The combination of silencing BAG3 and inhibition of the JNK pathway enhances hyperthermia sensitivity in human oral squamous cell carcinoma cells

Hyperthermia (HT) is a widely used physical treatment for various cancers, but its effect is often insufficient because of cytoprotective effects of heat shock proteins. BAG3, a co-chaperone of the heat shock protein 70, is a stress-inducible protein and demonstrates a cytoprotective property against various stresses, including heat stress. Here, we examined the effects of silencing the BAG3 on the sensitivity to HT in human oral squamous cell carcinoma (OSCC) HSC-3 cells. HT (44 °C, 90 min) was significantly increased in apoptotic cells concomitant with the activations of caspase-3 and c-Jun N-terminal kinase (JNK) pathway. Furthermore, the sensitivity to HT was remarkably enhanced in BAG3-downregulated HSC-3 cells. Interestingly, the effects of this combination treatment were significantly enhanced in the cells pretreated with a JNK inhibitor, SP600125. These findings indicated that the disruption of functions of both BAG3 and the JNK pathway may become an option in HT therapy in OSCC cells.     

Aloe-emodin induces apoptosis of human nasopharyngeal carcinoma cells via caspase-8-mediated activation of the mitochondrial death pathway

Aloe-emodin (AE), a natural, biologically active compound from the rhizome of Rheum palmatum, has been shown to induce apoptosis in several cancer cell lines in vitro. However, its molecular mechanism of action in the apoptosis induction of human nasopharyngeal carcinoma (NPC) cells has not been explored. This study shows that AE induced G₂/M phase arrest by increasing levels of cyclin B1 bound to Cdc2, and also caused an increase in apoptosis of NPC cells, which was characterized by morphological changes, nuclear condensation, DNA fragmentation, caspase-3 activation, cleavage of poly (ADP-ribose) polymerase (PARP) and increased sub-G₁ population. Treatment of NPC cells with AE also resulted in a decrease in Bcl-X_L and an increase in Bax expression. Ectopic expression of Bcl-X_L but not Bcl-2 or small interfering RNA (siRNA)-mediated attenuation of Bax suppressed AE-induced apoptotic cell death. AE-induced loss of mitochondrial membrane potential (MMP) and increase in cellular Ca⁺⁺ content, reactive oxygen species (ROS) and apoptotic cell death were suppressed by the treatment of cyclosporin A (CsA) or caspase-8 inhibitor Z-IETD-FMK. Co-treatment with caspase-9 inhibitor Z-LEHD-FMK could inhibit AE-induced cell death and the activation of caspase-3 and -9. In addition, suppression of caspase-8 with the specific inhibitor Z-IETD-FMK inhibited AE-induced the activation of Bax, the cleavage of Bid, the translocation of tBid to the mitochondria and the release of cytochrome c, apoptosis-inducing factor (AIF) and Endo G from the mitochondria and subsequent apoptosis. Taken together, these results indicate that the caspase-8-mediated activation of the mitochondrial death pathway plays a critical role in AE-induced apoptosis of NPC cells.     

Combined arsenic trioxide-cisplatin treatment enhances apoptosis in oral squamous cell carcinoma cells

Background

Oral squamous cell carcinoma (OSCC) accounts for the majority of oral cancers. Despite recent advances in OSCC diagnostics and therapeutics, the overall survival rate still remains low. Here, we assessed the efficacy of a combinatorial arsenic trioxide (ATO) and cisplatin (CDDP) treatment in human OSCC cells.

Methods

The combinatorial effect of ATO/CDDP on the growth and apoptosis of OSCC cell lines HSC-2, HSC-3, and HSC-4 was evaluated using MTT and annexin V assays, respectively. Chou–Talalay analyses were preformed to evaluate the combinatorial effects of ATO/CDDP on the dose-reduction index (DRI). To clarify the mechanism underlying the ATO/CDDP anticancer effect, we also examined the involvement of reactive oxygen species (ROS) in ATO/CDDP-induced apoptosis.

