Rapid and selective death of leukemia stem and progenitor cells induced by the compound 4-benzyl, 2-methyl, 1,2,4-thiadiazolidine, 3,5 dione (TDZD-8)

On the role of phosphatidylinositol 3-kinase, protein kinase b/Akt, and glycogen synthase kinase-3β in photodynamic injury of crayfish neurons and glial cells

Photodynamic treatment that causes intense oxidative stress and cell death is currently used in neurooncology. However, along with tumor cells, it may damage healthy neurons and glia. To study the involvement of signaling processes in photodynamic injury or protection of neurons and glia, we used crayfish mechanoreceptor consisting of a single neuron surrounded by glial cells. It was photosensitized with alumophthalocyanine Photosens. Application of specific inhibitors showed that phosphatidylinositol 3-kinase did not participate in photoinduced death of neurons and glia. Akt was involved in photoinduced necrosis but not in apoptosis of neurons and glia. Glycogen synthase kinase-3β participated in photoinduced apoptosis of glial cells and in necrosis of neurons. Therefore, phosphatidylinositol 3-kinase/protein kinase Akt/glycogen synthase kinase-3β pathway was not involved as a whole in photodynamic injury of crayfish neurons and glia but its components, Akt and glycogen synthase kinase-3β, independently and cell specifically regulated death of neurons and glial cells. According to these data, necrosis in this system was a controlled but not a non-regulated cell death mode. The obtained results may be used for the search of pharmacological agents selectively modulating death and survival of normal neurons and glial cells during photodynamic therapy of brain tumors.

Redox regulation in cancer: a double-edged sword with therapeutic potential

Oxidative stress, implicated in the etiology of cancer, results from an imbalance in the production of reactive oxygen species (ROS) and cell’s own antioxidant defenses. ROS deregulate the redox homeostasis and promote tumor formation by initiating an aberrant induction of signaling networks that cause tumorigenesis. Ultraviolet (UV) exposures, γ-radiation and other environmental carcinogens generate ROS in the cells, which can exert apoptosis in the tumors, thereby killing the malignant cells or induce the progression of the cancer growth by blocking cellular defense system. Cancer stem cells take the advantage of the aberrant redox system and spontaneously proliferate. Oxidative stress and gene-environment interactions play a significant role in the development of breast, prostate, pancreatic and colon cancer. Prolonged lifetime exposure to estrogen is associated with several kinds of DNA damage. Oxidative stress and estrogen receptor-associated proliferative changes are suggested to play important roles in estrogen-induced breast carcinogenesis. BRCA1, a tumor suppressor against hormone responsive cancers such as breast and prostate cancer, plays a significant role in inhibiting ROS and estrogen mediated DNA damage; thereby regulate the redox homeostasis of the cells. Several transcription factors and tumor suppressors are involved during stress response such as Nrf2, NFκB and BRCA1. A promising strategy for targeting redox status of the cells is to use readily available natural substances from vegetables, fruits, herbs and spices. Many of the phytochemicals have already been identified to have chemopreventive potential, capable of intervening in carcinogenesis.

Association of a leukemic stem cell gene expression signature with clinical outcomes in acute myeloid leukemia

CONTEXT

In many cancers, specific subpopulations of cells appear to be uniquely capable of initiating and maintaining tumors. The strongest support for this cancer stem cell model comes from transplantation assays in immunodeficient mice, which indicate that human acute myeloid leukemia (AML) is driven by self-renewing leukemic stem cells (LSCs). This model has significant implications for the development of novel therapies, but its clinical relevance has yet to be determined.

OBJECTIVE

To identify an LSC gene expression signature and test its association with clinical outcomes in AML.

DESIGN, SETTING, AND PATIENTS

Retrospective study of global gene expression (microarray) profiles of LSC-enriched subpopulations from primary AML and normal patient samples, which were obtained at a US medical center between April 2005 and July 2007, and validation data sets of global transcriptional profiles of AML tumors from 4 independent cohorts (n = 1047).

MAIN OUTCOME MEASURES

Identification of genes discriminating LSC-enriched populations from other subpopulations in AML tumors; and association of LSC-specific genes with overall, event-free, and relapse-free survival and with therapeutic response.

