Progesterone metabolites regulate induction, growth, and suppression of estrogen- and progesterone receptor-negative human breast cell tumors

The implications of hormone treatment for cancer risk, screening and treatment in transgender individuals

There is evidence that gender-affirming hormone treatment (GAHT) for transgender individuals modulates their risk for specific malignancies including breast and prostate cancer, and meningiomas. However, there is insufficient data to make precise risk estimates accounting for age and inherited cancer risk. As such, screening recommendations remain broad. Even less evidence exists for best practice in the management of active or historical cancers in the transgender population. Guidance is therefore mainly extrapolated from cisgender populations but with considerations of the significant benefits of GAHT in the face of any hormonal risk. Clinical experience, the multidisciplinary team and shared decision making with the patient are vital in providing person-centred care, while further research is acquired.

Effect of 3α-dihydroprogesterone and 5α-dihydroprogesterone on DCIS cells and possible impact for postmenopausal women

OBJECTIVE

Progesterone metabolites 5α-dihydroprogesterone (5αP) and 3α-dihydroprogesterone (3αP) have opposite effects on proliferation, apoptosis and metastasis in the breast. Evidence regarding their influence on ductal carcinoma in situ (DCIS) lesions is lacking.

METHODS

MCF10DCIS.com cells were cultured in a 3D culture system and treated with 5αP or 3αP. After 5 and 12 days of treatment, polymerase chain reaction (PCR) of proliferation, invasion/metastasis, anti-apoptotic or other markers was performed. Cells treated with the tumor-promoting 5αP were observed under the light and confocal microscopes to reveal possible morphological changes that could indicate a transition from an in situ to an invasive phenotype. As a control, the morphology of the MDA-MB-231 invasive cell line was examined. The invasive potential after exposure to 5αP was also assessed using a detachment assay.

RESULTS

The PCR analysis of the chosen markers showed no statistically significant difference between naive cells and cells treated with 5αP or 3αP. DCIS spheroids retained their in situ morphology after treatment with 5αP. The detachment assay showed no increased potential for invasion after exposure to 5αP. Progesterone metabolites 5αP and 3αP do not facilitate or prohibit tumor promotion/invasion in MCF10DCIS.com cells, respectively.

CONCLUSION

As oral micronized progesterone has been proved effective for hot flushes in postmenopausal women, first in vitro data propose that progesterone-only therapy could possibly be considered for women after DCIS suffering from hot flushes.

Allopregnanolone: Metabolism, Mechanisms of Action, and Its Role in Cancer

Allopregnanolone (3α-THP) has been one of the most studied progesterone metabolites for decades. 3α-THP and its synthetic analogs have been evaluated as therapeutic agents for pathologies such as anxiety and depression. Enzymes involved in the metabolism of 3α-THP are expressed in classical and nonclassical steroidogenic tissues. Additionally, due to its chemical structure, 3α-THP presents high affinity and agonist activity for nuclear and membrane receptors of neuroactive steroids and neurotransmitters, such as the Pregnane X Receptor (PXR), membrane progesterone receptors (mPR) and the ionotropic GABA_A receptor, among others. 3α-THP has immunomodulator and antiapoptotic properties. It also induces cell proliferation and migration, all of which are critical processes involved in cancer progression. Recently the study of 3α-THP has indicated that low physiological concentrations of this metabolite induce the progression of several types of cancer, such as breast, ovarian, and glioblastoma, while high concentrations inhibit it. In this review, we explore current knowledge on the metabolism and mechanisms of action of 3α-THP in normal and tumor cells.

Rewiring of the Endocrine Network in Triple-Negative Breast Cancer

The immunohistochemical definition of estrogen/progesterone receptors dictates endocrine feasibility in the treatment course of breast cancer. Characterized by the deficiency of estrogen receptor α, ERα-negative breast cancers are dissociated from any endocrine regimens in the routine clinical setting, triple-negative breast cancer in particular. However, the stereotype was challenged by triple-negative breast cancers’ retained sensitivity and vulnerability to endocrine agents. The interplay of hormone action and the carcinogenic signaling program previously underscored was gradually recognized along with the increasing investigation. In parallel, the overlooked endocrine-responsiveness in ERα-negative breast cancers attracted attention and supplied fresh insight into the therapeutic strategy in an ERα-independent manner. This review elaborates on the genomic and non-genomic steroid hormone actions and endocrine-related signals in triple-negative breast cancers attached to the hormone insensitivity label. We also shed light on the non-canonical mechanism detected in common hormone agents to showcase their pleiotropic effects.

Allopregnanolone Promotes Migration and Invasion of Human Glioblastoma Cells through the Protein Tyrosine Kinase c-Src Activation

Glioblastomas (GBs) are the most aggressive and common primary malignant brain tumors. Steroid hormone progesterone (P4) and its neuroactive metabolites, such as allopregnanolone (3α-THP) are synthesized by neural, glial, and malignant GB cells. P4 promotes cellular proliferation, migration, and invasion of human GB cells at physiological concentrations. It has been reported that 3α-THP promotes GB cell proliferation. Here we investigated the effects of 3α-THP on GB cell migration and invasion, the participation of the enzymes involved in its metabolism (AKR1C1-4), and the role of the c-Src kinase in 3α-THP effects in GBs. 3α-THP 100 nM promoted migration and invasion of U251, U87, and LN229 human-derived GB cell lines. We observed that U251, LN229, and T98G cell lines exhibited a higher protein content of AKR1C1-4 than normal human astrocytes. AKR1C1-4 silencing did not modify 3α-THP effects on migration and invasion. 3α-THP activated c-Src protein at 10 min (U251 cells) and 15 min (U87 and LN229 cells). Interestingly, the pharmacological inhibition of c-Src decreases the promoting effects of 3α-THP on cell migration and invasion. Together, these data indicate that 3α-THP promotes GB migration and invasion through c-Src activation.

