Apoptosis and cancer risk assessment

The Identification of a Novel Unsymmetrical Azine as an Apoptosis Inducer in Colorectal Cancer

BACKGROUND

Defects in the physiological mechanisms of apoptosis are one of the pivotal factors implicated in carcinogenesis. Thus, the development of novel compounds that target various apoptotic pathways has provided promising anticancer therapeutic opportunities.

OBJECTIVE

This study explores the cytotoxic effects of a novel unsymmetrical azine against specific cancer cell lines and investigates the mechanism of cytotoxicity.

METHODS

Molecular modeling was used to test the binding affinity of four new unsymmetrical azines to a model of an apoptosis inhibitor protein (XIAP). The compound with the highest binding affinity, C4, was further tested on different cell lines. Real-time Polymerase Chain Reaction (PCR) and Transmission Electron Microscope (TEM) were used to study apoptosis induction biochemically and morphologically.

RESULTS

In comparison to cisplatin as a control, the compound C4 exhibited notable cytotoxicity against all tested cancer cell lines, especially the human colorectal carcinoma cell line (HCT-116). Furthermore, C4-treated cells demonstrated marked overexpression of the pro-apoptotic proteins Bax and caspase-3 as well as the tumor suppressor p53. On the other hand, the expression of the anti-apoptotic protein Bcl-2 was inhibited. On TEM examination, C4-treated HCT-116 cells showed classical structural signs of apoptosis.

CONCLUSION

This study identifies a novel azine (C4), which induces remarkable cytotoxicity against the colorectal carcinoma cell line, mediated through apoptosis induction. These novel insights suggest C4 as a promising therapeutic agent in colorectal cancer.

Redox imbalance induced by docetaxel in the neuroblastoma SH-SY5Y cells: a study of docetaxel-induced neuronal damage

Objectives

In cancer survivors, chemotherapy-associated adverse neurological effects are described as side effects in non-targeted tissue. We investigated the role of redox-imbalance in neuronal damage by a relative low dose of Docetaxel (DTX).

Methods

The neuroblastoma cells (SH-SY5Y cells) were exposed to DTX at a dose of 1.25 nM for 6 h. Antioxidant defenses (i.e. ascorbic acid, glutathione, and catalase) and lipid oxidation products (i.e. F₂-isoprostanes) were evaluated. To investigate cell ultrastructure and tubulin localisation, transmission electron microscopy (TEM) and immunofluorescence techniques were applied.

Results

In the SH-SY5Y cells, DTX induced a significant reduction of total glutathione (P < 0.001) and ascorbic acid (P < 0.05), and an increase in both total F₂-Isoprostanes (P < 0.05) and catalase activity (P < 0.05), as compared to untreated cells. Additionally, TEM showed a significant increase in cells with apoptotic characteristics. Immunolocalisation of tubulin showed a compromised cytoskeletal organisation.

Discussion

The investigated sublethal dose of DTX, to which non-targeted cells may be exposed throughout the duration of chemotherapy treatment, induces a redox imbalance resulting in a specific modulation of the antioxidant response. This study provides new insights into DTX-induced cellular mechanisms useful for evaluating whether the concomitant use of antioxidants associated with chemotherapy mitigates chemotherapy side effects in cancer survivors.

Golgi reassembly and stacking protein 65 downregulation is required for the anti-cancer effect of dihydromyricetin on human ovarian cancer cells

Golgi reassembly and stacking protein 65 (GRASP65), which has been involved in cancer progression, is associated with tumor growth and cell apoptosis. Dihydromyricetin (DHM) has demonstrated antitumor activity in different types of human cancers. However, the pharmacological effects of DHM on ovarian cancer (OC) and the molecular mechanisms that underlie these effects are largely unknown. The present study showed that DHM reduced cell migration and invasion in a concentration- and time-dependent manner and induced cell apoptosis primarily through upregulation of Cleaved-caspase-3 and the Bax/Bcl-2 ratio in OCs. To further clarify the cancer therapeutic target, we assessed the effect of DHM on the expression of GRASP65, which is overexpressed in human ovarian cancer tissues. DHM activated caspase-3 and decreased GRASP65 expression to promote cell apoptosis, implying that downregulation of GRASP65 was related to DHM-induced cell apoptosis. Additionally, the knockdown of GRASP65 by siRNA resulted in increased apoptosis after DHM treatment, while western blot and flow cytometry analysis demonstrated that overexpression of GRASP65 attenuated DHM-mediated apoptosis. In addition, the JNK/ERK pathway may be involved in DHM-mediated caspase-3 activation and GRASP65 downregulation. Taken together, these findings provide novel evidence of the anti-cancer properties of DHM in OCs, indicating that DHM is a potential therapeutic agent for ovarian cancer through the inhibition of GRASP65 expression and the regulation of JNK/ERK pathway.

Docetaxel Combined with Thymoquinone Induces Apoptosis in Prostate Cancer Cells via Inhibition of the PI3K/AKT Signaling Pathway

Toxicity and the development of resistance by cancer cells are impediments for docetaxel (DTX), a primary drug for treating prostate cancer (PCa). Since the combination of DTX with natural compounds can increase its effectiveness by reducing its toxic concentrations, we evaluated a combination of thymoquinone (TQ) with DTX and determined its cytotoxicity against PCa cells (DU145 and C4-2B). This combination, in a concentration-dependent manner, resulted in synergistic cytotoxicity and apoptosis in comparison to either DTX or TQ alone. In addition, inhibition of cell survival pathways by PI3K/AKT inhibitors conferred sensitivity of DU145 and C4-2B cells to the combination as compared to the individual drugs. Moreover, the combined drugs (DTX+TQ) with inhibitors of PI3K/AKT increased the expression of pro-apoptotic markers (BAX and BID) along with caspase-3, PARP and decreased expression of the anti-apoptotic marker, BCL-XL. These data show that, for PCa cells, the cytotoxic effect of the DTX and TQ combination correlates with a block of the PI3K/AKT signaling pathway. These findings indicate that the combination of DTX and TQ, by blocking of the PI3K/AKT pathway, will improve the survival rate and quality of life of PCa patients.

