Tamoxifen: a personal retrospective

Optimization of small molecule degraders and antagonists for targeting estrogen receptor based on breast cancer: current status and future

The estrogen receptor (ER) is a classical receptor protein that plays a crucial role in mediating multiple signaling pathways in various target organs. It has been shown that ER-targeting therapies inhibit breast cancer cell proliferation, enhance neuronal protection, and promote osteoclast formation. Several drugs have been designed to specifically target ER in ER-positive (ER+) breast cancer, including selective estrogen receptor modulators (SERM) such as Tamoxifen. However, the emergence of drug resistance in ER+ breast cancer and the potential side effects on the endometrium which has high ER expression has posed significant challenges in clinical practice. Recently, novel ER-targeted drugs, namely, selective estrogen receptor degrader (SERD) and selective estrogen receptor covalent antagonist (SERCA) have shown promise in addressing these concerns. This paper provides a comprehensive review of the structural functions of ER and highlights recent advancements in SERD and SERCA-related small molecule drugs, especially focusing on their structural optimization strategies and future optimization directions. Additionally, the therapeutic potential and challenges of novel SERDs and SERCAs in breast cancer and other ER-related diseases have been discussed.

Early increase in tamoxifen dose in CYP2D6 poor metaboliser breast cancer patients and survival: A propensity score matching analysis

PURPOSE

Tamoxifen is a drug used for hormone receptor-positive breast cancers, primarily metabolised by the CYP2D6 enzyme into active metabolites such as endoxifen. CYP2D6 displays varying degrees of activity depending on its genotype. This study aims to analyse the effect of an early increase in tamoxifen dose in poor metabolisers (PM) on survival.

METHODS

We enrolled 220 patients diagnosed with breast cancer who were treated with tamoxifen. CYP2D6 polymorphisms were determined, and the phenotype was estimated according to the Clinical Pharmacogenetics Implementation Consortium. Disease-free survival (DFS) and overall survival (OS) were analysed considering the entire patient group, and a subgroup of 110 patients selected by Propensity Score Matching (PSM). All women were treated with 20 mg/day of tamoxifen for 5 years, except PM, who initially received 20 mg/day for 4 months, followed by 40 mg/day for 4 months and 60 mg/day for 4 months before returning to the standard dose of 20 mg/day until completing 5 years of treatment.

RESULTS

The analysis of the influence of CYP2D6 polymorphisms in the complete group and in the PSM subgroup revealed no significant differences for DFS or OS. Furthermore, DFS and OS were analysed in relation to various covariates such as age, histological grade, nodal status, tumour size, HER-2, Ki-67, chemotherapy, and radiotherapy. Only age, histological grade, nodal status, and chemotherapy treatment demonstrated statistical significance.

CONCLUSION

An early increase in tamoxifen dose in PM patients is not associated with survival differences among CYP2D6 phenotypes.

Serendipity in the search for "morning-after pills" led to clomiphene for the induction of ovulation

The approval of the oral contraceptive on June 23, 1960, by the United States Food and Drug Administration (FDA), changed society forever. For the first time, a pill designed and tested by men, supported by influential women, allowed women to control their fertility. For the first time, the FDA approved a medicine to be taken by humans without a disease. The chance discovery of a new group of medicines called nonsteroidal antiestrogens, created an opportunity for the pharmaceutical industry. These compounds were shown to be postcoital antifertility agents in rats and mice. In the 1960s, the development of a "morning-after pill" would have had an enormous market. Numerous companies focused discovery efforts to evaluate the development of their patented nonsteroidal antiestrogens: Merrell (clomiphene), Upjohn (U-11,100A), and ICI Pharmaceutical Division (ICI46,474). However, the antifertility effects of antiestrogens in rats and mice does not mean that the new medicine would be an antifertility agent in women. In this case, clomiphene did exactly the opposite of what it was predicted to prevent. Clomiphene became the first medicine to induce ovulation in subfertile women. This article describes the twists and turns of drug discovery and development over the past half century. The conclusion emphasizes the evolution of drug development over decades, based on fashions in medical research and discoveries in clinical pharmacology. As a result, new uses for old molecules, that started life as "nonsteroidal antiestrogens," have revolutionized women's health as members of the new group of medicines called selective estrogen receptor modulators.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators

