A century of deciphering the control mechanisms of sex steroid action in breast and prostate cancer: the origins of targeted therapy and chemoprevention

Nuclear receptor expression defines a set of prognostic biomarkers for lung cancer

BACKGROUND

The identification of prognostic tumor biomarkers that also would have potential as therapeutic targets, particularly in patients with early stage disease, has been a long sought-after goal in the management and treatment of lung cancer. The nuclear receptor (NR) superfamily, which is composed of 48 transcription factors that govern complex physiologic and pathophysiologic processes, could represent a unique subset of these biomarkers. In fact, many members of this family are the targets of already identified selective receptor modulators, providing a direct link between individual tumor NR quantitation and selection of therapy. The goal of this study, which begins this overall strategy, was to investigate the association between mRNA expression of the NR superfamily and the clinical outcome for patients with lung cancer, and to test whether a tumor NR gene signature provided useful information (over available clinical data) for patients with lung cancer.

METHODS AND FINDINGS

Using quantitative real-time PCR to study NR expression in 30 microdissected non-small-cell lung cancers (NSCLCs) and their pair-matched normal lung epithelium, we found great variability in NR expression among patients' tumor and non-involved lung epithelium, found a strong association between NR expression and clinical outcome, and identified an NR gene signature from both normal and tumor tissues that predicted patient survival time and disease recurrence. The NR signature derived from the initial 30 NSCLC samples was validated in two independent microarray datasets derived from 442 and 117 resected lung adenocarcinomas. The NR gene signature was also validated in 130 squamous cell carcinomas. The prognostic signature in tumors could be distilled to expression of two NRs, short heterodimer partner and progesterone receptor, as single gene predictors of NSCLC patient survival time, including for patients with stage I disease. Of equal interest, the studies of microdissected histologically normal epithelium and matched tumors identified expression in normal (but not tumor) epithelium of NGFIB3 and mineralocorticoid receptor as single gene predictors of good prognosis.

CONCLUSIONS

NR expression is strongly associated with clinical outcomes for patients with lung cancer, and this expression profile provides a unique prognostic signature for lung cancer patient survival time, particularly for those with early stage disease. This study highlights the potential use of NRs as a rational set of therapeutically tractable genes as theragnostic biomarkers, and specifically identifies short heterodimer partner and progesterone receptor in tumors, and NGFIB3 and MR in non-neoplastic lung epithelium, for future detailed translational study in lung cancer. Please see later in the article for the Editors' Summary.

Raloxifene-stimulated experimental breast cancer with the paradoxical actions of estrogen to promote or prevent tumor growth: a unifying concept in anti-hormone resistance

We have previously demonstrated that prolonged treatments with raloxifene (RAL) in vitro will result in phase II RAL resistance and RAL-induced tumor growth. Clinical interest prompted us to re-examine RAL resistance in vivo, particularly the effects of long-term treatments (a decade or more) on the evolution of RAL resistance. In this study, we have addressed the question of this being a reproducible phenomenon in wild-type estrogen receptor (ER)-positive human breast cell line MCF-7. MCF-7 cells cultured under estrogen-deprived conditions in the presence of 1 microM RAL for more than a year develop RAL resistance resulting in an independent cell line, MCF7-RAL. The MCF7-RAL cells grow in response to both estradiol E2 and RAL. Fulvestrant (FUL) blocks RAL and E2-mediated growth. Transplantation of MCF7-RAL cells into athymic ovariectomized mice and treatment with physiologic doses of E2 causes early E2-stimulated tumor growth. In contrast, continuous treatment of implanted animals with daily oral RAL (1.5 mg daily) causes growth of small tumors within 15 weeks. Continuous re-transplantation of the tumors growing in RAL-treated mice indicated that RAL stimulated tumor growth. Tumors in the untreated mice did not grow. Bi-transplantation of MCF7-E2 and MCF7-RAL tumors into the opposing mammary fat pads of the same ovariectomized animal demonstrated that MCF7-E2 grew with E2 stimulation and not with RAL. Conversely, MCF7-RAL tumors grew with RAL and not E2, a characteristic of phase II resistance. Established phase II resistance of MCF7-RAL tumors was confirmed following up to 7 years of serial transplantation in RAL-treated athymic mice. The ERalpha was retained in these tumors. The cyclical nature of RAL resistance was confirmed and extended during a 2-year evolution of the resistant phases of the MCF7-RAL tumors. The MCF7-RAL tumors that initially were inhibited by E2 grew in the presence of E2 and subsequently grew with either RAL or E2. RAL remained the major grow stimulus and RAL enhanced E2-stimulated growth. Subsequent transplantation of E2 stimulated tumors and evaluations of the actions of RAL, demonstrated robust E2-stimulated growth that was blocked by RAL. These are the characteristics of the anti-estrogenic actions of RAL on E2-stimulated breast cancer growth with a minor component of phase I RAL resistance. Continuous transplantation of the phase I RAL-stimulated tumors for >8 months causes reversion to phase II resistance. These data and literature reports of the cyclical nature of anti-androgen/androgen responsiveness of prostate cancer growth, illustrate the generality of the evolution of anti-hormonal resistance in sex steroid-sensitive target tissues.

