Inhibitor DHMEQ Research Articles

6635 A novel NF-kB inhibitor DHMEQ could suppress peritoneal dissemination of gastric cancer by anti-tumor/-adhesive effects in mice

6635 A novel NF-kB inhibitor DHMEQ could suppress peritoneal dissemination of gastric cancer by anti-tumor/-adhesive effects in mice

Inhibition of epithelial to mesenchymal transition in metastatic prostate cancer cells by the novel proteasome inhibitor, NPI-0052: pivotal roles of Snail repression and RKIP induction

Metastasis is associated with the loss of epithelial features and the acquisition of mesenchymal characteristics and invasive properties by tumor cells, a process known as epithelial to mesenchymal transition (EMT). Snail expression, through nuclear factor (NF)-kappaB activation, is an EMT determinant. The proteasome inhibitor, NPI-0052, induces the metastasis tumor suppressor/immune surveillance cancer gene, Raf kinase inhibitor protein (RKIP), via NF-kappaB inhibition. We hypothesized that NPI-0052 may inhibit Snail expression and, consequently, the metastatic phenotype in DU-145 prostate cancer cells. Cell treatment with NPI-0052 induced E-cadherin and inhibited Snail expression and both tumor cell invasion and migration. Inhibition of Snail inversely correlated with the induction of RKIP. The underlying mechanism of NPI-0052-induced inhibition of the metastatic phenotype was corroborated by: (1) treatment with Snail siRNA in DU-145 inhibited EMT and, in contrast, overexpression of Snail in the nonmetastatic LNCaP cells induced EMT, (2) NPI-0052-induced repression of Snail via inhibition of NF-kappaB was corroborated by the specific NF-kappaB inhibitor DHMEQ and (3) RKIP overexpression mimicked NPI-0052 in the inhibition of Snail and EMT. These findings demonstrate, for the first time, the role of NPI-0052 in the regulation of EMT via inhibition of NF-kappaB and Snail and induction of RKIP.

Molecular mechanisms regulating dissociation of cell–cell junction of epithelial cells by oxidative stress

Oxidative stress is regarded as a causative factor in aging and various degenerative diseases. Here, we show the mechanism by which oxidative stress induces disruption of cell-cell junctions using retinal pigment epithelial cells. We demonstrated that reactive oxygen species (ROS)-mediated activation of Src kinase increases the tyrosine phosphorylation state of p120-catenin and rapidly triggers translocation of p120-catenin and internalization of N-cadherin from the cell-cell adhesion sites to an early endosomal compartment. Endosomal accumulation of p120-catenin resulted in stress fiber formation and cell-cell dissociation through the activation of Rho/Rho kinase pathway. However, these cytoskeletal remodeling and cell-cell dissociation induced by oxidative stress were transient, due to the activation of nuclear factor-kappaB (NF-kappaB) and the expression of manganese superoxide dismutase (Mn-SOD). Using the NF-kappaB specific inhibitor DHMEQ, we found that NF-kappaB is part of a negative feedback loop to control intracellular ROS levels. Finally, we demonstrated that H(2)O(2) treatment alone does not induce the epithelial mesenchymal transition (EMT) in retinal pigment epithelial cells, which can be induced by TNF-alpha treatment. These findings suggest that oxidative stress is a crucial factor to induce the cell-cell dissociation, an initial step of EMT, but does not provide sufficient signals to establish and to maintain the EMT.

Sensitization of Rituximab-Sensitive and Rituximab-Resistant B-NHL Cell Lines/Clones to TRAIL-Induced Apoptosis by Bortezomib and NF-κB Inhibitors.

Patients with B-NHL respond initially to conventional chemotherapy and/or to immunotherapy with rituximab (alone or in combination with chemotherapy). However, patients develop resistance to these modalities and novel approaches are needed. TRAIL is a cytotoxic molecule that exerts selective anti-tumor cytotoxic activity with minimal toxicity to normal tissues. Further, TRAIL or agonist monoclonal antibody (mAb) to TRAIL receptors, DR4 and DR5, are currently being tested clinically. The present study investigated the sensitivity of B-NHL cell lines to TRAIL-mediated apoptosis using the AIDS-related NHL (ARL) B-cell line, 2F7, and the B-NHL cell lines, Ramos and Daudi. Also, to recapitulate various aspects of acquired rituximab-resistance, we have generated rituximab-resistant (RR) clones from the parental wild type (wt) cells. Rituximab failed to chemo-sensitize the RR clones and the clones exhibited higher resistance to various drugs (e.g., CDDP, VP-16, ADR, Vincristine, Taxol) and to TRAIL (1–250 ng/ml-18 h) compared to the wt cells as analyzed by DNA fragment on assay. The findings demonstrate that the wild type and RR1 cells were resistant to TRAIL-mediated apoptosis at a wide range of TRAIL concentrations. We then examined means to reverse TRAIL resistance. We and others have reported that inhibition of NF-κB activity can sensitize TRAIL-resistant tumor cells to TRAIL-induced apoptosis. Hence, we examined the effect of the proteasome and NF-κB inhibitor, Bortezomib (Velcade), Bay 11–7085 and the specific NF-κB inhibitor DHMEQ (Kikuchi et. al, Cancer Research 2003; 63:107). Pretreatment of the NHL tumor cells with Bortezomib, Bay 11–7085 or DHMEQ for 6 h followed by treatment with TRAIL for 18h resulted in significant augmentation of apoptosis and synergy was achieved. Both the rituximab-sensitive and rituximab-resistant tumor cells were sensitized by these inhibitors, though higher concentrations were required for sensitization of the RR clones. Interestingly, detailed analysis of the signaling pathways in the RR clones revealed constitutive hyper-activation of the NF-κB survival pathway leading to over-expression of anti-apoptotic gene products Bcl-2, Bcl-xL and Mcl-1. Based on the findings, we postulate that patients with resistant B-NHL can be treated with combination of TRAIL/anti-DR4 or DR5 mAb and NF-κB inhibitors. Alternatively, these patients can be treated with agents that up-regulate TRAIL expression on host effectors (e.g., T cells, NK cells) in combination with NF-κB inhibitors.