High expression of leptin receptor mRNA in breast cancer tissue predicts poor prognosis for patients with high, but not low, serum leptin levels

Obesity and breast cancer: status of leptin and adiponectin in pathological processes

It is well recognized that obesity increases the risk of various cancers, including breast malignancies in postmenopausal women. Furthermore, obesity may adversely affect tumor progression, metastasis, and overall prognosis in both pre- and postmenopausal women with breast cancer. However, the precise mechanism(s) through which obesity acts is/are still elusive and this relationship has been the subject of much investigation and speculation. Recently, adipose tissue and its associated cytokine-like proteins, adipokines, particularly leptin and adiponectin, have been investigated as mediators for the association of obesity with breast cancer. Higher circulating levels of leptin found in obese subjects could be a growth-enhancing factor as supported by in vitro and preclinical studies, whereas low adiponectin levels in obese women may be permissive for leptin's growth-promoting effects. These speculations are supported by in vitro studies which indicate that leptin promotes human breast cancer cell proliferation while adiponectin exhibits anti-proliferative actions. Further, estrogen and its receptors have a definite impact on the response of human breast cancer cell lines to leptin and adiponectin. More in-depth studies are needed to provide additional and precise links between the in vivo development of breast cancer and the balance of adiponectin and leptin.

Effect of chronic and intermittent calorie restriction on serum adiponectin and leptin and mammary tumorigenesis

The effect of chronic (CCR) and intermittent (ICR) caloric restriction on serum adiponectin and leptin levels was investigated in relation to mammary tumorigenesis. 10-wks old MMTV-TGF-α female mice were assigned to ad libitum fed (AL; AIN-93M diet), ICR (3-week 50% caloric restriction, AIN-93M-mod diet, 2× protein, fat, vitamins, and minerals followed by 3-wks 100% AL consumption of AIN-93M), and CCR (calorie and nutrient intake matched for each 6-wks ICR cycle, ∼ 75% of AL) groups. Mice were sacrificed at 79 (end of restriction) or 82 (end of refeeding) wks of age. Serum was obtained in cycles 1, 3, 5, 8, 11, and terminal. Mammary tumor incidence was 71.0%, 35.4%, and 9.1% for AL, CCR, and ICR mice, respectively. Serum adiponectin levels were similar among groups with no impact of either CCR or ICR. Serum leptin level rose in AL mice with increasing age but was significantly reduced by long-term CCR and ICR. The ICR protocol was also associated with an elevated adiponectin/leptin ratio. In addition, ICR-restricted mice had increased mammary tissue AdipoR1 expression and decreased leptin and ObRb expression compared with AL mice. Mammary fat pads from tumor-free ICR-mice had higher adiponectin expression than AL and CCR mice whereas all tumor-bearing mice had weak adiponectin signal in mammary fat pad. Although we did not show an association of either adiponectin or leptin with individual mice in relation to mammary tumorigenesis, we did find that reduced serum leptin and elevated adiponectin/leptin ratio were associated with the protective effect of intermittent calorie restriction.

Leptin pro-angiogenic signature in breast cancer is linked to IL-1 signalling

BACKGROUND

Leptin and interleukin-1 (IL-1) upregulate vascular endothelial growth factor (VEGF), promote angiogenesis and are related to worse prognosis of breast cancer. However, it is unknown whether leptin regulates IL-1, and whether these effects are related to leptin-induction of VEGF/VEGFR2 in breast cancer.

METHODS

Several genetic and pharmacological approaches were used to determine the mechanisms involved in leptin regulation of IL-1 system (IL-1α, IL-1β, IL-1Ra and IL-1R tI) and the impact of IL-1 signalling on leptin-induced VEGF/VEGFR2 expression in mouse mammary cancer 4T1 cells (a model that resembles invasive and highly metastatic human breast cancer).

RESULTS

Leptin increased protein and mRNA levels of all components of the IL-1 system. IL-1 upregulation involved leptin activation of JAK2/STAT3, MAPK/ERK 1/2, PI-3K/AKT1, PKC, p38 and JNK. Leptin-induced phosphorylation of mTOR/4E-BP1 increased IL-1β and IL-1Ra expression, but downregulated IL-1α. Leptin upregulation of IL-1α promoter was linked to SP1 and NF-κB transcription factors. In addition, leptin receptor (Ob-Rb) was upregulated by leptin. Interestingly, leptin upregulation of VEGF/VEGFR2 was partially mediated by IL-1/IL-1R tI signalling.

CONCLUSIONS

We show for the first time that leptin induces several signalling pathways to upregulate the translational and transcriptional expression of IL-1 system in breast cancer cells. Moreover, leptin upregulation of VEGF/VEGFR2 was impaired by IL-1 signalling blockade. These data suggest that leptin pro-angiogenic signature in breast cancer is linked to, or regulated, in part by IL-1 signalling.

Leptin as a potential therapeutic target for breast cancer prevention and treatment

IMPORTANCE OF THE FIELD

Obesity is considered to be an important risk factor for postmenopausal breast cancer. Elevated estrogen levels are thought to be a growth factor associated with this relationship. However, there is increasing evidence that factors produced directly in adipose tissue, adipokines, can also affect breast cancer development. Leptin is one of the adipokines that is measured in serum/plasma in increasing amounts as body weight/body fat increases.

AREAS COVERED IN THIS REVIEW

We highlight important aspects of leptin in relationship to mammary/breast tumor development. This includes findings from human, in vitro and animal studies. Information on leptin-related compounds which may have therapeutic use is presented. Additionally strategies to alter serum leptin levels by dietary and pharmacological interventions are discussed.

