Modulation Of Bcl-2 Research Articles

Protective effects of antioxidants against smokeless tobacco-induced oxidative stress and modulation of Bcl-2 and p53 genes in human oral kerathnocytes

The oral use of chewing tobacco has greatly increased in recent years, and this usage is associated with cancers of the mouth, lip, nasal cavities, esophagus and gut. Oral cancer accounts for 3% of all cancers in U.S.A. and is the seventh most common cancer. Previous studies in our laboratory have demonstrated the protective abilities of a novel IH636 grape seed proanthocyanidin extract (GSPE) against reactive oxygen species both in vitro and in vivo models, and provided significantly better protection as compared to vitamins C, E and β-carotene. In the recent past, we have demonstrated smokeless tobacco (STE)-induced oxidative stress, apoptotic cell death in a primary culture of normal human oral keratinocytes (NHOK), and have compared the protective abilities of vitamins C and E, singly and in combination, and GSPE in this pathobiology [Free Rad. Biol. Med., 26, 992–1000 (1999)]. In the present study, we have assessed the protective role of vitamins C and E, and GSPE against STE-induced modulation of intracellular oxidized states in NHOK cells as demonstrated by laser scanning confocal microscopy. Approximately 11%, 26%, 28% and 50% protection were observed following incubation with vitamin C, vitamin E, a combination of vitamins C plus E, and GSPE, respectively. DNA fragmentation was assessed as an index of oxidative DNA damage and similar results were observed. Furthermore, the cellular viability and functional roles of Bcl-2, p53 and c-myc genes were assessed in STE-induced oxidative stress in NHOK cells. NHOK cells were treated with STE (0–200 μg/ml) for 24h and changes in the expression of Bcl-2, p53 and c-myc genes were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), and the protective effect of GSPE was assessed. Approximately a 2.0-fold increase in p53 gene expression was observed following incubation of the oral keratinocytes with 100 μg/ml of STE, beyond which the expression of p53 decreased, confirming increased apoptotic cell death with a higher concentration of STE as reported earlier. GSPE significantly modulated STE-induced changes in p53. The expression of antiapoptotic Bcl-2 gene decreased with STE treatment and the expression of Bcl-2 gene increased significantly following preincubation with GSPE. No significant change in the expression of transcription factor c-myc gene responsible for cell cycle growth was observed following incubation with STE and/or GSPE. Thus, c-myc may not be involved in STE-induced cytotoxicity towards NHOK cells. These results suggest that antioxidant protection of STE-induced cellular injury is associated with alterations in Bcl-2 and p53 expression.

Amiodarone Induces CytochromecRelease and Apoptosis through an Iodine-Independent Mechanism1

Amiodarone (AMD) is one of the most effective antiarrhythmic drugs available. However, its use is often limited by side-effects, mainly hypo- or hyperthyroidism. As AMD displays direct toxic effect on different cell types, we investigated the cytotoxic effect of AMD and its main metabolite, desethylamiodarone (DEA), in thyroid (TAD-2) and nonthyroid (HeLa) cell lines. Both AMD and DEA displayed a dose-dependent toxicity in TAD-2 and HeLa cells, although DEA was more effective. Both TAD-2 and HeLa cells underwent apoptosis, as evidenced by plasma membrane phosphatidylserine exposure and DNA fragmentation. Inhibition of protein synthesis with cycloheximide and inhibition of endogenous peroxidase activity with propylthiouracil did not affect this AMD- and DEA-induced apoptosis in TAD-2 cells. Western blot analysis did not display variations in the expression of p53, Bcl-2, Bcl-XL, and Bax proteins during the treatment with AMD and DEA. Generation of reactive oxygen species, investigated by flow cytometry with dichlorofluorescein diacetate, did not show the production of free radicals during drug treatment. Furthermore, Western blot analysis of cytosolic and mitochondrial fractions prepared from AMD-treated cells demonstrated that AMD induces the release of cytochrome c into the cytosol from the mitochondria. These data indicate that AMD induces cytochrome c release from mitochondria, triggering apoptosis through an iodine-independent mechanism, and that this process is not mediated by modulation of p53, Bcl-2, Bcl-XL, or Bax protein expression and does not involve the generation of free radicals.

