Cladribine induces apoptosis in human leukaemia cells by caspase-dependent and -independent pathways acting on mitochondria

Cultured lymphocytes' mitochondrial genome integrity is not altered by cladribine

Cladribine tablets are a treatment for multiple sclerosis with effects on lymphocytes, yet its mode of action has not been fully established. Here, we analyzed the effects of cladribine on mitochondrial DNA integrity in lymphocytes. We treated cultured human T-cell lines (CCRF-CEM and Jurkat) with varying concentrations of cladribine to mimic the slow cell depletion observed in treated patients. The CCRF-CEM was more susceptible to cladribine than Jurkat cells. In both cells, mitochondrial protein synthesis, mitochondrial DNA copy number, and mitochondrial cytochrome-c oxidase-I mRNA mutagenesis was not affected by cladribine, while caspase-3 cleavage was detected in Jurkat cells at 100 nM concentration. Cladribine treatment at concentrations up to 10 nM in CCRF-CEM and 100 nM in Jurkat cells did not induce significant increase in mitochondrial DNA mutations. Peripheral blood mononuclear cells from eight multiple sclerosis patients and four controls were cultured with or without an effective dose of cladribine (5 nM). However, we did not find any differences in mitochondrial DNA somatic mutations in lymphocyte subpopulations (CD4+, CD8+, and CD19+) between treated versus nontreated cells. The overall mutation rate was similar in patients and controls. When different lymphocyte subpopulations were compared, greater mitochondrial DNA mutation levels were detected in CD8+ (P = 0.014) and CD4+ (P = 0.038) as compared to CD19+ cells, these differences were independent of cladribine treatment. We conclude that T cells have more detectable mitochondrial DNA mutations than B cells, and cladribine has no detectable mutagenic effect on lymphocyte mitochondrial genome nor does it impair mitochondrial function in human T-cell lines.

Anti-apoptotic effect of Buchholzia coriacea Engl. stem back extracts on AsPC-1 and mechanisms of action

Ethnopharmacological relevance

Buchholzia coriacea Engl. is popularly called wonderful cola due to its wide ethnomedicinal use for the treatment of various ailments. We investigated the possible cytotoxic effect of its various fractions on human pancreatic cancer cell (AsPC-1) and also determined its mechanisms of action.

Materials and methods

The AsPC-1 cells were cultivated and separately treated with 5-fluorouracil (5-FU) or Buchholzia coriacea Engl. bark (BC) (ethanol, aqueous, chloroform or ethyl acetate extract) for 72 h. Cell viability, caspase 3 and mitochondrial membrane potential (ΔΨm) were determined in vitro after the treatment. Nitric oxide (NO) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals’ scavenging property, ferric reducing power and lipid peroxidation assays were also done to examine the antioxidant effect of BC in vitro.

Results

Various extracts of BC, especially at 2500 μg/ml and 5000 μg/ml, increased the AsPC-1 viability while 5-FU decreased it. The activity of caspase 3 was increased by 5-FU but reduced by all concentrations of various extracts of BC. Incubation of AsPC-1 with 5-FU showed the majority of cells having the monomeric form of JC-1 dye (bright green fluorescence), which indicated de-energized mitochondria. However, fluorescence photomicrograph of cells incubated with different concentrations (20, 40 and 100 μg/ml) of BC extracts (aqueous, ethanol, chloroform and ethyl acetate) showed strong JC-1 aggregation (yellow), which indicated mitochondria with intact membrane potentials. BC extracts also scavenged NO and DPPH radicals, inhibited lipid peroxidation and increased ferric reduction, though not as much as ascorbic acid.

Conclusion

This study suggests that BC elicits anti-apoptotic activity in AsPC-1 by increasing cell viability, decreasing caspase 3 activity, stabilizing the ∆Ψm, and scavenging free radicals. Even though BC is used ethnomedicinally as anti-cancer agent, our findings in the present study suggest that it has pro-cancer potential in-vitro, especially on pancreatic cells. Its anti-apoptotic activity in AsPC-1 could be of clinical significance, especially to counteract the effect of apoptotic agents on pancreatic cells.

Multiple Sclerosis and Cancer: The Ying-Yang Effect of Disease Modifying Therapies

Over the past two decades, the field of multiple sclerosis (MS) has been transformed by the rapidly expanding arsenal of new disease modifying therapies (DMTs). Current DMTs for MS aim to modulate innate and adaptive immune responses toward a less inflammatory phenotype. Since the immune system is also critical for identifying and eliminating malignant cells, immunosuppression from DMTs may predictably increase the risk of cancer development in MS patients. Compared with healthy controls, patients with autoimmune conditions, such as MS, may already have a higher risk of developing certain malignancies and this risk may further be magnified by DMT treatments. For those patients who develop both MS and cancer, these comorbid presentations create a challenge for clinicians on how to therapeutically address management of cancer in the context of MS autoimmunity. As there are currently no accepted guidelines for managing MS patients with prior history of or newly developed malignancy, we undertook this review to evaluate the molecular mechanisms of current DMTs and their potential for instigating and treating cancer in patients living with MS.

Cladribine Induces ATF4 Mediated Apoptosis and Synergizes with SAHA in Diffuse Large B-Cell Lymphoma Cells

Cladribine is a purine nucleoside analog used to treat B-cell chronic lymphocytic leukemia and hairy cell leukemia, also functions as an inhibitor of DNA synthesis to block the repair of the damaged DNA. The therapeutic role of cladribine against diffuse large B-cell lymphoma cells (DLBCL) is still undefined. In the present study, we demonstrated that cladribine inhibited cell proliferation and induced G₁ phase arrest in human DLBCL cells. Furthermore, we showed that cladribine induced apoptosis by decreasing the expression of c-FLIP_L and increasing the expression of DR4 and the cleaved form of caspase8. Cladribine also upregulated the expression of Bax, and downregulated the expression of Mcl-1 and Bcl-2 in a dose-dependent manner. It also activated endoplasmic reticulum (ER) stress, and ATF4 expression was required for cladribine induced apoptosis. Also, we showed that suberoylanilide hydroxamic acid (SAHA) enhanced the pro-apoptotic role of cladribine. Collectively, cladribine activated extrinsic and intrinsic apoptotic signaling pathways via stimulating ER stress signaling pathway and eliciting synergistic effect with SAHA in DLBCL cells.

