Response after withdrawal of tamoxifen and progestogens in advanced breast cancer

Alternating 17β-Estradiol and Aromatase Inhibitor Therapies Is Efficacious in Postmenopausal Women with Advanced Endocrine-Resistant ER+ Breast Cancer

PURPOSE

Strategies to implement estrogen therapy for advanced estrogen receptor-positive (ER+) breast cancer are underdeveloped. Preclinical data suggest that cycling treatment with 17β-estradiol followed by estrogen deprivation can control tumor growth long-term.

PATIENTS AND METHODS

Postmenopausal women with advanced ER+/HER2- breast cancer with recurrence or progression on ≥ 1 antiestrogen or aromatase inhibitor (AI)-based therapy were eligible. Patients received 17β-estradiol (2 mg orally, three times a day) for 8 weeks followed by AI (physician's choice) for 16 weeks, alternating treatments on an 8-week/16-week schedule until disease progression. Patients then optionally received continuous single-agent treatment until a second instance of disease progression. Endpoints included 24-week clinical benefit and objective response per RECIST, and tumor genetic alterations.

RESULTS

Of 19 evaluable patients, clinical benefit rate was 42.1% [95% confidence interval (CI), 23.1%-63.9%] and objective response rate (ORR) was 15.8% (95% CI, 5.7%-37.9%). One patient experienced a grade 3 adverse event related to 17β-estradiol. Among patients who received continuous single-agent treatment until a second instance of disease progression, clinical benefit was observed in 5 of 12 (41.7%) cases. Tumor ER (ESR1) mutations were found by whole-exome profiling in 4 of 7 (57.1%) versus 2 of 9 (22.2%) patients who did versus did not experience clinical benefit from alternating 17β-estradiol/AI therapy. The only two patients to experience objective responses to initial 17β-estradiol had tumor ESR1 mutations.

CONCLUSIONS

Alternating 17β-estradiol/AI therapy may be a promising treatment for endocrine-refractory ER+ breast cancer, including following progression on CDK4/6 inhibitors or everolimus. Further study is warranted to determine whether the antitumor activity of 17β-estradiol differs according to ESR1 mutation status.

A Distinct Chromatin State Drives Therapeutic Resistance in Invasive Lobular Breast Cancer

Most invasive lobular breast cancers (ILC) are of the luminal A subtype and are strongly hormone receptor-positive. Yet, ILC is relatively resistant to tamoxifen and associated with inferior long-term outcomes compared with invasive ductal cancers (IDC). In this study, we sought to gain mechanistic insights into these clinical findings that are not explained by the genetic landscape of ILC and to identify strategies to improve patient outcomes. A comprehensive analysis of the epigenome of ILC in preclinical models and clinical samples showed that, compared with IDC, ILC harbored a distinct chromatin state linked to gained recruitment of FOXA1, a lineage-defining pioneer transcription factor. This resulted in an ILC-unique FOXA1-estrogen receptor (ER) axis that promoted the transcription of genes associated with tumor progression and poor outcomes. The ILC-unique FOXA1-ER axis led to retained ER chromatin binding after tamoxifen treatment, which facilitated tamoxifen resistance while remaining strongly dependent on ER signaling. Mechanistically, gained FOXA1 binding was associated with the autoinduction of FOXA1 in ILC through an ILC-unique FOXA1 binding site. Targeted silencing of this regulatory site resulted in the disruption of the feed-forward loop and growth inhibition in ILC. In summary, ILC is characterized by a unique chromatin state and FOXA1-ER axis that is associated with tumor progression, offering a novel mechanism of tamoxifen resistance. These results underscore the importance of conducting clinical trials dedicated to patients with ILC in order to optimize treatments in this breast cancer subtype.

SIGNIFICANCE

A unique FOXA1-ER axis in invasive lobular breast cancer promotes disease progression and tamoxifen resistance, highlighting a potential therapeutic avenue for clinical investigations dedicated to this disease. See related commentary by Blawski and Toska, p. 3668.

Estrogen therapy induces an unfolded protein response to drive cell death in ER+ breast cancer

Estrogens have been shown to elicit anticancer effects against estrogen receptor α (ER)-positive breast cancer. We sought to determine the mechanism underlying the therapeutic response. Response to 17β-estradiol was assessed in ER+ breast cancer models with resistance to estrogen deprivation: WHIM16 patient-derived xenografts, C7-2-HI and C4-HI murine mammary adenocarcinomas, and long-term estrogen-deprived MCF-7 cells. As another means to reactivate ER, the anti-estrogen fulvestrant was withdrawn from fulvestrant-resistant MCF-7 cells. Transcriptional, growth, apoptosis, and molecular alterations in response to ER reactivation were measured. 17β-estradiol treatment and fulvestrant withdrawal induced transcriptional activation of ER, and cells adapted to estrogen deprivation or fulvestrant were hypersensitive to 17β-estradiol. ER transcriptional response was followed by an unfolded protein response and apoptosis. Such apoptosis was dependent upon the unfolded protein response, p53, and JNK signaling. Anticancer effects were most pronounced in models exhibiting genomic amplification of the gene encoding ER (ESR1), suggesting that engagement of ER at high levels is cytotoxic. These data indicate that long-term adaptation to estrogen deprivation or ER inhibition alters sensitivity to ER reactivation. In such adapted cells, 17β-estradiol treatment and anti-estrogen withdrawal hyperactivate ER, which drives an unfolded protein response and subsequent growth inhibition and apoptosis. 17β-estradiol treatment should be considered as a therapeutic option for anti-estrogen-resistant disease, particularly in patients with tumors harboring ESR1 amplification or ER overexpression. Furthermore, therapeutic strategies that enhance an unfolded protein response may increase the therapeutic effects of ER reactivation.

Tamoxifen withdrawal in women with progressive metastatic breast cancer: a case series of six patients

Estrogen receptor (ER)-positive metastatic breast cancers after a period of response to tamoxifen develop resistance, and the disease progresses clinically. Domination of partial agonistic activity of tamoxifen over its antagonist activity has been implicated as one of the mechanisms for acquired tamoxifen resistance. Six patients with ER-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer who were treated with tamoxifen withdrawal were retrospectively reviewed. Three patients were premenopausal and three were postmenopausal at the beginning of this treatment. Three patients had stage IV disease and three had recurrent breast cancers with median disease-free intervals of 153 months. The treatment lines of tamoxifen therapy were first-line in two, second-line in two, and third-line in one patient. One patient had relapsed during adjuvant tamoxifen therapy. The median duration of tamoxifen therapy was 16 months. The metastatic disease sites at the time of tamoxifen withdrawal were lymph nodes in six, bone in three, chest wall in one, lung in two, pleura in one, and liver in one patient. The median duration of tamoxifen withdrawal was 6.5 months (range 5-> 23 months). Five of six patients had clinical benefits with tamoxifen withdrawal: partial response in one, long stable disease (SD) in four, and SD in one patient. Five patients were treated with aromatase inhibitors after tamoxifen withdrawal. Two patients had metastatic lymph nodes examined by multi-gene panel testing, and both of their tumors had the AKT1 E17K somatic mutation. One patient also had a BRCA1 germline mutation. Tamoxifen withdrawal at the time of tumor progression while on treatment might be an important treatment option, especially for women with highly endocrine-responsive disease.

