Project description:Resistance to tamoxifen in breast cancer patients is a serious therapeutic problem and major efforts are underway to understand underlying mechanisms. Resistance can be either intrinsic or acquired. We derived a series of subcloned MCF7 cell lines that were either highly sensitive or naturally resistant to tamoxifen and studied the factors that lead to drug resistance. Gene-expression studies revealed a signature of 67 genes that differentially respond to tamoxifen in sensitive vs. resistant subclones, which also predicts disease-free survival in tamoxifen-treated patients. High-throughput cell-based screens, in which >500 human kinases were independently ectopically expressed, identified 31 kinases that conferred drug resistance on sensitive cells. One of these, HSPB8, was also in the expression signature and, by itself, predicted poor clinical outcome in one cohort of patients. Further studies revealed that HSPB8 protected MCF7 cells from tamoxifen and blocked autophagy. Moreover, silencing HSBP8 induced autophagy and caused cell death. Tamoxifen itself induced autophagy in sensitive cells but not in resistant ones, and tamoxifen-resistant cells were sensitive to the induction of autophagy by other drugs. These results may point to an important role for autophagy in the sensitivity to tamoxifen. For defined estrogen culture experiments, sensitive (MCF7-B7TamS) and resistant (MCF7-G11TamR) subclones, were plated in 10-cm dish (Nunc) in DMEM supplemented with 5% FBS. The day after plating, the media was changed to steroid depleted media (phenol red-free DMEM) supplemented with 5% charcoal-dextran treated FBS and grown for 2 d. On day 3, cells were rinsed three times with PBS and treated in triplicate using one of four different conditions: (i) estrogen-depleted medium (control); (ii) estrogen (E) at 10 to 9 M; (iii) 4-OHT at 1 uM; and (iv) E plus 4-OHT, both drugs at the same concentrations as in (ii) and (iii). After 4 h, RNA was isolated and processed for gene-expression profiling according to the Affymetrix protocol (Human Genome U133 plus 2.0 Array) at the Microarray Core Facility at the Dana Farber Cancer Institute. The gene-expressionCEL files were normalized using dChip, using the invariant method and PM-MM difference methods for background subtraction. We identified genes that are differentially regulated by tamoxifen using the following criteria: (i) Genes that responded to estrogen in both MCF7-B7TamS andMCF7-G11TamR were identified if cells under tamoxifen treatment were more than 1.1-fold either up- or down-regulated [90% confidence interval (CI)] relative to its corresponding control cells; (ii) Genes unresponsive to tamoxifen in resistant cells: genes that showed more than 1.1-fold up- or down-regulation (90% CI) in MCF7-G11TamR but not in MCF7-B7TamS when comparing cells treated with both estradiol and tamoxifen with those treated with drug only.

Project description:Tamoxifen, an antagonist to estrogen receptor (ER), is a first line drug used in breast cancer treatment. However, this therapy is complicated by the fact that a substantial number of patients exhibit either de novo or acquired resistance. To characterize the signaling mechanisms underlying the resistance to tamoxifen, we established a tamoxifen-resistant cell line by treating the MCF7 breast cancer cell line with tamoxifen for over 6 months. We showed that this cell line exhibited resistance to tamoxifen both in vitro and in vivo. In order to quantify the phosphorylation alterations associated with tamoxifen resistance, we performed SILAC-based quantitative phosphoproteomic profiling on the resistant and vehicle-treated sensitive cell lines where we identified >5,600 unique phosphopeptides. We found phosphorylation levels of 1,529 peptides were increased (>2 fold) and 409 peptides were decreased (<0.5-fold) in tamoxifen resistant cells compared to tamoxifen sensitive cells. Gene set enrichment analysis revealed that focal adhesion pathway was the top enriched signaling pathway activated in tamoxifen resistant cells. We observed hyperphosphorylation of the focal adhesion kinases FAK1 and FAK2 in the tamoxifen resistant cells. Of note, FAK2 was not only hyperphosphorylated but also transcriptionally upregulated in tamoxifen resistant cells. Suppression of FAK2 by specific siRNA knockdown could sensitize the resistant cells to the treatment of tamoxifen. We further showed that inhibiting FAK activity using the small molecule inhibitor PF562271 repressed cellular proliferation in vitro and tumor formation in vivo. More importantly, our survival analysis revealed that high expression of FAK2 significantly associated with short metastasis-free survival of ER-positive breast cancer patients treated with tamoxifen-based hormone therapy. Our studies suggest that FAK2 is a great potential target for the development of therapy for the treatment of hormone refractory breast cancers.