Effects of Bcl-2 modulation with G3139 antisense oligonucleotide on human breast cancer cells are independent of inherent Bcl-2 protein expression.

We have investigated the effects of transient Bcl-2 down-regulation induced by the Bcl-2 antisense oligodeoxynucleotide (ODN) G3139 (Genta Incorporated) in high Bcl-2 protein expressing, estrogen receptor (ER) positive MCF-7 and low Bcl-2 expressing, ER negative MDA435/LCC6 human breast cancer cells. Treatment with Bcl-2 antisense ODN in vitro caused > 80% reduction of Bcl-2 protein levels in a sequence specific manner for both cell lines. Maximum mRNA reduction was achieved within 24 h of the first antisense ODN exposure whereas full protein down-regulation required antisense exposure over 48 h. This Bcl-2 reduction was associated with 80-95% loss of viable cells compared to untreated cells. Similar cytotoxic effects were observed in both cell lines despite a nine-fold intrinsic difference in Bcl-2 protein expression suggesting that the relative degree of down-regulation of Bcl-2 is more important than the absolute reduction. Cell death associated with G3139 exposure exhibited properties indicative of apoptosis such as mitochondrial membrane depolarization and caspase activation. Combined treatment with G3139 and cytotoxic agents resulted in additive cytotoxicity in both cell lines. However, under most conditions studied, the direct cytotoxic activity of G3139 antisense was not synergistic with the cytotoxic agents. These results suggest that while Bcl-2 clearly constitutes an attractive therapeutic target due to its role in regulating apoptosis in breast cancer cells, additional mechanisms are important in the control of apoptosis arising from exposure to anticancer agents in vitro.

Theophylline and cisplatin synergize in down regulation of BCL-2 induction of apoptosis in human granulosa cells transformed by a mutated p53 (p53 val135) and Ha-ras oncogene.

Cisplatin is in common use in ovarian cancer therapy, although it is also implicated in cytotoxicity in normal tissue. We have examined the effect of cisplatin alone and in combination with theophylline, a phoshodiesterase inhibitor, on modulation of Bcl-2/Bax expression and induction of apoptosis in human granulosa cells transformed by stable transfection with mutant p53 plus Ha-ras. Theophylline elicited cell death only at relatively high concentrations with an EC50 of 200 microg/ml. Cisplatin exerted its lethal effect with an EC50 of 7 microM. In the presence of 15 or 50 microg/ml of theophylline (in the range used against asthma in humans), the EC50 for cisplatin was reduced to 2 microM or 1.2 microM, respectively. Using fluorescence-activated cell sorting analysis of DNA stained cells and the terminal deoxy-nucleotide tranferase-mediated dUTP nick end-labeling method, we found that even at concentrations of 0. 3 and 1 microM cisplatin, theophylline at 15 and 50 microg/ml increased the incidence of apoptosis in these cells by 3-5-fold, while theophylline alone induced extremely low apoptosis. Neither drug had any measurable effect on Bax protein expression. In contrast Bcl-2 protein expression levels were markedly reduced by theophylline and cisplatin in a dose-dependent manner. The combination of theophylline and cisplatin resulted in a further dramatic reduction in Bcl-2, under-scoring the pronounced synergy of these two drugs. These observations suggest that suppression of Bcl-2 expression may play an important role in mediating the synergistic effect of cisplatin and theophylline on induction of apoptosis in ovarian cancer cells.

Induction of apoptosis by a novel intestinal metabolite of ginseng saponin via cytochrome c-mediated activation of caspase-3 protease

