Relationship between tamoxifen-induced transforming growth factor beta 1 expression, cytostasis and apoptosis in human breast cancer cells

The adverse effect of anticancer drug toremifene on vascular smooth muscle cells is an important aspect of its tumor growth inhibition

PURPOSE

Toremifene (TOR) is widely used as an antineoplastic drug and has an inhibitory effect on angiogenesis in mesenteric desmoid tumors and vascular intracranial solitary fibrous tumors. However, no study has investigated the direct effect of TOR on vascular cells. This study aimed at exploring the effect of TOR on the behaviors of vascular smooth muscle cells (VSMCs).

METHODS

Human aortic umbilical vascular smooth muscle cells (HAVSMCs) were treated by TOR. Cell morphology, migration, adhesion, and proliferation assay were investigated. The cell cycle, apoptosis, mitochondrial membrane potential, and reactive oxygen species were assessed using flow cytometry. Caspase-3 and 9 activities were assayed using Caspase-3 and Caspase-9 Activity Assay kits, respectively. Immunofluorescence and Western blot assays were carried out to characterize protein expressions of PCNA, p53, and Rho/ROCK signaling pathway.

RESULTS

TOR damaged cytoskeleton, inhibited VSMC proliferation, migration, and adhesion, and induced abnormal cell morphology and apoptosis. The antiproliferative activity of TOR was associated with the induction of G0/G1 phase arrest, blocking the cell cycle. TOR disrupted intracellular reactive oxygen species and mitochondrial membrane potential, and enhanced p53 expression and the activities of caspase-3 and caspase-9. Thus, TOR-induced apoptosis by the mitochondrial signaling pathway. Additionally, TOR induced decreased Rho, ROCK, MLC, and pMLC proteins. Collectively, TOR may affect multiple behaviors of VSMCs by damaging cytoskeleton through the Rho/ROCK pathway.

CONCLUSION

The adverse effect of TOR on VSMCs could be considered as an important aspect of tumor growth inhibition.

Effects of tamoxifen on normal breast tissue histological composition: Results from a randomised six-arm placebo-controlled trial in healthy women

Tamoxifen prevents recurrence of breast cancer and is suggested for preventive risk-reducing therapy. Tamoxifen reduces mammographic density, a proxy for therapy response, but little is known about its effects in remodelling normal breast tissue. Our study, a substudy within the double-blinded dose-determination trial KARISMA, investigated tamoxifen-specific changes in breast tissue composition and histological markers in healthy women. We included 83 healthy women randomised to 6 months daily intake of 20, 10, 5, 2.5, 1 mg of tamoxifen or placebo. The groups were combined to "no dose" (0-1 mg), "low-dose" (2.5-5 mg) or "high-dose" (10-20 mg) of tamoxifen. Ultrasound-guided biopsies were collected before and after tamoxifen exposure. In each biopsy, epithelial, stromal and adipose tissues was quantified, and expression of epithelial and stromal Ki67, oestrogen receptor (ER) and progesterone receptor (PR) analysed. Mammographic density using STRATUS was measured at baseline and end-of-tamoxifen-exposure. We found that different doses of tamoxifen reduced mammographic density and glandular-epithelial area in premenopausal women and associated with reduced epithelium and increased adipose tissue. High-dose tamoxifen also decreased epithelial ER and PR expressions in premenopausal women. Premenopausal women with the greatest reduction in proliferation also had the greatest epithelial reduction. In postmenopausal women, high-dose tamoxifen decreased the epithelial area with no measurable density decrease. Tamoxifen at both low and high doses influences breast tissue composition and expression of histological markers in the normal breast. Our findings connect epithelial proliferation with tissue remodelling in premenopausal women and provide novel insights to understanding biological mechanisms of primary prevention with tamoxifen.

Advances in Immunotherapy and the TGF-β Resistance Pathway in Metastatic Bladder Cancer

Simple Summary

Bladder cancer accounts for a significant burden to global public health. Despite advances in therapeutics with the advent of immunotherapy, only a small subset of patients benefit from immunotherapy. In this review, we examine the evidence that suggests that the TGF-β pathway may present a resistance mechanism to immunotherapy. In addition, we present possible therapies that may overcome the TGF-β resistance pathway in the treatment of bladder cancer.

Abstract

Bladder cancer accounts for nearly 200,000 deaths worldwide yearly. Urothelial carcinoma (UC) accounts for nearly 90% of cases of bladder cancer. Cisplatin-based chemotherapy has remained the mainstay of treatment in the first-line setting for locally advanced or metastatic UC. More recently, the treatment paradigm in the second-line setting was drastically altered with the approval of several immune checkpoint inhibitors (ICIs). Given that only a small subset of patients respond to ICI, further studies have been undertaken to understand potential resistance mechanisms to ICI. One potential resistance mechanism that has been identified in the setting of metastatic UC is the TGF-β signaling pathway. Several pre-clinical and ongoing clinical trials in multiple advanced tumor types have evaluated several therapies that target the TGF-β pathway. In addition, there are ongoing and planned clinical trials combining TGF-β inhibition with ICI, which may provide a promising therapeutic approach for patients with advanced and metastatic UC.

Candidate methylation sites associated with endocrine therapy resistance in ER+/HER2- breast cancer

BACKGROUND

Estrogen receptor (ER) positive breast cancer is often effectively treated with drugs that inhibit ER signaling, i.e., tamoxifen (TAM) and aromatase inhibitors (AIs). However, 30% of ER+ breast cancer patients develop resistance to therapy leading to tumour recurrence. Changes in the methylation profile have been implicated as one of the mechanisms through which therapy resistance develops. Therefore, we aimed to identify methylation loci associated with endocrine therapy resistance.

METHODS

We used genome-wide DNA methylation profiles of primary ER+/HER2- tumours from The Cancer Genome Atlas in combination with curated data on survival and treatment to predict development of endocrine resistance. Association of individual DNA methylation markers with survival was assessed using Cox proportional hazards models in a cohort of ER+/HER2- tumours (N = 552) and two sub-cohorts corresponding to the endocrine treatment (AI or TAM) that patients received (N = 210 and N = 172, respectively). We also identified multivariable methylation signatures associated with survival using Cox proportional hazards models with elastic net regularization. Individual markers and multivariable signatures were compared with DNA methylation profiles generated in a time course experiment using the T47D ER+ breast cancer cell line treated with tamoxifen or deprived from estrogen.

RESULTS

We identified 134, 5 and 1 CpGs for which DNA methylation is significantly associated with survival in the ER+/HER2-, TAM and AI cohorts respectively. Multi-locus signatures consisted of 203, 36 and 178 CpGs and showed a large overlap with the corresponding single-locus signatures. The methylation signatures were associated with survival independently of tumour stage, age, AI treatment, and luminal status. The single-locus signature for the TAM cohort was conserved among the loci that were differentially methylated in endocrine-resistant T47D cells. Similarly, multi-locus signatures for the ER+/HER2- and AI cohorts were conserved in endocrine-resistant T47D cells. Also at the gene set level, several sets related to endocrine therapy and resistance were enriched in both survival and T47D signatures.

CONCLUSIONS

We identified individual and multivariable DNA methylation markers associated with therapy resistance independently of luminal status. Our results suggest that these markers identified from primary tumours prior to endocrine treatment are associated with development of endocrine resistance.

Cytotoxicity of chlorhexidine and neem extract on cultured human gingival fibroblasts through fluorescence-activated cell sorting analysis : An in-vitro study

Objective:

To assess the influence of chlorhexidine (CHX), neem vehicle control (NVC), and neem extract (NE) on cultured human gingival fibroblasts (hGFs) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and fluorescence-activated cell sorting (FACS) analysis.

Materials and Methods:

Fibroblasts were derived from healthy gingival biopsy specimens harvested aseptically. The effects of CHX, NVC, and NE were evaluated on cultured hGFs through FACS and MTT assay.

