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Inhibition of BET bromodomain proteins as a therapeutic approach in prostate cancer.

Wyce A, Degenhardt Y, Bai Y, Le B, Korenchuk S, Crouthame MC, McHugh CF, Vessella R, Creasy CL, Tummino PJ, Barbash O - Oncotarget (2013)

Bottom Line: BET (bromodomain and extra-terminal) proteins regulate gene expression through their ability to bind to acetylated chromatin and subsequently activate RNA PolII-driven transcriptional elongation.Here we describe the effects of the highly specific BET inhibitor, I-BET762, on MYC expression in prostate cancer models.Our data suggests that I-BET762 effects are partially driven by MYC down-regulation and underlines the critical importance of additional mechanisms of I-BET762 induced phenotypes.

View Article: PubMed Central - PubMed

Affiliation: Cancer Epigenetics DPU, Oncology R and D GlaxoSmithKline, Collegeville, PA, USA.

ABSTRACT
BET (bromodomain and extra-terminal) proteins regulate gene expression through their ability to bind to acetylated chromatin and subsequently activate RNA PolII-driven transcriptional elongation. Small molecule BET inhibitors prevent binding of BET proteins to acetylated histones and inhibit transcriptional activation of BET target genes. BET inhibitors attenuate cell growth and survival in several hematologic cancer models, partially through the down-regulation of the critical oncogene, MYC. We hypothesized that BET inhibitors will regulate MYC expression in solid tumors that frequently over-express MYC. Here we describe the effects of the highly specific BET inhibitor, I-BET762, on MYC expression in prostate cancer models. I-BET762 potently reduced MYC expression in prostate cancer cell lines and a patient-derived tumor model with subsequent inhibition of cell growth and reduction of tumor burden in vivo. Our data suggests that I-BET762 effects are partially driven by MYC down-regulation and underlines the critical importance of additional mechanisms of I-BET762 induced phenotypes.

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Characterization of I-BET762 sensitivity in prostate cancer cell linesA, Average growth IC50 (gIC50) values observed for I-BET762 in a panel of prostate cancer cell lines obtained from a 6 day growth-death assay (minimum n=2). B, Histograms generated from cell cycle analysis in the indicated cell lines following 6 days treatment with vehicle, 0.5 µM, 1 µM, or 5 µM I-BET762. Data shown was from a single experiment representative of typical results. C, Stacked bar graphs representing the average population of cells in various phases of the cell cycle following treatment with I-BET762 for three days in the indicated cell lines (n=2). D, Western blot analysis of cleaved PARP in the indicated cell lines following three day treatment with a titration of I-BET762.
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Figure 1: Characterization of I-BET762 sensitivity in prostate cancer cell linesA, Average growth IC50 (gIC50) values observed for I-BET762 in a panel of prostate cancer cell lines obtained from a 6 day growth-death assay (minimum n=2). B, Histograms generated from cell cycle analysis in the indicated cell lines following 6 days treatment with vehicle, 0.5 µM, 1 µM, or 5 µM I-BET762. Data shown was from a single experiment representative of typical results. C, Stacked bar graphs representing the average population of cells in various phases of the cell cycle following treatment with I-BET762 for three days in the indicated cell lines (n=2). D, Western blot analysis of cleaved PARP in the indicated cell lines following three day treatment with a titration of I-BET762.

Mentions: We screened a panel of prostate cancer cell lines for sensitivity to I-BET762 in a 6 day growth assay. While some level of growth inhibition was observed in all cell lines, a subset of the cell line panel was particularly sensitive to I-BET762, with growth IC50 (gIC50) values ranging from 25 nM to 150 nM (Figure 1A). Cell cycle analysis in a subset of cell lines revealed a range of responses to I-BET762 treatment. Concentration-dependent G1 arrest was observed in the LNCaP cell line, whereas sub-G1 accumulation was detected in VCaP cells (Figure 1B, C; Supplemental Table S1). PC3 cells exhibited minimal growth inhibition in response to I-BET762; however cell cycle analysis revealed a slight increase in the sub-G1 fraction suggesting low-level cell death in response to compound treatment.