Ginseng saponins exert various important pharmacological effects with regard to the control of many diseases including cancer. The novel intestinal bacterial metabolites of ginseng protopanaxadiol saponins have recently been found and isolated after the oral administration of ginseng extract in human and rats. 20- O-(β- d-Glucopyranosyl)-20( S)-protopanaxadiol (IH-901) formed from ginsenosides Rb1, Rb2, and Rc is of particular interest in cancer chemoprevention and treatment. We investigated the effects of IH-901 on the human myeloid leukemia cell line HL-60 in terms of inhibition of proliferation and induction of apoptosis. IH-901 showed a significant cytotoxic activity in HL-60 cells ( ic 50 = 24.3 μM) following a 96-hr incubation. Treatment of HL-60 cells with IH-901 resulted in the formation of internucleosomal DNA fragments. The dose- and time-dependent induction of apoptosis by IH-901 was demonstrated in sandwich enzyme immunoassay and the results were confirmed by flow cytometric analysis. Morphological examination of IH-901-treated samples showed cells with chromatin condensation, cell shrinkage, and nuclear fragmentation, all typical characteristics of apoptotic cells. The treatment of HL-60 cells with IH-901 caused activation of caspase-3 protease and subsequent proteolytic cleavage of poly(ADP-ribose) polymerase. IH-901 did not affect the expression of antiapoptotic protein Bcl-2 but did cause a release of mitochondrial cytochrome c into cytosol. In conclusion, our results demonstrate that IH-901 dramatically suppresses HL-60 cell growth by inducing programed cell death through activation of caspase-3 protease, which occurs via mitochondrial cytochrome c release independently of Bcl-2 modulation. These results may provide a pivotal mechanism for the use of IH-901 in the prevention and treatment of leukemia.

Influence of dexamethasone, fludarabine, and their synergism on apoptosis and BCL-2 expression in b-cll cells in vitro according to differentiation stage of cells

Abstract The purpose of this work was to investigate apoptosis and bcl-2 expression in cells of classical CLL, CLL/PL and PLL, to examine the influence of dexamethason and fludarabine separately and in combination on these two phenomena. There is evidence in the literature that morphological types B-CLL can be regarded as stages of different cell maturation. The hypothesis was that different maturation stages differ in their tendency to spontaneous and drug-induced apoptosis. Another hypothesis concerning additive or synergistic effect of mentioned drug combination was tested. Cells collected from 15 B-CLL patients (5 typical CLL, 5-CLL/PL and 5-PLL) were divided into control cultures, cultures treated with single drug and cultures treated with drug combination. The percentage of apoptotic cell nuclei was calculated in the subdiploid DNA peak of the DNA fluorescent histogram at days 3 and 7 using a flow cytometric analysis of propidium iodide staining of DNA. In parallel, morphology was examined on MGG stained slides using light microscopy. Bcl-2 protein expression was estimated in 9 patients using semiquantitative analysis of antibody by flow cytometry. Results of this study do not show significant differences between spontaneous and drug induced apoptosis in all 3 different stages. On estimating of drug induced apoptosis, drug influence was corrected according to spontaneous apoptosis measured in cell population of the same source. Additive cytotoxic effect of dexamethasone and fludarabin combination was observed in all different stages with no significant differences between influence of each drug. Analysis of bcl-2-expression demonstrated bimodal pattern as described earlier, which disappears after drug addition. Percentage of cells in control and drug treated cultures positive for bcl-2 protein was constant and high in all stages for an entire period of incubation. Dexamethasone, fludarabine and their combination induced upregulation, downregulation or did not change bcl-2 expression in different cases. No specific pattern was shown to characterize individual differentiation stage; but each drug alone and their combination tended to influence bcl-2 expression in a similar way in every given case, suggesting existence of a common pathway of bcl-2 modulation for these drugs. In conclusion, this study of in vitro apoptosis of B-CLL cells demonstrated: 1) no significant differences between maturation stages of B-CLL according to their susceptibility to spontaneous or drug-induced apoptosis, 2) a cumulative effect of fludarabine and dexamethasone combination on apoptosis in comparison to a single drug, 3) bimodal pattern of bcl-2 expression evolving into different unimodal patterns after drug addition with no specific pattern characterizing each stage and with similar direction of change for each drug, suggesting a common pathway for bcl-2 modulation.

Spicamycin and KRN5500 induce apoptosis in myeloid and lymphoid cell lines with down-regulation of bcl-2 expression and modulation of promyelocytic leukemia protein.