Results:

MTT assay with hGFs indicated altered morphology with maximum cell death at 10% CHX, while NVC and NE showed similar results at a concentration of 75% and above. On FACS analysis, beyond 1%, CHX adversely affected the cell cycle phase distribution whereas NE exerted a detrimental effect only at 100%. Moreover, both with NVC and NE cells were well differentiated in all the three phases of the cell cycle, with distinction getting lost at 50% to finally causing cell death at 100%.

Conclusions:

CHX beyond 1% concentration exhibited a toxic effect on hGFs at 1, 5, and 15 min time exposure. However, NE did not adversely affect the fibroblasts even up to 50% concentration showing a less toxic effect in comparison with CHX on these cells. The cytoprotective and oral friendly quality of NE emphaisze the superiority of NE over CHX.

Molecular mechanisms involved in the protective actions of Selective Estrogen Receptor Modulators in brain cells

Synthetic selective modulators of the estrogen receptors (SERMs) have shown to protect neurons and glial cells against toxic insults. Among the most relevant beneficial effects attributed to these compounds are the regulation of inflammation, attenuation of astrogliosis and microglial activation, prevention of excitotoxicity and as a consequence the reduction of neuronal cell death. Under pathological conditions, the mechanism of action of the SERMs involves the activation of estrogen receptors (ERs) and G protein-coupled receptor for estrogens (GRP30). These receptors trigger neuroprotective responses such as increasing the expression of antioxidants and the activation of kinase-mediated survival signaling pathways. Despite the advances in the knowledge of the pathways activated by the SERMs, their mechanism of action is still not entirely clear, and there are several controversies. In this review, we focused on the molecular pathways activated by SERMs in brain cells, mainly astrocytes, as a response to treatment with raloxifene and tamoxifen.

Tamoxifen inhibits the proliferation of non‑melanoma skin cancer cells by increasing intracellular calcium concentration

Tamoxifen is an estrogen receptor (ER) antagonist used as first-line chemotherapy in breast cancer. Recent studies suggest that tamoxifen may be effective not only for ER‑positive but also for ER‑negative cancer cases. The aim of the present study was to investigate the antiproliferative effect of tamoxifen against human non‑melanoma skin cancer cells. Tamoxifen inhibited the proliferation of the skin squamous cell carcinoma (SCC) cell lines A431, DJM‑1 and HSC‑1. A431 cells did not express ER‑α or -β, suggesting that tamoxifen may exert antiproliferative effects on skin SCC cells via a non‑ER‑mediated pathway. Tamoxifen increased the intracellular calcium concentration of skin SCC cells, and this increase in intracellular calcium concentration by calcium ionophore A23187 suppressed the proliferation of skin SCC cells. These data indicate that tamoxifen inhibited the proliferation of human skin SCC cells via increasing intracellular calcium concentration. Voltage-gated calcium channels and non‑selective cation channels are involved in the increase in intracellular calcium concentration induced by tamoxifen. The broad-spectrum protein kinase C (PKC) inhibitor phloretin significantly attenuated the antiproliferative effect of tamoxifen on skin SCC cells. From these data, it may be concluded that tamoxifen inhibits the proliferation of skin SCC cells by induction of extracellular calcium influx via calcium channels in the plasma membrane and by subsequent activation of PKC.

Cytotoxic effects of seven Tunisian hospital wastewaters on the proliferation of human breast cancer cell line MDA-231: correlation with their chemical characterization

Hospital wastewaters contain large amounts of pharmaceutical residues, which may eventually be discharged into the aquatic environment through wastewater treatment plants, raising the question of their impact on human and environmental health. This has prompted the launch of several monitoring studies into the most commonly administered compounds in urban wastewater. The aim of this study was, therefore, to explore the cytotoxic potential of wastewaters samples collected from seven hospitals in Tunisia. The physicochemical analyses showed a large fluctuation of certain parameters in the collected samples, such as chemical oxygen demand (ranged from 860 to 1720 mg L^-1), biochemical oxygen demand (ranged from 385 to 747 mg L^-1), total organic carbon (ranged from 256 to 562 g L^-1), total suspended solids (ranged from 905 to 1450 mg L^-1), conductivity (ranged from 3.31 to 7.14 μsm/cm), and turbidity (ranged from 100 to 480 NTU). The analysis using inductively coupled plasma mass spectrometry (ICP-MS) also showed that hospital wastewater contains high concentrations of Hg (ranged from 0.0024 to 0.019 mg L^-1). This could be explained by the variation of the activity and the services in certain hospitals compared to others. All hospital wastewater samples induced the proliferation of human breast cancer cell line MDA-231, even at low concentrations (20 μL/assay). Moreover, the maximum induction reached at the concentration of 60 μL/assay in wastewater samples from hospitals located in Monastir, Sidi Bouzid, Mahdia, and Sfax with percentages of induction up to 42.33, 14, 7.61, and 5.42%, respectively. These observations could be due to the presence of endocrine disrupting compounds (EDCs) in these wastewaters. Given this, our results evidenced the potential risk of these hospital effluents to environmental and public health.

Oxidative stress contributes to the tamoxifen-induced killing of breast cancer cells: implications for tamoxifen therapy and resistance

Tamoxifen is the accepted therapy for patients with estrogen receptor-α (ERα)-positive breast cancer. However, clinical resistance to tamoxifen, as demonstrated by recurrence or progression on therapy, is frequent and precedes death from metastases. To improve breast cancer treatment it is vital to understand the mechanisms that result in tamoxifen resistance. This study shows that concentrations of tamoxifen and its metabolites, which accumulate in tumors of patients, killed both ERα-positive and ERα-negative breast cancer cells. This depended on oxidative damage and anti-oxidants rescued the cancer cells from tamoxifen-induced apoptosis. Breast cancer cells responded to tamoxifen-induced oxidation by increasing Nrf2 expression and subsequent activation of the anti-oxidant response element (ARE). This increased the transcription of anti-oxidant genes and multidrug resistance transporters. As a result, breast cancer cells are able to destroy or export toxic oxidation products leading to increased survival from tamoxifen-induced oxidative damage. These responses in cancer cells also occur in breast tumors of tamoxifen-treated mice. Additionally, high levels of expression of Nrf2, ABCC1, ABCC3 plus NAD(P)H dehydrogenase quinone-1 in breast tumors of patients at the time of diagnosis were prognostic of poor survival after tamoxifen therapy. Therefore, overcoming tamoxifen-induced activation of the ARE could increase the efficacy of tamoxifen in treating breast cancer.

Tamoxifen Action in ER-Negative Breast Cancer

Breast cancer is a highly heterogeneous disease. Tamoxifen is a selective estrogen receptor (ER) modulator and is mainly indicated for the treatment of breast cancer in postmenopausal women and postsurgery neoadjuvant therapy in ER-positive breast cancers. Interestingly, 5–10% of the ER-negative breast cancers have also shown sensitivity to tamoxifen treatment. The involvement of molecular markers and/or signaling pathways independent of ER signaling has been implicated in tamoxifen sensitivity in the ER-negative subgroup. Studies reveal that variation in the expression of estrogen-related receptor alpha, ER subtype beta, tumor microenvironment, and epigenetics affects tamoxifen sensitivity. This review discusses the background of the research on the action of tamoxifen that may inspire future studies to explore effective therapeutic strategies for the treatment of ER-negative and triple-negative breast cancers, the latter being an aggressive disease with worse clinical outcome.