The Divergent Effects of Ovarian Steroid Hormones in the MCF-7 Model for Luminal A Breast Cancer: Mechanistic Leads for Therapy

The growth modulating effects of the ovarian steroid hormones 17β-estradiol (E₂) and progesterone (PRG) on endocrine-responsive target tissues are well established. In hormone-receptor-positive breast cancer, E₂ functions as a potent growth promoter, while the function of PRG is less defined. In the hormone-receptor-positive Luminal A and Luminal B molecular subtypes of clinical breast cancer, conventional endocrine therapy predominantly targets estrogen receptor function and estrogen biosynthesis and/or growth factor receptors. These therapeutic options are associated with systemic toxicity, acquired tumor resistance, and the emergence of drug-resistant cancer stem cells, facilitating the progression of therapy-resistant disease. The limitations of targeted endocrine therapy emphasize the identification of nontoxic testable alternatives. In the human breast, carcinoma-derived hormone-receptor-positive MCF-7 model treatment with E₂ within the physiological concentration range of 1 nM to 20 nM induces progressive growth, upregulated cell cycle progression, and downregulated cellular apoptosis. In contrast, treatment with PRG at the equimolar concentration range exhibits dose-dependent growth inhibition, downregulated cell-cycle progression, and upregulated cellular apoptosis. Nontoxic nutritional herbs at their respective maximum cytostatic concentrations (IC₉₀) effectively increase the E₂ metabolite ratio in favor of the anti-proliferative metabolite. The long-term exposure to the selective estrogen-receptor modulator tamoxifen selects a drug-resistant phenotype, exhibiting increased expressions of stem cell markers. The present review discusses the published evidence relevant to hormone metabolism, growth modulation by hormone metabolites, drug-resistant stem cells, and growth-inhibitory efficacy of nutritional herbs. Collectively, this evidence provides proof of the concept for future research directions that are focused on novel therapeutic options for endocrine therapy-resistant breast cancer that may operate via E₂- and/or PRG-mediated growth regulation.

Progesterone Receptor Signaling in the Breast Tumor Microenvironment

The tumor microenvironment (TME) is a complex infrastructure composed of stromal, epithelial, and immune cells embedded in a vasculature ECM. The microenvironment surrounding mammary epithelium plays a critical role during the development and differentiation of the mammary gland, enabling the coordination of the complex multihormones and growth factor signaling processes. Progesterone/progesterone receptor paracrine signaling interactions in the microenvironment play vital roles in stem/progenitor cell function during normal breast development. In breast cancer, the female sex hormones, estrogen and progesterone, and growth factor signals are altered in the TME. Progesterone signaling modulates not only breast tumors but also the breast TME, leading to the activation of a series of cross-communications that are implicated in the genesis of breast cancers. This chapter reviews the evidence that progesterone and PR signaling modulates not only breast epitheliums but also the breast TME. Furthermore, crosstalk between estrogen and progesterone signaling affecting different cell types within the TME is discussed. A better understanding of how PR and progesterone affect the TME of breast cancer may lead to novel drugs or a therapeutic approach for the treatment of breast cancer shortly.

5alpha-dihydroprogesterone promotes proliferation and migration of human glioblastoma cells

Glioblastomas (GBMs) are the most common and deadliest intracranial tumors. Steroid hormones, such as progesterone (P4), at physiological concentrations, promote proliferation, and migration of human GBM cells in vivo and in vitro. Neuronal and glial cells, but also GBMs, metabolize P4 and synthesize different active metabolites such as 5α-dihydroprogesterone (5α-DHP). However, their contribution to GBM malignancy remains unknown. Here, we determined the 5α-DHP effects on the number of cells, proliferation, and migration of the U87 and U251 human GBM-derived cell lines. Of the tested concentrations (1 nM-1 µM), 5α-DHP 10 nM significantly increased the number of U87 and U251 cells from day 2 of treatment, and proliferation (at day 3) in a similar manner as P4 (10 nM). The treatment with the progesterone receptor (PR) antagonist RU486 (mifepristone), blocked the effects of 5α-DHP on the number of cells and proliferation. Besides, in U251 and LN229 GBM cells, 5α-DHP promoted cell migration (from 12 to 24 h). We also determined that GBM cells expressed the 3α-hydroxysteroid oxidoreductases (3α-HSOR), which reversibly reduce 5α-DHP to allopregnanolone (3α-THP). These data indicate that 5α-DHP induces proliferation and migration of human GBM through the activation of PR.

PGRMC1 Inhibits Progesterone-Evoked Proliferation and Ca2+ Entry Via STIM2 in MDA-MB-231 Cells

Progesterone receptor membrane component 1 (PGRMC1) has been shown to regulate some cancer hallmarks. Progesterone (P₄) evokes intracellular calcium (Ca²⁺) changes in the triple-negative breast cancer cell lines (MDA-MB-231, MDA-MB-468, and BT-20) and in other breast cancer cell lines like the luminal MCF7 cells. PGRMC1 expression is elevated in MDA-MB-231 and MCF7 cells as compared to non-tumoral MCF10A cell line, and PGRMC1 silencing enhances P₄-evoked Ca²⁺ mobilization. Here, we found a new P₄-dependent Ca²⁺ mobilization pathway in MDA-MB-231 cells and other triple-negative breast cancer cells, as well as in MCF7 cells that involved Stromal interaction molecule 2 (STIM2), Calcium release-activated calcium channel protein 1 (Orai1), and Transient Receptor Potential Channel 1 (TRPC1). Stromal interaction molecule 1 (STIM1) was not involved in this novel Ca²⁺ pathway, as evidenced by using siRNA STIM1. PGRMC1 silencing reduced the negative effect of P₄ on cell proliferation and cell death in MDA-MB-231 cells. In line with the latter observation, Nuclear Factor of Activated T-Cells 1 (NFAT1) nuclear accumulation due to P₄ incubation for 48 h was enhanced in cells transfected with the small hairpin siRNA against PGRMC1 (shPGRMC1). These results provide evidence for a novel P₄-evoked Ca²⁺ entry pathway that is downregulated by PGRMC1.

Association of Circulating Progesterone With Breast Cancer Risk Among Postmenopausal Women

IMPORTANCE

The role of endogenous progesterone in the development of breast cancer remains largely unexplored to date, primarily owing to assay sensitivity limitations and low progesterone concentrations in postmenopausal women. Recently identified progesterone metabolites may provide insights as experimental data suggest that 5α-dihydroprogesterone (5αP) concentrations reflect cancer-promoting properties and 3α-dihydroprogesterone (3αHP) concentrations reflect cancer-inhibiting properties.

OBJECTIVE

To evaluate the association between circulating progesterone and progesterone metabolite levels and breast cancer risk.

