CLDN1 Sensitizes Triple-Negative Breast Cancer Cells to Chemotherapy

Simple Summary

Triple-negative breast cancer (TNBC) treatment represents a major challenge in oncology. TNBC evolves into chemotherapy resistance for 60 to 70% of the patients. About 77% of the TNBC displays a lack of claudin-1 (CLDN1), a major tight junction component. We demonstrated that CLDN1 increased the sensitivity of TNBC cell lines to the main chemotherapeutic agents commonly used for breast cancer treatment. Our data support the idea that CLDN1 may be a good predictive chemotherapy response marker to help therapeutic management of TNBC patients. In longer terms, this study could allow new treatment protocols creation aimed to induce CLDN1 expression in TNBCs to increase their sensitivity to chemotherapy.

Abstract

Triple-negative breast cancer (TNBC) is an aggressive subtype that constitutes 15–20% of breast cancer cases worldwide. Current therapies often evolve into chemoresistance and lead to treatment failure. About 77% of the TNBC lacks claudin-1 (CLDN1) expression, a major tight junction component, and this absence is correlated with poorer prognostic. Little is known about CLDN1 role on the chemosensitivity of breast cancer. Our clinical data analysis reveals that CLDN1 low expression is correlated to a poor prognostic in TNBC patients. Next, the sensitivity of various TNBC “claudin-1-high” or “claudin-1-low” cells to three compounds belonging to the main class of chemotherapeutic agents commonly used for the treatment of TNBC patients: 5-fluorouracil (5-FU), paclitaxel (PTX) and doxorubicin (DOX). Using RNA interference and stable overexpressing models, we demonstrated that CLDN1 expression increased the sensitivity of TNBC cell lines to these chemotherapeutic agents. Taken together, our data established the important role of CLDN1 in TNBC cells chemosensitivity and supported the hypothesis that CLDN1 could be a chemotherapy response predictive marker for TNBC patients. This study could allow new treatment protocols creation aimed to induce CLDN1 expression in TNBCs to increase their sensitivity to chemotherapy.

Synthesis and evaluation of new designed multiple ligands directed towards both peroxisome proliferator-activated receptor-γ and angiotensin II type 1 receptor

Because of the complex biological networks, many pathologic disorders fail to be treated with a molecule directed towards a single target. Thus, combination therapies are often necessary, but they have many drawbacks. An alternative consists in building molecules intended to interact with multiple targets, called designed multiple ligands. We followed such a strategy in order to treat metabolic syndrome, by setting up molecules directed towards both type 1 angiotensin II (AT₁) receptor and peroxisome proliferator-activated receptor-γ (PPAR-γ). For this purpose, many molecules were prepared by merging both pharmacophores following three different strategies. Their ability to activate PPAR-γ and to block AT₁ receptors were evaluated in vitro. This strategy led to the preparation of many new PPAR-γ activating and AT₁ blocking molecules. Among them, some exhibited both activities, highlighting the convenience of this approach.

Biotinylation enhances the anticancer effects of 15d‑PGJ2 against breast cancer cells

15-Deoxy-∆12,14-prostaglandin J2 (15d‑PGJ2) is a natural agonist of peroxisome proliferator-activated receptor γ (PPARγ) that displays anticancer activity. Various studies have indicated that the effects of 15d‑PGJ2 are due to both PPARγ-dependent and -independent mechanisms. In the present study, we examined the effects of a biotinylated form of 15d‑PGJ2 (b‑15d‑PGJ2) on hormone-dependent MCF‑7 and triple‑negative MDA‑MB‑231 breast cancer cell lines. b‑15d‑PGJ2 inhibited cell proliferation more efficiently than 15d‑PGJ2 or the synthetic PPARγ agonist, efatutazone. b‑15d‑PGJ2 was also more potent than its non-biotinylated counterpart in inducing apoptosis. We then analyzed the mechanisms underlying this improved efficiency. It was found not to be the result of biotin receptor-mediated increased incorporation, since free biotin in the culture medium did not decrease the anti-proliferative activity of b‑15d‑PGJ2 in competition assays. Of note, b‑15d‑PGJ2 displayed an improved PPARγ agonist activity, as measured by transactivation experiments. Molecular docking analyses revealed a similar insertion of b‑15d‑PGJ2 and 15d‑PGJ2 into the ligand binding domain of PPARγ via a covalent bond with Cys285. Finally, PPARγ silencing markedly decreased the cleavage of the apoptotic markers, poly(ADP-ribose) polymerase 1 (PARP‑1) and caspase‑7, that usually occurs following b‑15d‑PGJ2 treatment. Taken together, our data indicate that biotinylation enhances the anti-proliferative and pro-apoptotic activity of 15d‑PGJ2, and that this effect is partly mediated via a PPARγ-dependent pathway. These results may aid in the development of novel therapeutic strategies for breast cancer treatment.