Loss of TGFβ Receptor Type 2 Expression Impairs Estrogen Response and Confers Tamoxifen Resistance

One third of the patients with estrogen receptor α (ERα)-positive breast cancer who are treated with the antiestrogen tamoxifen will either not respond to initial therapy or will develop drug resistance. Endocrine response involves crosstalk between ERα and TGFβ signaling, such that tamoxifen nonresponsiveness or resistance in breast cancer might involve aberrant TGFβ signaling. In this study, we analyzed TGFβ receptor type 2 (TGFBR2) expression and correlated it with ERα status and phosphorylation in a cohort of 564 patients who had been randomized to tamoxifen or no-adjuvant treatment for invasive breast carcinoma. We also evaluated an additional four independent genetic datasets in invasive breast cancer. In all the cohorts we analyzed, we documented an association of low TGFBR2 protein and mRNA expression with tamoxifen resistance. Functional investigations confirmed that cell cycle or apoptosis responses to estrogen or tamoxifen in ERα-positive breast cancer cells were impaired by TGFBR2 silencing, as was ERα phosphorylation, tamoxifen-induced transcriptional activation of TGFβ, and upregulation of the multidrug resistance protein ABCG2. Acquisition of low TGFBR2 expression as a contributing factor to endocrine resistance was validated prospectively in a tamoxifen-resistant cell line generated by long-term drug treatment. Collectively, our results established a central contribution of TGFβ signaling in endocrine resistance in breast cancer and offered evidence that TGFBR2 can serve as an independent biomarker to predict treatment outcomes in ERα-positive forms of this disease.

Breast cancer and osteoporosis

PURPOSE OF REVIEW

Over the past few years, a number of studies have examined the relationship between breast cancer and osteoporosis, the effect of breast cancer treatment on bone health, and the effect of osteoporosis therapies on aromatase inhibitor-induced bone loss and breast cancer recurrence. New guidelines have been released on the prevention of osteoporotic fractures in women with breast cancer who are on aromatase inhibitors for adjuvant therapy.

RECENT FINDINGS

Despite common factors linking high bone mineral density and increased risk of breast cancer, women with breast cancer are not protected from osteoporosis or osteoporotic fractures. Recent data suggest that aromatase inhibitors have a detrimental effect on bone mineral density and can increase the risk of fractures. Bisphosphonate therapy not only preserves aromatase inhibitor-induced bone loss, but may also improve disease-free survival and decrease risk of death in select women with breast cancer (i.e., postmenopausal women).

SUMMARY

Osteoporosis and breast cancer are common in women, especially in postmenopausal women. Current guidelines suggest that we need to pay special attention to those on aromatase inhibitors to prevent adverse bone outcomes.

Mechanisms of resistance to endocrine therapy in breast cancer: focus on signaling pathways, miRNAs and genetically based resistance

Breast cancer is the most frequent malignancy diagnosed in women. Approximately 70% of breast tumors express the estrogen receptor (ER). Tamoxifen and aromatase inhibitors (AIs) are the most common and effective therapies for patients with ERα-positive breast cancer. Alone or combined with chemotherapy, tamoxifen significantly reduces disease progression and is associated with more favorable impact on survival in patients. Unfortunately, endocrine resistance occurs, either de novo or acquired during the course of the treatment. The mechanisms that contribute to hormonal resistance include loss or modification in the ERα expression, regulation of signal transduction pathways, altered expression of specific microRNAs, balance of co-regulatory proteins, and genetic polymorphisms involved in tamoxifen metabolic activity. Because of the clinical consequences of endocrine resistance, new treatment strategies are arising to make the cells sensitive to tamoxifen. Here, we will review the current knowledge on mechanisms of endocrine resistance in breast cancer cells. In addition, we will discuss novel therapeutic strategies to overcome such resistance. Undoubtedly, circumventing endocrine resistance should help to improve therapy for the benefit of breast cancer patients.

GDF3 inhibits the growth of breast cancer cells and promotes the apoptosis induced by Taxol

PURPOSE

The aim of this study is to investigate whether GDF3 is related to the progression of human breast cancer and the effects of GDF3 on breast cancer cells.

METHODS

The expression of GDF3 in 24 breast cancer specimens paired with corresponding neighboring nontumorous tissue was studied by Western blot. Breast cancer cells were treated with different concentrations of recombinant human GDF3 protein. Using lentivirus containing sh-RNA, we knocked down the expression of GDF3. Soft agar assay was performed to explore the effects of GDF3 on colony formation. Different anti-tumor drugs dealt with MCF-7 cells stably expressing GDF3.

RESULTS

We found that GDF3 expression level was significantly down-regulated in breast cancer tissues compared to the surrounding nontumorous tissues. GDF3 proteins could inhibit the proliferation of MCF-7 and T47D cells. We also found that the knockdown of GDF3 resulted in the promotion of colony formation and enhanced the ability of anchorage-independent cell growth in soft agar. Furthermore, overexpression of GDF3 could promote the apoptosis induced by Taxol.

CONCLUSIONS

Our data indicated that GDF3 expression is significantly decreased in human breast cancer tissues, and reconstitution of GDF3 in breast cancer may be a potential therapeutic approach to inhibit aggressive growth of breast cancer.

Blockade of Autocrine TGF-β Signaling Inhibits Stem Cell Phenotype, Survival, and Metastasis of Murine Breast Cancer Cells

Transforming growth factor beta (TGF-β) signaling has been implicated in driving tumor progression and metastasis by inducing stem cell-like features in some human cancer cell lines. In this study, we have utilized a novel murine cell line NMuMG-ST, which acquired cancer stem cell (CSC) phenotypes during spontaneous transformation of the untransformed murine mammary cell line NMuMG, to investigate the role of autocrine TGF-β signaling in regulating their survival, metastatic ability, and the maintenance of cancer stem cell characteristics. We have retrovirally transduced a dominant-negative TGF-β type II receptor (DNRII) into the NMuMG-ST cell to abrogate autocrine TGF-β signaling. The expression of DNRII reduced TGF-β sensitivity of the NMuMG-ST cells in various cell-based assays. The blockade of autocrine TGF-β signaling reduced the ability of the cell to grow anchorage-independently and to resist serum deprivation-induced apoptosis. These phenotypes were associated with reduced levels of active and phosphorylated AKT and ERK, and Gli1 expression suggesting that these pathways contribute to the growth and survival of this model system. More interestingly, the abrogation of autocrine TGF-β signaling also led to the attenuation of several features associated with mammary stem cells including epithelial-mesenchymal transition, mammosphere formation, and expression of stem cell markers. When xenografted in athymic nude mice, the DNRII cells were also found to undergo apoptosis and induced significantly lower lung metastasis burden than the control cells even though they formed similar size of xenograft tumors. Thus, our results indicate that autocrine TGF-β signaling is involved in the maintenance and survival of stem-like cell population resulting in the enhanced metastatic ability of the murine breast cancer cells.

Centchroman induces G0/G1 arrest and caspase-dependent apoptosis involving mitochondrial membrane depolarization in MCF-7 and MDA MB-231 human breast cancer cells

Studies with Centchroman (CC) as a candidate anti-breast cancer agent are into phase III multicentric clinical trial in stage III/IV breast cancer. We have previously demonstrated its anti-neoplastic activity in Estrogen Receptor positive (ER+ve) MCF-7 Human Breast Cancer Cells (HBCCs). We now present the basis for anti-neoplastic activity of CC, mediated through apoptosis in both ER+ve/-ve MCF-7 and MDA MB-231 HBCCs respectively, compared to Tamoxifen (TAM) as a positive control. All the experiments were performed with 48 h estrogen-deprived cells exposed to CC/TAM for the subsequent 48 h. Cytotoxic potential of CC was assessed through SRB assay. Cell-cycle analysis, Time-dependent cytotoxicity, Reactive Oxygen Species (ROS) and Mitochondrial Membrane Permeability were investigated by Flow Cytometry. Early-stage apoptosis was detected by Annexin-PI staining. Caspases were assayed colorimetrically whereas nuclear derangements were assessed morphologically through PI staining and finally by DNA fragmentation analysis. Cell viability studies confirmed the IC50 of CC in MCF-7 and MDA MB-231 cells to be 10 and 20 microM (P < 0.001) respectively, suggesting enhanced susceptibility of the former cell type to CC. FACS data reveals CC mediated G0/G1 arrest (P < 0.01) along with the presence of prominent sub-G0/G1 peak (P < 0.001) in both the cell types suggesting ongoing apoptosis. Phosphatidylserine externalization, mitochondrial events, caspase evaluation and nuclear morphology changes reveal initiation/progression of caspase-dependent apoptosis even at a dose of 1 microM which eventually leads to DNA fragmentation in both the cell types. Results demonstrate that CC induces caspase-dependent apoptosis in MCF-7 and MDA MB-231 cells irrespective of ER status similar to TAM in terms of anti-neoplastic activity.