Estrogens are critical mediators of multiple and diverse physiologic effects throughout the body in both sexes, including the reproductive, cardiovascular, endocrine, nervous, and immune systems. As such, alterations in estrogen function play important roles in many diseases and pathophysiological conditions (including cancer), exemplified by the lower prevalence of many diseases in premenopausal women. Estrogens mediate their effects through multiple cellular receptors, including the nuclear receptor family (ERα and ERβ) and the G protein-coupled receptor (GPCR) family (GPR30/G protein-coupled estrogen receptor [GPER]). Although both receptor families can initiate rapid cell signaling and transcriptional regulation, the nuclear receptors are traditionally associated with regulating gene expression, whereas GPCRs are recognized as mediating rapid cellular signaling. Estrogen-activated pathways are not only the target of multiple therapeutic agents (e.g., tamoxifen, fulvestrant, raloxifene, and aromatase inhibitors) but are also affected by a plethora of phyto- and xeno-estrogens (e.g., genistein, coumestrol, bisphenol A, dichlorodiphenyltrichloroethane). Because of the existence of multiple estrogen receptors with overlapping ligand specificities, expression patterns, and signaling pathways, the roles of the individual receptors with respect to the diverse array of endogenous and exogenous ligands have been challenging to ascertain. The identification of GPER-selective ligands however has led to a much greater understanding of the roles of this receptor in normal physiology and disease as well as its interactions with the classic estrogen receptors ERα and ERβ and their signaling pathways. In this review, we describe the history and characterization of GPER over the past 15 years focusing on the pharmacology of steroidal and nonsteroidal compounds that have been employed to unravel the biology of this most recently recognized estrogen receptor.

Tamoxifen induces a pluripotency signature in breast cancer cells and human tumors

Tamoxifen is the treatment of choice in estrogen receptor alpha breast cancer patients that are eligible for adjuvant endocrine therapy. However, ∼50% of ERα-positive tumors exhibit intrinsic or rapidly acquire resistance to endocrine treatment. Unfortunately, prediction of de novo resistance to endocrine therapy and/or assessment of relapse likelihood remain difficult. While several mechanisms regulating the acquisition and the maintenance of endocrine resistance have been reported, there are several aspects of this phenomenon that need to be further elucidated. Altered metabolic fate of tamoxifen within patients and emergence of tamoxifen-resistant clones, driven by evolution of the disease phenotype during treatment, appear as the most compelling hypotheses so far. In addition, tamoxifen was reported to induce pluripotency in breast cancer cell lines, in vitro. In this context, we have performed a whole transcriptome analysis of an ERα-positive (T47D) and a triple-negative breast cancer cell line (MDA-MB-231), exposed to tamoxifen for a short time frame (hours), in order to identify how early pluripotency-related effects of tamoxifen may occur. Our ultimate goal was to identify whether the transcriptional actions of tamoxifen related to induction of pluripotency are mediated through specific ER-dependent or independent mechanisms. We report that even as early as 3 hours after the exposure of breast cancer cells to tamoxifen, a subset of ERα-dependent genes associated with developmental processes and pluripotency are induced and this is accompanied by specific phenotypic changes (expression of pluripotency-related proteins). Furthermore we report an association between the increased expression of pluripotency-related genes in ERα-positive breast cancer tissues samples and disease relapse after tamoxifen therapy. Finally we describe that in a small group of ERα-positive breast cancer patients, with disease relapse after surgery and tamoxifen treatment, ALDH1A1 (a marker of pluripotency in epithelial cancers which is absent in normal breast tissue) is increased in relapsing tumors, with a concurrent modification of its intra-cellular localization. Our data could be of value in the discrimination of patients susceptible to develop tamoxifen resistance and in the selection of optimized patient-tailored therapies.

