Discovery of BRM Targeted Therapies: Novel Reactivation of an Anti-cancer Gene
TL;DR: A cell-based luciferase assay was developed to identify BRM-restoring compounds, and it was shown that restoring BRM expression is not only feasible, but potentially a potent form of anticancer therapy.
Abstract: Drug discovery in the field of oncology has been advanced mainly through the targeting of receptor tyrosine kinases. Both antibodies and small molecule inhibitors have been found to have successful applications in blocking the proliferative functions of these cell surface receptors. Based on these early successes, additional kinases within the cytoplasm have been found to promote cancer and, as such, have been recognized as feasible targets for additional modes of therapies. Unlike these oncogene targets, most tumor suppressors are irreversibly altered during cancer progression and therefore are not feasible targets for therapy. However, a subset of these genes is reversibly epigenetically suppressed. One such gene is BRM, and when it is re-expressed in cancer cells, this gene halts their growth. Moreover, as the key catalytic subunit of the SWI/SNF complex, BRM is centrally important to a host of anticancer pathways and cellular mechanisms, and its status may serve as a biomarker. Restoring its expression will both reconnect a number of growth-controlling pathways and affect cellular adhesion, DNA repair, and immune functions. For these reasons, restoring BRM expression is not only feasible, but potentially a potent form of anticancer therapy. To identify BRM-restoring compounds, we developed a cell-based luciferase assay. In this review, we discuss some of the challenges we encountered, issues related to this type of drug discovery, and our future ambitions. We hope this review will provide insight to this type of endeavor and lead to more investigations pursuing this type of drug research.
Citations
More filters
TL;DR: SMARCA4-deficient thoracic sarcomas can be identified based on their distinctive high-grade rhabdoid morphology, and the diagnosis can be confirmed by immunohistochemistry.
118 citations
TL;DR: Concomitant loss of SMARCA2 andSMARCA4 is another hallmark of small cell carcinoma of the ovary, hypercalcemic type—a finding that offers new opportunities for therapeutic interventions.
55 citations
TL;DR: It is shown that BRM is regulated by transcription, thus demonstrating that the promoter region is important for BRM expression, and an increased risk of lung cancer when both BRM homozygous promoter insertion variants were present.
Abstract: Two novel BRM insertion promoter sequence variants are associated with loss of BRM expression and lung cancer risk
50 citations
Additional excerpts
...As in previous separate analyses, we had identified several additional promising compounds that promoted the re-expression of BRM (Gramling and Reisman, 2011) pharmacological methods of the future may modulate or reduce lung cancer risk in high-risk, homozygous variant-carrying smokers, through the…...
[...]
...As in previous separate analyses, we had identified several additional promising compounds that promoted the re-expression of BRM (Gramling and Reisman, 2011) pharmacological methods of the future may modulate or reduce lung cancer risk in high-risk, homozygous variant-carrying smokers, through the restoration of BRM function....
[...]
TL;DR: This work selectively knocked down GATA3, MEF2D, HDAC3 and HDAC9, and found that each gene-specific knockdown induced growth inhibition and identified a cadre of key proteins, which underlie the epigenetic regulation of BRM.
Abstract: Brahma (BRM) is a novel anticancer gene, which is frequently inactivated in a variety of tumor types. Unlike many anticancer genes, BRM is not mutated, but rather epigenetically silenced. In addition, histone deacetylase complex (HDAC) inhibitors are known to reverse BRM silencing, but they also inactivate it via acetylation of its C-terminus. High-throughput screening has uncovered many compounds that are effective at pharmacologically restoring BRM and thereby inhibit cancer cell growth. As we do not know which specific proteins, if any, regulate BRM, we sought to identify the proteins, which underlie the epigenetic suppression of BRM. By selectively knocking down each HDAC, we found that HDAC3 and HDAC9 regulate BRM expression, whereas HDAC2 controls its acetylation. Similarly, we ectopically overexpressed 21 different histone acetyltransferases and found that KAT6A, KAT6B and KAT7 induce BRM expression, whereas KAT2B and KAT8 induce its acetylation. We also investigated the role of two transcription factors (TFs) linked to either BRM (GATA3) or HDAC9 (MEF2D) expression. Knockdown of either GATA3 and/or MEF2D downregulated HDAC9 and induced BRM. As targets for molecular biotherapy are typically uniquely, or simply differentially expressed in cancer cells, we also determined if any of these proteins are dysregulated. However, by sequencing, no mutations were found in any of these BRM-regulating HDACs, HATs or TFs. We selectively knocked down GATA3, MEF2D, HDAC3 and HDAC9, and found that each gene-specific knockdown induced growth inhibition. We observed that both GATA3 and HDAC9 were greatly overexpressed only in BRM-negative cell lines indicating that HDAC9 may be a good target for therapy. We also found that the mitogen-activated protein (MAP) kinase pathway regulates both BRM acetylation and BRM silencing as MAP kinase pathway inhibitors both induced BRM as well as caused BRM deacetylation. Together, these data identify a cadre of key proteins, which underlie the epigenetic regulation of BRM.
