Overcoming endocrine resistance in breast cancer: importance of mTOR inhibition

Approaches to treatment for many patients with advanced breast cancer are based on the expression of specific receptors. Treatments targeting the hormone receptor (typically the estrogen receptor) are used to reduce signaling through these receptors and thereby inhibit proliferation of breast cancer cells expressing these receptors. Although these treatments are effective for many patients, resistance to treatment is common. Recent clinical trials suggest that using multiple agents targeting the same pathway is not sufficient to overcome resistance. New treatment approaches are needed for these patients. Inhibition of the mTOR signaling pathway, a key point of confluence for multiple signaling cascades, offers a promising approach to restoring sensitivity to endocrine therapy in breast cancer. This article reviews the current data from studies of mTOR inhibitors everolimus and temsirolimus in combination with endocrine therapies to overcome treatment resistance in patients with advanced breast cancer.     

mTOR表达与雌激素受体阳性乳腺癌辅助内分泌治疗预后的关系

目的探讨雌激素受体（estrogen receptor,ER）阳性乳腺癌中mTOR蛋白的表达与乳腺癌辅助内分泌治疗预后间的关系。方法采用免疫组化方法检测60例ER阳性且接受内分泌辅助治疗患者的原发乳腺癌组织中p-mTOR蛋白的表达情况,观察mTOR蛋白的表达特点.并分析其与临床特征间的关系及对无病生存的影响。结果 mTOR蛋白强阳性表达的乳腺癌细胞具有更多的组织学恶性特征,mTOR阴性组中位无病生存（56.4个月）显著优于阳性组（33.5个月）（P=0.015）,多因素回归分析中mTOR为阳性者发生肿瘤复发转移的风险比例（HR）是mTOR阴性者的3.212倍,其95%CI为1.291～7.992。结论 mTOR表达状态为ER阳性是乳腺癌复发转移的独立预后因素,提示辅助内分泌治疗联合mTOR抑制剂可为ER阳性乳腺癌患者带来生存获益。     

Disulfiram targets cancer stem-like cells and reverses resistance and cross-resistance in acquired paclitaxel-resistant triple-negative breast cancer cells

Background:

Triple-negative breast cancer (TNBC) has significantly worse prognosis. Acquired chemoresistance remains the major cause of therapeutic failure of TNBC. In clinic, the relapsed TNBC is commonly pan-resistant to various drugs with completely different resistant mechanisms. Investigation of the mechanisms and development of new drugs to target pan-chemoresistance will potentially improve the therapeutic outcomes of TNBC patients.

Methods:

In this study, 1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), combination index (CI)–isobologram, western blot, ALDEFLUOR analysis, clonogenic assay and immunocytochemistry were used.

Results:

The chemoresistant MDA-MB-231_PAC10 cells are highly cross-resistant to paclitaxel (PAC), cisplatin (CDDP), docetaxel and doxorubicin. The MDA-MB-231_PAC10 cells are quiescent with significantly longer doubling time (64.9 vs 31.7 h). This may be caused by high expression of p21^Waf1. The MDA-MB-231_PAC10 cells express high aldehyde dehydrogenase (ALDH) activity and a panel of embryonic stem cell-related proteins, for example, Oct4, Sox2, Nanog and nuclealisation of HIF2α and NF-κBp65. We have previously reported that disulfiram (DS), an antialcoholism drug, targets cancer stem cells (CSCs) and enhances cytotoxicity of anticancer drugs. Disulfiram abolished CSC characters and completely reversed PAC and CDDP resistance in MDA-MB-231_PAC10 cells.

Conclusion:

Cancer stem cells may be responsible for acquired pan-chemoresistance. As a drug used in clinic, DS may be repurposed as a CSC inhibitor to reverse the acquired pan-chemoresistance.     

Akt-induced endocrine therapy resistance is reversed by inhibition of mTOR signaling.

BACKGROUND: Resistance to endocrine therapy is a major impediment in breast cancer therapeutics. The Phosphatidylinositol-3-OH kinase (PI3K)/Protein kinase B (Akt/PKB) kinase signaling pathway has been implicated in altering breast cancer response to multiple therapies. How Akt modulates response is an area of significant clinical relevance. METHODS: We have used an in vitro model to discern the effects of robust Akt activity on breast cancer cellular response to endocrine therapies. RESULTS: High levels of Akt activity confer resistance to the aromatase inhibitor Letrozole (Let) and the selective estrogen receptor (ER) down-regulator Fulvestrant (ICI). Akt-induced resistance is not due to failure of these endocrine agents to inhibit estrogen receptor alpha activity. Instead, resistance is characterized by altered cell cycle and apoptotic response. Cotreatment with low concentrations of the mTOR inhibitor RAD-001 and either Let or ICI restores response of the resistant cells to levels observed in the responsive cells treated with either Let or ICI as a single agent. CONCLUSIONS: Our preliminary findings in experiments with RAD-001 indicate that cotreatment with mTOR inhibitors and either Let or ICI reverses the Akt-mediated resistance and restores responsiveness to antiestrogens. Concurrent ER and mTOR inhibition is therefore an effective strategy to overcome growth factor-induced resistance and bears significant implications for optimal clinical development of these agents in breast cancer treatment.     

