An estradiol-porphyrin conjugate selectively localizes into estrogen receptor-positive breast cancer cells

A conjugate of a C(11)-beta-derivative of estradiol and an asymmetric tetraphenylporphyrin was synthesized to study its potential selective uptake by breast cancer cells naturally over-expressing the nuclear receptor for estrogen (ER). Competitive radioligand binding assays of this conjugate with recombinant ER showed that the conjugate bound to ER in a dose-dependent manner with an EC50 of 274 nM, compared with 1 nM for estradiol, the natural ligand. Cellular uptake studies with ER-positive MCF-7 and ER-negative HS578t human breast cancer cells revealed that, the conjugate was taken up by MCF-7 cells in a dose-dependent manner, which was obliterated by co-incubation with a large excess of estradiol. On the other hand there was very little uptake of the un-conjugated porphyrin by MCF-7 and Hs578t cells. HS578t cells also showed insignificant uptake of the conjugate under the conditions of our experiment. These results strongly suggested that specific interaction between the endogenous ER in MCF-7 cells and the estrogen part of the conjugate enabled these cells to selectively internalize the conjugate over the un-conjugated porphyrin. Therefore, ER-binding conjugates of estradiol and porphyrins could potentially be used for ER-targeted photodynamic therapy of hormone-sensitive cancers of breast, ovary, gonads etc.     

Different anticancer effects of Saxifragifolin A on estrogen receptor-positive and estrogen receptor-negative breast cancer cells

BackgroundBreast cancer is the leading cause of cancer-related death among women worldwide. For treating breast cancer, numerous natural products have been considered as chemotherapeutic drugs.Hypothesis/purposeThe present study aims to investigate the apoptotic effect of Saxifragifolin A (Saxi A) isolated from Androsace umbellata in two different human breast cancer cells which are ER-positive MCF-7 cells and ER-negative MDA-MB-231 cells, and examine the molecular basis for its anticancer actions.Study designThe inhibitory effects of Saxi A on cell survival were examined in MCF-7 cells and MDA-MB-231 cells in vitro.MethodsMTT assays, Annexin V/PI staining analysis, ROS production assay, Hoechst33342 staining and Western blot analysis were performed.ResultsOur results showed that MDA-MB-231 cells were more sensitive to Saxi A-induced apoptosis than MCF-7 cells. Saxi A induced apoptosis in MDA-MB-231 cells through ROS-mediated and caspase-dependent pathways, whereas treatment with Saxi A induced apoptosis in MCF-7 cells in a caspase-independent manner. In spite of Saxi A-induced activation of MAPKs in both breast cancer cell lines, only p38 MAPK and JNK mediated Saxi A-induced apoptosis. In addition, cell survival of shERα-transfected MCF-7 cells was decreased, while MDA-MB-231 cells that overexpress ERα remained viable.ConclusionSaxi A inhibits cell survival in MCF-7 cells and MDA-MB-231 cells through different regulatory pathway, and ERα status appears to be important for regulating Saxi A-induced apoptosis in breast cancer cells. Thus, Saxi A may have a potential therapeutic use for treating breast cancer.     

Current medical treatment of estrogen receptor-positive breast cancer

Approximately 80% of breast cancers(BC) are estrogen receptor(ER)-positive and thus endocrine therapy(ET) should be considered complementary to surgery in the majority of patients. The advantages of oophorectomy, adrenalectomy and hypophysectomy in women with advanced BC have been demonstrated many years ago, and currently ET consist of(1) ovarian function suppression(OFS), usually obtained using gonadotropinreleasing hormone agonists(Gn RHa);(2) selective estrogen receptor modulators or down-regulators(SERMs or SERDs); and(3) aromatase inhibitors(AIs), or a combination of two or more drugs. For patients aged less than 50 years and ER+ BC, there is no conclusive evidence that the combination of OFS and SERMs(i.e., tamoxifen) or chemotherapy is superior to OFS alone. Tamoxifen users exhibit a reduced risk of BC, both invasive and in situ, especially during the first 5 years of therapy, and extending the treatment to 10 years further reduced the risk of recurrences. SERDs(i.e., fulvestrant) are especially useful in the neoadjuvant treatment of advanced BC, alone or in combination with either cytotoxic agents or AIs. There are two types of AIs: type Ⅰ are permanent steroidal inhibitors of aromatase, while type Ⅱ are reversible nonsteroidal inhibitors. Several studies demonstrated the superiority of the third-generation AIs(i.e., anastrozole and letrozole) compared with tamoxifen, and adjuvant therapy with AIs reduces the recurrence risk especially in patients with advanced BC. Unfortunately, some cancers are or became ET-resistant, and thus other drugs have been suggested in combination with SERMs or AIs, including cyclin-dependent kinase 4/6 inhibitors(palbociclib) and mammalian target of rapamycin(m TOR) inhibitors, such as everolimus. Further studies are required to confirm their real usefulness.     