Spicamycin is a potent inducer of differentiation of human myeloid leukemia cells (HL‐60) and murine myeloid leukemia cells (M1). One of the spicamycin derivatives, KRN5500, shows a broad spectrum of antitumor activity against human tumor xenografts in nude mice. In this study, we first investigated the differentiation efficacy of spicamycin and KRN5500 in HL‐60 and acute promyelocytic leukemia cell line, NB4, and found that low concentrations of both compounds induced differentiation to a small extent in both cell lines, but markedly induced apoptosis in NB4 cells. Further investigation in a myeloid leukemia cell line, NKM‐1, a lymphoma cell line, Daudi, and multiple myeloma cell line, NOP‐1, showed that high concentrations of both compounds also induced apoptosis in these cells. The 50% inhibitory concentration (IC50) determined by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay showed that myeloid cells were more sensitive to both compounds than lymphoid cells, and spicamycin was more potent than KRN5500. Western blot analysis of Bcl‐2, Bcl‐xL and Bax expression and immunofluorescence analysis of promyelocytic leukemia (PML) protein indicated that apoptosis induced by spicamycin and KRN5500 was associated with down‐regulation of Bcl‐2 expression and modulation of PML protein. Thus, spicamycin and KRN5500 may be useful for the treatment of myeloid and lymphoid neoplasms.

Modulation of bcl-2 and p27 in human primitive proliferating hematopoietic progenitors by autocrine TGF-β1 is a cell cycle–independent effect and influences their hematopoietic potential

Primitive, proliferating hematopoietic progenitors (defined as cytokine low-responding primitive progenitors; CLRPP), isolated from human CD34+ cells, expressed endoglin (CD105) and produced transforming growth factor-beta1 (TGF-beta1). Culture of CLRPP in serum-free conditions with anti-TGF-beta1 monoclonal antibody produced a substantial decrease in bcl-2 protein/RNA levels and a significant reduction of cloning and long-term culture-initiating cell (LTC-IC) activities. GATA-1 and PU.1 RNA levels were significantly up-regulated in anti-TGF-beta1-treated CLRPP, which generated an increased number of cells expressing CD15/CD11b/glycophorin-A. The described effects of TGF-beta1 neutralization were observed in the absence of any relevant effect on cell cycle; number of cell divisions; p53, c-myc, and p21 RNA levels; bcl-xL and bax protein levels; and c-myc/p16/p21/p107/Rb cell cycle-related protein levels. A relevant increase in p27 protein levels was observed in anti-TGF-beta1-treated CLRPP, suggesting a role for p27 in the regulation of the hematopoietic potential. The present study on human progenitors and previously reported data on TGF-beta1 knockout mice suggest that, at the autocrine level, the cell cycle inhibitor TGF-beta1 plays an important role in regulating the survival and differentiation of primitive proliferating hematopoietic progenitors by cell cycle-independent mechanisms.

Susceptibility to drug-induced apoptosis correlates with differential modulation of Bad, Bcl-2 and Bcl-xL protein levels.

To define the responses of apoptotic regulatory proteins to different chemotherapeutic agents, we investigated the expression of Bcl-2 family gene products, the release of cytochrome c, and the activation of pro-caspase-3 during apoptosis induced by Taxol and Thiotepa, in the MCF-7 breast carcinoma and the HL-60 leukemia cell lines. The earliest event induced by drug exposure was increase in Bad protein levels, followed by Bcl-2 down-regulation, cytochrome c release, and Bcl-xL and Bax up-regulation. Bak accumulation was a late event. Activation of pro-caspase-3 and cleavage of Bcl-2 protein occurred in the HL-60 cells only, and followed the cytochrome c release. The overall responses were qualitatively similar in both cell types, but MCF-7 cells treated with Taxol showed a significant delay in apoptosis, correlating with early up-regulation of Bcl-2 and delayed release of cytochrome c. We conclude that Bad up-regulation is an early indicator of a cellular response that will lead to cell death, but may be modulated by survival mechanisms, which cumulatively govern the ultimate susceptibility to apoptosis.

Iodide Excess Induces Apoptosis in Thyroid Cells through a p53-Independent Mechanism Involving Oxidative Stress