WHAT THE READER WILL GAIN

The reader will gain insights into the relationship of an adipose tissue protein and its potential role in breast cancer development as well as ways to intervene in leptin's actions.

TAKE HOME MESSAGE

Continued research will determine if interfering with the action of leptin has preventive or therapeutic applications in breast cancer.

Leptin upregulates VEGF in breast cancer via canonic and non-canonical signalling pathways and NFkappaB/HIF-1alpha activation

High levels of VEGF and leptin are strongly linked to worse prognosis of breast cancer. Leptin signalling upregulates VEGF in human and mouse mammary tumor cells (MT), but the specific molecular mechanisms are largely unknown. Pharmacologic and genetic approaches were used to dissect the mechanism of leptin regulation of VEGF protein and mRNA in MT (4T1, EMT6 and MMT). A series of VEGF-promoter Luc-reporters (full-length and transcription factor-binding deletions) were transfected into MT to analyze leptin regulation of VEGF transcription. Deletion analysis of VEGF promoter and RNA knockdown shows that HIF-1alpha and NFkappaB are essentials for leptin regulation of VEGF. Leptin activation of HIF-1alpha was mainly linked to canonic (MAPK, PI-3K) and non-canonic (PKC, JNK and p38 MAP) signalling pathways. Leptin non-canonic signalling pathways (JNK, p38 MAP and to less extent PKC) were linked to NFkappaB activation. SP1 was involved in leptin regulation of VEGF in 4T1 cells. AP1 was not involved and AP2 repressed leptin-induced increase of VEGF. Overall, these data suggest that leptin signalling regulates VEGF mainly through HIF-1alpha and NFkappaB. These results delineate a comprehensive mechanism for leptin regulation of VEGF in MT. Disruption of leptin signalling could be used as a novel way to treat breast cancer.

Correlation of body mass index and leptin with tumor size and stage of disease in hormone-dependent postmenopausal breast cancer: preliminary results and therapeutic implications

Obesity is considered the most important risk and prognostic factor for estrogen-dependent breast cancer in postmenopausal women. Adipokines, in particular leptin, are at the center of the etiopathogenetic mechanisms by which obesity and related metabolic disorders influence breast cancer risk and its prognosis. The present prospective observational study aims to investigate the relationship between body mass index (BMI), serum levels of leptin and proinflammatory cytokines, and breast cancer prognostic factors. In the study, 98 postmenopausal and 82 premenopausal patients with ER-positive breast cancer participated. During the same study period, 221 control subjects were simultaneously recruited. Women underwent baseline measurements pre-operatively, before any surgical and systemic treatments. Pathologic characteristics of tumors were abstracted from pathology reports. Leptin and proinflammatory cytokines were assayed in stored fasting blood specimens. In postmenopausal breast cancer patients, BMI, leptin, and interleukin-6 significantly correlated with pathological tumor classification (pT) and TNM stage. Multivariate regression analysis showed that BMI and leptin, but not interleukin-6, were independent predictive variables of pT and TNM stage. Our results seem to suggest a twofold role of leptin in the etiopathogenesis of postmenopausal estrogen-positive breast cancer. Indeed, leptin reflects the total amount of fat mass, which correlates to aromatase activity and subsequent estrogens levels. Further studies are warranted to clarify the role of leptin and interleukin-6 in breast carcinogenesis and identify new therapeutic options, beyond the use of aromatase inhibitors, acting selectively on adipokine-driven pathways.

Effect of Obesity on Breast Cancer Development

In recent years, obesity has been identified as a risk factor for the development of breast cancer in postmenopausal women, and it has been associated with a poor outcome. Many factors appear to be important in the mechanism of this increased risk, including estrogen, estrogen receptors, and the adipokines leptin and adiponectin. Estrogen, a potent mitogen for mammary cells, has long been implicated in the development of mammary tumors. Because adipose-associated aromatase activity increases the conversion of androgen to estrogen, mammary adipose tissue is thought to be an important source of local estrogen production. Leptin, which increases in the circulation in proportion to body fat stores, has been demonstrated in vitro to promote breast cancer cell growth. Animal models have also identified leptin as an important factor for the development of mammary tumors. In contrast to leptin, serum adiponectin concentrations are inversely related to body fat stores, and the addition of adiponectin to human breast cancer cells reduces cell proliferation and enhances apoptosis. This review explores the relationship between these factors and the development of mammary cancer in humans and mouse models.

Impact of a raised body mass index on breast cancer survival in relation to age and disease extent at diagnosis

The prognostic value of Body Mass Index (BMI) on breast cancer outcome is controversial and previous studies from this unit have not shown any significant relation to survival. The aim of this study was to re-examine any impact of a raised BMI on recurrence and survival related to age and disease stage at the time of diagnosis. Breast cancer patients (2,298) were reviewed and divided in groups by BMI. Recurrence Free Survival (RFS), Breast Cancer Specific Survival (BCSS), and Overall Survival (OS) were compared by Kaplan-Meier life table analysis. Known prognostic factors including BMI were tested for independent prognostic significance in a Cox's regression model. Obese patients (417) had on average larger tumors (median 2.3 versus 2.1 cm, p < 0.01). A trend to an increased positive node status (37% versus 33%) was not significant, p = 0.18. Seven-year RFS was 82% versus 77% in the obese, p < 0.01, BCSS was 87% versus 85%, p = 0.046 and OS 81% versus 77%, p = 0.02. BMI was independently associated with RFS in multivariate analysis (HR: 1.43, p < 0.01). In subgroup analysis, survival differences were most prominent in patients with node positive disease and in patients <60-years old. Breast cancer outcome was worse in patients with a raised BMI and this risk was greater in younger patients and in those with node positive disease. The difference may be related to diagnosis at a more advanced stage in the obese but there was also an independent effect of BMI on survival.

