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...

We searched for genetic alterations in human B cell lymphoma that affect the ubiquitin-proteasome system. This approach identified FBXO25 within a minimal common region of frequent deletion in mantle cell lymphoma (MCL). FBXO25 encodes an orphan F-box protein that determines the substrate specificity of the SCF (SKP1-CUL1-F-box)(FBXO25) ubiquitin ligase complex. An unbiased screen uncovered the prosurvival protein HCLS1-associated protein X-1 (HAX-1) as the bona fide substrate of FBXO25 that is targeted after apoptotic stresses. Protein kinase Cδ (PRKCD) initiates this process by phosphorylating FBXO25 and HAX-1, thereby spatially directing nuclear FBXO25 to mitochondrial HAX-1. Our analyses in primary human MCL identify monoallelic loss of FBXO25 and stabilizing HAX1 phosphodegron mutations. Accordingly, FBXO25 re-expression in FBXO25-deleted MCL cells promotes cell death, whereas expression of the HAX-1 phosphodegron mutant inhibits apoptosis. In addition, knockdown of FBXO25 significantly accelerated lymphoma development in Eμ-Myc mice and in a human MCL xenotransplant model. Together we identify a PRKCD-dependent proapoptotic mechanism controlling HAX-1 stability, and we propose that FBXO25 functions as a haploinsufficient tumor suppressor and that HAX1 is a proto-oncogene in MCL.

R e s e a R c h a R t i c l e5. Group 2 correlated with high STAT3 expression (i.e., STAT3 activation). (G) GSEA showed a significantly different distribution of the STAT3 activation-associated genes, with group 1 being negatively correlated (NES, -1.97; P < 0.001). Figure 1A; supplemental material available online with this article; doi:10.1172/JCI69094DS1). Gene set enrichment analysis (GSEA) showed a significantly different distribution of the STAT3 activation-associated genes among the hierarchical clustering-defined gene expression groups (normalized enrichment score [NES], -1.97; nominal P < 0.001; Figure 1G). In addition, mining the public repository Oncomine (www.oncomine. org) showed that STAT3 target genes were elevated in MM versus control tissue (Supplemental Figure 1B). Furthermore, we found the STAT3 signaling gene expression pattern to be associated with low bone disease, the MMSET groups, and the presence of a gain of the 1q21 locus, whereas we identified an inverse correlation with hyperdiploid disease (Supplemental Figure 1, C-E). Thus, STAT3 phosphorylation and target gene activation seems to be a major hallmark of a large subgroup of human MM. Constitutive GP130 signaling induces myeloma formation in a murine BM transduction-transplantation model. To test whether constitutive activation of GP130 signaling enables B cells to proliferate independently of cytokine stimulation, the IL-3-dependent Analysis of the malignant plasma cells revealed a t(12;15) translocation involving c-Myc (16). While Eμ-Myc transgenic mice (in which MYC expression is under control of the Eμ enhancer) develop aggressive pro-/pre-B cell lymphomas early in life (17), activationinduced deaminase-dependent expression of MYC in germinal center B cells leads to a high incidence of MM with a median survival of approximately 2 years (4). Transgenic mice expressing abnormally high levels of XBP-1, a protein involved in the terminal differentiation of B cells, develop monoclonal gammopathy of undetermined significance (MGUS), and some develop MM later in life (18). The Journal of Clinical Investigation R e s e a R c h a R t i c l e5In the present study, we showed that constitutive activation of GP130/JAK/STAT3 signal transduction in a retroviral murine BM transduction-transplantation model was sufficient to induce or facilitate MM development in mice. This model was characterized by very high penetrance and relatively short latency. Importantly, constitutive GP130 activation efficiently cooperated with MYC overexpression by driving cell growth and differentiation of malignant plasma cells. Our data indicate that constitutive GP130 signal transduction is a critical early step in myelomagenesis. Results STAT3 phosphorylation and target gene activation is a hallmark of human MM.Activation of the IL-6/IL-6R/GP130 complex is crucial for survival and proliferation of human myeloma (6,11,13), and the JAK/STAT3 pathway is a major target downstream of IL-6R/GP130 signaling (8,14). We therefore evaluated a series of BM biopsies from pati...

Drug efficacy strongly depends on the presence of the drug substance at the target site. As vascularization is an important factor for the distribution of drugs in tissues, we analyzed drug distribution as a function of blood vessel localization in tumor tissue. To explore distribution of the anticancer drugs afatinib, erlotinib, and sorafenib, a combined approach of matrix-assisted laser desorption/ionization (MALDI) drug imaging and immunohistochemical vessel staining was applied and examined by digital image analysis. The following two xenograft models were investigated: (1) mice carrying squamous cell carcinoma (FaDu) xenografts (ntumor = 13) were treated with afatinib or erlotinib, and (2) sarcoma (A673) xenograft bearing mice (ntumor = 8) received sorafenib treatment. MALDI drug imaging revealed a heterogeneous distribution of all anticancer drugs. The tumor regions containing high drug levels were associated with a higher degree of vascularization than the regions without drug signals (p < 0.05). When correlating the impact of blood vessel size to drug abundance in the sarcoma model, a higher amount of small vessels was detected in the tumor regions with high drug levels compared to the tumor regions with low drug levels (p < 0.05). With the analysis of coregistered MALDI imaging and CD31 immunohistochemical data by digital image analysis, we demonstrate for the first time the potential of correlating MALDI drug imaging and immunohistochemistry. Here we describe a specific and precise approach for correlating histological features and pharmacokinetic properties of drugs at microscopic level, which will provide information for the improvement of drug design, administration formula or treatment schemes.