Tamoxifen-resistant Disease Research Articles

Inhibition of O-GlcNAc transferase activates tumor-suppressor gene expression in tamoxifen-resistant breast cancer cells

In this study, we probed the importance of O-GlcNAc transferase (OGT) activity for the survival of tamoxifen-sensitive (TamS) and tamoxifen-resistant (TamR) breast cancer cells. Tamoxifen is an antagonist of estrogen receptor (ERα), a transcription factor expressed in over 50% of breast cancers. ERα-positive breast cancers are successfully treated with tamoxifen; however, a significant number of patients develop tamoxifen-resistant disease. We show that in vitro development of tamoxifen-resistance is associated with increased sensitivity to the OGT small molecule inhibitor OSMI-1. Global transcriptome profiling revealed that TamS cells adapt to OSMI-1 treatment by increasing the expression of histone genes. This is known to mediate chromatin compaction. In contrast, TamR cells respond to OGT inhibition by activating the unfolded protein response and by significantly increasing ERRFI1 expression. ERRFI1 is an endogenous inhibitor of ERBB-signaling, which is a known driver of tamoxifen-resistance. We show that ERRFI1 is selectively downregulated in ERα-positive breast cancers and breast cancers driven by ERBB2. This likely occurs via promoter methylation. Finally, we show that increased ERRFI1 expression is associated with extended survival in patients with ERα-positive tumors (p = 9.2e−8). In summary, we show that tamoxifen-resistance is associated with sensitivity to OSMI-1, and propose that this is explained in part through an epigenetic activation of the tumor-suppressor ERRFI1 in response to OSMI-1 treatment.

Abstract P3-05-04: Impact of androgen receptor expression in fluoxymesterone-treated, estrogen receptor–positive metastatic breast cancer exposed to contemporary hormonal therapy

Abstract Background: The use of the nonselective androgen fluoxymesterone in patients with metastatic breast cancer (MBC) diminished after the 1960s because of its adverse events and a limited understanding of its biological effects. Although fluoxymesterone has had efficacy against tamoxifen-resistant disease in clinical studies, its role in the era of contemporary hormonal therapy is unclear. Recent studies have shown that the androgen–androgen receptor (AR) complex acts as a suppressor of estrogen receptor (ER)+ breast cancer. We hypothesized that fluoxymesterone is effective against MBC that progresses despite contemporary hormonal therapy and that the drug has more clinical benefit in patients with ER+AR+ disease than in patients with ER+AR- disease. We evaluated the survival outcomes of patients with MBC who received fluoxymesterone after contemporary hormonal therapy failed and evaluated the association between ER/AR status and survival outcomes in these patients. Methods and Materials: We included 103 patients treated with fluoxymesterone who had already received at least one prior hormonal or cytotoxic treatment for MBC between January 1, 2000, and December 31, 2014, at a single institution. A pathologist reviewed these patients' tumors' ER and AR expression levels by immunohistochemical staining. Progression-free survival (PFS) was defined from the start of fluoxymesterone treatment to the date of disease progression or last follow-up. We used Cox regression analysis to examine univariate and multivariate correlates of PFS. Results: Patients received a median of 3 (range: 0-10) prior hormonal therapies (aromatase inhibitors, tamoxifen, and/or fulvestrant) before fluoxymesterone. Of the 103 patients, 33 (32%) discontinued fluoxymesterone because of physician decision or adverse events, which included toxicity in 14 patients, and 70 (68%) were eligible for tumor response assessment by Response Evaluation Criteria in Solid Tumors. Of these 70 patients, 2 (3%) had a complete response, 7 (10%) had a partial response, and 21 (30%) had stable disease for at least 6 months, yielding a clinical benefit rate of 43%. The median PFS was 3.9 months (95% confidence interval: 3.2–5.3 months). The multivariate analysis revealed no significant association between PFS and the type or number of prior treatments. Thirty-nine patients (38%) had archived tumor slides available for AR staining. All 39 patients had ER+ disease; 5 had ≤1%, 5 had >1% but <10%, 18 had ≥10%, and 11 had no AR nuclear expression. AR positivity defined by the presence of any AR+ cells, ≥1% AR+ cells, or ≥10% AR+ cells was not significantly associated with survival outcome. Conclusions: Fluoxymesterone showed objective tumor response and prolonged control of ER+ MBC refractory to contemporary endocrine therapy. The number and type of prior treatments did not impact the drug's clinical benefit, and AR+ status did not influence the clinical outcome. Fluoxymesterone should be considered for patients whose ER+ MBC progresses despite contemporary hormonal therapy, regardless of their AR status. Citation Format: Kono M, Fujii T, Lyons GR, Huo L, Bassett R, Gong Y, Karuturi MS, Tripathy D, Ueno NT. Impact of androgen receptor expression in fluoxymesterone-treated, estrogen receptor–positive metastatic breast cancer exposed to contemporary hormonal therapy [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-05-04.