Protein kinase C subspecies in estrogen receptor-positive and -negative human breast cancer cell lines

Estrogen receptor-positive (MCF7) and -negative (BT20) human breast cancer cell lines, which are frequently used for studies on cancer chemotherapy with triphenylethylene (TPE) anti-estrogens, express at least three protein kinase C subspecies. Two of them are identified as type II PKC having the beta-sequence and type III PKC having the alpha-sequence. The other one shows typical characteristics of PKC which responds to Ca2+, phosphatidylserine and diacylglycerol, but shows kinetic properties subtly different from the previously known PKC subspecies. Immunoblot analysis has shown that this enzyme does not correspond to any of the well defined subspecies with known sequence structures. All of these PKC subspecies are similarly susceptible to the TPE antiestrogens.     

Response of estrogen receptor-positive breast cancer tumorspheres to antiestrogen treatments

Estrogen signaling plays a critical role in the pathogenesis of breast cancer. Because the majority of breast carcinomas express the estrogen receptor ERα, endocrine therapy that impedes estrogen-ER signaling reduces breast cancer mortality and has become a mainstay of breast cancer treatment. However, patients remain at continued risk of relapse for many years after endocrine treatment. It has been proposed that cancer recurrence may be attributed to cancer stem cells (CSCs)/tumor-initiating cells (TICs). Previous studies in breast cancer have shown that such cells can be enriched and propagated in vitro by culturing the cells in suspension as mammospheres/tumorspheres. Here we established tumorspheres from ERα-positive human breast cancer cell line MCF7 and investigated their response to antiestrogens Tamoxifen and Fulvestrant. The tumorsphere cells express lower levels of ERα and are more tumorigenic in xenograft assays than the parental cells. Both 4-hydroxytamoxifen (4-OHT) and Fulvestrant attenuate tumorsphere cell proliferation, but only 4-OHT at high concentrations interferes with sphere formation. However, treated tumorsphere cells retain the self-renewal capacity. Upon withdrawal of antiestrogens, the treated cells resume tumorsphere formation and their tumorigenic potential remains undamaged. Depletion of ERα shows that ERα is dispensable for tumorsphere formation and xenograft tumor growth in mice. Surprisingly, ERα-depleted tumorspheres display heightened sensitivity to 4-OHT and their sphere-forming capacity is diminished after the drug is removed. These results imply that 4-OHT may inhibit cellular targets besides ERα that are essential for tumorsphere growth, and provide a potential strategy to sensitize tumorspheres to endocrine treatment.     

Natural history of estrogen receptor-negative,progesterone receptor-positive breast cancer

The biological significance of estrogen receptor-negative but progesterone receptor-positive breast carcinomas is not clear. In the present study the aggressiveness of breast carcinomas in relation to ER and PgR status has been investigated. The probability of disease-free survival in 297 node-negative breast carcinoma patients was monitored during a follow-up ranging from six to 96 months (median 45 months). Steroid hormone receptor content was assayed with the biochemical method recommended by the EORTC. The probability of disease-free survival was significantly worse for patients with ER-negative, PgR-positive carcinomas compared to the other three steroid hormone receptor phenotypes. Our results suggest that ER-negative, PgR-positive breast carcinomas are biologically different in terms of aggressiveness from the other steroid hormone receptor phenotypes.     

Induction of Hsp22 (HspB8) by estrogen and the metalloestrogen cadmium in estrogen receptor-positive breast cancer cells

