Progesterone receptor isoform ratio dictates antiprogestin/progestin effects on breast cancer growth and metastases: A role for NDRG1.

Progesterone receptors (PRs) ligands are being tested in luminal breast cancer. There are mainly two PR isoforms, PRA and PRB, and their ratio (PRA/PRB) may be predictive of antiprogestin response. Our aim was to investigate: the impact of the PR isoform ratio on metastatic behaviour, the PR isoform ratio in paired primary tumours and lymph node metastases (LNM) and, the effect of antiprogestin/progestins on metastatic growth. Using murine and human metastatic models, we demonstrated that tumours with PRB > PRA (PRB-H) have a higher proliferation index but less metastatic ability than those with PRA > PRB (PRA-H). Antiprogestins and progestins inhibited metastatic burden in PRA-H and PRB-H models, respectively. In breast cancer samples, LNM retained the same PRA/PRB ratio as their matched primary tumours. Moreover, PRA-H LNM expressed higher total PR levels than the primary tumours. The expression of NDRG1, a metastasis suppressor protein, was higher in PRB-H compared to PRA-H tumours and was inversely regulated by antiprogestins/progestins. The binding of the corepressor SMRT at the progesterone responsive elements of the NDRG1 regulatory sequences, together with PRA, impeded its expression in PRA-H cells. Antiprogestins modulate the interplay between SMRT and AIB1 recruitment in PRA-H or PRB-H contexts regulating NDRG1 expression and thus, metastasis. In conclusion, we provide a mechanistic interpretation to explain the differential role of PR isoforms in metastatic growth and highlight the therapeutic benefit of using antiprogestins in PRA-H tumours. The therapeutic effect of progestins in PRB-H tumours is suggested.

Progestin and antiprogestin responsiveness in breast cancer is driven by the PRA/PRB ratio via AIB1 or SMRT recruitment to the CCND1 and MYC promoters.

There is emerging interest in understanding the role of progesterone receptors (PRs) in breast cancer. The aim of this study was to investigate the proliferative effect of progestins and antiprogestins depending on the relative expression of the A (PRA) and B (PRB) isoforms of PR. In mifepristone (MFP)-resistant murine carcinomas antiprogestin responsiveness was restored by re-expressing PRA using demethylating agents and histone deacetylase inhibitors. Consistently, in two human breast cancer xenograft models, one manipulated to overexpress PRA or PRB (IBH-6 cells), and the other expressing only PRA (T47D-YA) or PRB (T47D-YB), MFP selectively inhibited the growth of PRA-overexpressing tumors and stimulated IBH-6-PRB xenograft growth. Furthermore, in cells with high or equimolar PRA/PRB ratios, which are stimulated to proliferate in vitro by progestins, and are inhibited by MFP, MPA increased the interaction between PR and the coactivator AIB1, and MFP favored the interaction between PR and the corepressor SMRT. In a PRB-dominant context in which MFP stimulates and MPA inhibits cell proliferation, the opposite interactions were observed. Chromatin immunoprecipitation assays in T47D cells in the presence of MPA or MFP confirmed the interactions between PR and the coregulators at the CCND1 and MYC promoters. SMRT downregulation by siRNA abolished the inhibitory effect of MFP on MYC expression and cell proliferation. Our results indicate that antiprogestins are therapeutic tools that selectively inhibit PRA-overexpressing tumors by increasing the SMRT/AIB1 balance at the CCND1 and MYC promoters.

[The role of estrogen receptor alpha in breast cancer cell proliferation mediated by progestins]. / El receptor de estrógenos alfa como mediador del efecto proliferativo de progestágenos en cáncer de mama.