Thyroid toxicity of iodide excess has been demonstrated in animals fed with an iodide-rich diet; in vitro iodide is cytotoxic, inhibits cell growth, and induces morphological changes in thyroid cells of some species. In this study, we investigated the effect of iodide excess in an immortalized thyroid cell line (TAD-2) in primary cultures of human thyroid cells and in cells of nonthyroid origin. Iodide displayed a dose-dependent cytotoxicity in both TAD-2 and primary thyroid cells, although at different concentrations, whereas it had no effect on cells of nonthyroid origin. Thyroid cells treated with iodide excess underwent apoptosis, as evidenced by morphological changes, plasma membrane phosphatidylserine exposure, and DNA fragmentation. Apoptosis was unaffected by protein synthesis inhibition, whereas inhibition of peroxidase enzymatic activity by propylthiouracil completely blocked iodide cytotoxicity. During KI treatment, reactive oxygen species were produced, and lipid peroxide levels increased markedly. Inhibition of endogenous p53 activity did not affect the sensitivity of TAD-2 cells to iodide, and Western blot analysis demonstrated that p53, Bcl-2, Bcl-XL, and Bax protein expression did not change when cells were treated with iodide. These data indicate that excess molecular iodide, generated by oxidation of ionic iodine by endogenous peroxidases, induces apoptosis in thyroid cells through a mechanism involving generation of free radicals. This type of apoptosis is p53 independent, does not require protein synthesis, and is not induced by modulation of Bcl-2, Bcl-XL, or Bax protein expression.

Iodide Excess Induces Apoptosis in Thyroid Cells through a p53-Independent Mechanism Involving Oxidative Stress1

Thyroid toxicity of iodide excess has been demonstrated in animals fed with an iodide-rich diet; in vitro iodide is cytotoxic, inhibits cell growth, and induces morphological changes in thyroid cells of some species. In this study, we investigated the effect of iodide excess in an immortalized thyroid cell line (TAD-2) in primary cultures of human thyroid cells and in cells of nonthyroid origin. Iodide displayed a dose-dependent cytotoxicity in both TAD-2 and primary thyroid cells, although at different concentrations, whereas it had no effect on cells of nonthyroid origin. Thyroid cells treated with iodide excess underwent apoptosis, as evidenced by morphological changes, plasma membrane phosphatidylserine exposure, and DNA fragmentation. Apoptosis was unaffected by protein synthesis inhibition, whereas inhibition of peroxidase enzymatic activity by propylthiouracil completely blocked iodide cytotoxicity. During KI treatment, reactive oxygen species were produced, and lipid peroxide levels increased markedly. Inhibition of endogenous p53 activity did not affect the sensitivity of TAD-2 cells to iodide, and Western blot analysis demonstrated that p53, Bcl-2, Bcl-XL, and Bax protein expression did not change when cells were treated with iodide. These data indicate that excess molecular iodide, generated by oxidation of ionic iodine by endogenous peroxidases, induces apoptosis in thyroid cells through a mechanism involving generation of free radicals. This type of apoptosis is p53 independent, does not require protein synthesis, and is not induced by modulation of Bcl-2, Bcl-XL, or Bax protein expression.

Thrombin induces apoptosis in human tumor cells

Thrombin is a serine protease that is produced during the coagulation process and plays an essential role for hemostasis, thrombosis and wound healing. It is a potent activator of platelets, induces proliferation of a wide variety of normal and malignant human cells, and enhances their invasiveness and metastatic potential. We studied the effect of thrombin on the proliferation of a wide variety of human tumor cells and report here that, at low concentrations, thrombin induces proliferation of these cells. However, at higher concentrations, thrombin inhibited their proliferation. We show that this inhibition of cell proliferation was due to apoptosis of the tumor cells. The thrombin-mediated apoptosis was inhibited significantly by its specific inhibitor, hirudin. Furthermore, no consistent pattern of induction and/or modulation of p53, p21 and bcl-2 was observed in the thrombin-mediated apoptosis. To our knowledge, this is the first report to describe the pro-apoptotic effects of thrombin on human tumor cells and may have implications for chemotherapy in cancer patients and for the pathogenesis of AIDS as well.

Selective induction of apoptosis by the cytotoxic analog AN-207 in cells expressing recombinant receptor for luteinizing hormone-releasing hormone