Bioengineered tumor microenvironments with naked mole rats high-molecular-weight hyaluronan induces apoptosis in breast cancer cells

The naked mole rat (nmr) is cancer resistant due to the abundant production of extremely high-molecular-weight hyaluronan (EHMW-HA). However, whether EHMW-HA has similar anti-cancer effects in mice and humans remains to be determined. The present study used breast cancer cells to clarify the effect of EHMW-HA on breast cancer. First, the overexpression of nmrHas2 in 4T1 and BT549 cell lines in both two-dimensional (2D) and three-dimensional (3D) models to mimic tumor microenvironment was established. The 4T1/BT549-nmrHas2 cells could secrete EHMW-HA (with a molecular weight of up to 6 MDa), which was similar to that found in the naked mole rat. Second, EHMW-HA altering tumor microenvironment in both 2D monolayers and 3D spheroids significantly enhanced apoptosis, inhibiting the proliferation of 4T1 and BT549 cells. The prominent anticancer effects of EHMW-HA on the cancer-cell apoptosis phenotype were further confirmed by inhibiting tumor formation in nude mice. Finally, EHMW-HA significantly induced higher p53 protein expression, which enhanced pro-apoptotic proteins p21 and Bax in breast cancer cells; this is in contrast with the triggering of hypersensitivity of the naked mole rat cells to early contact inhibition (ECI). These results have important implications for the design of therapeutic approaches based on the application of EHMW-HA.

Early 5-Fluorouracil-Induced Changes of Poly(A) Polymerase in Hela and Wish Cells

5-Fluorouracil (5-FU), a drug with numerous mechanisms of action which has a long-term suppressive effect on human cancer cell proliferation, mediates both partial dephosphorylation and inactivation of poly(A) polymerase (PAP) [EC. 2.7.7.19] as detected by immunoblotting analysis and non-specific enzyme assay, respectively, in human carcinoma HeLa and diploid WISH cells at a concentration of 100 μM. When the same experiment is done in the presence of phosphatase inhibitors, 5-FU-induced partial PAP dephosphorylation is abolished. Moreover, a cell type-modulated, differential response of HeLa cells (5-FU chemosensitive cells) versus WISH cells (drug-resistant diploid cells) is observed. These results suggest that 5-FU induces early direct or indirect changes in the structure and function of PAP and may regulate premRNA cleavage-polyadenylation.

Suppression of reactive oxygen species-mediated ERK and JNK activation sensitizes dihydromyricetin-induced mitochondrial apoptosis in human non-small cell lung cancer

Nonsmall cell lung cancer (NSCLC) is the most common type of lung cancer with a high mortality rate and still remains a therapeutic challenge. A strategy for targeting NSCLC is to identify agents that are effective against NSCLC cells while sparing normal cells. Dihydromyricetin (DHM) is the major flavonoid component derived from Ampelopsis grossedentata, which has a long history of use in medicine. Herein, the molecular mechanisms by which DHM exerts its anticancer effects against NSCLC cells were investigated. Results from MTS, colony formation, Western blot, flow cytometric, and JC-1 mitochondrial membrane potential assays revealed that DHM showed a selective cytotoxic effect against NSCLC cells (A549 and H1975), but not against normal lung (WI-38) fibroblasts, by inducing apoptosis. DHM-induced cell apoptosis occurred through Bcl-w suppression-mediated mitochondrial membrane depolarization, caspase-9/-7/-3 activation, and poly(ADP-ribose) polymerase (PARP) cleavage in A549 and H1975 cells. Moreover, treatment of A549 and H1975 cells with DHM induced increase of intracellular peroxide and sustained activation of extracellular signal-regulated kinase (ERK)1/2 and c-Jun N-terminal kinase (JNK)1/2, and the reactive oxygen species scavenger, N-acetylcysteine (NAC), reversed DHM-induced ERK and JNK activation. Furthermore, treatment of cells with specific inhibitors of ERK and JNK or NAC significantly promoted the DHM-induced activation of caspase-9/-7/-3 and PARP cleavage and also sensitized the antitumorigenic effect of DHM on NSCLC cells. These findings define and support a novel function of DHM of inducing mitochondrion-derived apoptosis in human NSCLC cells, and a combination of DHM with ERK and JNK inhibitors should be a good strategy for preventing NSCLC proliferation. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1426-1438, 2017.

Antiproliferative and Apoptosis-Inducing Activities of Thymoquinone in Lymphoblastic Leukemia Cell Line