Energy restriction mimetic agents to target cancer cells: comparison between 2-deoxyglucose and thiazolidinediones

The use of energy restriction mimetic agents (ERMAs) to selectively target cancer cells addicted to glycolysis could be a promising therapeutic approach. Thiazolidinediones (TZDs) are synthetic agonists of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ that were developed to treat type II diabetes. These compounds also display anticancer effects which appear mainly to be independent of their PPARγ agonist activity but the molecular mechanisms involved in the anticancer action are not yet well understood. Results obtained on ciglitazone derivatives, mainly in prostate cancer cell models, suggest that these compounds could act as ERMAs. In the present paper, we introduce how compounds like 2-deoxyglucose target the Warburg effect and then we discuss the possibility that the PPARγ-independent effects of various TZD could result from their action as ERMAs.

Optimization of troglitazone derivatives as potent anti-proliferative agents: towards more active and less toxic compounds

Δ2-Troglitazone derivatives were shown to exhibit anti-proliferative activity in a PPARγ-independent manner. We prepared various compounds in order to increase their potency and decrease their toxicity towards non-malignant primary cultured hepatocytes. Many compounds induced viabilities less than 20% at 10 μM on various cancer cell lines. Furthermore, five of them showed hepatocyte viability of 80% or more at 200 μM. In addition, compounds 17 and 18 exhibited promising maximum tolerated doses on a murine model, enabling future investigations.

PPARγ-inactive Δ2-troglitazone independently triggers ER stress and apoptosis in breast cancer cells

Our aim was to better understand peroxisome proliferator-activated receptor gamma (PPARγ)-independent pathways involved in anti-cancer effects of thiazolidinediones (TZDs). We focused on Δ2-troglitazone (Δ2-TGZ), a PPARγ inactive TZD that affects breast cancer cell viability. Appearance of TUNEL positive cells, changes in mitochondrial membrane potential, cleavage of poly(ADP-ribose) polymerase (PARP)-1 and caspase-7 revealed that apoptosis occurred in both hormone-dependent MCF7 and hormone-independent MDA-MB-231 breast cancer cells after 24 and 48 h of treatment. A microarray study identified endoplasmic reticulum (ER) stress as an essential cellular function since many genes involved in ER stress were upregulated in MCF7 cells following Δ2-TGZ treatment. Δ2-TGZ-induced ER stress was further confirmed in MCF7 cells by phosphorylation of pancreatic endoplasmic reticulum kinase-like endoplasmic reticulum kinase (PERK) and its target eIF2α after 1.5 h, rapid increase in activating transcription factor (ATF) 3 mRNA levels, splicing of X-box binding protein 1 (XBP1) after 3 h, accumulation of binding immunogloblulin protein (BiP) and CCAAT-enhancer-binding protein homologous protein (CHOP) after 6 h. Immunofluorescence microscopy indicated that CHOP was relocalized to the nucleus of treated cells. Similarly, in MDA-MB-231 cells, overexpression of ATF3, splicing of XBP1, and accumulation of BiP and CHOP were observed following Δ2-TGZ treatment. In MCF7 cells, knock-down of CHOP or the inhibition of c-Jun N-terminal kinase (JNK) did not impair cleavage of PARP-1 and caspase-7. Altogether, our results show that ER stress is an early response of major types of breast cancer cells to Δ2-TGZ, prior to, but not causative of apoptosis.