Efficacy of common salvage chemotherapy regimens in patients with refractory or relapsed acute myeloid leukemia: A retrospective cohort study

To assess treatment response and overall survival (OS) in refractory or relapsed acute myeloid leukemia (R/R AML) patients treated by different common salvage chemotherapy regimens.Medical records data from 142 R/R AML patients were reviewed in this retrospective study. Patients were treated with regimens based on the following drugs: cytarabine, granulocyte colony-stimulating factor (G-CSF), and fludarabine (FLAG) (n = 46); cytarabine and G-CSF in addition to aclarubicin or daunorubicin (CAG/DAG) (n = 30); cytarabine, G-CSF, and cladribine (CLAG) (n = 27); cytarabine, etoposide, and mitoxantrone (MEA) (n = 17); cytarabine plus idarubicin, daunorubicin, or mitoxantrone (IA/DA/MA) (n = 12); and homoharringtonine, cytarabine, and aclarubicin or daunorubicin (HAA/HAD) (n = 10).A total of 43 (35.2%) patients achieved complete remission (CR), 60 (49.2%) patients achieved overall remission rate (ORR), and 18 (14.8%) patients received allogeneic hematopoietic stem cell transplantation (allo-HSCT) after CR. Median OS was 8.0 (95% CI 6.6-9.4) months with a 1-year OS rate of (29.9 ± 3.9)% and 3-year OS rate of (11.1 ± 3.6)%. No difference of CR (P = .621), ORR (P = .385), and allo-HSCT (P = .537) achievement was observed among different chemotherapy regimens. Interestingly, we observed that the CLAG-based regimen did not affect CR (P = .165), while it achieved a numerically higher ORR (P = .093) and was an independent factor for prolonged OS (P = .016). No other regimens were determined to be correlated with CR, ORR, or OS.FLAG-, CAG/DAG-, CLAG-, MEA-, IA/DA/MA- and HAA/HAD-based regimens were found to achieve similar CR rates, while the CLAG-based regimen achieved numerically higher ORR rates and significant favorable OS. Therefore, CLAG-based regimens should be a prioritized treatment option for R/R AML patients.

Melilotus indicus extract induces apoptosis in hepatocellular carcinoma cells via a mechanism involving mitochondria-mediated pathways

Melilotus indicus, is a traditional medicine used as analgesic and emollient. Although Melilotus indicus extract (MIE) has recently been shown to suppress growth of several tumor cell lines, information regarding its antitumor mechanism is completely unknown. Here, we report the mechanism underlying the effects of MIE on human hepatocellular carcinoma cells, specifically HepG2, and SNU-182 cells. Methanolic MIE impaired the proliferation, and induced cell death in both HepG2 and SNU-182 cells but not in normal hepatic L-02 cells. Mechanistically, flow cytometric analysis revealed that MIE induces apoptosis in HepG2, and SNU-182 cells. However, MIE-induced apoptosis were not affected by a pan caspase inhibitor z-VAD-fmk as well as MIE did not stimulate caspase activation. Furthermore we found that MIE-induced apoptosis could be attributed to a mechanism involving mitochondria-mediated pathways evidenced by decrease in the mitochondrial membrane potential (ΔΨm), increase in the Bax/Bcl-2 ratio, and translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. Suppression in AIF expression by siRNA reduced MIE-induced apoptosis which suggested the dependency of MIE on AIF to induce apoptosis in hepatocellular carcinoma cells. To the best of our knowledge this is the first report elucidating the anticancer mechanism of MIE. Our findings suggested that MIE might be a good extract for developing anticancer drugs for human hepatocellular carcinoma treatment.

Cladribine Analogues via O⁶-(Benzotriazolyl) Derivatives of Guanine Nucleosides

Cladribine, 2-chloro-2'-deoxyadenosine, is a highly efficacious, clinically used nucleoside for the treatment of hairy cell leukemia. It is also being evaluated against other lymphoid malignancies and has been a molecule of interest for well over half a century. In continuation of our interest in the amide bond-activation in purine nucleosides via the use of (benzotriazol-1yl-oxy)tris(dimethylamino)phosphonium hexafluorophosphate, we have evaluated the use of O⁶-(benzotriazol-1-yl)-2'-deoxyguanosine as a potential precursor to cladribine and its analogues. These compounds, after appropriate deprotection, were assessed for their biological activities, and the data are presented herein. Against hairy cell leukemia (HCL), T-cell lymphoma (TCL) and chronic lymphocytic leukemia (CLL), cladribine was the most active against all. The bromo analogue of cladribine showed comparable activity to the ribose analogue of cladribine against HCL, but was more active against TCL and CLL. The bromo ribose analogue of cladribine showed activity, but was the least active among the C6-NH₂-containing compounds. Substitution with alkyl groups at the exocyclic amino group appears detrimental to activity, and only the C6 piperidinyl cladribine analogue demonstrated any activity. Against adenocarcinoma MDA-MB-231 cells, cladribine and its ribose analogue were most active.