Acute lymphoblastic leukemia is one of the malignant proliferations of lymphoid cells in the early stages of differentiation and accounts for about 80% of all cases of childhood leukemia. Side effects of available treatment are still main concern. Thymoquinone (TQ), a natural compound isolated from Nigella sativa, induces growth inhibition and apoptosis in several cancer cell lines. The aim of the present study was to investigate the effect of TQ alone and in combination with doxorubicine on the proliferation inhibition and apoptosis induction of TQ in a lymphoblastic leukemia cell line. Jurkat cell line was cultured in standard condition and with concentrations of TQ (0-30 μm) and doxorubicine for 24, 48 and 72 h. Cell viability was measured by MTS assay. Apoptosis induction by TQ was assessed by annexin V-FITC/PI and flow cytometry analysis. TQ and DOX decreased cell viability with a time and dose dependent manner. The IC50 values were 19.461 ± 1.141, 17.342 ± 1.949 and 14.123 ± 1.874 μM in 24, 48 and 72 h, respectively for TQ. IC50 values for DOX were. 075 ± .0124, .028 ± .007 and.007 ± .001 μM in 24, 48 and 72 h, respectively. The level of cell apoptosis in all used concentrations of TQ (4, 8, 12, 16 and 20 μm) was higher than control group (10.2, 14.1, 36.6, 87.5 and 93.3% respectively after 24 h; 10.7, 13.9, 64.6, 92.2 and 93.1 respectively after 48 h; 2.83, 5.83, 41.4, 71.6 and 86.6% respectively after 72 h) and reached to a significant level at 12, 16 and 20 μm concentration for 24 and 48 h and 16 and 20 μm for 72 h incubation. Combination of doxorubicine and TQ lead to a synergistic cytotoxicity as compared to any of them alone. The study indicated that TQ is effective on proliferation inhibition and is a strong apoptotic inducer in Jurkat lymphoblastic cell line and has synergistic effect in combination with DOX. This combination strategy can be an alternative way for more powerful anticancer effects. Therefore, the study of the mechanism of apoptosis induction of TQ can be a step forward to in target therapy which might be considered in the future studies.

PEG-PHB-glutaminase nanoparticle inhibits cancer cell proliferation in vitro through glutamine deprivation

In this study, we demonstrate that L-glutaminase, a marine bacterial enzyme with a molecular weight of 37 kDa, inhibits cancer cell proliferation in vitro through glutamine deprivation. The concentration of the enzyme reducing the viability of HeLa cells to 50% was determined to be 12.5 μg/mL; the function of L-glutaminase in controlling cell proliferation was further analysed by BrdU assays. To increase its stability and bioavailability, the enzyme was immobilized on polyethyleneglycol (PEG)-polyhydroxybutyrate (PHB) nanoparticles. A dented anatomy of the HeLa cells was observed under fluorescence and confocal microscopy when they were incubated with L-glutaminase and in glutamine-free medium, as also a 3-fold increase in caspase-3 activity was observed under the same conditions. Blebbed cytoplasm and shrunken nuclei were observed in treated cells under transmission electron microscopy (TEM). Finally, the influence of the enzyme on cell cycle and DNA damage was evaluated using flow cytometry and DNA fragmentation assays. The results confirmed significant damage to the DNA of HeLa cells incubated with L-glutaminase and in glutamine-free medium. These studies attest to the significant role played by L-glutaminase against proliferation in cancer cells through glutamine deprivation.

Quercetin induces mitochondrial-derived apoptosis via reactive oxygen species-mediated ERK activation in HL-60 leukemia cells and xenograft

Quercetin is a plant-derived bioflavonoid that was recently shown to have multiple anticancer activities in various solid tumors. Here, novel molecular mechanisms through which quercetin exerts its anticancer effects in acute myeloid leukemia (AML) cells were investigated. Results from Western blot and flow cytometric assays revealed that quercetin significantly induced caspase-8, caspase-9, and caspase-3 activation, poly ADP-ribose polymerase (PARP) cleavage, and mitochondrial membrane depolarization in HL-60 AML cells. The induction of PARP cleavage by quercetin was also observed in other AML cell lines: THP-1, MV4-11, and U937. Moreover, treatment of HL-60 cells with quercetin induced sustained activation of extracellular signal-regulated kinase (ERK), and inhibition of ERK by an ERK inhibitor significantly abolished quercetin-induced cell apoptosis. MitoSOX red and 2',7'-dichlorofluorescin fluorescence, respectively, showed that mitochondrial superoxide and intracellular peroxide levels were higher in quercetin-treated HL-60 cells compared with the control group. Moreover, both N-acetylcysteine and the superoxide dismutase mimetic, MnTBAP, reversed quercetin-induced intracellular reactive oxygen species production, ERK activation, and subsequent cell death. The in vivo xenograft mice experiments revealed that quercetin significantly reduced tumor growth through inducing intratumoral oxidative stress while activating the ERK pathway and subsequent cell apoptosis in mice with HL-60 tumor xenografts. In conclusions, our results indicated that quercetin induced cell death of HL-60 cells in vitro and in vivo through induction of intracellular oxidative stress following activation of an ERK-mediated apoptosis pathway.

Thymoquinone induces mitochondria-mediated apoptosis in acute lymphoblastic leukaemia in vitro

There has been a growing interest in naturally occurring compounds from traditional medicine with anti-cancer potential. Nigella sativa (black seed) is one of the most widely studied plants. This annual herb grows in countries bordering the Mediterranean Sea and India. Thymoquinone (TQ) is an active ingredient isolated from Nigella sativa. The anti-cancer effect of TQ, via the induction of apoptosis resulting from mitochondrial dysfunction, was assessed in an acute lymphocyte leukemic cell line (CEMss) with an IC₅₀ of 1.5 µg/mL. A significant increase in chromatin condensation in the cell nucleus was observed using fluorescence analysis. The apoptosis was then confirmed by Annexin V and an increased number of cellular DNA breaks in treated cells were observed as a DNA ladder. Treatment of CEMss cells with TQ encouraged apoptosis with cell death-transducing signals by a down-regulation of Bcl-2 and up-regulation of Bax. Moreover, the significant generation of cellular ROS, HSP70 and activation of caspases 3 and 8 were also observed in the treated cells. The mitochondrial apoptosis was clearly associated with the S phase cell cycle arrest. In conclusion, the results from the current study indicated that TQ could be a promising agent for the treatment of leukemia.