RESULTS

Expression levels of 52 genes distinguished LSC-enriched populations from other subpopulations in cell-sorted AML samples. An LSC score summarizing expression of these genes in bulk primary AML tumor samples was associated with clinical outcomes in the 4 independent patient cohorts. High LSC scores were associated with worse overall, event-free, and relapse-free survival among patients with either normal karyotypes or chromosomal abnormalities. For the largest cohort of patients with normal karyotypes (n = 163), the LSC score was significantly associated with overall survival as a continuous variable (hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.08-1.22; log-likelihood P <.001). The absolute risk of death by 3 years was 57% (95% CI, 43%-67%) for the low LSC score group compared with 78% (95% CI, 66%-86%) for the high LSC score group (HR, 1.9 [95% CI, 1.3-2.7]; log-rank P = .002). In another cohort with available data on event-free survival for 70 patients with normal karyotypes, the risk of an event by 3 years was 48% (95% CI, 27%-63%) in the low LSC score group vs 81% (95% CI, 60%-91%) in the high LSC score group (HR, 2.4 [95% CI, 1.3-4.5]; log-rank P = .006). In multivariate Cox regression including age, mutations in FLT3 and NPM1, and cytogenetic abnormalities, the HRs for LSC score in the 3 cohorts with data on all variables were 1.07 (95% CI, 1.01-1.13; P = .02), 1.10 (95% CI, 1.03-1.17; P = .005), and 1.17 (95% CI, 1.05-1.30; P = .005).

CONCLUSION

High expression of an LSC gene signature is independently associated with adverse outcomes in patients with AML.

Inhibition of glioblastoma growth by the thiadiazolidinone compound TDZD-8

BACKGROUND

Thiadiazolidinones (TDZD) are small heterocyclic compounds first described as non-ATP competitive inhibitors of glycogen synthase kinase 3β (GSK-3β). In this study, we analyzed the effects of 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), on murine GL261 cells growth in vitro and on the growth of established intracerebral murine gliomas in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

Our data show that TDZD-8 decreased proliferation and induced apoptosis of GL261 glioblastoma cells in vitro, delayed tumor growth in vivo, and augmented animal survival. These effects were associated with an early activation of extracellular signal-regulated kinase (ERK) pathway and increased expression of EGR-1 and p21 genes. Also, we observed a sustained activation of the ERK pathway, a concomitant phosphorylation and activation of ribosomal S6 kinase (p90RSK) and an inactivation of GSK-3β by phosphorylation at Ser 9. Finally, treatment of glioblastoma stem cells with TDZD-8 resulted in an inhibition of proliferation and self-renewal of these cells.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that TDZD-8 uses a novel mechanism to target glioblastoma cells, and that malignant progenitor population could be a target of this compound.

Tumor-initiating and -propagating cells: cells that we would like to identify and control

Identification of the cell types capable of initiating and sustaining growth of the neoplastic clone in vivo is a fundamental problem in cancer research. It is likely that tumor growth can be sustained both by rare cancer stem-like cells and selected aggressive clones and that the nature of the mutations, the cell of origin, and its environment will contribute to tumor propagation. Genomic instability, suggested as a driving force in tumorigenesis, may be induced by genetic and epigenetic changes. The feature of self-renewal in stem cells is shared with tumor cells, and deviant function of the stem cell regulatory networks may, in complex ways, contribute to malignant transformation and the establishment of a cancer stem cell-like phenotype. Understanding the nature of the more quiescent cancer stem-like cells and their niches has the potential to develop novel cancer therapeutic protocols including pharmacological targeting of self-renewal pathways. Drugs that target cancer-related inflammation may have the potential to reeducate a tumor-promoting microenvironment. Because most epigenetic modifications may be reversible, DNA methylation and histone deacetylase inhibitors can be used to induce reexpression of genes that have been silenced epigenetically. Design of therapies that eliminate cancer stem-like cells without eliminating normal stem cells will be important. Further insight into the mechanisms by which pluripotency transcription factors (e.g., OCT4, SOX2, and Nanog), polycomb repressive complexes and microRNA balance selfrenewal and differentiation will be essential for our understanding of both embryonic differentiation and human carcinogenesis and for the development of new treatment strategies.