Tipifarnib Plus Tamoxifen in Tamoxifen-Resistant Metastatic Breast Cancer: A Negative Phase II and Screening of Potential Therapeutic Markers by Proteomic Analysis

Tipifarnib, a farnesyltransferase inhibitor, has antitumor activity in heavily pretreated metastatic breast cancer patients. Preclinical data suggest that FTIs could restore tamoxifen responsiveness in tamoxifen-resistant disease. Thus, combining FTIs and tamoxifen may be a promising clinical approach after relapse or progression on tamoxifen. Postmenopausal patients with measurable estrogen receptor- and/or progesterone receptor-expressing metastatic breast cancers were enrolled. Only patients with disease progression on tamoxifen were eligible, but there was no limitation regarding prior chemotherapy or hormone therapy regimens. Patients were immediately treated with 300 mg (n = 12) or 200 mg (n = 10) tipifarnib twice daily for 21 of 28-day cycles plus tamoxifen once daily. Serum was collected at baseline and after 8 weeks of treatment to enable proteomic comparison and identify possible predictive response markers. Twenty patients were enrolled and evaluated for efficacy: one patient had an objective response (liver metastasis) and nine had stable disease after 6 months for a clinical benefit rate of 50%; median duration of benefit was 10.3 (range, 7.4-20.2) months. The proteomic analysis by SELDI-TOF and LTQ-FT-Orbitrap identified a known peptide of fibrinogen alpha, the intensity of which was significantly increased in patients with progression compared with patients who benefited from the combined treatment after 8 weeks. Because the primary end point of efficacy (three objective responses) was not achieved, the study is negative. Nevertheless, the identified peptide could be of interest in discriminating, at 8 weeks of treatment, responders from nonresponders.

Curcumin Modulates Tamoxifen Response in Resistant Breast Cancer Cells.

Abstract Despite significant improvement in both detection and treatment, breast cancer remains the second leading cause of cancer deaths for women in the United States. Tamoxifen is the most commonly used treatment for estrogen receptor positive (ER+) breast carcinoma, yet up to 50% of patients with metastatic disease present with de novo resistance to tamoxifen, and almost all patients will eventually become resistant to tamoxifen treatment. The mechanism(s) for this resistance appear to be largely dependent upon activation of growth factor signaling pathways. Aberrant activation of the PI3K/Akt and MAPK pathways and their cross talk with both the genomic and nongenomic activity of the ER is implicated in tamoxifen resistance. Breast cancer cell lines with constitutively activated Akt are characterized by high levels of the pro-survival transcription factor Nuclear Factor kappa B (NF-kB), estrogen-independent growth, and resistance to tamoxifen treatment. Studies have shown that curcumin, a polyphenol derived from the rhizome of the perennial herb Curcuma longa, is able to inhibit the activation of NF-kB, which is implicated as one mechanism by which breast cancer cells become resistant to tamoxifen treatment. Previous studies in our laboratory have demonstrated that inhibition of NF-kB is sufficient to sensitize MCF-7 cells that have constitutively activated Akt and elevated NF-kB levels to tamoxifen treatment. However, clinical NF-kB inhibitors such as Velcade generally involve suppression of the proteosome, leading to severe toxicities. Therefore, identification of alternative approaches for suppressing NF-kB activity in the absence of toxicity could prove beneficial for enhancing response to tamoxifen. In the present study, we assessed the efficacy of curcumin at inhibiting breast cancer cell proliferation and survival both as a single agent and in combination with tamoxifen in MCF-7 cells that expressed both “normal” levels of Akt (Control) activity as well as those that expressed the constitutively active form of Akt (myrAkt). As has been previously reported, curcumin treatment inhibited survival and proliferation in the Control MCF-7 cells, but importantly curcumin was also able to suppress survival and proliferation in the myrAKT MCF-7 cells. Curcumin and tamoxifen co-treatment was found to synergistically inhibit survival in myrAKT MCF-7 cells. These findings demonstrate that curcumin can sensitize myrAKT MCF-7 cells to tamoxifen treatment. This preliminary data suggests that the combination of natural NF-kB inhibitors such as curcumin with tamoxifen may be a viable strategy to either prevent tamoxifen resistant disease or to re-sensitize refractory disease to tamoxifen treatment. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3098.