TM6SF2 and MAC30, new enzyme homologs in sterol metabolism and common metabolic disease

Carriers of the Glu167Lys coding variant in the TM6SF2 gene have recently been identified as being more susceptible to non-alcoholic fatty liver disease (NAFLD), yet exhibit lower levels of circulating lipids and hence are protected against cardiovascular disease. Despite the physiological importance of these observations, the molecular function of TM6SF2 remains unknown, and no sequence similarity with functionally characterized proteins has been identified. In order to trace its evolutionary history and to identify functional domains, we embarked on a computational protein sequence analysis of TM6SF2. We identified a new domain, the EXPERA domain, which is conserved among TM6SF, MAC30/TMEM97 and EBP (D8, D7 sterol isomerase) protein families. EBP mutations are the cause of chondrodysplasia punctata 2 X-linked dominant (CDPX2), also known as Conradi-Hünermann-Happle syndrome, a defective cholesterol biosynthesis disorder. Our analysis of evolutionary conservation among EXPERA domain-containing families and the previously suggested catalytic mechanism for the EBP enzyme, indicate that TM6SF and MAC30/TMEM97 families are both highly likely to possess, as for the EBP family, catalytic activity as sterol isomerases. This unexpected prediction of enzymatic functions for TM6SF and MAC30/TMEM97 is important because it now permits detailed experiments to investigate the function of these key proteins in various human pathologies, from cardiovascular disease to cancer.

Design, synthesis and biological evaluation of novel triaryl (Z)-olefins as tamoxifen analogues

Tamoxifen (TAM) is used for the treatment and prevention of estrogen receptor positive breast cancer. However, the limited activity, toxicity and the development of resistance raised the current need for new potent nontoxic antiestrogen. Six novel TAM analogues 5a-f were synthesized using McMurry olefination reaction. Replacement of the dimethylamino group in TAM by piperidino, piperazino or N-methyl piperazino, substituting the phenyl ring with florine atom at p-position and changing the ethyl group by methyl, afforded compounds showing comparable activity to TAM (1). Compounds 5c and 5e showed significant increase in antiproliferative activity in two breast cancer cell lines (MCF-7 and MDA-MB-231) compared to tamoxifen, while other compounds showed similar activity. The increased anticancer activity of compounds 5c and 5e was attributed to their ability to induce ER-independent cell death.

Clinicogenetic care of women of BRCA mutation carrier women: prevention, diagnosis and therapy

Predictive genetics opens a considerable perspective in the diagnostics as well as the treatment of breast and ovarian cancer. Current recommendations and guidelines for the management of BRCA 1 and BRCA 2 mutation carriers are not based on controlled randomized trials, but on expert opinions. The existing options of prevention, early diagnosis and treatment must be clearly interpreted to the patient. In the context of a dedicated genetic counseling the participation of all involved professionals (geneticist, oncologist, surgeon, gynecologist) is required. The decision-making process concerning the possibilities of prevention, diagnosis and treatment is always deeply influenced by the patient’s own experience with the cancer occurred in the family, as well as by her values and expectations of life. The focused multidisciplinary approach, with the application of results from prospective studies in cohorts of BRCA mutation carriers allow the concerned individuals to benefit from this kind of approach of medical treatment. Orv. Hetil., 2011, 152, 913–918.

Triaryl (Z)-olefins suitable for radiolabeling with iodine-124 or fluorine-18 radionuclides for positron emission tomography imaging of estrogen positive breast tumors

A group of (Z)-1,2-diphenyl-1-[4-[2-(4-methylpiperazin-1-yl)ethoxy]phenyl]but-1-enes were synthesized using methodologies that will allow incorporation of a [(124)I]iodine substituent at the para-position of either the C-1 phenyl ring or the C-2 phenyl ring, or a [(18)F]OCH(2)CH(2)F substituent at the para-position of the C-2 phenyl ring. These [(124)I] and [(18)F] radiotracers are designed as potential radiopharmaceuticals to image estrogen positive breast tumors using positron emission tomography (PET).