Project description:Targeting the estrogen signaling pathway has proved to be of great value in the treatment of human breast cancer. Tamoxifen, a selective estrogen receptor modulator (SERM), is the most widely used antiestrogen. However, only 40-50% of patients with estrogen receptor (ER) positive breast cancer benefit from tamoxifen treatment and 30-50% acquire resistance and the disease progresses. Continuous treatment with conventional therapy may contribute to cancer progression in recurring cancers through the accumulation of drug resistant cancer progenitors. We found that MCF7 tamoxifen-resistant (TAM-R) cells possess a significantly higher proportion of cancer progenitor cells than tamoxifen-sensitive MCF7 cells. Our results indicate that the chemokine receptor CXCR4 plays an important role in the maintenance of cancer progenitors in a tamoxifen-resistant cell line and downregulation of CXCR4 signaling by small molecule antagonists specifically inhibits growth of a stem-like cell population in tamoxifen-resistant tumors both in vitro and in vivo. Whole genome gene expression analysis revealed aryl hydrocarbon receptor (AhR) signaling as one of the top networks that is differentially regulated in MCF7(TAM-R) xenograft tumors treated with the CXCR4 antagonist AMD3100 as compared to MCF7 tumors. Further, small molecule antagonists of AhR signaling specifically inhibit the progenitor population in MCF7(TAM-R) cells suggesting that the aryl hydrocarbon receptor could be a putative target for the treatment of tamoxifen-resistant breast cancers. Introduction transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSCs identified a purine derivative, StemRegenin 1 (SR1), that promotes the ex vivo expansion of CD34+ cells. Culture of HSCs with SR1 led to a 50-fold increase in cells expressing CD34 and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR). The identification of SR1 and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy. Tamoxifen resistant or sensitive xenografts; mice treated with estrogen and/or CXCR4 modulators

Project description:Resistance to tamoxifen is a major challenge in the treatment of estrogen receptor positive breast cancer. Acquired resistance to drug involves multilayered genetic and epigenetic regulation . The oncogene EZH2 plays significant role in the development of resistance against tamoxifen, widely used in the treatment of breast cancer. Inhibition of EZH2 has proven to reverse the tamoxifen resistance breast cancer cells back to the sensitive state. The molecular mechanism through which EZH2 inhibition triggers its effects are not known.This study was conducted to understand the global change in proteome profile of tamoxifen resistant MCF-7 breast cancer cells as a result of effect of EZH2 knockdown. Label Free Quantitative proteomics revealed a large number of proteins altered in acquired tamoxifen resistant cells compared to the sensitive cells. A total of 286 proteins were identified with normalized RT for each m/z out of which 86 proteins were upregulated by more than 1.3 fold and 98 proteins were down regulated by more than 1.3 fold in MCF-7 tamoxifen resistant breast cancer cells in comparison to the sensitive breast cancer cells. Upon EZH2 knockdown in tamoxifen resistant cells, a total of 115 proteins were found to be altered with 20 proteins upregulated by more than 1.3 fold and 49 proteins down regulated by more than 1.3 fold. Among the top upregulated proteins were L-lactate dehydrogenase A chain, Alpha and Gamma-enolase, Calreticulin, heat shock protein HSP-90-beta, Alpha-actinin-4, Elongation factor 1-alpha, Vimentin, Protein S100A6, Putative protein FAM10A5, Heterogeneous nuclear ribonucleoprotein A1 and Keratin 1. In addition, 15 proteins were found to be down regulated in EZH2si transfected tamoxifen sensitive cells which otherwise were highlyup regulated in resistant cells in the presence of normal level of EZH2. This indicates a possible regulation of these molecules by EZH2 leading to loss of resistance. Our data unveils important molecular players downstream to EZH2 knockdown leading to regain of sensitivity to tamoxifen in acquired tamoxifen resistance.Thus, EZH2 seems to exert its effects through regulation of metabolism, epithelial to mesenchymal transition and protein synthesis & folding. Hence, targeting EZH2 or the molecules down the cascade might be helpful in reacquiring sensitivity to tamoxifen intamoxifen-resistant cells.

Project description:Targeting the estrogen signaling pathway has proved to be of great value in the treatment of human breast cancer. Tamoxifen, a selective estrogen receptor modulator (SERM), is the most widely used antiestrogen. However, only 40-50% of patients with estrogen receptor (ER) positive breast cancer benefit from tamoxifen treatment and 30-50% acquire resistance and the disease progresses. Continuous treatment with conventional therapy may contribute to cancer progression in recurring cancers through the accumulation of drug resistant cancer progenitors. We found that MCF7 tamoxifen-resistant (TAM-R) cells possess a significantly higher proportion of cancer progenitor cells than tamoxifen-sensitive MCF7 cells. Our results indicate that the chemokine receptor CXCR4 plays an important role in the maintenance of cancer progenitors in a tamoxifen-resistant cell line and downregulation of CXCR4 signaling by small molecule antagonists specifically inhibits growth of a stem-like cell population in tamoxifen-resistant tumors both in vitro and in vivo. Whole genome gene expression analysis revealed aryl hydrocarbon receptor (AhR) signaling as one of the top networks that is differentially regulated in MCF7(TAM-R) xenograft tumors treated with the CXCR4 antagonist AMD3100 as compared to MCF7 tumors. Further, small molecule antagonists of AhR signaling specifically inhibit the progenitor population in MCF7(TAM-R) cells suggesting that the aryl hydrocarbon receptor could be a putative target for the treatment of tamoxifen-resistant breast cancers. Introduction transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSCs identified a purine derivative, StemRegenin 1 (SR1), that promotes the ex vivo expansion of CD34+ cells. Culture of HSCs with SR1 led to a 50-fold increase in cells expressing CD34 and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR). The identification of SR1 and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy.

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High-throughput ectopic expression screen for tamoxifen resistance

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