2-Chlorodeoxyadenosine (cladribine) induces apoptosis in human monocyte-derived dendritic cells

2-Chlorodeoxyadenosine (cladribine, CdA) is an immunosuppressive drug that is licensed to treat hairy cell leukaemia, and has been shown recently to have beneficial effects in patients with multiple sclerosis (MS). The therapeutic effects of CdA have been suggested to be mediated partly through its potent toxicity towards lymphocytes. However, the effects of CdA on other immune cells are poorly understood. In the present study, we investigated the effects of CdA on the induction of apoptosis in human monocytes, monocyte-derived immature (ImDC) and mature (mDC) dendritic cells. Treatment of monocytes with CdA strongly induced apoptosis after 24 h, while apoptosis induction in DC was evident after 72 h. Furthermore, CdA treatment strongly induced caspase-3 and caspase-9 in monocytes, whereas activation of caspases was undetected in DC. The mitochondrial membrane potential in DC was reduced significantly after CdA treatment. DNA hypodiploid assessment showed fragmented nuclei in DC after CdA treatment together with activation of p53 protein. These results revealed that CdA induces caspase-independent apoptosis in DC and suggest cell type specific effects of CdA. This mechanism may contribute to the effect of CdA in autoimmune diseases.

In vivo and ex vivo responses of CLL cells to purine analogs combined with alkylating agent

BACKGROUND

The heterogeneity of chronic lymphocytic leukemia (CLL) is thought to be due to differences in the expression of factors that regulate apoptosis and cell cycle, giving rise to diverse apoptotic disturbances and tumor properties. Therefore, the primary goal in CLL treatment is to overcome resistance to apoptosis and efficiently trigger this process in leukemic cells.

METHODS

Mononuclear cells were obtained from the blood of CLL patients by Histopaque-1077 sedimentation. CLL cell samples from the blood of drug treated patients, (cladribine or fludarabine with cyclophosphamide; CC or FC), as well as the cell samples of untreated patients exposed to the used drug combinations (CM, FM) or mafosfamide alone for 48 h were fractionated into nuclear and cytoplasmic fractions or were lysed. DNA fragmentation was evaluated by agarose electrophoresis and also cytometrically as sub-G1 population. The expression of apoptosis related proteins and H1.2 histone translocation were evaluated in lysates and nuclear and cytoplasmic fractions, respectively with appropriate antibodies.

RESULTS

Cladribine (C) and fludarabine (F) combined with cyclophosphamide/mafosfamide in vivo, as well as ex vivo trigger apoptosis in CLL cells. These drug combinations (CC; FC/CM; FM) induce leukemic cell apoptosis confirmed by DNA fragmentation, sub-G1 cell number, down-regulation of anti-apoptotic proteins (Mcl-1, Bcl-2), and H1.2 histone translocation in comparison with appropriate control cells, however, to a different degree.

CONCLUSIONS

The kinetics and rate of drug-induced apoptosis in leukemic cells under ex vivo experiments differ between patients, mirroring the differences noticed during in vivo treatment. Individual model cell samples indicate comparable susceptibility to the used drug combinations under in vivo and ex vivo conditions.

Relationships of diverse apoptotic death process patterns to mitochondrial membrane potential (Δψ(m)) evaluated by three-parameter flow cytometric analysis

Recently, it has been proposed that novel methodologies are needed to re-evaluate apoptotic cell death, as studies of apoptosis have shown it to be a complex process. Since mitochondria are key regulators in cell death pathways, we developed a simultaneous 3-parameter flow cytometric analysis that incorporates the change in mitochondrial membrane potential (Δψ_m) in an Annexin-V [for phosphatidyl-serine (PS)] and propidium iodide (PI) assay system (3 parameters with 4 colours), and evaluated the apoptotic process using various haematological malignant cell lines and death triggers. The present method enabled visualization of cell composition during apoptosis and captured complicated molecular events. For example, apoptotic cells that lost Δψ_m did not always externalize PS, while some late apoptotic cells had polarized Δψ_m. The findings of unchanged PS-externalization and aberrant cell death suggest that there is no relationship of PS externalization and apoptosis with an unknown apoptotic mechanism. Based on PS-externalization, sensitivity to staurosporine, and the combination of cell lines and triggers, the apoptotic process was classified into 2 types. Importantly, most of our findings could not be observed by PS–PI and Δψ_m assays when independently performed. Our method may be useful for examining mitochondrial-related apoptosis and death signalling pathways, as well as screening novel apoptosis-inducing cancer drugs.

The impact of CDK inhibition in human malignancies associated with pronounced defects in apoptosis: advantages of multi-targeting small molecules

Malignant cells in chronic lymphocytic leukemia (CLL) and related diseases are heterogeneous and consist primarily of long-lived resting cells in the periphery and a minor subset of dividing cells in proliferating centers. Both cell populations have different molecular signatures that play a major role in determining their sensitivity to therapy. Contemporary approaches to treating CLL are heavily reliant on cytotoxic chemotherapeutics. However, none of the current treatment regimens can be considered curative. Pharmacological CDK inhibitors have extended the repertoire of potential drugs for CLL. Multi-targeted CDK inhibitors affect CDKs involved in regulating both cell cycle progression and transcription. Their interference with transcriptional elongation represses anti-apoptotic proteins and, thus, promotes the induction of apoptosis. Importantly, there is evidence that treatment with CDK inhibitors can overcome resistance to therapy. The pharmacological CDK inhibitors have great potential for use in combination with other therapeutics and represent promising tools for the development of new curative treatments for CLL.

Can ex vivo evaluation (testing) predict the sensitivity of CLL cells to therapy with purine analogs in conjunction with an alkylating agent? A comparison of in vivo and ex vivo responses to treatment

Malfunctions in the regulation of apoptosis cause the accumulation of malignant, long-lived B CD19+/CD5+ cells in chronic lymphocytic leukemia (CLL). The primary goal in CLL therapy is to overcome resistance to apoptosis and efficiently trigger programmed cell death in leukemic cells. This study demonstrated that the in vivo responses of malignant cells from CLL patients after administration of purine analogs (cladribine/fludarabine) with cyclophosphamide vary significantly. For comparative purposes, the sensitivity of leukemic cells obtained from the same CLL patients to conventional purine analogs and the selective CDK inhibitor R-roscovitine (ROSC) was determined, with and without the addition of an alkylating agent, prior to the onset of in vivo therapy. The kinetics and rate of spontaneous and drug-induced apoptosis of CLL cells under ex vivo conditions differed significantly between patients, mirroring the variability observed during in vivo treatment. Interestingly, individual patients' leukemic cells were comparably sensitive to the drugs under both conditions. Of the drugs examined, ROSC exerted the highest therapeutic efficacy under ex vivo conditions. Our results indicate that ex vivo testing might be useful for identifying the most potent first-line therapeutic regimen for specific CLL patients and possibly for the design of therapies tailored for individual CLL patients.

