ag-490 and Lymphoma--Large-B-Cell--Diffuse

Survivin and STAT3 pathway have been reported to be important for the growth of diffuse large B-cell lymphoma (DLBCL) cells. Here we investigated the antitumor activity of sepantronium bromide (YM155), a survivin suppressant, in combination with STAT3 inhibitors in DLBCL cell lines in vitro. YM155 synergistically enhanced STAT3 inhibitors (AG490 and STA-21)-induced apoptosis in DLBCL cell lines. Moreover, rituximab, which shows inhibitory activity against STAT3, also sensitized DLBCL cell lines to YM155 regardless of sensitivity to rituximab. These results suggest that combining the inhibition of survivin with STAT3 pathway is an attractive and potentially effective way for the treatment of DLBCL.

Topics: Antineoplastic Agents; Apoptosis; Blotting, Western; Cell Cycle; Cell Proliferation; Drug Synergism; Drug Therapy, Combination; Flow Cytometry; Humans; Imidazoles; Inhibitor of Apoptosis Proteins; Lymphoma, Large B-Cell, Diffuse; Naphthoquinones; Polycyclic Compounds; STAT3 Transcription Factor; Survivin; Tumor Cells, Cultured; Tyrphostins

Diffuse large B-cell lymphoma (DLBCL) consists of at least 2 phenotypic subtypes; that is, the germinal center B-cell-like (GCB-DLBCL) and the activated B-cell-like (ABC-DLBCL) groups. It has been shown that GCB-DLBCL responds favorably to chemotherapy and expresses high levels of BCL6, a transcription repressor known to play a causative role in lymphomagenesis. In comparison, ABC-DLBCL has lower levels of BCL6, constitutively activated nuclear factor-kappaB, and tends to be refractory to chemotherapy. Here, we report that the STAT3 gene is a transcriptional target of BCL6. As a result, high-level STAT3 expression and activation are preferentially detected in ABC-DLBCL and BCL6-negative normal germinal center B cells. Most importantly, inactivating STAT3 by either AG490 or small interference RNA in ABC-DLBCL cells inhibits cell proliferation and triggers apoptosis. These phenotypes are accompanied by decreased expression of several known STAT3 target genes, including c-Myc, JunB, and Mcl-1, and increased expression of the cell- cycle inhibitor p27. In addition to identifying STAT3 as a novel BCL6 target gene, our results define a second oncogenic pathway, STAT3 activation, which operates in ABC-DLBCL, suggesting that STAT3 may be a new therapeutic target in these aggressive lymphomas.

Topics: Base Sequence; Cell Line, Tumor; Cell Proliferation; Cell Survival; DNA-Binding Proteins; Gene Expression Regulation; Germinal Center; Humans; Lymphocyte Activation; Lymphoma, Large B-Cell, Diffuse; Mutation; Proto-Oncogene Proteins c-bcl-6; RNA Interference; RNA, Messenger; STAT3 Transcription Factor; Transcription, Genetic; Tyrphostins

Signal transducer and activator of transcription 3 (STAT3), normally activated by Janus kinase (JAK) in response to cytokine stimulation, has been shown to have oncogenic potential. In addition to JAK, recent data suggest that STAT3 can also be activated by other proteins such as the aberrant fusion protein, NPM-ALK, which is expressed in a subset of systemic anaplastic large cell lymphoma (ALCL). In this study, we investigated the possible role of JAK in activating STAT3 in ALCL using two ALK-positive ALCL cell lines, Karpas 299 and SU-DHL-1. At the steady state, JAK3 showed detectable tyrosine phosphorylation by immunoprecipitation. Treatment with AG490, a JAK inhibitor, decreased but did not completely abrogate tyrosine phosphorylation of JAK3 and STAT3 in a concentration-dependent manner. Similar results were obtained using two other inhibitors of JAK3, WHI-P131 and WHI-P154. These biochemical changes were associated with apoptosis in both cell lines that was coupled with activation of caspase 3 and decreased bcl-xL and bcl-2. Cell cycle analysis revealed a decrease in the S phase, which may be attributed to cyclin D3 downregulation and p21(waf1) upregulation. Importantly, the tyrosine kinase activity of NPM-ALK, as assessed by an in vitro assay, decreased with increasing concentrations of AG490. Our findings highlight the importance of JAK3 in activating STAT3 in ALCL, and that NPM-ALK-mediated activation of STAT3 is influenced by the functional status of JAK3.

Topics: Anaplastic Lymphoma Kinase; Animals; Antineoplastic Agents; Apoptosis; Caspase 3; Caspases; DNA-Binding Proteins; G1 Phase; Humans; Janus Kinase 3; Lymphoma, Large B-Cell, Diffuse; Protein-Tyrosine Kinases; Receptor Protein-Tyrosine Kinases; STAT3 Transcription Factor; Trans-Activators; Tyrphostins