49 citations
TL;DR: Evidence from the literature is presented that these enzymes have both causal and enabling roles in the transition to advanced stage cancers; as such, they should be seriously considered as high-value therapeutic targets.
Abstract: The progression to advanced stage cancer requires changes in many characteristics of a cell. These changes are usually initiated through spontaneous mutation. As a result of these mutations, gene expression is almost invariably altered allowing the cell to acquire tumor-promoting characteristics. These abnormal gene expression patterns are in part enabled by the posttranslational modification and remodeling of nucleosomes in chromatin. These chromatin modifications are established by a functionally diverse family of enzymes including histone and DNA-modifying complexes, histone deposition pathways, and chromatin remodeling complexes. Because the modifications these enzymes deposit are essential for maintaining tumor-promoting gene expression, they have recently attracted much interest as novel therapeutic targets. One class of enzyme that has not generated much interest is the chromatin remodeling complexes. In this review, we will present evidence from the literature that these enzymes have both causal and enabling roles in the transition to advanced stage cancers; as such, they should be seriously considered as high-value therapeutic targets. Previously published strategies for discovering small molecule regulators to these complexes are described. We close with thoughts on future research, the field should perform to further develop this potentially novel class of therapeutic target.
45 citations
References
More filters
TL;DR: A screening window coefficient, called "Z- factor," is defined, which is reflective of both the assay signal dynamic range and the data variation associated with the signal measurements, and therefore is suitable for assay quality assessment.
Abstract: The ability to identify active compounds (³hits²) from large chemical libraries accurately and rapidly has been the ultimate goal in developing high-throughput screening (HTS) assays. The ability to identify hits from a particular HTS assay depends largely on the suitability or quality of the assay used in the screening. The criteria or parameters for evaluating the ³suitability² of an HTS assay for hit identification are not well defined and hence it still remains difficult to compare the quality of assays directly. In this report, a screening window coefficient, called ³Z-factor,² is defined. This coefficient is reflective of both the assay signal dynamic range and the data variation associated with the signal measurements, and therefore is suitable for assay quality assessment. The Z-factor is a dimensionless, simple statistical characteristic for each HTS assay. The Z-factor provides a useful tool for comparison and evaluation of the quality of assays, and can be utilized in assay optimization and validation.
6,474 citations
TL;DR: It is concluded that the Z score transformation normalization method accompanied by either Z ratios or Z tests for significance estimates offers a useful method for the basic analysis of microarray data.
896 citations
TL;DR: Evidence is presented that Rb forms a repressor containing histone deacetylase (HDAC) and the hSWI/SNF nucleosome remodeling complex, which inhibits transcription of genes for cyclins E and A and arrests cells in the G1 phase of the cell cycle.
670 citations
TL;DR: Using the yeast two-hybrid system, it is found that RB bound specifically to the protein BRG1, which shares extensive sequence similarity to Drosophila brahma, an activator of homeotic gene expression, and the yeast transcriptional activator SNF2/SW12.
648 citations
TL;DR: A substantial body of evidence indicates that several components of the SWI/SNF complexes function as tumor suppressors, with particular emphasis upon the two catalytic subunits of the NWF complexes, BRM and BRG1.
Abstract: The mammalian SWI/SNF complexes mediate ATP-dependent chromatin remodeling processes that are critical for differentiation and proliferation. Not surprisingly, loss of SWI/SNF function has been associated with malignant transformation, and a substantial body of evidence indicates that several components of the SWI/SNF complexes function as tumor suppressors. This review summarizes the evidence that underlies this conclusion, with particular emphasis upon the two catalytic subunits of the SWI/SNF complexes, BRM, the mammalian ortholog of SWI2/SNF2 in yeast and brahma in Drosophila, and Brahma-related gene-1 (BRG1).
556 citations