Stress In Human Cancer Cells Research Articles

Total Flavonoids Isolated from Diospyros kaki L. f. Leaves Induced Apoptosis and Oxidative Stress in Human Cancer Cells.

Persimmon (Diospyros kaki L.) leaves are popular as a tea infusion in Asia and their main active ingredients are flavonoids. The present study aimed to explore the anticancer properties of flavonoids isolated from persimmon leaves (PLF). We investigated the in vitro anti-proliferative activity of PLF against several human cancer cell lines. Apoptosis and intracellular reactive oxygen species (ROS) induced by PLF were accessed using high-content analysis with florescent staining. The ability of PLF to scavenge free radicals was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. PLF demonstrated significant inhibition of proliferation of liver, breast, and colorectal cancer cells in vitro. PLF induced apoptosis and increased intracellular ROS levels in HCT116 (colorectal cancer) and HepG2 (liver cancer) cells. In addition, PLF showed strong free radical scavenging ability. The anti-proliferation activity of PLF against cancer cells was related to the induction of apoptosis and oxidative stress.

Acrolein induces ribotoxic stress in human cancer cells regardless of p53 status

Acrolein (Acr) cytotoxicity contributes to chemotherapeutic activity of cyclophosphamide via metabolism of the anticancer drug. Our previous studies have shown that Acr causes ribosomal DNA (rDNA) damages, thus shuts down ribosomal RNA (rRNA) synthesis and leads to ribosomal stress in human cancer cells. Ribosome senses stress in 28S rRNA and induces subsequent activation of mitogen-activated protein kinase (MAPK) pathway which triggers ribotoxic stress response (RSR). Here, we report that cells harboring p53 or not responds differently to Acr-induced RSR. Our results show that Acr induced rRNA cleavage via the activated caspases in cancer cells with wild type p53, but not in cells with deficient p53. Furthermore, MAPK pathways were activated by Acr in cancer cells regardless of p53 status. Acr induced apoptosis in cells with wild type p53, while it induced G2/M cell cycle arrest in cancer cells with deficient p53. In conclusion, the presence of functional p53 plays a significant role in the mechanisms of Acr-induced rRNA cleavage and cell fates. Our results enhance our understanding of the molecular mechanisms of Acr-mediated antitumor activity which helps develop better therapeutic strategies for killing cancer cells with different p53 status.

Ag-doping regulates the cytotoxicity of TiO2 nanoparticles via oxidative stress in human cancer cells

We investigated the anticancer potential of Ag-doped (0.5–5%) anatase TiO2 NPs. Characterization study showed that dopant Ag was well-distributed on the surface of host TiO2 NPs. Size (15 nm to 9 nm) and band gap energy (3.32 eV to 3.15 eV) of TiO2 NPs were decreases with increasing the concentration of Ag dopant. Biological studies demonstrated that Ag-doped TiO2 NP-induced cytotoxicity and apoptosis in human liver cancer (HepG2) cells. The toxic intensity of TiO2 NPs was increases with increasing the amount of Ag-doping. The Ag-doped TiO2 NPs further found to provoke reactive oxygen species (ROS) generation and antioxidants depletion. Toxicity induced by Ag-doped TiO2 NPs in HepG2 cells was efficiently abrogated by antioxidant N-acetyl-cysteine (ROS scavenger). We also found that Ag-doped TiO2 NPs induced cytotoxicity and oxidative stress in human lung (A549) and breast (MCF-7) cancer cells. Interestingly, Ag-doped TiO2 NPs did not cause much toxicity to normal cells such as primary rat hepatocytes and human lung fibroblasts. Overall, we found that Ag-doped TiO2 NPs have potential to selectively kill cancer cells while sparing normal cells. This study warranted further research on anticancer potential of Ag-doped TiO2 NPs in various types of cancer cells and in vivo models.