Are current drug development programmes realising the full potential of new agents? Introduction to Sessions 7 and 8

Are current drug development programmes realising the full potential of new agents? Introduction to Sessions 7 and 8

Estrogen Receptors as Therapeutic Targets in Breast Cancer

The estrogen receptor α (ERα) has proven to be the single most important target in breast cancer over the last 30 years. The use of the selective ER modulator (SERM) tamoxifen for the treatment and prevention of breast cancer has changed therapeutics. The SERM raloxifene, approved for the treatment of osteoporosis, lacks tamoxifens increased risk for endometrial cancer and is being evaluated for the prevention of breast cancer. Other SERMs approved or under development for use against breast cancer or osteoporosis include toremifene, GW5638, GW7604 (the active metabolite of GW5638), idoxifene, lasofoxifene, arzoxifene, bazedoxifene, EM-800 and acolbifene (the active metabolite of EM- 800). Aromatase inhibitors (AIs) have recently proven to be more efficacious than tamoxifen as first-line therapy, efficacious for second-line therapy (e.g. against tamoxifen-resistant disease), and useful for extended adjuvant therapy after tamoxifen. The AIs include the non-steroidal agents letrozole and anastrole, and the steroidal agent exemestane. The pure antiestrogen fulvestrant has proven to be just as effective as AIs. Other pure antiestrogens, ZK-703, ZK-253, RU 58668 and TAS-108 show great promise. The development of resistance to endocrine therapy remains a clinically important problem, and laboratory models based on human breast cancer cells grown as tumors in immune-compromised mice have led to important insights into this problem. Progesterone receptor-negative status of ER-positive breast cancers may reflect altered growth factor receptor signaling, and helps to explain why this subclass of tumors exhibits lower response rates to tamoxifen compared to cancers typed progesterone receptor-positive. Crosstalk among plasma membrane-localized ER, growth factor receptor signaling, and nuclear-localized ER provide further insights into antihormonal-resistant breast cancer. Keywords: Estrogen receptor, selective estrogen receptor modulator, aromatase inhibitor, pure antiestrogen, breast cancer, antihormonal resistance

Life following aromatase inhibitors – where now for endocrine sequencing?

The third-generation non-steroidal aromatase inhibitors (AIs) are challenging tamoxifen as treatments of choice for early and advanced breast cancer in postmenopausal women with estrogen receptor (ER)-positive disease. However, patients who initially respond to AIs eventually develop resistance to treatment and experience disease progression. To establish the optimal endocrine therapy following AI resistance, it is essential to understand the mechanisms that contribute to the loss of response. Data from in vitro models have suggested that acquired AI resistance is due to enhanced sensitization to low estrogen levels during long-term estrogen deprivation (LTED). Cross-talk between the ER and various growth-factor-receptor signaling pathways, including human epidermal growth factor receptor 2, and the insulin-like growth factor pathway, may also be implicated. Therefore, endocrine therapies that abolish estrogen signaling via removal of the ER could be effective in patients with AI-resistant disease. Fulvestrant ('Faslodex') is a new ER antagonist with no agonist effects that binds, blocks and degrades the ER. Due to its unique mode of action and lack of cross-resistance with existing treatments, fulvestrant is an effective therapeutic agent for use in sequential endocrine regimens. Fulvestrant has established efficacy in tamoxifen-resistant disease and there is a growing body of evidence demonstrating its efficacy in patients with AI-resistant disease. In preclinical models, MCF-7 cells undergoing LTED are refractory to tamoxifen but sensitive to fulvestrant, suggesting fulvestrant is a more appropriate choice following AI resistance. The steroidal AI, exemestane is also an option in non-steroidal AI-resistant disease. Clinical trials are underway to compare fulvestrant with exemestane as an appropriate therapy following the onset of AI resistance.

