Project description:BRD4, a member of the BET family of histone readers, binds to acetylated lysine of histone H3 and promotes assembly of super-enhancer complexes that drive expression of key oncogenes in acute myeloid leukemia (AML) and other cancers. ARV-825 is a proteolysis-targeting chimera (PROTAC) that targets BRD4 for CRBN-mediated ubiquitination and degradation. We treated the AML cell line OCI-AML3, as well as primary tumor cells from a case of AML, with ARV-825 in vitro. At low concentrations, ARV-825 caused profound and sustained reduction in BRD4 protein levels. This caused reduction in transcription of key genes including MYC, anti-apoptotic BCL2 and BCLXL, PIM1, and CD44. Downstream effects included loss of CXCR4 surface expression and mitochondrial respiration; increased reactive oxygen species; toxicity to AML cells in vitro; and efficacy vs. OCI-AML3 cells in a mouse model of AML.
Project description:BRD4, a member of the BET family of histone readers, binds to acetylated lysine of histone H3 and promotes assembly of super-enhancer complexes that drive expression of key oncogenes in acute myeloid leukemia (AML) and other cancers. ARV-825 is a proteolysis-targeting chimera (PROTAC) that targets BRD4 for CRBN-mediated ubiquitination and degradation. BM-MSCs are an important element of the bone marrow microenvironment of AML. To understand how targeting BRD4 in BM-MSCs may contribute to the overall effect on AML of targeting BRD4, we treated BM-MSCs from two normal donors with ARV-825 in vitro. Treatment of BM-MSC monocultures with ARV-825 for 24 hr caused extensive changes in gene expression, highly uniform between triplicates. Although the cultures from the two normal donors showed different profiles, their changes with ARV-825 were highly similar. These changes implicated effects on oxidative stress, osteogenic differentiation, retinoid metabolism, F-actin polymerization, CXCL12, and proliferation.
Project description:Epigenetic pathways regulate gene expression by controlling and interpreting chromatin modifications. Cancer cells are characterized by altered epigenetic landscapes and commonly exploit the chromatin regulatory machinery to enforce oncogenic gene expression programs. While chromatin alterations are, in principle, reversible and often amendable to drug intervention, the promise of targeting such pathways therapeutically has been hampered by our limited understanding of cancer-specific epigenetic dependencies. Here we describe a non-biased approach to probe epigenetic vulnerabilities in acute myeloid leukemia (AML) – an aggressive hematopoietic malignancy often associated with aberrant chromatin states. By screening a custom shRNA library targeting known chromatin regulators in a genetically defined AML mouse model, we identify the bromodomain-containing protein Brd4 as a critical requirement for disease maintenance. Suppression of Brd4 using shRNAs or the small-molecule inhibitor JQ1 led to robust anti-leukemic effects in vitro and in vivo, accompanied by terminal myeloid differentiation. Extensive evaluation of JQ1-sensitivity in primary human leukemia samples and in established cell lines revealed a broad activity of this compound against diverse AML subtypes. These effects are, at least in part, due to a requirement for Brd4 in maintaining Myc expression and promoting aberrant self-renewal. Together, our results indicate that Brd4 is a promising therapeutic target in AML and identify a small molecule that efficiently targets Myc. These findings also highlight the utility of RNAi screening as a discovery platform for revealing epigenetic vulnerabilities for direct pharmacologic intervention in cancer. In order to understand downstream targets of Brd4, we performed array in murine or human MLL-AF9/NrasG12D cell line under the condition that Brd4 was suppressed by using shRNAs or the small molecule inhibitor JQ1. To test the hypothesis that Myc might be an important target of Brd4, we performed arrary on murine ectopic Myc overexpression MLL-AF9/NrasG12D cell under JQ1 treatment.
Project description:We identified differential gene expression after treatment with BRD4-PROTAC ARV771 in two ABC-like diffuse large B-cella lymphoma cell lines. We have identified cluster of gene expression regulated after BRD4 inhibition which are criticaly important for DLBCL malignancy.
Project description:Acute myeloid leukemia (AML) represents an aggressive hematopoietic malignancy with a prognosis inferior to that of other leukemias. Recent targeted therapies offer new opportunities to achieve better treatment outcomes. However, due to the complex heterogeneity of AML, its prognosis is remain dismal. In this study, we first identified the correlation between high expression of BRD4 and overall survival of AML patients. Targeted degradation of BRD2, BRD3, and BRD4 proteins by dBET1, a PROTAC against BET family members, showed cytotoxic effects on Kasumi (AML1-ETO), NB4 (PML-RARa), THP-1 (MLL-AF9), and MV4-11 (MLL-AF4) AML cell lines representing different molecular subtypes of AML. Furthermore, we determined that dBET1 treatment arrested cell cycling and enhanced apoptosis and c-MYC as the downstream target. Collectively, our results indicated that dBET1 has broad cytotoxic effects on AML cells with different molecular lesions and provide more benefits to AML patients.
