Processing/activation of caspases, -3 and -7 and -8 but not caspase-2, in the induction of apoptosis in B-chronic lymphocytic leukemia cells

Insights Regarding the Role of Inflammasomes in Leukemia: What Do We Know?

Inflammation is a physiological mechanism of the immune response and has an important role in maintaining the hematopoietic cell niche in the bone marrow. During this process, the participation of molecules produced by innate immunity cells in response to a variety of pathogen-associated molecular patterns and damage-associated molecular patterns is observed. However, chronic inflammation is intrinsically associated with leukemogenesis, as it induces DNA damage in hematopoietic stem cells and contributes to the creation of the preleukemic clone. Several factors influence the malignant transformation within the hematopoietic microenvironment, with inflammasomes having a crucial role in this process, in addition to acting in the regulation of hematopoiesis and its homeostasis. Inflammasomes are intracellular multimeric complexes responsible for the maturation and secretion of the proinflammatory cytokines interleukin-1β and interleukin-18 and the cell death process via pyroptosis. Therefore, dysregulation of the activation of these complexes may be a factor in triggering several diseases, including leukemias, and this has been the subject of several studies in the area. In this review, we summarized the current knowledge on the relationship between inflammation and leukemogenesis, in particular, the role of inflammasomes in different types of leukemias, and we describe the potential therapeutic targets directed at inflammasomes in the leukemic context.

Assessment of Phenylboronic Acid Nitrogen Mustards as Potent and Selective Drug Candidates for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) has limited treatment options and the worst prognosis among all types of breast cancer. We describe two prodrugs, namely, CWB-20145 (1) and its methyl analogue FAN-NM-CH3 (2) that reduced the size of TNBC-derived tumors. The DNA cross-linking of nitrogen mustard prodrugs 1 and 2 was superior to that of chlorambucil and melphalan once activated in the presence of H2O2. The cellular toxicity of 1 and 2 was demonstrated in seven human cancer cell lines. The TNBC cell line MDA-MB-468 was particularly sensitive toward 1 and 2. Compound 2 was 10 times more cytotoxic than chlorambucil and 16 times more active than melphalan. An evaluation of the gene expression demonstrated an upregulation of the tumor suppressor genes p53 and p21 supporting a transcriptional mechanism of a reduced tumor growth. Pharmacokinetic studies with 1 showed a rapid conversion of the prodrug. The introduction of a methyl group generated 2 with an increased half-life. An in vivo toxicity study in mice demonstrated that both prodrugs were less toxic than chlorambucil. Compounds 1 and 2 reduced tumor growth with an inhibition rate of more than 90% in athymic nude mice xenografted with MDA-MB-468 cells. Together, the in vivo investigations demonstrated that treatment with 1 and 2 suppressed tumor growth without affecting normal tissues in mice. These phenylboronic acid nitrogen mustard prodrugs represent promising drug candidates for the treatment of TNBC. However, the mechanisms underlying their superior in vivo activity and selectivity as well as the correlation between H2O2 level and in vivo efficacy are not yet fully understood.

Novel roles of apoptotic caspases in tumor repopulation, epigenetic reprogramming, carcinogenesis, and beyond

Apoptotic caspases have long been studied for their roles in programmed cell death and tumor suppression. With recent discoveries, however, it is becoming apparent these cell death executioners are involved in additional biological pathways beyond killing cells. In some cases, apoptotic cells secrete growth signals to stimulate proliferation of neighboring cells. This pathway functions to regenerate tissues in multiple organisms, but it also poses problems in tumor resistance to chemo- and radiotherapy. Additionally, it was found that activation of caspases does not irreversibly lead to cell death, contrary to the established paradigm. Sub-lethal activation of caspases is evident in cell differentiation and epigenetic reprogramming. Furthermore, evidence indicates spontaneous, unprovoked activation of caspases in many cancer cells, which plays pivotal roles in maintaining their tumorigenicity and metastasis. These unexpected findings challenge current cancer therapy approaches aimed at activation of the apoptotic pathway. At the same time, the newly discovered functions of caspases suggest new treatment approaches for cancer and other pathological conditions in the future.

RPPA-based protein profiling reveals eIF4G overexpression and 4E-BP1 serine 65 phosphorylation as molecular events that correspond with a pro-survival phenotype in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), the most common adult leukemia, remains incurable despite advancements in treatment regimens over the past decade. Several expression profile studies have been pursued to better understand CLL pathogenesis. However, these large-scale studies only provide information at the transcriptional level. To better comprehend the differential protein changes that take place in CLL, we performed a reverse-phase protein array (RPPA) analysis using 167 different antibodies on B-cell lysates from 18 CLL patients and 6 normal donors. From our analysis, we discovered an enrichment of protein alterations involved with mRNA translation, specifically upregulation of the translation initiator eIF4G and phosphorylation of the cap-dependent translation inhibitor 4E-BP1 at serine 65. Interestingly, 4E-BP1 phosphorylation occurred independently of AKT phosphorylation, suggesting a disconnect between PI3K/AKT pathway activation and 4E-BP1 phosphorylation. Based on these results, we treated primary CLL samples with NVP-BEZ235, a PI3K/mTOR dual inhibitor, and compared its apoptotic-inducing potential against the BTK inhibitor Ibrutinib and the PI3Kδ inhibitor Idelalisib. We demonstrated that treatment with NVP-BEZ235 caused greater apoptosis, greater apoptotic cleavage of eIF4G, and greater dephosphorylation of 4E-BP1 in primary CLL cells. Taken together, these results highlight the potential dependence of eIF4G overexpression and 4E-BP1 phosphorylation in CLL survival.