Knockdown of glycogen synthase kinase 3 beta attenuates 6-hydroxydopamine-induced apoptosis in SH-SY5Y cells

Glycogen synthase kinase 3 beta (GSK3β) plays a critical role in signal transductions concerning neuronal death. In the present study, we investigated the potential role of GSK3β in 6-hydroxydopamine (6-OHDA)-induced toxicity in human neuroblastoma cell line SH-SY5Y. We assessed the apoptotic proteins and the relative levels of pGSK3β (Ser9) and pGSK3β (Tyr216) to GSK3β in 6-OHDA-treated SH-SY5Y. Furthermore, we downregulated the expression of GSK3β by short hairpin RNA (shRNA) interference and compared the cell viability and expression of apoptotic proteins in knockdown group with those in control group under the treatment of 6-OHDA. We found that 6-OHDA increased the expression of caspase-3 and caspase-9 but not caspase-8. Additionally, 6-OHDA decreased the ratio of pGSK3β (Ser9)/GSK3β and increased the ratio of pGSK3β (Tyr216)/GSK3β. Moreover, 6-OHDA induced less cell viability loss and lower expression of caspase-9 and caspase-3 in GSK3β knockdown group compared with control. The present data indicate that 6-OHDA may induce apoptosis in SH-SY5Y via the intrinsic death pathway and GSK3β knockdown can partly attenuate 6-OHDA-induced neuronal death and apoptosis, suggesting that GSK3β may have the potential to serve as a therapeutic target for PD.

Chronic myelogenous leukemia stem cells: What's new?

Chronic myelogenous leukemia (CML) is a clonal myeloproliferative disorder that arises in the hematopoietic stem cell compartment. CML is one of the best-understood malignancies, as it results from a single genetic mutation, the fusion oncogene BCR-ABL, which has been widely studied. Specific tyrosine kinase inhibitors have been developed to target BCR-ABL in CML, but these agents fail to eliminate the CML stem cell population and thus are unlikely to cure CML. This article reviews recent developments in the biology and treatment of CML, specifically focusing on CML stem cells. Significant progress continues to be made in our understanding of CML stem cell biology, which has wider implications within the cancer stem cell field. We are also beginning to see the identification of novel therapies that specifically target the CML stem cell. These are exciting times in the quest to cure CML.

NCI first International Workshop on the biology, prevention, and treatment of relapse after allogeneic hematopoietic stem cell transplantation: report from the committee on the biological considerations of hematological relapse following allogeneic stem cell transplantation unrelated to graft-versus-tumor effects: state of the science

Hematopoietic malignant relapse still remains the major cause of death following allogeneic hematopoietic stem cell transplantation (HSCT). Although there has been a large focus on the immunologic mechanisms responsible for the graft-versus-tumor (GVT) effect or lack thereof, there has been little attention paid to investigating the biologic basis of hematologic malignant disease relapse following allogeneic HSCT. There are a large number of factors that are responsible for the biologic resistance of hematopoietic tumors following allogeneic HSCT. We have focused on 5 major areas including clonal evolution of cancer drug resistance, cancer radiation resistance, genomic basis of leukemia resistance, cancer epigenetics, and resistant leukemia stem cells. We recommend increased funding to pursue 3 broad areas that will significantly enhance our understanding of the biologic basis of malignant relapse after allogeneic HSCT, including: (1) genomic and epigenetic alterations, (2) cancer stem cell biology, and (3) clonal cancer drug and radiation resistance.