Adipose tissue as target organ in the treatment of hormone-dependent breast cancer: new therapeutic perspectives

Breast cancer is the female malignant neoplasia with the highest incidence in the industrialized world. Despite many undeniable therapeutic successes obtained, breast cancer still remains, however, a major health issue. In the last few years, thanks to aromatase inhibitors, the hormone therapy for oestrogen-dependent breast cancer has evolved in terms of efficacy and tolerability; at the same time, it has enabled us to better define the role of oestrogens in the etiopathogenesis of this tumour. Weight increase and obesity have been identified as the most important risk and prognostic factors for breast cancer in postmenopausal women. Several hypotheses have been proposed to explain the association of obesity with postmenopausal breast cancer. A more recent hypothesis suggests that adipocytes and their autocrine (paracrine and endocrine actions) are at the centre of such an etiopathogenetic mechanism. A better understanding of the main mechanisms that link together menopause, body-weight increase and hormone-dependent breast cancer is paramount to enable the identification of key molecules involved in the development of breast carcinoma and suggest new therapeutic options. The present review will discuss important findings on the therapeutic aspects of adipose tissue and adipokines as a target for treatment of hormone-dependent breast cancer.

Leptin and leptin receptor expression in breast cancer

PURPOSE

Leptin is a multifunctional hormone that's produced by adipose tissue and leptin is involved in the regulation of food intake and energy balance. The aims of this study were to determine the leptin and leptin receptor (Ob-R) expressions in human breast cancer and their corresponding influence on the prognosis of patients with breast cancer.

MATERIALS AND METHODS

We examined the correlations between the leptin and Ob-R expressions and the breast cancer-related pathobiologic markers by performing immunohistochemistry in 517 patients with breast cancer. We analyzed the leptin and Ob-R expressions with respect to overall survival and relapse-free survival (RFS).

RESULTS

Positive cytoplasmic immunoreactivity for leptin was noted in 39% of the patients and 79% of the patients showed positive cytoplasmic immunoreactivity for Ob-R. The expression of leptin in breast cancer was correlated with a high Ki-67 labeling index (p=0.019). Based on the univariate survival analysis, the clinicopathologic variables with prognostic value included the histologic grade, the T stage, the N stage, the HER2 status, the Bcl-2, p53 and Ki-67 expressions (p<0.05). The patients with leptin-positive breast cancers and a negative hormone receptor status had a significantly longer overall survival (p=0.021). Multivariate survival analysis showed that a positive expression of leptin was an independent prognostic marker for overall survival (hazard ratio, 0.20; 95% CI, 0.04~0.99; p=0.05).

CONCLUSION

A leptin expression in breast cancer is significantly associated with the Ki-67 labeling index, and this suggests there is an association of a leptin expression with the proliferation activity. In addition, a leptin expression is an indicator of better survival for breast cancer patients.

Functional analysis of the -2548G/A leptin gene polymorphism in breast cancer cells

Leptin is overexpressed in human breast tumors and is produced by breast cancer cells in response to obesity-related stimuli. The leptin promoter polymorphism Lep-2548G/A can be associated with increased leptin secretion by adipocytes and elevated cancer risk. However, molecular mechanisms underlying the link between Lep-2548G/A and breast cancer have never been addressed. Lep-2548G/A is proximal to a binding site for the transcriptional factor Sp1. Furthermore nucleolin, a transcriptional repressor, can bind Sp1 or its consensus site. Consequently, we focused on the impact of Lep-2548G/A on Sp1- and nucleolin-dependent leptin transcription in breast cancer cells. The Lep-2548G/A was identified in a homozygous conformation in BT-474 and SK-BR-3 breast cancer cells, in a heterozygous conformation in MDA-MB-231 cells, and a wild-type Lep-2548G/G sequence was present in MCF-7 and ZR-75-1 cells. The occurrence of Lep-2548A/A and Lep-2548G/A coincided with high and intermediate leptin mRNA expression, respectively, while cells containing Lep-2548G/G expressed low leptin mRNA levels. We demonstrated that the existence of Lep-2548G/A improved efficient recruitment of Sp1 to DNA under insulin treatment, while Sp1 loading on DNA containing Lep-2548G/G was not insulin-dependent. In contrast, nucleolin binding to Lep-2548G/A was downregulated in response to insulin, while it was not regulated on Lep-2548G/G. The presence of Lep-2548G/A was studied in breast cancer epithelial cells by IHC and LCM. Interestingly, all 14 tumors expressing high leptin levels contained Lep-2548A/A. In conclusion, the occurrence of Lep-2548G/A can enhance leptin expression in breast cancer cells via Sp1- and nucleolin-dependent mechanisms and possibly contribute to intratumoral leptin overexpression.

Common genetic variations in the LEP and LEPR genes, obesity and breast cancer incidence and survival

Obesity is a strong risk factor for breast cancer in postmenopausal women and adverse prognostic indicator regardless of menopausal status. Leptin is an important regulator of adipose tissue mass and has been associated with tumor cell growth. Leptin exerts its effects through interaction with the leptin receptor (LEPR). We investigated whether genetic variations in the leptin (LEP) and LEPR genes are associated with risk of breast cancer, or once diagnosed, with survival. The polymorphisms LEP G-2548A and LEPR Q223R were characterized in population-based study consisting of mostly European-American women. The study examined 1,065 women diagnosed with first, primary invasive breast cancer between 1996 and 1997. Controls were 1,108 women frequency matched to the cases by 5-year age group. A modest increase in risk of developing breast cancer was associated with the LEP -2548AA genotype when compared to the LEP -2548GG genotype (age-adjusted OR = 1.30; 95% CI = 1.01-1.66). This association was stronger among postmenopausal women who were obese (OR = 1.86; 95% CI = 0.95-3.64) although the interaction was of borderline statistical significance (P = 0.07). We found no evidence of an association with polymorphisms of either LEP or LEPR in relation to all-cause or breast cancer-specific mortality among women with breast cancer (mean follow-up time = 66.7 months). The effects of these genotypes on breast cancer risk and mortality did not vary significantly when stratified by menopausal status. In summary, our results show that a common variant in LEP may be associated with the risk of developing breast cancer supporting the hypothesis that leptin is involved in breast carcinogenesis.