Estrogen (E2) plays a critical role in the etiology and progression of human breast cancer. The estrogenic response is complex and not completely understood, including in terms of the involved responsive genes. Here we show that Hsp22 (synonyms: HspB8, E2lG1, H11), a member of the small heat shock protein (sHSP) superfamily, was induced by E2 in estrogen receptor-positive MCF-7 breast cancer cells, resulting in an elevated Hsp22 protein level, whereas it was not induced in estrogen receptor-negative MDA-MB-231 cells. This induction was prevented by the pure anti-estrogen ICI182780 (faslodex, fulvestrant), whereas tamoxifen, a substance with mixed estrogenic and antiestrogenic properties, had no major inhibitory effect on this induction, nor did it induce Hsp22 on its own. Cadmium (Cd) is an environmental pollutant with estrogenic properties (metalloestrogen) that has been implicated in breast cancer. Treatment of MCF-7 cells with Cd also resulted in induction of Hsp22, and this induction was also inhibited by ICI182780. In live MCF-7 cells, Hsp22 interacted at the level of dimers with Hsp27, a related sHSP, as was shown by quantitative fluorescence resonance energy transfer measurements. In cytosolic extracts of MCF-7 cells, most of the E2- and Cd-induced Hsp22 was incorporated into high-molecular mass complexes. In part, Hsp22 and Hsp27 were components of distinct populations of these complexes. Finally, candidate elements in the Hsp22 promoter were identified by sequence analysis that could account for the induction of Hsp22 by E2 and Cd. Taken together, Hsp22 induction represents a new aspect of the estrogenic response with potential significance for the biology of estrogen receptor-positive breast cancer cells.     

Growth inhibition of estrogen receptor-positive and aromatase-positive human breast cancer cells in monolayer and spheroid cultures by letrozole, anastrozole, and tamoxifen

Two third-generation aromatase inhibitors, letrozole and anastrozole, and the antiestrogen tamoxifen, were compared for growth-inhibiting activity in two estrogen receptor (ER)-positive aromatase-overexpressing human breast cancer cell lines, MCF-7aro and T-47Daro. Inhibition of hormone (1 nM testosterone)-stimulated proliferation was evaluated in both monolayer cultures and in three-dimensional spheroid cultures. Letrozole and anastrozole were also compared for effectiveness of aromatase inhibition, and relative affinity for aromatase, under both monolayer and spheroid growth conditions. Letrozole was an effective inhibitor of MCF-7aro monolayer cell proliferation, with an estimated 50% inhibitory concentration (IC50) of 50-100 nM, whereas an IC50 was not reached with anastrozole at any concentration tested (100-500 nM). An IC50 of tamoxifen was 1000 nM. Proliferation of T-47Daro monolayer cells was more sensitive to inhibition by all three agents; as with MCF-7aro cells, letrozole was the most effective inhibitor. MCF-7aro spheroids were slightly less sensitive than monolayer cells proliferation-inhibiting effects of letrozole (IC50 about 200 nM), and there was no significant inhibition with 100-200 nM anastrozole or 200-1000 nM tamoxifen. Letrozole and anastrozole significantly inhibited T-47Daro spheroid cell proliferation, at 15-25 and 50 nM, respectively, consistent with the greater sensitivity of T-47Daro monolayer cells to inhibition of proliferation by these agents. Tamoxifen failed to significantly inhibit T-47Daro spheroid cell proliferation over a 100-500 nM concentration range. Determination of aromatase inhibition in monolayers of both cell lines by a direct-access microsomal assay and an intact-cell assay revealed that letrozole was more active than anastrozole in monolayers of both cell lines and in both assays. In MCF-7aro spheroids following cell lysis, only letrozole significantly inhibited aromatase activity, supporting the conclusion that letrozole binds stronger to aromatase than anastrozole does. Our results demonstrate that MCF-7aro and T-47Daro spheroids could be a suitable model for evaluation of growth-inhibitory effects of agents used in hormonal therapy of breast cancer.     

Adiponectin mediates antiproliferative and apoptotic responses in human MCF7 breast cancer cells

It is well established that obesity is a risk factor for breast cancer and that blood levels of adiponectin, a hormone mainly secreted by white adipocytes, are inversely correlated with the body fat mass. As adiponectin elicits anti-proliferative effects in some cell types, we tested the hypothesis that adiponectin could influence human breast cancer MCF-7 cell growth. Here we show that MCF-7 cells express adiponectin receptors and respond to human recombinant adiponectin by reducing their growth, AMPkinase activation, and p42/p44 MAPkinase inactivation. Further, we demonstrate that the anti-proliferative effect of adiponectin involves activation of cell apoptosis and inhibition of cell cycle. These findings suggest that adiponectin could act in vivo as a paracrine/endocrine growth inhibitor towards mammary epithelial cells. Moreover, adipose adiponectin production being strongly reduced in obesity, this study may help to explain why obesity is a risk factor of developing breast cancers.     