Inhibition of BET bromodomain proteins as a therapeutic approach in prostate cancer.

Wyce A, Degenhardt Y, Bai Y, Le B, Korenchuk S, Crouthame MC, McHugh CF, Vessella R, Creasy CL, Tummino PJ, Barbash O - Oncotarget (2013)

Characterization of I-BET762 sensitivity in prostate cancer cell linesA, Average growth IC50 (gIC50) values observed for I-BET762 in a panel of prostate cancer cell lines obtained from a 6 day growth-death assay (minimum n=2). B, Histograms generated from cell cycle analysis in the indicated cell lines following 6 days treatment with vehicle, 0.5 µM, 1 µM, or 5 µM I-BET762. Data shown was from a single experiment representative of typical results. C, Stacked bar graphs representing the average population of cells in various phases of the cell cycle following treatment with I-BET762 for three days in the indicated cell lines (n=2). D, Western blot analysis of cleaved PARP in the indicated cell lines following three day treatment with a titration of I-BET762.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3926837&req=5

Figure 1: Characterization of I-BET762 sensitivity in prostate cancer cell linesA, Average growth IC50 (gIC50) values observed for I-BET762 in a panel of prostate cancer cell lines obtained from a 6 day growth-death assay (minimum n=2). B, Histograms generated from cell cycle analysis in the indicated cell lines following 6 days treatment with vehicle, 0.5 µM, 1 µM, or 5 µM I-BET762. Data shown was from a single experiment representative of typical results. C, Stacked bar graphs representing the average population of cells in various phases of the cell cycle following treatment with I-BET762 for three days in the indicated cell lines (n=2). D, Western blot analysis of cleaved PARP in the indicated cell lines following three day treatment with a titration of I-BET762.
Mentions: We screened a panel of prostate cancer cell lines for sensitivity to I-BET762 in a 6 day growth assay. While some level of growth inhibition was observed in all cell lines, a subset of the cell line panel was particularly sensitive to I-BET762, with growth IC50 (gIC50) values ranging from 25 nM to 150 nM (Figure 1A). Cell cycle analysis in a subset of cell lines revealed a range of responses to I-BET762 treatment. Concentration-dependent G1 arrest was observed in the LNCaP cell line, whereas sub-G1 accumulation was detected in VCaP cells (Figure 1B, C; Supplemental Table S1). PC3 cells exhibited minimal growth inhibition in response to I-BET762; however cell cycle analysis revealed a slight increase in the sub-G1 fraction suggesting low-level cell death in response to compound treatment.

Bottom Line: BET (bromodomain and extra-terminal) proteins regulate gene expression through their ability to bind to acetylated chromatin and subsequently activate RNA PolII-driven transcriptional elongation.Here we describe the effects of the highly specific BET inhibitor, I-BET762, on MYC expression in prostate cancer models.Our data suggests that I-BET762 effects are partially driven by MYC down-regulation and underlines the critical importance of additional mechanisms of I-BET762 induced phenotypes.

View Article: PubMed Central - PubMed

Affiliation: Cancer Epigenetics DPU, Oncology R and D GlaxoSmithKline, Collegeville, PA, USA.

ABSTRACT
BET (bromodomain and extra-terminal) proteins regulate gene expression through their ability to bind to acetylated chromatin and subsequently activate RNA PolII-driven transcriptional elongation. Small molecule BET inhibitors prevent binding of BET proteins to acetylated histones and inhibit transcriptional activation of BET target genes. BET inhibitors attenuate cell growth and survival in several hematologic cancer models, partially through the down-regulation of the critical oncogene, MYC. We hypothesized that BET inhibitors will regulate MYC expression in solid tumors that frequently over-express MYC. Here we describe the effects of the highly specific BET inhibitor, I-BET762, on MYC expression in prostate cancer models. I-BET762 potently reduced MYC expression in prostate cancer cell lines and a patient-derived tumor model with subsequent inhibition of cell growth and reduction of tumor burden in vivo. Our data suggests that I-BET762 effects are partially driven by MYC down-regulation and underlines the critical importance of additional mechanisms of I-BET762 induced phenotypes.

Show MeSH
Related in: MedlinePlus