Leptin-signaling inhibition results in efficient anti-tumor activity in estrogen receptor positive or negative breast cancer

Introduction

We have shown previously that treatment with pegylated leptin peptide receptor antagonist 2 (PEG-LPrA2) reduced the expression of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor type 2 (VEGFR2) and growth of 4T1-breast cancer (BC) in syngeneic mice. In this investigation, PEG-LPrA2 was used to evaluate whether the inhibition of leptin signaling has differential impact on the expression of pro-angiogenic and pro-proliferative molecules and growth of human estrogen receptor-positive (ER⁺) and estrogen receptor-negative (ER^-) BC xenografts hosted by immunodeficient mice.

Methods

To test the contribution of leptin signaling to BC growth and expression of leptin-targeted molecules, PEG-LPrA2 treatment was applied to severe immunodeficient mice hosting established ER⁺ (MCF-7 cells; ovariectomized/supplemented with estradiol) and ER^- (MDA-MB231 cells) BC xenografts. To further assess leptin and PEG-LPrA2 effects on ER⁺ and ER^- BC, the expression of VEGF and VEGFR2 (protein and mRNA) was investigated in cell cultures.

Results

PEG-LPrA2 more effectively reduced the growth of ER⁺ (>40-fold) than ER^- BC (twofold) and expression of pro-angiogenic (VEGF/VEGFR2, leptin/leptin receptor OB-R, and IL-1 receptor type I) and pro-proliferative molecules (proliferating cell nuclear antigen and cyclin D₁) in ER⁺ than in ER^- BC. Mouse tumor stroma in ER⁺ BC expressed high levels of VEGF and leptin that was induced by leptin signaling. Leptin upregulated the transcriptional expression of VEGF/VEGFR2 in MCF-7 and MDA-MB231 cells.

Conclusions

These results suggest that leptin signaling plays an important role in the growth of both ER⁺ and ER^- BC that is associated with the leptin regulation of pro-angiogenic and pro-proliferative molecules. These data provide support for the potential use of leptin-signaling inhibition as a novel treatment for ER⁺ and ER^- BC.

[Obesity and cancer]

Obesity which is now well recognized as a public health problem increases the risk of developing cancers. Some systematic review and meta-analyses assessed the strength of associations between body mass index and common cancers such as breast, endometrial, colon and adenocarcinoma of oesophagus. The causal mechanisms remain unexplained. However, epidemiological data and animal models have provided some evidence that hormonal alteration linked to obesity, such as hyperinsulinism, high insulin-like growth factor (IGF-1) levels or biodisponibility, low adiponectin serum level and high oestradiol serum level resulting from an enhanced aromatase activity may have mitogenic and antiapoptotic effects. The inflammation associated with visceral adiposity is another factor which promotes cancer. To date, there are no convincing data that weight loss could improve the prognosis of treated neoplasia. However, a regular physical activity and a limited caloric intake are probably safe in healthy subject to prevent cancer and also in cancer survivors.

Angiogenesis, adipokines and breast cancer

The prevalence of overweight and obesity is rapidly increasing world wide. Numerous epidemiological studies have shown that obesity is a risk factor for postmenopausal breast cancer and relapse. However, the biological factors that drive the growth and progression of these tumors and how obesity contributes to the tumor microenvironment are poorly understood. Tumor development and metastasis are dependent on the process of angiogenesis or the formation of new blood vessels. More importantly, a ready supply of adipose tissue-derived angiogenic adipokines, notably VEGF and leptin, and the production of inflammatory cytokines by infiltrating macrophages that occurs in adipose tissues with obesity, promotes the paracrine stimulation of vascular endothelial cell growth needed for adipogenesis, while maintaining a microenvironment that is favorable for breast tumorigenesis.

MicroRNA-200c mitigates invasiveness and restores sensitivity to microtubule-targeting chemotherapeutic agents

The transcription factor ZEB1 is normally not expressed in epithelial cells. When inappropriately expressed in carcinomas, ZEB1 initiates epithelial to mesenchymal transition due to its ability to repress E-cadherin and other genes involved in polarity. Recently, ZEB1 and ZEB2 have been identified as direct targets of the microRNA-200c family. We find that miR-200c levels are high in well-differentiated endometrial, breast, and ovarian cancer cell lines, but extremely low in poorly differentiated cancer cells. Low or absent miR-200c results in aberrant expression of ZEB1 and consequent repression of E-cadherin. Reinstatement of miR-200c to such cells restores E-cadherin and dramatically reduces migration and invasion. Microarray profiling reveals that in addition to ZEB1 and ZEB2, other mesenchymal genes (such as FN1, NTRK2, and QKI), which are also predicted direct targets of miR-200c, are indeed inhibited by addition of exogenous miR-200c. One such gene, class III β-tubulin (TUBB3), which encodes a tubulin isotype normally found only in neuronal cells, is a direct target of miR-200c. This finding is of particular significance because we show that restoration of miR-200c increases sensitivity to microtubule-targeting agents by 85%. Because expression of TUBB3 is a common mechanism of resistance to microtubule-binding chemotherapeutic agents in many types of solid tumors, the ability of miR-200c to restore chemosensitivity to such agents may be explained by its ability to reduce TUBB3. Because miR-200c is crucial for maintenance of epithelial identity, behavior, and sensitivity to chemotherapy, we propose that it warrants further investigation as a therapeutic strategy for aggressive, drug-resistant cancers.