mTOR 抑制剂在乳腺癌内分泌及 HER-2靶向治疗耐药中的研究进展

哺乳动物雷帕霉素靶蛋白（mTOR）位于磷脂酰肌醇3激酶（PI3K）-蛋白激酶 B（Akt）细胞信号通路的下游,已有研究表明该通路的异常激活与乳腺癌的内分泌及抗人表皮生长因子受体-2（HER-2）的靶向治疗耐药相关。在既往传统药物的基础上通过联合 mTOR 抑制剂阻断该条通路的异常活化,在防止肿瘤细胞的耐药性发展及恢复初始敏感性方面均体现出了良好的应用前景,mTOR 抑制剂将有望成为乳腺癌治疗的新希望。     

乳腺癌内分泌治疗耐药相关机制的研究进展

内分泌治疗作为雌激素受体（estrogen receptor,ER）阳性乳腺癌的主要治疗方案被广泛应用。他莫西芬（tamoxifen,Tam）是乳腺癌内分泌治疗最常用的药物,它通过与雌激素竞争性结合ERα来降低雌激素的生物学活性,抑制细胞的增殖,从而治疗乳腺癌。然而,肿瘤细胞所表现出的原发性或获得性的他莫西芬耐药使得其临床应用受到了限制,寻找克服他莫西芬耐药的治疗策略已经刻不容缓。目前为止,他莫西芬耐药的相关机制已部分明确,但仍需进一步研究。有证据表明ERα、生长因子受体信号通路及microRNA的表达异常等多种机制均与他莫西芬耐药有关。本文对他莫西芬耐药的相关机制进行了具体分析,以期为ER阳性乳腺癌的治疗提供新思路。     

Tetramethylpyrazine reverses multidrug resistance in breast cancer cells through regulating the expression and function of P-glycoprotein

Tumor multidrug resistance (MDR) has become the major obstacle to cancer chemotherapy. Recent studies suggest that tetramethylpyrazine (TMP) could reverse tumor MDR although the mechanism by which TMP overcomes tumor MDR remains elusive. Therefore, in this study, we examined the effects of TMP on MDR in drug-resistant breast cancer cells and investigated the underlying mechanisms. MCF-7 cells and the derived P-glycoprotein (Pgp) overexpressing MCF-7/dox cells were treated with TMP, and their growth was examined by MTT assay. Doxorubicin accumulation in the cells was evaluated by flow cytometry, and the expression of Pgp was detected by Western blot and RT–PCR analysis. The results showed that TMP increased the intracellular concentration of doxorubicin and inhibited Pgp-mediated efflux of doxorubicin in a dose-dependent manner. Moreover, TMP inhibited the ATPase activity of P-gp and suppressed the expression of Pgp in MCF-7/dox cells. Taken together, these data suggest that TMP has potential application in the treatment of chemotherapy-resistant breast cancer.     

Impact of dual mTORC1/2 mTOR kinase inhibitor AZD8055 on acquired endocrine resistance in breast cancer in vitro

Introduction

Upregulation of PI3K/Akt/mTOR signalling in endocrine-resistant breast cancer (BC) has identified mTOR as an attractive target alongside anti-hormones to control resistance. RAD001 (everolimus/Afinitor®), an allosteric mTOR inhibitor, is proving valuable in this setting; however, some patients are inherently refractory or relapse during treatment requiring alternative strategies. Here we evaluate the potential for novel dual mTORC1/2 mTOR kinase inhibitors, exemplified by AZD8055, by comparison with RAD001 in ER + endocrine resistant BC cells.

Methods

In vitro models of tamoxifen (TamR) or oestrogen deprivation resistance (MCF7-X) were treated with RAD001 or AZD8055 alone or combined with anti-hormone fulvestrant. Endpoints included growth, cell proliferation (Ki67), viability and migration, with PI3K/AKT/mTOR signalling impact monitored by Western blotting. Potential ER cross-talk was investigated by immunocytochemistry and RT-PCR.