The selectivity of ligands specific for certain cells can be used to preferentially target chemotherapeutic compounds to neoplastic cells. Human breast, ovarian, endometrial, and prostatic cancers express receptors that can mediate the delivery of targeted cytotoxic compounds to neoplastic cells. Recently, a potent derivative of 2-pyrrolinodoxorubicin (AN-201) conjugated to [D-Lys6] luteinizing hormone-releasing hormone (LH-RH) (AN-207), was demonstrated to be less toxic than the nonconjugated chemotherapeutic radical and significantly more active in slowing neoplastic cellular growth. In this study we investigate the molecular mechanisms underlying the cytotoxic action of AN-207. We stably transfected COS cells with a LH-RH receptor (LH-RH-Rc) mammalian expression vector and examined the effect of AN-207 on known markers of cellular apoptosis. Apoptotic induction by AN-207, as measured by Bax and Bcl-2 protein levels, was increased in stable cells that express LH-RH-Rc compared with parental cells. DNA fragmentation also was increased by AN-207 treatment when compared with AN-201. Clinically used LH-RH antagonists partially inhibited apoptotic Bax expression and DNA fragmentation induced by AN-207, and blocked AN-207 induced down-regulation of Bcl-2 steady-state protein levels. In cell proliferation studies, after 72 h AN-207 exhibited greater cytotoxicity than AN-201 at equivalent concentrations, in COS cells expressing LH-RH-Rc but not in parental COS cells. In addition, survival of LH-RH-Rc positive cells treated with AN-207 was partially restored by LH-RH antagonist. This study demonstrates the receptor-specific cytotoxic effect of 2-pyrrolinodoxorubicin conjugated to [D-Lys6] LH-RH, exerted through induction of apoptosis and modulation of Bax, Bcl-2, and DNA fragmentation.

Modulation of constitutive nitric oxide synthase, bcl-2 and Fas expression in cultured human coronary endothelial cells exposed to anoxia-reoxygenation and angiotensin II: role of AT1 receptor activation.

Angiotensin II (Ang II) plays a critical role in the pathophysiology of myocardial ischemia-reperfusion injury. We have recently shown that reoxygenation following a period of anoxia causes apoptosis of cultured human coronary artery endothelial cells (HCAECs). Ang II further enhances apoptosis of HCAECs via Ang II type 1 receptor (AT1R) activation. Recent studies suggest an important role of constitutive nitric oxide synthase (cNOS), Fas and bcl-2 proteins in apoptosis. This study was designed to examine the modulation of cNOS, and Fas and bcl-2 expression in HCAECs during exposure to anoxia-reoxygenation and Ang II. HCAECs were exposed to anoxia-reoxygenation and Ang II. Anoxia-reoxygenation significantly decreased cNOS mRNA, protein and activity in cultured HCAECs (P < 0.05 vs. control). Anoxia-reoxygenation also caused an increase in Fas and a decrease in bcl-2 protein expression in cultured HCAECs (both P < 0.05 vs. control). The presence of Ang II (0.3 microM) further enhanced these effects of anoxia-reoxygenation on cNOS, Fas and bcl-2 expression. The effects of Ang II were significantly attenuated by the AT1R inhibitor losartan (10 microM). During exposure of HCAECs to anoxia-reoxygenation and Ang II, AT1R activation induces important changes in cNOS mRNA, protein expression and activity, as well as bcl-2 and Fas protein expression which may have a bearing on the development of apoptosis.

Flavopiridol Induces Apoptosis in Chronic Lymphocytic Leukemia Cells Via Activation of Caspase-3 Without Evidence of bcl-2 Modulation or Dependence on Functional p53

Flavopiridol has been reported to induce apoptosis in lymphoid cell lines via downregulation of bcl-2. The in vitro activity of flavopiridol against human chronic lymphocytic leukemia (CLL) cells and potential mechanisms of action for inducing cytotoxicity were studied. The in vitro viability of mononuclear cells from CLL patients (n = 11) was reduced by 50% at 4 hours, 24 hours, and 4 days at a flavopiridol concentration of 1.15 micromol/L (95% confidence interval [CI] +/-0.31), 0.18 micromol/L (95% CI +/-0.04), and 0.16 micromol/L (95% CI +/-0.04), respectively. Loss of viability in human CLL cells correlated with early induction of apoptosis. Exposure of CLL cells to 0.18 micromol/L of flavopiridol resulted in both decreased expression of p53 protein and cleavage of the caspase-3 zymogen 32-kD protein with the appearance of its 20-kD subunit. Contrasting observations of others in tumor cell lines, flavopiridol cytotoxicity in CLL cells did not correlate with changes in bcl-2 protein expression alterations. We evaluated flavopiridol's dependence on intact p53 by exposing splenocytes from wild-type (p53(+/+)) and p53 null (p53(-/-)) mice that demonstrated no preferential cytotoxicity as compared with a marked differential with F-ara-a and radiation. Incubation of CLL cells with antiapoptotic cytokine interleukin-4 (IL-4) did not alter the LC50 of flavopiridol, as compared with a marked elevation noted with F-ara-a in the majority of patients tested. These data demonstrate that flavopiridol has significant in vitro activity against human CLL cells through activation of caspase-3, which appears to occur independently of bcl-2 modulation, the presence of IL-4, or p53 status. Such findings strongly support the early introduction of flavopiridol into clinical trials for patients with B-CLL.

