Different epigenetic mechanisms of ERα implicated in the fate of fulvestrant-resistant breast cancer

Lasofoxifene Monotherapy Induces Durable Complete Remission in a Patient with Estrogen Receptor-Positive, Metastatic Breast Cancer with an ESR1 Mutation

Complete clinical remission on lasofoxifene in post-CDK4/6i metastatic breast cancer patient with ESR1 mutation.

Targeting Breast Cancer: An Overlook on Current Strategies

Breast cancer (BC) is one of the most widely diagnosed cancers and a leading cause of cancer death among women worldwide. Globally, BC is the second most frequent cancer and first most frequent gynecological one, affecting women with a relatively low case-mortality rate. Surgery, radiotherapy, and chemotherapy are the main treatments for BC, even though the latter are often not aways successful because of the common side effects and the damage caused to healthy tissues and organs. Aggressive and metastatic BCs are difficult to treat, thus new studies are needed in order to find new therapies and strategies for managing these diseases. In this review, we intend to give an overview of studies in this field, presenting the data from the literature concerning the classification of BCs and the drugs used in therapy for the treatment of BCs, along with drugs in clinical studies.

Characterization of HCI-EC-23 a novel estrogen- and progesterone-responsive endometrial cancer cell line

Most endometrial cancers express the hormone receptor estrogen receptor alpha (ER) and are driven by excess estrogen signaling. However, evaluation of the estrogen response in endometrial cancer cells has been limited by the availability of hormonally responsive in vitro models, with one cell line, Ishikawa, being used in most studies. Here, we describe a novel, adherent endometrioid endometrial cancer (EEC) cell line model, HCI-EC-23. We show that HCI-EC-23 retains ER expression and that ER functionally responds to estrogen induction over a range of passages. We also demonstrate that this cell line retains paradoxical activation of ER by tamoxifen, which is also observed in Ishikawa and is consistent with clinical data. The mutational landscape shows that HCI-EC-23 is mutated at many of the commonly altered genes in EEC, has relatively few copy-number alterations, and is microsatellite instable high (MSI-high). In vitro proliferation of HCI-EC-23 is strongly reduced upon combination estrogen and progesterone treatment. HCI-EC-23 exhibits strong estrogen dependence for tumor growth in vivo and tumor size is reduced by combination estrogen and progesterone treatment. Molecular characterization of estrogen induction in HCI-EC-23 revealed hundreds of estrogen-responsive genes that significantly overlapped with those regulated in Ishikawa. Analysis of ER genome binding identified similar patterns in HCI-EC-23 and Ishikawa, although ER exhibited more bound sites in Ishikawa. This study demonstrates that HCI-EC-23 is an estrogen- and progesterone-responsive cell line model that can be used to study the hormonal aspects of endometrial cancer.

FKBP52 and FKBP51 differentially regulate the stability of estrogen receptor in breast cancer

SignificanceEstrogen receptor α (ERα) is a transcription factor that induces cell proliferation and exhibits increased expression in a large subset of breast cancers. We comprehensively searched for indicators of poor prognosis in ERα-positive breast cancer through the multiple databases, including interactome, transcriptome, and survival analysis, and identified FKBP52. We found that two immunophilins, FKBP52 and FKBP51, have opposing effects on ERα stability and propose that therapeutic targeting of FKBP52 could be useful for the prevention and treatment of ERα-positive breast cancers, including endocrine therapy-resistant breast cancers.

Nuclear Mechanisms Involved in Endocrine Resistance

Endocrine therapy is a standard treatment offered to patients with ERα (estrogen receptor α)-positive breast cancer. In endocrine therapy, ERα is either directly targeted by anti-estrogens or indirectly by aromatase inhibitors which cause estrogen deficiency. Resistance to these drugs (endocrine resistance) compromises the efficiency of this treatment and requires additional measures. Endocrine resistance is often caused by deregulation of the PI3K/AKT/mTOR pathway and/or cyclin-dependent kinase 4 and 6 activities allowing inhibitors of these factors to be used clinically to counteract endocrine resistance. The nuclear mechanisms involved in endocrine resistance are beginning to emerge. Exploring these mechanisms may reveal additional druggable targets, which could help to further improve patients' outcome in an endocrine resistance setting. This review intends to summarize our current knowledge on the nuclear mechanisms linked to endocrine resistance.