Selective oestrogen receptor modulators, aromatase inhibitors and the female breast

Tamoxifen has been available for over 20 years and remains the most commonly recognized endocrine therapy. This review was prompted by a wealth of new data on several newer endocrine agents, including selective oestrogen receptor modulators, aromatase inhibitors and a new oestrogen receptor antagonist, fulvestrant, which unlike the selective oestrogen receptor modulators has no oestrogen agonist effects. Completed analysis of the 'Arimidex', Tamoxifen, Alone or in Combination trial demonstrated that anastrozole as initial adjuvant therapy significantly improved disease-free survival and time to recurrence compared with tamoxifen, as well as reducing the incidence of contralateral breast cancer deaths. The Italian Tamoxifen Anastrozole trial and the Austrian Breast and Colorectal Cancer Study Group 8/Arimidex Nolvadex 95 trial have indicated that anastrozole may also be beneficial in women who have already received 2-3 years of tamoxifen. Similarly, the Intergroup Exemestane Study demonstrated the efficacy of exemestane in this setting. Women who have completed a full 5-year course of tamoxifen may also benefit from aromatase inhibitor treatment as indicated by the MA 17 trial, which investigated letrozole as extended adjuvant therapy. Fulvestrant is effective in tamoxifen-resistant disease, and phase II trial data suggest that fulvestrant may also be effective following aromatase inhibitor failure. The introduction of the third-generation aromatase inhibitors has caused a paradigm shift in adjuvant endocrine treatment. Research into the optimal use of selective oestrogen receptor modulators continues and the evidence base for fulvestrant, the first in a new class of endocrine agents, continues to grow, confirming its value in the treatment of hormone-responsive breast cancer.

A comparison of fulvestrant and the third-generation aromatase inhibitors in the second-line treatment of postmenopausal women with advanced breast cancer

Fulvestrant, a new type of oestrogen receptor antagonist with no agonist effects, is now licensed in the EU and USA for the treatment of postmenopausal women with hormone-sensitive advanced breast cancer following progression on prior antioestrogen therapy. Approval was based on data from two phase III trials that demonstrated fulvestrant was at least as effective as the third-generation aromatase inhibitor (AI) anastrozole as a second-line treatment for advanced breast cancer. The third-generation AIs letrozole and exemestane also demonstrate efficacy after tamoxifen failure. To compare the performance of fulvestrant and contemporary endocrine treatments (anastrozole, letrozole and exemestane) in tamoxifen-resistant disease, we conducted a literature review using the PubMed database. These indirect comparisons suggest that fulvestrant offers similar efficacy and tolerability to other second-line treatments for postmenopausal women with advanced breast cancer. Findings from these comparisons support the use of fulvestrant as an additional second-line endocrine treatment option in this setting. New trials are assessing the efficacy of fulvestrant as a second-line treatment following AI failure. The integration of new agents such as fulvestrant into the endocrine sequence may extend the endocrine treatment window, before cytotoxic chemotherapy needs to be considered, and therefore improve patient quality of life.

Endocrine treatment options for advanced breast cancer – the role of fulvestrant

For many years, tamoxifen has been the ‘gold standard’ amongst anti-oestrogen therapies for breast cancer. However, the selective aromatase inhibitors (AIs), anastrozole, letrozole and exemestane, have demonstrated advantages over tamoxifen as first-line treatments for advanced disease. Anastrozole is also more effective as an adjuvant treatment in early, operable breast cancer and is being increasingly used in the adjuvant setting. Generally, the selective oestrogen receptor modulators (SERMs), such as toremifene, droloxifene, idoxifene, raloxifene, and arzoxifene, show minimal activity in tamoxifen-resistant disease and show no superiority over tamoxifen as first-line treatments. In addition to these agents, other treatment options for advanced disease include high-dose oestrogens and progestins. Response rates for high-dose oestrogens and tamoxifen are similar, but the use of oestrogens is limited by their toxicity profile. Consequently, there is a need for new endocrine treatment options for breast cancer, particularly for use in disease that is resistant to tamoxifen or AIs. Fulvestrant (‘Faslodex’) is a new type of steroidal oestrogen receptor (ER) antagonist that downregulates cellular levels of the ER and progesterone receptor and has no agonist activity. This paper reviews the key efficacy and tolerability data for fulvestrant in postmenopausal women in the context of other endocrine therapies and explores the potential role of fulvestrant within the sequencing of endocrine therapies for advanced breast cancer.

Fulvestrant: a review of its use in hormone receptor-positive metastatic breast cancer in postmenopausal women with disease progression following antiestrogen therapy.