The chronic myeloid leukemia stem cell

Chronic myeloid leukemia (CML) is a clonal stem cell disorder that is characterized by the acquired chromosomal translocation BCR-ABL. This gives rise to a constitutively active tyrosine kinase deregulation of the normal mechanisms of cell cycle control. In the normal hematopoietic system, hematopoietic stem cells (HSC) self-renew to form identical daughter cells but also differentiate to mature blood cells. Leukemic stem cells (LSC) share these properties of self-renewal and also differentiate to mature leukemic cells. LSC have been isolated from patients with CML: these cells give rise to leukemia following transplantation into NOD-SCID mice models. Further characterization of CML stem cells has demonstrated that a small percentage of these cells are quiescent despite culture with growth factors. The CML stem cell arises from a normal HSC that has acquired the Philadelphia chromosome. In advanced phase, more mature cells such as granulocyte/monocyte progenitors might also acquire the ability to self-renew and function as LSC. This might be one of the mechanisms underlying the progression to blast crisis. Quiescent stem cells are resistant to treatment with imatinib in vitro and are thought also to show resistance in vivo. The properties of the stem cells that lead to this drug resistance are still being characterized. However, this drug insensitivity leads to disease persistence that may lead to disease relapse even despite an initial response to imatinib. Newer molecular therapies are in development that act to specifically target and eradicate the stem cell pool.

Glioma stem cell research for the development of immunotherapy

Glioma, especially high-grade glioblastoma multiforme (GBM), is the most common and aggressive type of brain tumor, accounting for about half of all the primary brain tumors. Despite continued advances in surgery, chemotherapy, and radiotherapy, the clinical outcomes remain dismal. The 2-year survival rate of GBM is less than 30%. Better understanding of GBM biology is needed to develop novel therapies. Recent studies have demonstrated the existence of a small subpopulation of cells with stemlike features called cancer stem cells (CSCs). These GBM CSCs are self renewable and highly tumorigenic. They not only are chemo-radio resistant but also often contain multidrug resistance genes and drug transporter genes. These characteristics enable GBM CSCs to survive standard cytotoxic therapies. Among GBM CSCs, CD133(+) cells are a well-defined population and are prospectively isolated by their cell-surface marker. Increasing data show that the presence of CD133(+) CSCs highly correlates with patient survival, making these cells an ideal immunotherapy target population. The authors have reviewed recent studies related with GBM CSCs (particularly CD133(+) CSCs) and the novel therapeutic strategies targeting these cells.

Identification and targeting of cancer stem cells

Cancer stem cells (CSC) represent malignant cell subsets in hierarchically organized tumors, which are selectively capable of tumor initiation and self-renewal and give rise to bulk populations of non-tumorigenic cancer cell progeny through differentiation. Robust evidence for the existence of prospectively identifiable CSC among cancer bulk populations has been generated using marker-specific genetic lineage tracking of molecularly defined cancer subpopulations in competitive tumor development models. Moreover, novel mechanisms and relationships have been discovered that link CSC to cancer therapeutic resistance and clinical tumor progression. Importantly, proof-of-principle for the potential therapeutic utility of the CSC concept has recently been provided by demonstrating that selective killing of CSC through a prospective molecular marker can inhibit tumor growth. Herein, we review these novel and translationally relevant research developments and discuss potential strategies for CSC-targeted therapy in the context of resistance mechanisms and molecular pathways preferentially operative in CSC.

Advances in complex multiparameter flow cytometry technology: Applications in stem cell research

Flow cytometry and cell sorting are critical tools in stem cell research. Recent advances in flow cytometric hardware, reagents, and software have synergized to permit the stem cell biologist to more fully identify and isolate rare cells based on their immunofluorescent and light scatter characteristics. Some of these improvements include physically smaller air-cooled lasers, new designs in optics, new fluorescent conjugate-excitation pairs, and improved software to visualize data, all which combine to open up new horizons in the study of stem cells, by enhancing the resolution and specificity of inquiry. In this review, these recent improvements in technology will be outlined and important cell surface and functional antigenic markers useful for the study of stem cells described.

The BH3-only protein Bim plays a critical role in leukemia cell death triggered by concomitant inhibition of the PI3K/Akt and MEK/ERK1/2 pathways

