gsk1210151a and Multiple-Myeloma

The bromodomain and extra-terminal (BET) family of proteins, consisting of the bromodomains containing protein 2 (BRD2), BRD3, BRD4, and the testis-specific BRDT, are key epigenetic regulators of gene transcription and has emerged as an attractive target for anticancer therapy. Herein, we describe the discovery of a novel potent BET bromodomain inhibitor, using a systematic structure-based approach focused on improving potency, metabolic stability, and permeability. The optimized dimethylisoxazole aryl-benzimidazole inhibitor exhibited high potency towards BRD4 and related BET proteins in biochemical and cell-based assays and inhibited tumor growth in two proof-of-concept preclinical animal models.

Topics: Administration, Oral; Animals; Benzimidazoles; Biological Availability; Cell Line, Tumor; Cell Proliferation; Cell Survival; Dose-Response Relationship, Drug; Drug Discovery; Humans; Isoxazoles; Mice; Molecular Structure; Multiple Myeloma; Neoplasms, Experimental; Protein Domains; Structure-Activity Relationship; Transcription Factors

Topics: Animals; Cell Cycle Proteins; Cells, Cultured; Cytokines; Heterocyclic Compounds, 4 or More Rings; Humans; Mice; Multiple Myeloma; NF-kappa B; Osteoclasts; Osteogenesis; RANK Ligand; RAW 264.7 Cells; Signal Transduction; Transcription Factors; Tumor Cells, Cultured

Bromodomain and extraterminal protein (BET) inhibitors suppress the expression of c-MYC. U266, a human myeloma cell line, expresses the MYCL gene, but not the c-MYC gene. Our aim was to analyse the antimyeloma activity of BET inhibitors on U266 cells. Two BET inhibitors, I-BET151 and JQ1, were tested. U266 cell proliferation decreased to 61.5 and 54.0% of the control after incubation with 500 nmol/l I-BET151 for 72 and 96 h and to 53.5 and 56.4% of control after incubation with 500 nmol/l JQ1 for 72 and 96 h by MTS tetrazolium, respectively. BET inhibitors induced cell cycle arrest at the G1 phase in U266 cells, but did not induce apoptosis by flow cytometry. According to Gene Set Enrichment Analysis, MYC-related genes were significantly downregulated in U266 cells treated with I-BET151 similar to KMS11 cells that expressed c-MYC. The MYCL1 was expressed in U266 cells, whereas c-MYC and MYCN were not by quantitative real-time reverse-transcription-PCR. Incubation with I-BET151 induced downregulation of MYCL1 in U266 cells. BET inhibitors decreased the cell proliferation in U266 cells with overexpression of MYCL less than those without overexpression of MYCL. BET inhibitors induce G1 arrest without apoptosis and interfere with the proliferation of U266 myeloma cells, which express MYCL, but not c-MYC. BET inhibitors might be active in cancers that express MYCL, but not c-MYC.

Topics: Antineoplastic Agents; Azepines; Cell Line, Tumor; Cell Proliferation; Down-Regulation; Gene Expression Regulation, Neoplastic; Heterocyclic Compounds, 4 or More Rings; Humans; Molecular Targeted Therapy; Multiple Myeloma; N-Myc Proto-Oncogene Protein; Protein Domains; Proto-Oncogene Proteins c-myc; Triazoles

The bromodomain and extraterminal (BET) protein BRD2-4 inhibitors hold therapeutic promise in preclinical models of hematologic malignancies. However, translation of these data to molecules suitable for clinical development has yet to be accomplished. Herein we expand the mechanistic understanding of BET inhibitors in multiple myeloma by using the chemical probe molecule I-BET151. I-BET151 induces apoptosis and exerts strong antiproliferative effect in vitro and in vivo. This is associated with contrasting effects on oncogenic MYC and HEXIM1, an inhibitor of the transcriptional activator P-TEFb. I-BET151 causes transcriptional repression of MYC and MYC-dependent programs by abrogating recruitment to the chromatin of the P-TEFb component CDK9 in a BRD2-4-dependent manner. In contrast, transcriptional upregulation of HEXIM1 is BRD2-4 independent. Finally, preclinical studies show that I-BET762 has a favorable pharmacologic profile as an oral agent and that it inhibits myeloma cell proliferation, resulting in survival advantage in a systemic myeloma xenograft model. These data provide a strong rationale for extending the clinical testing of the novel antimyeloma agent I-BET762 and reveal insights into biologic pathways required for myeloma cell proliferation.

Topics: Animals; Antineoplastic Agents; Apoptosis; Benzodiazepines; Cell Cycle Checkpoints; Down-Regulation; Heterocyclic Compounds, 4 or More Rings; Humans; Mice; Multiple Myeloma; Proto-Oncogene Proteins c-myc; RNA-Binding Proteins; Transcription Factors; Transcriptional Activation; Tumor Cells, Cultured