Cladribine inhibits cytokine secretion by T cells independently of deoxycytidine kinase activity

Cladribine (2-chloro-2'-deoxyadenosine) is a purine nucleoside analogue (PNA) which causes targeted and sustained reduction of peripheral lymphocyte counts. Cladribine tablets produced significant treatment benefit for patients with relapsing-remitting multiple sclerosis in the phase 3 CLARITY study. In addition to the well-characterised cell-specific phosphorylation of PNAs responsible for lymphocyte reduction, the mode of action of cladribine may encompass distinct activities contributing to its overall effects on the immune system. Here we demonstrate that clinically relevant concentrations of cladribine also inhibit cytokine secretion by human peripheral blood T cells in vitro through mechanisms independent of the induction of lymphocyte death.

Cladribine as a therapeutic option in multiple sclerosis

There is an unmet need for more potent and convenient drugs in the treatment of patients diagnosed with multiple sclerosis (MS). Among five currently investigated oral drugs with an ongoing or completed phase III program, promising efficacy data for oral cladribine have recently been published. However, benefits need to be weighed against potential risks to define the role of this compound within current treatment regimens. Here we review present data on efficacy of oral cladribine and discuss known and anticipated risks of this drug.

Induction of the Intrinsic Apoptotic Pathway by 3-Deazaadenosine Is Mediated by BAX Activation in HL-60 Cells

3-Deazaadenosine (DZA), a potent inhibitor of S-adenosylhomocysteine hydrolase, was previously proposed to induce intrinsic apoptosis in human leukemic cells. In the present study, we analyzed the mechanism underlying the DZA-induced intrinsic apoptotic pathway. DZA activated typical caspase-dependent apoptosis in HL-60 cells, as demonstrated by an accumulation of hypo-diploidic cells, the processing of multiple procaspases and an inhibitory effect of z-VAD-Fmk on this cell death. During DZA-induced apoptosis, cytochrome c (cyt c) was released into the cytosol. This was neither prevented by z-VAD-Fmk and nor was it associated with the dissipation of mitochondrial membrane potential (ΔΨ(m)). Prior to the release of cyt c, BAX was translocated from the cytosol to mitochondria and underwent oligomerization. Finally, the overexpression of BCL-XL protected HL-60 cells from apoptosis by blocking both the cyt c release and BAX oligomerization. Collectively, these findings suggest that DZA may activate intrinsic apoptosis by stimulating BAX activation and thereby the release of cyt c.

Cladribine and Fludarabine Nucleoside Change the Levels of CD Antigens on B-Lymphoproliferative Disorders

The purine analogs, fludarabine nucleoside (FdA), and cladribine (CdA) (1 μM, 24 hours), significantly changed the levels of some surface antigens on the human B-cell lines MEC2 and Raji. Changes in the surface proteins were identified using a Cluster of Differentiation (CD) antibody microarray that captures live cells and confirmed by flow cytometry. For Raji cells, CdA up-regulated CD10, CD54, CD80, and CD86, with repression of CD22, while FdA up-regulated CD20, CD54, CD80, CD86 and CD95. For MEC2 cells, CdA up-regulated CD11a, CD20, CD43, CD45, CD52, CD54, CD62L, CD80, CD86, and CD95, but FdA had no effect. Up-regulation of particular CD antigens induced on a B-cell lymphoproliferative disorder by a purine analog could provide targets for therapeutic antibodies with synergistic cell killing.

Current status of older and new purine nucleoside analogues in the treatment of lymphoproliferative diseases

For the past few years more and more new cytotoxic agents active in the treatment of hematological malignancies have been synthesized and become available for either in vitro studies or clinical trials. Among them the class of antineoplastic drugs belonging to the purine nucleoside analogues group (PNAs) plays an important role. Three of them: pentostatin (DCF), cladribine (2-CdA) and fludarabine (FA) were approved by Food and Drug Administration (FDA) for the treatment of hematological malignancies. Recently three novel PNAs: clofarabine (CAFdA), nelarabine (ara-G) and forodesine (immucillin H, BCX-1777) have been synthesized and introduced into preclinical studies and clinical trials. These agents seem to be useful mainly for the treatment of human T-cell proliferative disorders and they are currently undergoing clinical trials in lymphoid malignancies. However, there are also several studies suggesting the role of these drugs in B-cell malignancies. This review will summarize current knowledge concerning the mechanism of action, pharmacologic properties, clinical activity and toxicity of PNAs accepted for use in clinical practice, as well as new agents available for clinical trials.

Calorimetric study as a potential test for choosing treatment of B-cell chronic lymphocytic leukemia

Differential scanning calorimetry (DSC) and complementary techniques were utilized to evaluate the sensitivity of B-cell chronic lymphocytic leukemia (B-CLL) cell samples in vitro exposed to cladribine or fludarabine in combination with mafosfamide. Mafosfamide, the active in vitro form of cyclophosphamide with both purine analogs produced the cytotoxic effect on mononuclear cell probes, however, to a different degree. Our results indicated that higher sensitivity of examined leukemic cell samples to the used drug combinations was usually accompanied by a marked decrease or even a complete loss of thermal transition at 95+/-3 degrees C in DSC scans of nuclear preparations as well as by more significant reduction of cell viability, higher extent of DNA damage estimated by the comet assay and by dropping/disappearance of anti-apoptotic protein Mcl-1 in comparison with untreated cells. We have also observed that the reduction of transition at 95+/-3 degrees C in thermal scans of nuclear preparations isolated from blood of B-CLL randomized patients who showed response to cladribine or fludarabine combined with cyclophosphamide, i.e., CC and FC, respectively, corresponded with the decrease or disappearance of anti-apoptotic proteins Bcl-2 and/or Mcl 1. In conclusion, these in vitro and in vivo studies revealed that quick DSC technique, usually supplemented by other methods, is a potent tool to distinguish efficacy of B-CLL treatment and could be helpful in choosing the most effective manner of treatment for this type of leukemia.