In C4-HD murine mammary carcinomas and in human breast cancer T47D cells, we showed that medroxyprogesterone acetate (MPA) induces a nuclear physical association between estrogen receptor alpha (ERa) and progesterone receptors (PR). The blockade of ERa inhibits cell proliferation mediated by progestins. We hypothesized that this nuclear association between ERa/PR is necessary to trigger progestin-induced cell proliferation and tumor growth. We demonstrated that fulvestrant (FUL, ICI182.780) induced complete regression of C4-HD tumors growing with progestins. MPA treatment induced an early increase in both CCND1 and MYC expression in T47D cells. The blockade of ERa prevented the MPA-dependent transcription of both genes. Specific binding of PR/ERa was observed at the same MPA-sensitive regions at the CCND1 and MYC gene promoters after chromatin immunoprecipitation (ChIP) analysis. ICI inhibited binding of ERa to both gene regulatory sequences while PR binding was unaffected. The nuclear colocalization between both receptors in T47D cells was confirmed by: confocal microscopy, Duolink assays and co-immunoprecipitation assays. In breast cancer samples we also observed a nuclear interaction between both steroid receptors. Our results indicate that the presence of ERa interacting with activated PR at the CCND1 and MYC promoters is required to trigger progestin-induced gene transcription and cell proliferation in breast cancer cells.

Hypermethylation of the progesterone receptor A in constitutive antiprogestin-resistant mouse mammary carcinomas.

Most breast carcinomas that are estrogen receptor (ER) and progesterone receptor (PR) positive respond initially to an endocrine therapy, but over time, they develop resistance (acquired hormone resistance). Others, however, fail to respond from the beginning (constitutive resistance). Overcoming hormone resistance is one of the major desirable aims in breast cancer treatment. Using the medroxyprogesterone acetate (MPA)-induced breast cancer mouse model, we have previously demonstrated that antiprogestin-responsive tumors show a higher expression level of PR isoform A (PRA) than PR isoform B (PRB), while tumors with constitutive or acquired resistance show a higher expression level of PRB. The aim of this study was to investigate whether PRA silencing in resistant tumors was due to PRA methylation. The CpG islands located in the PRA promoter and the first exon were studied by methylation-specific PCR (MSP) in six different tumors: two antiprogestin-responsive, two constitutive-resistant, and two with acquired resistance. Only in constitutive-resistant tumors, PRA expression was silenced by DNA methylation. Next, we evaluated the effect of a demethylating agent, 5-aza-2'-deoxycytidine, on PRA expression and antiprogestin responsiveness. In constitutive-resistant tumors, 5-aza-2'-deoxycytidine treatment in vitro and in vivo restored PRA expression and antiprogestin RU-486 responsiveness. Furthermore, high levels of DNA methyltransferase (Dnmts) 1 and 3b were detected in these tumors. In conclusion, our results suggest that methyltransferase inhibitors in combination with antiprogestins may be effective in the treatment of constitutive-resistant carcinomas with a high DNA methyltransferase level.

Inhibition of mammary tumor growth by estrogens: is there a specific role for estrogen receptors alpha and beta?

To evaluate the extent to which each estrogen receptor (ER) subtype contributes to the stimulation or to the inhibition of mammary tumor growth, we evaluated the effects of specific agonists in MC4-L2 cells, which are stimulated by 17ß-estradiol (E(2)), and in mammary carcinomas of the MPA mouse breast cancer model, which are inhibited by E(2). Both express ERα and ERß. In MC4-L2 cells, 4,4',4"-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT; ERα agonist) and (4-hydroxy-phenyl)-propionitrile (DPN; ERß agonist) stimulated cell proliferation, whereas the opposite occurred in C4-HI primary cultures. The inhibitory effect was associated with a decrease in ERα and cyclin D1 expression and an increase in progesterone receptor (PR) expression as well as in the Bax/Bcl-xl ratio. In vivo, mice carrying C4-HI or 32-2-HI tumors were treated with E(2), PPT or DPN (3 mg/kg/day) or with vehicle. PPT and DPN inhibited tumor size, as did E(2), during the first 72 h. After a few days, DPN-treated tumors started to grow again, while PPT-treated tumors remained quiescent for a longer period of time. A pronounced decrease in the mitotic index and an increase in the apoptotic index was associated with tumor regression. All treated tumors showed: (a) an increase in integrin α6 and Bax expression, (b) an increased stromal laminin redistribution, and (c) a decrease in ERα, Bcl-xl and Bcl-2 expression (P < 0.001). Apoptosis-inducing factor (Aif) expression was increased in DPN-treated tumors, while active caspase 9 was up-regulated in PPT-treated mice, demonstrating the involvement of the intrinsic apoptotic pathway in estrogen-induced regression in this model. In conclusion, our data indicate that although there may be some preferences for activation pathways by the different agonists, the stimulatory or inhibitory effects triggered by estrogens are cell-context dependent rather than ER isoform dependent.