Synthesis of new troglitazone derivatives: anti-proliferative activity in breast cancer cell lines and preliminary toxicological study

Breast cancer is the most prevalent cancer in women. The development of resistances to therapeutic agents and the absence of targeted therapy for triple negative breast cancer motivate the search for alternative treatments. With this aim in mind, we synthesised new derivatives of troglitazone, a compound which was formerly used as an anti-diabetic agent and which exhibits anti-proliferative activity on various cancer cell lines. Among the compounds prepared, some displayed micromolar activity against hormone-dependent and hormone-independent breast cancer cells. Furthermore, the influence of the compounds on the viability of primary cultures of human hepatocytes was evaluated. This enabled us to obtain for the first time interesting structure-toxicity relationships in this family of compounds, resulting in 6b and 8b, which show good anti-proliferative activities and poor toxicity towards hepatocytes, compared to troglitazone.

EGR1 expression: a calcium and ERK1/2 mediated PPARγ-independent event involved in the antiproliferative effect of 15-deoxy-Δ12,14-prostaglandin J2 and thiazolidinediones in breast cancer cells

Our aim was to get new information about the Peroxisome Proliferator Activated Receptor gamma (PPARγ)-independent pathway involved in the antiproliferative action of PPARγ ligands in breast cancer cells. We investigated the effects of Troglitazone (TGZ), Ciglitazone (CGZ), Rosiglitazone (RGZ) and, 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ(2)) on the hormone-dependent breast cancer cell line MCF7. The early transcription factor EGR1 (Early Growth Response gene 1) mRNA and protein levels peaked after 3h of incubation with 25μM TGZ, CGZ or 15d-PGJ(2) and then gradually decreased. RGZ, the most potent activator of PPARγ, did not show this effect. The PPARγ antagonist GW 9662 did not block EGR1 mRNA induction which also still occurred in case of PPARγ silencing as well as in case of treatment with the PPARγ-inactive compound Δ2-TGZ. EGR1 mRNA induction required ERK1/2 phosphorylation which was not blocked by EGF Receptor (EGFR) inhibition. The ERK1/2 pathway was also involved in Δ2-TGZ-induced EGR1 mRNA expression in the hormone-independent breast cancer cell line MDA-MB-231. Using the fluorescent dye Fura2, we showed in MCF7 that TGZ or Δ2-TGZ induced an immediate increase in cytosolic calcium which was required for ERK1/2 phosphorylation and EGR1 mRNA induction as demonstrated by calcium chelation experiments. Furthermore, in MCF7 transfected with siRNA targeting EGR1, Δ2-TGZ inhibited less efficiently cell proliferation.

Crosstalk between adenosine receptor (A2A isoform) and ERalpha mediates ethanol action in MCF-7 breast cancer cells

Alcohol consumption increases the risk of breast cancer but the underlying mechanisms are not well understood. We have shown previously that ethanol activates ER signalling pathway in a cAMP/PKA-mediated ligand-independent manner. Since the activation of A2A adenosine receptor (A2AAR) by ethanol has been reported in other cell types, here we tested if cross-talk between this Gs-coupled receptor and ERalpha could be involved in ethanol effects in breast cancer cells. Our study shows that A2AAR is expressed and functional in the hormone-dependent breast cancer cell line MCF-7. Interestingly, activation of this receptor by the selective agonist CGS21680 stimulates the transcription of progesterone receptor, a well known estrogen target gene. CGS21680 also stimulates the pEREtkLuc reporter activity in transfected MCF-7 cells, an effect antagonized by the antiestrogen ICI182,780. Moreover, CGS21680 stimulates the proliferation of MCF-7 cells similarly to E2. Finally, the A2AAR antagonist MSX-3 inhibits the ethanol-induced activation of ERalpha signalling pathway. These results demonstrate cross-talk between A2AAR and ERalpha that is involved in ethanol action. This could open new perspectives for the therapy of estrogen-dependent breast cancer.

