods: A total of 188 cases with breast cancer after receiving tamoxifen treatment in the Tianjin Medical University Cancer Institute and Hospital from June 2008 to July 2013 were enrolled in this study.Using immunohistochemical SP method to detect AIB1and AR expression in breast cancer tissue, analyzing the relationship of AIB1 and AR expression and the effect of tamoxifen.And verify the results of the experiment through the GEPIA database. Results: The response of tamoxifen was 80.3%. The response rate in AR positive group and AR negative group was 79.6% and 82.4%, with no significant difference (P=0.669). The response rate in AIB1 High expression group and AIB1 Low expression group was 68.4% and 93.3%, respectively, with a significant difference (P<0.001).The response rate in AR negative and AIB1 Low expression group, AR negative and AIB1 High expression group, AR positive and AIB1 Low expression group, AR positive and AIB1High expression group was 89.7%, 71.4%, 96.7%, 66.2%respectively, with a significant difference (P<0.001). Conclusions: The expression level of AIB1 is correlated with the therapeutic effect of tamoxifen in breast cancer. Its high expression can cause tamoxifen resistance, while AR positive and High expression of AIB1 are more likely to cause tamoxifen resistance, and AIB1 can be used as an independent influencing factor for breast cancer tamoxifentreatment.

BRK confers tamoxifen-resistance in breast cancer via regulation of tyrosine phosphorylation of CDK1

Tamoxifen (Tam) has been the first-line therapy for estrogen receptor-positive breast cancer since its FDA-approval in 1998. Tam-resistance, however, presents a challenge and the mechanisms that drive it have yet to be fully elucidated. The non-receptor tyrosine kinase BRK/PTK6 is a promising candidate as previous research has shown that BRK knockdown resensitizes Tam-resistant breast cancer cells to the drug. However, the specific mechanisms that drive its importance to resistance remain to be investigated. Here, we investigate the role and mechanism of action of BRK in Tam-resistant (TamR), ER+, and T47D breast cancer cells using phosphopeptide enrichment and high throughput phopshoproteomics analysis. We conducted BRK-specific shRNA knockdown in TamR T47D cells and compared phosphopeptides identified in these cells with their Tam-resistant counterpart and parental, Tam-sensitive cells (Par). A total of 6492 STY phosphosites were identified. Of these sites, 3739 high-confidence pST sites and 118 high-confidence pY sites were analyzed for significant changes in phosphorylation levels to identify pathways that were differentially regulated in TamR versus Par and to investigate changes in these pathways when BRK is knocked down in TamR. We observed and validated increased CDK1 phosphorylation at Y15 in TamR cells compared to BRK-depleted TamR cells. Our data suggest that BRK is a potential Y15-directed CDK1 regulatory kinase in Tam-resistant breast cancer.

Pterostilbene-isothiocyanate reduces miR-21 level by impeding Dicer-mediated processing of pre-miR-21 in 5-fluorouracil and tamoxifen-resistant human breast cancer cell lines.

Converging evidences identifies that microRNA-21 (miR-21) is responsible for drug resistance in breast cancer. This study aims to evaluate the miR-21-modulatory potential of a hybrid compound, pterostilbene-isothiocyanate (PTER-ITC), in tamoxifen-resistant MCF-7 (TR/MCF-7) and 5-fluorouracil-resistant MDA-MB 231 (5-FUR/MDA-MB 231) breast cancer cell lines, established by repeated exposure to gradually increasing the concentrations of tamoxifen and 5-fluorouracil, respectively. The outcome of this study shows that PTER-ITC effectively reduced the TR/MCF-7 (IC50: 37.21µM) and 5-FUR/MDA-MB 231 (IC50: 47.00µM) cell survival by inducing apoptosis, inhibiting cell migration, colony and spheroid formations in TR/MCF-7 cells, and invasiveness of 5-FUR/MDA-MB 231 cells. Most importantly, PTER-ITC significantly reduced the miR-21 expressions in these resistant cell lines. Moreover, the downstream tumor suppressor target gene of miR-21 such as PTEN, PDCD4, TIMP3, TPM1, and Fas L were upregulated after PTER-ITC treatment, as observed from transcriptional (RT-qPCR) and translational (immunoblotting) data. In silico and miR-immunoprecipitation (miR-IP) results showed reduced Dicer binding to pre-miR-21, after PTER-ITC treatment, indicating inhibition of miR-21 biogenesis. Collectively, the significance of this study is indicated by preliminary evidence for miR-21-modulatory effects of PTER-ITC that highlights the potential of this hybrid compound as an miR-21-targeting therapeutic agent.

Reduced Expression of RBP7 is Associated with Resistance to Tamoxifen In Luminal A Breast Cancer.

Tamoxifen is the most commonly used hormonal treatment for ERα-positive breast cancer. Tamoxifen resistance is still a big problem for ERα target therapy. RBP7 is a member of the cellular retinol-binding protein family. This study aims to investigate the prognostic role of RBP7 and the relationship between RBP7 expression and sensitivity or resistance to tamoxifen in ERα-positive breast cancer. A bioinformatics method was used to investigate RBP7 expression and the prognostic value of RBP7 in different subtypes of breast cancer. The relationship between RBP7 expression and sensitivity or resistance to tamoxifen was studied using clinical data (GSE1379) and cell line data (GSE27473, GSE2645923, GSM3715281, and GSM3715282). Transfection of RBP7 experiments was used to testify to the function of RBP7 in MCF7 cell. RBP7 is a member of the family of cellular retinol-binding proteins. RBP7 expression was down-regulated at both mRNA and protein levels in breast cancer and was not associated with different TNM (Tumor, Node, Metastasis) stages. High expression of RBP7 was significantly related to good relative percent survival in the luminal A subtype, but in negative breast cancer, the result was opposite. The ROC plot showed that RBP7 had a significant predictive value for the tamoxifen response in the luminal A subtype. The expression of RBP7 from patients with recurrence treated with tamoxifen was significantly reduced. Gene Expression Omnibus showed that RBP7 expression was reduced considerably in tamoxifen-resistant MCF7 cells and T47D cells. The expression of RBP7 was positively correlated with some microRNAs involved in negatively regulating tamoxifen-resistant breast cancer. We also found that the expression of RBP7 decreased significantly in tamoxifen-resistant MCF7 cells, and transfection of RBP7 increased the sensitivity of resistant cells to tamoxifen. Reduced expression of RBP7 is associated with resistance to tamoxifen in luminal A breast cancer. Our research may help to explore the mechanisms of resistance of breast cancer to tamoxifen.