Mifepristone inhibits MPA-and FGF2-induced mammary tumor growth but not FGF2-induced mammary hyperplasia.

We have previously demonstrated a crosstalk between fibroblast growth factor 2 (FGF2) and progestins inducing experimental breast cancer growth. The aim of the present study was to compare the effects of FGF2 and of medroxyprogesterone acetate (MPA) on the mouse mammary glands and to investigate whether the antiprogestin RU486 was able to reverse the MPA- or FGF2-induced effects on both, mammary gland and tumor growth. We demonstrate that FGF2 administered locally induced an intraductal hyperplasia that was not reverted by RU486, suggesting that FGF2-induced effects are progesterone receptor (PR)-independent. However, MPA-induced paraductal hyperplasia was reverted by RU486 and a partial agonistic effect was observed in RU486-treated glands. Using C4-HD tumors which only grow in the presence of MPA, we showed that FGF2 administered intratumorally was able to stimulate tumor growth as MPA. The histology of FGF2-treated tumors showed different degrees of gland differentiation. RU486 inhibited both, MPA or FGF2 induced tumor growth. However, only complete regression was observed in MPA-treated tumors. Our results support the hypothesis that stromal FGF2 activates PR inducing hormone independent tumor growth.

The MPA mouse breast cancer model: evidence for a role of progesterone receptors in breast cancer.

More than 60% of all breast neoplasias are ductal carcinomas expressing estrogen (ER) and progesterone receptors (PR). By contrast, most of the spontaneous, chemically or mouse mammary tumor virus induced tumors, as well as tumors arising in genetically modified mice do not express hormone receptors. We developed a model of breast cancer in which the administration of medroxyprogesterone acetate to BALB/c female mice induces mammary ductal carcinomas with a mean latency of 52 weeks and an incidence of about 80%. These tumors are hormone-dependent (HD), metastatic, express both ER and PR, and are maintained by syngeneic transplants. The model has been further refined to include mammary carcinomas that evolve through different stages of hormone dependence, as well as several hormone-responsive cell lines. In this review, we describe the main features of this tumor model, highlighting the role of PR as a trigger of key signaling pathways mediating tumor growth. In addition, we discuss the relevance of this model in comparison with other presently used breast cancer models pointing out its advantages and limitations and how, this model may be suitable to unravel key questions in breast cancer.

Reversal of antiprogestin resistance and progesterone receptor isoform ratio in acquired resistant mammary carcinomas.

To explore mechanisms related to hormone resistance, three resistant variants of the MPA mouse breast cancer tumor model with low levels of progesterone receptor (PR) isoform A (PR-A)/high PR-B expression were developed by prolonged selective pressure with antiprogestins. The resistant phenotype of one tumor line was reversed spontaneously after several consecutive passages in syngeneic BALB/c mice or by 17-beta-estradiol or tamoxifen treatment, and this reversion was significantly associated with an increase in PR-A expression. The responsive parental tumors disclosed low activation of ERK and high activation of AKT; resistant tumors on the other hand, showed the opposite, and this was associated with a higher metastatic potential, that did not revert. This study shows for the first time in vivo a relationship between PR isoform expression and antiprogestin responsiveness, demonstrating that, whereas acquired resistance may be reversed, changes in kinase activation and metastatic potential are unidirectional associated with tumor progression.

