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Chaetocin,a thiodioxopiperazine natural product previously unreported to have anticancer effects,was found to have potent antimyeloma activity in IL-6-dependent and -independent myeloma cell lines in freshly collected sorted and unsorted patient CD138(+) myeloma cells and in vivo. Chaetocin largely spares matched normal CD138(-) patient bone marrow leukocytes,normal B cells,and neoplastic B-CLL (chronic lymphocytic leukemia) cells,indicating a high degree of selectivity even in closely lineage-related B cells. Furthermore,chaetocin displays superior ex vivo antimyeloma activity and selectivity than doxorubicin and dexamethasone,and dexamethasone- or doxorubicin-resistant myeloma cell lines are largely non-cross-resistant to chaetocin. Mechanistically,chaetocin is dramatically accumulated in cancer cells via a process inhibited by glutathione and requiring intact/unreduced disulfides for uptake. Once inside the cell,its anticancer activity appears mediated primarily through the imposition of oxidative stress and consequent apoptosis induction. Moreover,the selective antimyeloma effects of chaetocin appear not to reflect differential intracellular accumulation of chaetocin but,instead,heightened sensitivity of myeloma cells to the cytotoxic effects of imposed oxidative stress. Considered collectively,chaetocin appears to represent a promising agent for further study as a potential antimyeloma therapeutic. View Publication

CTLs act as the effector arm of the cell-mediated immune system to kill undesirable cells. Two processes regulate these effector cells to prevent self reactivity: a thymic selection process that eliminates autoreactive clones and a multistage activation or priming process that endows them with a license to kill cognate target cells. Hitherto no subsequent regulatory restrictions have been ascribed for properly primed and activated CTLs that are licensed to kill. In this study we show that CTLs possess a novel postpriming regulatory mechanism(s) that influences the outcome of their encounter with cognate target cells. This mechanism gauges the degree of Ag density,whereupon reaching a certain threshold significant changes occur that induce anergy in the effector T cells. The biological consequences of this Ag-induced postpriming control includes alterations in the expression of cell surface molecules that control immunological synapse activity and cytokine profiles and induce retarded cell proliferation. Most profound is genome-wide microarray analysis that demonstrates changes in the expression of genes related to membrane potential,TCR signal transduction,energy metabolism,and cell cycle control. Thus,a discernible and unique gene expression signature for anergy as a response to high Ag density has been observed. Consequently,activated T cells possess properties of a self-referential sensory organ. These studies identify a new postpriming control mechanism of CTL with anergenic-like properties. This mechanism extends our understanding of the control of immune function and regulation such as peripheral tolerance,viral infections,antitumor immune responses,hypersensitivity,and autoimmunity. View Publication

Obesity increases the risk of developing multiple myeloma (MM). Adiponectin is a cytokine produced by adipocytes,but paradoxically decreased in obesity,that has been implicated in MM progression. Herein,we evaluated how prolonged exposure to adiponectin affected the survival of MM cells as well as putative signaling mechanisms. Adiponectin activates protein kinase A (PKA),which leads to decreased AKT activity and increased AMP-activated protein kinase (AMPK) activation. AMPK,in turn,induces cell cycle arrest and apoptosis. Adiponectin-induced apoptosis may be mediated,at least in part,by the PKA/AMPK-dependent decline in the expression of the enzyme acetyl-CoA-carboxylase (ACC),which is essential to lipogenesis. Supplementation with palmitic acid,the preliminary end product of fatty acid synthesis,rescues MM cells from adiponectin-induced apoptosis. Furthermore,5-(tetradecyloxy)-2-furancarboxylic acid (TOFA),an ACC inhibitor,exhibited potent antiproliferative effects on MM cells that could also be inhibited by fatty acid supplementation. Thus,adiponectin's ability to reduce survival of MM cells appears to be mediated through its ability to suppress lipogenesis. Our findings suggest that PKA/AMPK pathway activators,or inhibitors of ACC,may be useful adjuvants to treat MM. Moreover,the antimyeloma effect of adiponectin supports the concept that hypoadiponectinemia,as occurs in obesity,promotes MM tumor progression. View Publication

Human B cells can be cultured ex vivo for a few weeks,following stimulation of the CD40 cell surface molecule in the presence of recombinant cytokines such as interleukin-4 (IL-4). However,attempts to produce polyclonal antigen-specific human antibodies by in vitro culture of human B cells obtained from immunized donors have not been successful. It has been shown in mice that lipopolysaccharide (LPS) is a potent mitogen for B cells and plays an important role in the generation of antigen-specific antibody responses. Although it has long been believed that LPS has no direct effect on human B cells,recent data indicating that IL-4-activated human B cells are induced to express Toll-like receptor-4,the main LPS receptor,prompted us to study the effects of LPS on the proliferation and antibody secretion of human B cells. Our results showed that LPS caused a reduction in the expansion of CD40-activated human B cells,accompanied by an increase in antigen-specific antibody secretion. This result suggested that some,but not all,B cells were able to differentiate into antibody-secreting cells in response to LPS. This increased differentiation could be explained by the observation that LPS-stimulated human B cells were induced to secrete higher amounts of IL-6,a pleiotropic cytokine well-known for its B-cell differentiation activity. In vivo,the effect of LPS on cytokine secretion by B cells may not only enhance B-cell differentiation but also help to sustain a local ongoing immune response to invading Gram-negative bacteria,until all pathogens have been cleared from the organism. View Publication