Genetic susceptibility to multiple primary neoplasms in the upper aero-digestive tract: genotype score and phenotype correlation

Early detection and treatment of head and neck cancer has led to increased patient survival. However such patients are at a high risk for multiple primary neoplasm(s) (MPN). In order to study the genetic susceptibility to MPN, 22 candidate SNPs were genotyped based on which a distinctive Genotype Score was created using Additive, Dominant and Recessive models. Using lymphoblastoid cell lines (LCLs) generated from these individuals, the Genotype Score was correlated with carcinogen sensitivity in vitro. LCLs from MPN patients exhibited significantly higher Genotype Score and showed resistance to genotoxic agents compared to matched controls. This report demonstrates quantitative assessment of cumulative effect of gene polymorphisms and its correlation with carcinogen sensitivity for predicting susceptibility to MPN.

Chloroquine and its analogs: a new promise of an old drug for effective and safe cancer therapies

Chloroquine (CQ), N'-(7-chloroquinolin-4-yl)-N,N-diethyl-pentane-1,4-diamine, is widely used as an effective and safe anti-malarial and anti-rheumatoid agent. CQ was discovered 1934 as "Resochin" by Andersag and co-workers at the Bayer laboratories. Ironically, CQ was initially ignored for a decade because it was considered too toxic to use in humans. CQ was "re-discovered" during World War II in the United States in the course of anti-malarial drug development. The US government-sponsored clinical trials during this period showed unequivocally that CQ has a significant therapeutic value as an anti-malarial drug. Consequently, CQ was introduced into clinical practice in 1947 for the prophylaxis treatment of malaria (Plasmodium vivax, ovale and malariae). CQ still remains the drug of choice for malaria chemotherapy because it is highly effective and well tolerated by humans. In addition, CQ is widely used as an anti-inflammatory agent for the treatment of rheumatoid arthritis, lupus erythematosus and amoebic hepatitis. More recently, CQ has been studied for its potential as an enhancing agent in cancer therapies. Accumulating lines of evidence now suggest that CQ can effectively sensitize cell-killing effects by ionizing radiation and chemotherapeutic agents in a cancer-specific manner. The lysosomotrophic property of CQ appears to be important for the increase in efficacy and specificity. Although more studies are needed, CQ may be one of the most effective and safe sensitizers for cancer therapies. Taken together, it appears that the efficacy of conventional cancer therapies can be dramatically enhanced if used in combination with CQ and its analogs.

Diallyl sulfide induces apoptosis in Colo 320 DM human colon cancer cells: involvement of caspase-3, NF-kappaB, and ERK-2

Chemoprevention is regarded as one of the most promising and realistic approaches in the prevention of human cancer. Diallyl sulfide (DAS), an organosulfur component of garlic has been known for its chemopreventive activities against various cancers and also in recent years, numerous investigations have shown that sulfur-containing compounds induce apoptosis in multiple cell lines and experimental animals. Thus the present study was focused to elucidate the anticancerous effect and the mode of action of DAS against Colo 320 DM colon cancer cells. DAS induced apoptosis in Colo 320 DM cells was revealed by flow cytometer analysis and phosphatidyl serine exposure. DAS also promoted cell cycle arrest substantially at G2/M phase in Colo 320 DM cells. The production of reactive oxygen intermediates, which were examined by 2,7-dichlorodihydrofluorescein diacetate (H2DCF-DA), increased with time, after treatment with DAS. The activities of alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) were decreased upon DAS treatment, which shows the antiproliferative and the cytotoxic effects, respectively. The expression of NF-kappaB was upregulated in DAS treated cells, compared to normal cells. Further, DAS promoted the expression of caspase-3 and suppression of Extracellular Regulatory Kinase-2 (ERK-2) activity in Colo 320 DM cells that was determined by Western blot analysis. In conclusion, DAS increased the production of ROS, caused cell cycle arrest, decreased cell proliferation and induced apoptosis in Colo 320 DM cells. Thus, this study put forward DAS as a drug that can possibly be used to treat cancers.

Effects of Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the urinary bladder of male Wistar rats

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a substituted urea herbicide widely used on agricultural crops such as soy, cotton and sugar cane. In a previous long-term study this herbicide exerted carcinogenic activity on the urinary bladder mucosa of male Wistar rats. In general, the genotoxic and mutagenic potentials of Diuron are considered to be negative. The present study aimed to evaluate the mode of action of Diuron on the urinary bladder mucosa of male Wistar rats. Six-week old male Wistar rats were fed pelleted Nuvilab diet mixed with Diuron at 125, 500 and 2500 ppm. As a positive control, 8.3% sodium saccharin (NaS) was fed in the diet. Preceding the sacrifice of the animals at the 20th week, urinary pH was measured and the genotoxic potential of Diuron was evaluated by the comet assay. Histological urothelial lesions in the urinary bladder and in the renal pelvis mucosa, cell proliferation/apoptosis evaluations, and scanning electron microscopy (SEM) of the urinary bladder mucosa were also performed. No DNA changes were found in urothelial or peripheral blood cells, and urinary pH was comparable to controls in all Diuron groups. In the urinary bladder urothelium, the incidence of simple hyperplasia (SH) by light microscopy was significantly increased (7/10; p<0.005) in the 2500 ppm Diuron group but not at the lower doses. By SEM, three of five animals treated with 2500 ppm Diuron showed urothelial cell necrosis and hyperplasia. In the renal pelvis, the incidence of SH was significantly increased in the Diuron 500 and 2500 ppm and in the NaS 8.3% groups. Cell proliferation was significantly increased in the Diuron 2500 ppm (p<0.05) and NaS 8.3% (p<0.05) groups. The results indicate that a high dietary concentration of Diuron is associated with urothelial necrosis and continuous regenerative cell proliferation that leads to urothelial hyperplasia.