Leptin utilizes Jun N-terminal kinases to stimulate the invasion of MCF-7 breast cancer cells

In breast tumors, high levels of leptin have been associated with increased incidence of breast cancer metastasis. Breast cancer metastasis is directly associated with breast cancer cell invasion. However, whether leptin could augment breast cancer cell invasion is not known. Here we showed that leptin increased the invasiveness and the matrix metallo-proteinase-2 (MMP-2) activity of the MCF-7 breast cancer cell line. Leptin stimulated the phosphorylation of extracellular signals regulated kinases, signal transducers and activators of transcription 3 and Jun N-terminal kinases (JNK); however, only inhibition of JNK decreased leptin-mediated activation of MMP-2. Furthermore, inhibition of JNK suppressed leptin-mediated breast cancer cell invasion. Here we report the novel findings that leptin increased invasion of breast cancer cells by activating JNK, resulting in increased MMP-2 activity.

IL-1 family in breast cancer: potential interplay with leptin and other adipocytokines

Obesity is associated with an increased risk of breast cancer. interleukin-1 (IL-1), a pro-inflammatory cytokine secreted by adipose tissue, is involved in breast cancer development. There is also convincing evidence that other adipocytokines including leptin not only have a role in haematopoiesis, reproduction and immunity but are also growth factors in cancer. Therefore, IL-1 family and leptin family are adipocytokines which could represent a major link between obesity and breast cancer progression. This minireview provides insight into recent findings on the prognostic significance of IL-1 and leptin in mammary tumours, and discusses the potential interplay between IL-1 family members and adipocyte-derived hormones in breast cancer.

Cancer cells, adipocytes and matrix metalloproteinase 11: a vicious tumor progression cycle

This brief review focuses on the emerging role of matrix metalloproteinase 11 (MMP-11) in cancer progression. It has recently been shown that MMP-11 is induced in adipose tissue by cancer cells as they invade their surrounding environment. MMP-11 negatively regulates adipogenesis by reducing pre-adipocyte differentiation and reversing mature adipocyte differentiation. Adipocyte dedifferentiation in turn leads to the accumulation of nonmalignant peritumoral fibroblast-like cells, which favor cancer cell survival and tumor progression. This MMP-11-mediated bi-directional cross-talk between invading cancer cells and adjacent adipocytes/pre-adipocytes highlights the central role that MMP-11 plays during tumor desmoplasia and represents a molecular link between obesity and cancer.

Association between alcohol intake and serum sex hormones and peptides differs by tamoxifen use in breast cancer survivors

OBJECTIVE

To measure the association between alcohol intake and 11 hormones and peptides in postmenopausal breast cancer survivors and to evaluate whether this association differs by tamoxifen use.

METHODS

Self-reported alcohol intake was assessed via food frequency questionnaire on average 30 months post-breast cancer diagnosis in 490 postmenopausal women from three western states. Concurrently, a fasting blood sample was obtained for assay of estrone, estradiol, free estradiol, testosterone, free testosterone, dehydroepiandrosterone sulfate (DHEAS), sex hormone-binding globulin (SHBG), leptin, C-peptide, insulin-like growth factor-I (IGF-I), and IGF-binding protein-3. Adjusted means of these hormones and peptides were calculated for categories of alcohol intake, overall and stratified by tamoxifen use.

RESULTS

The association between alcohol intake and serum hormone and peptide levels differed by tamoxifen use. We found statistically significant inverse associations between alcohol intake and both leptin and SHBG values but only among tamoxifen users. In women not using tamoxifen, we found a positive association between alcohol intake and DHEAS but no association in tamoxifen users.

CONCLUSION

Tamoxifen may modify the association between alcohol intake and serum hormones and peptides. The significant associations found for DHEAS and SHBG are in a direction considered unfavorable for breast cancer prognosis. Postmenopausal breast cancer survivors may benefit from decreasing their alcohol intake.

Leptin/HER2 crosstalk in breast cancer: in vitro study and preliminary in vivo analysis

Background

Obesity in postmenopausal women is associated with increased breast cancer risk, development of more aggressive tumors and resistance to certain anti-breast cancer treatments. Some of these effects might be mediated by obesity hormone leptin, acting independently or modulating other signaling pathways. Here we focused on the link between leptin and HER2. We tested if HER2 and the leptin receptor (ObR) can be coexpressed in breast cancer cell models, whether these two receptors can physically interact, and whether leptin can transactivate HER2. Next, we studied if leptin/ObR can coexist with HER2 in breast cancer tissues, and if presence of these two systems correlates with specific clinicopathological features.

Methods

Expression of ObR, HER2, phospo-HER2 was assessed by immonoblotting. Physical interactions between ObR and HER2 were probed by immunoprecipitation and fluorescent immunostaining. Expression of leptin and ObR in breast cancer tissues was detected by immunohistochemistry (IHC). Associations among markers studied by IHC were evaluated using Fisher's exact test for count data.