Chimeric oncoproteins resulting from fusion of MLL to a wide variety of partnering proteins cause biologically distinctive and clinically aggressive acute leukemias. However,the mechanism of MLL-mediated leukemic transformation is not fully understood. Dot1,the only known histone H3 lysine 79 (H3K79) methyltransferase,has been shown to interact with multiple MLL fusion partners including AF9,ENL,AF10,and AF17. In this study,we utilize a conditional Dot1l deletion model to investigate the role of Dot1 in hematopoietic progenitor cell immortalization by MLL fusion proteins. Western blot and mass spectrometry show that Dot1-deficient cells are depleted of the global H3K79 methylation mark. We find that loss of Dot1 activity attenuates cell viability and colony formation potential of cells immortalized by MLL oncoproteins but not by the leukemic oncoprotein E2a-Pbx1. Although this effect is most pronounced for MLL-AF9,we find that Dot1 contributes to the viability of cells immortalized by other MLL oncoproteins that are not known to directly recruit Dot1. Cells immortalized by MLL fusions also show increased apoptosis,suggesting the involvement of Dot1 in survival pathways. In summary,our data point to a pivotal requirement for Dot1 in MLL fusion protein-mediated leukemogenesis and implicate Dot1 as a potential therapeutic target. View Publication

To further clarify the transformation from monoclonal gammopathy of undetermined significance (MGUS) to plasma cell myeloma (PCM),we compared interphase fluorescence in situ hybridization (FISH) patterns in 381 MGUS and 301 PCM patients. According to the World Health Organization and the International Myeloma Working Group,a threshold of 10% of bone marrow plasma cells separated MGUS from PCM. After magnetic activated cell sorting for CD138(+) cells,FISH succeeded in 272 of 301 (90.4%) PCM,but in only 302 of 381 (79.3%) MGUS cases (P textless 0.001). Cytogenetic alterations were more frequent in PCM (237 of 272; 87.1%) than MGUS (169 of 302; 56.0%; P = 0.0002). PCM showed a median of two cytogenetic alterations (range,0-9) and MGUS one (range,0-6). Considering only cases with a yield of plasma cells allowing five or more FISH probes,del(13)(q14) was found in 99 of 251 (39.3%) PCM but in only 59 of 267 (22.1%) MGUS (P = 0.0001),del(17p) in 15 PCM (6.0%) and in 6 MGUS (2.2%) patients (P = 0.029). A t(4;14)/IGH-FGFR3 was detected in 28 PCM (11.1%) and 5 MGUS (1.9%; P textless 0.001). The t(11;14)/IGH-CCND1 and the t(14;16)/IGH-MAF showed no significant differences. Cytomorphology detected higher numbers of plasma cells than multiparameter flow cytometry (median ratio 4.25). This study underlines the genetic heterogeneity of MGUS similar to PCM. Genetic analysis might contribute to more diversified monitoring strategies for MGUS patients. View Publication

Although toll-like receptor (TLR) agonists,such as CpG,are used as immunotherapeutic agents in clinical trials for cancer and infectious diseases,their effects are limited and the underlying mechanism(s) that restrains CpG efficacy remains obscure. Here,we show that signal transducer and activator of transcription 3 (Stat3) plays a key role in down-modulating immunostimulatory effects of CpG. In the absence of interleukin-6 (IL-6) and IL-10 induction,CpG directly activates Stat3 within minutes through TLR9. Ablating Stat3 in hematopoietic cells results in rapid activation of innate immunity by CpG,with enhanced production of IFN-gamma,tumor necrosis factor-alpha,IL-12,and activation of macrophages,neutrophils,and natural killer cells marked with Stat1 activation. Innate immune responses induced by CpG in mice with a Stat3-ablated hematopoietic system cause potent antitumor effects,leading to eradication of large (textgreater1 cm) B16 melanoma tumors within 72 h. Moreover,ablating Stat3 in myeloid cells increases CpG-induced dendritic cell maturation,T-cell activation,generation of tumor antigen-specific T cells,and long-lasting antitumor immunity. A critical role of Stat3 in mediating immunosuppression by certain cytokines and growth factors in the tumor microenvironment has been recently documented. By demonstrating direct and rapid activation of Stat3 by TLR agonists,we identify a second level of Stat3-mediated immunosuppression. Our results further suggest that targeting Stat3 can drastically improve CpG-based immunotherapeutic approaches. View Publication