Results

Combination index (CI) analyses revealed that a synergistic interaction of ATO and CDDP elicits a wide range of effects in HSC-2 cells, with CI values ranging from 0.78 to 0.90, where CI?<?1 defines synergism. The CI values in HSC-3 and HSC-4 cells ranged from 0.34 to 0.45 and from 0.60 to 0.92, respectively. In addition, ATO/CDDP yielded favorable DRI values ranging from 1.6-fold to 7.71-fold dose reduction. Compared to mono-therapy, ATO/CDDP combinatorial therapy significantly augmented the loss of mitochondrial potential, caspase-3/7 activity and subsequent apoptosis. These changes were all abrogated by the antioxidant N-acetylcysteine.

Conclusions

This study provides the first evidence for a synergistic ATO/CDDP anticancer (apoptotic) activity in OSCC cells with a favorable DRI, thereby highlighting its potential as a combinational therapeutic regime in OSCC.     

Enhanced susceptibility to apoptosis of oral squamous cell carcinoma cells subjected to combined treatment with anticancer drugs and phosphatidylinositol 3-kinase inhibitors

The purpose of this study was to determine whether phosphatidylinositol 3-kinase (PI 3-K) inhibitors could modulate the apoptotic activity of the anticancer drugs cisplatin, 5-fluorouracil or docetaxel in an oral squamous cell carcinoma (OSCC) cell line, HSC-2. In preliminary experiments, cisplatin, 5-fluorouracil and docetaxel inhibited the proliferation of OSCC cells in a dose-dependent manner. We found that two PI 3-K inhibitors, wortmannin and LY294002, markedly suppressed the phosphorylation of Akt in OSCC cells. Treatment of OSCC cells with PI 3-K inhibitors significantly enhanced cisplatin-, 5-fluorouracil- or docetaxel-induced apoptosis. Caspase-3 and -9 inhibitors, but not a caspase-8 inhibitor, reduced anticancer drug-mediated apoptosis in PI 3-K inhibitor-treated OSCC cells, suggesting that the apoptotic pathway induced by the combination of anticancer drug therapy and PI 3-K inhibition may be functionally related to the intrinsic apoptotic pathway in OSCC cells. Expression of Bcl-2, cellular inhibitor of apoptosis protein-1 (cIAP-1), and X-linked IAP was down-regulated, and expression of Bax was up-regulated by PI 3-K inhibitors, while that of Bcl-xL, Bak and cIAP-2 was not attenuated. We also found that Bad phosphorylation was down-regulated by PI 3-K inhibitors. These results suggested that inhibition of PI 3-K enhances the susceptibility of OSCC cells to anticancer drug-mediated apoptosis through regulation of expression and post-translational modification of both pro- and anti-apoptotic proteins. These findings could potentially lead to new strategies for improving the efficacy of anticancer drugs in OSCC cells.     

Epidermal growth factor receptor inhibitors enhance susceptibility to Fas-mediated apoptosis in oral squamous cell carcinoma cells

Molecular inhibition of epidermal growth factor receptor (EGFR) signaling is a promising cancer treatment strategy. We examined whether inhibition of EGFR signaling would affect the susceptibility of oral squamous cell carcinoma (OSCC) cells to Fas-mediated apoptosis. Treatment of OSCC cells with an anti-EGFR monoclonal antibody, C225, and an EGFR tyrosine kinase inhibitor, AG1478, which target the extracellular and intracellular domains of the receptor, respectively, inhibited phosphorylation of EGFR and its downstream effector molecule Akt and amplified the induction of Fas-mediated apoptosis. In OSCC cells treated with EGFR inhibitors, Fas-mediated apoptosis was accompanied by caspase-8 activation but not Bid cleavage. Caspase-3 and -8 inhibitors reduced the effect of EGFR inhibitors on Fas-mediated apoptosis in OSCC cells, but a caspase-9 inhibitor did not. These results indicate that the pro-apoptotic activity of EGFR inhibitors in OSCC cells depends on the extrinsic pathway of the caspase cascade. Although EGFR inhibitors did not affect the expression of Fas, the Fas-associated death domain protein, or procaspase-8 in OSCC cells, the inhibition downregulated cellular FLICE-inhibitory protein (c-FLIP). Moreover, knockdown of c-FLIP in HSC-2 cells with a small interfering RNA strongly enhanced Fas-mediated apoptosis. These results suggest that the EGFR signaling pathway may, in part, regulate Fas-mediated apoptosis in OSCC cells through c-FLIP expression.     