Flavopiridol Induces Apoptosis in Chronic Lymphocytic Leukemia Cells Via Activation of Caspase-3 Without Evidence of bcl-2 Modulation or Dependence on Functional p53

Flavopiridol has been reported to induce apoptosis in lymphoid cell lines via downregulation of bcl-2. The in vitro activity of flavopiridol against human chronic lymphocytic leukemia (CLL) cells and potential mechanisms of action for inducing cytotoxicity were studied. The in vitro viability of mononuclear cells from CLL patients (n = 11) was reduced by 50% at 4 hours, 24 hours, and 4 days at a flavopiridol concentration of 1.15 μmol/L (95% confidence interval [CI] ±0.31), 0.18 μmol/L (95% CI ±0.04), and 0.16 μmol/L (95% CI ±0.04), respectively. Loss of viability in human CLL cells correlated with early induction of apoptosis. Exposure of CLL cells to 0.18 μmol/L of flavopiridol resulted in both decreased expression of p53 protein and cleavage of the caspase-3 zymogen 32-kD protein with the appearance of its 20-kD subunit. Contrasting observations of others in tumor cell lines, flavopiridol cytotoxicity in CLL cells did not correlate with changes in bcl-2 protein expression alterations. We evaluated flavopiridol’s dependence on intact p53 by exposing splenocytes from wild-type (p53+/+) and p53 null (p53−/−) mice that demonstrated no preferential cytotoxicity as compared with a marked differential with F-ara-a and radiation. Incubation of CLL cells with antiapoptotic cytokine interleukin-4 (IL-4) did not alter the LC50 of flavopiridol, as compared with a marked elevation noted with F-ara-a in the majority of patients tested. These data demonstrate that flavopiridol has significant in vitro activity against human CLL cells through activation of caspase-3, which appears to occur independently of bcl-2 modulation, the presence of IL-4, or p53 status. Such findings strongly support the early introduction of flavopiridol into clinical trials for patients with B-CLL.

Fludarabine ability to down-regulate Bcl-2 gene product in CD5+ leukaemic B cells: in vitro/in vivo correlations.

CD5+ B-chronic lymphocytic leukaemia (B-CLL) and mantle cell lymphoma (MCL) in leukaemic phase are characterized by defects in cell death induction that primarily involves the Bcl-2 family of genes. Fludarabine (9-beta-D-arabinofuranosyl-2-fluoradenine, F-ara-A) is a potent inducer of apoptosis in CLL cells. This study aimed to determine whether F-ara-A-induced apoptosis might be related to Bcl-2 modifications and to evaluate in vitro/in vivo correlations. Peripheral blood lymphocytes from eight B-CLL and four leukaemic MCL were cultured in the presence of different concentrations of F-ara-A +/- methylprednisolone (MP). F-ara-A down-regulated the expression of Bcl-2 in 5/12 cases. mRNA down-regulation was maximal at 48 h; protein down-regulation was prominent after 48 h. Both events were dose-dependent. The amount of apoptosis was significantly higher in the samples treated with F-ara-A than in those exposed to MP alone. In the seven remaining cases, no Bcl-2 down-regulation was observed after exposure to F-ara-A and the degree of F-ara-A-induced apoptosis overlapped that induced by MP. The in vivo outcome after treatment with three to six courses of F-ara-A was evaluable in 10 patients: 4/5 cases, whose cells had shown in vitro Bcl-2 down-regulation and prominent apoptosis after exposure to F-ara-A, had a complete response (CR) and a partial response (PR) was observed in the remaining patient. Of the five patients whose cells had shown no in vitro Bcl-2 modulation after exposure to F-ara-A, two had a PR, but the other three did not show any in vivo clinical response.

