The BET bromodomain inhibitor JQ1 suppresses growth of pancreatic ductal adenocarcinoma in patient-derived xenograft models

The primary aim of this study was to evaluate the antitumor efficacy of the bromodomain inhibitor JQ1 in pancreatic ductal adenocarcinoma (PDAC) patient-derived xenograft (tumorgraft) models. A secondary aim of the study was to evaluate whether JQ1 decreases expression of the oncogene c-Myc in PDAC tumors, as has been reported for other tumor types. We used five PDAC tumorgraft models that retain specific characteristics of tumors of origin to evaluate the antitumor efficacy of JQ1. Tumor-bearing mice were treated with JQ1 (50 mg/kg daily for 21 or 28 days). Expression analyses were performed with tumors harvested from host mice after treatment with JQ1 or vehicle control. An nCounter PanCancer Pathways Panel (NanoString Technologies) of 230 cancer-related genes was used to identify gene products affected by JQ1. Quantitative RT-PCR, immunohistochemistry and immunoblots were carried out to confirm that changes in RNA expression reflected changes in protein expression. JQ1 inhibited the growth of all five tumorgraft models (P<0.05), each of which harbors a KRAS mutation; but induced no consistent change in expression of c-Myc protein. Expression profiling identified CDC25B, a regulator of cell cycle progression, as one of the three RNA species (TIMP3, LMO2 and CDC25B) downregulated by JQ1 (P<0.05). Inhibition of tumor progression was more closely related to decreased expression of nuclear CDC25B than to changes in c-Myc expression. JQ1 and other agents that inhibit the function of proteins with bromodomains merit further investigation for treating PDAC tumors. Work is ongoing in our laboratory to identify effective drug combinations that include JQ1.

Syntheses and discovery of a novel class of cinnamic hydroxamates as histone deacetylase inhibitors by multimodality molecular imaging in living subjects

Histone deacetylases (HDAC) that regulate gene expression are being explored as cancer therapeutic targets. In this study, we focused on HDAC6 based on its ability to inhibit cancerous Hsp90 chaperone activities by disrupting Hsp90/p23 interactions. To identify novel HDAC6 inhibitors, we used a dual-luciferase reporter system in cell culture and living mice by bioluminescence imaging (BLI). On the basis of existing knowledge, a library of hydrazone compounds was generated for screening by coupling cinnamic hydroxamates with aldehydes and ketones. Potency and selectivity were determined by in vitro HDAC profiling assays, with further evaluation to inhibit Hsp90(α/β)/p23 interactions by BLI. In this manner, we identified compound 1A12 as a dose-dependent inhibitor of Hsp90(α/β)/p23 interactions, UKE-1 myeloid cell proliferation, p21(waf1) upregulation, and acetylated histone H3 levels. 1A12 was efficacious in tumor xenografts expressing Hsp90(α)/p23 reporters relative to carrier control-treated mice as determined by BLI. Small animal (18)F-FDG PET/CT imaging on the same cohort showed that 1A12 also inhibited glucose metabolism relative to control subjects. Ex vivo analyses of tumor lysates showed that 1A12 administration upregulated acetylated-H3 by approximately 3.5-fold. Taken together, our results describe the discovery and initial preclinical validation of a novel selective HDAC inhibitor.

Repression of BIM mediates survival signaling by MYC and AKT in high-risk T-cell acute lymphoblastic leukemia