Synergy of Irofulven in combination with various anti-metabolites, enzyme inhibitors, and miscellaneous agents in MV522 lung carcinoma cells: marked interaction with gemcitabine and 5-fluorouracil

The novel agent Irofulven (HMAF, NSC 683863) has demonstrated significant antitumor activity against solid tumors in various xenograft models and human clinical trials. The antitumor potential of combining irofulven with 72 different anti-metabolite, enzyme inhibiting, and miscellaneous agents was investigated in this study. The human lung carcinoma MV522 cell line and its corresponding xenograft model were used to evaluate the activity of irofulven in combination with these different agents. Irofulven in combination with select anti-metabolites, notably cytidine or adenine-derived agents, displayed strong synergistic activity in both in vitro and in vivo studies. Agents demonstrating strong synergistic interaction with irofulven included gemcitabine, cyclocytidine, cytarabine, fludarabine phosphate, cladribine, and 5-fluorouracil. Other anti-metabolites, enzyme inhibitors, and a variety of miscellaneous agents failed to interact beneficially when administered in combination with irofulven. The therapeutic activity of irofulven is enhanced considerably when irofulven is combined with select anti-metabolite agents, and further clinical evaluation of these combinations is warranted. The synergistic interaction with these combinations may stem from a variety of actions including inhibition of the nucleotide excision repair (NER) pathway, topoisomerase I activity, and caspase-dependent and independent induction of apoptosis.

Apoptotic cell death: A possible key event in mediating the in vitro anti-proliferative effect of a novel copper(II) complex, [Cu(4-Mecdoa)(phen)2] (phen=phenanthroline, 4-Mecdoa=4-methylcoumarin-6,7-dioxactetate), in human malignant cancer cells

The central objective of the current study was to investigate the potential in vitro anti-proliferative effect of the parent ligand, 4-methylcoumarin-6,7-dioxyacyeic acid (4-MecdoaH(2)), and its copper (II) complex, bis(phenanthroline4-methylcoumarin-6,7-dioxacetatocopper(II) ([Cu(4-Mecdoa)(phen)(2)]) using four human model cell lines. In addition, selected mechanistic studies were carried out using the most sensitive of the four cell lines. Results obtained show that the complex could alter proliferation of both human neoplastic renal (A-498) and hepatic (HepG2) cells. Furthermore, non-neoplastic hepatic (CHANG) cells appeared to be less sensitive. However, this effect was not duplicated with non-neoplastic renal (HK-2) cells, a profile shared by cisplatin. The observed anti-proliferative effect appeared to be dose-and time-dependent, and could be attributed to the complex, rather than any of the free components i.e. the 1,10-phenanthroline or coumarin ligand, or the simple metal salt. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Based on IC(50) values, [Cu(4-Mecdoa)(phen)(2)] was shown to be almost 12 times more potent than cisplatin. Moreover, there was no evidence that P-glycoprotein-mediated multi-drug resistance was likely to decrease anti-proliferative activity. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein], showed that cell death could switch between apoptosis and necrosis, and this effect appeared to be concentration-dependent. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Cu(4-Mecdoa)(phen)(2)] has been shown to be a more potent anti-proliferative agent than either the ligand or cisplatin, and is capable of altering key biochemical events leading to the execution of apoptotic and/or necrotic cell death, suggesting that it is worthy of further investigation.

Cadmium induces apoptosis in human embryonic kidney (HEK) 293 cells by caspase-dependent and -independent pathways acting on mitochondria

Cadmium (Cd) is a well-known toxic compound for the kidney in vivo and in vitro. It has been demonstrated to induce nephrotoxicity via in part by apoptotic cell death, but the precise mechanism is still unclear. Therefore, we have studied the effects of Cd on HEK 293 cells and investigated the mechanisms of Cd-induced apoptosis. Studies of morphology and oligonucleosomal DNA fragmentation demonstrated that 30-60 microM Cd induced apoptosis as early as 6-9h with strong effects on MTT activity, whereas 120 microM Cd revealed mainly necrosis, and the result of flow cytometry confirmed it. A concomitant time-dependent decrease of mitochondrial transmembrane potential (DeltaPsi(m)) and Bcl-2 expression was observed, subsequently, release of cytochrome c (Cyt c) and activation of caspase-3 were detected, suggesting a caspase-dependent pathway. Meanwhile, mitochondrial AIF was released to cytoplasm and nucleus, suggesting a caspase-independent pathway. Furthermore, when cells were transfected with pcDNA3/Bcl-2 before exposed to CdCl(2), alleviated apoptosis was assessed by part of the apoptotic features in this study. Taken together, our results showed that CdCl(2) caused time- and dose-dependent apoptosis or even necrosis in HEK 293 cells depending on the exposure conditions. The apoptotic events may involve mitochondrial disruption including both caspase-dependent and -independent pathways.

Lipid raft disruption prevents apoptosis induced by 2-chloro-2′-deoxyadenosine (Cladribine) in leukemia cell lines

To clarify the role of lipid rafts in 2-chloro-2'-deoxyadenosine (2CdA; Cladribine)-induced apoptosis, the effects of disruption of lipid rafts by methyl-beta-cyclodextrin (MbetaCD) and filipin on 2CdA-induced apoptosis were investigated in four human acute lymphoblastic leukemia (ALL) cell lines comprised of T cells (MOLT-4, Jurkat) and B cells (NALM, BALL-1). The disruption of lipid rafts significantly inhibited 2CdA-induced apoptosis, indicating the crucial role of lipid rafts in the induction of apoptosis in leukemia cells. These reagents significantly inhibited 2CdA-induced elevation of the intracellular calcium concentration ([Ca(2+)](i)) in MOLT-4 cells, and 2CdA-induced apoptosis was partly inhibited by the Ca(2+) chelators BAPTA-AM and EGTA, and the L-type Ca(2+) channel blocker nifedipine. On the other hand, they had no effects on the cellular uptake of 2CdA. These results indicated that lipid rafts partly contributed to 2CdA-induced apoptosis by regulating Ca(2+) influx via the plasma membrane.