Alpha-chaconine, a potato glycoalkaloid, induces apoptosis of HT-29 human colon cancer cells through caspase-3 activation and inhibition of ERK 1/2 phosphorylation

Although alpha-chaconine, one of the two major potato trisaccharide glycoalkaloids, have shown cytotoxic effects on human cancer cells, the exact mechanism of this action of alpha-chaconine is not completely understood. In this study, we found that alpha-chaconine induced apoptosis of HT-29 cells in a time- and concentration-dependent manner by using flow cytometric analysis. We also found that caspase-3 activity and the active form of caspase-3 were increased 12 h after alpha-chaconine treatment. Caspase inhibitors, N-Ac-DEVD-CHO and Z-VAD-fmk, prevented alpha-chaconine-induced apoptosis, whereas alpha-chaconine-induced apoptosis was potentiated by PD98059, an extracellular signal-regulated kinase (ERK) inhibitor. However, pretreatment of the cells with LY294002 and SB203580, inhibitors of PI3K and p38, respectively, BAPTA-AM, an intracellular Ca(2+) chelator, and antioxidants such as N-acetylcysteine (NAC) and Trolox had no effect on the alpha-chaconine-induced cell death. In addition, phosphorylation of ERK was reduced by the treatment with alpha-chaconine. Moreover, alpha-chaconine-induced caspase-3 activity was further increased by the pretreatment with PD98059. Thus, the results indicate that alpha-chaconine induces apoptosis of HT-29 cells through inhibition of ERK and, in turn, activation of caspase-3.

Carcinogenicity and mechanism of action of fumonisin B1: a mycotoxin produced by Fusarium moniliforme (= F. verticillioides)

Fumonisins are fungal metabolites and suspected human carcinogens. They inhibit ceramide synthase in vitro, enhance tumor necrosis factor alpha (TNFalpha) production, and cause apoptosis. Fumonisin B1 (FB1) was fed to rats and mice for 2 years or, in separate studies, given to rats or mice for up to 4 weeks. Kidney tubule adenomas and carcinomas were found in male rats fed > or = 50 ppm, whereas liver adenomas and carcinomas were found in female mice fed > or = 50 ppm for 2 years. In the short-term studies, increases in tissue concentration of the ceramide synthase substrate sphinganine (Sa) and the Sa to sphingosine (So) ratio were correlated with apoptosis. Further, hepatotoxicity was ameliorated in mice lacking either the TNFR1 or the TNFR2 TNFalpha receptors. Thus, FB1 was carcinogenic to rodents and thefindings support the hypothesis that disrupted sphingolipid metabolism and TNFalpha play important roles in its mode of action.

Prostatic stem cells

Multipotent cells within the epithelial compartment, together with phenotypically 'plastic' mesenchyma cells (stromal stem cells), provide a repository of protected genetic information from which the structure, stability and functionality of the prostate gland can be maintained. However, mere preservation of cells in a non-dividing state is insufficient to provide the necessary reservoir of information from which the structure and function of the prostate gland can be retained or recreated. Rather, there is a constant dynamic interaction, at the level of information exchange, between stem cells (whether epithelial or mesenchymal) and their surrounding environment (both humoral and physical). Thus, with respect to epithelial stem cells, these reside within environmental 'niches' which allow their controlled and limited proliferation while preserving genomic integrity. Similar 'mesenchymal niches' are also predicted to occur, although not yet identified, thus providing the multipotent source from which the full spectrum of stromal phenotypes might be regenerated. Recent data from studies of the haematopoietic and hepato-biliary systems indicate that the potential scope of stem cells far exceeds the immediate phenotypic complement of those tissues within which they originate, being dependent upon their precise environment as well as their genomic integrity.

Quantitation of the cancer process in C57BL/6J, B6C3F1 and C3H/HeJ mice

This study examines growth alterations in liver foci and tumor development as a basis for the different susceptibility in hepatocarcinogenesis found among different strains of mice. Male C57, B6C3F1, and C3H mice treated with a single dose (1 mg/kg) of N,N-diethylnitrosamine (DEN) at 15 days of age and followed up to 12 months displayed a strain-dependent (C3H > B6C3F1 > C57) increase in incidence, number, volume fraction, and size of foci and macroscopic lesions (masses). DEN-treated mice exhibited a time-dependent increase in foci size but not in foci number. Phenobarbital (PB) treatment (500 ppm) in the drinking water starting 2 weeks after DEN-initiation did not affect the incidence or number of masses and foci. In all 3 strains, the bromodeoxyuridine labeling index in foci correlated with foci growth, supporting the major role of cell proliferation in foci growth. Measurements of apoptosis by morphological criteria with H&E staining suggest that intrafocal apoptosis may be a late event preventing foci growth and possibly also promoting focal cell selection, whereas extrafocal apoptosis may facilitate clonal growth by removing adjacent normal cells. The onset of conversion of foci to masses also correlated with strain susceptibility to hepatocarcinogenesis.

Sphingolipid perturbations as mechanisms for fumonisin carcinogenesis

There is a great deal of evidence that altered sphingolipid metabolism is associated with fumonisin-induced animal diseases including increased apoptotic and oncotic necrosis, and carcinogenesis in rodent liver and kidney. The biochemical consequences of fumonisin disruption of sphingolipid metabolism most likely to alter cell regulation are increased free sphingoid bases and their 1-phosphates, alterations in complex sphingolipids, and decreased ceramide (CER) biosynthesis. Because free sphingoid bases and CER can induce cell death, the fumonisin inhibition of CER synthase can inhibit cell death induced by CER but promote free sphingoid base-induced cell death. Theoretically, at any time the balance between the intracellular concentration of effectors that protect cells from apoptosis (decreased CER, increased sphingosine 1-phosphate) and those that induce apoptosis (increased CER, free sphingoid bases, altered fatty acids) will determine the cellular response. Because the balance between the rates of apoptosis and proliferation is important in tumorigenesis, cells sensitive to the proliferative effect of decreased CER and increased sphingosine 1-phosphate may be selected to survive and proliferate when free sphingoid base concentration is not growth inhibitory. Conversely, when the increase in free sphingoid bases exceeds a cell's ability to convert sphinganine/sphingosine to dihydroceramide/CER or their sphingoid base 1-phosphate, then free sphingoid bases will accumulate. In this case cells that are sensitive to sphingoid base-induced growth arrest will die and insensitive cells will survive. If the cells selected to die are normal phenotypes and the cells selected to survive are abnormal, then cancer risk will increase.

