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.

Identification of MRP4/ABCC4 as a Target for Reducing the Proliferation of Pancreatic Ductal Adenocarcinoma Cells by Modulating the cAMP Efflux.

Pancreatic cancer is one of the most lethal types of tumors with no effective therapy available; is currently the third leading cause of cancer in developed countries; and is predicted to become the second deadliest cancer in the United States by 2030. Due to the marginal benefits of current standard chemotherapy, the identification of new therapeutic targets is greatly required. Considering that cAMP pathway is commonly activated in pancreatic ductal adenocarcinoma (PDAC) and its premalignant lesions, we aim to investigate the multidrug resistance-associated protein 4 (MRP4)-dependent cAMP extrusion process as a cause of increased cell proliferation in human PDAC cell lines. Our results from in silico analysis indicate that MRP4 expression may influence PDAC patient outcome; thus, high MRP4 levels could be indicators of poor survival. In addition, we performed in vitro experiments and identified an association between higher MRP4 expression levels and more undifferentiated and malignant models of PDAC and cAMP extrusion capacity. We studied the antiproliferative effect and the overall cAMP response of three MRP4 inhibitors, probenecid, MK571, and ceefourin-1 in PDAC in vitro models. Moreover, MRP4-specific silencing in PANC-1 cells reduced cell proliferation (P < 0.05), whereas MRP4 overexpression in BxPC-3 cells significantly incremented their growth rate in culture (P < 0.05). MRP4 pharmacological inhibition or silencing abrogated cell proliferation through the activation of the cAMP/Epac/Rap1 signaling pathway. Also, extracellular cAMP reverted the antiproliferative effect of MRP4 blockade. Our data highlight the MRP4-dependent cAMP extrusion process as a key participant in cell proliferation, indicating that MRP4 could be an exploitable therapeutic target for PDAC. SIGNIFICANCE STATEMENT: ABCC4/MRP4 is the main transporter responsible for cAMP efflux. In this work, we show that MRP4 expression may influence PDAC patient outcome and identify an association between higher MRP4 expression levels and more undifferentiated and malignant in vitro models of PDAC. Findings prove the involvement of MRP4 in PDAC cell proliferation through a novel extracellular cAMP mitogenic pathway and further support MRP4 inhibition as a promising therapeutic strategy for PDAC treatment.

FGFR3 Down-Regulation is Involved in bacillus Calmette-Guérin Induced Bladder Tumor Growth Inhibition.

PURPOSE: Bacillus Calmette-Guérin is the standard treatment for patients with nonmuscle invasive high histological grade bladder cancer. Previously we found that bacillus Calmette-Guérin induces murine bladder cancer MB49 cell death in vitro and in vivo, generating tissue remodeling, which involves the release of fibroblast growth factor (FGF)-2. MATERIALS AND METHODS: We studied the effect of bacillus Calmette-Guérin treatment on FGF-2 and FGF receptor (FGFR) expression in bladder cancer. RESULTS: In vitro FGF-2 increased MB49 cell proliferation but did not reverse bacillus Calmette-Guérin induced cell death. Increased FGF-2 expression was detected after bacillus Calmette-Guérin treatment. Moreover MB49 cells expressed high FGFR3 levels, which decreased after treatment. Similar results were observed in human T24 bladder cancer cells. In vivo MB49 tumors expressed higher FGFR3 levels than normal urothelium. Tumor FGFR3 decreased after treatment and correlated with tumor growth inhibition in response to bacillus Calmette-Guérin. In a pilot bioassay using 11 human bladder tumors treated ex vivo with bacillus Calmette-Guérin we found a subgroup of 41% of patients in whom FGFR3 was decreased after treatment. CONCLUSIONS: Based on bladder cancer murine model results we infer that down-regulation of FGFR3 is a predictive marker of a good response to bacillus Calmette-Guérin therapy. The decrease in FGFR3 in response to bacillus Calmette-Guérin occurred not only in a murine model but also in a human bladder cancer cell line and in some patient samples. More patients and increased followup are needed to establish the predictive role of FGFR3 as a marker in human bladder cancer.