Tamoxifen Resistance Trumped and Oral Selective Estrogen Receptor Degraders Arrive

Predictive tests, to refine the estrogen receptor assay, for the adjuvant treatment of breast cancer with tamoxifen and oral selective estrogen receptor degraders (SERD) are required. A splice variant of the corepressor NCOR2, BQ2313636.1 predicts tamoxifen resistance to adjuvant tamoxifen and AZ9496, the first oral SERD, completes phase I studies. Clin Cancer Res; 24(15); 3480-2. ©2018 AACRSee related articles by Gong et al., p. 3681 and Hamilton et al., p. 3510.

A unifying biology of sex steroid-induced apoptosis in prostate and breast cancers

Prostate and breast cancer are the two cancers with the highest incidence in men and women, respectively. Here, we focus on the known biology of acquired resistance to antihormone therapy of prostate and breast cancer and compare laboratory and clinical similarities in the evolution of the disease. Laboratory studies and clinical observations in prostate and breast cancer demonstrate that cell selection pathways occur during acquired resistance to antihormonal therapy. Following sex steroid deprivation, both prostate and breast cancer models show an initial increased acquired sensitivity to the growth potential of sex steroids. Subsequently, prostate and breast cancer cells either become dependent upon the antihormone treatment or grow spontaneously in the absence of hormones. Paradoxically, the physiologic sex steroids now kill a proportion of selected, but vulnerable, resistant tumor cells. The sex steroid receptor complex triggers apoptosis. We draw parallels between acquired resistance in prostate and breast cancer to sex steroid deprivation. Clinical observations and patient trials confirm the veracity of the laboratory studies. We consider therapeutic strategies to increase response rates in clinical trials of metastatic disease that can subsequently be applied as a preemptive salvage adjuvant therapy. The goal of future advances is to enhance response rates and deploy a safe strategy earlier in the treatment plan to save lives. The introduction of a simple evidence-based enhanced adjuvant therapy as a global healthcare strategy has the potential to control recurrence, reduce hospitalization, reduce healthcare costs and maintain a healthier population that contributes to society.

Opportunities and challenges of long term anti-estrogenic adjuvant therapy: treatment forever or intermittently?

INTRODUCTION

Extended adjuvant (5-10 years) therapy targeted to the estrogen receptor (ER) has significantly decreased mortality from breast cancer (BC). Areas covered: Translational research advanced clinical testing of extended adjuvant therapy with tamoxifen or aromatase inhibitors (AIs). Short term therapy or non-compliance increase recurrence, but surprisingly recurrence and death does not increase dramatically after 5 years of adjuvant therapy stops. Expert commentary: Compliance ensures optimal benefit from extended antihormone adjuvant therapy.Retarding acquired resistance using CDK4/6 or mTOR inhibitors is discussed. Preventing acquired resistance from mutations of ER could be achieved with Selective ER Downregulators (SERDs), eg fulvestrant. Fulvestrant is a depot injectable so oral SERDs are sought for extended use. In reality, a 'super SERD' which destroys ER but improves women's health like a Selective ER Modulator (SERM), would aid compliance to prevent recurrence and death. Estrogen-induced apoptosis occurs in 30% of BC with antihormone resistance. The 'one in three' rule that dictates that one in three unselected patients respond to either hormonal or antihormonal therapy in BC occurs with estrogen or antiestrogen therapy and must be improved. The goal is to maintain patients for their natural lives by blocking cancer cell survival through precision medicine using short cycles of estrogen apoptotic salvage therapy, and further extended antihormone maintenance.

Endocrine Therapy for Hormone Receptor-Positive Metastatic Breast Cancer: American Society of Clinical Oncology Guideline

PURPOSE

To develop recommendations about endocrine therapy for women with hormone receptor (HR) -positive metastatic breast cancer (MBC).

METHODS

The American Society of Clinical Oncology convened an Expert Panel to conduct a systematic review of evidence from 2008 through 2015 to create recommendations informed by that evidence. Outcomes of interest included sequencing of hormonal agents, hormonal agents compared with chemotherapy, targeted biologic therapy, and treatment of premenopausal women. This guideline puts forth recommendations for endocrine therapy as treatment for women with HR-positive MBC.

RECOMMENDATIONS

Sequential hormone therapy is the preferential treatment for most women with HR-positive MBC. Except in cases of immediately life-threatening disease, hormone therapy, alone or in combination, should be used as initial treatment. Patients whose tumors express any level of hormone receptors should be offered hormone therapy. Treatment recommendations should be based on type of adjuvant treatment, disease-free interval, and organ function. Tumor markers should not be the sole criteria for determining tumor progression; use of additional biomarkers remains experimental. Assessment of menopausal status is critical; ovarian suppression or ablation should be included in premenopausal women. For postmenopausal women, aromatase inhibitors (AIs) are the preferred first-line endocrine therapy, with or without the cyclin-dependent kinase inhibitor palbociclib. As second-line therapy, fulvestrant should be administered at 500 mg with a loading schedule and may be administered with palbociclib. The mammalian target of rapamycin inhibitor everolimus may be administered with exemestane to postmenopausal women with MBC whose disease progresses while receiving nonsteroidal AIs. Among patients with HR-positive, human epidermal growth factor receptor 2-positive MBC, human epidermal growth factor receptor 2-targeted therapy plus an AI can be effective for those who are not chemotherapy candidates.

The molecular, cellular and clinical consequences of targeting the estrogen receptor following estrogen deprivation therapy

During the past 20 years our understanding of the control of breast tumor development, growth and survival has changed dramatically. The once long forgotten application of high dose synthetic estrogen therapy as the first chemical therapy to treat any cancer has been resurrected, refined and reinvented as the new biology of estrogen-induced apoptosis. High dose estrogen therapy was cast aside once tamoxifen, from its origins as a failed "morning after pill", was reinvented as the first targeted therapy to treat any cancer. The current understanding of the mechanism of estrogen-induced apoptosis is described as a consequence of acquired resistance to long term antihormone therapy in estrogen receptor (ER) positive breast cancer. The ER signal transduction pathway remains a target for therapy in breast cancer despite "antiestrogen" resistance, but becomes a regulator of resistance. Multiple mechanisms of resistance come into play: Selective ER modulator (SERM) stimulated growth, growth factor/ER crosstalk, estrogen-induced apoptosis and mutations of ER. But it is with the science of estrogen-induced apoptosis that the next innovation in women's health will be developed. Recent evidence suggests that the glucocorticoid properties of medroxyprogesterone acetate blunt estrogen-induced apoptosis in estrogen deprived breast cancer cell populations. As a result breast cancer develops during long-term hormone replacement therapy (HRT). A new synthetic progestin with estrogen-like properties, such as the 19 nortestosterone derivatives used in oral contraceptives, will continue to protect the uterus from unopposed estrogen stimulation but at the same time, reinforce apoptosis in vulnerable populations of nascent breast cancer cells.

A phase II trial of low-dose estradiol in postmenopausal women with advanced breast cancer and acquired resistance to aromatase inhibition

BACKGROUND

High-dose oestrogen (HDE) is effective but toxic in postmenopausal women with advanced breast cancer (ABC). Prolonged oestrogen deprivation sensitises BC cell lines to estrogen and we hypothesised that third-generation aromatase inhibitors (AIs) would sensitise BCs to low-dose estradiol (LDE).

METHODS

A single-arm phase II study of LDE (2 mg estradiol valerate daily) in postmenopausal women with estrogen receptor-positive (ER+) ABC. The primary end-point was clinical benefit (CB) rate. If LDE was ineffective, HDE was offered. If LDE was effective, retreatment with the pre-LDE AI was offered on progression.