Mechanisms underlying apoptosis induced by concomitant interruption of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 (MEK/ERK1/2) and phosphatidylinositol 3-kinase (PI3K)/Akt pathways were investigated in human leukemia cells. Inhibition of these pathways using the MEK inhibitor PD184352 or U0126 and the PI3K/Akt inhibitor perifosine strikingly induced apoptosis in multiple malignant human hematopoietic cells, and substantially reduced the colony-forming capacity of primary acute myeloblastic leukemia, but not normal CD34+ cells. These events were associated with pronounced Bim up-regulation, Mcl-1 down-regulation, marked Bak/Bax conformational change accompanied by Bax membrane translocation, and a pronounced increase in Bax/Bak association. Molecular studies using tet-inducible Akt, constitutively active MEK1, dominant-negative Akt, and MEK1 small interfering RNA revealed that inhibition of both MEK/ERK1/2 and Akt pathways plays a critical functional role in perifosine/PD184352-mediated lethality. Ectopic Mcl-1 expression potently inhibited perifosine/PD184352-induced apoptosis, as did Bak or Bax knockdown. Notably, knockdown of Bim, but not Bad, blocked Bak and Bax conformational change, inhibited Bax membrane translocation, diminished Bax/Bak binding, and sharply attenuated perifosine/PD184352-induced apoptosis. Finally, enforced expression of Bim significantly enhanced apoptosis induced by PI3K/Akt inhibitors, analogous to the effects of MEK1/2 inhibitors. Collectively, these findings suggest that Bim, and Mcl-1, but not Bad, integrate death signaling triggered by concomitant disruption of the PI3K/Akt and MEK1/2/ERK1/2 pathways in human leukemia cells.

Targeting cancer cells by ROS-mediated mechanisms: a radical therapeutic approach?

Increased generation of reactive oxygen species (ROS) and an altered redox status have long been observed in cancer cells, and recent studies suggest that this biochemical property of cancer cells can be exploited for therapeutic benefits. Cancer cells in advanced stage tumours frequently exhibit multiple genetic alterations and high oxidative stress, suggesting that it might be possible to preferentially eliminate these cells by pharmacological ROS insults. However, the upregulation of antioxidant capacity in adaptation to intrinsic oxidative stress in cancer cells can confer drug resistance. Abrogation of such drug-resistant mechanisms by redox modulation could have significant therapeutic implications. We argue that modulating the unique redox regulatory mechanisms of cancer cells might be an effective strategy to eliminate these cells.

Cancer stem/progenitor cell active compound 8-quinolinol in combination with paclitaxel achieves an improved cure of breast cancer in the mouse model

Increasing evidence suggests that breast cancer is caused by cancer stem cells and the cure of breast cancer requires eradication of breast cancer stem cells. In this study, we established and characterized a sphere culture model derived from side population cells from the human breast cancer cell line MCF7. The sphere culture could be maintained long term and was enriched in cells expressing known breast cancer stem cell marker CD44+CD24-. These sphere cells showed higher colony formation ability in vitro and higher tumorigenicity in vivo than MCF7 cells, suggesting the enrichment of breast cancer stem/progenitor cells. To identify compounds that preferentially inhibit the sphere cells, we performed a compound library screening. Two lead compounds, NSC24076 and NSC125034 and an analog of NSC125034, 8-quinolinol (8Q), were identified as having preferential activity against the sphere cells. 8Q showed some antitumor activity alone but had much better therapeutic effect and relapse prevention when combined with paclitaxel than either 8Q or paclitaxel alone in both MCF7 and MDA-MB-435 xenograft models. We propose that compounds selectively targeting cancer stem/progenitor cells when combined with standard chemotherapy drugs may produce an improved treatment of cancer without significant relapse.

Cancer stem cells: relevance to SCT

The cancer stem cell (CSC) hypothesis suggests that clonogenic growth potential within an individual tumor is restricted to a specific and phenotypically defined cell population. Evidence for CSC in human tumors initially arose from studies of AML, but functionally similar cell populations have been identified in an increasing number of malignancies. Despite these findings, controversy surrounds the CSC hypothesis, especially the generalization that clonogenic tumor cells are rare. Nevertheless, efforts to define the cellular processes regulating self-renewal and resistance to anticancer therapeutics, two of the major properties ascribed to CSC, are likely to provide useful insights into tumor biology as a whole. BMT has been at the forefront of clinically translating basic stem cell concepts starting with the original hypothesis that normal hematopoietic precursors could rescue patients from myeloablative doses of radiation or chemotherapy. Even today, a better understanding of CSC may enhance ongoing efforts to induce specific and effective anti-tumor immune responses in both the allogeneic and autologous setting. It is also likely that new clinical research approaches will be required to accurately evaluate novel CSC-targeting strategies. Owing to the capacity to produce remissions in most diseases, SCT may provide the ideal clinical platform to carry out these investigations by studying the ability of anti-CSC agents to prolong relapse free and overall survival.

