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High levels of Tissue Inhibitor of Metalloproteinases-1 (TIMP1) are associated with poor prognosis, reduced response to chemotherapy, and, potentially, also poor response to endocrine therapy in breast cancer patients. Our objective was to further investigate the hypothesis that TIMP1 is associated with endocrine sensitivity. We established a panel of 11 MCF-7 subclones with a wide range of TIMP1 mRNA and protein expression levels. Cells with high expression of TIMP1 versus low TIMP1 displayed significantly reduced sensitivity to the antiestrogen fulvestrant (ICI 182,780, Faslodex®), while TIMP1 levels did not influence the sensitivity to 4-hydroxytamoxifen. An inverse correlation between expression of the progesterone receptor and TIMP1 was found, but TIMP1 levels did not correlate with estrogen receptor levels or growth-promoting effects of estrogen (estradiol, E2). Additionally, the effects of fulvestrant, 4-hydroxytamoxifen, or estrogen on estrogen receptor expression were not associated with TIMP1 levels. Gene expression analyses revealed associations between expression of TIMP1 and genes involved in metabolic pathways, epidermal growth factor receptor 1/cancer signaling pathways, and cell cycle. Gene and protein expression analyses showed no general defects in estrogen receptor signaling except from lack of progesterone receptor expression and estrogen inducibility in clones with high TIMP1. The present study suggests a relation between high expression level of TIMP1 and loss of progesterone receptor expression combined with fulvestrant resistance. Our findings in vitro may have clinical implications as the data suggest that high tumor levels of TIMP1 may be a predictive biomarker for reduced response to fulvestrant. [ABSTRACT FROM AUTHOR]

Pathogenic germline mutations in BRCA1 or BRCA2 are detected in less than one third of families with a strong history of breast cancer. It is therefore expected that mutations still remain undetected by currently used screening methods. In addition, a growing number of BRCA1/2 sequence variants of unclear pathogen significance are found in the families, constituting an increasing clinical challenge. New methods are therefore needed to improve the detection rate and aid the interpretation of the clinically uncertain variants. In this study we analyzed a series of 33 BRCA1, 22 BRCA2, and 128 sporadic tumors by RNA profiling to investigate the classification potential of RNA profiles to predict BRCA1/2 mutation status. We found that breast tumors from BRCA1 and BRCA2 mutation carriers display characteristic RNA expression patterns, allowing them to be distinguished from sporadic tumors. The majority of BRCA1 tumors were basal-like while BRCA2 tumors were mainly luminal B. Using RNA profiles, we were able to distinguish BRCA1 tumors from sporadic tumors among basal-like tumors with 83% accuracy and BRCA2 from sporadic tumors among luminal B tumors with 89% accuracy. Furthermore, subtype-specific BRCA1/2 gene signatures were successfully validated in two independent data sets with high accuracies. Although additional validation studies are required, indication of BRCA1/2 involvement (“BRCAness”) by RNA profiling could potentially be valuable as a tool for distinguishing pathogenic mutations from benign variants, for identification of undetected mutation carriers, and for selecting patients sensitive to new therapeutics such as PARP inhibitors. [ABSTRACT FROM AUTHOR]

Introduction Development of resistance to tamoxifen is an important clinical issue in the treatment of breast cancer. Tamoxifen resistance may be the result of acquisition of epigenetic regulation within breast cancer cells, such as DNA methylation, resulting in changed mRNA expression of genes pivotal for estrogen-dependent growth. Alternatively, tamoxifen resistance may be due to selection of pre-existing resistant cells, or a combination of the two mechanisms. Methods To evaluate the contribution of these possible tamoxifen resistance mechanisms, we applied modified DNA methylation-specific digital karyotyping (MMSDK) and digital gene expression (DGE) in combination with massive parallel sequencing to analyze a well established tamoxifen-resistant cell line model (TAMR), consisting of 4 resistant and one parental cell line. Another tamoxifen-resistant cell line model system (LCC1/LCC2) was used to validate the DNA methylation and gene expression results. Results Significant differences were observed in global gene expression and DNA methylation profiles between the parental tamoxifen-sensitive cell line and the 4 tamoxifen-resistant TAMR sublines. The 4 TAMR cell lines exhibited higher methylation levels as well as an inverse relationship between gene expression and DNA methylation in the promoter regions. A panel of genes, including NRIP1, HECA and FIS1, exhibited lower gene expression in resistant vs. parental cells and concurrent increased promoter CGI methylation in resistant vs. parental cell lines. A major part of the methylation, gene expression, and pathway alterations observed in the TAMR model were also present in the LCC1/LCC2 cell line model. More importantly, high expression of SOX2 and alterations of other SOX and E2F gene family members, as well as RB-related pocket protein genes in TAMR highlighted stem cellassociated pathways as being central in the resistant cells and imply that cancer-initiating cells/cancer stem-like cells may be involved in tamoxifen resistance in this model. Conclusion Our data highlight the likelihood that resistant cells emerge from cancer-initiating cells/cancer stem-like cells and imply that these cells may gain further advantage in growth via epigenetic mechanisms. Illuminating the expression and DNA methylation features of putative cancer-initiating cells/cancer stem cells may suggest novel strategies to overcome tamoxifen resistance. [ABSTRACT FROM AUTHOR]