DESIGN, SETTING, AND PARTICIPANTS

Using a sensitive liquid chromatography-tandem mass spectrometry assay, prediagnostic serum levels of progesterone and progesterone metabolites were quantified in a case-cohort study nested within the Breast and Bone Follow-up to the Fracture Intervention Trial (n = 15 595). Participation was limited to women not receiving exogenous hormone therapy at the time of blood sampling (1992-1993). Incident breast cancer cases (n = 405) were diagnosed during 12 follow-up years and a subcohort of 495 postmenopausal women were randomly selected within 10-year age and clinical center strata. Progesterone assays were completed in July 2017; subsequent data analyses were conducted between July 15, 2017, and December 20, 2018.

EXPOSURES

Circulating concentrations of pregnenolone, progesterone, and their major metabolites.

MAIN OUTCOMES AND MEASURES

Development of breast cancer, with hazard ratios (HRs) and 95% CIs was estimated using Cox proportional hazards regression adjusted for key confounders, including estradiol. Evaluation of hormone ratios and effect modification were planned a priori.

RESULTS

The present study included 405 incident breast cancer cases and a subcohort of 495 postmenopausal women; the mean (SD) age at the time of the blood draw was 67.2 (6.2) years. Progesterone concentrations were a mean (SD) of 4.6 (1.7) ng/dL. Women with higher circulating progesterone levels were at an increased risk for breast cancer per SD increase in progesterone levels (HR, 1.16; 95% CI, 1.00-1.35; P = .048). The association with progesterone was linear in a 5-knot spline and stronger for invasive breast cancers (n = 267) (HR, 1.24; 95% CI, 1.07-1.43; P = .004). Among women in the lowest quintile (Q1) of circulating estradiol (<6.30 pg/mL) elevated progesterone concentrations were associated with reduced breast cancer risk per SD increase in progesterone levels (HR, 0.38; 95% CI, 0.15-0.95; P = .04) and increased risk among women in higher quintiles of estradiol (Q2-Q5; ≥6.30 pg/mL) (HR, 1.18; 95% CI, 1.04-1.35; P = .01; P = .04 for interaction).

CONCLUSIONS AND RELEVANCE

In this case-cohort study of postmenopausal women, elevated circulating progesterone levels were associated with a 16% increase in the risk of breast cancer. Additional research should be undertaken to assess how postmenopausal breast cancer risk is associated with both endogenous progesterone and progesterone metabolites and their interactions with estradiol.

Progesterone and Breast Cancer

Synthetic progestogens (progestins) have been linked to increased breast cancer risk; however, the role of endogenous progesterone in breast physiology and carcinogenesis is less clearly defined. Mechanistic studies using cell culture, tissue culture, and preclinical models implicate progesterone in breast carcinogenesis. In contrast, limited epidemiologic data generally do not show an association of circulating progesterone levels with risk, and it is unclear whether this reflects methodologic limitations or a truly null relationship. Challenges related to defining the role of progesterone in breast physiology and neoplasia include: complex interactions with estrogens and other hormones (eg, androgens, prolactin, etc.), accounting for timing of blood collections for hormone measurements among cycling women, and limitations of assays to measure progesterone metabolites in blood and progesterone receptor isotypes (PRs) in tissues. Separating the individual effects of estrogens and progesterone is further complicated by the partial dependence of PR transcription on estrogen receptor (ER)α-mediated transcriptional events; indeed, interpreting the integrated interaction of the hormones may be more essential than isolating independent effects. Further, many of the actions of both estrogens and progesterone, particularly in "normal" breast tissues, are driven by paracrine mechanisms in which ligand binding to receptor-positive cells evokes secretion of factors that influence cell division of neighboring receptor-negative cells. Accordingly, blood and tissue levels may differ, and the latter are challenging to measure. Given conflicting data related to the potential role of progesterone in breast cancer etiology and interest in blocking progesterone action to prevent or treat breast cancer, we provide a review of the evidence that links progesterone to breast cancer risk and suggest future directions for filling current gaps in our knowledge.

Effect of progesterone and first evidence about allopregnanolone action on the progression of epithelial human ovarian cancer cell lines

Ovarian carcinoma is one of the most common cause of death by gynecologic cancer. Several epidemiological and in vitro studies have shown controversial data about progesterone effects in ovarian cancer. Progesterone can be converted in its active metabolite, allopregnanolone, its effects in ovarian cancer are still unknown. Previously, we demonstrated that allopregnanolone modifies ovarian morphophysiology, being able to alter critical process of tumor development such as proliferation, apoptosis and angiogenesis. Taking into account these antecedents, we investigated the effect of progesterone and allopregnanolone on proliferation, apoptosis, clonogenic capacity and migration on two epithelial human ovarian cancer cell lines, IGROV-1 and SKOV-3. To this end, IGROV-1 and SKOV-3 cells were exposed to a range of progesterone and allopregnanolone concentrations (10^-11 to 10^-5 M) for 72 h. Proliferation was analyzed by MTT and Ki67 expression. Apoptosis was measured by immunocytochemistry of cleaved caspase 3. Clonogenic capacity was evaluated by counting colonies. Migration was analyzed by wound assay. We found that allopregnanolone increased proliferation and Ki67 expression respect to control on IGROV-1 cells, while expression of cleaved caspase 3 did not change in any cell line studied. IGROV-1 clonogenic capacity was also increased by allopregnanolone treatment. Both steroids, progesterone and allopregnanolone, increased IGROV-1 migration in a concentration dependent manner. None of the steroids tested modified SKOV-3 biological behavior analized. This is the first evidence that allopregnanolone, a progesterone metabolite, affects critical events in tumor development of human epithelial ovarian cancer. These results could have an impact in the future in clinic diagnosis, prognosis and treatment of ovarian cancer patients. The regulation of progesterone and allopregnanolone steroideogenesis and their molecular mechanisms might be considered as potential therapeutic tool in ovarian cancer.