Targeting Amino Acid Metabolic Reprogramming via L-Type Amino Acid Transporter 1 (LAT1) for Endocrine-Resistant Breast Cancer

The PI3K/Akt/mTOR pathway has been well known to interact with the estrogen receptor (ER)-pathway and to be also frequently upregulated in aromatase inhibitor (AI)-resistant breast cancer patients. Intracellular levels of free amino acids, especially leucine, regulate the mammalian target of rapamycin complex 1 (mTORC1) activation. L-type amino acid transporters such as LAT1 and LAT3 are associated with the uptake of essential amino acids. LAT1 expression could mediate leucine uptake, mTORC1 signaling, and cell proliferation. Therefore, in this study, we explored amino acid metabolism, including LAT1, in breast cancer and clarified the potential roles of LAT1 in the development of therapeutic resistance and the eventual clinical outcome of the patients. We evaluated LAT1 and LAT3 expression before and after neoadjuvant hormone therapy (NAH) and examined LAT1 function and expression in estrogen deprivation-resistant (EDR) breast carcinoma cell lines. Tumors tended to be in advanced stages in the cases whose LAT1 expression was high. LAT1 expression in the EDR cell lines was upregulated. JPH203, a selective LAT1 inhibitor, demonstrated inhibitory effects on cell proliferation in EDR cells. Hormone therapy changed the tumor microenvironment and resulted in metabolic reprogramming through inducing LAT1 expression. LAT1 expression then mediated leucine uptake, enhanced mTORC1 signaling, and eventually resulted in AI resistance. Therefore, LAT1 could be the potential therapeutic target in AI-resistant breast cancer patients.

Molecular targeted drugs resistance impairs double-strand break repair and sensitizes ER-positive breast cancer to PARP inhibitors

BACKGROUND

There are various treatments for estrogen-positive breast cancer, mainly hormone therapy and molecular-targeted drugs. Acquiring resistance to these drugs is a major clinical problem. Additionally, little is known about the effect of drug resistance on the DNA repair mechanism. Poly ADP ribose polymerase (PARP) inhibitors currently used for treating HER2-negative metastatic breast cancer with BRCA mutations have been shown to be effective in BRCA-deficient cells with impaired homologous recombination repair. Here, we investigated the effect of drug resistance acquisition on the DNA repair mechanism and the effect of PARP inhibitors on ER (estrogen receptor) -positive breast cancer.

METHODS

We investigated changes in the expression of DNA repair mechanism-related factors and repair ability of double-strand breaks (DSB) in various drug-resistant cell lines established in our laboratory. Additionally, PARP inhibitor susceptibility was investigated using olaparib.

RESULTS

DSB repairs in MCF-7 and hormone therapy-resistant model cells were normal, and these cells demonstrated low sensitivity to olaparib. The resistant cell lines against CDK4/6 inhibitors, fulvestrant and mTOR/PI3K inhibitors showed decreased DSB repair ability and high olaparib sensitivity. They showed low sensitivity to CDK4/6 inhibitors, a close link between acquiring resistance to CDK4/6 inhibitors and hypersensitivity to olaparib.

CONCLUSIONS

Our study suggests some cases of acquiring drug resistance impairs DSB repair ability and sensitizes ER-positive breast cancer to PARP inhibitors.

Lasofoxifene as a potential treatment for therapy-resistant ER-positive metastatic breast cancer

Background

Endocrine therapy remains the mainstay of treatment for estrogen receptor-positive (ER+) breast cancer. Constitutively active mutations in the ligand binding domain of ERα render tumors resistant to endocrine agents. Breast cancers with the two most common ERα mutations, Y537S and D538G, have low sensitivity to fulvestrant inhibition, a typical second-line endocrine therapy. Lasofoxifene is a selective estrogen receptor modulator with benefits on bone health and breast cancer prevention potential. This study investigated the anti-tumor activity of lasofoxifene in breast cancer xenografts expressing Y537S and D538G ERα mutants. The combination of lasofoxifene with palbociclib, a CDK4/6 inhibitor, was also evaluated.

Methods

Luciferase-GFP tagged MCF7 cells bearing wild-type, Y537S, or D538G ERα were injected into the mammary ducts of NSG mice (MIND model), which were subsequently treated with lasofoxifene or fulvestrant as single agents or in combination with palbociclib. Tumor growth and metastasis were monitored with in vivo and ex vivo luminescence imaging, terminal tumor weight measurements, and histological analysis.