Abstract: The four human epidermal growth factor receptors (HER1-4) are involved in growth stimulation and may play a role in endocrine resistance. The receptors form dimers, leading to activation by mutual phosphorylation. Our purpose was to explore the role of the activated receptors (pHER1, pHER2, pHER3) in endocrine treated breast cancer in terms of co-expression and association with disease-free survival (DFS) in 1062 patients with ER-positive tumors. Furthermore, HER2 amplification was evaluated. We found positive associations between the phosphorylated receptors. pHER1 and pHER3 were co-expressed with one or two of the other activated receptors in 85% and 89% of tumors, respectively, whereas pHER2 was co-expressed with the other activated receptors in 54% of tumors. Except for HER2, which was associated with poor prognosis, none of the remaining markers were associated with DFS. However, frequent co-expression indicates a role of the other HER-family members in activation of HER2. [Copyright &y& Elsevier]

Development of resistance to antiestrogen treatment in breast cancer patients is a serious therapeutic problem. The molecular mechanisms contributing to resistance are currently unclear; however it is known that increased activation of growth signaling pathways is involved. Protein Kinase C ɑ (PKCɑ) is associated with a diverse range of cancers and is previously shown to be overexpressed in three out of four antiestrogen resistant breast cancer cell lines. In this study we investigated whether PKCɑ contributes to antiestrogen resistant growth. A panel of nine resistant cell lines was investigated, all of which displayed elevated levels of PKCɑ expression relative to parental MCF-7 cells. Stable PKCɑ overexpression in MCF-7 cells significantly reduced sensitivity to the antiestrogens, tamoxifen and ICI 182,780. Two resistant cell lines were chosen for further studies: tamoxifen resistant MCF-7/TAMR-1 (TAMR-1) and ICI 182,780 resistant MCF-7/182R-6 (182R-6). Treatment with the PKCɑ inhibitor Ro-32-0432 resulted in a preferential growth inhibition of these two cell lines relative to MCF-7 cells. Moreover, transient down-regulation of PKCɑ resulted in a 30-40% growth inhibition of TAMR-1 and 182R-6, while MCF-7 remained unaffected. Stable PKCɑ knock-down in TAMR-1 using small hairpin RNA, resulted in a tamoxifen sensitive ''MCF-7-like'' growth phenotype, while the same approach in 182R-6 cells did not alter their sensitivity to ICI 182,780. These results demonstrate a functional contribution of PKCa to tamoxifen resistant growth. Furthermore, our data suggest the potential for PKCɑ as a marker for antiestrogen resistance and as a promising therapeutic target in the treatment of tamoxifen resistant breast cancer. [ABSTRACT FROM AUTHOR]

Acquired resistance to tamoxifen (Tam) in breast cancer patients is a serious therapeutic problem. We have previously reported that protein kinase C-delta (PKC-d) plays a major role in estrogen (E2)-mediated cell proliferation. To determine if PKC-dis one of the major alternate signaling pathways that supports cell growth in the presence of Tam, we determined the levels of PKC isoforms in four different models of antiestrogen-resistant cells. Three out of four antiestrogen resistance cell lines (Tam/MCF-7, ICI/MCF-7 and HER-2/MCF-7) expressed significantly high levels of both total and activated PKC-dlevels compared to sensitive cells. Estrogen receptor (ER) alpha content and function are maintained in all the antiestrogen-resistant cell lines. Overexpressing active PKC-din Tam-sensitive MCF-7 cells (PKC-d/MCF-7) led to Tam resistance both in vitro and in vivo. Inhibition of PKC-dby rottlerin (a relatively specific inhibitor of PKC-d) or siRNA significantly inhibited estrogen- and Tam-induced growth in antiestrogen-resistant cells. PKC-dlevels are significantly higher in Tam-resistant tumors compared to Tam-sensitive tumors in xenograft model (P<0.05). Taken together, these data suggest that PKC-dplays a major role in antiestrogen resistance in breast tumor cells and thus provides a new target for treatment.Oncogene (2005) 24, 3166-3176. doi:10.1038/sj.onc.1208502 Published online 21 February 2005 [ABSTRACT FROM AUTHOR]

