Clinical significance of IL-18 gene over-expression in AML

Little is known about the clinical significance of interleukin (IL)-18, a novel immunoregulatory cytokine, in acute myeloid leukemia (AML). Using reverse transcriptase polymerase chain reaction (RT-PCR) analysis, levels of IL-18 mRNA were assessed in bone marrow mononuclear cells (BMMC) from 47 adult patients with de novo or CR AML in order to explore the clinical significance of IL-18. The relationship between expression levels and the established prognostic factors such as age, cytogenetic aberrations, CD34 expression and FAB subtypes was investigated. Either disease status, age or CD34 expression were found to significantly correlate with the expression of IL-18. With respect to FAB cytotypes, expression of IL-18 gene in M4/M5 (n=15) was statistically higher than that in other subtypes (n=32, P<0.001). Moreover, a significant difference in IL-18 gene expression was obtained between the high risk group and the intermediate risk group (0.5627 versus 0.3111, P=0.038). In addition, a relationship between IL-18 expression of BMMC and initial white blood cell (WBC) was clearly demonstrated by a statistical analysis (r=0.806, P<0.001). These observations suggest that IL-18 gene over-expression might reflect the convergence of several important unfavorable prognostic factors in AML.

The glutathione disulfide mimetic NOV-002 inhibits cyclophosphamide-induced hematopoietic and immune suppression by reducing oxidative stress

The oxidized glutathione mimetic NOV-002 is a unique anti-tumor agent that not only has the ability to inhibit tumor cell proliferation, survival, and invasion, but in some settings can also ameliorate cytotoxic chemotherapy-induced hematopoietic and immune suppression. However, the mechanisms by which NOV-002 protects the hematopoietic and immune systems against the cytotoxic effects of chemotherapy are not known. Therefore, in this study we investigated the mechanisms of action of NOV-002 using a mouse model in which hematopoietic and immune suppression was induced by cyclophosphamide (CTX) treatment. We found that NOV-002 treatment in a clinically comparable dose regimen attenuated CTX-induced reduction in bone marrow hematopoietic stem and progenitor cells (HSPCs) and reversed the immunosuppressive activity of myeloid-derived suppressor cells (MDSCs), which led to a significant improvement in hematopoietic and immune functions. These effects of NOV-002 may be attributable to its ability to modulate cellular redox. This suggestion is supported by the finding that NOV-002 treatment upregulated the expression of superoxide dismutase 3 and glutathione peroxidase 2 in HSPCs, inhibited CTX-induced increases in reactive oxygen species production in HSPCs and MDSCs, and attenuated CTX-induced reduction of the ratio of reduced glutathione to oxidized glutathione in splenocytes. These findings provide a better understanding of the mechanisms whereby NOV-002 modulates chemotherapy-induced myelosuppression and immune dysfunction and a stronger rationale for clinical utilization of NOV-002 to reduce chemotherapy-induced hematopoietic and immune suppression.

Dependence on PI3K/Akt signaling for malignant rhabdoid tumor cell survival

PURPOSE

Malignant rhabdoid tumors (MRT), although rare, are one of the most aggressive pediatric malignancies. Loss of INI1, a tumor suppressor gene and member of the SWI/SNF chromatin remodeling complex, is a recurrent genetic characteristic of these tumors and an important diagnostic marker. We have previously demonstrated a novel interaction between the serine/threonine kinase Akt and INI1, as well as other SWI/SNF subunits. This, coupled with experiments in the literature suggesting that the PI3K/Akt pathway is dysregulated in MRT cells, caused us to investigate the activation and importance of this pathway in this tumor type.

METHODS

In this study, we used MTT assays to evaluate the sensitivity of MRT cell lines to PI3K inhibition. Western blot analysis and Raf pulldown assays were used to examine potential mechanisms of PI3K/Akt dysregulation.

RESULTS

Inhibition of the PI3K/Akt pathway caused a significant reduction in the survival of the four MRT cell lines tested, and three cell lines demonstrated constitutively active Akt. Two of these constitutively active Akt cell lines abundantly expressed IGF-1R and an inhibitor of IGF-1R, NVP-AEW541, reduced Akt phosphorylation in one of them. The third constitutively active Akt cell line appeared to express a mutant IGF-1R.

CONCLUSIONS

Our data suggests that the PI3K/Akt pathway is a crucial means of maintaining the survival and growth of MRT cells. The cells therefore employ various mechanisms to stimulate this pathway, and growth factor receptor dysregulation appears to be a common method. Drugs that inhibit the PI3K pathway or interfere with IGF autocrine loops may be of great value in treating MRT, which is largely resistant to conventional chemotherapeutic approaches.

Nrf2-modulation by seleno-hormetic agents and its potential for radiation protection

The trace element selenium (Se) is an essential component of selenoproteins and plays a critical role in redox signaling via regulating the activity of selenoenzymes such as thioredoxin reductase-1 and glutathione peroxidases. Se compounds and its metabolites possess a wide range of biological functions including anticancer and cytoprotection effects, modulation of hormetic genes and antioxidant enzyme activities. Radiation-induced injury of normal tissues is a significant side effect for cancer patients who receive radiotherapy in the clinic and the development of new and effective radioprotectors is an important goal of research. Others and we have shown that seleno-compounds have the potential to protect ionizing radiation-induced toxicities in various tissues and cells both in in vitro and in vivo studies. In this review, we discuss the potential utilization of Se compounds with redox-dependent hormetic activity as novel radio-protective agents to alleviate radiation toxicity. The cellular and molecular mechanisms underlying the radioprotection effects of these seleno-hormetic agents are also discussed. These include Nrf2 transcription factor modulation and the consequent upregulation of the adaptive stress response to IR in bone marrow stem cells and hematopoietic precursors.