Cadmium-induced apoptosis in rat hepatocytes does not necessarily involve caspase-dependent pathways

Cadmium (Cd) is a well-known hepatotoxic environmental pollutant. Depending on the exposure conditions, Cd may cause necrosis or apoptosis. Oxidative stress is believed to participate in Cd toxicity but the molecular signaling responsible for Cd-induced apoptosis in non-malignant liver cells still needs to be clarified. Therefore we have studied apoptosis in primary cultures of rat hepatocytes incubated with low levels of Cd for short exposure times. Studies of nuclear morphology, chromatin condensation, and oligonucleosomal DNA fragmentation demonstrate that 1-5 microM Cd induces apoptosis as early as 6-12 h with minor effects on MTT activity. A concomitant time- and concentration-dependent increase in caspase-9 and -3 activities was observed, whereas Cd did not affect caspase-8 activity as much, suggesting a minor role of the death-receptor pathway. Significant release of cytochrome c into the cytosol demonstrated the involvement of a mitochondrial-dependent apoptotic pathway. However, cell pre-treatment with caspase inhibitors (Z-VAD-fmk or Ac-DEVD-CHO) did not prevent apoptosis. Increases in the cytosolic levels of the mitochondrial apoptosis-inducing factor (AIF) were also observed: kinetics of cytochrome c and AIF release were similar. These results show that Cd-induced apoptosis in rat hepatocytes is time- and concentration-dependent. The early apoptotic events involved mitochondrial-dependent pathways but not necessarily caspase-dependent signaling.

Involvement of caspase activation and mitochondrial stress in taxol-induced apoptosis of Epstein–Barr virus-infected Akata cells

Taxol (paclitaxel) is one of the most potent antimicrotubule agents currently used in cancer chemoprevention and treatment. However, the effects of taxol on the induction of apoptosis in Epstein-Barr virus (EBV)-infected cells are unknown. This study investigated the mechanisms of taxol on cell cycle arrest and apoptosis induction using the EBV-infected cell line, Akata. Taxol treatment sensitively and dose-independently induced growth inhibition, cytotoxicity, and apoptosis in the cells, which was demonstrated by the decreased level of tritium incorporation and cell viability, the increased number of positively stained cells in the trypan blue staining and TUNEL assay, the increased population of cells in the sub-G(0)/G(1) phase in flow cytometric analysis, and ladder formation of the genomic DNA. Treatment with z-VAD-fmk almost completely protected the cells from taxol-induced apoptosis indicating that the taxol-induced apoptosis of Akata cells is caspase-dependent. In addition, taxol-induced apoptosis is proposed to be associated with a lower mitochondrial membrane potential and G(2)/M arrest. However, the tubulin expression level doses not appear to be a direct mediator of taxol-induced apoptosis in cells. The presence of EBV in these cells was not related to the sensitivity of the cells to the induction of apoptosis by taxol. Overall, these results demonstrate that taxol induces apoptosis in EBV-infected Akata cells in a dose-independent manner, and that caspase activation and mitochondrial stress are involved in the induction.

Plant programmed cell death and the point of no return

The point of no return during programmed cell death (PCD) is defined as the step beyond which the cell is irreversibly committed to die. Some plant cells can be saved before this point by inducing the formation of functional chloroplasts. A visibly senescent tissue will then become green again and live for months or years. The mechanism of this reversal is only partially known. The point of no return in fungi and animals is often associated with lack of mitochondrial function. In plant cells that do not regreen, there is no evidence for PCD reversal that results in a long life. It is unclear why chloroplast-containing cells, in contrast to those with only mitochondria, have long lives after PCD reversal.

Resistance of human astrocytoma cells to apoptosis induced by mitochondria-damaging agents: possible implications for anticancer therapy

The success of anticancer chemotherapy is often hampered by resistance to apoptosis, which may depend on defects in intracellular cell death pathways. Characterizing the alterations of these pathways is a prerequisite for developing alternative and effective antitumoral strategies. Here, we investigated the susceptibility of a human astrocytoma cell line, ADF, to apoptotic cell death induced by mitochondria-damaging agents. Neither the anticancer agent betulinic acid nor the "mitochondriotropic" poisons 2-deoxy-d-ribose and potassium cyanide induced apoptosis of these cells, despite induction of highly significant mitochondrial depolarization, eventually resulting in necrotic death. Resistance to apoptosis was not due to presence of the multidrug resistance pump or to impaired expression of caspase-8, caspase-9, or "executioner" caspase-3. Cloning of caspase-9 revealed the presence of full-length caspase-9alpha and a short variant (caspase-9beta), which, in other tumors, acts as a dominant negative of the long isoform. All analyzed clones showed a point mutation in the prodomain region that is known to interact with mitochondria-released factors. Thus, in these human astrocytoma cells, mitochondria-damaging agents induce a regulated form of mitochondrial-dependent necrotic cell death (oncosis). Resistance to apoptosis is due to an intrinsic defect of caspase-9, leading to inhibition of enzyme activation and/or impaired interaction with proteins released from depolarized mitochondria. These results may have implications for developing strategies aimed at overcoming tumor resistance to chemotherapy.