Proteasome inhibitor sensitizes oral squamous cell carcinoma cells to TRAIL-mediated apoptosis

Oral squamous cell carcinoma (OSCC) cells are relatively resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis during culture. We investigated the role of a proteaosome inhibitor in the survival and apoptosis of these cells. We found that the proteasome inhibitor MG132 markedly accelerated TRAIL-mediated apoptosis in OSCC cell lines HSC-2 and HSC-3. Addition of TRAIL to MG132-treated cells resulted in Bid cleavage. Furthermore, the inhibitors of caspase-3, caspase-8 and caspase-9 reduced the accelerative effect of MG132 on TRAIL-mediated apoptosis. These results suggest that the pro-apoptotic effect of a proteasome inhibitor on TRAIL-mediated apoptosis may contribute to both extrinsic and intrinsic pathways. MG132 enhanced the expression of the TRAIL receptors DR4 and DR5, and neutralization of DR5 receptors showed a marked reduction of TRAIL-mediated apoptosis, whereas that of DR4 was a partial reduction. MG132 also markedly reduced cellular FLICE-inhibitory protein (c-FLIP), cellular inhibitor of apoptosis protein-1 (cIAP-1), X-linked IAP (XIAP) and survivin. Therefore, MG132 provides partial regulation of TRAIL-mediated apoptosis in OSCC cells via modulation of DR5, c-FLIP, cIAP-1, XIAP and survivin. The proteasome inhibitor MG132 may therefore represent a novel strategy for overcoming resistance to TRAIL-mediated apoptosis in OSCC cells.     

Quercetin induces tongue squamous cell carcinoma cell apoptosis via the JNK activation-regulated ERK/GSK-3α/β-mediated mitochondria-dependent apoptotic signaling pathway

Tongue squamous cell carcinoma (SCC) is a most common type of oral cancer. Due to its highly invasive nature and poor survival rate, the development of effective pharmacological therapeutic agents is urgently required. Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is a polyphenolic flavonoid found in plants and is an active component of Chinese herbal medicine. The present study investigated the pharmacological effects and possible mechanisms of quercetin on apoptosis of the tongue SCC-derived SAS cell line. Following treatment with quercetin, cell viability was assessed via the MTT assay. Apoptotic and necrotic cells, mitochondrial transmembrane potential and caspase-3/7 activity were analyzed via flow cytometric analyses. A caspase-3 activity assay kit was used to detect the expression of caspase-3 activity. Western blot analysis was performed to examine the expression levels of proteins associated with the MAPKs, AMPKα, GSK3-α/β and caspase-related signaling pathways. The results revealed that quercetin induced morphological alterations and decreased the viability of SAS cells. Quercetin also increased apoptosis-related Annexin V-FITC fluorescence and caspase-3 activity, and induced mitochondria-dependent apoptotic signals, including a decrease in mitochondrial transmembrane potential and Bcl-2 protein expression, and an increase in cytosolic cytochrome c, Bax, Bak, cleaved caspase-3, cleaved caspase-7 and cleaved poly (ADP-ribose) polymerase protein expression. Furthermore, quercetin significantly increased the protein expression levels of phosphorylated (p)-ERK, p-JNK1/2 and p-GSK3-α/β, but not p-p38 or p-AMPKα in SAS cells. Pretreatment with the pharmacological JNK inhibitor SP600125 effectively reduced the quercetin-induced apoptosis-related signals, as well as p-ERK1/2 and p-GSK3-α/β protein expression. Both ERK1/2 and GSK3-α/β inhibitors, PD98059 and LiCl, respectively, could significantly prevent the quercetin-induced phosphorylation of ERK1/2 and GSK3-α/β, but not JNK activation. Taken together, these results suggested that quercetin may induce tongue SCC cell apoptosis via the JNK-activation-regulated ERK1/2 and GSK3-α/β-mediated mitochondria-dependent apoptotic signaling pathway.     