Steroid enzyme and receptor expression and regulations in breast tumor samples - A statistical evaluation of public data

In spite of the significant progress of estrogen-dependent breast cancer (BC) treatment, aromatase inhibitor resistance is a major problem limiting the clinical benefit of this frontier endocrine-therapy. The aim of this study was to determine the differential expression of steroid-converting enzymes between tumor and adjacent normal tissues, as well as their correlation in modulating intratumoral steroid-hormone levels in post-menopausal estrogen-dependent BC. RNA sequencing dataset (n = 1097) of The-Cancer-Genome-Atlas (Breast Invasive Carcinoma) retrieved through the data portal of Genomic Data Commons was used for differential expressions and expression correlation analyses by Mann-Whitney U and Spearman's rank test, respectively. The results showed significant up-regulation of 17β-HSD7 (2.50-fold, p < 0.0001) in BC, supporting its effect in sex-hormone control. Besides, suppression of 11β-HSD1 expression (-8.29-fold, p < 0.0001) and elevation of 11β-HSD2 expression (2.04-fold, p < 0.0001) provide a low glucocorticoid environment diminishing BC anti-proliferation. Furthermore, 3α-HSDs were down-regulated (-1.59-fold, p < 0.01; -8.18-fold, p < 0.0001; -33.96-fold, p < 0.0001; -31.85-fold, p < 0.0001 for type 1-4, respectively), while 5α-reductases were up-regulated (1.41-fold, p < 0.0001; 2.85-fold, p < 0.0001; 1.70-fold, p < 0.0001 for type 1-3, respectively) in BC, reducing cell proliferation suppressers 4-pregnenes, increasing cell proliferation stimulators 5α-pregnanes. Expression analysis indicates significant correlations between 11β-HSD1 with 3α-HSD4 (r = 0.605, p < 0.0001) and 3α-HSD3 (r = 0.537, p < 0.0001). Significant expression correlations between 3α-HSDs were also observed. Our results systematically present the regulation of steroid-converting enzymes and their roles in modulating the intratumoral steroid-hormone levels in BC with a vivid 3D-schema, supporting novel therapy targeting the reductive 17β-HSD7 and proposing a new combined therapy targeting 11β-HSD2 and 17β-HSD7.

Relationship of Serum Progesterone and Progesterone Metabolites with Mammographic Breast Density and Terminal Ductal Lobular Unit Involution among Women Undergoing Diagnostic Breast Biopsy

The association of progesterone/progesterone metabolites with elevated mammographic breast density (MBD) and delayed age-related terminal duct lobular unit (TDLU) involution, strong breast cancer risk factors, has received limited attention. Using a reliable liquid chromatography-tandem mass-spectrometry assay, we quantified serum progesterone/progesterone metabolites and explored cross-sectional relationships with MBD and TDLU involution among women, ages 40–65, undergoing diagnostic breast biopsy. Quantitative MBD measures were estimated in pre-biopsy digital mammograms. TDLU involution was quantified in diagnostic biopsies. Adjusted partial correlations and trends across MBD/TDLU categories were calculated. Pregnenolone was positively associated with percent MBD-area (MBD-A, rho: 0.30; p-trend = 0.01) among premenopausal luteal phase women. Progesterone tended to be positively associated with percent MBD-A among luteal phase (rho: 0.26; p-trend = 0.07) and postmenopausal (rho: 0.17; p-trend = 0.04) women. Consistent with experimental data, implicating an elevated 5α-pregnanes/3α-dihydroprogesterone (5αP/3αHP) metabolite ratio in breast cancer, higher 5αP/3αHP was associated with elevated percent MBD-A among luteal phase (rho: 0.29; p-trend = 0.08), but not postmenopausal women. This exploratory analysis provided some evidence that endogenous progesterone and progesterone metabolites might be correlated with MBD, a strong breast cancer risk factor, in both pre- and postmenopausal women undergoing breast biopsy. Additional studies are needed to understand the role of progesterone/progesterone metabolites in breast tissue composition and breast cancer risk.

Progesterone Metabolites Inhibit the Human Ether-a-go-go-Related Gene and Predict QT Interval Length

A decrease in the human ether-a-go-go-related gene (hERG/KCNH2)-related channel has been linked to intrauterine fetal death. The formation of cytochrome P450 (CYP) 3A-mediated progesterone metabolites, 6-beta-hydroxy-progesterone (6β-OHP) and 16α-hydroxy-progesterone (16α-OHP), is variable among adults and differs from fetal metabolism. The primary objective of this study was to assess the potential for progesterone metabolites to inhibit hERG-related current and predict QTc intervals. Whole-cell voltage-clamp electrophysiology was performed on human embryonic kidney 293 cells stably expressing hERG exposed to progesterone or metabolites. Both 6β-OHP and 16α-OHP positively shifted the voltage dependence of activation relative to vehicle from -4.0 ± 0.8 to -0.3 ± 0.8 mV, P < .01; and 1.0 ± 0.6 mV, P < .01, respectively. In addition, 6β-OHP decreased maximal outward tail currents from 49.4 ± 4.9 to 32.5 ± 4.1 pA/pF, P < 0.01, and reduced the expression of fully glycosylated hERG by 42%. Healthy female subjects were administered progesterone 400 mg orally for 7 days, ibutilide 0.003 mg/kg was infused, and serial electrocardiograms and blood samples collected. Relationships between rate-corrected QT intervals (QTcI) with circulating hormones and metabolites were assessed. The 6β-OHP and 16α-OHP metabolites were independent predictors of QTcI intervals prior to and following ibutilide administration. In conclusion, the progesterone metabolites formed via CYP3A cause inhibitory effects on hERG channels and predict QTcI intervals in healthy women pretreated with progesterone. Further study into maternal and fetal exposure to these metabolites and potential to prolong cardiac repolarization is warranted.

In vivo study on biotransformation of pentacyclic analogs of progesterone: Identification of their metabolites by HPLC-MS method

Progesterone derivatives containing the D' additional cyclohexane ring in the 16α,17α-positions of steroid core (pregna-D'-pentaranes) exhibited high in vitro and in vivo selective progestogenic activity. The assessment of their biotransformation in the body, and the identification of possible metabolites are integral parts of a potential drug studies. Here we describe the results of in vivo metabolic transformation of 6α-methyl-16α,17α-cyclohexanopregn-4-ene-3,20-dione 1 and its 6-demethylated analog 2 and identification of their metabolites in rat urine. We synthesized and fully characterized (1D and 2D NMR, HRMS) 11 possible metabolites as the standards. Then we developed the LC-MS/MS assay including sample preparation and chromatography conditions for identification of the detected metabolites of 1 and 2. The 5α- and 5β-3,20-diketo-, 3β-hydroxy-20-keto-5α-, 3-keto-20(S)-hydroxy-5α-, 3β,20(S)-dihydroxy-5α-metabolites of compounds 1 and 2 were found in rat urine samples. The starting steroids 1 and 2, as well as both 3β,20(R)-dihydroxy metabolites were not detected in the examined biological urine samples. Thus, we demonstrate for the first time that exogenous progestines - pregna-D'-pentaranes - and endogenous progesterone follow similar metabolic pathways. Therefore, despite the presence of an additional ring D' and the methyl group in position 6, the main enzymatic transformations are similar to those of the natural hormone.