Results

HER2 and ObR were coexpressed in all studied breast cancer cell lines. In MCF-7 cells, HER2 physically interacted with ObR and leptin treatment increased HER2 phosphorylation on Tyr 1248. In 59 breast cancers, the presence of leptin was correlated with ObR (the overall association was about 93%). This result was confirmed both in HER2-positive and in HER2-negative subgroups. The expression of leptin or ObR was numerically more frequent in larger (> 10 mm) tumors.

Conclusion

Coexpression of HER2 and the leptin/ObR system might contribute to enhanced HER2 activity and reduced sensitivity to anti-HER2 treatments.

Effects of high-fat diet and/or body weight on mammary tumor leptin and apoptosis signaling pathways in MMTV-TGF-alpha mice

INTRODUCTION

Obesity is a risk factor for postmenopausal breast cancer and is associated with shortened mammary tumor (MT) latency in MMTV-TGF-alpha mice with dietary-induced obesity. One link between obesity and breast cancer is the adipokine, leptin. Here, the focus is on diet-induced obesity and MT and mammary fat pad (MFP) leptin and apoptotic signaling proteins.

METHODS

MMTV-TGF-alpha mice were fed low-fat or high-fat diets from 10 to 85 weeks of age. High-Fat mice were divided into Obesity-Prone and Obesity-Resistant groups based on final body weights. Mice were followed to assess MT development and obtain serum, MFP, and MT.

RESULTS

Incidence of palpable MTs was significantly different: Obesity-Prone > Obesity-Resistant > Low-Fat. Serum leptin was significantly higher in Obesity-Prone compared with Obesity-Resistant and Low-Fat mice. Low-Fat mice had higher MFP and MT ObRb (leptin receptor) protein and Jak2 (Janus kinase 2) protein and mRNA levels in comparison with High-Fat mice regardless of body weight. Leptin (mRNA) and pSTAT3 (phosphorylated signal transducer and activator of transcription 3) (mRNA and protein) also were higher in MTs from Low-Fat versus High-Fat mice. Expression of MT and MFP pro-apoptotic proteins was higher in Low-Fat versus High-Fat mice.

CONCLUSION

These results confirm a connection between body weight and MT development and between body weight and serum leptin levels. However, diet impacts MT and MFP leptin and apoptosis signaling proteins independently of body weight.

Leptin augments proliferation of breast cancer cells via transactivation of HER2

Excessive fat mass is a risk factor for postmenopausal breast cancer. Leptin, a fat cell-derived peptide hormone, elicits a growth-stimulating effect in breast cancer cells with leptin receptor expression, although the leptin-induced signal in malignant cells is not fully understood. Here, we found that exogenous leptin induced tyrosine phosphorylation of HER2 in SKBR3 cells, which showed marked overexpression of HER2. Phosphorylation of HER2 was detected at 2 min and continued up to 120 min after the start of stimulation. Leptin-induced HER2 phosphorylation was partially reduced by an epidermal growth factor receptor inhibitor, AG1478, or a Janus-activated kinase inhibitor, AG490. Leptin also induced phosphorylation of extracellular signal-regulated kinase 1/2, which was mostly abrogated by a HER2 tyrosine kinase inhibitor, AG825. In a proliferation assay, addition of 500 ng/mL leptin increased the proliferation of SKBR3, which was totally inhibited by AG825. Collectively, our data suggest that leptin can transactivate HER2 through both epidermal growth factor receptor and Janus-activated kinase 2 activation, which can cause the growth of breast cancer cells with HER2 overexpression.

The roles of serum leptin concentration and polymorphism in leptin receptor gene at codon 109 in breast cancer

AIMS

We investigated the relationship between serum leptin concentrations and polymorphism of the leptin receptor gene and breast cancer.

METHODS

Serum leptin concentrations were measured by enzyme-linked immunosorbent assay in 47 women with invasive breast cancer compared with 41 age-matched controls without cancer. Genomic DNA was extracted from peripheral blood leukocytes. Genotyping of the leptin receptor gene at codon 109 (LEPR-109) was performed by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Patients with breast cancer had a higher mean serum leptin concentration than women in the control group, but the difference was not statistically significant. Among those with breast cancer, the serum leptin concentration was higher in women with high-grade cancers (p = 0.020). The LEPR-109RR genotype was more frequent in premenopausal patients with tumors larger than 2 cm (p = 0.039) and in premenopausal women who were overweight (p = 0.029). Among patients with the LEPR-109RR genotype, higher mean serum leptin concentrations were present in those with triple-negative cancers (p = 0.048).

CONCLUSIONS

Our study suggests an association between serum leptin concentration and tumor progression. LEPR-109 polymorphism in premenopausal women appears to be associated with obesity and tumor progression.

Dietary soy and tea combinations for prevention of breast and prostate cancers by targeting metabolic syndrome elements in mice

BACKGROUND

The prevalence of metabolic syndrome is high and is increasing in parallel with increasing incidences of breast and prostate cancers. The combination of soy with tea was shown to have synergistic effects on preventing breast and prostate tumors, but the effects of soy and tea combinations on metabolic syndrome-related elements have not been investigated.

OBJECTIVE

We aimed to determine the effects of soy and tea components, alone and in combination, on abdominal adipose mass and serum concentrations of adipokines, growth factors, and sex hormones in male and female mice.

DESIGN

Male and female FVB/N mice were treated with soy, tea components, or both. Food intake and body weight were monitored weekly. At the end of the experiment, abdominal white adipose tissue was weighed, and serum concentrations of biomarkers were measured.

RESULTS

Whole teas, but not the tea polyphenol extracts, significantly reduced abdominal white adipose tissue by 43-60% in female mice and by 65-70% in male mice. The combination of soy phytochemical concentrate and green tea reduced serum insulin-like growth factor-I concentrations in both male and female mice in a synergistic manner. The soy phytochemical concentrate and tea combinations reduced serum estrogen concentrations in female mice in a synergistic manner. Soy phytochemical concentrate and teas also significantly reduced serum leptin concentrations in both male and female mice and testosterone concentrations in male mice.