RESULTS

Twenty-one patients were recruited before the trial was closed early due to slow accrual; 19 were assessable for efficacy and toxicity. CB was seen in 5 in 19 patients (26%; 95% confidence interval 9.1-51.2%), all with prolonged SD (median duration 16.8 months; range 11.0-29.6). Treatment was discontinued for toxicity in 4 in 19 patients (21%) and 8 in 11 women without hysterectomy experienced vaginal bleeding (VB). After primary LDE failure, three patients received HDE and one achieved a partial response (PR). Following CB on LDE, four patients restarted pre-LDE AI and three achieved CB including one PR. Those with CB to LDE had a significantly longer duration of first-line endocrine therapy for ABC than those without (54.9 versus 16.8 months; p < 0.01) CONCLUSION: LDE is an effective endocrine option in women with evidence of prolonged sensitivity to AI therapy. LDE is reasonably well tolerated although VB is an issue. Re-challenge with the pre-LDE AI following progression confirms re-sensitisation as a true phenomenon.

Estrogen receptor mutations found in breast cancer metastases integrated with the molecular pharmacology of selective ER modulators

The consistent reports of mutations at Asp538 and Tyr537 in helix 12 of the ligand-binding domain (LBD) of estrogen receptors (ERs) from antihormone-resistant breast cancer metastases constitute an important advance. The mutant amino acids interact with an anchor amino acid, Asp351, to close the LBD, thereby creating a ligand-free constitutively activated ER. Amino acids Asp 538, Tyr 537, and Asp 351 are known to play a role in either the turnover of ER, the antiestrogenic activity of the ER complex, or the estrogen-like actions of selective ER modulators. A unifying mechanism of action for these amino acids to enhance ER gene activation and growth response is presented. There is a range of mutations described in metastases vs low to zero in primary disease, so the new knowledge is of clinical relevance, thereby confirming an additional mechanism of acquired resistance to antihormone therapy through cell population selection pressure and enrichment during treatment. Circulating tumor cells containing ER mutations can be cultured ex vivo, and tumor tissues can be grown as patient-derived xenografts to add a new dimension for testing drug susceptibility for future drug discovery.

The new biology of estrogen-induced apoptosis applied to treat and prevent breast cancer

The successful use of high-dose synthetic estrogens to treat postmenopausal metastatic breast cancer is the first effective 'chemical therapy' proven in clinical trial to treat any cancer. This review documents the clinical use of estrogen for breast cancer treatment or estrogen replacement therapy (ERT) in postmenopausal hysterectomized women, which can either result in breast cancer cell growth or breast cancer regression. This has remained a paradox since the 1950s until the discovery of the new biology of estrogen-induced apoptosis at the end of the 20th century. The key to triggering apoptosis with estrogen is the selection of breast cancer cell populations that are resistant to long-term estrogen deprivation. However, estrogen-independent growth occurs through trial and error. At the cellular level, estrogen-induced apoptosis is dependent upon the presence of the estrogen receptor (ER), which can be blocked by nonsteroidal or steroidal antiestrogens. The shape of an estrogenic ligand programs the conformation of the ER complex, which, in turn, can modulate estrogen-induced apoptosis: class I planar estrogens (e.g., estradiol) trigger apoptosis after 24 h, whereas class II angular estrogens (e.g., bisphenol triphenylethylene) delay the process until after 72 h. This contrasts with paclitaxel, which causes G2 blockade with immediate apoptosis. The process is complete within 24 h. Estrogen-induced apoptosis is modulated by glucocorticoids and cSrc inhibitors, but the target mechanism for estrogen action is genomic and not through a nongenomic pathway. The process is stepwise through the creation of endoplasmic reticulum stress and inflammatory responses, which then initiate an unfolded protein response. This, in turn, initiates apoptosis through the intrinsic pathway (mitochondrial) with the subsequent recruitment of the extrinsic pathway (death receptor) to complete the process. The symmetry of the clinical and laboratory studies now permits the creation of rules for the future clinical application of ERT or phytoestrogen supplements: a 5-year gap is necessary after menopause to permit the selection of estrogen-deprived breast cancer cell populations to cause them to become vulnerable to apoptotic cell death. Earlier treatment with estrogen around menopause encourages growth of ER-positive tumor cells, as the cells are still dependent on estrogen to maintain replication within the expanding population. An awareness of the evidence that the molecular events associated with estrogen-induced apoptosis can be orchestrated in the laboratory in estrogen-deprived breast cancers now supports the clinical findings regarding the treatment of metastatic breast cancer following estrogen deprivation, decreases in mortality following long-term antihormonal adjuvant therapy, and the results of treatment with ERT and ERT plus progestin in the Women's Health Initiative for women over the age of 60. Principles have emerged for understanding and applying physiological estrogen therapy appropriately by targeting the correct patient populations.

Acquired resistance to selective estrogen receptor modulators (SERMs) in clinical practice (tamoxifen & raloxifene) by selection pressure in breast cancer cell populations

Tamoxifen, a pioneering selective estrogen receptor modulator (SERM), has long been a therapeutic choice for all stages of estrogen receptor (ER)-positive breast cancer. The clinical application of long-term adjuvant antihormone therapy for the breast cancer has significantly improved breast cancer survival. However, acquired resistance to SERM remains a significant challenge in breast cancer treatment. The evolution of acquired resistance to SERMs treatment was primarily discovered using MCF-7 tumors transplanted in athymic mice to mimic years of adjuvant treatment in patients. Acquired resistance to tamoxifen is unique because the growth of resistant tumors is dependent on SERMs. It appears that acquired resistance to SERM is initially able to utilize either E2 or a SERM as the growth stimulus in the SERM-resistant breast tumors. Mechanistic studies reveal that SERMs continuously suppress nuclear ER-target genes even during resistance, whereas they function as agonists to activate multiple membrane-associated molecules to promote cell growth. Laboratory observations in vivo further show that three phases of acquired SERM-resistance exists, depending on the length of SERMs exposure. Tumors with Phase I resistance are stimulated by both SERMs and estrogen. Tumors with Phase II resistance are stimulated by SERMs, but are inhibited by estrogen due to apoptosis. The laboratory models suggest a new treatment strategy, in which limited-duration, low-dose estrogen can be used to purge Phase II-resistant breast cancer cells. This discovery provides an invaluable insight into the evolution of drug resistance to SERMs, and this knowledge is now being used to justify clinical trials of estrogen therapy following long-term antihormone therapy. All of these results suggest that cell populations that have acquired resistance are in constant evolution depending upon selection pressure. The limited availability of growth stimuli in any new environment enhances population plasticity in the trial and error search for survival.

Selective estrogen-induced apoptosis in breast cancer

Antihormone therapy remains the gold standard of care in the treatment of estrogen receptor (ER) positive breast cancer. However, development of acquired long term antihormone resistance exposes a vulnerability to estrogen that induces apoptosis. Laboratory and clinical studies indicate that successful therapy with estrogens is dependent on the duration of estrogen withdrawal and menopausal status of a woman. Interrogation of estradiol (E2) induced apoptosis using molecular studies indicate treatment of long term estrogen deprived MCF-7 breast cancer cells with estrogen causes an endoplasmic reticulum stress response that induces an unfolded protein response signal to inhibit protein translation. E2 binds to the ER and mediates apoptosis through the classical genomic pathway. Furthermore, the induction of apoptosis by estrogens is dependent on the conformation of the estrogen-ER complex. In this review, we explore the mechanism and the processes involved in the paradox of estrogen induced apoptosis and the new selectivity of estrogen action on different cell populations that is correctly been deciphered for clinical practice.