Results

As a monotherapy, lasofoxifene was more effective than fulvestrant at inhibiting primary tumor growth and reducing metastases. Adding palbociclib improved the effectiveness of both lasofoxifene and fulvestrant for tumor suppression and metastasis prevention at four distal sites (lung, liver, bone, and brain), with the combination of lasofoxifene/palbociclib being generally more potent than that of fulvestrant/palbociclib. X-ray crystallography of the ERα ligand binding domain (LBD) shows that lasofoxifene stabilizes an antagonist conformation of both wild-type and Y537S LBD. The ability of lasofoxifene to promote an antagonist conformation of Y537S, combined with its long half-life and bioavailability, likely contributes to the observed potent inhibition of primary tumor growth and metastasis of MCF7 Y537S cells.

Conclusions

We report for the first time the anti-tumor activity of lasofoxifene in mouse models of endocrine therapy-resistant breast cancer. The results demonstrate the potential of using lasofoxifene as an effective therapy for women with advanced or metastatic ER+ breast cancers expressing the most common constitutively active ERα mutations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01431-w.

miRNA Expression Profiles in Luminal A Breast Cancer-Implications in Biology, Prognosis, and Prediction of Response to Hormonal Treatment

Breast cancer, which is the most common malignancy in women, does not form a uniform nosological unit but represents a group of malignant diseases with specific clinical, histopathological, and molecular characteristics. The increasing knowledge of the complex pathophysiological web of processes connected with breast cancercarcinogenesis allows the development of predictive and prognostic gene expressionand molecular classification systems with improved risk assessment, which could be used for individualized treatment. In our review article, we present the up-to-date knowledge about the role of miRNAs and their prognostic and predictive value in luminal A breast cancer. Indeed, an altered expression profile of miRNAs can distinguish not only between cancer and healthy samples, but they can classify specific molecular subtypes of breast cancer including HER2, Luminal A, Luminal B, and TNBC. Early identification and classification of breast cancer subtypes using miRNA expression profilescharacterize a promising approach in the field of personalized medicine. A detection of sensitive and specific biomarkers to distinguish between healthy and early breast cancer patients can be achieved by an evaluation of the different expression of several miRNAs. Consequently, miRNAs represent a potential as good diagnostic, prognostic, predictive, and therapeutic biomarkers for patients with luminal A in the early stage of BC.

Decreased ER dependency after acquired resistance to CDK4/6 inhibitors

BACKGROUND

Cyclin-dependent kinase (CDK) 4/6 inhibitors represent a significant advancement in the treatment of estrogen receptor (ER)-positive human epidermal growth factor receptor 2-negative advanced breast cancer. However, mechanisms of alterations after acquired resistance to CDK4/6 inhibitors and the optimal treatment options are still not established.

METHODS

Abemaciclib-resistant cell lines were established from the models of estrogen deprivation-resistant cell lines which retained ER expression and activated ER function derived from MCF-7 breast cancer cell lines. Ribocilib-resistant cell lines were established in the same method as previously reported.

RESULTS

Both abemaciclib- and ribociclib-resistant cell lines showed decreased ER expression. ER transcriptional activity was maintained in these cell lines; however, the sensitivity to 4-hydroxytamoxifen and fulvestrant was almost completely lost. These cell lines did not exhibit any ERα gene mutation. Abemaciclib-resistant cell lines demonstrated low sensitivity to other CDK4/6 inhibitors; sensitivities to PI3K inhibitor, mTOR inhibitor, and chemotherapeutic drugs were maintained.

CONCLUSIONS

Dependence on ER signaling appears to decrease after the development of acquired resistance to CDK4/6 inhibitors. Further, CDK4/6 inhibitor-resistant cells acquired cross-resistance to other CDK4/6 inhibitors, PI3K/Akt/mTOR inhibitor therapy and chemotherapeutic drugs might serve as optimal treatment options for such breast cancers.