Stem cell concepts renew cancer research

Although uncontrolled proliferation is a distinguishing property of a tumor as a whole, the individual cells that make up the tumor exhibit considerable variation in many properties, including morphology, proliferation kinetics, and the ability to initiate tumor growth in transplant assays. Understanding the molecular and cellular basis of this heterogeneity has important implications in the design of therapeutic strategies. The mechanistic basis of tumor heterogeneity has been uncertain; however, there is now strong evidence that cancer is a cellular hierarchy with cancer stem cells at the apex. This review provides a historical overview of the influence of hematology on the development of stem cell concepts and their linkage to cancer.

Deregulation of c-Myc Confers distinct survival requirements for memory B cells, plasma cells, and their progenitors

Deregulation of the c-Myc oncogene is tightly associated with human and murine plasma cell (PC) neoplasms. Through the analysis of Ag-specific B cell responses in mice where Myc is targeted to the Igh Calpha locus, we show here that c-Myc dramatically impairs the primary and secondary Ab response. This impairment is differentiation stage specific, since germinal center B cell formation, affinity maturation, and class switch recombination were intact. Examination of PC viability revealed that c-Myc triggered apoptosis only upon final maturation when Ab is secreted and is resistant to the survival factor BAFF (B cell-activating factor belonging to the TNF family). In contrast, PC precursors (PC(pre)) that ultimately give rise to mature PCs survived normally and vigorously expanded with BAFF signaling. We further show that c-Myc also facilitates the apoptosis of memory B cells. Thus, Calpha-Myc controls both cellular arms of long-lived B cell immunity than previously anticipated. Only when deregulation of c-Myc was combined with enforced Bcl-x(L) expression were mature PCs able to survive in response to BAFF. These data indicate that the survival requirements for tumor-susceptible PC(pre) and PCs are distinct and that tumor progression likely develops as PC(pre) transition to functional PCs when apoptotic pathways such as members of the Bcl-2 family are disabled.

Cancer stem cell-directed therapies: recent data from the laboratory and clinic

Cancer stem cells (CSCs) are defined by their ability to (i) fully recapitulate the tumor of origin when transplanted into immunodeficient mouse hosts, and (ii) self-renew, demonstrated by their ability to be serially transplanted. These properties suggest that CSCs are required for tumor maintenance and metastasis; thus, it has been predicted that CSC elimination is required for cure. This prediction has profoundly altered paradigms for cancer research, compelling investigators to prospectively isolate CSCs to characterize the molecular pathways regulating their behavior. Many potential strategies for CSC-directed therapy have been proposed, but few studies have rigorously demonstrated their efficacy using in vivo models. Herein, we highlight recent studies that demonstrate the utility of CSC-directed therapies and discuss the implications of the CSC hypothesis to experimental design and therapeutic strategies.

Can we finally target the leukemic stem cells?

Two key issues must be addressed in the discussion of targeting leukemic stem cells: (1) can the leukemic stem cell be targeted in vivo, and (2) how to assess whether the leukemic stem cell is actually being targeted. Currently several small molecule and antibody- or ligand-based agents have shown activity in selectively targeting the leukemic stem cell. However, there is debate about how to use these targeted agents and how to identify and quantitate the leukemic stem cell to determine whether or not it is being targeted. Parameters are suggested here to help identify and quantitate leukemic stem cells in the clinical context.

Protein kinase C signalling in leukemia

The protein kinase C (PKC) family of proteins includes several kinases that share structural homology, but at the same time exhibit substantial functional diversity. There is a significant amount of evidence establishing distinct patterns of expression and function for different PKC isoforms and groups in different leukemias. Although most members of this family promote leukemic cell survival and growth, others exhibit opposing effects and participate in the generation of antileukemic responses. This review summarizes work in this field on the relevance of distinct members of the PKC family in the pathophysiology of myeloid and lymphoid leukemias. The clinical-therapeutic potential of such ongoing work for the treatment of future development of novel approaches for the treatment of different types of leukemias is discussed.