Drug withdrawal in women with progressive metastatic breast cancer while on aromatase inhibitor therapy

BACKGROUND

Acquiring resistance to endocrine therapy is common in metastatic hormone-receptor-positive breast cancer (MBC). These patients most often transition either to next-line endocrine therapy or to systemic chemotherapy. However, withdrawal of endocrine therapy and observation as is selectively practiced in prostate cancer is another potential strategy for breast cancer patients.

METHODS

A prospective, single-arm phase II trial of aromatase inhibitor (AI) withdrawal was performed in women with MBC, who had disease progression on AI therapy. The primary objective was to estimate the clinical benefit rate (defined as complete or partial response, or stable disease for at least 24 weeks, by RECIST criteria). Participants were monitored clinically and radiographically off all therapy at 8, 16 and 24 weeks after treatment and every 12 weeks thereafter until disease progression.

RESULTS

Twenty-four patients (of 40 intended) were enrolled when the study was closed due to slow accrual. Clinical benefit rate overall was 46% (95% CI 26% to 67%). Median progression-free survival from time of AI withdrawal was 4 months. Two patients have remained progression free, off all treatment, for over 60 months.

CONCLUSIONS

Despite suboptimal patient accrual, our results suggest that selected patients with metastatic breast cancer progressing on AI therapy can experience disease stabilisation and a period of observation after AI withdrawal. A randomised phase II trial is planned.

Specific transcriptional response of four blockers of estrogen receptors on estradiol-modulated genes in the mouse mammary gland

Novel agents for the endocrine therapy of breast cancer are needed, especially in order to take advantage of the multiple consecutive responses observed in metastatic progressing breast cancer following previous hormone therapy, thus delaying the use of cytotoxic chemotherapy with its frequent poor tolerance and serious side effects. Acolbifene (ACOL) is a novel and unique antiestrogen which represents a unique opportunity to achieve the most potent and specific blockade of estrogen action in the mammary gland and uterus while exerting estrogen-like beneficial effects in other tissues, especially the bones. To better understand the specificity of action of ACOL, we have used Affymetrix GeneChips containing 45,000 probe sets to analyze 34,000 genes to determine the specificity of this compound compared to the pure antiestrogen fulvestrant, as well as to the mixed antagonists/agonists tamoxifen and raloxifene to block the effect of estradiol (E(2)) and to induce effects of their own on the genomic profile in the mouse mammary gland. The genes modulated by E(2) were those identified in two separate experiments and validated by quantitative real-time PCR (qPCR). Three hours after the single subcutaneous injection of E(2) (0.05 μg), the simultaneous administration of ACOL, fulvestrant, tamoxifen, and raloxifene blocked by 98, 61, 43, and 92 % the number of E(2)-upregulated genes, respectively. On the other hand, 70, 10, 25, and 55 % of the genes down-regulated by E(2) were blocked by the same compounds. Of the 128 genes modulated by E(2), 49 are associated with tumorigenesis while 22 are known to be associated with breast cancer. When used alone, ACOL modulated the smallest number of genes also influenced by E(2), namely 4 %, thus possibly explaining potential utilities of this compound in breast cancer prevention and therapy.

Dual IGF-1R/InsR inhibitor BMS-754807 synergizes with hormonal agents in treatment of estrogen-dependent breast cancer

Insulin-like growth factor (IGF) signaling has been implicated in the resistance to hormonal therapy in breast cancer. Using a model of postmenopausal, estrogen-dependent breast cancer, we investigated the antitumor effects of the dual IGF-1R/InsR tyrosine kinase inhibitor BMS-754807 alone and in combination with letrozole or tamoxifen. BMS-754807 exhibited antiproliferative effects in vitro that synergized strongly in combination with letrozole or 4-hydroxytamoxifen and fulvestrant. Similarly, combined treatment of BMS-754807 with either tamoxifen or letrozole in vivo elicited tumor regressions not achieved by single-agent therapy. Notably, hormonal therapy enhanced the inhibition of IGF-1R/InsR without major side effects in animals. Microarray expression analysis revealed downregulation of cell-cycle control and survival pathways and upregulation of erbB in response to BMS-754807 plus hormonal therapy, particularly tamoxifen. Overall, these results offer a preclinical proof-of-concept for BMS-754807 as an antitumor agent in combination with hormonal therapies in hormone-sensitive breast cancer. Cooperative cell-cycle arrest, decreased proliferation, and enhanced promotion of apoptosis may contribute to antitumor effects to be gauged in future clinical investigations justified by our findings.

Clinical relevance of "withdrawal therapy" as a form of hormonal manipulation for breast cancer

BACKGROUND

It has been shown in in-vitro experiments that "withdrawal" of tamoxifen inhibits growth of tumor cells. However, evidence is scarce when this is extrapolated into clinical context. We report our experience to verify the clinical relevance of "withdrawal therapy".

METHODS

Breast cancer patients since 1998 who fulfilled the following criteria were selected from the departmental database and the case-notes were retrospectively reviewed: (1) estrogen receptor positive, operable primary breast cancer in elderly (age > 70 years), locally advanced or metastatic breast cancer; (2) disease deemed suitable for treatment by hormonal manipulation; (3) disease assessable by UICC criteria; (4) received "withdrawal" from a prior endocrine agent as a form of therapy; (5) on "withdrawal therapy" for ≥ 6 months unless they progressed prior.

RESULTS

Seventeen patients with median age of 84.3 (53.7-92.5) had "withdrawal therapy" as second to tenth line of treatment following prior endocrine therapy using tamoxifen (n = 10), an aromatase inhibitor (n = 5), megestrol acetate (n = 1) or fulvestrant (n = 1). Ten patients (58.8%) had clinical benefit (CB) (complete response/partial response/stable disease ≥ 6 months) with a median duration of Clinical Benefit (DoCB) of 10+ (7-27) months. Two patients remain on "withdrawal therapy" at the time of analysis.

CONCLUSION

"Withdrawal therapy" appears to produce sustained CB in a significant proportion of patients. This applies not only to "withdrawal" from tamoxifen, but also from other categories of endocrine agents. "Withdrawal" from endocrine therapy is, therefore, a viable intercalating option between endocrine agents to minimise resistance and provide additional line of therapy. It should be considered as part of the sequencing of endocrine therapy.

Hormone replacement therapy and breast cancer

There is evidence that hormone replacement therapy (HRT) may both stimulate and inhibit breast cancers, giving rise to a spectrum of activities, which are frequently hard to understand. Here we summarise the evidence for these paradoxical effects and, given the current data, attempt to give an indication where it may or may not be appropriate to prescribe HRT.It is clear that administration of oestrogen-progestin (E-P) and oestrogen alone (E) HRT is sufficient to stimulate the growth of overt breast tumours in women since withdrawal of HRT results in reduction of proliferation of primary tumours and withdrawal responses in metastatic tumours. E-P, E including tibolone are associated with increased local and distant relapse when given after surgery for breast cancer. For women given HRT who do not have breast cancer the only large randomised trial (WHI) of E-P or E versus placebo has produced some expected and also paradoxical results. E-P increases breast cancer risk as previously shown in observational studies. Risk is increased, particularly in women known to be compliant. Conversely, E either has no effect or reduces breast cancer risk consistent with some but not all observational studies. Two observational studies report a decrease or at least no increase in risk when E-P or E are given after oophorectomy in young women with BRCA1/2 mutations. Early oophorectomy increases death rates from cardiovascular and other conditions and there is evidence that this may be reversed by the use of E post-oophorectomy. HRT may thus reduce the risk of breast cancer and other diseases (e.g., cardiovascular) in young women and increase or decrease them in older women.