Re-directing an alkylating agent to mitochondria alters drug target and cell death mechanism

We have successfully delivered a reactive alkylating agent, chlorambucil (Cbl), to the mitochondria of mammalian cells. Here, we characterize the mechanism of cell death for mitochondria-targeted chlorambucil (mt-Cbl) in vitro and assess its efficacy in a xenograft mouse model of leukemia. Using a ρ° cell model, we show that mt-Cbl toxicity is not dependent on mitochondrial DNA damage. We also illustrate that re-targeting Cbl to mitochondria results in a shift in the cell death mechanism from apoptosis to necrosis, and that this behavior is a general feature of mitochondria-targeted Cbl. Despite the change in cell death mechanisms, we show that mt-Cbl is still effective in vivo and has an improved pharmacokinetic profile compared to the parent drug. These findings illustrate that mitochondrial rerouting changes the site of action of Cbl and also alters the cell death mechanism drastically without compromising in vivo efficacy. Thus, mitochondrial delivery allows the exploitation of Cbl as a promiscuous mitochondrial protein inhibitor with promising therapeutic potential.

PI3-Kinase Regulates Survival of Chronic Lymphocytic Leukemia B-Cells by Preventing Caspase 8 Activation

Studies to investigate signal transduction pathways that support viability and prevent apoptosis of chronic lymphocytic leukemia cells (CLL) were initiated as a result of microarray cDNA analyses which revealed expression of genes whose products regulate cell cycle progression. Immunoblots revealed translation of several genes including caspases, cyclin D1, and the PI3-kinase dependent, survival kinase, Akt. Akt was found to be activated. Inhibition of PI3-kinase with specific inhibitor, LY294002, led to the induction of apoptosis that was caspase 8 dependent, but independent of Akt as LY294002 did not depress a high basal level of Akt activity found in CLL cells. Phosphorylation of Akt was maintained, enzymatic activity undiminished, and phosphorylation of substrates sustained. Caspases, however were activated, PARP cleaved and DNA fragmented. Caspase inhibitors revealed that initiator caspase 8 was required for classic apoptosis when PI3-kinase was inhibited, and specific activity assays demonstrated its early activation. GSK-3beta a kinase regulated via PI3-kinase dependent, down-stream kinases, was responsible for regulating cyclin D1 levels in CLL cells, but neither GSK-3beta nor calpain was responsible for induction of apoptosis, or activation of executioner caspase 3, following LY294002 treatment. PI3-kinase mediated protection against caspase activation in CLL B-cells therefore is not mediated through classic Akt survival pathways. The data further support the hypothesis that signal transducing, membrane associated receptors triggered by extrinsic factors, maintain CLL leukemic B-cell survival in vivo by preventing caspase activation.

Colchicine, a microtubule depolymerizing agent, inhibits myocardial apoptosis in rats

Heart failure is the most common cardiovascular disease with high mortality and morbidity. Both enhanced microtubule polymerization and cardiomyocyte apoptosis are involved in the pathogenesis of heart failure. However, the link between the two mechanisms remains to be elucidated. In this study, we thus address this important issue in cultured cardiomyocytes from Wistar rats in vitro and in angiotensin II (ATII)-infused rats in vivo. Confocal microscopy examination showed that in cultured rat cardiomyocytes, micrographic density of microtubules was increased by paclitaxel, a microtubule-polymerizing agent, and decreased by colchicine, a microtubule-depolymerizing agent, but not affected by ATII, isoproterenol, or tumor necrosis factor-alpha alone. Immunoblotting analysis showed that Bax/Bcl-2 ratio, which is associated with the activation of caspase-3, was significantly increased in ATII-stimulated cultured cardiomyocytes in vitro and in ATII-infused rats in vivo, both of which were inhibited by co-treatment with colchicine. Caspase-3 and TUNEL assay to detect apoptosis in vitro demonstrated that paclitaxel or ATII alone significantly enhanced and their combination further accelerated cardiomyocyte apoptosis, which was again significantly inhibited by colchicine. Caspase-3 and TUNEL assay in vivo also demonstrated that ATII infusion significantly increased myocardial apoptosis and that co-treatment with colchicine significantly suppressed the apoptosis. In conclusion, these results indicate that a microtubule-depolymerizing agent could be a potential therapeutic strategy for treatment of heart failure.

Bortezomib induces different apoptotic rates in B-CLL cells according to IgVH and BCL-6 mutations

BACKGROUND

B-cell chronic lymphocytic leukemia (B-CLL) is a remarkably heterogeneous disorder. Some patients have an indolent disease whereas others undergo a more agressive presentation needing treatment. New therapeutics approaches are necessary for the treatment of B-CLL. Bortezomib (Btz), is a proteasome inhibitor, currently undergoing clinical trials whose function, at least in part, by stabilizing the IkappaBalpha protein and inhibiting NFkappaB activation.

OBJECTIVE

The objective of this work was to study the effects of Btz on isolated human B-CLL cells, in vitro, and to correlate the differential rates of apoptosis induction with biological variables.

MATERIAL AND METHODS

31 B-CLL samples, from patients in stage A of Binet were used for this study, and the apoptotic effect of Btz on these cells was measured.

RESULTS

Our data show that Btz treatment of B-CLL cells induces apoptosis in a time and dose-dependent manner. The apoptosis induction is mediated in part by inhibition of NFkappaB and is dependent on caspases activation. Interesting, in IgVH mutated cells, Btz have statistically significant differences in their in vitro activity on B-CLL cells according to their BCL-6 mutational status.

CONCLUSIONS

Btz is a promising pharmacologic agent for the treatment of B-CLL, but its efficacy seems to be related to IgVH and BCL-6 mutational status, therefore, it could be interesting to further investigate the mechanisms involved in the different behavior of the cells in response to apoptosis induction by this drug.