Salinomycin induces cell death with autophagy through activation of endoplasmic reticulum stress in human cancer cells

Salinomycin is perhaps the first promising compound that was discovered through high throughput screening in cancer stem cells. This novel agent can selectively eliminate breast and other cancer stem cells, though the mechanism of action remains unclear. In this study, we found that salinomycin induced autophagy in human non-small cell lung cancer (NSCLC) cells. Furthermore, we demonstrated that salinomycin stimulated endoplasmic reticulum stress and mediated autophagy via the ATF4-DDIT3/CHOP-TRIB3-AKT1-MTOR axis. Moreover, we found that the autophagy induced by salinomycin played a prosurvival role in human NSCLC cells and attenuated the apoptotic cascade. We also showed that salinomycin triggered more apoptosis and less autophagy in A549 cells in which CDH1 expression was inhibited, suggesting that the inhibition of autophagy might represent a promising strategy to target cancer stem cells. In conclusion, these findings provide evidence that combination treatment with salinomycin and pharmacological autophagy inhibitors will be an effective therapeutic strategy for eliminating cancer cells as well as cancer stem cells.

Ras inhibits endoplasmic reticulum stress in human cancer cells with amplified Myc

In neuroblastoma LAN-1 cells harboring an amplified MycN gene, disruption of cooperation between Ras and MycN proteins by the Ras inhibitor farnesylthiosalicylic acid (FTS, Salirasib) reportedly arrests cell growth. Our aim was to establish whether this is a general phenomenon. We examined the effects of FTS on gene-expression profiles, growth and death of NCIH929 myeloma cells and K562 leukemia cells, which-like LAN-1 cells-exhibit Myc gene amplification and harbor active Ras. Under specified conditions, FTS reduced Ras and Myc and induced cell growth arrest and death in all Myc-amplified cell lines but not in SHEP, a neuroblastoma cell line without Myc gene amplification. Gene-expression analysis revealed a common pattern of FTS-induced endoplasmic reticulum (ER) stress, known as the unfolded protein response (UPR), in Myc-amplified cells, but not in SHEP. Thus, Ras negatively regulates ER stress in cells with amplified Myc. ER stress was also inducible by dominant-negative (DN)-Ras or shRNA to Ras isoforms, all of which induced an increase in BIP (the master regulator of ER stress) and its downstream targets Nrf2 and eIF2alpha, both regulated by active p-PERK. FTS also induced an increase in p-PERK, while small interfering RNA to PERK reduced Nrf2 and ATF4 and rescued cells from FTS-induced death. BIP and its downstream targets were also increased by inhibitors of MAPK p38 and MEK. Ras, acting through MAPK p38 and MEK, negatively regulates the ER stress cascades BIP/PERK/Nrf2 and eIF2alpha/ATF4/ATF3. These findings can explain the Ras-dependent protection of Myc-amplified cells from ER stress-associated death.

Glucose deprivation increases nuclear DNA repair protein Ku and resistance to radiation induced oxidative stress in human cancer cells

Recent studies have indicated that nutrient deprivation particularly glucose may play a major role in tumor cell tolerance to a generally oxidative stress environment in solid tumors. Here, we studied the impact of glucose deprivation on the response of human colon (HT29) and prostate (DU145) cancer cells to gamma radiation. A significant decrease in intracellular glucose level was observed in glucose deprived cells as measured by bioreductive assay. The survival of HT29 and DU145 were increased by 30 and 100% respectively when these cells were exposed to gamma radiation in the absence of glucose compared to that in the presence of glucose. In glucose depleted medium, glutathione (GSH), a free radical scavenger, content remained the same, and showed no correlation with the radiation resistance induced by glucose deprivation. Glucose regulated protein78 (GRP78), a stress response survival protein, was not significantly increased in cells deprived of glucose for 4 h compared to those cells in glucose. DNA repair protein Ku, which is known to play a major role in cellular resistance to radiation, was significantly increased in glucose deprived cancer cells that showed enhanced radiation resistance. These results have demonstrated, for the first time, that glucose deprivation mediated stress increased the expression of nuclear Ku and resistance to radiation induced oxidative stress in human cancer cells. The additional resistance caused by glucose deprivation in cancer cells has clinical significance since solid tumors are known to have low level of glucose due to diffusion limited blood supply and higher metabolic activity.