Redox regulation of cell survival

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulation of cell survival. In general, moderate levels of ROS/RNS may function as signals to promote cell proliferation and survival, whereas severe increase of ROS/RNS can induce cell death. Under physiologic conditions, the balance between generation and elimination of ROS/RNS maintains the proper function of redox-sensitive signaling proteins. Normally, the redox homeostasis ensures that the cells respond properly to endogenous and exogenous stimuli. However, when the redox homeostasis is disturbed, oxidative stress may lead to aberrant cell death and contribute to disease development. This review focuses on the roles of key transcription factors, signal-transduction pathways, and cell-death regulators in affecting cell survival, and how the redox systems regulate the functions of these molecules. The current understanding of how disturbance in redox homeostasis may affect cell death and contribute to the development of diseases such as cancer and degenerative disorders is reviewed. We also discuss how the basic knowledge on redox regulation of cell survival can be used to develop strategies for the treatment or prevention of those diseases.

Multispectral imaging of hematopoietic cells: where flow meets morphology

Normal and abnormal blood cells are typically analyzed by either histologic or flow cytometric approaches. Histology allows morphological examination of complex visual traits but with relatively limited numbers of cells. Flow cytometry can quantify multiple fluorescent parameters on millions of cells, but lacks morphological or sub-cellular spatial detail. In this review we present how a new flow technology, the ImageStream (Amnis Corporation, Seattle, WA), blends morphology and flow cytometry and can be used to analyze cell populations in ways not possible by standard histology or flow cytometry alone. The ImageStream captures brightfield, darkfield and multiple fluorescent images of individual cells in flow. The images can then be analyzed for levels of fluorescence intensity in multiple ways (i.e. maximum, minimum, or mean) as well as the shape and size of the area of fluorescence. Combinatorial measurements can also be defined to compare levels and spatial associations for multiple fluorescent channels. We demonstrate an application of this technology to distinguish six stages of erythroid maturation which have been classically defined by morphological criteria, by measuring changes in Ter119 mean intensity and area, DNA (DRAQ5 stain) mean intensity and area, and RNA content (thiazole orange stain). Using this approach, we find that other characteristics of erythroid maturation, such as marker expression and nuclear offset, vary appropriately within the defined cell subsets. Finally, we show that additional measurements of cell characteristics not classically analyzed in cytometry, including surface unevenness and unusually high contrast in brightfield images combined with fluorescent markers allow complex discriminations of rare populations of cells.

Getting to the stem of chronic myeloid leukaemia

Tyrosine kinase inhibitor (TKI) therapy for chronic myeloid leukaemia (CML) is the consummate success story for targeted therapy, yet relapse is a nearly inevitable consequence of cessation or interruption of therapy. Primitive TKI-refractory CML stem cells are the likely source of these relapses, as they provide sanctuary for the Philadelphia chromosome. In advanced disease, their progressively anaplastic progeny ultimately maintain CML independently of the CML haematopoietic stem cell (HSC). Interestingly, there are at least two distinct cell types capable of self-renewal in different phases of CML: first, a primitive HSC with BCR-ABL mutation, which maintains the more indolent chronic-phase disease and, second, a coexisting mutated progenitor cell which acquires stem cell characteristics responsible for rapid cell expansion in advanced disease.

Recent advances in cancer stem cells

The theory of cancer stem cells states that a subset of cancer cells within a tumor has the ability to self-renew and differentiate. Only those cells within a tumor that have these two properties are called cancer stem cells. This concept was first demonstrated in the study of leukemia where only cells with specific surface antigen profiles were able to cause leukemia when engrafted into immunodeficient mice. In recent years solid tumors were studied utilizing similar techniques in mice. Human tumors where evidence of cancer stem cells has been published include tumors of the breast, brain, pancreas, head and neck, and colon. If this difference in tumorigenicity of cancer cells also occurs in patients, then the ability to enrich for cancer stem cells lays an important groundwork for future studies where mechanisms involved in cancer stem cells can now be investigated.