Treatment resistance in T-cell acute lymphoblastic leukemia (T-ALL) is associated with phosphatase and tensin homolog (PTEN) deletions and resultant phosphatidylinositol 3'-kinase (PI3K)-AKT pathway activation, as well as MYC overexpression, and these pathways repress mitochondrial apoptosis in established T-lymphoblasts through poorly defined mechanisms. Normal T-cell progenitors are hypersensitive to mitochondrial apoptosis, a phenotype that is dependent on the expression of proapoptotic BIM. In a conditional zebrafish model, MYC downregulation induced BIM expression in T-lymphoblasts, an effect that was blunted by expression of constitutively active AKT. In human T-ALL cell lines and treatment-resistant patient samples, treatment with MYC or PI3K-AKT pathway inhibitors each induced BIM upregulation and apoptosis, indicating that BIM is repressed downstream of MYC and PI3K-AKT in high-risk T-ALL. Restoring BIM function in human T-ALL cells using a stapled peptide mimetic of the BIM BH3 domain had therapeutic activity, indicating that BIM repression is required for T-ALL viability. In the zebrafish model, where MYC downregulation induces T-ALL regression via mitochondrial apoptosis, T-ALL persisted despite MYC downregulation in 10% of bim wild-type zebrafish, 18% of bim heterozygotes and in 33% of bim homozygous mutants (P=0.017). We conclude that downregulation of BIM represents a key survival signal downstream of oncogenic MYC and PI3K-AKT signaling in treatment-resistant T-ALL.

Differential transactivation by alternative EWS-FLI1 fusion proteins correlates with clinical heterogeneity in Ewing's sarcoma

The t(11;22)(q24;q12) translocation is present in up to 95% of cases of Ewing's sarcoma and results in the formation of an EWS-FLI1 fusion gene which encodes a chimeric transcription factor. The proximate role of EWS-FLI1 in the pathogenesis of Ewing's sarcoma is thought to involve the activation of as yet largely unknown target genes. Many alternative forms of EWS-FLI1 exist because of variations in the locations of the EWS and FLI1 genomic breakpoints. The most common form, designated "type 1," consists of the first seven exons of EWS joined to exons 6-9 of FLI1 and accounts for approximately 60% of cases. The "type 2" EWS-FLI1 fusion also includes FLI1 exon 5 and is present in another 25%. We and others have observed previously that the type 1 fusion is associated with a significantly better prognosis than the other fusion types. Because EWS-FLI1 is an aberrant transcription factor, we investigated whether these differences in clinical behavior may be correlated to functional differences by comparing transactivation by the type 1 EWS-FLI1 with other types in both heterologous cells (HeLa, NIH3T3) and homologous cells (Ewing's sarcoma cell lines). In a panel of seven Ewing's sarcoma cell lines, we found transactivation of a transiently transfected FLI1-responsive reporter construct to be significantly lower in cell lines with the type 1 fusion than in cell lines with the type 2 fusion (P = 0.003). Cotransfection of the same reporter construct with each of a series of seven EWS-FLI1 expression constructs (corresponding to the two major fusion types and five less common types) also showed that type 1 EWS-FLI1 was a significantly weaker transactivator than the type 2 product in both HeLa and NIH3T3 cells (P = 0.003, and P = 0.033, respectively). Electromobility shift assays showed equivalent binding of the type 1 and type 2 EWS-FLI1 to the consensus FLI1-responsive binding site, indicating that differences in transactivation were not due simply to differences in DNA binding affinity. The finding that the type 1 EWS-FLI1 fusion, associated with less aggressive clinical behavior, encodes a less active chimeric transcription factor may provide the basis for a molecular explanation of clinical heterogeneity in Ewing's sarcoma.

DNA-bend modulation in a repressor-to-activator switching mechanism

Recent discoveries of activator proteins that distort DNA but bear no obvious activation domains have focused attention on the role of DNA structure in transcriptional regulation. Here we describe how the transcription factor MerR can mediate repression as well as activation through stereospecific modulation of DNA structure. The repressor form of MerR binds between the -10 and -35 promoter elements of the bacterial mercury-detoxification genes, PT, allowing RNA polymerase to form an inactive complex with PT and MerR at this stress-inducible promoter. Upon mercuric ion binding, Hg-MerR converts this polymerase complex into the transcriptionally active or 'open' form. We show here that MerR bends DNA towards itself in a manner similar to the bacterial catabolite-activator protein CAP, namely at two loci demarked by DNase I sensitivity, and that the activator conformation, Hg-MeR, relaxes these bends. This activator-induced unbending, when coupled with the previously described untwisting of the operator, remodels the promoter and makes it a better template for the poised polymerase.