Natural products as inhibitors of carcinogenesis

BACKGROUND

Although carcinogenesis and cancer have been studied intensively for > 50 years, the rates of cancer incidence and mortality remain high. The most successful approach for reducing these rates has been primary prevention. For individuals at a high risk of developing cancer owing to certain genetic, environmental and occupational factors, cancer chemoprevention is a logical approach.

OBJECTIVE

This review discusses natural products as inhibitors of carcinogenesis.

CONCLUSION

Natural product chemopreventive agents are inherently biologically active and have been demonstrated to prevent and reverse the carcinogenic process in a pleiotropic manner. Derivatives of compounds discovered by screening natural products for chemopreventive agents have shown efficacy in clinical trials. Despite the obstacles that must be overcome before chemopreventive drugs become an integral component of standard medical practice for cancer prophylaxis, there is vast potential for significant improvement in cancer morbidity and mortality through the use of natural product chemopreventive drugs.

Trilostane in advanced breast cancer

Antiestrogens, principally tamoxifen, and aromatase inhibitors have been used as the first- and second-line therapy in patients with advanced postmenopausal breast cancer for many years. However, some patients acquire resistance to these treatments and, at present, further endocrine treatment is achieved by merely substituting the current medication with a different antiestrogen or aromatase inhibitor. Trilostane offers an alternative endocrine treatment due to its unique mode of action. It is an allosteric modulator of the estrogen receptor and targets both the estrogen- and growth factor-dependent pathways through which estradiol stimulates cell proliferation. In clinical trials, trilostane has been shown to be an effective treatment for breast cancer in patients who have relapsed after receiving treatment with one or more forms of endocrine therapy. Ongoing and future clinical trials are examining the potential for the use of trilostane in premenopausal breast cancer, as well as in other malignancies such as prostate cancer.

Loss of antagonistic activity of tamoxifen by replacement of one N-methyl of its side chain by fluorinated residues

Efforts to limit the metabolic alteration of the aminoalkyl side chain of tamoxifen by fluorination largely decrease its ER-mediated antagonistic properties in MCF-7 cells (i.e., ability to inhibit growth, to stabilize ER, and to modulate ERE and AP-1 transcriptional activity). This loss is associated with an enhancement of agonistic activity. Loss of interaction between Asp 351 and the nitrogen atom of tamoxifen provoked by the fluorination of its side chain may explain this property.

Assessment of anti-estrogenic activity of tamoxifen in transgenic mice expressing an enhanced green fluorescent protein gene regulated by estrogen response element

Tamoxifen is an anti-estrogenic agent for the treatment of breast cancer, while exhibiting estrogenic activity in such tissues as the uterus. This study aimed to test whether these opposite properties of tamoxifen in the uterus can be evaluated separately in vivo. We employed two transgenic murine models named, respectively, the ERE-EGFP Ar+/+ mouse and ERE-EGFP Ar-/- mouse. Both types of mice possess an enhanced green fluorescent protein (EGFP) gene regulated by four copies of estrogen response elements (EREs), while the latter lacks a functional aromatase gene, which encodes an enzyme catalyzing conversion of androgens to estrogens. Tamoxifen clearly exhibited estrogenic activity in the uteri of ERE-EGFP Ar-/- mice, as it caused uterine wet weight gain and E2-target gene induction, as 17beta-estradiol (E2) did. However, tamoxifen did not enhance the EGFP expression in ERE-EGFP Ar-/- mice, although E2 induced it significantly. In ERE-EGFP Ar+/+ mice, tamoxifen suppressed the EGFP expression in a time- and dose-dependent manner. Thus, the present study demonstrated that estrogenic and anti-estrogenic activities of tamoxifen can be evaluated by using ERE-EGFP Ar-/- and ERE-EGFP Ar+/+ mice, respectively. Furthermore, these animal models are useful to select and evaluate estrogenic and anti-estrogenic activities of chemical compounds.