5-Aza-2'-deoxycytidine induces p21WAF expression by demethylation of p73 leading to p53-independent apoptosis in myeloid leukemia

The DNA methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-CdR) has significant therapeutic value for the treatment of patients with myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). The demethylating effect of 5-Aza-CdR has been well characterized. In contrast, less is known about the molecular events downstream of the methylation inhibition. Here, 5-Aza-CdR induced apoptosis in AML cells (both p53 mutant and wild-type) but not in epithelial or normal PBMCs. Cell death was accompanied by activation of the mitochondrial apoptosis pathway, as shown by release of cytochrome c and AIF and loss of mitochondrial membrane potential (DeltaPsim). Activation of caspase-3 (but not -6 and -8) was detectable using Western blot analysis and measurement of caspase enzymatic activity. 5-Aza-CdR treatment resulted in the induction of p21, which correlated with the arrest of AML cells in the G1 cell cycle phase. Induction of p21 expression was independent of its promoter methylation status but mediated by 5-Aza-CdR-induced reexpression of the tumor-suppressor p73, a known upstream regulator of p21. The p73 promoter was hypermethylated in AML cell lines and in primary AML cells but not in epithelial cells, which were resistant toward 5-Aza-CdR. Therefore, 5-Aza-CdR-mediated specific killing of myeloid cells might be dependent on its ability to revert p73 promoter methylation and to reexpress p73 mRNA. In addition, exogenous expression of p73 rendered epithelial cells sensitive to apoptosis induced by 5-Aza-CdR or other cytostatic drugs. We therefore conclude that p73 is a relevant target for methylation-dependent efficacy of 5-Aza-CdR in AML cells.

Hyperthermia induces translocation of apoptosis-inducing factor (AIF) and apoptosis in human glioma cell lines

In the hyperthermal treatment, the wild type (wt) p53 plays an important role in apoptosis induction in the tumor cells. In human gliomas, p53 frequently has some form of mutation. The mutant type (mt) p53 does not work properly as a tumor suppressor and this may result in poor responses during treatment. We investigated the relationship between apoptosis-inducing factor (AIF) and apoptosis under various thermal conditions (43, 45, and 47 degrees C for 1 h) using four p53-wild or -mutant human glioma cell lines (A172, T98G, U251MG, and YKG-1). AIF translocation from the mitochondria to the nucleus under hyperthermal conditions was demonstrated by confocal laser microscopy. The percentage of AIF-positive nuclei increased significantly in comparison with the control in all cell lines and in all temperature groups except for YKG-1 at 47 degrees C. Immunoblot analyses of the nuclear fraction of each cell line revealed temperature-dependent increases in AIF. A simultaneous release of cytochrome c from the mitochondria to the cytosol was noted. A flow cytometric analysis showed that apoptosis induction occurred more often in a temperature-dependent manner in the 45 and 47 degrees C groups than in the control group. These findings indicate that the hyperthermal conditions can lead to AIF translocation and apoptotic cell death in the p53-mutant human glioma cells. The present report is the first description of AIF-induced apoptosis in hyperthermia.

Influence of 2-chlorodeoxyadenosine (cladribine) on human erythrocytes

2-Chlorodeoxyadenosine (2-CdA, cladribine) is one of the newest chemotherapy drugs which has been around and in use for a few years. Drug in tumour cells causes the inhibition of DNA synthesis and repair processes in replication cells, and the accumulation of DNA strand breaks in nonproliferating cells. The present study was undertaken to characterize the influence of cladribine on the fluidity of the lipid bilayer and protein conformation in human erythrocytes. The effect of cladribine on the erythrocyte membrane structure was examined by electron spin resonance (ESR) spectroscopy and fluorescence measurements. It was observed that under the studied conditions (c: 0.1-5 microg/ml, t = 1 h, 37 degrees C), cladribine localised mainly in the erythrocyte membrane and affected its organization. The alterations in the fluidity were observed mainly in the deeper regions of the cell membrane. The incorporation of drug into human erythrocytes also caused negligible conformational alterations of membrane cytoskeletal proteins and did not change the internal viscosity of the cells. We can conclude from these data that 2-CdA in vitro is significantly much less toxic to erythrocytes than anthracycline drugs, which are used in treatment of leukemias. However, the higher concentrations of 2-CdA (about 5 microg/ml) can be also toxic to erythrocytes.

Pharmacological basis for cladribine resistance

The inherent or acquired resistance of leukemic cells to cytostatic agents is a major clinical challenge. The purpose of this review was to elucidate and analyse the available data concerning mechanisms of resistance of cladribine with emphasis on recent advances in the characterization of activating and inactivating enzymes in the induction of resistance to cladribine. All available in vitro and clinical data on cladribine was undertaken. Cladribine, unlike many other drugs, is toxic to both dividing and indolent lymphoid malignancies. Cladribine is a prodrug and must be phosphorylated intracellularly to cladribine-monophosphate (MP) by the nuclear/cystosol enzyme deoxycytidine kinase (dCK) and the mitochondrial enzyme deoxyguanosine kinase. The cytotoxicity mainly depends on the accumulation of cladribine-triphosphates (TP) after phosphorylation of cladribine-MP by nucleoside monophosphate kinase and nucleoside diphosphate kinase. 5'-Nucleotidase (5'-NT) dephosphorylates cladribine-MP and the accumulation of cladribine-TP depends on the ratio of dCK and 5'-NT in the cells. The mechanisms underlying cladribine resistance are multifactorial, e.g. decreased nucleoside transport, decreased activity or deficiency of dCK, altered intracellular pools of competing nucleotides, altered regulation of ribonucleotide reductase and increased drug inactivation by 5'-NT. Finally, cladribine resistance may be a consequence of a defective induction of apoptosis. In spite of the fact that more than one mechanism can contribute to a cladribine resistance phenotype, a reduction in dCK activity is probably the major determinant of cladribine resistance. Insight into the mechanism of action and resistance to cladribine is crucial for its optimal use as well as for the development of newer analogues.