Expression and methylation status of female-predominant GH-dependent liver genes are modified by neonatal androgenization in female mice.

Neonatal androgenization masculinizes the GH axis and thus may impact on liver gene regulation. Neonatal testosterone administration to female mice decreased (defeminized) female predominant GH-dependent liver gene expression (Hnf6, Adh1, Prlr, Cyp3a41) and did not modify male predominant genes (Cyp7b1, Cyp4a12, Slp). Female predominance of Cis mRNA, an inhibitor of episodic GH signaling pathway, was unaltered. At birth, Cyp7b1 promoter exhibited a higher methylation status in female livers, while the Hnf6 promoter was equally methylated in both sexes; no differences in gene expression were detected at this age. In adulthood, consistent with sex specific predominance, lower methylation status was determined for the Cyp7b1 promoter in males, and for the Hnf6 promoter in females, and this last difference was prevented by neonatal androgenization. Therefore, early steroid treatment or eventually endocrine disruptor exposure may alter methylation status and sexual dimorphic expression of liver genes, and consequently modify liver physiology in females.

Multidrug resistance protein 4/ ATP binding cassette transporter 4: a new potential therapeutic target for acute myeloid leukemia.

Less than a third of adults patients with acute myeloid leukemia (AML) are cured by current treatments, emphasizing the need for new approaches to therapy. We previously demonstrated that besides playing a role in drug-resistant leukemia cell lines, multidrug resistance protein 4 (MRP4/ABCC4) regulates leukemia cell proliferation and differentiation through the endogenous MRP4/ABCC4 substrate, cAMP. Here, we studied the role of MRP4/ABCC4 in tumor progression in a mouse xenograft model and in leukemic stem cells (LSCs) differentiation. We found a decrease in the mitotic index and an increase in the apoptotic index associated with the inhibition of tumor growth when mice were treated with rolipram (PDE4 inhibitor) and/or probenecid (MRPs inhibitor). Genetic silencing and pharmacologic inhibition of MRP4 reduced tumor growth. Furthermore, MRP4 knockdown induced cell cycle arrest and apoptosis in vivo. Interestingly, when LSC population was isolated, we observed that increased cAMP levels and MRP4/ABCC4 blockade resulted in LSCs differentiation. Taken together, our findings show that MRP4/ABCC4 has a relevant role in tumor growth and apoptosis and in the eradication of LSCs, providing the basis for a novel promising target in AML therapy.

Novel, low cost, highly effective, handmade steroid pellets for experimental studies.

The basic component of Silastic® glue (Dow Corning) used to prepare Silastic® pellets is polydimethylsiloxane. This compound is also present in other commercial adhesives such as FASTIX® (Akapol SA) that are available in any store for that category. In the present study we developed low cost, easy to prepare handmade steroid pellets (HMSP) by mixing 17ß-estradiol, progesterone or other synthetic steroids with FASTIX® adhesive. We assessed serum levels of 17ß-estradiol, progesterone, prolactin and luteinizing hormone in ovariectomized mice treated for 24 and 48 h or 7, 14 and 28 days with 20 µg or 5 mg of 17ß-estradiol or 5 mg progesterone HMSP. We found a time dependent and significant increase in the levels of both natural hormones, and a downregulation of serum luteinizing hormone levels, while both 17ß-estradiol doses increased serum prolactin. Uterine weights at sacrifice and histological examination of the uteri and the mammary glands correlated with estrogen or progestin action. Finally, we evaluated the biological effects of HMSP compared to commercial pellets or daily injections in the stimulation or inhibition of hormone dependent mammary tumor growth, and found that HMSP were as effective as the other methods of hormone administration. These data show that HMSP represent a useful, low cost, easily accessible method for administering steroids to mice.