The functional implications of Akt activity and TGF-beta signaling in tamoxifen-resistant breast cancer

Development of acquired resistance to tamoxifen is a major clinical problem during endocrine treatment in estrogen receptor positive breast cancer. Transforming growth factor-beta1 (TGF-beta) has been implicated in tamoxifen-induced cellular signaling in breast cancer, and increased Akt activation is associated with tamoxifen-resistant cell types. We hypothesized that the relationship between TGF-beta and Akt signaling may be involved in the development and progression of tamoxifen resistance. Tamoxifen-resistant (Tam-R) cells were established from parental MCF-7 cells by continuously exposing them to 4-hydroxytamoxifen (4-OHT). Tam-R cells were associated with a decrease in TGF-beta1 secretion, TGF-beta-mediated transcriptional response, and growth inhibitory effects of 4-OHT. Tam-R cells expressed significantly higher levels of phosphorylated Akt and lower levels of phosphorylated Smad 3 in both the absence and presence of 4-OHT when compared to MCF-7 cells treated with 4-OHT. Ectopic expression of constitutively active Akt (Myc-Akt(Myr)) rendered MCF-7 cells resistant to activation by TGF-beta and the growth inhibitory effects of 4-OHT, while over-expression of kinase-dead Akt (Myc-Akt(K179M)) or LY294002 treatment of Tam-R cells enhanced TGF-beta activation and blocked cell growth. These results suggest that suppression of TGF-beta signaling by activated Akt is correlated with the development of tamoxifen resistance in breast cancer.

Tamoxifen Induction of CCAAT Enhancer-binding Protein α Is Required for Tamoxifen-induced Apoptosis

Low concentrations of tamoxifen or its active metabolite 4-hydroxytamoxifen (OHT) induce estrogen receptor alpha (ERalpha)-dependent apoptosis. To analyze the pathway of OHT-ERalpha-induced apoptosis, we developed stably transfected lines of HeLa cells expressing wild-type ER and an inactive mutant ERalpha unable to bind estrogen response elements. HeLa cells expressing the mutant ERalpha and HeLa cells expressing wild-type ERalpha in which the ER was knocked down with an ER-specific small interfering RNA were not killed by Tam or OHT, suggesting that estrogen response element-mediated transcription is required for Tam- and OHT-induced apoptosis. Microarray analysis to identify a gene(s) whose expression is important in OHT-ER-mediated apoptosis identified 19 mRNAs that OHT up-regulated by >1.6-fold and 15 down-regulated mRNAs. Gene function and the time course of induction by OHT-ERalpha led us to further investigate CCAAT enhancer-binding protein alpha (C/EBPalpha), which has roles in cell cycle progression and apoptosis, and p21. Quantitative reverse transcription-PCR, Western blot analysis, and RNA interference knockdown suggest that cell cycle arrest resulting from OHT-ERalpha induction of p21 may facilitate apoptosis. OHT-ERalpha, but not E2-ERalpha, induced C/EBPalpha mRNA and protein. RNA interference knockdown of C/EBPalpha nearly abolished OHT-ERalpha-induced apoptosis. We isolated stable cell lines that were resistant to OHT-induced apoptosis, contain full-length functional ERalpha, and undergo apoptosis in response to etoposide. In these OHT-resistant cell lines both before and after OHT treatment, C/EBPalpha levels are much lower than in OHT-sensitive cells. These studies establish a novel molecular site responsible for Tam- and OHT-ERalpha-induced apoptosis of cancer cells.

The role of tamoxifen in combination with cisplatin on oral squamous cell carcinoma cell lines

The purpose of this study was to evaluate the effect of tamoxifen (TAM) when used in combination with cisplatin on oral squamous cell carcinoma (OSCC). For this, the relation between estrogen receptor (ER) expression level and the cytotoxic effect of TAM, the apoptotic effect and its molecular mechanisms of TAM were investigated using OSCC cell lines. Combination treatment demonstrated a superior cytotoxic and apoptotic effect on OSCC cell lines. Considerable amount of ER was detected in some OSCC cell lines, but there were no significant differences of cytotoxic effect of TAM. TAM inhibited PKC activity and up-regulated TGF-beta1 secretion.

Effect of ionizing radiation on the pteridine metabolic pathway and evaluation of its cytotoxicity in exposed hospital staff

Investigations carried out to estimate the effect of long-term occupational exposure to low levels of external ionizing radiation indicated that exposed hospital staff showed an increase in chromosome aberrations. The purpose of this study was to evaluate whether genomic instability or an alteration in pteridine synthesis could be used as a marker of the potential hazard of ionizing radiation in hospital workers. Twenty gamma-radiation- and 33 X-ray-exposed technicians working in radiotherapy and radio-diagnostic units were included in this study, along with 22 healthy matched individuals. Plasma concentrations of nitrite plus nitrate (NO(x)) were measured to estimate reactive nitrogen species. Urinary neopterin, biopterin and creatinine concentrations were measured by high-performance liquid chromatography to determine metabolic activity along the pteridine pathway. Sister chromatid exchange was used as a measure of mutagenicity. Apoptosis was evaluated morphologically and also with a DNA-fragmentation test. The plasma NO(x) levels of both gamma-radiation- and X-ray-exposed technicians were significantly higher than those of the healthy controls (p<0.05). While the urinary biopterin concentrations were significantly higher in radiation-exposed groups compared with the healthy subjects (p<0.05), urinary neopterin concentrations remained unchanged. The apoptosis rates of gamma-radiation- and X-ray-exposed workers were significantly elevated in comparison with those in the control group (both p<0.05). Also, the increase in sister chromatid exchange frequency was significant in each of the radiation-exposed groups (exposed groups versus controls; p<0.05). These results indicate that long-term exposure to low-dose ionizing radiation, even below the permitted levels, could result in increased oxidative stress, which may lead to DNA damage and mutagenicity.

Role of transforming growth factor Beta in human cancer

Transforming growth factor beta (TGF-beta) is a ubiquitous and essential regulator of cellular and physiologic processes including proliferation, differentiation, migration, cell survival, angiogenesis, and immunosurveillance. Alterations in the TGF-beta signaling pathway, including mutation or deletion of members of the signaling pathway and resistance to TGF-beta-mediated inhibition of proliferation are frequently observed in human cancers. Although these alterations define a tumor suppressor role for the TGF-beta pathway in human cancer, TGF-beta also mediates tumor-promoting effects, either through differential effects on tumor and stromal cells or through a fundamental alteration in the TGF-beta responsiveness of the tumor cells themselves. TGF-beta and members of the TGF-beta signaling pathway are being evaluated as prognostic or predictive markers for cancer patients. Ongoing advances in understanding the TGF-beta signaling pathway will enable targeting of this pathway for the chemoprevention and treatment of human cancers.