Lentivirus-mediated CDglyTK gene-modified free flaps by intra-artery perfusion show targeted therapeutic efficacy in rat model of breast cancer

Background

Free flap-mediated gene therapy in the tumor bed following surgical resection is a promising approach in cancer targeted treatment of residual disease. We investigated the selective killing efficacy of a lentivirus-mediated cytosine deaminase-thymidine kinase (CDglyTK) gene in transplanted breast cancer delivered into a free flap by intra-artery perfusion.

Methods

Proliferation, apoptosis, and cell cycle of rat SHZ-88 breast cancer cells transfected with a lentivirus-mediated CD/TK gene were measured following treatment with ganciclovir and 5-flucytosine in vitro. A model of residual disease of breast cancer in a rat superficial inferior epigastric artery (SIEA) flap model was used to study the therapeutic potential of a double suicide CD/TK and prodrug system in vivo.

Results

Killing efficacy of the double suicide CD/TK and prodrug system on SHZ-88 cells was mediated by increased apoptosis and cell cycle arrest at the G1 phase with significant bystander effect. Following recombinant lentivirus transfection of rat SIEA flap by intra-artery perfusion, CD/TK gene expression was limited to the flap, and the volume and weight of transplanted tumors were significantly reduced without observable toxicity.

Conclusions

SIEA flaps transfected with a lentivirus-mediated CDglyTK gene by intra-artery perfusion effectively suppress transplanted breast tumor growth without obvious systemic toxic effects in rats.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-6111-5) contains supplementary material, which is available to authorized users.

Differential metabolism of clinically-relevant progestogens in cell lines and tissue: Implications for biological mechanisms

Steroid hormones regulate a variety of physiological processes, including reproductive function, and are widely used in hormonal therapy. Synthetic progestogens, or progestins, were designed to mimic progesterone (P₄) for use in contraception and hormonal replacement therapy in women. Medroxyprogesterone acetate (MPA) and norethisterone (NET) are the most widely used injectable contraceptives in the developing world, while other progestins such as levonorgestrel (LNG), etonogestrel (ETG) and nestorone (NES) are used in or being developed for other forms of contraception. As concerns remain about the most appropriate choice of progestin and dosage, and the associated side-effects, the mechanisms and biological effects of progestins are frequently investigated in various in vitro mammalian cell line and tissue models. However, whether progestogens are differentially metabolised in different cell types in vivo or in vitro is unknown. For nine mammalian cell lines commonly used to investigate progestogen mechanisms of action, we developed and validated an ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) protocol for simultaneously quantifying the metabolism of the above-mentioned steroids. We show for the first time that, while 50-100% of P₄ was metabolised within 24 h in all cell lines, the metabolism of the progestins is progestin- and cell line-specific. We also show that MPA and NET are significantly metabolised in human cervical tissue, but to a lesser extent than P₄. Taken together, our findings suggest that differential progestogen metabolism may play a role in cell-specific therapeutic and side-effects. Relative affinities for binding to steroid receptors as well as potencies, efficacies and biocharacters for transcriptional activity of progestins, relative to P₄, are most frequently determined using some of the cell lines investigated. Our results, however, suggest that differential metabolism of progestins and P₄ may confound these results. In particular, metabolism may under-estimate the receptor-mediated intrinsic in vitro binding and dose-response values and predicted endogenous physiological effects of P₄.

Targeting progesterone metabolism in breast cancer with l-proline derived new 14-azasteroids

Breast cancer cell proliferation is promoted by a variety of mitogenic signals. Classically estrogen is considered as most predominant mitogenic signal in hormone-dependent breast cancer and progesterone is primarily considered to have protective effect. However, it is suggested that some progesterone metabolite may promote breast cancer and progesterone metabolites like 5α-pregnane and 4-pregnene could serve as regulators of estrogen-responsiveness of breast cancer cells. Here, we estimated the potential of alternate targeting of breast cancer via progesterone signalling. l-Proline derived novel 14-azasteroid compounds were screened against MCF-7 and MDA-MB-231 cell lines using MTT assay. In silico studies, cell cycle, Annexin-V-FITC/PI, JC-1 mitochondrial assay, ROS analysis were performed to analyse the impact of hit compound 3b on breast cancer cells. Further, we analysed the impact of hit 3b on the progesterone, its metabolites and enzymes responsible for the conversion of progesterone and its metabolites using ELISA. Data suggests that compound 3b binds and down regulates of 5α-reductase by specifically inhibiting production of progesterone metabolites that are capable of promoting breast cancer proliferation, epithelial mesenchymal transition and migration. This study establishes the proof of concept and generation of new leads for additional targeting of breast cancer.

Aldo-Keto Reductase AKR1C1-AKR1C4: Functions, Regulation, and Intervention for Anti-cancer Therapy

Aldo-keto reductases comprise of AKR1C1-AKR1C4, four enzymes that catalyze NADPH dependent reductions and have been implicated in biosynthesis, intermediary metabolism, and detoxification. Recent studies have provided evidences of strong correlation between the expression levels of these family members and the malignant transformation as well as the resistance to cancer therapy. Mechanistically, most studies focus on the catalytic-dependent function of AKR1C isoforms, like their impeccable roles in prostate cancer, breast cancer, and drug resistance due to the broad substrates specificity. However, accumulating clues showed that catalytic-independent functions also played critical roles in regulating biological events. This review summarizes the catalytic-dependent and -independent roles of AKR1Cs, as well as the small molecule inhibitors targeting these family members.

Allopregnanolone promotes proliferation and differential gene expression in human glioblastoma cells

Allopregnanolone (3α-THP) is one of the main reduced progesterone (P₄) metabolites that is recognized as a neuroprotective and myelinating agent. 3α-THP also induces proliferation of different neural cells. It has been shown that P₄ favors the progression of glioblastomas (GBM), the most common and aggressive primary brain tumors. However, the role of 3α-THP in the growth of GBMs is unknown. Here, we studied the effects of 3α-THP on the number of cells, proliferation and gene expression in U87 cell line derived from a human GBM. 3α-THP (10, 100nM and 1μM) increased the number of U87 cells, and at 10nM exerted a similar increase in both the number of total and proliferative U87 cells as compared with P₄ (10nM). Interestingly, finasteride (F; 100nM), an inhibitor of 5α-reductase (5αR), an enzyme necessary to metabolize P₄ and produce 3α-THP, blocked the increase in the number of U87 cells induced by P₄. By using RT-qPCR, we determined that U87 cells express 5α-R isoenzymes 1 and 2 (5αR1 and 5αR2), being 5αR1 the predominant one in these cells. 3α-THP (10nM) increased the expression of TGFβ1, EGFR, VEGF and cyclin D1 genes. P₄ increased TGFβ1 and EGFR expression, and this effect was blocked by F. These data provide evidence that P₄, through its metabolite 3α-THP, can promote in part cell proliferation of human GBM cells by changing the expression of genes involved in tumor progression.