Differential Reponses of Hematopoietic Stem and Progenitor Cells to mTOR Inhibition

Abnormal activation of the mammalian target of rapamycin (mTOR) signaling pathway has been observed in a variety of human cancers. Therefore, targeting of the mTOR pathway is an attractive strategy for cancer treatment and several mTOR inhibitors, including AZD8055 (AZD), a novel dual mTORC1/2 inhibitor, are currently in clinical trials. Although bone marrow (BM) suppression is one of the primary side effects of anticancer drugs, it is not known if pharmacological inhibition of dual mTORC1/2 affects BM hematopoietic stem and progenitor cells (HSPCs) function and plasticity. Here we report that dual inhibition of mTORC1/2 by AZD or its analogue (KU-63794) depletes mouse BM Lin(-)Sca-1(+)c-Kit(+) cells in cultures via the induction of apoptotic cell death. Subsequent colony-forming unit (CFU) assays revealed that inhibition of mTORC1/2 suppresses the clonogenic function of hematopoietic progenitor cells (HPCs) in a dose-dependent manner. Surprisingly, we found that dual inhibition of mTORC1/2 markedly inhibits the growth of day-14 cobblestone area-forming cells (CAFCs) but enhances the generation of day-35 CAFCs. Given the fact that day-14 and day-35 CAFCs are functional surrogates of HPCs and hematopoietic stem cells (HSCs), respectively, these results suggest that dual inhibition of mTORC1/2 may have distinct effects on HPCs versus HSCs.

BAY 11-7082 inhibits the secretion of interleukin-6 by senescent human microglia

The accumulation of senescent cells in aged tissues has been implicated in a variety of age-related diseases, including cancer and neurodegenerative disorders. Recent studies have demonstrated a link between age-associated increase of senescent glial cells in the brain and the pathogenesis of Alzheimer's disease (AD). However, there is a lack of in vitro cellular models of senescent human microglia, which significantly limits our approaches to study AD pathogenesis. Here, we show for the first time that ionizing radiation (IR) dose-dependently induces premature senescence in HMC3 human microglial cells. Senescence-associated β-galactosidase activity, a well-characterized marker of cellular senescence, was substantially increased in irradiated HMC3 cells compared with control cells. Furthermore, we found that phosphorylated p53 levels and p21 expression levels were markedly higher in IR-induced senescent microglia than in control cells. Senescent human microglia exhibited the senescence-associated secretory phenotype (SASP), as evidenced by the increased secretion of pro-inflammatory cytokine interleukin-6 (IL-6). Treatment with an NF-κB inhibitor, BAY 11-7082, inhibits the secretion of IL-6 by senescent HMC3 cells. Collectively, our studies have established an in vitro cellular model of human microglial senescence and suggest that the NF-κB pathway may play a critical role in regulating the SASP of senescent HMC3 cells.

Ionizing radiation and busulfan induce premature senescence in murine bone marrow hematopoietic cells

Exposure of murine bone marrow (BM) cells to ionizing radiation (IR; 4 Gy) resulted in >95% inhibition of the frequency of various day types of cobblestone area-forming cells in association with the induction of apoptosis in hematopoietic stem cell alike cells (Lin(-) ScaI(+) c-kit(+) cells; IR: 64.8 +/- 0.4% versus control: 20.4 +/- 0.5%; P < 0.001) and progenitors (Lin(-) ScaI(-) c-kit(+) cells; IR: 46.2 +/- 1.4% versus control: 7.8 +/- 0.5%; P < 0.001). Incubation of murine BM cells with busulfan (BU; 30 micro M) for 6 h also inhibited the cobblestone area-forming cell frequency but failed to cause a significant increase in apoptosis in these two types of hematopoietic cells. After 5 weeks of long-term BM cell culture, 33% and 72% of hematopoietic cells survived IR- and BU-induced damage, respectively, as compared with control cells, but they could not form colony forming units-granulocyte macrophages. Moreover, these surviving cells expressed an increased level of senescence-associated beta-galactosidase, p16(Ink4a), and p19(Arf). These findings suggest that IR inhibits the function of hematopoietic stem cell alike cells and progenitors primarily by inducing apoptosis, whereas BU does so mainly by inducing premature senescence. In addition, induction of premature senescence in BM hematopoietic cells also contributes to IR-induced inhibition of their hematopoietic function. Interestingly, the induction of hematopoietic cell senescence by IR, but not by BU, was associated with an elevation in p53 and p21(Cip1/Waf1) expression. This suggests that IR induces hematopoietic cell senescence in a p53-p21(Cip1/Waf1)-dependent manner, whereas the induction of senescence by BU bypasses the p53-p21(Cip1/Waf1) pathway.