Tamoxifen treatment failure in cancer and the nonlinear dynamics of TGFbeta

The process of cancer invasion involves a complex interplay between cell-cell and cell-medium adhesion, proteolytic enzyme secretion, cell birth and death processes, random and directed motility, and immune response, as well as many other factors. The growth factor TGF beta is known to have a complex effect on this process. It inhibits mitosis and promotes apoptosis in a concentration-dependent manner in vitro, and it is for this reason that its secretion is thought to be helpful in inhibiting tumour growth. However, recent in vitro and in vivo results have shown a significant effect of this growth factor in promoting the sensitivity of malignantly transformed cells to gradients of extracellular matrix proteins--an effect which tends to increase invasiveness. The drug tamoxifen has been demonstrated to be therapeutically effective in the treatment of patients with breast cancer; however, it is known also that many patients become resistant to the effect of this drug after a few years, and the reasons for this remain controversial. In this work we take our established model of cancer invasion (J. Theor. Biol. 216(1) (2002) 85), and extend it to include the effect of TGF beta. In so doing we demonstrate that a tamoxifen-stimulated upregulation of the secretion of TGF beta may give rise to a tumour which has a smaller number of cells but which has a greater invasiveness, greater metastatic potential, and a tumour histology which is known to correlate with a poorer prognosis. These data suggest that tamoxifen-stimulated secretion of TGF beta might explain treatment failure in some patients.

PC cell-derived growth factor mediates tamoxifen resistance and promotes tumor growth of human breast cancer cells

PC cell-derived growth factor, also known as progranulin, is an M(r) 88,000 growth factor (referred as PCDGF/GP88) overexpressed in human breast cancer. Antisense inhibition of PCDGF/GP88 expression in MDA-MB-468 cells inhibited tumor formation in nude mice. In estrogen receptor-positive cells, PCDGF/GP88 was expressed in response to estradiol and shown to mediate its mitogenic effect. Pathologic studies indicated that PCDGF/GP88 was expressed in 80% of invasive ductal carcinomas in correlation with parameters of poor prognosis. In the present article, the relationship between PCDGF/GP88 expression and tamoxifen resistance was examined in MCF-7 cells. PCDGF/GP88 overexpression rendered MCF-7 cells able to proliferate in the absence of estrogen and in the presence of tamoxifen. The PCDGF/GP88-overexpressing cells formed tumors in ovariectomized nude mice in the absence of estradiol and in its presence, in contrast to MCF-7 cells. Tumor growth of the overexpressing cells was increased significantly when the mice were treated with tamoxifen. PCDGF/GP88 blocked tamoxifen-induced apoptosis by preventing down-regulation of bcl-2 expression and poly(ADP-ribose) polymerase cleavage. In addition, PCDGF/GP88-overexpressing cells presented higher level of the angiogenic factors vascular endothelial growth factor and angiopoietin-1 than MCF-7 control cells. Tamoxifen treatment additionally increased the level of vascular endothelial growth factor. These studies suggest that PCDGF/GP88 plays a critical role in breast cancer tumorigenesis and in the transition to estrogen independence and tamoxifen resistance, a hallmark of poor prognosis. On the basis of the in vivo studies, it is postulated that tamoxifen treatment of patients with estrogen receptor-positive breast tumors overexpressing PCDGF/GP88 could have adverse clinical consequences.

Tamoxifen increases apoptosis but does not influence markers of proliferation in an MCF-7 xenograft model of breast cancer

Twenty-four nude mice bearing MCF-7 breast cancer cells grown as xenografts and treated with tamoxifen (2.5 mg slow-release pellet) were studied for up to 35 days. Tumour size was measured in 2 dimensions at regular time-intervals and tumours were harvested on each of days 2, 4, 7, 14, 28 and 35 after the start of treatment. Control animals (8) received no treatment and the tumours were harvested after 0 or 35 days. Tumour sections were assessed for prevalence of apoptosis and mitosis and examined immunocytochemically for Ki(67)(MIB-1) and bcl-2 expression. Tumours increased in size during tamoxifen-treatment, but at a significantly slower rate (max. 2.6-fold) than in the untreated control animals; thus tumours not actually regressing may, nevertheless, be responding significantly to tamoxifen. MIB-1 and bcl-2 immunostaining and mitosis failed to show any consistent change over the period of study. Apoptosis, however, increased progressively and significantly to day-28 in tamoxifen-treated tumours, reaching approximately a 5-fold increase over day-0 values, then decreasing again to nearly 3-fold by day-35 (P= 0.0002). The apoptosis: mitosis ratio in treated tumours also increased to approximately 10-fold on day-28 over day-0 values, decreasing to nearly 4-fold by day-35 (P= 0.037). Within the treated group, apoptosis was significantly inversely correlated with both mitosis (R = -0.38, P= 0.03) and expression of bcl-2 (R = -0.48, P= 0.0056) and strongly positively correlated with both time on tamoxifen (R = +0.63, P= 0.0003) and the % inhibition of growth by tamoxifen (R = +0.58,P = 0.0012) in the 28 individual, treated tumours (estimated relative to the mean growth rate in the controls). The apoptosis: mitosis ratio was also inversely correlated with bcl-2 expression (R = -0.56, P= 0.0021) and positively correlated with both time on tamoxifen (R = +0.50, P= 0.0068) and % inhibition of growth (R = +0.56, P= 0.0019). In this hormone-sensitive tumour model for breast cancer, in which tamoxifen caused inhibition rather than regression, it was not possible to detect significant changes in the marker proteins Ki(67)and bcl-2, or in the prevalence of mitosis in relation to treatment; these factors may therefore not be accurate indices of response to tamoxifen in all situations. By contrast, however, tamoxifen induced a significant, early increase in the prevalence of apoptosis associated with inhibition of tumour growth and an inverse relationship in both mitosis and bcl-2 expression, suggesting that apoptosis may be an accurate and sensitive early marker of even a moderate response to tamoxifen.

Effects of low dose tamoxifen on normal breast tissue from premenopausal women

The aim of this study was to determine the effects of low doses of tamoxifen (5 and 10mg/day) for 50 days compared with the standard dose (20 mg/day) on breast biomarkers measured in normal breast tissue from premenopausal patients. A randomised double-blind study was performed using tissue from 56 premenopausal women with a diagnosis of fibroadenoma of the breast. Excisional biopsy was performed on the 50th day of therapy. Normal breast tissue samples were collected during surgery. The patients were divided in groups: A (placebo, n=11); group B (5 mg, n=16), group C (10 mg, n=14) and group D (20 mg, n=15). In this cross-sectional study, differences in the expression of Oestrogen Receptor alpha (ERalpha), Progesterone Receptor (PR), Ki-67, apoptotic bodies and mitotic index between the different groups after treatment can be seen on the normal breast tissue. We believe that a lower dose of tamoxifen could reduce the side-effects associated with treatment without affecting its chemopreventive activity in the breast.

Smad4 as a transcription corepressor for estrogen receptor alpha

Antiestrogen compounds exhibit a variety of different effects in different tissues and are widely used for the treatment of osteoporosis, breast cancer, and other diseases. Upon examining the molecular mechanisms, we found that Smad4, a common signal transducer in the bone morphogenetic protein (BMP)/transforming growth factor-beta (TGF-beta) signaling pathway, functions as a transcription corepressor for human estrogen receptor alpha (ERalpha). Endogenous ERalpha was co-immunoprecipitated with Smad4, and the interaction was induced by antiestrogen ligands such as tamoxifen, raloxifene, and droloxifen, which was confirmed in chromatin immunoprecipitation assays. Smad4 and ERalpha form a complex when ERalpha binds to the estrogen-responsive element within the estrogen target gene promoter. Importantly, the expression of Smad4 inhibits both antiestrogen-induced luciferase activity and estrogen downstream target gene transcription in breast cancer cells. Mapping of the interaction domains indicates that the activation function 1 (AF1) domain of ERalpha is essential for its interaction with Smad4, while the MH1 domain and linker region of Smad4 are essential for the interaction. Our findings represent a novel mechanism that TGF-beta may regulate cell fate through Smad4-mediated cross-talk with estrogen.