Multiple Routes to Oestrogen Antagonism

Several lines of evidence attest to the existence of alternative ligand binding sites on the oestrogen receptor (ER), including non-competitive inhibition by trilostane or tamoxifen. It is possible that the inhibitory action of conventional oestrogen agonists at high concentrations may indicate that they too interact at alternative ER sites, albeit at low affinity. To test this possibility an oestrogen reporter assay was used to compare the activity of different oestrogens and antagonists in breast cancer and prostate cell lines. All four cell lines tested contained different amounts of oestrogen receptor α (ERα), ERβ, progesterone receptor and coregulator mRNA. Though differences were observed in response to stimulation and inhibition, these correlated only with the presence or absence of ERα, and not with the other components. Thus stimulation of the reporter by oestradiol and oestrone was biphasic in the breast cancer cells, while prostate cells were unable to respond. Only T47D cells were stimulated by oestriol or diethylstilboestrol, however reporter activity of all the cell lines was repressed by 10μM diethylstilboestrol. Reporter activity of MCF-7 cells was inhibited by tamoxifen, raloxifene and ICI 182,780, but stimulated by trilostane, yet all these antioestrogens inhibited agonist-stimulated activity. Trilostane also inhibited the agonism seen in cells co-treated with E2 and tamoxifen. It is clear that several of the compounds tested may have either agonist or antagonist effects under different conditions and at different concentrations, acting through ERα alone. Though biphasic dose response curves, or hormesis, have been attributed to various mechanisms, we here provide evidence that alternative ligand binding sites may contribute to this phenomenon.

3-methylcholanthrene induces differential recruitment of aryl hydrocarbon receptor to human promoters

The paper by Pansoy and coworkers investigates the effects of the aryl hydrocarbon receptor (AHR) ligand 3-methylcholanthrene (3MC) on recruitment of the AHR complex to human promoters in T47D breast cancer cells. The results are particularly important because they can be compared with a prior study using the potent AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the same cell line. The chromatin immunoprecipitation and promoter-focused microarrays (ChIP-chip) demonstrated that after treatment of T47D cells with 1microM 3MC, there were 241 AHR-3MC bound regions and many of these contained AHR-responsive elements. However, they also observed interactions with regions that do not contain these responsive elements, and subsequent analysis of selected target genes show that 3MC-dependent AHR binding did not necessarily predict Ah-responsiveness because induction, repression, and no effects were observed. A prior study with TCDD demonstrated that both 3MC and TCDD induced AHR binding to 127 common regions; however, there were significant differences in ligand (3MC vs. TCDD)-dependent AHR bound regions. The results illustrate the complexity of AHR signaling and also demonstrate that compared with TCDD as a reference ligand, 3MC is a selective AHR modulator.

The role of estrogen receptor beta (ERbeta) in malignant diseases--a new potential target for antiproliferative drugs in prevention and treatment of cancer

The discovery of ERbeta in the middle of the 1990s represents a paradigm shift in our understanding of estrogen signaling. It has turned out that estrogen action is not mediated by one receptor, ERalpha, but by two balancing factors, ERalpha and ERbeta, which are often antagonistic to one another. Excitingly, ERbeta has been shown to be widespread in the body and to be involved in a multitude of physiological and pathophysiological events. This has led to a strong interest of the pharmaceutical industry to target ERbeta by drugs against various diseases. In this review, focus is on the role of ERbeta in malignant diseases where the anti proliferative activity of ERbeta gives hope of new therapeutic approaches.