An overview of rodent toxicities: liver and kidney effects of fumonisins and Fusarium moniliforme

Fumonisins are produced by Fusarium moniliforme F. verticillioides) and other Fusarium that grow on corn worldwide. They cause fatal toxicoses of horses and swine. Their effects in humans are unclear, but epidemiologic evidence suggests that consumption of fumonisin-contaminated corn contributes to human esophageal cancer in southern Africa and China. Much has been learned from rodent studies about fumonisin B1(FB1), the most common homologue. FB1 is poorly absorbed and rapidly eliminated in feces. Minor amounts are retained in liver and kidneys. Unlike other mycotoxins, fumonisins cause the same liver cancer promotion and subchronic (studies (3/4) 90 days) liver and kidney effects as (italic)F. moniliforme. FB 1 induces apoptosis of hepatocytes and of proximal tubule epithelial cells. More advanced lesions in both organs are characterized by simultaneous cell loss (apoptosis and necrosis) and proliferation (mitosis). Microscopic and other findings suggest that an imbalance between cell loss and replacement develops, a condition favorable for carcinogenesis. On the molecular level, fumonisins inhibit ceramide synthase, and disrupt sphingolipid metabolism and, theoretically, sphingolipid-mediated regulatory processes that influence apoptosis and mitosis. Liver sphingolipid effects and toxicity are correlated, and ceramide synthase inhibition occurs in liver and kidney at doses below their respective no-observed-effect levels. FB1 does not cross the placenta and is not teratogenic in vivoin rats, mice, or rabbits, but is embryotoxic at high, maternally toxic doses. These data have contributed to preliminary risk evaluation and to protocol development for carcinogenicity and chronic toxicity studies of FB1 in rats and mice.

Age-related cell proliferation and apoptosis in the kidney of male Fischer 344 rats with observations on a spontaneous tubular cell adenoma

Cell proliferation rate and apoptosis were examined in archival kidneys from young, middle-aged, and old male F344 rats. Immunohistochemical expression of proliferating cell nuclear antigen (PCNA) and apoptosis were quantified in the same cell populations of the proximal tubule epithelium. A total of 79 kidneys from 40 rats were examined. There was a progressive increase in cell proliferation rates in rats from 4 and 6-10 months of age. In 23-month-old rats, proliferative activity appeared to be reduced. No age-related variations in apoptotic indices were found. One of the 16 rats aged 23 months had a tubular cell adenoma. In the tumor-affected kidney, cell proliferation rate was dramatically higher than in the contralateral kidney as well as in all the other kidneys examined. This high proliferative activity was not balanced by variation in cell death.

The use of structure-activity relationships and markers of cell toxicity to detect non-genotoxic carcinogens

In contrast to the situation for genotoxic carcinogens, few in vitro tests exist that can detect early markers of the events thought to be associated with non-genotoxic carcinogenesis. Also, comparatively little is known about the quantitative structure-activity relationships (Q)SARs of these agents. This review discusses published SAR studies conducted on non-genotoxic carcinogens, in relation to the use of several markers of in vitro cell toxicity (inhibition of gap-junctional intercellular communication, inhibition of tubulin polymerization, modulation of apoptosis and induction of cell proliferation), which are used as endpoints for screening this class of carcinogen. Much of the work has involved the identification of new biophores (substructural features of molecules associated with toxicity), as well as other structural features, which are thought to predispose the chemicals to ligand binding with specific target molecules acting as possible receptors (e.g. protein kinase C, the oestrogen, peroxisome-proliferator and tubulin protein receptors), implicated in the mechanism of toxicity involved. It is concluded that (a) there is an urgent need for more information on (Q)SARs for non-genotoxic carcinogens; (b) this information should be acquired by using several different approaches in a variety of laboratories; and (c) such research should proceed together with more studies on the mechanisms of cell toxicity caused by these chemicals, including the identification and characterisation of further specific receptors involved in mediating the various types of cell toxicity associated with this type of carcinogenesis.

Is there a metabolic basis for dietary supplementation?

To be efficacious, dietary supplements must either provide a nutrient that is normally undersupplied to cells or exert a pharmacologic effect on cellular processes. In the first case, optimal function is achieved when a nutrient required by the organism reaches a specific concentration within the cell. A supplement has benefit only when the normal intake of a bioavailable form of a nutrient is lower than the amount that would provide maximum benefit as judged from all biological perspectives. Metabolic, environmental, and genetic factors can make individual nutrient requirements differ from the estimated needs calculated from population-based data. For example, under certain circumstances intracellular antioxidants may be depleted and a dietary supplement might restore optimal antioxidant protection. In the second case, the dietary supplement contains a constituent that is normally not required by the cell, but this substance is capable of altering normal cell function. For example, herbal preparations may contain ephedrine (a drug), which might alter heart rate so that the amount of blood pumped by the heart is enhanced. An understanding of how the variation in nutrient requirements comes about and of the pharmacologic actions of nutrient supplements can help to identify which individuals are most likely to benefit from dietary supplements.