Project description:Epigenetic pathways regulate gene expression by controlling and interpreting chromatin modifications. Cancer cells are characterized by altered epigenetic landscapes and commonly exploit the chromatin regulatory machinery to enforce oncogenic gene expression programs. While chromatin alterations are, in principle, reversible and often amendable to drug intervention, the promise of targeting such pathways therapeutically has been hampered by our limited understanding of cancer-specific epigenetic dependencies. Here we describe a non-biased approach to probe epigenetic vulnerabilities in acute myeloid leukemia (AML) – an aggressive hematopoietic malignancy often associated with aberrant chromatin states. By screening a custom shRNA library targeting known chromatin regulators in a genetically defined AML mouse model, we identify the bromodomain-containing protein Brd4 as a critical requirement for disease maintenance. Suppression of Brd4 using shRNAs or the small-molecule inhibitor JQ1 led to robust anti-leukemic effects in vitro and in vivo, accompanied by terminal myeloid differentiation. Extensive evaluation of JQ1-sensitivity in primary human leukemia samples and in established cell lines revealed a broad activity of this compound against diverse AML subtypes. These effects are, at least in part, due to a requirement for Brd4 in maintaining Myc expression and promoting aberrant self-renewal. Together, our results indicate that Brd4 is a promising therapeutic target in AML and identify a small molecule that efficiently targets Myc. These findings also highlight the utility of RNAi screening as a discovery platform for revealing epigenetic vulnerabilities for direct pharmacologic intervention in cancer.
Project description:The RNA decapping scavenger, DcpS, has recently been identified as a dependency in acute myeloid leukemia. The potent DcpS inhibitor RG3039 attenuates AML cell viability, and shRNA knockdown of DcpS is also antiproliferative. Importantly, DcpS was found to be non-essential in normal human hematopoietic cells, which opens a therapeutic window for AML treatment by modulation of DcpS. Considering this strong dependence of AML cell lines on DcpS, we wanted to explore PROTAC-mediated degradation as an alternative strategy to modulate DcpS activity. Herein, we report the development of JCS-1, the first PROTAC capable of degrading an mRNA-decapping enzyme. JCS-1 non-covalently binds DcpS with an RG3039-based warhead and recruits the E3 ligase VHL, which induces potent, rapid, and sustained DcpS degradation in several AML cell lines. JCS-1 will serve as a chemical biology tool to interrogate DcpS function in different cellular contexts and may be an applicable strategy for the treatment of AML and other DcpS-dependent genetic disorders.
Project description:Targeted protein degradation is a groundbreaking modality in drug discovery ; however, the regulatory mechanisms are still not fully understood. Here, we identify cellular signaling pathways that modulate the targeted degradation of the anticancer target BRD4 and related hard-to-degrade targets BRD2/3 induced by CRL2VHL- or CRL4CRBN -based PROTACs. The chemicals identified as degradation enhancers include inhibitors of cellular signaling pathways such as poly-ADP ribosylation (PARG inhibitor PDD00017273), unfolded protein response (PERK inhibitor GSK2606414), and protein stabilization (HSP90 inhibitor luminespib). Mechanistically, PARG inhibition promotes TRIP12-mediated K29/K48-linked branched ubiquitylation of BRD4 by facilitating chromatin dissociation of BRD4 and formation of the BRD4–PROTAC–CRL2VHL ternary complex; by contrast, HSP90 inhibition promotes BRD4 degradation after the ubiquitylation step. Consequently, these signal inhibitors sensitize cells to the PROTAC-induced apoptosis. These results suggest that various cell-intrinsic signaling pathways spontaneously counteract chemically induced target degradation at multiple steps, which could be liberated by specific inhibitors.
Project description:AURKA is a potential kinase target in various malignancies. The kinase-independent oncogenic functions partially disclose the inadequate efficacy of the kinase inhibitor in a Phase III clinical trial. Simultaneously targeting the catalytic and noncatalytic functions of AURKA may be a feasible approach. Here, a set of AURKA proteolysis targeting chimeras (PROTACs) are developed. The CRBN-based dAurA383 preferentially degrades the highly abundant mitotic AURKA, while cIAP-based dAurA450 degrades the lowly abundant interphase AURKA in acute myeloid leukemia (AML) cells. The proteomic and transcriptomic analyses indicate that dAurA383 triggers the "mitotic cell cycle" and "stem cell" processes, while dAurA450 inhibits the "MYC/E2F targets" and "stem cell" processes. dAurA383 and dAurA450 are combined as a PROTAC cocktail. The cocktail effectively degrades AURKA, relieves the hook effect, and synergistically inhibits AML stem cells. Furthermore, the PROTAC cocktail induces AML regression in a xenograft mouse model and primary patient blasts. These findings establish the PROTAC cocktail as a promising spatial-temporal drug administration strategy to sequentially eliminate the multifaceted functions of oncoproteins, relieve the hook effect, and prevent cancer stem cell-mediated drug resistance.