Discovery of agents that eradicate leukemia stem cells using an in silico screen of public gene expression data

Increasing evidence indicates that malignant stem cells are important for the pathogenesis of acute myelogenous leukemia (AML) and represent a reservoir of cells that drive the development of AML and relapse. Therefore, new treatment regimens are necessary to prevent relapse and improve therapeutic outcomes. Previous studies have shown that the sesquiterpene lactone, parthenolide (PTL), ablates bulk, progenitor, and stem AML cells while causing no appreciable toxicity to normal hematopoietic cells. Thus, PTL must evoke cellular responses capable of mediating AML selective cell death. Given recent advances in chemical genomics such as gene expression-based high-throughput screening (GE-HTS) and the Connectivity Map, we hypothesized that the gene expression signature resulting from treatment of primary AML with PTL could be used to search for similar signatures in publicly available gene expression profiles deposited into the Gene Expression Omnibus (GEO). We therefore devised a broad in silico screen of the GEO database using the PTL gene expression signature as a template and discovered 2 new agents, celastrol and 4-hydroxy-2-nonenal, that effectively eradicate AML at the bulk, progenitor, and stem cell level. These findings suggest the use of multicenter collections of high-throughput data to facilitate discovery of leukemia drugs and drug targets.

Chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is typified by robust marrow and extramedullary myeloid cell production. In the absence of therapy or sometimes despite it, CML has a propensity to progress from a relatively well tolerated chronic phase to an almost uniformly fatal blast crisis phase. The discovery of the Philadelphia chromosome followed by identification of its BCR-ABL fusion gene product and the resultant constitutively active P210 BCR-ABL tyrosine kinase, prompted the unraveling of the molecular pathogenesis of CML. Ground-breaking research demonstrating that BCR-ABL was necessary and sufficient to initiate chronic phase CML provided the rationale for targeted therapy. However, regardless of greatly reduced mortality rates with BCR-ABL targeted therapy, most patients harbor quiescent CML stem cells that may be a reservoir for disease progression to blast crisis. While the hematopoietic stem cell (HSC) origin of CML was first suggested over 30 years ago, only recently have the HSC and progenitor cell-specific effects of the molecular mutations that drive CML been investigated. This has provided the impetus for investigating the genetic and epigenetic events governing HSC and progenitor cell resistance to therapy and their role in disease progression. Accumulating evidence suggests that the acquired BCR-ABL mutation initiates chronic phase CML and results in aberrant stem cell differentiation and survival. This eventually leads to the production of an expanded progenitor population that aberrantly acquires self-renewal capacity resulting in leukemia stem cell (LSC) generation and blast crisis transformation. Therapeutic recalcitrance of blast crisis CML provides the rationale for targeting the molecular pathways that drive aberrant progenitor differentiation, survival and self-renewal earlier in disease before LSC predominate.

BMS-214662 potently induces apoptosis of chronic myeloid leukemia stem and progenitor cells and synergizes with tyrosine kinase inhibitors

Chronic myeloid leukemia (CML), a hematopoietic stem-cell disorder, cannot be eradicated by conventional chemotherapy or the tyrosine kinase inhibitor imatinib mesylate (IM). To target CML stem/progenitor cells, we investigated BMS-214662, a cytotoxic farnesyltransferase inhibitor, previously reported to kill nonproliferating tumor cells. IM or dasatinib alone reversibly arrested proliferation of CML stem/progenitor cells without inducing apoptosis. In contrast, BMS-214662, alone or in combination with IM or dasatinib, potently induced apoptosis of both proliferating and quiescent CML stem/progenitor cells with less than 1% recovery of Philadelphia-positive long-term culture-initiating cells. Normal stem/progenitor cells were relatively spared by BMS-214662, suggesting selectivity for leukemic stem/progenitor cells. The ability to induce selective apoptosis of leukemic stem/progenitor cells was unique to BMS-214662 and not seen with a structurally similar agent BMS-225975. BMS-214662 was cytotoxic against CML blast crisis stem/progenitor cells, particularly in combination with a tyrosine kinase inhibitor and equally effective in cell lines harboring wild-type vs mutant BCR-ABL, including the T315I mutation. This is the first report of an agent with activity in resistant and blast crisis CML that selectively kills CML stem/progenitor cells through apoptosis and offers potential for eradication of chronic phase CML.