29 research outputs found
Cytotoxic effects of bortezomib in myelodysplastic syndrome/acute myeloid leukemia depend on autophagy-mediated lysosomal degradation of TRAF6 and repression of PSMA1
Bortezomib (Velcade) is used widely for
the treatment of various human cancers;
however, its mechanisms of action are
not fully understood, particularly in
myeloid malignancies. Bortezomib is a
selective and reversible inhibitor of the
proteasome. Paradoxically, we find that
bortezomib induces proteasomeindependent
degradation of the TRAF6
protein, but not mRNA, in myelodysplastic
syndrome (MDS) and acute myeloid
leukemia (AML) cell lines and primary
cells. The reduction in TRAF6 protein coincides
with bortezomib-induced autophagy,
and subsequently with apoptosis
in MDS/AML cells. RNAi-mediated
knockdown of TRAF6 sensitized
bortezomib-sensitive and -resistant cell
lines, underscoring the importance of
TRAF6 in bortezomib-induced cytotoxicity.
Bortezomib-resistant cells expressing
an shRNA targeting TRAF6 were
resensitized to the cytotoxic effects of
bortezomib due to down-regulation of the
proteasomal subunit -1 (PSMA1). To determine
the molecular consequences of
loss of TRAF6 in MDS/AML cells, in the
present study, we applied gene-expression
profiling and identified an apoptosis
gene signature. Knockdown of TRAF6 in
MDS/AML cell lines or patient samples
resulted in rapid apoptosis and impaired
malignant hematopoietic stem/progenitor
function. In summary, we describe
herein novel mechanisms by which
TRAF6 is regulated through bortezomib/
autophagy\u2013mediated degradation and by
which it alters MDS/AML sensitivity to
bortezomib by controlling PSMA1 expressio
Constitutive IRAK4 Activation Underlies Poor Prognosis and Chemoresistance in Pancreatic Ductal Adenocarcinoma
PURPOSE: Aberrant activation of the NF-κB transcription factors underlies the aggressive behavior and poor outcome of pancreatic ductal adenocarcinoma (PDAC). However, clinically effective and safe NF-κB inhibitors are not yet available. Because NF-κB transcription factors can be activated by the Interleukin-1 Receptor-Associated Kinase (IRAK) downstream of the Toll-like receptors (TLRs), but has not been explored in PDAC, we sought to investigate the role of IRAK in the pathobiology of PDAC. EXPERIMENTAL DESIGN: We examined the phosphorylation status of IRAK4 (p-IRAK4), the master regulator of TLR signaling, in PDAC cell lines, in surgical samples and commercial tissue microarray. We then performed functional studies using small molecule IRAK1/4 inhibitor, RNA-interference and CRISPR/Cas9n techniques to delineate the role of IRAK4 in NF-κB activity, chemoresistance, cytokine production and growth of PDAC cells in vitro and in vivo. RESULTS: p-IRAK4 staining was detectable in the majority of PDAC lines and about 60% of human PDAC samples. Presence of p-IRAK4 strongly correlated with phospho-NF-κB/p65 staining in PDAC samples and is predictive of postoperative relapse and poor overall survival. Inhibition of IRAK4 potently reduced NF-κB activity, anchorage-independent growth, chemoresistance and secretion of pro-inflammatory cytokines from PDAC cells. Both pharmacologic suppression and genetic ablation of IRAK4 greatly abolished PDAC growth in mice and augmented the therapeutic effect of gemcitabine by promoting apoptosis, reducing tumor cell proliferation and tumor fibrosis. CONCLUSIONS: Our data established IRAK4 as a novel therapeutic target for PDAC treatment. Development of potent IRAK4 inhibitors is needed for clinical testing
AZD5153: a novel bivalent BET bromodomain inhibitor highly active against hematologic malignancies
The bromodomain and extraterminal (BET) protein BRD4 regulates gene expression via recruitment of transcriptional regulatory complexes to acetylated chromatin. Pharmacological targeting of BRD4 bromodomains by small-molecule inhibitors has proven to be an effective means to disrupt aberrant transcriptional programs critical for tumor growth and/or survival. Herein, we report AZD5153, a potent, selective, and orally available BET/BRD4 bromodomain inhibitor possessing a bivalent binding mode. Unlike previously described monovalent inhibitors, AZD5153 ligates two bromodomains in BRD4 simultaneously. The enhanced avidity afforded through bivalent binding translates into increased cellular and antitumor activity in preclinical hematologic tumor models. In vivo administration of AZD5153 led to tumor stasis or regression in multiple xenograft models of Acute Myeloid Leukemia (AML), Multiple Myeloma (MM), and Diffuse Large B-cell Lymphoma (DLBCL). The relationship between AZD5153 exposure and efficacy suggests that prolonged BRD4 target coverage is a primary efficacy driver. AZD5153 treatment markedly impacts transcriptional programs of MYC, E2F, and mTOR. Of note, mTOR pathway modulation is associated with cell line sensitivity to AZD5153. Transcriptional modulation of MYC and HEXIM1 was confirmed in AZD5153-treated human whole blood, thus supporting their use as clinical pharmacodynamic biomarkers. This report establishes AZD5153 as a highly potent, orally available BET/BRD4 inhibitor and provides rationale for clinical development in hematologic malignancies