Apoptosis inhibition and ornithine decarboxylase superinduction as early epigenetic events in morphological transformation of Syrian hamster embryo cells exposed to 2-methoxyacetaldehyde, a metabolite of 2-methoxyethanol

We have conducted a study to determine the carcinogenic potential of ethylene glycol monomethyl ether (EGME), a member of the glycol ether family, as compared to its reactive metabolite 2-methoxy-acetaldehyde (MALD). Since disruption of equilibrium between cell proliferation and cell death is thought to play a key role in multistage carcinogenesis, we investigated, in Syrian hamster embryo (SHE) cells exposed to various doses of EGME and MALD, impairment in apoptosis rate and in ornithine decarboxylase (ODC) metabolism. The activity of this rate-limiting enzyme of polyamine biosynthesis is closely related to cell proliferation and cell transformation. At the end-point, comparative action of the two products on SHE cell morphological transformation frequency was evaluated. One-stage exposure of SHE cells to 2 mM EGME and 200 microM MALD for 5 h did not change basal apoptotic level, whereas 0.16 microM phorbol ester (TPA) decreased it. Using two-stage exposure protocol (1 h xenobiotic followed by 5 h TPA), MALD strongly inhibited apoptosis more than did TPA alone; the parent compound EGME did not have any effect on TPA inhibiting action. Western blotting analysis showed that sequential treatment (MALD/TPA) increased Bcl-2 oncoprotein expression, whereas Bcl-XL and Bax proteins were not changed. The same staged exposure of SHE cells to MALD/TPA strongly induced ODC activity, and the rate was higher than that obtained with TPA alone: this was accompanied by an increase of ODC protein level. This ODC superinduction was not observed with EGME/TPA treatment. In long-term SHE-cell morphological transformation assay, staged exposure to MALD (800 microM or 1 mM for 24 h) followed by TPA applications increased the number of transformed colonies at the seventh day. Such early cooperative events as apoptosis inhibition and ODC superinduction, followed by the increase of SHE-cell transformation frequency, are highly indicative of a carcinogenic potential for the metabolite, MALD.

Comparison of the effects of some CYP3A and other enzyme inducers on replicative DNA synthesis and cytochrome P450 isoforms in rat liver

The aim of this study was to investigate the mitogenic effects of some inducers of cytochrome P450 (CYP) isoforms in rat liver. Female Sprague-Dawley CD rats were treated with 100 mg/kg per day of either sodium phenobarbitone (NaPB), barbituric acid (BA), isoniazid (ISN), beta-naphthoflavone (BNF), pregnenolone-16alpha-carbonitrile (PCN), miconazole (MIC) or clotrimazole (CLOT), 75 mg/kg per day methylclofenapate (MCP), 50 mg/kg per day dexamethasone (DEX) and 500 mg/kg per day troleandomycin (TAO) by daily oral gavage for four days. Treatment with all compounds except BA, ISN and MIC, significantly increased relative liver weight. Administration of NaPB, PCN, DEX, MIC, CLOT and TAO all induced total CYP content, and by Western immunoblotting, levels of CYP3A isoforms in hepatic microsomal fractions. Apart from CLOT, all these compounds induced microsomal testosterone 6beta-hydroxylase activity. By measurement of marker enzyme activities and Western immunoblotting with antibodies to CYP1A2, CYP2B1/2 and CYP2E1, BNF, NaPB, ISN and MCP were shown to induce CYP1A2, CYP2B1/2, CYP2E and CYP4A isoforms, respectively. Replicative DNA synthesis was studied by implanting osmotic pumps containing 5-bromo-2'-deoxyuridine 1 day before the commencement of treatment with the enzyme inducers. Hepatocyte labelling index values were significantly increased by treatment with NaPB, PCN, MCP, CLOT and TAO, but not by BA, ISN, BNF, DEX and MIC. These studies demonstrate that while CYP2B and CYP4A enzyme inducers may stimulate replicative DNA synthesis, only some CYP3A enzyme inducers are mitogenic agents in rat liver.

Upregulation of apoptosis with dietary restriction: implications for carcinogenesis and aging

The maintenance of cell number homeostasis in normal tissues reflects a highly regulated balance between the rates of cell proliferation and cell death. Under pathologic conditions such as exposure to cytotoxic, genotoxic, or nongenotoxic agents, an imbalance in these rates may indicate subsequent risk of carcinogenesis. Apoptotic cell death, as opposed to necrotic cell death, provides a protective mechanism by selective elimination of senescent, preneoplastic, or superfluous cells that could negatively affect normal function and/or promote cell transformation. The relative efficiency or dysfunction of the cell death program could therefore have a direct impact on the risk of degenerative or neoplastic disease. Dietary restriction of rodents is a noninvasive intervention that has been reproducibly shown to retard tumor development and most physiologic indices of aging relative to ad libitum-fed animals. As such, it provides a powerful model in which to study common mechanistic processes associated with both aging and cancer. In a recent study we established that chronic dietary restriction (DR) induces an increase in spontaneous apoptotic rate and a decrease in cell proliferation rate in hepatocytes of 12-month-old B6C3F1 DR mice relative to ad libitum (AL)-fed mice. This diet-induced shift in cell death/proliferation rates was associated with a marked reduction in subsequent development of spontaneous hepatoma and a marked increase in disease-free life span in DR relative to AL-fed mice. These results suggest that total caloric intake may modulate the rates of cell death and proliferation in a direction consistent with a cancer-protective effect in DR mice and a cancer-promoting effect in AL mice. To determine whether the increase in spontaneous apoptotic rate was maintained over the life span of DR mice, apoptotic rates were quantified in 12-, 18-, 24- and 30-month-old DR and AL mice. The rate of apoptosis was elevated with age in both diet groups; however, the rate of apoptosis was significantly and consistently higher in DR mice regardless of age. In double-labeling experiments, an age-associated increase in the glutathione S-transferase-II expression in putative preneoplastic hepatocytes in AL mice was rapidly reduced by apoptosis upon initiation of DR. Thus, intervention that promote a low-level increase in apoptotic cell death may be expected to protect genotypic and phenotypic stability with age. If during tumor promotion an adaptive increase in apoptosis effectively balances the dysregulated increase proliferation, the risk of permanent genetic error and carcinogenesis would be minimized.