Results

RAD001 was a poor growth inhibitor of MCF7-derived TamR and MCF7-X cells (IC₅₀ ≥1 μM), rapidly inhibiting mTORC1 but not mTORC2/AKT signalling. In contrast AZD8055, which rapidly inhibited both mTORC1 and mTORC2/AKT activity, was a highly effective (P <0.001) growth inhibitor of TamR (IC₅₀ 18 nM) and MCF7-X (IC₅₀ 24 nM), and of a further T47D-derived tamoxifen resistant model T47D-tamR (IC₅₀ 19 nM). AZD8055 significantly (P <0.05) inhibited resistant cell proliferation, increased cell death and reduced migration. Furthermore, dual treatment of TamR or MCF7-X cells with AZD8055 plus fulvestrant provided superior control of resistant growth versus either agent alone (P <0.05). Co-treating with AZD8055 alongside tamoxifen (P <0.01) or oestrogen deprivation (P <0.05) also effectively inhibited endocrine responsive MCF-7 cells. Although AZD8055 inhibited oestrogen receptor (ER) ser167 phosphorylation in TamR and MCF7-X, it had no effect on ER ser118 activity or expression of several ER-regulated genes, suggesting the mTOR kinase inhibitor impact was largely ER-independent. The capacity of AZD8055 for ER-independent activity was further evidenced by growth inhibition (IC₅₀18 and 20 nM) of two acquired fulvestrant resistant models lacking ER.

Conclusions

This is the first report demonstrating dual mTORC1/2 mTOR kinase inhibitors have potential to control acquired endocrine resistant BC, even under conditions where everolimus fails. Such inhibitors may prove of particular benefit when used alongside anti-hormonal treatment as second-line therapy in endocrine resistant disease, and also potentially alongside anti-hormones during the earlier endocrine responsive phase to hinder development of resistance.     

Fumitremorgin C reverses multidrug resistance in cells transfected with the breast cancer resistance protein

Fumitremorgin C (FTC) is a potent and specific chemosensitizing agent in cell lines selected for resistance to mitoxantrone that do not overexpress P-glycoprotein or multidrug resistance protein. The gene encoding a novel transporter, the breast cancer resistance protein (BCRP), was recently found to be overexpressed in a mitoxantrone-selected human colon cell line, S1-M1-3.2, which was used to identify FTC. Because the drug-selected cell line may contain multiple alterations contributing to the multidrug resistance phenotype, we examined the effect of FTC on MCF-7 cells transfected with the BCRP gene. We report that FTC almost completely reverses resistance mediated by BCRP in vitro and is a pharmacological probe for the expression and molecular action of this transporter.     

乳腺癌内分泌治疗耐药机制的研究进展

内分泌治疗是雌激素受体阳性乳腺癌的重要系统治疗手段,但原发性与继发性耐药是当前内分泌治疗面临的难题。耐药机制主要包括:ER表达缺失或表观遗传修饰;共调因子表达失衡;雌激素受体通路与生长因子受体（growth factor receptor,GFR）通路的交叉效应;特异性miRNA表达改变;乳腺癌上皮间质转化（EMT）等。根据PubMed检索获取相关资料,就近年来雌激素受体阳性乳腺癌内分泌耐药机制及治疗策略研究进展进行综述。     

GPR30在乳腺癌内分泌治疗耐受中的作用研究

G蛋白偶联受体-30(G protein-coupled receptor 30,GPR30)是一种新型膜性结合性雌激素受体(estrogen receptor,ER).他莫昔芬(tamoxifen,TAM)及其代谢产物44}他莫昔芬(4-hydroxtamoxifen,OHT)是GPR30激动剂.GPR30的激活可能导致TAM耐药性的发生,GPR30可反式激活表皮生长因子受体(epidermal growth factor receptor,EGFR),介导E2增殖效应,可能与ERα具有协同作用,参与乳腺癌细胞增殖、侵袭和转移等行为.TAM作为ERα(+)的竞争性抑制剂,在乳腺癌内分泌治疗中占据着重要的地位,但是长期应用TAM的耐药限制了其临床应用.EGFR及ER相关信号途径,在TAM耐药机制中扮演重要角色.研究证实GPR30可反转TAM变成促生长激动剂,促进肿瘤生长.本文从GPR30的作用机制和TAM的耐药性机制联系为出发点,探讨GPR30在TAM耐药性中的作用.     