Her4 mediates ligand-dependent antiproliferative and differentiation responses in human breast cancer cells

The function of the epidermal growth factor receptor (EGFR) family member HER4 remains unclear because its activating ligand, heregulin, results in either proliferation or differentiation. This variable response may stem from the range of signals generated by HER4 homodimers versus heterodimeric complexes with other EGFR family members. The ratio of homo- and heterodimeric complexes may be influenced both by a cell's EGFR family member expression profile and by the ligand or even ligand isoform used. To define the role of HER4 in mediating antiproliferative and differentiation responses, human breast cancer cell lines were screened for responses to heregulin. Only cells that expressed HER4 exhibited heregulin-dependent antiproliferative responses. In-depth studies of one line, SUM44, demonstrated that the antiproliferative and differentiation responses correlated with HER4 activation and were abolished by stable expression of a kinase-inactive HER4. HB-EGF, a HER4-specific ligand in this EGFR-negative cell line, also induced an antiproliferative response. Moreover, introduction and stable expression of HER4 in HER4-negative SUM102 cells resulted in the acquisition of a heregulin-dependent antiproliferative response, associated with increases in markers of differentiation. The role of HER2 in these heregulin-dependent responses was examined through elimination of cell surface HER2 signaling by stable expression of a single-chain anti-HER2 antibody that sequestered HER2 in the endoplasmic reticulum. In the cell lines with either endogenously (SUM44) or exogenously (SUM102) expressed HER4, elimination of HER2 did not alter HER4-dependent decreases in cell growth. These results suggest that HER4 is both necessary and sufficient to trigger an antiproliferative response in human breast cancer cells.     

Effect of tamoxifen and 2-methoxyestradiol alone and in combination on human breast cancer cell proliferation

Endocrine therapy is widely accepted for the treatment of hormone receptor-positive breast cancer. However, in many cases eventually resistance will develop and tumor regrows. Combination therapy may be one way to resolve this problem. In the present study we investigated the effect of a combination of the widely used antiestrogen tamoxifen with the endogenous estradiol metabolite 2-methoxyestradiol (2-ME) on the proliferation of human estrogen receptor-positive and receptor-negative breast cancer cells.The receptor-positive cell line MCF-7 and the receptor-negative cell line BM were treated with 4-hydroxytamoxifen (4-OHTam) and 2-methoxyestradiol in the concentration range of 0.8-25 microM alone and equimolar combinations for 4 days. The proliferation of the cells was determined using the ATP-chemosensitivity test.4-Hydroxytamoxifen inhibited proliferation of MCF-7 and BM cells with IC(50) values of 31 and 10 microM, the corresponding figures for 2-methoxyestradiol were 52 and 8 microM. The combination showed IC(50) values of 6 microM and 4 microM.These results indicate that a combination of tamoxifen with 2-methoxyestradiol showed an additive inhibitory effect concerning the proliferation of estrogen receptor-positive and receptor-negative breast cancer cell lines. Thus a combination of these substances may allow ameliorating of adverse events of tamoxifen by reducing its concentrations and probably also drug resistance and should be tested in clinical trials.     

Prolylcarboxypeptidase regulates proliferation, autophagy, and resistance to 4-hydroxytamoxifen-induced cytotoxicity in estrogen receptor-positive breast cancer cells

Endocrine therapy with tamoxifen (TAM) significantly improves outcomes for patients with estrogen receptor-positive breast cancer. However, intrinsic (de novo) or acquired resistance to TAM occurs in a significant proportion of treated patients. To identify genes involved in resistance to TAM, we introduced full-length cDNA expression library into estrogen receptor-positive MCF7 cells and exposed them to a cytotoxic dose of 4-hydroxytamoxifen (4OHTAM). Four different library inserts were isolated from surviving clones. Re-introduction of the genes individually into naive MCF7 cells made them resistant to 4OHTAM. Cells overexpressing these genes had an increase in acidic autophagic vacuoles induced by 4OHTAM, suggesting their role in autophagy. One of them, prolylcarboxypeptidase (PRCP), was investigated further. Overexpression of PRCP increased cell proliferation, boosted several established markers of autophagy, including expression of LC3-2, sequestration of monodansylcadaverine, and proteolysis of BSA in an ER-α dependent manner, and increased resistance to 4OHTAM. Conversely, knockdown of endogenous PRCP in MCF7 cells increased cell sensitivity to 4OHTAM and at the same time decreased cell proliferation and expression of LC3-2, sequestration of monodansylcadaverine, and proteolysis of BSA. Inhibition of enzymatic activity of PRCP enhanced 4OHTAM-induced cytotoxicity in MCF7 cells. Cells with acquired resistance to 4OHTAM exhibited increased PRCP activity, although inhibition of PRCP prevented development of 4OHTAM resistance in parental MCF7 cells and restored response to 4OHTAM in MCF7 cells with acquired resistance to 4OHTAM. Thus, we have for the first time identified PRCP as a resistance factor for 4OHTAM resistance in estrogen receptor-positive breast cancer cells.