Antiprogestins in breast cancer treatment: are we ready?

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in females worldwide. It is accepted that breast cancer is not a single disease, but instead constitutes a spectrum of tumor subtypes with distinct cellular origins, somatic changes, and etiologies. Molecular gene expression studies have divided breast cancer into several categories, i.e. basal-like, ErbB2 enriched, normal breast-like (adipose tissue gene signature), luminal subtype A, luminal subtype B, and claudin-low. Chances are that as our knowledge increases, each of these types will also be subclassified. More than 66% of breast carcinomas express estrogen receptor alpha (ERα) and respond to antiestrogen therapies. Most of these ER+ tumors also express progesterone receptors (PRs), the expression of which has been considered as a reliable marker of a functional ER. In this paper we will review the evidence suggesting that PRs are valid targets for breast cancer therapy. Experimental data suggest that both PR isoforms (A and B) have different roles in breast cancer cell growth, and antiprogestins have already been clinically used in patients who have failed to other therapies. We hypothesize that antiprogestin therapy may be suitable for patients with high levels of PR-A. This paper will go over the experimental evidence of our laboratory and others supporting the use of antiprogestins in selected breast cancer patients.

Estrogen receptor alpha mediates progestin-induced mammary tumor growth by interacting with progesterone receptors at the cyclin D1/MYC promoters.

Synthetic progesterone used in contraception drugs (progestins) can promote breast cancer growth, but the mechanisms involved are unknown. Moreover, it remains unclear whether cytoplasmic interactions between the progesterone receptor (PR) and estrogen receptor alpha (ERα) are required for PR activation. In this study, we used a murine progestin-dependent tumor to investigate the role of ERα in progestin-induced tumor cell proliferation. We found that treatment with the progestin medroxyprogesterone acetate (MPA) induced the expression and activation of ERα, as well as rapid nuclear colocalization of activated ERα with PR. Treatment with the pure antiestrogen fulvestrant to block ERα disrupted the interaction of ERα and PR in vitro and induced the regression of MPA-dependent tumor growth in vivo. ERα blockade also prevented an MPA-induced increase in CYCLIN D1 (CCND1) and MYC expression. Chromatin immunoprecipitation studies showed that MPA triggered binding of ERα and PR to the CCND1 and MYC promoters. Interestingly, blockade or RNAi-mediated silencing of ERα inhibited ERα, but not PR binding to both regulatory sequences, indicating that an interaction between ERα and PR at these sites is necessary for MPA-induced gene expression and cell proliferation. We confirmed that nuclear colocalization of both receptors also occurred in human breast cancer samples. Together, our findings argued that ERα-PR association on target gene promoters is essential for progestin-induced cell proliferation.

Responsiveness to PI3K and MEK inhibitors in breast cancer. Use of a 3D culture system to study pathways related to hormone independence in mice.

BACKGROUND: A significant proportion of breast cancer patients face failure of endocrine therapy due to the acquisition of endocrine resistance. We have explored mechanisms involved in such disease progression by using a mouse breast cancer model that is induced by medroxyprogesterone acetate (MPA). These tumors transit through different stages of hormone sensitivity. However, when cells from tumor variants were seeded on plastic, all were stimulated by progestins and inhibited by antiprogestins such as RU486. Furthermore, cells from a RU486-resistant tumor variant recovered antiprogestin sensitivity. HYPOTHESIS: A three-dimensional (3D) culture system, by maintaining differential cellular organization that is typical of each tumor variant, may allow for the maintenance of particular hormone responses and thus be appropriate for the study of the effects of specific inhibitors of signaling pathways associated with disease progression. METHOD: We compared the behavior of tumors growing in vivo and cancer cells ex vivo (in 3D Matrigel). In this system, we evaluated the effects of kinase inhibitors and hormone antagonists on tumor growth. PRINCIPAL FINDINGS: LY294002, a PI3K/AKT pathway inhibitor, decreased both tumor growth in vivo and cell survival in Matrigel in MPA-independent tumors with higher AKT activity. Induction of cell death by anti-hormones such as ICI182780 and ZK230211 was more effective in MPA-dependent tumors with lower AKT activity. Inhibition of MEK with PD98059 did not affect tumor growth in any tested variant. Finally, while Matrigel reproduced differential responsiveness of MPA-dependent and -independent breast cancer cells, it was not sufficient to preserve antiprogestin resistance of RU486-resistant tumors. CONCLUSION: We demonstrated that the PI3K/AKT pathway is relevant for MPA-independent tumor growth. Three-dimensional cultures were useful to test the effects of kinase inhibitors on breast cancer growth and highlight the need for in vivo models to validate experimental tools used for selective therapeutic targeting.