CONCLUSION

Further research is warranted to investigate whether soy and tea combinations may prevent breast or prostate cancer in a synergistic manner in part by alleviating metabolic disorders.

Baseline leptin levels predict change in leptin levels during weight loss in obese breast cancer survivors

Leptin is an adipocyte-derived hormone involved in regulation of satiety, and it also appears to have a role in breast cancer risk. Leptin therefore might be a useful indicator of the potential preventive effects of weight loss in breast cancer survivors. In this study we examined whether the change in leptin levels could be predicted by weight loss in obese breast cancer survivors. The subjects in this study were participating in a randomized trial of an individualized approach towards weight loss in Detroit, MI. Breast cancer survivors (body mass index of 30-44 kg/m(2)) were enrolled and fasting blood samples were obtained for leptin analysis over 1 year of study. Leptin levels were available from at least two time points for 36 women, and weight change ranged from a gain of 11% to a loss of 25% of baseline weight. Using a repeated-measures regression model, both baseline leptin level and concurrent percent body fat were found to synergistically predict leptin levels. Thus, for women with the same body fat, those with higher baseline leptin levels are predicted to exhibit smaller decreases in leptin with weight loss. Similar results were obtained for body weight and body weight change, but the associations with body fat were stronger. Breast cancer survivors with initially higher leptin levels may differ with regard to regulation of change in leptin during weight loss resulting in relatively smaller changes in leptin with equivalent amounts of weight loss.

Relation of Body Mass Index (BMI) to Disease Free (DFS) and Distant Disease Free Survivals (DDFS) Among Turkish Women with Operable Breast Carcinoma

BACKGROUND

The correlation between body mass index (BMI) and patient and tumor characteristics related to prognosis has not been well explored and may help to elucidate the mechanisms involved in the carcinogenesis. Because of the equivocal, inconsistent and uncertain research results as well as racial and ethnic differences, we aimed to evaluate the prognostic significance of high BMI in Turkish women with operable breast carcinoma.

METHODS

Two hundred and sixty-six patients who had operable invasive breast carcinoma diagnosed from 2000 through 2004 in a single institution were evaluated for their demographic features, BMI, histopathological/immunohistochemical examinations and treatments. Quetelet BMI [weight (kg)/height (m)2] categories were selected according to the World Health Organization definition. Disease free survival (DSF) as well as distant disease free survival (DDSF) analyses were performed to identify independent prognostic factors.

RESULTS

Post-menopausal patients were significantly in the higher quartile of BMI than pre-menopausal patients (P = 0.003). While post-menopausal obese patients had worse DSF and DDFS (P = 0.001), vascular invasion was the independent prognostic factor for both survival indices (P = 0.031).

CONCLUSIONS

Post-menopausal obese Turkish women are at increased risk of developing breast tumors with aggressive phenotype and obesity is a strong predictor of poor DSF and DDFS. Preventive strategies to reduce not only the prevalence of obesity and breast cancer but also the mortality must be recognized as the cost-effective public-health policy for Turkey.

Mechanisms of Disease: adipokines and breast cancer—endocrine and paracrine mechanisms that connect adiposity and breast cancer

A vast number of epidemiological studies suggest an important, but still controversial, role for obesity and adipose tissue mass in breast cancer risk and an association with tumor phenotype. The main conclusions from these studies raise the possibility that the adipose tissue can act as an effector organ that influences both cancer risk and tumor behavior. Here we also review heterotypic mechanisms in breast-cancer tumorigenesis; these mechanisms involve soluble secreted factors from peritumoral cells, extracellular-matrix components and interactions between stromal cells and tumor cells that create a specific and local peritumoral microenvironment. As a special focus, we discuss the increasing evidence for a role of peritumoral adipose tissue and secreted adipokines (such as adiponectin and leptin) in breast cancer; furthermore, the cellular and molecular basis of the peritumoral 'desmoplastic' tissue reaction observed in breast cancer is reviewed in detail.

Diet-induced obesity and mammary tumor development in relation to estrogen receptor status

Leptin enhances proliferation of estrogen receptor (ER)-positive breast cancer cells in vitro. Here, we compared mammary tumor (MT) formation from ER-positive (MCF-7) and ER-negative (MDA-MB-231) breast cancer cells in athymic mice fed a High-Fat diet to elevate serum leptin. Neither body weight, diet or serum leptin levels impacted MT latency, burden or tumor grade. However, protein expression in mammary fat pads exhibited elevated PCNA and Cyclin D1 while in MTs, Ob-Rb, IGF-IR, Bcl-2, and Bax were lower in Low-Fat versus High-Fat mice. In conclusion, diet rather than serum leptin impacted breast cancer cell tumor metabolism.