The p21 levels have the potential to be a monitoring marker for ribociclib in breast cancer

Although cyclin-dependent kinase (CDK) 4/6 inhibitors have exhibited remarkable results for patients with estrogen receptor (ER)–positive breast cancer in clinical trials, the mechanism of CDK4/6 inhibitor resistance remains unclear. Thus, this study aimed to investigate the mechanism of CDK4/6 inhibitor resistance using two CDK4/6 inhibitor resistant breast cancer cell lines. We established CDK6 overexpressed cell lines (MCF7-C6) from MCF-7 cells using the stably transfected CDK6 expression vector. Additionally, acquired ribociclib-resistant (RIBR) cell lines were created using ER-positive hormone-resistant cell lines by long-term exposure to ribociclib. CDK6 overexpression and the knockdown of CDK4 experiments highlight the significance of high levels of CDK4 and low levels of CDK6 in CDK4/6 inhibitor sensitivity. Moreover, RIBR cell lines did not exhibit incremental CDK6 compared with ER-positive hormone-resistant cell lines. In MCF7-C6 and RIBR cell lines, p21 levels decreased, and p21 levels were proportional to CDK4/6 inhibitor sensitivity. This study suggests that overexpression of CDK6 is one of the many possible mechanisms of resistance to CDK4/6 inhibitors. Furthermore, p21 levels have the potential to serve as a marker for CDK4/6 inhibitors independent of the resistance mechanism.

Differential microRNA expression profiles determined by next-generation sequencing in three fulvestrant-resistant human breast cancer cell lines

Fulvestrant resistance is a major clinical issue in the treatment of endocrine-based breast cancer. MicroRNAs (miRNAs) are known to serve an important role in tumor chemoresistance. In the present study, the association between miRNA expression profiles and fulvestrant resistance was investigated in human breast cancer cell lines. Three fulvestrant-resistant breast cancer cell lines, namely MCF-7-CC, MCF-7-TT and MCF-7-21, were established using the human breast cancer cell line MCF-7 as the parental cell line and fulvestrant as the screening drug in vitro. Next-generation sequencing was used to determine the miRNA expression profiles in these cell lines. Subsequently, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to determine the biological functions of differentially expressed miRNAs. In total, 1,536 miRNAs were detected in all the samples, including 1,240 known miRNAs and 296 predicted miRNAs. It was observed that the differential miRNA expression profiles varied among the three fulvestrant-resistant cell lines (MCF-7-CC, MCF-7-TT and MCF-7-21), and certain differentially expressed miRNAs were only detected in one or two of the cell lines. A total of 257 miRNAs that were differentially expressed between MCF-7-CC and MCF-7 cells were detected, among which 69 miRNAs were upregulated and 188 miRNAs were downregulated. In addition, 270 miRNAs with significantly different expression between MCF-7-TT and MCF-7 cells were observed, including 180 upregulated and 90 downregulated miRNAs. Between MCF-7-21 and MCF-7 cells, a total of 227 miRNAs were differentially expressed, among which 52 miRNAs were upregulated and 175 miRNAs were downregulated. The miRNAs that were differentially expressed in the three fulvestrant-resistant cell lines as compared with the parental MCF-7 cell line were primarily involved in the following biological processes: Biological regulation, extracellular matrix-receptor interaction, the Notch signaling pathway and focal adhesion. Taken together, the results suggested that miR-143, miR-145, miR-137, miR-424 and miR-21 may serve important roles in fulvestrant resistance in breast cancer. The study findings may provide a basis for further research on the treatment of fulvestrant-resistant breast cancer.

Clinical and genetic risk factors for Fulvestrant treatment in post-menopause ER-positive advanced breast cancer patients

Background

Among breast cancer (BC) patients, near 40% are post-menopause, and 70%–80% are hormone receptor (HR)-positive. About 30%–40% BC patients who are diagnosed as invasive carcinoma HR-positive BC would eventually develop metastatic breast cancers. In 2016, FALCON trial proves Fulvestrant as an effective first-line endocrine therapy for post-menopause HR-positive advanced BC (ABC) patients. But even after FALCON published, Fulvestrant is rarely used as first-line in real world ABC patients in China.

Method

In this study, 136 Fulvestrant users were enrolled from 2015. To investigate the clinical and genetic risk factors for Fulvestrant treatment response in real world data, biostatistic and bioinformatic analysis tools were adopted.

Result

KM curves showed that Fulvestrant first-line users had a median progression-free survival (mPFS) of 15.67 months, which was longer than the second-line users and third (or higher)-line users (mPFS = 7.47 and 5.43 months, respectively). 16 s (or higher)-line users were voluntarily received circulating tumor DNA (ctDNA) testing after progression. ctDNA testing results showed that compared to patients with PFS longer than 6 months, Fulvestrant users with PFS less than 6 months had a significantly higher mutation rate of ESR1 or ERBB2 gene (0/6 vs 6/10, Fisher’s Exact p-value = 0.03). Multivariate COX regression analysis showed that clinical features, including lymph node metastasis and HER-2 positive, were significant risk factors for poor PFS [hazard ratio (HR) = 2.396 and 2.863, respectively]; high portion of estrogen receptor-positive cells was significant protective factor (HR = 0.663). Propensity-score matching (PMS) analysis suggested that visceral metastasis, prior palliative chemotherapy, and old age at Fulvestrant usage were not significant influential factor for PFS.