Increased levels of superoxide and H2O2 mediate the differential susceptibility of cancer cells versus normal cells to glucose deprivation

Cancer cells, relative to normal cells, demonstrate increased sensitivity to glucose-deprivation-induced cytotoxicity. To determine whether oxidative stress mediated by O(2)(*-) and hydroperoxides contributed to the differential susceptibility of human epithelial cancer cells to glucose deprivation, the oxidation of DHE (dihydroethidine; for O(2)(*-)) and CDCFH(2) [5- (and 6-)carboxy-2',7'-dichlorodihydrofluorescein diacetate; for hydroperoxides] was measured in human colon and breast cancer cells (HT29, HCT116, SW480 and MB231) and compared with that in normal human cells [FHC cells, 33Co cells and HMECs (human mammary epithelial cells)]. Cancer cells showed significant increases in DHE (2-20-fold) and CDCFH(2) (1.8-10-fold) oxidation, relative to normal cells, that were more pronounced in the presence of the mitochondrial electron-transport-chain blocker, antimycin A. Furthermore, HCT116 and MB231 cells were more susceptible to glucose-deprivation-induced cytotoxicity and oxidative stress, relative to 33Co cells and HMECs. HT29 cells were also more susceptible to 2DG (2-deoxyglucose)-induced cytotoxicity, relative to FHC cells. Overexpression of manganese SOD (superoxide dismutase) and mitochondrially targeted catalase significantly protected HCT116 and MB231 cells from glucose-deprivation-induced cytotoxicity and oxidative stress and also protected HT29 cells from 2DG-induced cytotoxicity. These results show that cancer cells (relative to normal cells) demonstrate increased steady-state levels of ROS (reactive oxygen species; i.e. O(2)(*-) and H(2)O(2)) that contribute to differential susceptibility to glucose-deprivation-induced cytotoxicity and oxidative stress. These studies support the hypotheses that cancer cells increase glucose metabolism to compensate for excess metabolic production of ROS and that inhibition of glucose and hydroperoxide metabolism may provide a biochemical target for selectively enhancing cytotoxicity and oxidative stress in human cancer cells.

2-Deoxy-d-Glucose Combined with Cisplatin Enhances Cytotoxicity via Metabolic Oxidative Stress in Human Head and Neck Cancer Cells

Glucose deprivation has been hypothesized to cause cytotoxicity by inducing metabolic oxidative stress in human cancer cells. The current work tests the hypothesis that 2-deoxy-d-glucose (2DG) combined with cisplatin [cis-diamminedichloroplatinum(II)] can enhance cytotoxicity in human head and neck cancer cells (FaDu) by mechanisms involving oxidative stress. Exposure of FaDu cells to the combination of 2DG and cisplatin resulted in a significant decrease in cell survival when compared with 2DG or cisplatin alone. Treatment with 2DG and cisplatin also caused perturbations in parameters indicative of oxidative stress, including decreased intracellular total glutathione and increased percentage of glutathione disulfide. Simultaneous treatment with the thiol antioxidant N-acetylcysteine (NAC) inhibited parameters indicative of oxidative stress, as well as protected FaDu cells from the cytotoxic effects of cisplatin alone and the combination of 2DG and cisplatin. In addition, polyethylene glycol-conjugated antioxidant enzymes (PEG-superoxide dismutase and PEG-catalase) also protected FaDu cells from 2DG toxicity. An inhibitor of glutathione synthesis, l-buthionine-[S,R]-sulfoximine (BSO), sensitized FaDu cells to the cytotoxic effects of 2DG and cisplatin, and these effects were inhibited by NAC. Furthermore, the combination of 2DG, cisplatin, and BSO significantly increased the percentage of glutathione disulfide, which was also inhibited by NAC. These results support the hypothesis that exposure of human head and neck cancer cells to 2DG combined with cisplatin enhances cytotoxicity via metabolic oxidative stress. These findings provide a strong biochemical rationale for evaluating inhibitors of glucose and hydroperoxide metabolism in combination with cisplatin for the treatment of head and neck cancer.