Control of mitochondrial integrity by Bcl-2 family members and caspase-independent cell death

Programmed cell death (PCD) is essential for normal development and maintenance of tissue homeostasis in multicellular organisms. While it is now evident that PCD can take many different forms, apoptosis is probably the most well-defined cell death programme. The characteristic morphological and biochemical features associated with this highly regulated form of cell death have until recently been exclusively attributed to the caspase family of cysteine proteases. As a result, many investigators affiliate apoptosis with its pivotal execution system, i.e. caspase activation. However, it is becoming increasingly clear that PCD or apoptosis can also proceed in a caspase-independent manner and maintain key characteristics of apoptosis. Mitochondrial integrity is central to both caspase-dependent and-independent cell death. The release of pro-apoptotic factors from the mitochondrial intermembrane space is a key event in a cell's commitment to die and is under the tight regulation of the Bcl-2 family. However, the underlying mechanisms governing the efflux of these pro-death molecules are largely unknown. This review will focus on the regulation of mitochondrial integrity by Bcl-2 family members with particular attention to the controlled release of factors involved in caspase-independent cell death.

Mitochondrial dysfunction in CD47-mediated caspase-independent cell death: ROS production in the absence of cytochrome c and AIF release

Ligation of CD47 by its natural ligand thrombospondin (TSP), or cross-linking by CD47 antibodies, triggers caspase-independent cell death in normal and leukemic cells. This kind of cell death is characterised by the cytoplasmic events of apoptosis including externalisation of phosphatidylserines and mitochondria swelling. We report herein selective mitochondrial changes in CD47-dependent cell death of T cells. After T cell stimulation via CD47, a rapid mitochondrial transmembrane potential (deltapsi(m)) disruption is accompanied by the production of reactive oxygen species (ROS) and phosphatidylserine exposure. Surprisingly, mitochondrial dysfunction does not induce cytochrome c or AIF release. Moreover, the dying cells do not exhibit caspase-3 activation and display intact nuclei without any large-scale, or oligonucleosomal DNA fragmentation. We conclude that DeltaPsi(m) loss and ROS production are an early step in CD47-dependent killing and neither cytochrome c, nor AIF are implicated in this new cell death pathway.

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.

A key role for caspase-2 and caspase-3 in the apoptosis induced by 2-chloro-2'-deoxy-adenosine (cladribine) and 2-chloro-adenosine in human astrocytoma cells

Both the anticancer agent 2-chloro-2'-deoxy-adenosine (Cladribine) and its derivative 2-chloro-adenosine induce apoptosis of human astrocytoma cells (J Neurosci Res 60:388-400, 2000). In this study, we have analyzed the involvement of caspases in these effects. Both compounds produced a gradual and time-dependent activation of "effector" caspase-3, which preceded the appearance of the nuclear signs of apoptosis, suggesting a temporal correlation between these two events. Moreover, the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-dl-Asp-fluoromethylketone (fmk) suppressed both caspase-3 activation and apoptosis induction. "Initiator" caspase-9 and caspase-8 were only marginally activated at later times in the apoptotic process. Accordingly, at concentrations that selectively inhibit these caspases, neither N-benzyloxycarbonyl-Leu-Glu-His-Asp-fmk nor N-benzyloxycarbonyl-Ile-Glu-Thr-Asp-fmk could prevent adenosine analog-induced cell death. To definitively rule out a role for the caspase-9/cytochrome c-dependent mitochondrial pathway of cell death, neither adenosine analog had any effect on mitochondrial membrane potential, which was instead markedly reduced by other apoptotic stimuli (e.g., deoxyribose, NaCN, and betulinic acid). Consistently, although the latter triggered translocation of mitochondrial cytochrome c to the cytoplasm, no cytosolic accumulation of cytochrome c was detected with adenosine analogs. Conversely, 1 to 7 h after addition of either adenosine analog (i.e., before the appearance of caspase-3 activation), caspase-2 activity was surprisingly and markedly increased. The selective caspase-2 inhibitor N-benzyloxy carbonyl-Val-Asp-Val-Ala-Asp-fmk significantly reduced both adenosine analogs-induced caspase-2 activation and the associated cell death. We conclude that adenosine analogs induce the apoptosis of human astrocytoma cells by activating an atypical apoptotic cascade involving caspase-2 as an initiator caspase, and effector caspase-3. Therefore, these compounds could be effectively used in the pharmacological manipulation of tumors characterized by resistance to cell death via either the mitochondrial or caspase-8/death receptor pathways.

Apoptosis during ectromelia orthopoxvirus infection is DEVDase dependent: in vitro and in vivo studies

Ectromelia virus (EV), which causes mousepox, is a member of the orthopoxviruses that are defined as being able to suppress apoptosis. Caspase-3 is one of the key effector proteases which regulates the apoptotic cascade and which is responsible for DNA fragmentation observed during apoptosis. It is well known that viruses, especially poxviruses, can inhibit caspase activity. Here, we report that EV can regulate apoptosis in vitro, suppressing the activity of caspases recognizing the DEVD (Asp-Glu-Val-Asp) motif (caspase-3 and -7) before successful virus replication is completed. Caspase-3 activity measurement showed that an increase in caspase-3 activity preceded the peak of DNA fragmentation demonstrated by TUNEL staining of L929 and RK-13 cells. By using specific caspase inhibitors (Ac-DEVD-CHO, Ac-IETD-CHO and zVAD-fmk), we showed that caspase-3 and -7 (DEVDases) are major effector caspases during EV-induced apoptosis in permissive L929 and RK-13 cell cultures. Apoptosis in vivo seems to play an important role during viraemia as well as during the clearance of EV from genetically susceptible BALB/c (H-2(d)) mice. However, as shown by measurement of caspase-3 activity, caspase-3 protein detection and M30-antibody staining, both DEVDases seem to play an important role during EV clearance from draining lymph nodes and conjunctivae at 15 days p.i. up to 20 days p.i., whereas in the liver and spleen DNA fragmentation coexisted with viral multiplication and secondary viraemia. Apoptosis was DEVDase dependent only in the liver, while spleen DNA fragmentation observed between 5 and 10 days p.i. was caspase independent. Therefore, we conclude that DEVDase- (caspase-3- and caspase-7-) dependent apoptosis is an important mechanism regulating the resolution of EV infection.