A noncompetitive small molecule inhibitor of estrogen-regulated gene expression and breast cancer cell growth that enhances proteasome-dependent degradation of estrogen receptor {alpha}

The mechanisms responsible for 17β-estradiol (E(2))-stimulated breast cancer growth and development of resistance to tamoxifen and other estrogen receptor α (ERα) antagonists are not fully understood. We describe a new tool for dissecting ERα action in breast cancer, p-fluoro-4-(1,2,3,6,-tetrahydro-1,3-dimethyl-2-oxo-6-thionpurin-8-ylthio) (TPSF), a potent small-molecule inhibitor of estrogen receptor α that does not compete with estrogen for binding to ERα. TPSF noncompetitively inhibits estrogen-dependent ERα-mediated gene expression with little inhibition of transcriptional activity by NF-κB or the androgen or glucocorticoid receptor. TPSF inhibits E(2)-ERα-mediated induction of the proteinase inhibitor 9 gene, which is activated by ERα binding to estrogen response element DNA, and the cyclin D1 gene, which is induced by tethering ERα to other DNA-bound proteins. TPSF inhibits anchorage-dependent and anchorage-independent E(2)-ERα-stimulated growth of MCF-7 cells but does not inhibit growth of ER-negative MDA-MB-231 breast cancer cells. TPSF also inhibits ERα-dependent growth in three cellular models for tamoxifen resistance; that is, 4-hydroxytamoxifen-stimulated MCF7ERαHA cells that overexpress ERα, fully tamoxifen-resistant BT474 cells that have amplified HER-2 and AIB1, and partially tamoxifen-resistant ZR-75 cells. TPSF reduces ERα protein levels in MCF-7 cells and several other cell lines without altering ERα mRNA levels. The proteasome inhibitor MG132 abolished down-regulation of ERα by TPSF. Thus, TPSF affects receptor levels at least in part due to its ability to enhance proteasome-dependent degradation of ERα. TPSF represents a novel class of ER inhibitor with significant clinical potential.

New hypotheses and opportunities in endocrine therapy: amplification of oestrogen-induced apoptosis

AIMS

To outline the progress being made in the understanding of acquired resistance to long term therapy with the selective oestrogen receptor modulators (SERMs, tamoxifen and raloxifene) and aromatase inhibitors. The question to be addressed is how we can amplify the new biology of oestrogen-induced apoptosis to create more complete responses in exhaustively antihormone treated metastatic breast cancer.

METHODS AND RESULTS

Three questions are posed and addressed. (1) Do we know how oestrogen works? (2) Can we improve adjuvant antihormonal therapy? (3) Can we enhance oestrogen-induced apoptosis? The new player in oestrogen action is GPR30 and there are new drugs specific for this target to trigger apoptosis. Similarly, anti-angiogenic drugs can be integrated into adjuvant antihormone therapy or to enhance oestrogen-induced apoptosis in Phase II antihormone resistant breast cancer. The goal is to reduce the development of acquired antihormone resistance or undermine the resistance of breast cancer cells to undergo apoptosis with oestrogen respectively. Finally, drugs to reduce the synthesis of glutathione, a subcellular molecule compound associated with drug resistance, can enhance oestradiol-induced apoptosis.

CONCLUSIONS

We propose an integrated approach for the rapid testing of agents to blunt survival pathways and amplify oestrogen-induced apoptosis and tumour regression in Phase II resistant metastatic breast cancer. This Pharma platform will provide rapid clinical results to predict efficacy in large scale clinical trials.

Safety, tolerability and pharmacokinetics of TAS-108, a novel anti-oestrogen, in healthy post-menopausal Japanese women: a phase I single oral dose study

TAS-108 is a novel steroidal anti-oestrogen, expected to be useful for the treatment of breast cancer. The present study was conducted to investigate the safety, tolerability and pharmacokinetics of TAS-108 following the administration at a single oral dose of 40 mg to up to 120 mg in 12 post-menopausal women and the effect of food on the pharmacokinetics of the drug. All adverse events were mild and involved transient symptoms that resolved without therapeutic intervention. TAS-108 was readily absorbed and plasma levels of TAS-108 steadily declined, apparently in a multi-exponential manner. C(max) and AUC(0-12) were proportionally increased with increasing dose of TAS-108. The C(max) and AUC(0-t) of TAS-108 and its metabolite, deEt-TAS-108, were significantly increased to approximately 150% when TAS-108 was administered after a meal. Food did not affect the elimination half-life of TAS-108 or its metabolites. In this escalating dose-study of TAS-108, the drug was well tolerated by healthy post-menopausal Japanese women. The pharmacokinetics of TAS-108 indicated dose proportionality, and its bioavailability was significantly increased by food intake.

Incidence of invasive breast cancer in postmenopausal women after discontinuation of long-term raloxifene administration

BACKGROUND

Postmenopausal women with osteoporosis had a 66% relative risk reduction for invasive breast cancer over 8 years of raloxifene therapy in the randomized, placebo-controlled 4-year MORE (Multiple Outcomes of Raloxifene Evaluation) trial and the CORE (Continuing Outcomes Relevant to Evista) trial, a 4-year follow-up to MORE.

PATIENTS AND METHODS

The first post hoc analysis examined the effects of raloxifene on the cumulative incidence of invasive breast cancer on a yearly basis. Another analysis compared the incidence of invasive breast cancer in 3967 patients who continued raloxifene for 8 years (RLX-C, n = 2280), discontinued raloxifene after 4 years in MORE (RLX-D, n = 401), or took placebo (n = 1286) for a mean 2.9 years' treatment duration (57,338 patient-years).

RESULTS

The unadjusted breast cancer incidence rate was 5.39 per 1000 patient-years in the placebo group compared with 2.26 in the RLX-C group (hazard ratio [HR], 0.41 [95% CI 0.21-0.81]) and 3.59 in the RLX-D group (HR, 0.69 [95% CI 0.23-2.01]). Because the choice of taking the study drug was not randomized in CORE, propensity scores were used to adjust for potential imbalances in baseline characteristics before CORE. Results after adjustment by the propensity score method were similar to the unadjusted results.

CONCLUSION

This analysis suggests a persistent effect for breast cancer risk reduction in patients who discontinued raloxifene, although this conclusion is limited by the small sample size.