Role of JNK signaling pathway in sensitivity to radiotherapy of nasopharyngeal carcinoma

Objective

The aim of the study was to investigate the effect of c-Jun N-terminal protein kinase (JNK) signaling pathway on influencing the sensitivity to radiotherapy of human nasopharyngeal carcinoma CNE cells.

Methods

Human nasopharyngeal carcinoma CNE multicellular spheroids (MCS) were constructed with three dimensional cell culture methods. Western blot was employed to analyze the activity of JNK signaling pathway in MCS after X-ray irradiation, and the expression of caspase-3 protein before and after using SP600125 (a special inhibitor of JNK). X-ray induced cell apoptosis in MCS before and after treated with SP600125 were detected by TUNEL.

Results

The level of JNK phosphorylation in MCS was a dynamic course after radiation, and there was a phosphorylation peaks at 2 h later, the apoptotic rate of MCS (P < 0.05) and the expression of caspase-3 protein (P < 0.05) were significantly increased after treated with SP600125.

Conclusion

The transient activation of JNK played a important role in sensitivity to radiotherapy of CNE MCS via mediating survival signals, blocking this pathway accelerate cell apoptosis, which may be related to the increased expression of caspase-3.     

Delphinidin induces cell cycle arrest and apoptosis in HER-2 positive breast cancer cell lines by regulating the NF-κB and MAPK signaling pathways

Delphinidin is an anthocyanidin monomer, commonly found in vegetables and fruits, and has demonstrated antitumor effects in the HER-2-positive MDA-MB-453 breast cancer cell line, with low cytotoxicity on normal breast cells. However, the direct functional mechanisms underlying the effect of delphinidin on HER-2-positive breast cancer cells has not been fully characterized. In the present study, it was found that delphinidin could induce G₂/M phase cell cycle arrest by inhibiting the protein expression level of cyclin B1 and Cdk1 in HER-2-positive breast cancer cell lines. In addition, delphinidin promoted the mitochondrial apoptosis pathway by inhibiting the ERK and NF-κB signaling pathway and activating the JNK signaling pathway. Therefore, delphinidin markedly suppressed the viability of the HER-2-positive breast cancer cell lines by modulating the cell cycle and inducing apoptosis. Overall, the findings from the present study demonstrated that delphinidin treatment could induce the mitochondrial apoptosis pathway in human HER-2-positive breast cancer cell lines, providing an experimental basis for the prevention and treatment of HER-2-positive breast cancer by flavonoids.     

Inhibition of EGFR signaling augments oridonin-induced apoptosis in human laryngeal cancer cells via enhancing oxidative stress coincident with activation of both the intrinsic and extrinsic apoptotic pathways

Oridonin, a bioactive diterpenoid isolated from Rabdosia rubescens, has been reported to have anti-tumor effects, while the epidermal growth factor receptor (EGFR) signal pathway has been reported to play a vital role in the biological progression of several tumors and to be a target for therapeutic intervention. In this work, we show that inhibition of EGFR with tyrphostin AG1478 enhances oridonin-induced cell death in human laryngeal cancer cells HEp-2, a cell line characterized by EGFR gene amplification. The enhanced apoptotic effect correlates with high expression and activation of Bax, FADD, caspase-8 as well as caspase-3 and decreased protein levels of Bcl₂ and SIRT1, suggesting that both the extrinsic and intrinsic apoptosis pathways are involved in the apoptotic processes. However, treatment with oridonin and AG1478 greatly enhances nuclear translocation of apoptosis inducing factor (AIF) without caspase-9 activation, indicating that the apoptosis occurs via a caspase-9-independent mitochondrial pathway. Here, it is the active form of caspase-8 but not caspase-9 that activates downstream effector caspase-3, resulting in the cleavage of critical cellular proteins and apoptosis. Furthermore, the combined use of AG1478 and oridonin augments the production of reactive oxygen species (ROS). Incubation of cells with N-Acetylcysteine (NAC) attenuates the apoptosis and the mitochondrial membrane potential (Δψm) disruption induced by the combination of oridonin and AG1478, which indicates that ROS plays a pivotal role in cell death. In conclusion, targeting EGFR combined with other conventional pro-apoptotic drugs should be a potentially very effective anti-neoplastic therapy for laryngeal cancer.     