New perspectives on growth factor-sex steroid interaction in the prostate

Many organs respond to both sex steroids and growth factors. Regulation of these pathways is integral to cell-cell communications during development and aberrant changes cause disease pathogenesis. Traditionally, paracrine and endocrine actions of growth factors and steroid hormones are considered independently. Recently, new data indicated that activin/TGFbeta and sex steroid signalling are linked; explicitly, that the pathways cross-talk intracellularly. Here we present new perspectives on these interactions, using examples predominantly from the prostate, as it is a well-characterised organ in this context. While this information provides insight to the potential mechanisms behind these interactions, it also presents a new challenge; the action of any of these factors cannot be considered exclusively without considering the impact on the other biological pathways.

Effects of transforming growth factor-beta1 and tumour necrosis factor-alpha on cultured fibroblasts from skin fibroma as modulated by toremifene

To determine how toremifene, an anti-oestrogen triphenylethylene derivate, reduces tumour mass, we investigated its modulation of TGF-beta1 and TNF-alpha in fibroma fibroblasts. Normal and fibroma fibroblasts, isolated from patients affected by Gardner's syndrome without or with fibroma manifestation, were cultured in vitro. Secretion of GAG, collagen and TGF-beta1 was increased in fibroma fibroblasts compared to healthy cells. The increase in TGF-beta1 secretion into the medium was associated with a parallel increase in TGF-beta1 gene expression and receptor number. Receptor cross-linking studies using radiolabelled TGF-beta1 revealed more receptors, particularly types I and II, in fibroma fibroblasts than in normal cells. Normal and fibroma fibroblasts did not synthesise TNF-alpha, but they had TNF-alpha membrane receptors, as shown by TNF-alpha assay. TNF-alpha secreted by human monocytes, which may be present in the peritumoral area, increased cell proliferation and GAG accumulation and was, in turn, enhanced by TGF-beta1 treatment. Both growth factors increased angiogenesis, as shown by the CAM assay. Toremifene reduced TGF-beta1 secretion by fibroma fibroblasts and TNF-alpha secretion by monocytes, thus downregulating cell proliferation, ECM macromolecule accumulation and angiogenic progression. We hypothesise that increased TGF-beta1 gene expression and TGF-beta1 secretion in fibroma fibroblasts as well as the subsequent rise in TNF-alpha production by monocytes may facilitate fibroma growth and that toremifene inhibits autocrine and paracrine growth factor production.

Evaluation of the cytotoxicity of selected systemic and intravitreally dosed drugs in the cultures of human retinal pigment epithelial cell line and of pig primary retinal pigment epithelial cells

The cytotoxicity of the selected systemic and intravitreally dosed drugs tamoxifen, toremifene, chloroquine, 5-fluorouracil, gentamicin and ganciclovir was studied in retinal pigment epithelium (RPE) in vitro. The cytotoxicity was assayed in the human RPE cell line D407 and the pig RPE cell culture using the WST-1 test, which is an assay of cell proliferation and viability. The effects of experimental conditions on the WST-1 test (cell density, serum content in the culture medium, the exposure time) were evaluated. The EC50 values in tamoxifen-treated D407 cells ranged between 6.7 and 8.9 micromol/l, and in pig RPE cells between 10.1 and 12.2 micromol/l, depending on the cell density used. The corresponding values for toremifene were 7.4 to 11.1 micromol/l in D407 cells and 10.0 to 11.6 micromol/l in pig RPE cells. In chloroquine-treated cells, the EC50 values were 110.0 micromol/l for D407 cells and 58.4 micromol/l for pig RPE cells. Gentamicin and ganciclovir did not show any toxicity in micromolar concentrations. The exposure time was a significant factor, especially when the drug did not induce cell death, but was antiproliferative (5-fluorouracil). Serum protected the cells from the toxic effects of the drugs. Both cell cultures were most sensitive to tamoxifen and toremifene, and next to chloroquine. The drug toxicities obtained in the present study were quite similar in both cell types; that is, the pig RPE cells and the human D 407 cell line, despite the differences in, for example, the growth rate and melanin contents of the cell types. Owing to the homeostatic functions important for the whole neuroretina, RPE is an interesting in vitro model for the evaluation of retinal toxicity, but, in addition to the WST-1 test, more specific tests and markers based on the homeostatic functions of the RPE are needed.

Estrogens and environmental estrogens

The natural female sex hormone estrogens binds once inside the cell to a protein receptor to form a 'ligand-hormone receptor complex'. The binding activates the hormone receptor, which triggers specific cellular processes. The activated hormone receptor then turns on specific genes, causing cellular changes that lead to responses typical of a ligand-hormone receptor complex. Estrogens (especially estradiol) bring out the feminine characteristics, control reproductive cycles and pregnancy, influence skin, bone, the cardiovascular system and immunity. Natural hormones are more potent than any of the known synthetic environmental estrogens (except drugs such as diethylstilbestrol [DES]). Estrogen production varies according to different factors (gender, age and reproductive cycles). Women produce more estrogen than men and the production is more abundant during fetal development than in the postmenopausal period. Most natural estrogens are short-lived, do not accumulate in tissue and are easily broken down in the liver. In contrast to natural estrogens, estrogenic drugs such as ethynylestradiol diethylstilbestrol (DES), synthetic environmental estrogens such as beta-hexachlorocyclohexane (beta-HCH), polychlorinated biphenyls (PCBs), o, p, p'DDT, 4-nonylphenol (NP) and phytoestrogens such as isoflavones or lignans, are more stable and remain in the body longer than natural estrogens. Because most of these compounds are lipophilic, they tend to accumulate within the fat and tissue of animals and humans. Thus, depending on the natural estrogen levels, environmental estrogens may have different influences (mimicking, blocking or cancelling out estrogen's effects) on estrogen activities.

Synthesis and secretion of transforming growth factor-beta1 by human desmoid fibroblast cell line and its modulation by toremifene

The present study provides evidence that the in vitro cultured fibroblast cell line from desmoid tumors differs from normal fibrobasts in its extracellular matrix (ECM) macromolecule composition and is modulated by treatment with toremifene, an antiestrogen that reduces tumor mass by an unknown mechanism. The results showed increased transforming growth factor-beta 1 (TGF-beta1) production, TGF-beta1 mRNA expression, and TGF-beta1 receptor number in desmoid fibroblasts compared with normal cells. As desmoid fibroblasts did not produce tumor necrosis factor-alpha (TNF-alpha) but were sensitive to it, which enhanced glycosaminoglycans (GAG) accumulation, we assessed the TGF-beta1 effects on TNF-alpha production by human monocytes. Our results showed TGF-beta1 significantly increased TNF-alpha secretion by monocytes. Toremifene mediated its effects in desmoid fibroblasts via an estrogen receptor-independent pathway. It inhibited GAG accumulation and the secretion of both latent and active forms of TGF-beta1 and had an inhibitory effect on TNF-alpha production by monocytes. Our results suggest that in reducing TGF-beta1 production by desmoid fibroblasts and TNF-alpha production by monocytes, toremifene may restore the balance between the two growth factors.

Apoptosis: the quiet death silences the immune system

Apoptosis plays an essential role in maintaining cellular homeostasis during development, differentiation, and pathophysiological processes. In the immune system, recent investigations reveal that during the course of T-cell development in the thymus, negative selection of autoreactive immature T-cells is a typical apoptotic process. In addition, apoptosis is also involved in cytotoxic killing of target cells and the regulation of lymphocyte homeostasis during immune responses. Interestingly, recent evidence has suggested that cells dying by apoptosis are actively involved in immunosuppression in various circumstances. We have shown that apoptotic cells could inhibit the expression of CD69 during T-cell activation. Furthermore, apoptotic cells phagocytosed by macrophages and/or dendritic cells are immunosuppressive, a process likely mediated by the production of transforming growth factor-beta1. Since apoptosis is a common mechanism by which excessive cells in many tissues and organs are eliminated in various pathophysiological processes, we believe that further investigation into the mechanisms by which apoptotic cells affect the immune system will not only lead to a better understanding of the significance of apoptosis during immune responses, but will also provide novel strategies for the management of autoimmune diseases and transplantation.