The Paradox of Oestradiol-Induced Breast Cancer Cell Growth and Apoptosis

High dose oestrogen therapy was used as a treatment for postmenopausal patients with breast cancer from the 1950s until the introduction of the safer antioestrogen, tamoxifen in the 1970s. The anti-tumour mechanism of high dose oestrogen therapy remained unknown. There was no enthusiasm to study these signal transduction pathways as oestrogen therapy has almost completely been eliminated from the treatment paradigm. Current use of tamoxifen and the aromatase inhibitors seek to create oestrogen deprivation that prevents the growth of oestrogen stimulated oestrogen receptor (ER) positive breast cancer cells. However, acquired resistance to antihormonal therapy does occur, but it is through investigation of laboratory models that a vulnerability of the cancer cell has been discovered and is being investigated to provide new opportunities in therapy with the potential for discovering new cancer-specific apoptotic drugs. Laboratory models of resistance to raloxifene and tamoxifen, the selective oestrogen receptor modulators (SERMs) and aromatase inhibitors demonstrate an evolution of drug resistance so that after many years of oestrogen deprivation, the ER positive cancer cell reconfigures the survival signal transduction pathways so oestrogen now becomes an apoptotic trigger rather than a survival signal. Current efforts are evaluating the mechanisms of oestrogen-induced apoptosis and how this new biology of oestrogen action can be amplified and enhanced, thereby increasing the value of this therapeutic opportunity for the treatment of breast cancer. Several synergistic approaches to therapeutic enhancement are being advanced which involve drug combinations to impair survival signaling with the use of specific agents and to impair bcl-2 that protects the cancer cell from apoptosis. We highlight the historical understanding of oestrogen's role in cell survival and death and specifically illustrate the progress that has been made in the last five years to understand the mechanisms of oestrogen-induced apoptosis. There are opportunities to harness knowledge from this new signal transduction pathway to discover the precise mechanism of this oestrogen-induced apoptotic trigger. Indeed, the new biology of oestrogen action also has significance for understanding the physiology of bone remodeling. Thus, the pathway has a broad appeal in both physiology and cancer research.

Hormetic Effects of Hormones, Antihormones, and Antidepressants on Cancer Cell Growth in Culture: In Vivo Correlates

Evidence is presented that the ability of hormones and antihormones to cause biphasic (hormetic) proliferative responses in cancer cells in vitro correlates with a similar effect of these substances in humans with cancer. Certain antidepressants also produce biphasic growth responses of cancer cells in vitro and stimulate cancer growth in rodents, correlating with an increased risk of breast and other cancers in some, but not all, epidemiological studies assessing early and/or late cancer incidence in patients on antidepressant drugs. The observation that certain drugs with biphasic effects on cancer cell growth in vitro may also produce an "up-down" effect on cancer growth in humans supports Calabrese's suggestion that the concept of the hormetic dose response must be taken seriously by toxicologists and regulators.

Low-dose estrogen therapy to reverse acquired antihormonal resistance in the treatment of breast cancer

Estrogen is a potent stimulus for growth in its target organs: the uterus, vagina, and some estrogen receptor-positive breast cancers. However, estrogen is also able to control menopausal symptoms and maintain bone density in postmenopausal women. Until recently, there was also believed to be a link between estrogen and the prevention of cardiovascular disease. For these reasons, hormone replacement therapy (HRT) with an orally active estrogen and progesterone has been used routinely for more than 50 years to maintain physiologic homeostasis after menopause. Not surprisingly, HRT increases the risk of developing breast cancer. The link between estrogen and breast cancer growth served as the incentive to develop long-term tamoxifen therapy and, subsequently, the aromatase inhibitors (AIs) as successful "anti-estrogenic" treatments. Unfortunately, the consequence of exhaustive therapy is drug resistance. Laboratory studies have defined the evolution of tumor drug resistance to tamoxifen, raloxifene (used for breast and osteoporosis chemoprevention), and the AIs. Remarkably, the long-term exposure of breast cancers to antihormonal therapy also exposes a vulnerability that is being exploited in the clinic. Years of antihormonal therapy alters the cellular response mechanism to estrogen. Normally, estrogen is classified as a survival signal in breast cancer, but in sensitive antihormone-resistant cells, estrogen induces apoptosis. When resistant cells are killed, antihormonal therapy is once again effective. This new targeted approach to the treatment of metastatic breast cancer could open the door to novel approaches to treatment with drug combinations.

Fulvestrant (Faslodex) -- how to make a good drug better

Fulvestrant (Faslodex); AstraZeneca Pharmaceuticals, Wilmington, DE) is an estrogen receptor (ER) antagonist with a novel mode of action; it binds, blocks, and increases degradation of ER. Fulvestrant (at the approved dose [250 mg/month]) is at least as effective as anastrozole (1 mg/day) in the treatment of postmenopausal women with hormone receptor-positive advanced breast cancer (HR(+) ABC) progressing or recurring on antiestrogen therapy, and is also an active first-line treatment. Although fulvestrant (250 mg/month) is clearly effective, it takes 3-6 months to achieve steady-state plasma levels. Steady-state concentrations are approximately twofold higher than those achieved with a single dose; reaching this earlier, for example, via a loading-dose (LD) regimen (250 mg/month plus 500 mg on day 0 and 250 mg on day 14 of month 1), may allow responses to be achieved more quickly and limit the possibility of early relapse. Fulvestrant high-dose (HD) regimens (500 mg/month) offer the possibility of greater antitumor activity, because (a) ER downregulation is a dose-dependent process (an approximately 70% reduction is observed with a single 250 mg dose of fulvestrant) and (b) evidence correlates greater ER downregulation with superior efficacy. A fulvestrant HD regimen offers the potential of achieving near 100% ER downregulation. There is also potential to increase fulvestrant-ER binding by reducing plasma estrogen levels, for example, with concomitant aromatase inhibitor treatment. Several ongoing trials use LD, HD, and combination regimens; results from these studies are awaited with interest. Meanwhile, fulvestrant (250 mg/month) remains a valuable additional endocrine treatment for postmenopausal women with HR(+) ABC recurring or progressing on antiestrogen therapy.

Tamoxifen-stimulated growth of breast cancer due to p21 loss

Tamoxifen is widely used for the treatment of hormonally responsive breast cancers. However, some resistant breast cancers develop a growth proliferative response to this drug, as evidenced by tumor regression upon its withdrawal. To elucidate the molecular mediators of this paradox, tissue samples from a patient with tamoxifen-stimulated breast cancer were analyzed. These studies revealed that loss of the cyclin-dependent kinase inhibitor p21 was associated with a tamoxifen growth-inducing phenotype. Immortalized human breast epithelial cells with somatic deletion of the p21 gene were then generated and displayed a growth proliferative response to tamoxifen, whereas p21 wild-type cells demonstrated growth inhibition upon tamoxifen exposure. Mutational and biochemical analyses revealed that loss of p21's cyclin-dependent kinase inhibitory property results in hyperphosphorylation of estrogen receptor-alpha, with subsequent increased gene expression of estrogen receptor-regulated genes. These data reveal a previously uncharacterized molecular mechanism of tamoxifen resistance and have potential clinical implications for the management of tamoxifen-resistant breast cancers.

Optimizing the antihormonal treatment and prevention of breast cancer

The incidence of breast cancer is rising throughout the world. Breast cancer is slowly becoming more prevalent in countries which previously had low rates of cancer as well as becoming a leading cause of cancer death in some countries. Fortunately, a large number of these tumors are estrogen receptor (ER) positive and respond to anti-hormonal adjuvant therapy which until recently has been 5 years of tamoxifen treatment. Unfortunately, a significant number of patients develop recurrent cancers and the recurrent tumors are resistant to tamoxifen treatment. In addition, because of tamoxifen's selective estrogenic actions, there have been reports of venous thrombosis, endometrial cancer, and strokes in patients receiving tamoxifen therapy. Thus, there are other novel therapies such as aromatase inhibitors that block estrogen production in postmenopausal women or fulvestrant that destroys the estrogen receptor. This paper will summarize the therapeutic options for anti-hormonal therapy, the role of anti-hormonal agents in advanced breast cancer, and adjuvant therapy and the current status of chemoprevention with selective ER modulators.