Apoptotic effect of CKD-602 (Camtobell) on oral squamous cell carcinoma cell lines

The purposes of this study were to measure the cytotoxic effect of CKD-602 on oral squamous cell carcinoma (OSCC) cell lines, to evaluate the apoptotic aspect of dead cells, and to identify the signaling molecules involved in apoptosis. The human OSCC cell lines A253, HSC-3 and KB were treated with CKD-602. The apoptotic proportion of the cells was analyzed using flow cytometry. The expression of Bax, Bcl-2, and p53 were detected by western blotting analysis. CKD-602 showed excellent cytotoxicity to the OSCC cell lines. Most cell death was attributed to apoptosis rather than necrosis. CKD-602 induced the down-regulation of Bcl-2 in A253 and HSC-3 cells, and p53 was expressed in the KB cell line after treatment with CKD-602.     

Plumbagin induces cell cycle arrest and apoptosis through reactive oxygen species/c-Jun N-terminal kinase pathways in human melanoma A375.S2 cells

This study is the first to investigate the anticancer effect of plumbagin in human melanoma A375.S2 cells. Plumbagin exhibited effective cell growth inhibition by inducing cancer cells to undergo S-G2/M phase arrest and apoptosis. Further investigation revealed that plumbagin's inhibition of cell growth was also evident in a nude mice model. Blockade of cell cycle was associated with increased levels of p21, and reduced amounts of cyclin B1, cyclin A, Cdc2, and Cdc25C. Plumbagin also enhanced the levels of inactivated phosphorylated Cdc2 and Cdc25C. Plumbagin triggered the mitochondrial apoptotic pathway indicated by a change in Bax/Bcl-2 ratios, resulting in caspase-9 activation. We also found the generation of ROS is a critical mediator in plumbagin-induced cell growth inhibition. Plumbagin increased the activation of apoptosis signal-regulating kinase 1, JNK and extracellular signal-regulated kinase 1/2 (ERK1/2), but not p38. In addition, antioxidants vitamin C and catalase significantly decreased plumbagin-mediated c-Jun N-terminal kinase (JNK) activation and apoptosis. Moreover, blocking ERK and JNK by specific inhibitors suppressed plumbagin-triggered mitochondrial apoptotic pathway. Taken together, these results imply a critical role for ROS and JNK in the plumbagin's anticancer activity.     

Hexane extracts of garlic cloves induce apoptosis through the generation of reactive oxygen species in Hep3B human hepatocarcinoma cells

Garlic (Allium sativum) compounds have recently received increasing attention due to their cancer chemopreventive properties, and their anticancer activities are extensively reported in many cancer cell lines. However, the anticancer activity and the signaling pathway associated with the induction of apoptosis by extracts of garlic cloves have not been elucidated. In this study, we examined the effects of hexane extracts of garlic cloves (HEGCs) on reactive oxygen species (ROS) production and the association of these effects with apoptotic cell death, using a Hep3B human hepatocarcinoma cell line in?vitro. The results demonstrated that HEGCs mediate ROS production, and that this mediation is followed by a collapse of mitochondrial membrane potential (MMP, ΔΨm), the downregulation of anti-apoptotic Bcl-2 and Bcl-xL and the activation of caspase-9 and -3. HEGCs also promoted the activation of caspase-8 and the downregulation of Bid, a BH3-only pro-apoptotic member of the Bcl-2. However, the apoptotic phenomena displayed by HEGCs were significantly diminished by the presence of z-VAD-fmk (non-selective caspase inhibitor). Moreover, N-acetyl-L-cysteine (NAC), a widely used ROS scavenger, effectively blocked the HEGC-induced apoptotic effects via the inhibition of ROS production and MMP collapse. These observations clearly indicate that HEGC-induced ROS are key mediators of MMP collapse, which leads to the induction of apoptosis, followed by caspase activation.     