Fulvestrant (Faslodex) is a novel estrogen receptor (ER) antagonist that competitively binds to the ER with a much greater affinity than that of tamoxifen. The downregulation of cellular levels of the ER protein results in complete abrogation of estrogen-sensitive gene transcription. This distinct mechanism of action ensures a lack of cross resistance with other hormonal agents and, in contrast to tamoxifen, fulvestrant has no known estrogen-agonist effects. Fulvestrant is administered via monthly intramuscular injections (250mg) and is recommended for the treatment of hormone receptor-positive metastatic breast cancer in postmenopausal women with disease progression following antiestrogen therapy. The efficacy of fulvestrant was similar to that of the aromatase inhibitor anastrozole (1 mg/day) in two, well designed studies in postmenopausal women with locally advanced or metastatic breast cancer that had progressed during prior antiestrogen therapy. Time to disease progression (primary endpoint) and treatment failure, rates of objective response and clinical benefit, overall survival and quality of life were similar in patients treated with fulvestrant or anastrozole. In retrospective noninferiority analyses, fulvestrant was at least as effective as anastrozole in all randomised patients, and in those with or without visceral metastases. Fulvestrant is generally well tolerated and was tolerated as well as anastrozole in clinical trials. Treatment-related adverse events were mostly mild to moderate and led to treatment withdrawal in about 1% of patients who received fulvestrant or anastrozole. The main adverse effects associated with therapy are nausea, asthenia, pain, vasodilation and headache.In conclusion, monthly intramuscular injections of fulvestrant are at least as effective and as well tolerated as oral anastrozole once daily in the treatment of postmenopausal women with advanced breast cancer that has progressed on prior antiestrogen therapy. Because of a different mode of action to that of other hormonal agents, fulvestrant is effective in the treatment of tamoxifen-resistant disease and, unlike tamoxifen, has no known estrogen agonist effects. Thus, fulvestrant provides an effective and well tolerated option for the treatment of hormone receptor-positive metastatic breast cancer in postmenopausal women with disease progression following antiestrogen therapy.

Chemoprevention for high-risk women: tamoxifen and beyond.

The demonstration by the National Surgical Adjuvant Breast Project (NSABP) that 5 years of tamoxifen therapy is associated with an approximate 50% reduction in breast cancer incidence in high-risk women was a milestone in breast cancer prevention. Because tamoxifen is associated with increased risk of side-effects such as hot flashes, menstrual abnormalities, uterine cancer, and thromboembolic phenomena, its use will not be advisable or acceptable for all high-risk women. Women over 50 years of age appear to be at highest risk for serious adverse events, such as uterine cancer and thromboembolic phenomena. Individuals in whom tamoxifen-associated breast cancer risk reduction appears to outweigh risk of serious side-effects include women with prior in situ or estrogen receptor (ER)-positive invasive cancer, atypical hyperplasia, and/or women ages 35-49 with a calculated Gail 5-year risk of > or =1.7%, hysterectomized women aged 50 and older with a 5-year Gail risk of > or =2.5%, and nonhysterectomized women aged 50 and older with a 5-year Gail risk of >5.0%. It is not yet clear whether tamoxifen can reduce breast cancer incidence in women with BRCA1 and BRCA2 mutations, although preliminary evidence favors benefit for at least those with a BRCA2 mutation. Raloxifene is a selective ER modulator with less uterine estrogen agonist activity than tamoxifen, and it is hoped that it will result in fewer uterine cancers but will be equally efficacious in reducing the risk of breast cancer. The NSABP is currently conducting a randomized study of tamoxifen versus raloxifene in high-risk postmenopausal women. Approximately one third of invasive cancers are ER negative. Tamoxifen does not reduce the incidence of ER-negative cancers, nor does it appear to be effective in preventing the appearance of one third of ER-positive cancers. Priorities in prevention research are to develop (a) biomarkers to refine short-term risk assessments based on epidemiologic models, (b) biomarkers predictive of response to specific classes of preventive agents, (c) drugs with fewer side-effects and/or effective in ER-negative or ER-positive tamoxifen-resistant precancerous disease, and (d) efficient clinical trial models to assess new agent efficacy. Breast intraepithelial neoplasia (IEN) may be sampled by minimally invasive techniques and is an attractive short-term risk biomarker. Molecular abnormalities observed in IEN may be used to select potential agents for testing/therapy, and modulation of these abnormalities may be used in phase I trials to select appropriate doses and in phase II trials to assess response. Breast density volume and certain serum markers such as insulin-like growth factor-1 are also being studied as potential risk and response biomarkers. Reversal or prevention of advanced IEN as well as modulation of other risk biomarkers in randomized phase II and phase III trials is being evaluated as a means of more efficiently evaluating prevention drugs in the future. A number of agents are being developed that target molecular abnormalities in IEN, have fewer or different side effects than tamoxifen, and may be effective in ER-negative or tamoxifen-resistant disease.