Escherichia coli cyclomodulin Cif induces G2arrest of the host cell cycle without activation of the DNA-damage checkpoint-signalling pathway

The cycle inhibiting factor (Cif) belongs to a family of bacterial toxins and effector proteins, the cyclomodulins, that deregulate the host cell cycle. Upon injection into HeLa cells by the enteropathogenic Escherichia coli (EPEC) type III secretion system, Cif induces a cytopathic effect characterized by the recruitment of focal adhesion plates and the formation of stress fibres, an irreversible cell cycle arrest at the G(2)/M transition, and sustained inhibitory phosphorylation of mitosis inducer, CDK1. Here, we report that the reference typical EPEC strain B171 produces a functional Cif and that lipid-mediated delivery of purified Cif into HeLa cells induces cell cycle arrest and actin stress fibres, implying that Cif is necessary and sufficient for these effects. EPEC infection of intestinal epithelial cells (Caco-2, IEC-6) also induces cell cycle arrest and CDK1 inhibition. The effect of Cif is strikingly similar to that of cytolethal distending toxin (CDT), which inhibits the G(2)/M transition by activating the DNA-damage checkpoint pathway. However, in contrast to CDT, Cif does not cause phosphorylation of histone H2AX, which is associated with DNA double-stranded breaks. Following EPEC infection, the checkpoint effectors ATM/ATR, Chk1 and Chk2 are not activated, the levels of the CDK-activating phosphatases Cdc25B and Cdc25C are not affected, and Cdc25C is not sequestered in host cell cytoplasm. Hence, Cif activates a DNA damage-independent signalling pathway that leads to inhibition of the G(2)/M transition.

Induction of CD95 upregulation does not render chronic lymphocytic leukemia B-cells susceptible to CD95-mediated apoptosis

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by a progressive accumulation of long-lived and well-differentiated clonal B-lymphocytes in peripheral blood, lymphoid tissue and bone marrow. Although B-CLL pathogenesis is not entirely understood, the progressive increase in lymphocyte counts coupled with the very low proportion of proliferating cells suggests that B-CLL may be primarily determined by defective apoptosis. Consistently, freshly analyzed CLL B-cells express very low levels of membrane CD95, one of the best-known receptors involved in triggering apoptosis. In this study, CD95 upregulation on CLL B-cells was induced by culturing clonal B-cells in the presence of supernatants from preactivated autologous T-lymphocytes. Intracellular cytokine staining of preactivated autologous T-lymphocytes using monoclonal antibodies (moAbs) specific for Th1 or Th2 cytokines, namely interleukin (IL)-2, IL-4, IL-5, IL-10 and interferon (IFN)-gamma, showed these cells to be positive for IL-2 and IFN-gamma. Blocking experiments using moAbs specific for IL-2 and/or IFN-gamma revealed that CD95 upregulation on CLL B-cells was mainly driven by IFN-gamma. However, CD95-expressing CLL B-cells were demonstrated to be resistant to CD95-mediated apoptosis, thus arguing against strategies aimed at exploiting CD95-mediated apoptosis for immunotherapy of B-CLL.

High expression of bfl-1 contributes to the apoptosis resistant phenotype in B-cell chronic lymphocytic leukemia

In order to identify regulatory genes involved in the development of an apoptosis-resistant phenotype in patients with chemotherapy refractory B-cell chronic lymphocytic leukemia (B-CLL) expression of apoptosis-regulating genes in B-CLL cells was quantified using cDNA arrays and RT-PCR. Data were obtained from and compared between 2 groups of B-CLL patients with either nonprogressive, indolent, previously untreated disease and with leukemic cells sensitive to in vitro fludarabine-induced apoptosis, referred to as sensitive B-CLL (sB-CLL) or with progressive, chemotherapy refractory disease and with leukemic cells resistant to in vitro fludarabine-induced apoptosis, referred to as resistant B-CLL (rB-CLL). By performing a supervised clustering of genes that most strongly discriminated between rB-CLL vs. sB-CLL a small group of genes was identified, where bfl-1 was the strongest discriminating gene (p < 0.05), with higher expression in rB-CLL. A group of apoptosis-regulating genes were modulated during induction of apoptosis by serum deprivation in vitro in a similar manner in all cases studied. However, bfl-1 was preferentially downregulated in sB-CLL as compared to rB-CLL (p < 0.05). We conclude that bfl-1 may be an important regulator of B-CLL apoptosis, which could contribute to disease progression and resistance to chemotherapy, and as such represent a future potential therapeutic target.

Simvastatin induces apoptosis of B-CLL cells by activation of mitochondrial caspase 9

BACKGROUND AND OBJECTIVES

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the western world. Despite several advances in therapeutic options, the disease remains incurable. Recently, it was repeatedly demonstrated that statins, competitive inhibitors of 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase, have antineoplastic effects. Therefore we aimed to study the effects of simvastatin (Sim) on malignant B cells derived from patients with CLL and mechanisms of action of the drug.

METHODS AND RESULTS

Purified B-CLL cells from 15 patients were cultured either alone or with Sim at concentrations of 10, 50, and 100 microM. Viability, measured by the activity of mitochondrial dehydrogenases, was reduced significantly in the cells treated with Sim at 50 and 100 microM for 24 hours (p<0.005). The level of apoptosis, as measured by annexin binding to exposed phosphatidylserine moieties, increased significantly in the treated cells at concentrations higher than 50 microM for 24 hours (p<0.003). The level of necrosis, as measured by propidium iodide internalization, increased significantly after 24 hours exposure to Sim at 50 microM (p<0.01). The apoptotic cascade was studied by immunoblot analysis of caspases following Sim treatment. These showed cleavage of caspases 9, 8, and 3. Addition of the caspase inhibitor Z-VAD.fmk inhibited caspase 8 and 3 significantly but did not affect caspase 9.

CONCLUSION

Exposure of clonal B lymphocytes from patients with CLL to simvastatin decreases viability significantly by the induction of apoptosis. The apoptosis induced by Sim is probably initiated by the mitochondrial caspase 9, which indirectly leads to activation of caspase 3 and 8.