Reproducibility of an assay to measure serum progesterone metabolites that may be related to breast cancer risk using liquid chromatography-tandem mass spectrometry

Recent data suggest a novel role of progesterone in breast cancer etiology involving the progesterone metabolites 3α-dihydroprogesterone (3αHP), 5α-dihydroprogesterone (5αP), and 20α-dihydroprogesterone (20αHP). Accurate and precise measures of progesterone metabolites are needed for etiologic studies of hormonally related cancers. We have developed a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method to measure five hormones, including progesterone, its precursor pregnenolone, and three progesterone metabolites, 5αP, 3αHP, and 20αHP. Hormone levels were measured in serum from 20 healthy volunteers (7 men, 5 premenopausal women, and 8 postmenopausal women). Two blinded, randomized aliquots per individual were assayed in each of four batches. The coefficients of variation (CV) and intraclass correlation coefficients (ICC) were calculated from the individual components of variance. The overall laboratory CVs were <3% and ICCs were uniformly high (>98%) for all hormones measured across sex/menopausal status groups. Our HPLC-MS/MS assay of progesterone metabolites demonstrated excellent sensitivity, laboratory reproducibility, and interindividual variation, suggesting that this serum assay is suitable for epidemiologic research. The high sensitivity of the assay, and thus the ability to quantify concentrations among postmenopausal women and men, further supports that this novel assay is suitable for studies of serum progesterone metabolite concentrations and risk of breast cancer or other hormonally related cancer.

Novel thiosemicarbazides induced apoptosis in human MCF-7 breast cancer cells via JNK signaling

In this study, novel thiosemicarbazides and 1,3,4-oxadiazoles were synthesized and evaluated for their anticancer effects on human MCF-7 breast cancer cell lines. Among the synthesized derivatives studied, compound 2-(3-(4-chlorophenyl)-3-hydroxybutanoyl)-N-phenylhydrazinecarbothioamide 4c showed the highest cytotoxicity against MCF-7 breast cancer cells as it reduced cell viability to approximately 15% compared to approximately 25% in normal breast epithelial cells. Therefore, we focused on 4c for further investigations. Our data showed that 4c induced apoptosis in MCF-7 cells which was further confirmed by TUNEL assay. Western blotting analysis showed that compound 4c up-regulated the pro-survival proteins Bax, Bad and ERK1/2, while it down-regulated anti-apoptotic proteins Bcl-2, Akt and STAT-3. Additionally, 4c induced phosphorylation of SAPK/JNK in MCF-7 cells. Pretreatment of MCF-7 cells with 10 µM of JNK inhibitor significantly reduced 4c-induced apoptosis. Molecular docking results suggested that compound 4c showed a binding pattern close to the pattern observed in the structure of the lead fragment bound to JNK1. Collectively, the data of current study suggested that the thiosemicarbazide 4c might trigger apoptosis in human MCF-7 cells by targeting JNK signaling.

Nipple Aspirate Fluid Hormone Concentrations and Breast Cancer Risk

Prior reports identify higher serum concentrations of estrogens and androgens as risk factors for breast cancer, but steroids in nipple aspirate fluid (NAF) may be more related to risk. Incident breast cancer cases and mammography controls were recruited. Sex steroids were measured in NAF from the unaffected breasts of cases and one breast of controls. Menopausal status and menstrual cycle phase were determined. NAF steroids were purified by HPLC and quantified by immunoassays. Conditional logistic regression models were used to examine associations between NAF hormones and case-control status. NAF samples from 160 cases and 157 controls were evaluable for hormones. Except for progesterone and dehydroepiandrosterone (DHEA), the NAF and serum concentrations were not significantly correlated. NAF estradiol and estrone were not different between cases and controls. Higher NAF (but not serum) DHEA concentrations were associated with cases, particularly among estrogen receptor (ER)-positive cases (NAF odds ratio (OR) = 1.18, 95 % confidence interval (CI) 1.02, 1.36). NAF DHEA was highly correlated with NAF estradiol and estrone but not with androstenedione or testosterone. Higher progesterone concentrations in both NAF and serum were associated with a lower risk of ER-negative cancer (NAF OR = 0.69, 95 % CI 0.51, 0.92). However, this finding may be explained by case-control imbalance in the number of luteal phase subjects (2 cases and 19 controls). The significantly higher concentration of DHEA in NAF of cases and its correlation with NAF estradiol indicates a potentially important role of this steroid in breast cancer risk; however, the negative association of progesterone with risk is tentative.

Mechanism of action of the breast cancer-promoter hormone, 5α-dihydroprogesterone (5αP), involves plasma membrane-associated receptors and MAPK activation

Previous studies have shown that breast tissues and breast cell lines can convert progesterone to 5α-pregnane-3,20-dione (5aP), and that 5αP stimulates breast cell proliferation and detachment in vitro, and tumor formation in vivo, regardless of presence or absence of receptors for progesterone (PR) or estrogen (ER). Recently it was demonstrated, both in vitro and in vivo, that pro-cancer actions attributed to administered progesterone are due to the in situ produced 5αP. Because of the significant role of 5αP in breast cancers, it is important to understand its molecular mechanisms of action. The aims of the current studies were to identify 5αP binding sites and to determine if the mechanisms of action of 5αP involve the mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinases (ERK1/2) pathway. Binding studies, using tritium-labeled 5αP ([(3)H]5αP), carried out on membrane, cytosol and nuclear fractions from human breast cells (MCF-7, PR/ER-positive; MDA-MB-231, PR/ER-negative) and on highly enriched membrane fractions, identified the plasma membrane as the site of ligand specific 5αP receptors. Localization of 5αP receptors to the cell membrane was confirmed visually with fluorescently labeled conjugate (5αP-BSA-FITC). Treatment of cells with either 5αP or membrane-impermeable 5αP-BSA resulted in significant increases in cell proliferation and detachment. 5αP and 5αP-BSA equally activated the MAPK/ERK1/2 pathway as evidenced by phosphorylation of ERK1/2. Inhibitors (PD98059, mevastatin and genistein) of specific sites along the Ras/Raf/MEK/ERK signaling pathway, blocked the phosphorylation and concomitantly inhibited 5αP-induced stimulation of cell proliferation and detachment. The study has identified high affinity, stereo-specific binding sites for 5αP that have the characteristics of a functional membrane 5αP receptor, and has shown that the cancer-promoter actions of 5αP are mediated from the liganded receptor via the MAPK/ERK1/2 signaling cascade. The findings enhance our understanding of the role of the progesterone metabolite 5αP in breast cancer and should promote new approaches to the development of breast cancer diagnostics and therapeutics.