Enhanced susceptibility of oral squamous cell carcinoma cell lines to FAS-mediated apoptosis by cisplatin and 5-fluorouracil

Our study was conducted to investigate whether anticancer drugs, cisplatin (CDDP) and/or 5-fluorouracil (5-FU), can modulate Fas-mediated apoptosis in oral squamous cell carcinoma (OSCC) cell lines. When OSCC cell lines, NA and HSC-4, were treated with CDDP and/or 5-FU, Fas and its mRNA expression on the plasma membrane were enhanced. An increase in caspase-3 and -8 activities was then observed by the addition of agonistic anti-Fas antibody, CH-11. Apoptosis of OSCC cells treated with anticancer drugs were significantly enhanced by CH-11, whereas untreated cells were nearly resistant to apoptosis. Moreover, the combination of CDDP and 5-FU resulted in an increasing susceptibility to apoptosis. Caspase-3 and -8 inhibitors, but not caspase-9 inhibitor, reduced Fas-mediated apoptosis enhanced by the anticancer drugs. Furthermore, OSCC cells treated with anticancer drugs exhibited decreased cellular FADD-like interleukin 1-converting enzyme-inhibitory protein (c-FLIP) levels, whereas neither the Fas-associated death domain-containing protein (FADD) nor procaspase-8 changed the expression. Moreover, antisense oligonucleotide to c-FLIP confirmed that down-regulation of c-FLIP induced sensitization to Fas-mediated apoptosis. These results suggest that CDDP and 5-FU may enhance the susceptibility to Fas-mediated apoptosis through down-regulation of c-FLIP. From these findings, a new potential strategy may be developed to improve the efficacy of anticancer drugs.     

Diosgenin induces cell cycle arrest and apoptosis in human leukemia K562 cells with the disruption of Ca2+ homeostasis

Purpose Diosgenin is a steroidal sapogenin with estrogenic and antitumor properties. In order to elucidate the mechanism of its antiproliferative activity, we investigated its effects on the cell cycle and apoptosis in human chronic myelogenous leukemia K562 cells.Methods Cell viability was assessed via an MTT assay. Apoptosis was investigated in terms of nuclear morphology, DNA fragmentation, and phosphatidylserine externalization. Cell cycle analysis was performed via PI staining and flow cytometry (FCM). Western blotting and immunofluorescence methods were used to determine the levels of p53, cell cycle-related proteins and Bcl-2 family members. FCM was also used to estimate the changes in mitochondrial membrane potential (MMP), intracellular Ca²⁺ concentration and reactive oxygen species (ROS) generation.Results Cell cycle analysis showed that diosgenin caused G₂/M arrest independently of p53. The levels of cyclin B1 and p21^Cip1/Waf1 were decreased, whereas cdc2 levels were increased. Subsequent apoptosis was demonstrated with the dramatic activation of caspase-3. A dramatic decline in intracellular Ca²⁺ concentration was observed as an initiating event in the process of cell cycle arrest and apoptosis, which was followed by the hyperpolarization and depolarization of MMP. Generation of ROS was observed in the progression of apoptosis. The antiapoptotic Bcl-2 and Bcl-x_L proteins were downregulated, whereas the proapoptotic Bax was upregulated.Conclusions Diosgenin inhibits K562 cell proliferation via cell cycle G₂/M arrest and apoptosis, with disruption of Ca²⁺ homeostasis and mitochondrial dysfunction playing vital roles.     