Depsipeptide (FR901228) induces histone acetylation and inhibition of histone deacetylase in chronic lymphocytic leukemia cells concurrent with activation of caspase 8-mediated apoptosis and down-regulation of c-FLIP protein

Depsipeptide is in clinical trials for chronic lymphocytic leukemia (CLL) on the basis of earlier observations demonstrating selective in vitro activity in CLL. We sought to determine the relationship of histone H3 and H4 acetylation, inhibition of histone deacetylase, and apoptosis observed in CLL cells to justify a pharmacodynamic end point in these clinical trials. We demonstrate that in vitro depsipeptide induces histone H3 and H4 acetylation and histone deacetylase enzyme inhibition at concentrations corresponding to the LC50 (concentration producing 50% cell death) for cultured CLL cells (0.038 microM depsipeptide). The changes in histone acetylation are lysine specific, involving H4 K5, H4 K12, and H3 K9, and to a lesser extent H4 K8, but not H4 K16 or H3 K14. Depsipeptide-induced apoptosis is caspase dependent, selectively involving the tumor necrosis factor (TNF) receptor (extrinsic pathway) initiating caspase 8 and effector caspase 3. Activation of caspase 8 was accompanied by the down-regulation of cellular FLICE-inhibitory protein (c-FLIP, I-FLICE) without evidence of Fas (CD95) up-regulation. Changes in other apoptotic proteins, including Bcl-2, Bax, Mcl-1, and X-linked inhibitor of apoptosis (XIAP), were not observed. Our results demonstrate a relationship between target enzyme inhibition of histone deacetylase, histone H3 and H4 acetylation, and apoptosis involving the TNF-receptor pathway of apoptosis that is not used by other therapeutic agents in CLL. These data suggest use of histone H3 and H4 acetylation, inhibition of histone deacetylase, and down-regulation of FLIP as pharmacodynamic end points for further evaluation of this drug in patients.

Caspase-mediated cell death in hematological malignancies: theoretical considerations, methods of assessment, and clinical implications

Apoptosis, the caspase-mediated cell death, plays an important role in the etiology, pathogenesis and therapy of a variety of diseases. Abnormalities of apoptosis regulation, resulting in either its inhibition or enhancement, play a key role in the development of various malignant hematological disorders. Several routine and new therapeutic strategies in Oncohematology are based on apoptosis modulation. Cytotoxic effects of most antineoplastic drugs are based on induction of apoptosis. The accurate estimate of incidence of apoptosis, therefore, is of importance in Oncohematology. In this review we provide an overview of the methods designed to measure the incidence of apoptosis, including the recently developed assays that are based on detection of caspases activation. We also review recent findings on the role of caspase-mediated cell death in hematological malignancies and discuss their clinical implications, including new therapeutical strategies that evolve from these findings.

Tetrocarcin-A--induced ER stress mediates apoptosis in B-CLL cells via a Bcl-2--independent pathway

Tetrocarcin-A (TC-A), an antibiotic agent isolated from actinomycetes, has recently been described to antagonize Bcl-2 functions, thereby sensitizing tumor cells to cell death signals under control of Bcl-2. In this study, we analyzed the direct proapoptotic effect of TC-A in the B-chronic lymphocytic leukemia (B-CLL) model. We focused on the signal cascade triggered by TC-A in B-CLL cells and identified activated mitochondrial as well as endoplasmatic reticulum (ER) stress signals. The expression levels of known effector molecules mediating mitochondrial signaling, such as Bax and Bid, and the antagonistic molecule Bcl-2 did not influence sensitivity of B-CLL cells to TC-A. Furthermore, the molecular chaperone and sensor of ER stress, HSP70, though significantly up-regulated in B-CLL cells undergoing TC-A-triggered apoptosis, was ineffective to exert its anti-apoptotic function described in multiple cell death pathways. Autologous T cells of B-CLL patients were significantly less sensitive to TC-A as were also T cells from healthy donors when compared with their normal B-cell fraction. Furthermore, sensitivity of B-CLL cells to TC-A treatment in vitro was dependent neither on the expression levels of CD38-a prognostic factor for survival of B-CLL patients as well as for their response to therapy-nor on the clinical stage or pretreatment status of patients. From our data showing that TC-A induced a cell death pathway via ER stress preferentially in B cells and that it acted independently of important markers of drug sensitivity and of clinical markers, we conclude that TC-A might represent an attractive candidate drug for further evaluation in preclinical trials.

Aberrant expression of B-lymphocyte stimulator by B chronic lymphocytic leukemia cells: a mechanism for survival

B-cell chronic lymphocytic leukemia (B-CLL) is defined by the accumulation of CD5(+) B cells in the periphery and bone marrow. This disease is not characterized by highly proliferative cells but rather by the presence of leukemic cells with significant resistance to apoptosis and, therefore, prolonged survival. B-lymphocyte stimulator (BLyS) is a newly identified tumor necrosis factor (TNF) family member shown to be critical for maintenance of normal B-cell development and homeostasis and it shares significant homology with another TNF superfamily member, APRIL. The striking effects of BLyS on normal B-cell maintenance and survival raises the possibility that it may be involved in pathogenesis and maintenance of hematologic malignancies, including B-CLL. In this study, we investigated the status of APRIL and BLyS expression, as well as their receptors, in this disease. All B-CLL patient cells studied expressed one or more of 3 known receptors for BLyS; however, the pattern of expression was variable. In addition, we demonstrate for the first time that B-CLL cells from a subset of patients aberrantly express BLyS and APRIL mRNA, whereas these molecules were not detectable in normal B cells. Furthermore, we provide in vitro evidence that BLyS protects B-CLL cells from apoptosis and enhances cell survival. Because these molecules are key regulators of B-cell homeostasis and tumor progression, leukemic cell autocrine expression of BLyS and APRIL may be playing an important role in the pathogenesis of this disease.