Ceefourin-1, a MRP4/ABCC4 inhibitor, induces apoptosis in AML cells enhanced by histamine.

BACKGROUND: Ceefourin-1 is a specific MRP4/ABCC4 inhibitor with potential antileukemic activity. In this study, we evaluate the ability of ceefourin-1 alone or in combination with histamine, an approved antileukemic agent, to induce cell differentiation or apoptosis in human acute myeloid leukemic cells. We also examine ceefourin-1 toxicity in mice. METHODS: U937, HL-60, and KG1a cells were used as models for human acute myeloid leukemia. Cyclic AMP efflux was estimated by measuring intracellular and extracellular cAMP levels. Cell differentiation was assessed by levels of CD14 and CD11b by FACS, and CD88 by western blot, and by cell morphology. Apoptosis was evaluated by cleavage of caspase-3 and PARP by western blot, and by annexin V binding assay. Subacute toxicity study of ceefourin-1 was carried out in BALB/c mice. RESULTS: Ceefourin-1 inhibits cAMP exclusion in AML cells and promotes intracellular signaling via CREB. Ceefourin-1 leads AML cells to apoptosis and histamine potentiates this effect, without evidence of cell differentiation. Intraperitoneal administration of ceefourin-1 shows no important alterations in mice blood parameters, hepatic, and renal functions, nor signs of histologic damage. CONCLUSIONS: These results show that ceefourin-1 promotes apoptosis in AML cells that is enhanced by histamine. GENERAL SIGNIFICANCE: This work indicates that ceefourin-1 represents a promising molecule that could be used alone or in combination with histamine for in vivo evaluation in acute myeloid leukemia malignancies.

Associated expressions of FGFR-2 and FGFR-3: from mouse mammary gland physiology to human breast cancer.

Fibroblast growth factor receptors (FGFRs) are tyrosine kinase receptors which have been implicated in breast cancer. The aim of this study was to evaluate FGFR-1, -2, -3, and -4 protein expressions in normal murine mammary gland development, and in murine and human breast carcinomas. Using immunohistochemistry and Western blot, we report a hormonal regulation of FGFR during postnatal mammary gland development. Progestin treatment of adult virgin mammary glands resulted in changes in localization of FGFR-3 from the cytoplasm to the nucleus, while treatment with 17-ß-estradiol induced changes in the expressions and/or localizations of FGFR-2 and -3. In murine mammary carcinomas showing different degrees of hormone dependence, we found progestin-induced increased expressions, mainly of FGFR-2 and -3. These receptors were constitutively activated in hormone-independent variants. We studied three luminal human breast cancer cell lines growing as xenografts, which particularly expressed FGFR-2 and -3, suggesting a correlation between hormonal status and FGFR expression. Most importantly, in breast cancer samples from 58 patients, we found a strong association (P < 0.01; Spearman correlation) between FGFR-2 and -3 expressions and a weaker correlation of each receptor with estrogen receptor expression. FGFR-4 correlated with c-erbB2 over expression. We conclude that FGFR-2 and -3 may be mechanistically linked and can be potential targets for treatment of estrogen receptor-positive breast cancer patients.

MRP4/ABCC4 expression is regulated by histamine in acute myeloid leukemia cells, determining cAMP efflux.