An alpha-fetoprotein-derived peptide reduces the uterine hyperplasia and increases the antitumour effect of tamoxifen

Tamoxifen (Tam) is effective for the treatment and prevention of breast cancer. However, it has toxic drawbacks and has limited-duration utility because, over time, human tumours become refractory to Tam. Recently, a new nontoxic peptide, alpha-fetoprotein-derived peptide (AFPep) has been proposed for the treatment and prevention of breast cancer. The purpose of this paper is to determine whether combining AFPep with Tam would increase efficacy and reduce toxicity in experimental models of breast cancer. Low doses of AFPep and Tam were more effective in combination than either agent alone against breast cancer growth in cell culture, in tumour-xenografted mice, and in carcinogen-exposed rats. alpha-Fetoprotein-derived peptide interfered with Tam-induced uterine hyperplasia in immature mice, and showed no toxic effects. Unlike Tam, AFPep did not inhibit binding of oestradiol (E(2)) to oestrogen receptor (ER). Thus, these two agents utilise different mechanisms to interfere with ER functionality, yet work cooperatively to reduce breast cancer growth and alleviate Tam's troubling toxicity of uterine hyperplasia and appear to be a rational combination for the treatment of ER-positive breast cancer.

Development and therapeutic options for the treatment of raloxifene-stimulated breast cancer in athymic mice

PURPOSE

Selective estrogen receptor modulators (SERM) are used for the treatment and prevention of breast cancer (tamoxifen) and osteoporosis (raloxifene). Mechanisms of tamoxifen-resistance in breast cancer are incompletely understood but current research is focused on crosstalk between growth factor receptors and the estrogen receptor alpha (ERalpha) pathway. There is increasing clinical use of raloxifene for the treatment of osteoporosis, but the widespread use of this SERM will have consequences for the treatment of breast cancer in raloxifene-exposed women.

EXPERIMENTAL DESIGN

We took the strategic step of developing a raloxifene-resistant tumor (MCF-7RALT) model in vivo and investigating the mechanisms responsible for resistance.

RESULTS

MCF-7RALT tumors exhibited phase I SERM resistance, growing in response to SERMs and 17beta-estradiol. Epidermal growth factor receptor/HER1 and HER2/neu mRNAs were increased in MCF-7RALT tumors. The HER2/neu blocker, trastuzumab, but not the epidermal growth factor receptor blocker, gefitinib, decreased the growth of MCF-7RALT tumors in vivo. Consequently, trastuzumab decreased prosurvival/proliferative proteins: phospho-HER2/neu, total HER2/neu, phospho-Akt (protein kinase B), glycogen synthetase kinase-3, cyclin D1, and the antiapoptotic protein X chromosome-linked inhibitor of apoptosis, whereas increasing the proapoptotic protein, caspase-7, in raloxifene-treated MCF-7RALT tumors. Interestingly, ERalpha protein was overexpressed in untreated MCF-7RALT tumors and hyperactivated in cells derived from these tumors. Only fulvestrant completely inhibited the growth and ERalpha activity of MCF-7RALT tumors. The coactivator of ERalpha, amplified in breast cancer-1 protein was modestly increased in the raloxifene-treated MCF-7RALT tumors and increased both basal and estradiol-induced activity of ERalpha in cells derived from the MCF-7RALT tumors.

CONCLUSIONS

These results suggest that overexpression and increased activity of HER2/neu might be responsible for the development of raloxifene-resistant breast cancer. The results also suggest that increased expression of basal activity of ERalpha could contribute to the hypersensitivity of MCF-7RALT tumors in response to estradiol because only fulvestrant blocked growth and ERalpha activity.

Prior hormone therapy and breast cancer risk in the Women's Health Initiative randomized trial of estrogen plus progestin

OBJECTIVES

To assess the extent to which prior hormone therapy modifies the breast cancer risk found with estrogen plus progestin (E+P) in the Women's Health Initiative (WHI) randomized trial.

METHODS

Subgroup analyses of prior hormone use on invasive breast cancer incidence in 16,608 postmenopausal women in the WHI randomized trial of E+P over an average 5.6 years of follow-up.

RESULTS

Small but statistically significant differences were found between prior HT users and non-users for most breast cancer risk factors but Gail risk scores were similar. Duration of E+P use within the trial (mean 4.4 years, S.D. 2.0) did not vary by prior use. Among 4311 prior users, the adjusted hazard ratio (HR) for E+P versus placebo was 1.96 (95% confidence interval [CI]: 1.17-3.27), significantly different (p=0.03) from that among 12,297 never users (HR 1.02; 95% CI: 0.77-1.36). The interaction between study arm and follow-up time was significant overall (p=0.01) and among never users (p=0.02) but not among prior users (p=0.10). The cumulative incidence over time for the E+P and placebo groups appeared to cross after about 3 years in prior users, and after about 5 years in women with no prior use. No interaction was found with duration (p=0.08) or recency of prior use (p=0.17). Prior hormone use significantly increased the E+P hazard ratio for larger, more advanced tumors.

CONCLUSION

A safe interval for combined hormone use could not be reliably defined with these data. However, the significant increase in breast cancer risk in the trial overall after only 5.6 years of follow-up, initially concentrated in women with prior hormone exposure, but with increasing risk over time in women without prior exposure, suggests that durations only slightly longer than those in the WHI trial are associated with increased risk of breast cancer. Longer-term exposure and follow-up data are needed.

Estrogen induces death of tamoxifen-resistant MCF-7 cells: contrasting effect of the estrogen receptor downregulator fulvestrant

A common problem in breast cancer therapy is resistance to the antiestrogen tamoxifen. However, tamoxifen-resistant breast tumors can still respond to other hormonal therapies. In animal models of tamoxifen-resistant breast cancer cells, physiological levels of estrogen can induce tumor regression. Recently, the estrogen receptor downregulator fulvestrant was shown to promote tumor growth of tamoxifen-resistant cells when added in combination with physiological levels of estrogen. Here, we show, using a cell culture model, that continuous exposure of tamoxifen-resistant cells to physiological levels of estrogen leads to cell death. Addition of the estrogen receptor downregulator fulvestrant prevents estrogen-induced death in a dose-dependent manner. Our data indicate that endogenous levels of estrogen affect the response of tamoxifen-resistant cells to fulvestrant. These results suggest that failure of fulvestrant to inhibit tumor growth in some tamoxifen-resistant patients may be due to endogenous estrogen levels. Moreover, these studies support short-term treatment with estrogen as a second-line hormonal therapy for tamoxifen-resistant breast cancer.

Tamoxifen and estradiol interact with the flavin mononucleotide site of complex I leading to mitochondrial failure

This study evaluated the action of tamoxifen and estradiol on the function of isolated liver mitochondria. We observed that although tamoxifen and estradiol per se did not affect mitochondrial complexes II, III, or IV, complex I is affected, this effect being more drastic (except for state 4 of respiration) when mitochondria were coincubated with both drugs. Furthermore, using two respiratory chain inhibitors, rotenone and diphenyliodonium chloride, we identified the flavin mononucleotide site of complex I as the target of tamoxifen and/or estradiol action(s). Tamoxifen (25 microm) per se induced a significant increase in hydrogen peroxide production and state 4 of respiration. Additionally, a significant decrease in respiratory control ratio, transmembrane, and depolarization potentials were observed. Estradiol per se decreased carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)-stimulated respiration, state 3 of respiration, and respiratory control ratio and increased lag phase of repolarization. With the exception of state 4 of respiration whose increase induced by tamoxifen was reversed by the presence of estradiol, the effects of tamoxifen were highly exacerbated when estradiol was present. We observed that 10 microm tamoxifen in the presence of estradiol affected mitochondria significantly by decreasing FCCP-stimulated respiration, state 3 of respiration, respiratory control ratio, and ADP depolarization and increasing the lag phase of repolarization. All of the deleterious effects induced by 25 microm tamoxifen were highly exacerbated in the presence of estradiol. Furthermore, we observed that the effects of both compounds were independent of estrogen receptors because the pure estrogen antagonist ICI 182,780 did not interfere with tamoxifen and/or estradiol detrimental effects. Altogether, our data provide a mechanistic explanation for the multiple cytotoxic effects of tamoxifen including its capacity to destroy tamoxifen-resistant breast cancer cells in the presence of estradiol. This new piece of information provides a basis for the development of new and promising anticancer therapeutic strategies.