Progesterone-induced stimulation of mammary tumorigenesis is due to the progesterone metabolite, 5α-dihydroprogesterone (5αP) and can be suppressed by the 5α-reductase inhibitor, finasteride

Progesterone has long been linked to breast cancer but its actual role as a cancer promoter has remained in dispute. Previous in vitro studies have shown that progesterone is converted to 5α-dihydroprogesterone (5αP) in breast tissue and human breast cell lines by the action of 5α-reductase, and that 5αP acts as a cancer-promoter hormone. Also studies with human breast cell lines in which the conversion of progesterone to 5αP is blocked by a 5α-reductase inhibitor, have shown that the in vitro stimulation in cell proliferation with progesterone treatments are not due to progesterone itself but to the metabolite 5αP. No similar in vivo study has been previously reported. The objective of the current studies was to determine in an in vivo mouse model if the presumptive progesterone-induced mammary tumorigenesis is due to the progesterone metabolite, 5αP. BALB/c mice were challenged with C4HD murine mammary cells, which have been shown to form tumors when treated with progesterone or the progestin, medroxyprogesterone acetate. Cells and mice were treated with various doses and combinations of progesterone, 5αP and/or the 5α-reductase inhibitor, finasteride, and the effects on cell proliferation and induction and growth of tumors were monitored. Hormone levels in serum and tumors were measured by specific RIA and ELISA tests. Proliferation of C4HD cells and induction and growth of tumors was stimulated by treatment with either progesterone or 5αP. The progesterone-induced stimulation was blocked by finasteride and reinstated by concomitant treatment with 5αP. The 5αP-induced tumors expressed high levels of ER, PR and ErbB-2. Hormone measurements showed significantly higher levels of 5αP in serum from mice with tumors than from mice without tumors, regardless of treatments, and 5αP levels were significantly higher (about 4-fold) in tumors than in respective sera, while progesterone levels did not differ between the compartments. The results indicate that the stimulation of C4HD tumor growth in BALB/c mice treated with progesterone is due to the progesterone metabolite 5αP formed at elevated levels in mammary cells as a result of the 5α-reductase action on progesterone. The results provide the first in vivo demonstration that stimulation of breast cell tumorigenesis and tumor growth accompanying progesterone treatment is due to the progesterone metabolite 5αP, and that breast tumorigenesis can be blocked with the 5α-reductase inhibitor, finasteride.

Nifuroxazide induces apoptosis and impairs pulmonary metastasis in breast cancer model

Breast carcinoma is the most common female cancer with considerable metastatic potential. Signal transducers and activators of the transcription 3 (Stat3) signaling pathway is constitutively activated in many cancers including breast cancer and has been validated as a novel potential anticancer target. Here, we reported our finding with nifuroxazide, an antidiarrheal agent identified as a potent inhibitor of Stat3. The potency of nifuroxazide on breast cancer was assessed in vitro and in vivo. In this investigation, we found that nifuroxazide decreased the viability of three breast cancer cell lines and induced apoptosis of cancer cells in a dose-dependent manner. In addition, western blot analysis demonstrated that the occurrence of its apoptosis was associated with activation of cleaved caspases-3 and Bax, downregulation of Bcl-2. Moreover, nifuroxazide markedly blocked cancer cell migration and invasion, and the reduction of phosphorylated-Stat3^Tyr705, matrix metalloproteinase (MMP) MMP-2 and MMP-9 expression were also observed. Furthermore, in our animal experiments, intraperitoneal administration of 50 mg/kg/day nifuroxazide suppressed 4T1 tumor growth and blocked formation of pulmonary metastases without detectable toxicity. Meanwhile, histological and immunohistochemical analyses revealed a decrease in Ki-67-positive cells, MMP-9-positive cells and an increase in cleaved caspase-3-positive cells upon nifuroxazide. Notably, nifuroxazide reduced the number of myeloid-derived suppressor cell in the lung. Our data indicated that nifuroxazide may potentially be a therapeutic agent for growth and metastasis of breast cancer.

Important roles of the AKR1C2 and SRD5A1 enzymes in progesterone metabolism in endometrial cancer model cell lines

Endometrial cancer is the most frequently diagnosed gynecological malignancy. It is associated with prolonged exposure to estrogens that is unopposed by progesterone, whereby enhanced metabolism of progesterone may decrease its protective effects, as it can deprive progesterone receptors of their active ligand. Furthermore, the 5α-pregnane metabolites formed can stimulate proliferation and may thus contribute to carcinogenesis. The aims of our study were to: (1) identify and quantify progesterone metabolites formed in the HEC-1A and Ishikawa model cell lines of endometrial cancer; and (2) pinpoint the enzymes involved in progesterone metabolism, and delineate their roles. Progesterone metabolism studies combined with liquid chromatography-tandem mass spectrometry enabled identification and quantification of the metabolites formed in these cells. Further quantitative PCR analysis and small-interfering-RNA-mediated gene silencing identified individual progesterone metabolizing enzymes and their relevant roles. In Ishikawa and HEC-1A cells, progesterone was metabolized mainly to 20α-hydroxy-pregn-4-ene-3-one, 20α-hydroxy-5α-pregnane-3-one, and 5α-pregnane-3α/β,20α-diol. The major difference between these cell lines was rate of progesterone metabolism, which was faster in HEC-1A cells. In the Ishikawa and HEC-1A cells, expression of AKR1C2 was 110-fold and 6800-fold greater, respectively, than expression of AKR1C1, which suggests that 20-ketosteroid reduction of 5α-pregnanes and 4-pregnenes is catalyzed mainly by AKR1C2. AKR1C1/AKR1C2 gene silencing showed decreased progesterone metabolism in both cell lines, thus further supporting the significant role of AKR1C2. SRD5A1 was also expressed in these cells, and its silencing confirmed that 5α-reduction is catalyzed by 5α-reductase type 1. Silencing of SRD5A1 also had the most pronounced effects, with decreased rate of progesterone metabolism, and consequently higher concentrations of unmetabolized progesterone. Our data confirm that in model cell lines of endometrial cancer, AKR1C2 and SRD5A1 have crucial roles in progesterone metabolism, and may represent novel targets for treatment.