Mechanisms of resistance to TRAIL-induced apoptosis in primary B cell chronic lymphocytic leukaemia

Primary B cells from B cell chronic lymphocytic leukaemia (B-CLL) were resistant to the novel selective cytotoxic agent, TNF-related apoptosis-inducing ligand (TRAIL). Low levels of the death-inducing TRAIL receptors, TRAIL-R1 and TRAIL-R2 but not the putative 'decoy' receptors, TRAIL-R3 and TRAIL-R4, were expressed on the surface of B-CLL cells. Resistance to TRAIL was upstream of caspase-8 activation, as little or no caspase-8 was processed in TRAIL-treated B-CLL cells. Low levels of a TRAIL death-inducing signalling complex (DISC) were formed in these cells, accompanied by the recruitment of endogenous FADD, caspase-8 and c-FLIP(L) but not c-FLIP(S). Both caspase-8 and c-FLIP(L) were cleaved to form two stable intermediates of approximately 43 kDa, which remained associated with the DISC. Caspase-8 was not further processed to its active heterotetramer. Thus the resistance of B-CLL cells to TRAIL may be due partly to low surface expression of the death receptors resulting in low levels of DISC formation and also to the high ratio of c-FLIP(L) to caspase-8 within the DISC, which would prevent further activation of caspase-8. Our results highlight the possibility of sensitising B-CLL cells to TRAIL by modulation of c-FLIP levels or by upregulation of surface expression of death receptors.

In vitro evaluation of bendamustine induced apoptosis in B-chronic lymphocytic leukemia

Bendamustine is a novel cytostatic agent, with activity in non-Hodgkin's lymphomas including B-chronic lymphocytic leukemia (B-CLL). The knowledge about its mode of action, however, is still limited. Here, we investigated the in vitro ability of bendamustine to induce apoptosis on freshly isolated peripheral lymphocytes in B-CLL and analyze the potential underlying mechanisms of action for inducing apoptosis. In CLL cells taken from 37 previously treated and untreated CLL patients, we investigated the influence of bendamustine alone, and in combination with fludarabine, on the induction of apoptosis and changes of Bcl-2 and Bax expression on mRNA and protein level using the RNase protection assay or flow cytometry, respectively. Apoptotic cells were determined with flow cytometry using the fluorescent DNA-binding agent 7-ADD. Using bendamustine alone in concentrations from 1 microg/ml to 50 microg/ml, a dose- and time-dependent manner of cytotoxicity from 30.4% to 94.8% after 48 h could be observed. The LD50 for untreated and pretreated CLL cells was 7.3 or 4.4 microg/ml, respectively. The median apoptotic rate was similar in both groups. The combination of bendamustine with fludarabine led to a highly synergistic effect in inducing apoptosis, which was 150% higher than expected for bendamustine plus fludarabine. The level of the initial Bcl-2 and Bax protein and the m-RNA expression remained unchanged during the incubation with bendamustine. In conclusion, this study demonstrates for the first time the in vitro efficacy of bendamustine in inducing apoptosis in B-CLL cells alone and in combination with fludarabine.

Modulation of the activity of calcium-activated neutral proteases (calpains) in chronic lymphocytic leukemia (B-CLL) cells

Decreased susceptibility to apoptosis and impaired proliferative control are thought to be responsible for prolonged life span and accumulation of chronic lymphocytic leukemia (B-CLL) cells. The activity of calpains (calcium-dependent, neutral proteases, active in the cells responding to signals inducing a rise of cytoplasmic Ca(++)) is involved in the regulation of apoptosis of some cell types by interaction with caspase-3. This work verifies the hypothesis of the abnormal activity of calpains and its role in reduced apoptosis of the B-CLL cells. Casein zymography, reverse transcriptase-polymerase chain reaction, and Western blotting were used for identification and quantification of the activity and expression of calpains in B-CLL cells and purified normal B lymphocytes. The activity and expression of mu-calpain (requiring micromolar Ca(++) for activation) are significantly higher in the leukemic than in nonmalignant cells. Contrarily, the activity and expression of m-calpain (requiring millimolar Ca(++)) as well as the expression of calpastatin (an endogenous inhibitor of calpains) are unchanged or reduced in the B-CLL lymphocytes. Correspondingly, the activity of caspase-3 is many times lower in the B-CLL cells than in normal B lymphocytes. Inhibition of overexpressed mu-calpain in living B-CLL cells in vitro results in doubling of the proportion of the cells undergoing spontaneous apoptosis. This observation suggests a possible role for calpains in longer survival of the B-CLL cells and may open new therapeutic possibilities.

CD5-induced apoptosis of B cells in some patients with chronic lymphocytic leukemia

Although B chronic lymphocytic leukemia (B-CLL) is characterized by prolonged survival of CD5(+) B cells in vivo, these cells apoptose spontaneously in vitro. The effect of CD5 ligation on apoptosis was studied in 27 newly diagnosed patients with B-CLL, in relation to the expression of surface IgM (sIgM), CD79b, CD38, CD72 and CD19. B cells from 15 patients (group I) were resistant to anti-CD5-induced apoptosis, whereas apoptosis above spontaneous levels was seen in the remaining 12 studied (group II). Group II was then subdivided on the basis of differences in the time required to reach maximum apoptosis: whilst B cells from seven patients underwent apoptosis by 18 h, those from the remaining five needed 36 h to apoptose. The expression of sIgM, CD5, CD79b and CD38 was higher in group II than group I, suggesting that signaling for apoptosis might operate via CD79, and that CD38 expression was required. As shown by flow cytometry and confirmed by Western blotting, apoptosis was associated with a decrease in the ratios of Bcl-2/Bax and Bcl(XL)/Bax, due to an increase in the level of Bax, but no change in that of Bcl-2. This heterogeneous apoptotic response to CD5 ligation offers an explanation for the incomplete success of anti-CD5 monoclonal therapy, and might help identify patients who would respond to such treatment.

