Faculty Publications

ABSTRACT: The link between estrogen and the development and proliferation of breast cancer is well documented. Estrogen stimulates growth and inhibits apoptosis through estrogen receptor-mediated mechanisms in many cell types. Interestingly, there is strong evidence that estrogen induces apoptosis in breast cancer and other cell types. Forty years ago, before the development of tamoxifen, high-dose estrogen was used to induce tumor regression of hormone-dependent breast cancer in post-menopausal women. While the mechanisms by which estrogen induces apoptosis were not completely known, recent evidence from our laboratory and others demonstrates the involvement of the extrinsic (Fas/FasL) and the intrinsic (mitochondria) pathways in this process. We discuss the different apoptotic signaling pathways involved in E2 (17beta-estradiol)-induced apoptosis, including the intrinsic and extrinsic apoptosis pathways, the NF-kappaB (nuclear factor-kappa-B)-mediated survival pathway as well as the PI3K (phosphoinositide 3-kinase)/Akt signaling pathway. Breast cancer cells can also be sensitized to estrogen-induced apoptosis through suppression of glutathione by BSO (L-buthionine sulfoximine). This finding has implications for the control of breast cancer with low-dose estrogen and other targeted therapeutic drugs.

Dietary antioxidants have radioprotective effects after gamma-radiation exposure that limit hematopoietic cell depletion and improve animal survival. The purpose of this study was to determine whether a dietary Supplement consisting of L-selenomethionine, vitamin C, vitamin E succinate, a-lipoic acid and N-acetyl cysteine could improve survival of mice after proton total-body irradiation (TBI). Antioxidants significantly increased 30-day survival of mice only when given after irradiation at a dose less than the calculated LD50/30; for these data, the dose-modifying factor (DMF) was 1.6. Pretreatment of animals with antioxidants resulted in significantly higher serum total white blood cell, polymorphonuclear cell and lymphocyte cell counts at 4 h after 1 Gy but not 7.2 Gy proton TBI. Antioxidants significantly modulated plasma levels of the hematopoietic cytokines Flt-3L and TGF beta 1 and increased bone marrow cell counts and spleen mass after TBI. Maintenance of the antioxidant diet resulted in improved recovery of peripheral leukocytes; and platelets after sublethal and potentially lethal TBI. Taken together, oral supplementation with antioxidants appears to be an effective approach for radioprotection of hematopoietic cells and improvement of animal survival after proton TBI. (C) 2009 by Radiation Research Society

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.

ABSTRACT: INTRODUCTION: Estrogen deprivation using aromatase inhibitors is one of the standard treatments for postmenopausal women with estrogen receptor (ER)-positive breast cancer. However, one of the consequences of prolonged estrogen suppression is acquired drug resistance. Our group is interested in studying antihormone resistance and has previously reported the development of an estrogen deprived human breast cancer cell line, MCF-7:5C, which undergoes apoptosis in the presence of estradiol. In contrast, another estrogen deprived cell line, MCF-7:2A, appears to have elevated levels of glutathione (GSH) and is resistant to estradiol-induced apoptosis. In the present study, we evaluated whether buthionine sulfoximine (BSO), a potent inhibitor of glutathione (GSH) synthesis, is capable of sensitizing antihormone resistant MCF-7:2A cells to estradiol-induced apoptosis. METHODS: Estrogen deprived MCF-7:2A cells were treated with 1 nM 17beta-estradiol (E2), 100 muM BSO, or 1 nM E2 + 100 muM BSO combination in vitro, and the effects of these agents on cell growth and apoptosis were evaluated by DNA quantitation assay and annexin V and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) staining. The in vitro results of the MCF-7:2A cell line were further confirmed in vivo in a mouse xenograft model. RESULTS: Exposure of MCF-7:2A cells to 1 nM E2 plus 100 muM BSO combination for 48 to 96 h produced a sevenfold increase in apoptosis whereas the individual treatments had no significant effect on growth. Induction of apoptosis by the combination treatment of E2 plus BSO was evidenced by changes in Bcl-2 and Bax expression. The combination treatment also markedly increased phosphorylated c-Jun N-terminal kinase (JNK) levels in MCF-7:2A cells and blockade of the JNK pathway attenuated the apoptotic effect of E2 plus BSO. Our in vitro findings corroborated in vivo data from a mouse xenograft model in which daily administration of BSO either as a single agent or in combination with E2 significantly reduced tumor growth of MCF-7:2A cells. CONCLUSIONS: Our data indicates that GSH participates in retarding apoptosis in antihormone-resistant human breast cancer cells and that depletion of this molecule by BSO may be critical in predisposing resistant cells to E2-induced apoptotic cell death. We suggest that these data may form the basis of improving therapeutic strategies for the treatment of antihormone resistant ER-positive breast cancer.