Reactive oxygen species-mitochondria pathway involved in LYG-202-induced apoptosis in human hepatocellular carcinoma HepG2 cells

Previously, we demonstrated that LYG-202, a newly synthesized flavonoid with a piperazine substitution, exhibited obvious antitumor activity in vivo and in vitro. The exact mechanism of this new compound remains unclear. In the present study, we examined the effects of LYG-202 on reactive oxygen species (ROS) production and the downstream signaling pathway in the apoptosis of human hepatocellular carcinoma HepG₂ cells. Pretreatment with NAC (N-acetylcysteine), a ROS production inhibitor, partly inhibited the apoptosis induced by LYG-202 via blocking the ROS generation. Further data revealed that LYG-202 induced ROS accumulation followed by a decrease in mitochondrial membrane potential (MMP), release of cytochrome c (Cyt c) and apoptosis-inducing factor (AIF) to cytosol, which induced apoptosis of the cells. Moreover, the mitogen-activated protein kinases (MAPK), the downstream effect of ROS accumulation including c-Jun N-terminal kinase (JNK) and p38 MAPK, could be activated by LYG-202. Taken together, the generation of ROS might play an important role in LYG-202-induced mitochondrial apoptosis pathway, which provided further support for LYG-202 as a novel anticancer therapeutic candidate.     

Naturally occurring asteriscunolide A induces apoptosis and activation of mitogen‐activated protein kinase pathway in human tumor cell lines

Sesquiterpene lactones have attracted much attention because they display a wide range of biological activities, including antitumor properties. Here, we show the effects of the naturally occurring sesquiterpene lactone asteriscunolide A (AS) on viability of human melanoma, leukemia and cells that overexpress antiapoptotic proteins, namely Bcl‐2 and Bcl‐x_L. All cell lines were sensitive to this compound, with IC₅₀ values of ～5 µM. The cytotoxic effects of AS were accompanied by a G₂‐M phase arrest of the cell cycle and a concentration‐ and time‐dependent appearance of apoptosis as determined by DNA fragmentation, translocation of phosphatidylserine to the cell surface and sub‐G₁ ratio. Apoptosis was associated with caspase‐3 activity and poly(ADP‐ribose) polymerase cleavage and was prevented by the nonspecific caspase inhibitor z‐VAD‐fmk, indicating that caspases are essential components in this pathway. The apoptotic effect of AS was also associated with (i) the release of cytochrome c from mitochondria which was accompanied by dissipation of the mitochondrial membrane potential (ΔΨ_m) and (ii) the activation of the mitogen‐activated protein kinases (MAPKs) pathway. AS‐induced cell death was potentiated by inhibition of extracellular signal‐regulated kinases (ERK) 1/2 signaling with U0126 and PD98059. Intracellular reactive oxygen species (ROS) seem to play a pivotal role in this process since high levels of ROS were produced early (1 h) and apoptosis was completely blocked by the free radical scavenger N‐acetyl‐L ‐cysteine (NAC). The present study demonstrates that AS‐induced cell death is mediated by an intrinsic‐dependent apoptotic event involving mitochondria and MAPKs, and through a mechanism dependent on ROS generation. © 2010 Wiley‐Liss, Inc.     

Possible role of glutathione in mitochondrial apoptosis of human oral squamous cell carcinoma caused by inorganic selenium compounds

Selenium (Se) is a very effective anti-cancer agent. We studied the effects of inorganic Se compounds on induction of apoptosis by which Se compounds exert cancer chemopreventive activity. With the use of HSC-3 human oral squamous cell carcinoma cells, the present study showed that treatment with Se for 72 h, in the form of SeO2 and Na2SeO3, but not Na2SeO4, markedly induced apoptosis in a dose-dependent manner. Treatment of HSC-3 cells with 100 microM SeO2 resulted in the caspase-3-like and -9-like activation. Se compounds induced a loss of mitochondrial membrane potential (DeltaPsim), but did not induce the generation of reactive oxygen species. Treatment with SeO2 for 18 h resulted in 80% loss of reduced glutathione (GSH), which is known to be involved in the metabolism of Se. Treatment with N-acetyl-L-cysteine, or exogenous GSH, prevented the SeO2-induced apoptosis. Treatment with GSH led to the partial reverse in reduction of DeltaPsim caused by SeO2, while buthionine sulfoximine augmented the SeO2- or Na2SeO3-induced apoptosis.These results suggest that modulation of the mitochondrial redox equilibrium by Se contributes to the mitochondrial pathway, regulating caspase-9-mediated apoptosis without a concurrent increase in ROS.