Non-malignant leukocytes delay spontaneous B-CLL cell apoptosis

Malignant B cells from chronic lymphocytic leukemia (B-CLL) patients have a long survival in vivo, although, in culture, they spontaneously die by apoptosis. Here, we analyzed the capacity of accessory leukocytes to modulate apoptosis of B-CLL cells in vitro. To this end, we performed long-term cultures using total mononuclear cells (TMC) from B-CLL patients and TMC depleted from monocytes, NK cells and T lymphocytes (B-CLL cells). In all the patients studied (n = 25) the presence of accessory leukocytes markedly prolonged the survival of B-CLL cells. The anti-apoptotic effect was exerted by monocytes and, to a lesser degree, NK cells, partially through the release of soluble factors. Indeed, accessory leukocytes separated from leukemic cells by semipermeable membranes were still able to prolong B-CLL cell survival. By flow cytometric analysis we found that the protective effect of non-malignant cells was associated with delayed down-regulation of Bcl-2 expression on leukemic cells. By contrast, the expression of Fas and Fas ligand proteins was unchanged in most samples. Our findings suggest that monocytes and NK cells, by delaying leukemic cell apoptosis, may play a role in B-CLL cell accumulation in vivo.

Caspase 8 activation independent of Fas (CD95/APO-1) signaling may mediate killing of B-chronic lymphocytic leukemia cells by cytotoxic drugs or gamma radiation

Ligation of the cell-surface Fas molecule by its ligand (Fas-L) or agonistic anti-Fas monoclonal antibodies results in the cleavage and activation of the cysteine protease procaspase 8 followed by the activation of procaspase 3 and by apoptosis. In some leukemia cell lines, cytotoxic drugs induce expression of Fas-L, which may contribute to cell killing through the ligation of Fas. The involvement of Fas, Fas-L, and caspase 8 was studied in the killing of B-cell chronic lymphocytic leukemia (B-CLL) cells by chlorambucil, fludarabine, or gamma radiation. Spontaneous apoptosis was observed at 24-hour incubation, with additional apoptosis induced by each of the cytotoxic treatments. Although Fas mRNA expression was elevated after exposure to chlorambucil, fludarabine, or gamma radiation, Fas protein levels only increased after irradiation. Therefore, Fas expression may be regulated by multiple mechanisms that allow the translation of Fas mRNA only in response to restricted cytotoxic stimuli. None of the cytotoxic stimuli studied here induced Fas-L expression. An agonistic anti-Fas monoclonal antibody (CH-11) did not significantly augment apoptosis induction by any of the death stimuli. A Fas-blocking antibody (ZB4) did not inhibit spontaneous, chlorambucil-, fludarabine-, or radiation-induced apoptosis. However, procaspase 8 processing was induced by all cytotoxic stimuli. These data suggest that the Fas/Fas-L signaling system does not play a major role in the induction of apoptosis in B-CLL cells treated with cytotoxic drugs or radiation. However, Fas-independent activation of caspase 8 may play a crucial role in the regulation of apoptosis in these cells.

Upstream mediators of the Fas apoptotic transduction pathway are defective in B-chronic lymphocytic leukemia

Data concerning the presence and the functionality of Fas receptor in malignant B-cells are controversial. We have analyzed Fas molecules on B-cells from patients with B-chronic lymphocytic leukemia (B-CLL) cells. We observed a large variability, both of percentage of Fas-positive cells and of intensity of Fas level. Fas triggering was inefficient in inducing apoptosis whatever the number of Fas-positive B-cells, the amount of Fas receptors. B-cells were also resistant to etoposide treatment, but able to undergo apoptosis after dexamethasone treatment. We suggest that the Fas apoptotic pathway is altered in B-CLL patients at the initial step(s) of apoptotic machinery.

IFN-gamma induces the apoptosis of WEHI 279 and normal pre-B cell lines by expressing direct inhibitor of apoptosis protein binding protein with low pI

Interferon-gamma plays a crucial role in induction of Th1 response but is predominantly a negative regulator of B cell differentiation and Th2 response, so it is a key molecule in determining cellular or humoral immunity. In this study, we demonstrate that IFN-gamma induces apoptosis in WEHI 279 mouse B cells and IL-7-dependent mouse pre-B cells by disrupting mitochondrial membrane potential and cytochrome c release via down-regulation of Bcl-2 and Bcl-x(L). Furthermore, this apoptotic signal is promoted by the de novo synthesis of endogenous direct inhibitor of apoptosis protein binding protein with low pI (DIABLO) by IFN-gamma and its release from mitochondria into the cytosol. Inhibition of DIABLO expression by antisense oligonucleotide is sufficient to decrease caspase activities and DNA fragmentation, but not cytochrome c release from mitochondria, suggesting that DIABLO plays a critical role in promoting apoptotic signals downstream of mitochondrial events. Thus, these findings demonstrate a signaling pathway during B cell apoptosis induced by IFN-gamma and possible mechanisms by which B cell differentiation is negatively regulated by Th1-type cytokines.

Proteasome inhibitor-induced apoptosis of B-chronic lymphocytic leukaemia cells involves cytochrome c release and caspase activation, accompanied by formation of an approximately 700 kDa Apaf-1 containing apoptosome complex

Proteasome inhibitors, including lactacystin and MG132 (carbobenzoxyl-leucinyl-leucinyl-leucinal), potently induce apoptosis in leukaemic B cells from patients with B cell chronic lymphocytic leukaemia (B-CLL). This pro-apoptotic effect occurs in cells from patients at all stages of the disease, including those resistant to conventional chemotherapy, suggesting that proteasome inhibitors may be useful for treatment of B-CLL. Following initial inhibition of proteasomal activity, these agents induce mitochondrial cytochrome c release and caspase-dependent apoptosis, involving cleavage/activation of caspases -2, -3, -7, -8 and -9. Pre-treatment with the cell permeable caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe)fluoromethyl ketone (Z-VAD.fmk), did not prevent the release of cytochrome c or partial processing of caspase-9 but prevented activation of effector caspases and the induction of apoptosis. These results suggest that the release of cytochrome c is caspase independent and that caspase-9 is the initiator caspase in proteasome inhibitor-induced apoptosis of B-CLL cells. Activation of B-CLL lysates with dATP results in the formation of an approximately 700 kDa caspase-activating apoptosome complex containing Apaf-1. We describe for the first time the formation of a similar approximately 700 kDa caspase-activating apoptosome complex in B-CLL cells induced to undergo apoptosis by proteasome inhibitors.