Intracellular cAMP (i-cAMP) levels play an important role in acute myeloid leukemia (AML) cell proliferation and differentiation. Its levels are the result of cAMP production, degradation, and exclusion. We have previously described histamine H2 receptors and MRP4/ABCC4 as two potential targets for AML therapy. Acting through histamine H2 receptors, histamine increases cAMP production/synthesis, while MRP4/ABCC4 is responsible for the exclusion of this cyclic nucleotide. In this study, we show that histamine treatment induces MRP4/ABCC4 expression, augmenting cAMP efflux, and that histamine, in combination with MRP inhibitors, is able to reduce AML cell proliferation. Histamine, through histamine H2 receptor, increases i-cAMP levels and induces MRP4 transcript and protein levels in U937, KG1a, and HL-60 cells. Moreover, histamine induces MRP4 promoter activity in HEK293T cells transfected with histamine H2 receptor (HEK293T-H2 R). Our results support that the cAMP/Epac-PKA pathway, and not MEK/ERK nor PI3K/AKT signaling cascades, is involved in histamine-mediated upregulation of MRP4 levels. Finally, the addition of histamine potentiates the inhibition of U937, KG1a, and HL-60 cell proliferation induced by MRP4 inhibitors. Our data highlight that the use of a poly-pharmacological approach aimed at different molecular targets would be beneficial in AML treatment.

Enhanced Antitumor Immunity via Endocrine Therapy Prevents Mammary Tumor Relapse and Increases Immune Checkpoint Blockade Sensitivity.

The role of active antitumor immunity in hormone receptor-positive (HR+) breast cancer has been historically underlooked. The aim of this study was to determine the contribution of the immune system to antiprogestin-induced tumor growth inhibition using a hormone-dependent breast cancer model. BALB/c-GFP+ bone marrow (BM) cells were transplanted into immunodeficient NSG mice to generate an immunocompetent NSG/BM-GFP+ (NSG-R) mouse model. Treatment with the antiprogestin mifepristone (MFP) inhibited growth of 59-2-HI tumors with similar kinetics in both animal models. Interestingly, MFP treatment reshaped the tumor microenvironment, enhancing the production of proinflammatory cytokines and chemokines. Tumors in MFP-treated immunocompetent mice showed increased infiltration of F4/80+ macrophages, natural killer, and CD8 T cells, displaying a central memory phenotype. Mechanistically, MFP induced immunogenic cell death (ICD) in vivo and in vitro, as depicted by the expression and subcellular localization of the alarmins calreticulin and HMGB-1 and the induction of an ICD gene program. Moreover, MFP-treated tumor cells efficiently activated immature dendritic cells, evidenced by enhanced expression of MHC-II and CD86, and induced a memory T-cell response, attenuating tumor onset and growth after re-challenge. Finally, MFP treatment increased the sensitivity of HR+ 59-2-HI tumor to PD-L1 blockade, suggesting that antiprogestins may improve immunotherapy response rates. These results contribute to a better understanding of the mechanisms underlying the antitumor effect of hormonal treatment and the rational design of therapeutic combinations based on endocrine and immunomodulatory agents in HR+ breast cancer. SIGNIFICANCE: Antiprogestin therapy induces immunogenic tumor cell death in PRA-overexpressing tumors, eliciting an adaptive immune memory response that protects mice from future tumor recurrence and increases sensitivity to PD-L1 blockade. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/5/1375/F1.large.jpg.

Inoculated mammary carcinoma-associated fibroblasts: contribution to hormone independent tumor growth.