Ethanol-induced ligand-independent activation of ERalpha mediated by cyclic AMP/PKA signaling pathway: an in vitro study on MCF-7 breast cancer cells

Alcohol consumption is an increased risk factor for hormone-dependent breast cancer but the underlying molecular bases are unknown. Several studies suggest that ethanol could activate the estrogen signaling pathway. We have performed an in vitro study in order to investigate the molecular players involved in this phenomenon. Exposure of MCF-7 breast cancer cells to ethanol induced an increase in the mRNA level of two well known estrogen target genes: progesterone receptor (PR) and pS2. This result was confirmed by an increase in luciferase activity in pEREtkLuc-transfected MCF-7 cells exposed to ethanol. These effects, whose intensity was similar to those of E2, were observed also in steroid-free medium and were inhibited by the antiestrogen ICI 182,780. This suggested a ligand-independent activation of ERalpha that was confirmed by the absence of ERalpha proteolysis in ethanol-treated cells. Using PKA inhibitor (H89), the study of phospho-CREB by Western blot and transfection experiments with a CRE-reporter construct demonstrated that PKA was involved in ethanol-induced transcription of ERalpha target genes. Adenylyl cyclase inhibition impaired the activation of estrogen signaling pathway induced by ethanol. The results obtained in vitro, are discussed in regard to alcohol consumption and relevance to humans.

Ethanol stimulates the secretion of matrix metalloproteinases 2 and 9 in MCF-7 human breast cancer cells

Alcohol consumption is a well-established risk factor for hormone-dependent breast cancer. In vitro studies performed to understand the mechanisms by which ethanol acts on breast cancer cells have shown that this compound stimulates both proliferation and migration. In the present study, we show by gelatin zymography that, when exposed to ethanol, MCF-7 human breast cancer cells display a higher amount of active metalloproteinases (MMP) 2 and 9 in their culture medium. This increase is somewhat higher than those observed in the case of 17beta-estradiol (E2) exposure. As expected, anti-estrogen ICI 182,780 inhibits the E2-induced overexpression of a well-known estrogen responsive gene, the progesterone receptor, in MCF-7 cells. ICI 182,780 also inhibits the E2-induced increase in MMP-2 and -9 secretion. Nevertheless, in the case of ethanol exposure, this ER ant-agonist was only efficient on MMP-9 secretion. In addition, although MMP-9 transcription was not sensitive to E2 or ethanol, MMP-2 transcription was stimulated in MCF-7 cells exposed to ethanol. Collectively, these results give new insights into the effects of alcohol on breast cancer cell migration, which are not due solely to an estrogen-like activity of alcohol.

Analysis of the effects of different alcohols on MCF-7 human breast cancer cells

Alcohol consumption is known to be an increased risk factor for breast cancer, but the underlying molecular mechanisms are not well understood. We have recently shown that the exposure of MCF-7 breast cancer cells to 0.1% ethanol enhanced their proliferation and increased their content in both estrogen receptor-alpha (ERalpha) and aromatase. The aim of the present work was to determine if the effects of ethanol could be mimicked by other short-chain aliphatic alcohols such as methanol and 1-butanol. Our results show that these compounds do not stimulate MCF-7 cell proliferation. An increase in ERalpha content was observed by Western blot in methanol-treated cells, but this parameter was not affected in butanol-treated cells. Neither of these two alcohols induced an increase in aromatase mRNA level. So despite a similarity in molecular structure, these primary alcohols do not exert the same effects. Taken together, these results suggest that the increase in aromatase expression might be a key event required for the enhanced proliferation observed in the presence of ethanol.

Ethanol stimulates proliferation, ERalpha and aromatase expression in MCF-7 human breast cancer cells

It is well documented that alcohol is associated with an increased risk factor for breast carcinogenesis although the underlying mechanisms are not clearly understood. It has been reported that in vitro, the culture of estrogen receptor (ER) expressing breast cancer cells in ethanol containing medium was associated with an increase in the proliferation rate, in the ERalpha content as well as in ER transcriptional activity. Since these changes are not observed in ER negative breast cancer cells, and since alcohol intake has been associated to an increased level of circulating estrogens, we have postulated that aromatase expression could be increased following ethanol exposure. The results of our studies show a 1.3-fold increase in cell proliferation after 6 days of culture of MCF-7 cells in the presence of 0.1% ethanol. This enhanced proliferation is confirmed by the use of clonogenic assays which show a 1.5-fold increase in clonal growth in the presence of 0.1% ethanol. No statistically significant changes were observed in the presence of higher ethanol concentration (0.3%). After a 6-day exposure to 0.1% ethanol, RT-PCR analyses reveal a 1.7-fold increase in ERalpha mRNA that was not significant, whereas western blot analyses show a significant 3.3-fold increase in ERalpha content. At the same stage, RT-PCR studies demonstrate a 2.4-fold increase in aromatase mRNA level which is confirmed at the protein level by western blots performed after immuno-precipitation of the enzyme. Taken together, these results are in agreement with the involvement of ER signalling in ethanol-induced stimulation of breast cancer cell proliferation and could help to understand why alcohol consumption is associated with breast cancer risk.