Caspases: conductors of the cell death machinery in lymphoma cells

The present review focuses on recent insights into the regulation of caspases by other components of the apoptotic pathway, including the mechanisms by which caspase activation influence the death of lymphoma cells. In the light of our recent findings and similar observations of other investigators, it is likely that lymphoma cells possess the complete caspase machinery required for the apoptotic process. Inhibition of caspases activation appears as a potential mechanism to explain apoptotic defects of malignant B-cells, and thus may constitute the basis for new cancer therapies.

p53-independent upregulation of KILLER/DR5 TRAIL receptor expression by glucocorticoids and interferon-gamma

KILLER/DR5 is a death-domain-containing proapoptotic receptor that binds to the cytotoxic ligand TRAIL. It was originally reported that induction of KILLER/DR5 mRNA following DNA damage was p53-dependent, but some drugs that induce apoptosis can upregulate KILLER/DR5 mRNA expression in cell lines with mutated p53. We further extend those findings by classifying the capability of various apoptosis-inducing drugs to increase the expression of KILLER/DR5 mRNA in a p53-independent manner. beta-Lapachone, a topoisomerase inhibitor, increased KILLER/DR5 mRNA in colon cancer cell lines with wild-type p53 but not with mutant p53. In contrast, betulinic acid, a novel chemotherapeutic compound, induced apoptosis and KILLER/DR5 mRNA in melanoma and glioblastoma cells through a p53-independent mechanism. The synthetic glucocorticoid dexamethasone elevated KILLER/DR5 mRNA in glioblastoma, ovarian cancer, and colon cancer cell lines with mutant p53 undergoing apoptosis, and this induction was inhibited by the transcriptional inhibitor actinomycin D. Although another glucocorticoid, prednisolone, also induced apoptosis, it did not increase KILLER/DR5 mRNA. Finally, the cytokine interferon-gamma (IFN-gamma) induced apoptosis and KILLER/DR5 in cell lines with mutant p53, and the induction of KILLER/DR5 mRNA by IFN-gamma was delayed in cells lacking wild-type STAT1, a transcription factor implicated in IFN-gamma signaling. Similarly, the induction of KILLER/DR5 mRNA by the cytokine TNF-alpha was also delayed in cell lines with mutated STAT1. These findings suggest that KILLER/DR5 may play a role in p53-independent apoptosis induced by specific drugs and warrants further investigation as a novel target for chemotherapy of tumors lacking wild-type p53.

Contribution of nitric oxide to the apoptotic process in human B cell chronic lymphocytic leukaemia

B cell chronic lymphocytic leukaemia (B-CLL) is characterised by defective apoptosis that cannot be explained solely on the basis of the known chromosomal abnormalities. We and other have now reported that the leukemic cells spontaneously display the inducible isoform of nitric oxide synthase, iNOS. Inhibition of the iNOS pathway leads to increased apoptosis of the tumoral cells in vitro, indicating that the endogenous release of NO contributes to their resistance to the normal apoptotic process. The factors that induce the expression of iNOS in vivo in the leukemic cells are not yet identified. Yet, as interaction of B-CLL leukemic cells with bone marrow stromal cells promotes their survival, the involvement of adhesion molecules and integrins may be suspected. The engagement of CD23 stimulates iNOS activation in the tumoral cells, suggesting that in vivo interaction of CD23 with one of its recognised ligands may contribute to iNOS induction. A role for CD40-CD40 ligand interaction may also be hypothesised. The mechanisms involved in the anti-apoptotic role of NO are not fully understood, but may implicate the inhibition of caspase activity, hence the impairment of the Fas pathway. In addition, the mitochondrial membrane potential disruption appears to be a NO-sensitive step in the apoptosis cascade. The presence of a NOS displaying anti-apoptotic properties has now been recognised in different cell types, including various leukaemia. A better knowledge of the mechanisms governing the ultimate fate of NO, anti- versus pro-apoptotic would allow the development of new therapeutic approaches for the treatment of these diseases.

The apoptotic pathway: a target for therapy in chronic lymphocytic leukemia

Cell division and apoptosis (programmed cell death) are the two major physiological processes which control the size of cell populations. Chronic lymphocytic leukaemia arises as a result of the clonal expansion of, usually B-, lymphocytes in which a dysregulation of apoptosis leads to prolonged cell survival. The same process becomes exaggerated with increasing drug resistance, the usual cause of treatment failure in this condition. The identification of points in the apoptotic pathway at which dysregulation occurs is beginning to open up new therapeutic opportunities where the conventional cytotoxic chemotherapy approach is found to fail. Although these strategies are still in their infancy they may increase understanding of the pathogenesis of the disorder and overcome the problem of drug resistance.

The most unkindest cut of all: on the multiple roles of mammalian caspases

The caspases, first discovered almost a decade ago, are intracellular cysteine proteases which have been shown to play an essential role in the initiation and execution phases of apoptotic cell death. Numerous strategies for the activation and inhibition of these 'killer' proteases have evolved, including the regulation of caspase expression and function at the transcriptional and post-translational level, as well as the expression of viral and cellular inhibitors of caspases. Emerging evidence in recent years has also implicated the caspases in various, nonapoptotic aspects of cellular physiology, such as cytokine processing during inflammation, differentiation of progenitor cells during erythropoiesis and lens fiber development, and proliferation of T lymphocytes, thus attesting to the pleiotropic functions of these proteases. The present review aims to discuss the multiple roles of the mammalian caspases with particular emphasis on their activation and regulation in cells of leukemic origin and the attendant possibilities of therapeutic intervention.