Inmunohistoquímica y expresión de receptores de estrógenos y progesterona en neoplasias mamarias malignas caninas en distintos estadios clínicos / Immunohistochemistry and expression of estrogen and progesterone receptors in canine malignant mammary tumors in different clinical stages

La técnica de inmunohistoquímica descrita por Walker y col. (1998) y Mote y col. (2001) es de utilidad para la determinación de receptores de estrógenos y de progesterona en tumores mamarios de la hembra canina. Existe bastante controversia respecto al porcentaje de receptores de estrógenos y de progesterona, con valor pronóstico o predictivo en tumores malignos caninos debido, muy probablemente, a la falta de uniformidad en criterios de inclusión de los casos en los estudios realizados. El presente trabajo se realizó en una población de 51 perras. Los tumores fueron escindidos quirúrgicamente mediante mastectomía de las glándulas afectadas. Para la determinación de receptores hormonales, se analizó la muestra con mayores características histológicas de malignidad de cada animal. Se contabilizó el porcentaje de células tumorales positivas para cada uno de los receptores (receptor de estrógeno alfa, receptor de estrógeno beta y receptores de progesterona) en los distintos estadios clínicos (I, II, II, IV). Se consideró positivo todo corte ³ 20% de células tumorales positivas para cada uno de los receptores. Se realizó una estadística descriptiva (media y error estándar) con los animales positivos para cada uno de los receptores en los distintos estadios clínicos. En línea con reportes de otros autores, más de la mitad de caninos portadores de tumores mamarios malignos expresaron receptores de estrógenos y de progesterona. Conociendo que el comportamiento biológico de una neoplasia varía con el estadio clínico del paciente, resulta interesante estudiar la expresión de los receptores en cada uno de éstos, en animales con neoplasias mamarias malignas. Adicionalmente, a este objetivo incluye la puesta a punto la de técnica de inmunohistoquímica para la determinación de receptores hormonales en la especie.

receptors in canine mammary tumors. There is considerable controversy regarding the percentage of estrogen and progesterone receptors that having prognostic or predictive value in malignant tumors in dogs because, most likely, the lack of uniform criteria for inclusion of cases. This study was conducted in a population of 51 female dogs. The tumors were surgically treated by mastectomy of the affected glands. For the determination of hormone receptors, the sample analyzed was showed higher histological malignancy features of each animal. It was counted the percentage of tumor cells positive for each of the receptors (estrogen receptor alpha, estrogen receptor beta and progesterone receptor) in animals in various clinical stages (I, II, III, IV). It was considered positive cut-off ³ 20% tumor cells positive for each of the recipients. It was conducted a descriptive statistics (mean and standard error) which positive animals for each of the receptors in different clinical stages. In line with reports of other authors, more than half of canine carriers of malignant mammary tumors expressed estrogen and progesterone receptors. Knowing that the biological behavior of cancer varies with the clinical stage of the animal, objective was to study the expression of receptors in each of the clinical stages in animals with malignant mammary tumors. Additionally, this includes the preparation of the immunohistochemical technique for the determination of hormone receptors in this species.