Loss of function of NF1 is a mechanism of acquired resistance to endocrine therapy in lobular breast cancer

BackgroundInvasive lobular carcinoma (ILC) as a disease entity distinct from invasive ductal carcinoma (IDC) has merited focused studies of the genomic landscape, but those to date are largely limited to the assessment of early-stage cancers. Given that genomic alterations develop as acquired resistance to endocrine therapy, studies on refractory ILC are needed.Patients and methodsTissue from 336 primary-enriched, breast-biopsied ILC and 485 estrogen receptor (ER)-positive IDC and metastatic biopsy specimens from 180 ILC and 191 ER-positive IDC patients was assayed with hybrid-capture-based comprehensive genomic profiling for short variant, indel, copy number variants, and rearrangements in up to 395 cancer-related genes.ResultsWhereas ESR1 alterations are enriched in the metastases of both ILC and IDC compared with breast specimens, NF1 alterations are enriched only in ILC metastases (mILC). NF1 alterations are predominantly under loss of heterozygosity (11/14, 79%), are mutually exclusive with ESR1 mutations [odds ratio = 0.24, P<0.027] and are frequently polyclonal in ctDNA assays. Assessment of paired specimens shows that NF1 alterations arise in the setting of acquired resistance. An in vitro model of CDH1 mutated ER-positive breast cancer demonstrates that NF1 knockdown confers a growth advantage in the presence of 4-hydroxy tamoxifen. Our study further identified a significant increase in tumor mutational burden (TMB) in mILCs relative to breast ILCs or metastatic IDCs (8.9% >20 mutations/mb; P<0.001). Most TMB-high mILCs harbor an APOBEC trinucleotide signature (14/16; 88%).ConclusionsThis study identifies alteration of NF1 as enriched specifically in mILC. Mutual exclusivity with ESR1 alterations, polyclonality in relapsed ctDNA, and de novo acquisition suggest a role for NF1 loss in endocrine therapy resistance. Since NF1 loss leads to RAS/RAF kinase activation, patients may benefit from a matched inhibitor. Moreover, for an independent subset of mILC, TMB was elevated relative to breast ILC, suggesting possible benefit from immune checkpoint inhibitors.     

Inhibition of mitochondrial glutaminase activity reverses acquired erlotinib resistance in non-small cell lung cancer

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) erlotinib has been approved based on the clinical benefit in non-small cell lung cancer (NSCLC) patients over the past decade. Unfortunately, cancer cells become resistant to this agent via various mechanisms, and this limits the improvement in patient outcomes. Thus, it is urgent to develop novel agents to overcome erlotinib resistance. Here, we propose a novel strategy to overcome acquired erlotinib resistance in NSCLC by inhibiting glutaminase activity. Compound 968, an inhibitor of the glutaminase C (GAC), when combined with erlotinib potently inhibited the cell proliferation of erlotinib-resistant NSCLC cells HCC827ER and NCI-H1975. The combination of compound 968 and erlotinib not only decreased GAC and EGFR protein expression but also inhibited GAC activity in HCC827ER cells. The growth of erlotinib-resistant cells was glutamine-dependent as proved by GAC gene knocked down and rescue experiment. More importantly, compound 968 combined with erlotinib down-regulated the glutamine and glycolysis metabolism in erlotinib-resistant cells. Taken together, our study provides a valuable approach to overcome acquired erlotinib resistance by blocking glutamine metabolism and suggests that combination of EGFR-TKI and GAC inhibitor maybe a potential treatment strategy for acquired erlotinib-resistant NSCLC.     

乳腺癌内分泌治疗耐药分子机制的研究进展

乳腺癌内分泌治疗针对激素受体阳性乳腺癌患者,但内分泌治疗的疗效却受到耐药的限制。随着高通量二代测序技术和基因组学研究的进展,乳腺癌内分泌治疗耐药的分子机制得到深入研究。ESR1基因、细胞生长旁路途径、细胞周期检查点等发生改变均可能导致乳腺癌的内分泌治疗耐药。目前,针对其中某些与肿瘤发生、发展和转移密切相关的分子靶点已研制出新型的靶向药物。利用靶向治疗联合内分泌治疗来克服特定人群的内分泌治疗耐药现象,可为激素受体阳性乳腺癌患者的精准治疗提供更多的选择。笔者就乳腺癌内分泌治疗耐药的分子机制及其可能克服耐药的靶向治疗进行综述。     

Cannibalism,cell survival,and endocrine resistance in breast cancer

Breast cancer cells often respond to an endocrine therapy by altering expression of specific estrogen-responsive genes and inducing autophagy, a cannibalistic lysosomal pathway. Autophagy eliminates damaged or other organelles, allowing the recovery of the energy stored in their macromolecules to attempt restoration of metabolic homeostasis. Induction of autophagy can result from activation of the unfolded protein response following metabolic stress, the final cell fate often being determined by the extent and duration of autophagy. A study by Gonzalez-Malerva and colleagues builds upon this extensive knowledge, adding HSPB8 to the list of altered genes associated with endocrine resistance in breast cancer and describing the ability of HSPB8 to regulate autophagy and confer tamoxifen resistance.