Morphological and immunophenotypic features of chronic lymphocytic leukemia

In this review, we summarize the morphological features and immunophenotypic profile of chronic lymphocytic leukemia (CLL) cells, discuss the value of these investigations as front line diagnostic tests, and emphasize their correlation with the clinical features, disease progression, molecular genetics and pathogenesis of CLL. In CLL, the morphology of the circulating cells is characteristic and typical in the majority of cases. However, 15% of patients, either at diagnosis or during the course of the disease, show atypical morphology reflected by either (1) an increased (> 10%) number of circulating prolymphocytes, designated CLL/PL, or (2) an increased (> 15%) number of circulating lymphoplasmacytic and cleaved cells, designated 'atypical' CLL. There is strong evidence of a close association between atypical morphology (CLL/PL) and atypical (CLL) and clinical features, e.g. disease progression, advanced stage and survival, molecular genetics, particularly trisomy 12, but also the rare cases with t(11;14) or t(14;19), p53 abnormalities, unmutated immunoglobulin (Ig) VH genes and origin of the cell (naive, pregerminal center cell). CLL cells have a distinct immunological repertoire different from that of other lymphoproliferative disorders. The typical CLL phenotype is CD5+, CD23+, FMC7-, weak expression of surface Ig (sIg) and weak or absent expression of membrane CD22 and CD79b. The latter marker identifies an extracellular epitope of the B-cell receptor (BCR) beta chain and its weak or absent expression in CLL may derive from the expression of a truncated form. This, together with the low expression of CD22, might explain the abnormal signal transduction of CLL cells similar to that of anergic B lymphocytes. Because no single marker is specific for CLL, a composite phenotype considering this set of 5 or 6 markers compounded into a scoring system helps to distinguish CLL from the other B-cell malignancies. Immunophenotypic analysis has also been shown to be useful for minimal residual disease detection and adds valuable prognostic information because the expression of certain markers, such as FMC7 or CD38, seems to be associated with a poor outcome. In addition, CLL cells express a variety of Bcl-2 family proteins with a profile that favors inhibition of apoptosis which, together with the interaction with microenvironmental (e.g. stromal) cells and the release of cytokines, explains the long life span and subsequent accumulation of CLL cells in various organs. Despite controversies relating to the expression of adhesion molecules (selectins and integrins) in CLL cells, it appears that some of these molecules do play a role in the pathogenesis, biology and clinical patterns of the disease. In conclusion, morphology and immunophenotype are the two essential investigations, which must be carried out in all cases of CLL. Both provide relevant information in terms of diagnosis, course of the disease, prognosis and pathogenesis.

FADD expression and caspase activation in B-cell lymphomas resistant to Fas-mediated apoptosis

We have previously shown that malignant B cells from non-Hodgkin's lymphomas (NHL) are resistant to Fas-mediated apoptosis. To determine the mechanisms underlying this resistance, we analysed by Western blotting the expression of several apoptotic regulators, caspase 3, caspase 8, FADD and poly(ADP-ribose) polymerase (PARP) in fresh lymphoma cells, isolated from 16 B-NHL biopsy samples of different histological subtypes, and displaying variable levels of Fas expression. The profiles of expression of these apoptotic regulators were monitored in cell lysates at different times following Fas with or without CD40 stimulation. Expression of FADD and of the uncleaved forms of PARP, caspase 3 and caspase 8 were detected in all untreated NHL samples. Low levels of PARP cleavage were noted in three untreated samples. Fas stimulation alone induced neither significant apoptosis nor significant changes in the expression profiles of FADD, caspases 3 and 8 and PARP in the 16 samples, except for variations in FADD and caspase 8 expression levels in a minority of samples. Fas/CD40 co-stimulation induced apoptosis and cleavage of caspase 3, caspase 8 and PARP in the five NHLs tested; expression of FADD was not modified. Our results showed (1) that induction of apoptosis in B-NHLs by Fas/CD40 co-stimulation used the same caspase executioner machinery as the normal Fas pathway, and (2) that NHL cells which resisted Fas-mediated apoptosis displayed no defect in either expression or functionality of caspases 3 and 8, nor in FADD expression. The dysfunction underlying NHL resistance to apoptosis must therefore lie upstream of caspase 8, or could alternatively be influenced by anti-apoptotic regulators of the Bcl-2 family.

Chronic lymphocytic leukemia

Significant strides have been made in our understanding of the biology and treatment of B cell chronic lymphocytic leukemia. Recent studies have defined cytogenetic and molecular lesions that may be responsible for leukemogenesis or disease progression. Molecular analyses of immunoglobulin genes have delineated two or more subgroups of chronic lymphocytic leukemia that may differ in their clinical behavior. Research in the biochemistry of chronic lymphocytic leukemia has provided insight into the noted resistance of leukemia cells to cytotoxic drugs. Investigations into the immunology has revealed mechanisms whereby chronic lymphocytic leukemia cells can contribute to the immune deficiency that commonly develops in patients with this disease. Clinical studies have delineated factors that are helpful in predicting prognosis and have provided data on promising new therapies for patients with this disease, including stem cell transplantation, monoclonal antibodies, and gene therapy.

Free radicals and reactive oxygen species in programmed cell death

Oxidative stress, originating from reactive oxygen species and free radicals provides a constant challenge to eukaryotic cell survival. While implicated in a number of degenerative diseases, some associated with aging and with aging itself, the manner and extent to which oxidative stress contributes to the initiation or implementation of programmed-cell death is problematic. If oxidative stress is an important modulator of programmed-cell death, any ability intentionally to augment or inhibit it might ameliorate diseases in which the process is abnormally underactive or overactive.