Selenium disrupts estrogen receptor α signaling and potentiates tamoxifen antagonism in endometrial cancer cells and tamoxifen-resistant breast cancer cells

Tamoxifen, a selective estrogen receptor (ER) modulator, is the most widely prescribed hormonal therapy treatment for breast cancer. Despite the benefits of tamoxifen therapy, almost all tamoxifen-responsive breast cancer patients develop resistance to therapy. In addition, tamoxifen displays estrogen-like effects in the endometrium increasing the incidence of endometrial cancer. New therapeutic strategies are needed to circumvent tamoxifen resistance in breast cancer as well as tamoxifen toxicity in endometrium. Organic selenium compounds are highly effective chemopreventive agents with well-documented benefits in reducing total cancer incidence and mortality rates for a number of cancers. The present study shows that the organic selenium compound methylseleninic acid (MSA, 2.5 micromol/L) can potentiate growth inhibition of 4-hydroxytamoxifen (10(-7) mol/L) in tamoxifen-sensitive MCF-7 and T47D breast cancer cell lines. Remarkably, in tamoxifen-resistant MCF-7-LCC2 and MCF7-H2Delta16 breast cancer cell lines and endometrial-derived HEC1A and Ishikawa cells, coincubation of 4-hydroxytamoxifen with MSA resulted in a marked growth inhibition that was substantially greater than MSA alone. Growth inhibition by MSA and MSA + 4-hydroxytamoxifen in all cell lines was preceded by a specific decrease in ER(alpha) mRNA and protein without an effect on ER(beta) levels. Estradiol and 4-hydroxytamoxifen induction of endogenous ER-dependent gene expression (pS2 and c-myc) as well as ER-dependent reporter gene expression (ERE(2)e1b-luciferase) was also attenuated by MSA in all cell lines before effect on growth inhibition. Taken together, these data strongly suggest that specific decrease in ER(alpha) levels by MSA is required for both MSA potentiation of the growth inhibitory effects of 4-hydroxytamoxifen and resensitization of tamoxifen-resistant cell lines.

Estradiol-induced ezrin overexpression in ovarian cancer: a new signaling domain for estrogen

We have for the first time exposed estrogen's role in the epithelial ovarian cancer (OVCA) metastatic cascade and discovered that it is related to the induction of ezrin over-expression. 17beta Estradiol (E2) was administered to SKOV3 (ERalpha>beta) and DOV13 (ERalpha<ERbeta) OVCA cells in serum-and phenol red-free medium fortified with transferrin and insulin. Incubated cells that penetrated Matrigel membranes were counted, immunostained and analyzed for immunoreactive ezrin. E2 induced an invasive phenotype with translocation of ezrin to cell edges, including pseudopodia and ruffles. A strong correlation was found between ezrin expression and Matrigel penetration induced by E2. Increases in cell number and ezrin expression were confirmed by flask incubations. E2 stimulation of OVCA cell proliferation, motility and Matrigel penetration was dose-related and raloxifene or tamoxifen blocked E2's effect, supporting an ER action. This previously unreported effect of estrogen on ezrin expression may play a role in the clinical course of estrogen-sensitive cancers and other normal or diseased cell actions.

Antitumour efficacy of VEGFR2 tyrosine kinase inhibitor correlates with expression of VEGF and its receptor VEGFR2 in tumour models

During the development of indazolylpyrimidines as novel and potent inhibitors of vascular endothelial growth factor (VEGF) receptor-2 (VEGFR2) tyrosine kinase, we observed that some human tumour xenografts are more sensitive to VEGFR2 kinase inhibitors than others. A better understanding of the basis for this differential response may help to identify a predictive marker that would greatly aid in the identification of a suitable patient population for treatment. One representative compound from the indazolylpyrimidine series is GW654652 that inhibited all three VEGFRs with similar potency. The inhibition of VEGFR2 kinase by GW654652 was about 150 to >8800 more potent than the inhibition of eight other kinases tested. GW654652 inhibited VEGF- and bFGF-induced proliferation in endothelial cells with an IC(50) of 110 and 1980 nM, respectively, and has good pharmacokinetic profile in mouse and dog. We investigated the association between VEGF and VEGFR2 expression and the antitumour efficacy of GW654652, in various xenograft models. Statistically significant associations were observed between the antitumour efficacy of GW654652 in xenografts and VEGF protein (P=0.005) and VEGFR2 expression (P=0.041). The oral dose of GW654652 producing 50% inhibition of tumour growth (ED(50)) decreased with increasing levels of VEGF (r=-0.94); and, in contrast, the ED(50) increased with the increased expression of VEGFR2 (r=0.82). These results are consistent with the observed inverse correlation between VEGF and VEGFR2 expression in tumours. These findings support the hypothesis that VEGF and VEGFR2 expression by tumours may predict the therapeutic outcome of VEGFR kinase inhibitors.