Steroids, aromatase and sex differentiation of the newt Pleurodeles waltl

In the newt Pleurodeles waltl, genetic sex determination obeys female heterogamety (female ZW, male ZZ). In this species as in most of non-mammalian vertebrates, steroid hormones play a key role in sexual differentiation of gonads. In that context, male to female sex reversal can be obtained by treatment of ZZ larvae with estradiol. Male to female sex reversal has also been observed following treatment of ZZ larvae with testosterone, a phenomenon that was called the "paradoxical effect". Female to male sex reversal occurs when ZW larvae are reared at 32 degrees C during a thermosensitive period (TSP) that takes place from stage 42 to stage 54 of development. Since steroids play an important part in sex differentiation, we focussed our studies on the estrogen-producing enzyme aromatase during normal sex differentiation as well as in experimentally induced sex reversal situations. Our results based on treatment with non-aromatizable androgens, aromatase activity measurements and aromatase expression studies demonstrate that aromatase (i) is differentially active in ZZ and ZW larvae, (ii) is involved in the paradoxical effect and (iii) might be a target of temperature. Thus, the gene encoding aromatase might be one of the master genes in the process leading to the differentiation of the gonad in Pleurodeles waltl.

Effect of cadmium on gonadogenesis and metamorphosis in Pleurodeles waltl (urodele amphibian)

In the amphibian Pleurodeles waltl, steroid hormones play a key role in sex differentiation. Since cadmium has been reported to block receptors of sex steroid hormones, we analyzed the effects of this heavy metal on Pleurodeles larvae gonadogenesis. At stage 42, larvae die in the presence of 10.9 microM Cd in the rearing tap water, with TL(50) of 46.3 h, but the concentration of 5.5 microM is tolerated for more than 60 days. When used at 5.5 microM cadmium accumulation measured by atomic absorption spectrophotometry (AAS) in total homogenates of larvae at stage 54 (after 77 days of exposure to the heavy metal) reached 58.1 microg/g of dry weight. At stage 54, we did not detect inhibitory effects on gonadogenesis in larvae reared in the presence of 5.5 microM Cd since stage 42. When the exposure to 5.5 microM Cd was lengthened after stage 54, metamorphosis was delayed and could not be completed. When larvae were exposed to 10.9 microM Cd from stage 54, metamorphosis did not occur and gonad development was stopped. Our study demonstrates a lack of a direct effect of cadmium on sex determination-differentiation but a strong inhibitory effect on metamorphosis, which impairs further gonadal development.

Differential expression of P450 aromatase during gonadal sex differentiation and sex reversal of the newt Pleurodeles waltl

A better understanding of vertebrate sexual differentiation could be provided by a study of models in which genetic sex determination (GSD) of gonads can be reversed by temperature. In the newt Pleurodeles waltl, a P450 aromatase cDNA was isolated from adult gonads, and the nucleotide or deduced amino acid sequences showed a high level of identity with various vertebrate species. In adults, aromatase expression was found in gonads and brain. In developing gonads, the expression was found to fit with the thermo-sensitive period (TSP) and was detected in both ZZ and ZW larvae, as well as in ZW submitted during the whole TSP to a masculinizing temperature. In the latter individuals, in situ hybridization and semi quantitative RT-PCR showed that, at the end of TSP, aromatase expression was at the same level than in normal ZZ larvae and was significantly lower than in normal ZW ones. Furthermore, temperature-induced down regulation did not occur when heating was performed at the end of TSP. Our results confirm the importance of aromatase regulation in female versus male differentiation and demonstrate that a down regulation of aromatase expression is involved in the process of sex reversal.