Leptin Signaling Promotes the Growth of Mammary Tumors and Increases the Expression of Vascular Endothelial Growth Factor (VEGF) and Its Receptor Type Two (VEGF-R2)

To gain insight into the mechanism(s) by which leptin contributes to mammary tumor (MT) development we investigated the effects of leptin, kinase inhibitors, and/or leptin receptor antagonists (LPrA2) on 4T1 mouse mammary cancer cells in vitro and LPrA2 on 4T1-MT development in vivo. Leptin increases the expression of vascular endothelial growth factor (VEGF), its receptor (VEGF-R2), and cyclin D1 through phosphoinositide 3-kinase, Janus kinase 2/signal transducer and activator of transcription 3, and/or extracellular signal-activated kinase 1/2 signaling pathways. In contrast to leptin-induced levels of cyclin D1 the changes in VEGF or VEGF-R2 were more dependent on specific signaling pathways. Incubation of 4T1 cells with anti-VEGF-R2 antibody increased leptin-mediated VEGF expression suggesting an autocrine/paracrine loop. Pretreatment of syngeneic mice with LPrA2 prior to inoculation with 4T1 cells delayed the development and slowed the growth of MT (up to 90%) compared with controls. Serum VEGF levels and VEGF/VEGF-R2 expression in MT were significantly lower in mice treated with LPrA2. Interestingly, LPrA2-induced effects were more pronounced in vivo than in vitro suggesting paracrine actions in stromal, endothelial, and/or inflammatory cells that may impact the growth of MT. Although all the mechanism(s) by which leptin contributes to tumor development are unknown, it appears leptin stimulates an increase in cell numbers, and the expression of VEGF/VEGF-R2. Together, these results provide further evidence suggesting leptin is a MT growth-promoting factor. The inhibition of leptin signaling could serve as a potential adjuvant therapy for treatment of breast cancer and/or provide a new target for the designing strategies to prevent MT development.

Messenger RNA expression of leptin and leptin receptors and their prognostic value in 322 human primary breast cancers

PURPOSE

Leptin and obesity are clearly related, and obesity is associated with an increased risk of breast cancer. We therefore measured the expression of leptin and its two main receptor isoforms, OBR-L and OBR-S, in 322 breast cancers. We analyzed their relations with the classical prognostic factors and with survival to establish their links with breast cancer.

EXPERIMENTAL DESIGN

The expression of leptin and its receptors was quantified by real-time reverse transcription-PCR, using TaqMan fluorogenic probes and an ABI PRISM 7700 sequence detector system (Applied Biosystems, Courtaboeuf, France). TATA box binding protein was used to normalize expression. The human breast cancer cell, SK-BR-3, expressing the three targets, was chosen as the calibrator sample (i.e., target expression = 1).

RESULTS

All the tumors expressed both receptors, and 318 of 322 expressed leptin. These three variables correlated positively with each other and with estradiol and progesterone receptors, whereas they correlated negatively with histoprognostic grading and tumor diameter. OBR-L/OBR-S expression was inversely correlated with progesterone receptors. Patients with elevated OBR-S expression had longer relapse-free survival (P = 0.008), whereas high OBR-L/OBR-S was associated with a shorter relapse-free survival (P = 0.05). In Cox multivariate analyses, OBR-S maintained its prognostic value (P = 0.02; relative risk, 0.51).

CONCLUSIONS

This study shows that (a) almost all of the breast cancers coexpress leptin and its two main isoforms of receptors, suggesting that the human epithelial breast cancer cells respond to leptin acting via an autocrine pathway; (b) high expression levels of leptin and leptin receptors are biological markers of a more differentiated phenotype; and that (c) OBR-S is an independent prognostic factor.

Effects of the expression of leptin and leptin receptor (OBR) on the prognosis of early-stage breast cancers

PURPOSE

Obesity-related leptin and leptin receptor (OBR) have a relation to the development of cancer and metastasis and also the low survival rate for breast cancer patients. Leptin has been associated with increased aromatase activity and it displays functional cross-talk with estrogen. This study was designed to determine the relationship between the expression of leptin and OBR in breast cancer tissue and the prognosis of early-stage breast cancer patients, and especially for the tamoxifen-treated patients.

MATERIALS AND METHODS

Ninety-five patients with early-stage breast cancer and who had undergone surgical treatment at Kyung Hee University Hospital between January 1994 and June 2004 were analyzed. The surgical specimens underwent immunohistochemical analysis for leptin and OBR. The patients' survival and clinical characteristics were obtained from the medical records.

RESULTS

Of the 95 patients, 79 (83%) and 32 (33.7%) showed the expression of leptin and OBR in breast cancer tissue, respectively. The expression of leptin and OBR in breast cancer tissue was not significantly related to the clinicopathological characteristics, including obesity, the expression of hormonal receptor, the HER-2/neu expression, menopause, stage and the nuclear grade. The expression of leptin and OBR was not significantly related to the overall disease-free survival (DFS). For the tamoxifen-treated postmenopausal obese patients, the DFS of the leptin-positive group was higher than that of the leptin-negative group (p=0.017).

CONCLUSION

The expression of leptin and OBR in breast cancer tissue may be not a prognostic factor for disease-free survival of breast cancer patients. In the future, further studies are needed to determine whether leptin expression could be a predictive factor for tamoxifen therapy in the postmenopausal obese subgroup among the early breast cancer patients.

Leptin--from regulation of fat metabolism to stimulation of breast cancer growth

Leptin restricts intake of calories as a satiety hormone. It probably stimulates neoplastic proliferation in breast cancer, too. Growth of malignant cells could be regulated by various leptin-induced second messengers like STAT3 (signal transducers and activators of transcription 3), AP-1 (transcription activator protein 1), MAPK (mitogen-activated protein kinase) and ERKs (extracellular signal-regulated kinases). They seem to be involved in aromatase expression, generation of estrogens and activation of estrogen receptor alpha (ERalpha) in malignant breast epithelium. Leptin may maintain resistance to antiestrogen therapy. Namely, it increased activation of estrogen receptors, therefore, it was suspected to reduce or even overcome the inhibitory effect of tamoxifen on breast cell proliferation. Although several valuable reviews have been focused on the role of leptin in breast cancer, the status of knowledge in this field changes quickly and our insight should be continuously revised. In this summary, we provide refreshed interpretation of intensively reported scientific queries of the topic.