Urokinase-type plasminogen activator system in breast cancer: association with tamoxifen therapy in recurrent disease

The prognostic value of components of the urokinase-type plasminogen activator (uPA) system, its receptor uPAR (CD87), and plasminogen activator inhibitors PAI-1 and PAI-2 is well established. We studied the predictive value of these proteolytic factors by evaluating the association of their tumor expression level and the efficacy of tamoxifen therapy in patients with recurrent breast cancer. The antigen levels of the four factors were determined by ELISA in cytosols prepared from estrogen receptor-positive primary breast tumors of 691 hormone-naive breast cancer patients with recurrent disease and treated with tamoxifen as first-line systemic therapy. High tumor levels of uPA (P < 0.001), uPAR (P < 0.01), and PAI-1 (P = 0.01) were associated with a lower efficacy of tamoxifen therapy. In the multivariable analysis, uPA (P < 0.001) provided additional information independent of the traditional predictive factors to predict benefit from tamoxifen therapy. High levels of uPA, uPAR, and PAI-1 predicted a shorter progression-free survival (PFS) on tamoxifen in an analysis of the first 9 months of therapy. However in the analysis during the total follow-up period, high PAI-2 levels (P = 0.01) showed a longer response to tamoxifen. In conclusion, uPA, uPAR, and PAI-1, components of the urokinase system, are predictive for the efficacy of tamoxifen therapy in patients treated for recurrent breast cancer. Knowledge of their tumor expression levels might be helpful for future individualized therapy protocols, including possible new-targeted therapies based on the interference in the urokinase system.

Selective estrogen receptor modulator regulated proteins in endometrial cancer cells

Tamoxifen is the primary hormonal therapy for breast cancer and is also used as a breast cancer chemopreventative agent. A major problem with tamoxifen therapy is undesirable endometrial proliferation. To identify proteins associated with the growth stimulatory effects of tamoxifen in an ER-positive model, the present study profiled total cellular and secreted proteins regulated by estradiol and selective estrogen receptor modifiers (SERMs) in the Ishikawa endometrial adenocarcinoma cell line using two-dimensional gel electrophoresis. Following 24 h incubation with 10(-8) M estradiol, 10(-7) M 4-hydroxytamoxifen, or 10(-7) M EM-652 (Acolbifene), nine proteins exhibited significant increase in expression. The proteins identified were heat shock protein 90-alpha, and -beta, heterogeneous nuclear ribonucleoprotein F, RNA polymerase II-mediating protein, cytoskeletal keratin 8, cytoskeletal keratin 18, ubiquitin-conjugating enzyme E2-18 kDa and nucleoside diphosphate kinase B. These protein profiles may serve as novel indices of SERM response and may also provide insight into novel mechanisms of SERM-mediated growth.

Molecular classification of selective oestrogen receptor modulators on the basis of gene expression profiles of breast cancer cells expressing oestrogen receptor alpha