Estrogen receptor alpha controls a gene network in luminal-like breast cancer cells comprising multiple transcription factors and microRNAs

Luminal-like breast tumor cells express estrogen receptor alpha (ERalpha), a member of the nuclear receptor family of ligand-activated transcription factors that controls their proliferation, survival, and functional status. To identify the molecular determinants of this hormone-responsive tumor phenotype, a comprehensive genome-wide analysis was performed in estrogen stimulated MCF-7 and ZR-75.1 cells by integrating time-course mRNA expression profiling with global mapping of genomic ERalpha binding sites by chromatin immunoprecipitation coupled to massively parallel sequencing, microRNA expression profiling, and in silico analysis of transcription units and receptor binding regions identified. All 1270 genes that were found to respond to 17beta-estradiol in both cell lines cluster in 33 highly concordant groups, each of which showed defined kinetics of RNA changes. This hormone-responsive gene set includes several direct targets of ERalpha and is organized in a gene regulation cascade, stemming from ligand-activated receptor and reaching a large number of downstream targets via AP-2gamma, B-cell activating transcription factor, E2F1 and 2, E74-like factor 3, GTF2IRD1, hairy and enhancer of split homologue-1, MYB, SMAD3, RARalpha, and RXRalpha transcription factors. MicroRNAs are also integral components of this gene regulation network because miR-107, miR-424, miR-570, miR-618, and miR-760 are regulated by 17beta-estradiol along with other microRNAs that can target a significant number of transcripts belonging to one or more estrogen-responsive gene clusters.

Implications of corticotropin releasing factor in targeted anticancer therapy

There is a need to develop novel anticancer therapies that eliminate adverse side effects produced by current treatments. Corticotropin releasing factor (CRF), an endogenous neuroedocrine factor, which typically regulates biological and psychological indicators of stress, has recently been found to be expressed by tumor malignancies. Here, we discuss the implications of CRF as a target for antitumor therapy through regulation of tumor immune escape mechanisms.

New selective estrogen and androgen receptor modulators

PURPOSE OF REVIEW

The present review focuses on the most significant recent findings regarding selective estrogen receptor modulators (SERMs) and selective androgen receptor modulators (SARMs). SERMs, which interact with estrogen receptor-alpha and estrogen receptor-beta in multiple tissues, continue to generate clinical interest in potential applications in as many disorders as the tissues in which the two known receptors are found. SARMs have been demonstrated to have fewer clinical applications to date, but continue to be investigated for use in multiple disorders in which androgen receptor modulation is likely to be important. Both types of compounds hold great promise for therapeutic use in multiple hormonal disorders involving tissue-specific effects mediated by estrogen or androgen receptors.

RECENT FINDINGS

Although SERMs have been available for clinical use for 50 years, recent investigation has focused on large randomized clinical trials for newer indications of older agents or smaller clinical trials of newer agents with improved clinical activity and reduced side effects in specific tissues. In particular, the large, prospective, randomized, controlled, multiyear Study of Tamoxifen and Raloxifene and Raloxifene Use in the Heart clinical trials have recently shown interesting similarities and differences between tamoxifen and raloxifene in estrogen-responsive tissues. Lasofoxifene and arzoxifene are two newer SERMs that have recently been demonstrated to improve bone mineral density and lower serum cholesterol values compared with older SERMs in smaller clinical trials. SARMs are a newer category of drug still being investigated mostly at the basic and preclinical level, with fewer clinical trials available for review. SARMs are currently being investigated mostly for use in prostate cancer at different stages but hold promise for multiple other applications.

SUMMARY

Recent clinical trials indicate that SERMs are useful in treatment of disorders of bone and mineral metabolism and breast cancer and in reduction of cardiovascular risk factors. SARMs offer important benefits for management of prostate cancer at different stages, as well as other disorders.