The ubiquitous application of selective oestrogen receptor modulators (SERMs) and aromatase inhibitors for the treatment and prevention of breast cancer has created a significant advance in patient care. However, the consequence of prolonged treatment with antihormonal therapy is the development of drug resistance. Nevertheless, the systematic description of models of drug resistance to SERMs and aromatase inhibitors has resulted in the discovery of a vulnerability in tumour homeostasis that can be exploited to improve patient care. Drug resistance to antihormones evolves, so that eventually the cells change to create novel signal transduction pathways for enhanced oestrogen (GPR30+OER) sensitivity, a reduction in progesterone receptor production and an increased metastatic potential. Most importantly, antihormone resistant breast cancer cells adapt with an ability to undergo apoptosis with low concentrations of oestrogen. The oestrogen destroys antihormone resistant cells and reactivates sensitivity to prolonged antihormonal therapy. We have initiated a major collaborative program of genomics and proteomics to use our laboratory models to map the mechanism of subcellular survival and apoptosis in breast cancer. The laboratory program is integrated with a clinical program that seeks to determine the minimum dose of oestrogen necessary to create objective responses in patients who have succeeded and failed two consecutive antihormonal therapies. Once our program is complete, the new knowledge will be available to translate to clinical care for the long-term maintenance of patients on antihormone therapy.

Endocrine therapy that targets the estrogen receptor (ER) is a std. of care for the treatment of postmenopausal women with ER-pos. breast cancer. The selective ER modulator (SERM) tamoxifen has been in use for the treatment of advanced breast cancer for more than 30 years and is currently a treatment option for all stages of ER-pos. disease. Tamoxifen blocks the action of estrogen by binding to the ER, and possesses both ER-agonist and antagonist properties. Unfortunately, long-term use of tamoxifen is assocd. with several important concerns including an increased risk of endometrial cancer and thromboembolic complications. In addn., many patients who initially respond to tamoxifen eventually relapse with resistant disease. New treatment approaches are therefore required. A no. of alternative SERMs have been tested as substitutes for tamoxifen. These include; toremifene, droloxifene, idoxifene, and keoxifene. Unfortunately, the SERMs have not proved to be more effective than tamoxifen for the treatment of advanced breast cancer and have shown a high level of cross-resistance with tamoxifen. The subsequent development of the aromatase inhibitors (AIs) is an important therapeutic advance by creating a \"no estrogen\" environment. Another approach is the development of pure antiestrogens. Fulvestrant is a novel ER antagonist that destroys the ER and its signaling pathway and is not assocd. with tamoxifen-like agonist effects. It produces high response rates compared with other SERMs and is not cross-resistant to tamoxifen or aromatase inhibitors and is equally as effective as the AI anastrozole in the treatment of postmenopausal women with advanced breast cancer who have progressed on prior adjuvant tamoxifen therapy. This review article discusses the significant and continuing value of SERMs for the treatment of postmenopausal ER-pos. breast cancer. [on SciFinder (R)]

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 tr eatment. Low-dose estrogen could be used to debulk patients followed by fulvestrant in a tow estrogen environment (aromatase treatment) to maintain tumor control. (c) 2005 Elsevier Ltd. All rights reserved.

Endocrine therapy that targets the estrogen receptor (ER) is a standard of care for the treatment of postmenopausal women with ER-positive breast cancer. The selective ER modulator (SERM) tamoxifen has been in use for the treatment of advanced breast cancer for more than 30 years and is currently a treatment option for all stages of ER-positive disease. Tamoxifen blocks the action of estrogen by binding to the ER, and possesses both ER-agonist and antagonist properties. Unfortunately, long-term use of tamoxifen is associated with several important concerns including an increased risk of endometrial cancer and thromboembolic complications. In addition, many patients who initially respond to tamoxifen eventually relapse with resistant disease. New treatment approaches are therefore required. A number of alternative SERMs have been tested as substitutes for tamoxifen. These include; toremifene, droloxifene, idoxifene, and keoxifene. Unfortunately, the SERMs have not proved to be more effective than tamoxifen for the treatment of advanced breast cancer and have shown a high level of cross-resistance with tamoxifen. The subsequent development of the aromatase inhibitors (AIs) is an important therapeutic advance by creating a "no estrogen" environment. Another approach is the development of pure antiestrogens. Fulvestrant is a novel ER antagonist that destroys the ER and its signaling pathway and is not associated with tamoxifen-like agonist effects. It produces high response rates compared with other SERMs and is not cross-resistant to tamoxifen or aromatase inhibitors and is equally as effective as the AI anastrozole in the treatment of postmenopausal women with advanced breast cancer who have progressed on prior adjuvant tamoxifen therapy. This review article discusses the significant and continuing value of SERMs for the treatment of postmenopausal ER-positive breast cancer.