The purpose of this study was to classify selective oestrogen receptor modulators based on gene expression profiles produced in breast cancer cells expressing either wtERalpha or mutant(351)ERalpha. In total, 54 microarray experiments were carried out by using a commercially available Atlas cDNA Expression Arrays (Clontech), containing 588 cancer-related genes. Nine sets of data were generated for each cell line following 24 h of treatment: expression data were obtained for cells treated with vehicle EtOH (Control); with 10(-9) or 10(-8) M oestradiol; with 10(-6) M 4-hydroxytamoxifen; with 10(-6) M raloxifene; with 10(-6) M idoxifene, with 10(-6) M EM 652, with 10(-6) M GW 7604; with 5 x 10(-5) M resveratrol and with 10(-6) M ICI 182,780. We developed a new algorithm 'Expression Signatures' to classify compounds on the basis of differential gene expression profiles. We created dendrograms for each cell line, in which branches represent relationships between compounds. Additionally, clustering analysis was performed using different subsets of genes to assess the robustness of the analysis. In general, only small differences between gene expression profiles treated with compounds were observed with correlation coefficients ranged from 0.83 to 0.98. This observation may be explained by the use of the same cell context for treatments with compounds that essentially belong to the same class of drugs with oestrogen receptors related mechanisms. The most surprising observation was that ICI 182,780 clustered together with oestrodiol and raloxifene for cells expressing wtERalpha and clustered together with EM 652 for cells expressing mutant(351)ERalpha. These data provide a rationale for a more precise and elaborate study in which custom made oligonucleotide arrays can be used with comprehensive sets of genes known to have consensus and putative oestrogen response elements in their promoter regions.

The evolution of tamoxifen therapy in breast cancer: selective oestrogen-receptor modulators and downregulators

Tamoxifen is the most widely used hormonal treatment for all stages of breast cancer and has been approved for the prevention of breast cancer in high-risk women. The observation that tamoxifen acts as an antioestrogen on the breast but has paradoxical oestrogenic effects on bones and lipids heralded the development of the selective oestrogen-receptor modulators (SERM). Raloxifene, another of these drugs, is being used to prevent osteoporosis in postmenopausal women, but it seems, like tamoxifen, to prevent breast cancer. The molecular basis for these target-site-specific actions remains unclear but may involve the relative expressions of coregulatory proteins in target tissues. Several new SERM agents are in clinical development in an attempt to decrease the unwanted effects. Furthermore, two different classes of hormonal agents, the aromatase inhibitors and oestrogen-receptor downregulators, which have no oestrogen-like properties at any site, are promising new treatments for breast cancer.

Chemoprevention with antiestrogens: the beginning of the end for breast cancer. Daniel G. Miller Lecture

In the 1960s, compounds known as nonsteroidal antiestrogens were identified as potential contraceptives, but the drugs caused the induction of ovulation in subfertile women. Tamoxifen and clomiphene were marketed for this indication. However, tamoxifen was advanced for the treatment of breast cancer in the 1970s through a close cooperation between the laboratory and the clinical trials community. The extensive use of long-term adjuvant tamoxifen has resulted in saving the lives of 400,000 women with breast cancer. Tamoxifen is a selective estrogen receptor modulator (SERM) that produces antiestrogenic actions in the breast but estrogen-like actions in bone and lowers serum cholesterol. These properties not only allowed the application of tamoxifen as the first chemopreventive in high-risk pre- and postmenopausal women but also the development of raloxifene to prevent osteoporosis with the potential to prevent breast cancer in postmenopausal women. The future development of SERMs holds the promise of preventing osteoporosis and coronary heart disease as well as breast and endometrial cancer.

Familiar drugs may prevent cancer

Despite positive results in large scale chemoprevention trials, many physicians are unaware of the potential cancer preventive properties of drugs in common usage. The antioestrogen tamoxifen and the selective cyclo-oxygenase-2 inhibitor celecoxib have been licensed in the USA for the chemoprevention of breast and colorectal cancers respectively in selected high risk individuals. Similarly, folate and retinol have been shown to decrease the incidence of colorectal cancer and squamous cell carcinoma of the skin respectively in large scale intervention trials. Other retinoids have proved efficacious in the tertiary chemoprevention of cancers of the breast and head/neck. Epidemiological evidence also exists in favour of aspirin, non-steroidal anti-inflammatory drugs, and angiotensin converting enzyme inhibitors preventing certain cancers. Phytochemicals may represent less toxic alternatives to these agents. Although some of these drugs are available without prescription and most are not yet licensed for use in cancer chemoprevention, physicians and students of medicine should be aware of this accumulating evidence base. Practitioners should be amenable to patient referral to discuss complex issues such as risk estimation or potential benefit from intervention.