Conclusion

First-line Fulvestrant usage could guarantee a better prognosis than higher-line usage. ESR1 or ERBB2 mutation was found to be related to poor PFS in higher-line Fulvestrant users.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1734-x) contains supplementary material, which is available to authorized users.

Compensatory role of insulin-like growth factor 1 receptor in estrogen receptor signaling pathway and possible therapeutic target for hormone therapy-resistant breast cancer

BACKGROUND

Hormone therapy targeting the estrogen receptor (ER) pathway is the most common treatment used for ER-positive breast cancer. However, some patients experience de novo or acquired resistance, which becomes a critical problem. Activation of the insulin-like growth factor (IGF) pathway allows breast cancer cells to proliferate and is associated with the ER pathway. Little is known about the role of the IGF pathway in hormone therapy and resistance; therefore, we investigated whether the inhibition of this pathway may represent a novel therapeutic target for overcoming hormone therapy resistance in ER-positive breast cancers.

METHODS

Crosstalk between the ER and IGF pathways was analyzed in breast cancer cell lines by inhibiting or stimulating either one or both pathways. We studied the effect of insulin-like growth factor one receptor (IGF1R) inhibition in aromatase inhibitor-resistant breast cancer cell lines and fulvestrant-resistant cell lines which were uniquely established in our laboratory.

RESULTS

Under normal conditions, IGF signaling is controlled by ER signaling to promote cell growth. Temporary disruption of the estrogen supply results in attenuated ER signaling, and IGF-1 dramatically increased relative growth compared with normal conditions. In addition, IGF1R inhibitor strongly suppressd cell growth in hormone-resistant breast cancer cells where ER remains than cells where ER decreased or was almost lost.

CONCLUSIONS

Our study suggests that inhibition of the IGF pathway may be an effective strategy for ER-positive breast cancer therapy, even in hormone therapy-resistant cases.

Exosome-Mediated Transfer of Cancer Cell Resistance to Antiestrogen Drugs

Exosomes are small vesicles which are produced by the cells and released into the surrounding space. They can transfer biomolecules into recipient cells. The main goal of the work was to study the exosome involvement in the cell transfer of hormonal resistance. The experiments were performed on in vitro cultured estrogen-dependent MCF-7 breast cancer cells and MCF-7 sublines resistant to SERM tamoxifen and/or biguanide metformin, which exerts its anti-proliferative effect, at least in a part, via the suppression of estrogen machinery. The exosomes were purified by differential ultracentrifugation, cell response to tamoxifen was determined by MTT test, and the level and activity of signaling proteins were determined by Western blot and reporter analysis. We found that the treatment of the parent MCF-7 cells with exosomes from the resistant cells within 14 days lead to the partial resistance of the MCF-7 cells to antiestrogen drugs. The primary resistant cells and the cells with the exosome-induced resistance were characterized with these common features: decrease in ERα activity and parallel activation of Akt and AP-1, NF-κB, and SNAIL1 transcriptional factors. In general, we evaluate the established results as the evidence of the possible exosome involvement in the transferring of the hormone/metformin resistance in breast cancer cells.

Mechanisms of resistance to selective estrogen receptor down-regulator in metastatic breast cancer

Based on the prominent role estrogen receptor (ER) plays in breast cancer, endocrine therapy has been developed to block the ER pathway and has shown great effectiveness. Fulvestrant, the first selective ER down-regulator (SERD), was demonstrated to completely suppress ERα and notably efficient. However, resistance to fulvestrant occurs, either intrinsic or acquired during the treatment. Several potential mechanisms inducing fulvestrant resistance have been proposed, composed of activated ERα-independent compensatory growth factor signaling, stimulated downstream kinases, altered cell cycle mediators, etcetera. Experimentally, combinations of fulvestrant with targeted treatments were reported to eliminate the resistance and improve the effect of fulvestrant. Meanwhile, some clinical trials associated with the targeted combination therapies are in progress. This review focuses on the underlying mechanisms that contribute to fulvestrant resistance in ER-positive breast cancer and provides an overview of combined fulvestrant with targeted agents to shed light on optimal therapies for patients with ER-positive breast cancer.