BET and HDAC inhibitors induce similar genes and biological effects and synergize to kill in Myc-induced murine lymphoma

Abstract

The bromodomain and extraterminal (BET) domain family of proteins binds to acetylated lysines on histones and regulates gene transcription. Recently, BET inhibitors (BETi) have been developed that show promise as potent anticancer drugs against various solid and hematological malignancies. Here we show that the structurally novel and orally bioavailable BET inhibitor RVX2135 inhibits proliferation and induces apoptosis of lymphoma cells arising in Myctransgenic mice in vitro and in vivo. We find that BET inhibition exhibits broad transcriptional effects in Myc-transgenic lymphoma cells affecting many transcription factor networks. By examining the genes induced by BETi, which have largely been ignored to date, we discovered that these were similar to those induced by histone deacetylase inhibitors (HDACi). HDACi also induced cell-cycle arrest and cell death of Myc-induced murine lymphoma cells and synergized with BETi. Our data suggest that BETi sensitize Myc-overexpressing lymphoma cells partly by inducing HDAC-silenced genes, and suggest synergistic and therapeutic combinations by targeting the genetic link between BETi and HDACi.T he bromodomain and extraterminal (BET) domain family of proteins Brd2, Brd3, Brd4, and BrdT bind via their tandem bromodomains (BD1 and BD2) to acetylated lysines in histones and other proteins (1). On binding, they regulate the transcription of genes critical for cell-cycle progression and apoptosis. Therefore, BET proteins have emerged as interesting proteins for targeted intervention of cancer.Recently, the small-molecule BET inhibitor (+)-JQ-1 (hereafter JQ1) was found to be a potent and specific suppressor of B cell-lineage malignancies (2, 3). In acute myelogenous leukemia, BRD4 is essential for tumor maintenance, and JQ1 recapitulates the effects of RNA interference of BRD4 (4, 5). JQ1 was subsequently shown to have an antiproliferative effect in other hematological malignancies and solid organ tumors including glioblastoma, prostate cancer, and neuroblastoma (6-10). The current model of how BET inhibitors (BETi) inhibit tumor cell proliferation places inhibition of MYC as mediating activity in lymphoid tumors, with Myc-independent activity in some solid tumor types such as lung adenocarcinoma (11). However, it has not been clear in hematopoietic tumor types whether the antiproliferative effects of BETi are mediated by suppression of MYC expression or whether effects on MYC are a correlative bystander of the mechanism, perhaps useful as a biomarker but not necessarily mechanistic (12).We have assessed the effect of RVX2135, a novel and orally bioavailable selective inhibitor of Brd2, Brd3, Brd4, and BrdT, in in vitro and in vivo models of Myc-induced lymphoma. We find that the effects are mediated by broad transcriptional changes and that these are genetically and functionally linked to histone deacetylase inhibitors. Results RVX2135 Blocks Proliferation of Myc-Induced Mouse Lymphoma Cellsand Induces Caspase-Dependent Apoptosis. RVX2135 is a novel small-molecule BET bromodoma...

The Bromodomain Inhibitor JQ1 and the Histone Deacetylase Inhibitor Panobinostat Synergistically Reduce N-Myc Expression and Induce Anticancer Effects

“…Our study therefore suggests that when neuroblastoma patients are treated with BET bromodomain inhibitors in the future, they may be cotreated with the HDAC inhibitor panobinostat. The finding is consistent with recent reports that the BET bromodomain inhibitor RVX2135 and the HDAC inhibitor vorinostat synergistically kill Myc-induced murine lymphoma cells (20), and that JQ1 and panobinostat synergistically induce leukemia cell apoptosis (6).…”

Targeting BET proteins improves the therapeutic efficacy of BCL-2 inhibition in T-cell acute lymphoblastic leukemia

“…Two T-ALL samples were sensitive at concentrations below 100nM, whereas the remaining cases were more resistant to venetoclax (Supplementary Figure 1B). This variability in venetoclax sensitivity amongst T-ALL patient samples corresponded to large differences in the area under the curve (AUC), a parameter that captures both IC 50 and E max as relevant endpoints of drug activity ( Figure 1B). Next, we generated dose response curves (1nM, 10 nM, 100nM, 1µM and 10µM) for the 21 compounds in the presence or absence of a …”

Dual HDAC and PI3K Inhibitor CUDC-907 Downregulates MYC and Suppresses Growth of MYC-dependent Cancers

“…For example, HDAC inhibitors have been shown to suppress MYC transcription, in part by upregulating the transcription of MYC suppressor genes, such as FOXO1, in some (14)(15)(16)(17) but not all cancer types (18). HDACs also facilitate MYC's oncogenic function as a transcription factor, as they are often recruited to the promoter regions of some MYC-targeted genes to facilitate MYC-mediated regulation of transcription.…”