BACKGROUND: Increasing evidence has underscored the role of carcinoma associated fibroblasts (CAF) in tumor growth. However, there are controversial data regarding the persistence of inoculated CAF within the tumors. We have developed a model in which murine metastatic ductal mammary carcinomas expressing estrogen and progesterone receptors transit through different stages of hormone dependency. Hormone dependent (HD) tumors grow only in the presence of progestins, whereas hormone independent (HI) variants grow without hormone supply. We demonstrated previously that CAF from HI tumors (CAF-HI) express high levels of FGF-2 and that FGF-2 induced HD tumor growth in vivo. Our main goal was to investigate whether inoculated CAF-HI combined with purified epithelial (EPI) HD cells can induce HD tumor growth. METHODS: Purified EPI cells of HD and HI tumors were inoculated alone, or together with CAF-HI, into female BALB/c mice and tumor growth was evaluated. In another set of experiments, purified EPI-HI alone or combined with CAF-HI or CAF-HI-GFP were inoculated into BALB/c or BALB/c-GFP mice. We assessed whether inoculated CAF-HI persisted within the tumors by analyzing inoculated or host CAF in frozen sections of tumors growing in BALB/c or BALB/c-GFP mice. The same model was used to evaluate early stages of tumor development and animals were euthanized at 2, 7, 12 and 17 days after EPI-HI or EPI-HI+CAF-HI inoculation. In angiogenesis studies, tumor vessels were quantified 5 days after intradermal inoculation. RESULTS: We found that admixed CAF-HI failed to induce epithelial HD tumor growth, but instead, enhanced HI tumor growth (p < 0.001). Moreover, inoculated CAF-HI did not persist within the tumors. Immunofluorescence studies showed that inoculated CAF-HI disappeared after 13 days. We studied the mechanisms by which CAF-HI increased HI tumor growth, and found a significant increase in angiogenesis (p < 0.05) in the co-injected mice at early time points. CONCLUSIONS: Inoculated CAF-HI do not persist within the tumor mass although they play a role during the first stages of tumor formation promoting angiogenesis. This angiogenic environment is unable to replace the hormone requirement of HD tumors that still need the hormone to recruit the stroma from the host.

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.

MRP4/ABCC4 As a New Therapeutic Target: Meta-Analysis to Determine cAMP Binding Sites as a Tool for Drug Design.

MRP4 transports multiple endogenous and exogenous substances and is critical not only for detoxification but also in the homeostasis of several signaling molecules. Its dysregulation has been reported in numerous pathological disorders, thus MRP4 appears as an attractive therapeutic target. However, the efficacy of MRP4 inhibitors is still controversial. The design of specific pharmacological agents with the ability to selectively modulate the activity of this transporter or modify its affinity to certain substrates represents a challenge in current medicine and chemical biology. The first step in the long process of drug rational design is to identify the therapeutic target and characterize the mechanism by which it affects the given pathology. In order to develop a pharmacological agent with high specific activity, the second step is to systematically study the structure of the target and identify all the possible binding sites. Using available homology models and mutagenesis assays, in this review we recapitulate the up-to-date knowledge about MRP structure and aligned amino acid sequences to identify the candidate MRP4 residues where cyclic nucleotides bind. We have also listed the most relevant MRP inhibitors studied to date, considering drug safety and specificity for MRP4 in particular. This meta-analysis platform may serve as a basis for the future development of inhibitors of MRP4 cAMP specific transport.

Involvement of histamine H1 and H2 receptor inverse agonists in receptor's crossregulation.

Histamine [2-(4-Imidazolyl)-ethylamine] modulates different biological processes, through histamine H1 and H2 receptors, and their respective blockers are widely used in treating allergic and gastric acid-related disorders. Histamine H1 and H2 receptor crossdesensitization and cointernalization induced by its agonists have been previously described. In this study, we show how this crosstalk determines the response to histamine H1 and H2 receptor inverse agonists and how histamine H1 and H2 receptor inverse agonists interfere with the other receptor's response to agonists. By desensitization assays we demonstrate that histamine H1 and H2 receptor inverse agonists induce a crossregulation between both receptors. In this sense, the histamine H1 receptor inverse agonists desensitize the cAMP response to amthamine, a histamine H2 receptor agonist. In turn, histamine H2 receptor inverse agonists interfere with histamine H1 receptor signaling. We also determine that the crossdesensitization induced by histamine H1 or H2 receptor agonists alters the histamine inverse agonists receptor response: activation of histamine H1 receptor affects cAMP response induced by histamine H2 receptor inverse agonists, whereas histamine H2 receptor agonist induces a negative regulation on the anti-inflammatory response of histamine H1 receptor inverse agonists. Binding studies revealed that histamine H1 and H2 receptors cointernalize after stimulus with histamine receptor inverse agonists. In addition, the inhibition of the internalization process prevents receptor crossregulation. Our study provides new insights in the mechanisms of action of histamine H1 and H2 receptors that explain the effect of histamine H1 and H2 receptor inverse agonists and opens up new venues for novel therapeutic applications.