The apoptotic action of estrogen following exhaustive antihormonal therapy: A new clinical treatment strategy

Long-term antihormonal therapy is effective at controlling the recurrence of estrogen receptor (ER)-positive breast cancer, but there may be unanticipated consequences for the development of new forms of drug resistance. Laboratory studies of exhaustive antihormonal therapy demonstrate there are at least two phases of resistance to selective ER modulators (SERMs; tamoxifen and raloxifene) and to estrogen withdrawal (aromatase inhibitors). In Phase I drug resistance, estrogen or a SERM promote tumor growth, but in Phase II drug resistance estrogen induces apoptosis. Understanding of the new biology of estrogen action has clinical relevance. There are paradoxical interactions between fulvestrant and postmenopausal levels of estrogen that cause robust growth of Phase II tamoxifen resistance or autonomous aromatase-resistant tumors. These new data suggest a rational approach for the treatment of patients with ER-positive breast cancer that have failed exhaustive antihormonal treatment. Low-dose estrogen could be used to debulk patients followed by fulvestrant in a low estrogen environment (aromatase treatment) to maintain tumor control.

Safety, tolerability, and pharmacokinetics of TAS-108 in normal healthy post-menopausal female subjects: a phase I study on single oral dose

OBJECTIVES

The present study was conducted to evaluate the safety, tolerability, and pharmacokinetics of TAS-108 after ascending single oral doses and to analyse preliminarily the effect of food on the pharmacokinetics of TAS-108 in normal healthy post-menopausal female subjects.

METHODS

Twelve healthy subjects participated in an open-label, ascending single-dose, alternating group, safety, tolerance, and pharmacokinetic study of TAS-108 administered orally to two groups of the subjects, one given alternating doses of 10, 40, 120 mg (group A) and the other of 20, 80, 160 mg (group B), in the fasting state. In addition, six subjects (group A) were administered an additional dose at 120 mg TAS-108 after food consumption. Plasma and urine samples for measurement of TAS-108 were analysed by validated analytical procedures using a liquid chromatographic method with tandem mass spectrometric detection (LC/MS/MS).

RESULTS

There was no dose-dependent increase in any adverse events (AEs), and there were no serious AEs or deaths. TAS-108 was readily absorbed following oral administration of the 80-, 120- and 160-mg doses. Plasma TAS-108 levels steadily declined, generally in a mono-exponential manner, with overall mean t(1/2) values ranging from 3.04 to 4.43 h in the fasting groups. Administration of TAS-108 after a high-fat meal markedly increased the bioavailability of the drug. The mean C(max) and AUC(0--t) values increased after a high-fat breakfast by 182 and 191% compared with the fasting value respectively.

CONCLUSIONS

In this escalating dose study of TAS-108, the drug was well tolerated by the participants. The maximum and systemic exposure to TAS-108 tended to increase with increasing dose and its bioavailability markedly increased after high-fat food intake.

The therapeutic potential of novel aromatase inhibitors in breast cancer

For over 20 years, aromatase inhibitors have played a role in the treatment of breast cancer. However, until relatively recently, their utility has been limited by a lack of selectivity and significant toxicity. Several second and third generation aromatase inhibitors which are highly selective for the aromatase enzyme have reached clinical trials this decade. As a result of these initial studies, aromatase inhibitors are now established as second line agents in the treatment of postmenopausal women with advanced breast cancer. They are now under evaluation in several other settings, including adjuvant and neoadjuvant therapy, and as part of combination treatment in premenopausal women. This review focuses on recent and ongoing clinical trials and the effect these have had on the clinical use of aromatase inhibitors.

Role of Fulvestrant in Sequential Hormonal Therapy for Advanced, Hormone Receptor—Positive Breast Cancer in Postmenopausal Women

The introduction of antiendocrine agents with differing mechanisms of action now mandates the design of rational sequential hormonal regimens for breast cancer. The aromatase inhibitors (AIs), including the nonsteroidal compounds anastrozole and letrozole and the steroidal compound exemestane, are important alternatives or adjuncts to the antiestrogen agent tamoxifen in postmenopausal women with hormone receptor-positive breast cancer in the first-line management of advanced disease and in the adjuvant treatment of early-stage disease. These and other endocrine agents, including the newer estrogen receptor antagonist fulvestrant and also tamoxifen itself, have not been extensively evaluated within the context of hormonal sequencing. Based on a retrospective analysis of data from 3 phase III trials, patients treated with fulvestrant in the first- or second-line hormonal management of advanced breast cancer may derive further clinical benefit from subsequent treatment with an endocrine agent from another class. The need for prospective investigation of post-AI hormonal therapy is intensifying as a result of the increasing clinical use of the AIs. Sophisticated sequencing regimens designed to exploit different mechanisms of action have the potential to confer greater clinical benefit than the historical approach of selecting the agent with the next highest single-agent clinical activity upon disease progression.

Estrogen-induced apoptosis in a breast cancer model resistant to long-term estrogen withdrawal

Estrogen suppression through the use of an aromatase inhibitor is an effective endocrine treatment option for postmenopausal breast cancer patients with estrogen receptor (ER)-positive disease, however, there are concerns that long-term estrogen deprivation will inevitably lead to resistance. To address the issue of acquired resistance to long-term estrogen deprivation our laboratory has developed an ER+/PR- hormone-independent breast cancer cell line, MCF-7:5C which is a variant clone of wild-type MCF-7 cells. Originally, these cells were cultured in estrogen-free MEM containing 5% charcoal-stripped calf serum and were found to be resistant to both estradiol (E(2)) and antiestrogens. Interestingly, a completely different phenomenon was observed when MCF-7:5C cells were cultured in phenol red-free RPMI 1640 medium containing 10% charcoal-stripped fetal bovine serum (SFS). Using DNA quantitation assays, we examined the effect of E(2) on the growth of MCF-7:5C cells under different media conditions. Our results showed that 10(-9)M E(2) caused a dramatic 90% reduction in the growth of MCF-7:5C cells cultured in RPMI medium containing 10% SFS but did not have any significant inhibitory effects on cells cultured in MEM media. Additional experiments were performed to determine whether the medium or the serum facilitated the inhibitory effects of E(2) and the results indicated that it was the serum. Annexin V and DAPI staining confirmed that the E(2)-induced growth inhibition of MCF-7:5C cells was due to apoptosis. We also examined the tumorigenic potential of MCF-7:5C cells by injecting 1x10(7)cells/site into ovariectomized athymic mice and found that these cells, previously cultured in RPMI media, spontaneously grew into tumors in the absence of E(2). Overall, these results show that low concentrations (>10(-11)M) of E(2) are capable of inducing apoptosis in an aromatase resistant breast cancer cell model and that this effect is highly influenced by the medium in which the cells are grown.