Chemically induced rat mammary tumor treated with tamoxifen showed decreased expression of cyclin D1, cyclin E, and p21(Cip1)

We studied the effects of tamoxifen (TAM) on the growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor and the expression of cyclin D1, cyclin E, p21(Cip1), and estrogen receptors (ER) by performing immunohistochemistry and Western blot analysis. When tumor size reached between 10 and 15mm in the largest dimension, the rats were divided into a DMBA-control group and a DMBA-TAM group. The administration of TAM markedly decreased the tumor development and showed decreased expression of bromodeoxyuridine, cyclin D1, cyclin E, and p21(Cip1) when compared with those of the DMBA-control group; however, a few tumors showed progressive growth in spite of TAM treatment. These tumors had decreased expression of ER. This study suggests that TAM suppresses tumor development through the down-expression of cyclin D1 and cyclin E.

Lactoferrin: a tamoxifen-responsive protein in normal and malignant human endometrial cells in culture

We investigated the possible role of the estrogen-regulated protein lactoferrin (Lf) in the response of isolated normal human endometrial epithelial cells (NHEC) and established human endometrial carcinoma (EC) cell lines to tamoxifen (TAM). Using confocal laser scanning microscopy and a monospecific antibody, Lf was localized to the cytoplasm of normal and EC cells. Antibody neutralization of secreted Lf inhibited, whereas exogenous Lf (0--100 microg/ml) enhanced, cell proliferation in both classes of cells. Treatment of NHEC with TAM inhibited cell growth via a protein kinase-C-mediated pathway, concomitant with a reduction in the staining intensity for Lf. Importantly, in EC cells, TAM greatly enhanced the staining intensity for Lf, but did not affect cell growth. We propose that stable expression of Lf protein by EC cells may impart a survival advantage to these cells, which may, in part, account for the resistance of these cells to tamoxifen.

Angiogenesis in breast cancer: the role of transforming growth factor beta and CD105

The progression of breast cancer depends on the establishment of a neovasculature, by a process called angiogenesis. Angiogenesis is an invasive cellular event that requires the co-ordination of numerous molecules including growth factors and their receptors, extracellular proteins, adhesion molecules, and proteolytic enzymes. TGFbeta has emerged to be a major modulator of angiogenesis by regulating endothelial cell proliferation, migration, extracellular matrix (ECM) metabolism, and the expression of adhesion molecules. It is a potent growth inhibitor of normal mammary epithelial cells and a number of breast cancer cell lines. It seems that TGFbeta exerts pleiotropic effects in the oncogenesis of breast cancers in a contextual manner, i.e., it suppresses tumourigenesis at an early stage by direct inhibition of angiogenesis and tumour cell growth. However, over-production of TGFbeta by an advanced tumour may accelerate disease progression through indirect stimulation of angiogenesis and immune suppression. The cell membrane antigen CD105 (endoglin) binds TGFbeta1 and TGFbeta3 and is preferentially expressed in angiogenic vascular endothelial cells. The reduction of CD105 levels in HUVEC leads to in vitro angiogenesis inhibition and massive cell mortality in the presence of TGFbeta1. CD105 null mice die in utero with impaired vasculature, indicating the pivotal role of CD105 in vascular development. The administration of an immunotoxin-conjugate, mab to CD105, induces long-term and complete regression of breast cancer growth in SCID mice. Therefore, CD105 is a promising vascular target for antiangiogenic therapy.

Antiestrogens--tamoxifen, SERMs and beyond

Estrogens play a central role in reproductive physiology. The cellular effects of estrogens are mediated by binding to nuclear receptors (ER) which activate transcription of genes involved in cellular growth control. At least two such receptors, designated ERalpha and ERbeta, mediate these effects in conjunction with a number of coactivators. These receptors can directly interact with other members of the steroid receptor superfamily. A complex cross-talk exists between the estrogen-signaling pathways and the downstream signaling events initiated by growth factors, such as epidermal growth factor and insulin-like growth factors. Estrogens are also a causative factor in the pathogenesis of a variety of neoplastic and non-neoplastic diseases, including breast cancer, endometrial cancer, endometriosis, and uterine fibroids, among others. Antiestrogens, such as tamoxifen, are widely used for the treatment of breast cancer. Tamoxifen produces objective tumor shrinkage in advanced breast cancer, reduces the risk of relapse in women treated for invasive breast cancer, and prevents breast cancer in high-risk women. Although, initially developed as an antiestrogen, tamoxifen can also prevent postmenopausal osteoporosis as well as reduce cholesterol, due to its estrogen-agonist effects. Its estrogen-agonist activity, however, can lead to significant side-effects such as endometrial cancer and thromboembolic phenomena. This has led to the concept of "ideal" selective estrogen receptor modulators (SERMs), drugs that would have the desired, tissue selective, estrogen-agonist or -antagonist effects. Raloxifene is a SERM which has the desirable mixed agonist/antagonist effects of tamoxifen but does not cause uterine stimulation. "Pure" antiestrogens may provide very potent estrogen-antagonist drugs, but are likely to be devoid of beneficial effects on bone and lipids. Future drug development efforts should focus on developing superior SERMs that have a greater efficacy against ER-positive tumors and do not cause hot flashes or thromboembolism, and explore combination strategies to simultaneously target hormone-dependent as well as hormone-independent breast cancer.

Anti-HER2 antibody enhances the growth inhibitory effect of anti-oestrogen on breast cancer cells expressing both oestrogen receptors and HER2

Anti-oestrogen is effective for the treatment of oestrogen receptor (ER)-positive breast carcinomas, but most of these tumours become resistant to anti-oestrogen. It has been suggested that anti-oestrogen therapy may induce a HER2 signalling pathway in breast cancer cells and this may cause resistance to anti-oestrogen. Thus, it is conceivable that combined therapy with anti-oestrogen and anti-HER2 antibody might be more effective. In the present study, we investigated the effect of combined treatment with a humanized anti-HER2 monoclonal antibody, rhumAbHER2 (trastuzumab), and an anti-oestrogen, ICI 182,780, on the cell growth of three human breast cancer cell lines which respectively express different levels of ER and HER2. The combined treatment enhanced the growth inhibitory effect on ML-20 cells, which express a high level of ER and a moderate level of HER2, but showed no additive effect on either KPL-4 cells, which express no ER and a moderate level of HER2, or MDA-MB-231 cells, which express no ER and a low level of HER2. It is also suggested that both the antibody and anti-oestrogen induce a G1-S blockade and apoptosis. These findings indicate that combined treatment with anti-HER2 antibody and anti-oestrogen may be useful for the treatment of patients with breast cancer expressing both ER and HER2.

Connective tissue growth factor induces apoptosis in human breast cancer cell line MCF-7

Connective tissue growth factor (CTGF) is a member of an emerging CCN gene family that is implicated in various diseases associated with fibro-proliferative disorder including scleroderma and atherosclerosis. The function of CTGF in human cancer is largely unknown. We now show that CTGF induces apoptosis in the human breast cancer cell line MCF-7. CTGF mRNA was completely absent in MCF-7 but strongly induced by treatment with transforming growth factor beta (TGF-beta). TGF-beta by itself induced apoptosis in MCF-7, and this effect was reversed by co-treatment with CTGF antisense oligonucleotide. Overexpression of CTGF gene in transiently transfected MCF-7 cells significantly augmented apoptosis. Moreover, recombinant CTGF protein significantly enhanced apoptosis in MCF-7 cells as evaluated by DNA fragmentation, Tdt-mediated dUTP biotin nick end-labeling staining, flow cytometry analysis, and nuclear staining using Hoechst 33258. Finally, recombinant CTGF showed no effect on Bax protein expression but significantly reduced Bcl2 protein expression. Taken together, these results suggest that CTGF is a major inducer of apoptosis in the human breast cancer cell line MCF-7 and that TGF-beta-induced apoptosis in MCF-7 cells is mediated, in part, by CTGF.