Purpose: We evaluated miproxifene phosphate (TAT-59) to elucidate its efficacy in antiestrogen therapy for breast cancer patients and to assess its tissue-selective estrogenic/antiestrogenic activity.Methods: Using DP-TAT-59, a major and active metabolite of TAT-59, an in vitro cell growth inhibition test was performed. Antitumor activity was determined using TAT-59 against human tumor xenografts of the MCF-7 and the Br-10 cell lines and MCF-7-derived tamoxifen-resistant cell lines, R-27 and FST-1. The antitumor activity of DP-TAT-59 and DM-DP-TAT-59, major metabolites of TAT-59 found in human blood following a TAT-59 dose, was also examined after intravenous administration to experimental animals. The residual estrogenic activity of TAT-59, evaluated in terms of bone and lipid metabolism in ovariectomized rats, was then compared with that of tamoxifen.Results: DP-TAT-59 significantly inhibited the proliferation of estrogen receptor-positive MCF-7 and T-47D tumor cells in the presence of 1 nM estradiol. TAT-59, given to mice bearing MCF-7 or Br-10 xenografts, at the dose level of 5 mg/kg, exerted a significant growth inhibitory effect that was stronger than that of tamoxifen. Moreover, R-27 and FST-1 tumors, which show a resistance to tamoxifen, responded strongly to TAT-59, suggesting that TAT-59 might be effective against tumors resistant to tamoxifen. The metabolites of TAT-59, DP-TAT-59 and DM-DP-TAT-59, showed similar antitumor activity. Both TAT-59 and tamoxifen suppressed the decrease in bone density and reduced the blood cholesterol levels in ovariectomized rats, suggesting that the estrogenic activity of TAT-59 is comparable to that of tamoxifen.Conclusions: On the basis of the above results, one may expect TAT-59 to become an effective drug in patients with tumors less sensitive to tamoxifen, while its estrogenic activity as determined by bone and lipid metabolism is similar to that of tamoxifen. [ABSTRACT FROM AUTHOR]

To elucidate the mechanisms involved in anti-oestrogen resistance, two human breast cancer cell lines MCF-7 and the ICI 182780-resistant cell line, MCF-7/182[SUPR]-6, have been compared with regard to oestrogen receptor (ER) expression, ER function, ER regulation, growth requirements and differentially expressed gene products. MCF-7/182[SUPR]-6 cells express a reduced level of ER protein. The ER protein is functional with respect to binding of oestradiol and the anti-oestrogens tamoxifen, 4-hydroxy-tamoxifen and ICI 182780, whereas expression and oestrogen induction of the progesterone receptor is lost in MCF-7/182[SUPR]-6 cells. The ER protein and the ER mRNA are regulated similarly in the two cell lines when subjected to treatment with oestradiol or ICI 182780. Oestradiol down-regulates ER mRNA and ER protein expression. ICI 182780 has no initial effect on ER mRNA expression whereas the ER protein level decreases rapidly in cells treated with ICI 182780, indicating a severely decreased stability of the ER protein when bound to ICI 182780. In vitro growth experiments revealed that the ICI 182780-resistant cell line had evolved to an oestradiol-independent phenotype, able to grow with close to maximal growth rate both in the absence of oestradiol and in the presence of ICI 182780. Comparison of gene expression between the two cell lines revealed relatively few differences, indicating that a limited number of changes is involved in the development of anti-oestrogen resistance. Identification of the differentially expressed gene products are currently in progress. To elucidate the mechanisms involved in anti-oestrogen resistance, two human breast cancer cell lines MCF-7 and the ICI 182780-resistant cell line, MCF-7/182[SUPR]-6, have been compared with regard to oestrogen receptor (ER) expression, ER function, ER regulation, growth requirements and differentially expressed gene products. MCF-7/182[SUPR]-6 cells express a reduced level of ER protein. The ER protein... [ABSTRACT FROM AUTHOR]