Suppression of nitric oxide–induced apoptosis by N-acetyl-l-cysteine through modulation of glutathione, bcl-2, and bax protein levels

It has been demonstrated that nitric oxide (NO) can promote apoptosis in human cancer cells. To test the protective effects of antioxidants (N-acetyl-L-cysteine (LNAC) and free-radical spin traps (5,5-dimethyl-1-pyrroline N-oxide and 2,2,6,6,-tetramethyl-1-piperidinyloxy) against NO-induced apoptosis, a human colon cancer cell line (COLO 205) was treated with NO, and its survival rate was evaluated both with and without antioxidant therapy. LNAC arrested the development of progression of apoptosis in COLO 205 cells in a dose-dependent manner, promoted long-term survival, and prevented the internucleosomal DNA cleavage induced by NO. The intracellular level of glutathione (GSH) was found to be elevated in cells after exposure to LNAC. The bax protein levels were elevated by NO treatment, and this effect was blocked by LNAC. On the other hand, the bcl-2 oncoprotein level in the LNAC-pretreated cells was significantly elevated in a time-dependent manner compared to cells that received NO pretreatment. In summary, our results suggest that the protective effect of LNAC may be linked to its inducement of increases in cellular GSH and bcl-2 protein levels and to its suppression of cellular bax protein in treated cells.

Vitamin C and E prevent lipopolysaccharide-induced apoptosis in human endothelial cells by modulation of Bcl-2 and Bax

Lipopolysaccharide induced apoptosis and necrosis of human umbilicial venous endothelial cells in a time-dependent manner. Lipopolysaccharide (1 μg/ml)-induced apoptosis was maximal after 18 h, whereas necrosis occurred after prolonged incubation for more than 24 h. The increase in apoptosis correlated with a reduction in Bcl-2, a potent cell death inhibitor. Furthermore, lipopolysaccharide treatment upregulated Bax, which heterodimerizes with and thereby inhibits Bcl-2. Both the antioxidant N-acetylcysteine and the combination of vitamin C and E (10 μM) completely inhibited lipopolysaccharide-induced apoptosis, whereas vitamin C or E alone was less effective. The reduction of lipopolysaccharide-induced apoptosis by vitamin C and E was paralleled by an increase in Bcl-2 and a decrease in Bax protein levels. Thus, vitamin C and E seem to interfere with the Bcl-2 family of apoptosis regulators in human umbilicial venous endothelial cells.

In Vitro Studies on Cellular and Molecular Mechanisms of Arsenic Trioxide (As2O3) in the Treatment of Acute Promyelocytic Leukemia: As2O3 Induces NB4 Cell Apoptosis With Downregulation of Bcl-2 Expression and Modulation of PML-RARα/PML Proteins

It has been shown recently in China that arsenic trioxide (As2O3) is a very effective treatment for acute promyelocytic leukemia (APL). APL patients resistant to all-trans retinoic acid (ATRA) and conventional chemotherapy can still respond to AS2O3. In this study, we addressed the possible cellular and molecular mechanisms of this treatment by using NB4 cells as a model. The results show that: (1) As2O3 triggers relatively specific NB4 cell apoptosis at micromolar concentration, as proved by morphology, histogramic related nuclear DNA contents, and DNA gel eletrophoresis. (2) As2O3 does not influence bax, bcl-x, c-myc, and p53 gene expression, but downregulates bcl-2 gene expression at both mRNA and protein levels. (3) As2O3 induces a significant modulation of the PML staining pattern in NB4 cells and HL-60 cells. The micropunctates characteristic of PML-RAR alpha in NB4 cells dissappear after treatment with As2O3, whereas a diffuse PML staining occurs in the perinuclear cytoplasmic region. In addition, a low percentage of untreated NB4 cells exhibits an accumulation of PML positive particles in a compartment of cytoplasm. The percentage of these cells can be significantly increased after As2O3 treatment. A similar PML staining pattern is observed in apoptotic cells. (4) ATRA pretreatment does not influence As2O3-induced apoptosis. These results suggest that induction of cell apoptosis can be one of the mechanisms of the therapeutic effect of As2O3. Moreover, this apoptosis induction occurs independently of the retinoid pathway and may be mediated, at least partly, through the modulation of bcl-2, as well as PML-RAR alpha and/ or PML proteins.