Performance enhancement in the measurement of 5 endogenous steroids by LC-MS/MS combined with differential ion mobility spectrometry

BACKGROUND

Challenges for steroid analysis by LC-MS/MS include low ionization efficiency, endogenous isobars with similar fragmentation patterns and chromatographic retention. Differential ion mobility spectrometry (DMS) provides an additional degree of separation prior to MS/MS detection, and shows promise in improving specificity of analysis. We developed a sensitive and specific method for measurement of corticosterone, 11-deoxycortisol, 11-deoxycorticosterone, 17-hydroxyprogesterone and progesterone in human serum and plasma using an ABSciex 5500 mass spectrometer equipped with a differential ion mobility interface.

METHODS

250μL aliquots of serum were spiked with deuterated internal standards and extracted with MTBE. The samples were analyzed using positive mode electrospray LC-DMS-MS/MS. The method was validated and compared with immunoassays and LC-MS/MS methods of reference laboratories.

RESULTS

Inter and intra assay imprecision was <10%. Limits of quantification and detection in nmol/L were 0.18, 0.09 for corticosterone and 17-hydroxyprogesterone, 0.30, 0.16 for 11-deoxycortisol, 0.12, 0.06 for progesterone and 0.06, 0.03 for 11-deoxycorticosterone. Comparison for progesterone and 17-hydroxyprogesterone with immunoassay showed slopes of 0.97 and 1.0, intercepts of 0.16 and 0.10 and coefficients of determination (r(2)) of 0.92 and 0.97, respectively. Progesterone by immunoassay showed positive bias in samples measuring <3.18nmol/L. Reference intervals for progesterone and 11-deoxycorticosterone in post-menopausal women were found to be <2.88 and <0.28nmol/L respectively.

CONCLUSIONS

We developed and validated an LC-DMS-MS/MS method for analysis of five endogenous steroids suitable for routine measurements in clinical diagnostic laboratories. Specificity gained with DMS allows reducing the complexity of sample preparation, decreasing LC run times and increasing speed of the analysis.

Recent advances in structure of progestins and their binding to progesterone receptors

The role of progesterone in women's cancers as well as the knowledge of the progesterone receptor (PR) structure has prompted the design of different therapies. The aim of this review is to describe the basic structure of PR agonists and antagonists as well as the recent treatments for illness associated with the progesterone receptor. The rational design for potent and effective drugs for the treatment of female cancer must consider the structural changes of the androgen and progestogen skeleton which are an indicator of their activity as progestins or antiprogestins. The presence of a hydroxyl group at C-17 in the progesterone skeleton brings about a loss of progestational activity whereas acetylation induces a progestational effect. The incorporation of an ethynyl functional group to the testosterone framework results in a loss of androgenic activity with a concomitant enhancement of the progestational effect. On the other hand, an ester function at C-3 of dehydroepiandrosterone skeleton induces partial antagonism to the PR.

Pregnancy without progesterone in horses defines a second endogenous biopotent progesterone receptor agonist, 5α-dihydroprogesterone

One of the most widely accepted axioms of mammalian reproductive biology is that pregnancy requires the (sole) support of progesterone, acting in large measure through nuclear progesterone receptors (PRs) in uterine and cervical tissues, without which pregnancy cannot be established or maintained. However, mares lack detectable progesterone in the latter half of pregnancy. Instead of progesterone, several (mainly 5α-reduced) pregnanes are elevated and have long been speculated to provide progestational support in lieu of progesterone itself. To the authors' knowledge, evidence for the bioactivity of a second potent endogenously synthesized pregnane able to support pregnancy in the absence of progesterone has never before been reported. The 5α-reduced progesterone metabolite dihydroprogesterone (DHP) was shown in vivo to stimulate endometrial growth and progesterone-dependent gene expression in the horse at subphysiological concentrations and to maintain equine pregnancy in the absence of luteal progesterone in the third and fourth weeks postbreeding. Results of in vitro studies indicate that DHP is an equally potent and efficacious endogenous progestin in the horse but that the PR evolved with increased agonistic potency for DHP at the expense of potency toward progesterone based on comparisons with human PR responses. Sequence analysis and available literature indicate that the enzyme responsible for DHP synthesis, 5α-reductase type 1, also adapted primarily to metabolize progesterone and thereby to serve diverse roles in the physiology of pregnancy in mammals. Our confirmation that endogenously synthesized DHP is a biopotent progestin in the horse ends decades of speculation, explaining how equine pregnancies survive without measurable circulating progesterone in the last 4 to 5 mo of gestation.

The anthelmintic drug niclosamide induces apoptosis, impairs metastasis and reduces immunosuppressive cells in breast cancer model

Breast carcinoma is the most common female cancer with considerable metastatic potential. Discovery of new therapeutic approaches for treatment of metastatic breast cancer is still needed. Here, we reported our finding with niclosamide, an FDA approved anthelmintic drug. The potency of niclosamide on breast cancer was assessed in vitro and in vivo. In this investigation, we found that niclosamide showed a dramatic growth inhibition against breast cancer cell lines and induced apoptosis of 4T1 cells in a dose-dependent manner. Further, Western blot analysis demonstrated the occurrence of its apoptosis was associated with activation of Cleaved caspases-3, down-regulation of Bcl-2, Mcl-1 and Survivin. Moreover, niclosamide blocked breast cancer cells migration and invasion, and the reduction of phosphorylated STAT3(Tyr705), phosphorylated FAK(Tyr925) and phosphorylated Src(Tyr416) were also observed. Furthermore, in our animal experiments, intraperitoneal administration of 20 mg/kg/d niclosamide suppressed 4T1 tumor growth without detectable toxicity. Histological and immunohistochemical analyses revealed a decrease in Ki67-positive cells, VEGF-positive cells and microvessel density (MVD) and an increase in Cleaved caspase-3-positive cells upon niclosamide. Notably, niclosamide reduced the number of myeloid-derived suppressor cells (MDSCs) in tumor tissues and blocked formation of pulmonary metastases. Taken together, these results demonstrated that niclosamide may be a promising candidate for breast cancer.