Targeting FGFR with BGJ398 in Breast Cancer: Effect on Tumor Growth and Metastasis.

BACKGROUND: Endocrine resistance and metastatic dissemination comprise major clinical challenges for breast cancer treatment. The fibroblast growth factor receptor family (FGFR) consists of four tyrosine kinase transmembrane receptors, involved in key biological processes. Genomic alterations in FGFR have been identified in advanced breast cancer and thus, FGFR are an attractive therapeutic target. However, the efficacy of FGFR inhibitors on in vivo tumor growth is still controversial. OBJECTIVE: The purpose of this study was to evaluate the role of FGFR in tumor growth and breast cancer progression. METHODS: Cell proliferation was assessed by 3H-thymidine uptake and cell counting in primary cultures of endocrine resistant mammary carcinomas and a human cell line, respectively. Tumor transplants and cell injections were used to determine in vivo growth and spontaneous metastasis. FGFR1-3 and αSMA expression were evaluated on primary tumors by immunohistochemistry. RESULTS: Antiprogestin resistant murine transplants and a human xenograft express high levels of total FGFR1-3. In vitro treatment with the FGFR inhibitor, BGJ398, impaired cell proliferation of resistant variants versus vehicle. In vivo, versus control, BGJ398 treatment decreased one out of four resistant tumors, however all tumors showed a decreased epithelial/stromal ratio. Finally, in a model of hormone resistant mammary cancer that spontaneously metastasizes to the lung, BGJ398 decreased the number of mice with lung metastasis. CONCLUSION: FGFR inhibitors are promising tools that require further investigation to identify sensitive tumors. These studies suggest that targeting FGFR combined with other targeted therapies will be useful to impair breast cancer progression.

Increased High Molecular Weight FGF2 in Endocrine-Resistant Breast Cancer.

Endocrine resistance may develop as a consequence of enhanced growth factor signaling. Fibroblast growth factor 2 (FGF2) consists of a low and several high molecular weight forms (HMW-FGF2). We previously demonstrated that antiprogestin-resistant mammary carcinomas display lower levels of progesterone receptor A isoforms (PRA) than B isoforms (PRB). Our aim was to evaluate the role of FGF2 isoforms in breast cancer progression. We evaluated FGF2 expression, cell proliferation, and pathway activation in models with different PRA/PRB ratios. We performed lentiviral infections of different FGF2 isoforms using the human hormone-responsive T47D-YA cells, engineered to only express PRA, and evaluated tumor growth, metastatic dissemination, and endocrine responsiveness. We assessed FGF2 expression and localization in 81 human breast cancer samples. Antiprogestin-resistant experimental mammary carcinomas with low PRA/PRB ratios and T47D-YB cells, which only express PRB, displayed higher levels of HMW-FGF2 than responsive variants. HMW-FGF2 overexpression in T47D-YA cells induced increased tumor growth, lung metastasis, and antiprogestin resistance compared to control tumors. In human breast carcinomas categorized by their PRA/PRB ratio, we found nuclear FGF2 expression in 55.6% of tumor cells. No differences were found between nuclear FGF2 expression and Ki67 proliferation index, tumor stage, or tumor grade. In low-grade tumor samples, moderate to high nuclear FGF2 levels were associated to carcinomas with low PRA/PRB ratio. In conclusion, we show that HMW-FGF2 isoforms are PRB targets which confer endocrine resistance and are localized in the nuclei of breast cancer samples. Hence, targeting intracellular FGF2 may contribute to overcome tumor progression.

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.