TGF-beta and cancer

The relationships between transforming growth factor-beta (TGF-beta) and cancer are varied and complex. The paradigm that is emerging from the experimental evidence accumulated over the past decade or so is that TGF-beta can play two different and opposite roles with respect to the process of malignant progression. During early stages of carcinogenesis, TGF-beta acts predominantly as a potent tumor suppressor and may mediate the actions of chemopreventive agents such as retinoids and nonsteroidal anti-estrogens. However, at some point during the development and progression of malignant neoplasms, bioactive TGF-betas make their appearance in the tumor microenvironment and the tumor cells escape from TGF-beta-dependent growth arrest. In many cases, this resistance to TGF-beta is the consequence of loss or mutational inactivation of the genes that encode signaling intermediates. These include the types I and II TGF-beta receptors, as well as receptor-associated and common-mediator Smads. The stage of tumor development or progression at which TGF-beta-resistant clones come to dominate the tumor cell population in different types of neoplasm remains to be defined. The phenotypic switch from TGF-beta-sensitivity to TGF-beta-resistance that occurs during carcinogenesis has several important implications for cancer prevention and treatment.

Differential effect of estradiol on antibody secretion of murine hybridomas

The need for increased antibody production by hybridomas has been approached by the addition to cell cultures of different growth factors; in vitro addition of estradiol-17beta (E2) to human blood lymphocytes increases the accumulation of plasma-blasts and Ig-secreting cells. Four different murine-murine hybridomas secreting different monoclonal antibodies (MAbs) were treated with E2. Specific antibody concentration was measured by enzyme-linked immunoadsorbent assay (ELISA) in culture supernatants whereas expression of E2-receptor in the hybridoma cells was determined by polymerase chain reaction (PCR). When E2 was added as a growth supplement to alpha-estrogen receptor positive murine-murine hybridomas it enhanced MAb secretion by as much as 255%, in a dose-dependant manner. This effect lasted for as long as the alpha-estrogen receptor was detected in the hybridoma cells, was inhibited by tamoxifen and was not observed in alpha-estrogen receptor negative hybridomas. The synthetic estrogen analogue diethylstilbestrol had no effect. Estradiol-17beta should be added to the list of hybridoma-inducing growth factors.

Apoptosis and tumorigenesis in human cholangiocarcinoma cells. Involvement of Fas/APO-1 (CD95) and calmodulin

We have previously demonstrated that tamoxifen inhibits the growth of human cholangiocarcinoma cells in culture and inhibits tumor growth when cells are injected into nude mice. However, the mechanism of action of tamoxifen remains unknown. Here we demonstrate that tamoxifen and trifluoperazine, both potent calmodulin antagonists, induce apoptosis in vitro, probably acting via the Fas system, in human cholangiocarcinoma cells. Human cholangiocarcinoma cell lines heterogeneously express Fas antigen on their surface. Fas-negative and Fas-positive surface-expressing cells were isolated, cloned, and cultured. Fas antibody, tamoxifen, and trifluoperazine induced dose-dependent apoptosis only in Fas-positive cells; Fas-negative cells were unaffected. Furthermore, apoptosis induced by tamoxifen in Fas-positive cells was blocked by an inhibitory Fas antibody. Tamoxifen was not acting through an anti-estrogenic mechanism, because neither Fas-negative nor Fas-positive cells expressed estrogen receptors and the pure anti-estrogen compound, ICI 182780, did not induce apoptosis in either cell line. Fas-negative cells, but not Fas-positive cells, were able to produce tumors when subcutaneously injected into nude mice. These findings suggest Fas may be a candidate oncogene involved in the pathogenesis of cholangiocarcinoma. Furthermore, the similarity between the pro-apoptotic effects of tamoxifen and trifluoperazine support an underlying molecular mechanism for Fas-mediated apoptosis that involves calmodulin.

Combination effects of tamoxifen plus 5-fluorouracil on gastric cancer cell lines in vitro

We tested the effect of tamoxifen alone and tamoxifen plus 5-fluorouracil (5-FU) on proliferation of two different types of gastric cancer cell lines using the WST-1 method. A high dose of tamoxifen suppressed the proliferation of KATOIII cells (poorly differentiated adenocarcinoma), but MKN28 cells (well-differentiated adenocarcinoma) were not affected. The combination of the two drugs resulted in a synergistic anti-proliferative activity on KATOIII cells. On the other hand, in the combination therapy, tamoxifen stimulated MKN28 cells to proliferate in a dose-dependent manner. TGF-beta1 secretion was not changed in KATOIII cells by tamoxifen plus 5-FU treatment but was down-regulated in MKN28 cells. Both cancer cell lines were judged as intracellular estrogen receptor (ER) negative. These data suggest that the anti-proliferative effects of tamoxifen plus 5-FU on KATOIII cells were not dependent on ER expression or TGF-beta1 secretion. On the other hand, their proliferative effects on MKN28 cells might be, in part, caused by the reduced secretion of TGF-beta1.

Growth factors, apoptosis, and survival of mammary epithelial cells

Programmed cell death (apoptosis) occurs regularly during normal growth and development of the mammary gland. One of the most dramatic examples of apoptosis is evident during the remodeling of the breast that accompanies postlactational involution. Transgenic mouse models have demonstrated that overexpression of polypeptides such as transforming growth factor alpha (TGFalpha) and insulin like growth factor I (IGF-I) can block this remodeling, suggesting that these growth factors may be acting as survival factors for the mammary epithelium. In contrast, transgenic mice that overexpress the growth inhibitor transforming growth factor beta (TGF-beta) show increased apoptosis in the mammary epithelium throughout mammary development, suggestive of a mechanism working to counterbalance the survival factors. Experiments with mammary epithelial cell lines cultured in vitro have confirmed that these growth factors can indeed regulate apoptosis and survival in mammary epithelial cells; EGF, IGF-I, and basic fibroblast growth factor (bFGF) act as survival factors for mammary epithelial cells, while TGF-beta induces their death. In breast cancer, cytotoxic drugs and hormone ablation increase the expression of TGF-beta, which may function to induce cell death by either paracrine or autocrine mechanisms. Lastly, although it has very limited expression in the breast, TNFalpha has been shown to be effective in the rapid, direct induction of cell death in breast cancer cell lines. Together, these studies describe a complex dynamic pattern of cell death-inducing and survival factors that promote the development of the mature mammary gland and that rapidly remodel the tissue after lactation.

Prostate cancer cell growth inhibition by tamoxifen is associated with inhibition of protein kinase C and induction of p21(waf1/cip1)

BACKGROUND

Inhibition of protein kinase C (PKC) and modulation of transforming growth factor-beta (TGF-beta) are both associated with tamoxifen treatment, and both appear to be important in the regulation of prostate cancer cell growth. Investigations were performed which sought to measure the efficacy, and to elucidate the mechanism of growth inhibition by tamoxifen, in hormone-refractory prostate cancer.

METHODS

Growth assays were performed on PC3, PC3-M, and DU145 prostate cancer cells. TGF-beta was measured by ELISA; p21(waf1/cip1) and retinoblastoma (Rb) protein levels were measured by Western blot; PKC activity was measured by kinase assay; and effects upon cell cycle were measured by flow cytometric analysis.

RESULTS

IC50s for growth inhibition ranged from 5.5-10 microM, and were not affected by estrogen. Tamoxifen-mediated growth inhibition was not associated with induction of TGF-beta. However, tamoxifen treatment was associated with inhibition of PKC, which was followed by induction of p21(waf1/cip1), Rb dephosphorylation, and G1/S phase cell cycle arrest. Similar effects were observed with the known PKC inhibitor, Ro31-8220.

CONCLUSIONS

These data suggest that micromolar concentrations of tamoxifen inhibit prostate cancer cell growth by inhibition of PKC, resulting in induction of the p21(waf1/cip1) protein.