Thioamido Coordination in a Thioxo-1,2,4-triazole Copper(II) Complex Enhances Nonapoptotic Programmed Cell Death Associated with Copper Accumulation and Oxidative Stress in Human Cancer Cells

The thioamido function of [CuCl2(1H)]Cl (2) (1=4-amino-1,4-dihydro-3-(2-pyridyl)-5-thioxo-1,2,4-triazole), a cytotoxic copper complex, was converted into thioether moieties, leading to the synthesis of [CuCl2(3)]2 (4) and [CuCl2(5)] (6) (3=6-methyl-3-pyridin-2-yl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine; 5=4-amino-5-ethylthio-3-(2-pyridyl)-1,2,4-triazole). These complexes were structurally characterized, and their stability constants, along with their biological activity, were determined. 4 and 6 were slightly less stable and significantly less active than 2. However, as 2, both complexes induced nonapoptotic vacuolar cell death. Copper uptake, investigated in both 2-sensitive and -insensitive cell types, was markedly higher in sensitive cells where it was associated with an increase in oxidized glutathione. These data suggest that the thioamido function enhances the cytotoxicity of copper complexes in cancer cells promoting the accumulation of the metal and its interaction with cell thiols.

Mitochondrial [formula omitted] and H2O2 Mediate Glucose Deprivation-induced Stress in Human Cancer Cells

The hypothesis that glucose deprivation-induced cytotoxicity in transformed human cells is mediated by mitochondrial O2*- and H2O2 was first tested by exposing glucose-deprived SV40-transformed human fibroblasts (GM00637G) to electron transport chain blockers (ETCBs) known to increase mitochondrial O2*- and H2O2 production (antimycin A (AntA), myxothiazol (Myx), or rotenone (Rot)). Glucose deprivation (2-8 h) in the presence of ETCBs enhanced parameters indicative of oxidative stress (i.e. GSSG and steady-state levels of oxygen-centered radicals) as well as cytotoxicity. Glucose deprivation in the presence of AntA also significantly enhanced cytotoxicity and parameters indicative of oxidative stress in several different human cancer cell lines (PC-3, DU145, MDA-MB231, and HT-29). In addition, human osteosarcoma cells lacking functional mitochondrial electron transport chains (rho0) were resistant to glucose deprivation-induced cytotoxicity and oxidative stress in the presence of AntA. In the absence of ETCBs, aminotriazole-mediated inactivation of catalase in PC-3 cells demonstrated increases in intracellular steady-state levels of H2O2 during glucose deprivation. Finally, in the absence of ETCBs, overexpression of manganese containing superoxide dismutase and/or mitochondrial targeted catalase using adenoviral vectors significantly protected PC-3 cells from toxicity and oxidative stress induced by glucose deprivation with expression of both enzymes providing greater protection than was seen with either alone. Overall, these findings strongly support the hypothesis that mitochondrial O2*- and H2O2 significantly contribute to glucose deprivation-induced cytotoxicity and metabolic oxidative stress in human cancer cells.

MTOR as a positive regulator of tumor cell responses to hypoxia.

Rapamycin is a clinically approved immunosuppressive agent that has recently shown promising antitumor activities in human patients. In contrast to many conventional chemotherapeutic agents, rapamycin displays a remarkably high level of selectivity for certain types of tumors. The pharmacological activities of rapamycin are attributable to the functional inhibition of a single target protein, termed the mammalian target of rapamycin (mTOR). Because mTOR is widely expressed in both normal and transformed cells, variations in mTOR expression levels are likely not a primary determinant of tumor sensitivity to rapamycin. However, recent studies highlighted an intriguing link between cancer cell sensitivity to rapamycin and deregulated signaling through the phosphoinositide (PI) 3-kinase pathway. These findings have prompted a search for cancer-related responses that are jointly regulated by the PI 3-kinase signaling cascade and mTOR. The oxygen-regulated transcription factor, hypoxia-induced factor (HIF)-1, has emerged as a candidate target for both of these two highly interactive signaling proteins. Here we review evidence that mTOR functions as a positive regulator of HIF-1-dependent responses to hypoxic stress in human cancer cells.