Furan-induced liver cell proliferation and apoptosis in female B6C3F1 mice

Furan is a potent rodent hepatocarcinogen that probably acts through non-genotoxic mechanisms involving hepatotoxicity and regenerative hepatocyte proliferation. In addition to inducing necrosis, cytotoxicants like furan may also induce cytolethality through apoptosis which has been suggested to play a key role in carcinogenesis. Hepatocyte proliferation and apoptosis were studied in female B6C3F1 mice exposed to furan by oral gavage for 3 weeks at National Toxicology Program (NTP) bioassay doses (8 and 15 mg/kg body weight) and lower (4 mg/kg). Furan treatment led to a 2- to 3-fold significant increase in liver-related enzymes and bile acids in blood serum as compared to the control group. These changes were accompanied by minor subcapsular inflammation and minimal necrosis at 8 and 15 mg furan/kg. A dose-related increase in bromodeoxyuridine-labeling index (1.4- to 1.7-fold) and hematoxylin- and eosin-defined apoptotic index (6- to 15-fold) was observed at 8 and 15 mg/kg. Co-treatment of mice with aminobenzotriazole, an irreversible inhibitor of cytochromes P-450, prevented the observed hepatotoxic effects induced by furan. These results indicate that furan elicits hepatotoxicity in a dose-related manner through a toxic metabolite and, furthermore, suggest that apoptosis is an important form of cell death at hepatocarinogenic doses under short-term conditions.

Role of increased DNA replication in the carcinogenic risk of nonmutagenic chemical carcinogens

DNA replication is not an error-free process; therefore induction of cell proliferation with the requisite increase in DNA replication may be an important mechanism by which carcinogenesis can be induced by chemicals. Data presented in this overview indicate a positive association between increased cell proliferation and carcinogenesis, and illustrate the value of performing mechanistic studies such as cell proliferation assays in conjunction with short-term tests to further investigate the results of cancer bioassays. Whereas chemically-induced cell proliferation per se may not be sufficient to induce carcinogenesis, it creates a favorable environment for tumor development. There are two types of chemically-induced cell proliferation, mitogenic and cytotoxic, and they have different consequences regarding the mechanism of carcinogenesis of a chemical. Mitogenic chemical such as phenobarbital, oxazepam, and the peroxisome proliferating agents exert a short-term cell proliferative response that may exert its primary effect in carcinogenesis at the promotion stages. It is not clear at what stage(s) cytotoxic agents such as methapyrilene, alpha 2u-globulin inducers or saccharin exert their effects in carcinogenesis. A confounding factor in evaluation of cell proliferation in risk assessments is the production of chemical specific pleiotropic effects that may contribute to the carcinogenicity of a chemical. It is clear that mechanistic studies performed to understand the relationship of sex, species and dose in rodent carcinogenicity assays of chemicals is critical for the extrapolation of such data for human health assessments.

Risk assessment and the use of information on underlying biologic mechanisms: a perspective

Recent years have seen the rapid expansion of scientific understanding of the underlying biologic bases of toxic reactions to chemicals. Use of this information in health risk assessment is expanding, but it has yet to reach its full potential. This article considers what has successfully been done, what approaches are now being developed, and what impediments and difficulties have been encountered in attempts to bring case-specific, mechanistic toxicological information to bear on risk estimation. In hazard identification, mechanistic information can help explain the bearing of various empirical experimental results for inferring human hazard, can increase the sensitivity of detection, and can be considered in attempts to replace 2-year animal bioassays with hazard identification methods that rest on identifying key biological properties underlying carcinogenicity rather than relying only on the experimental observation of tumors. In carcinogen potency estimation, mechanistic information can potentially extend relevant observation to lower dose levels, provide the basis for choosing among empirically based dose-response models, lead to potency estimates through relationships with quantitative measures of short-term test outcomes, and can be considered as a basis for providing direct observation of the biological parameters in biologically based dose-response modeling.

U.S. Environmental Protection Agency guidelines for carcinogen risk assessment: past and future

The U.S. Environmental Protection Agency (USEPA) recently proposed new guidelines to update and replace the 1986 USEPA Guidelines for Carcinogen Risk Assessment. Today, there is a better understanding of the variety of modes by which carcinogens can operate that did not exist when the 1986 USEPA guidelines were published. Many laboratories are adding new test protocols in their programs directed at questions concerning the mechanisms of action of carcinogens. In response to the evolving science of carcinogenesis, the new guidelines provide an analytical framework for incorporating all relevant biological information and recognizing a variety of situations regarding cancer risk. In addition, the guidelines are flexible enough to allow consideration of future scientific advances.

Future approaches to genetic toxicology risk assessment

Short-term genetic toxicology tests were developed for the purpose of identifying chemical carcinogens in the environment. After two decades of development and validation, the tests are well-established in routine testing schemes, but our views of their utility for safety evaluation have undergone re-assessment. The correlation between identified mutagens and identified carcinogens has turned out to be significantly less than one. Processes or mechanisms that are not directly genotoxic appear to play a role in carcinogenesis. While short term test data are still components of the assessment of carcinogenic risk, genetic damage also has been recognized as important in its own right, in relation to heritable genetic risk and other health-related effects, such as aging, reproductive failure and developmental toxicity. The revolution in molecular biology and genetic analysis occurring over the past 20 years has contributed to the wealth of new information on the complexities of cell regulation, differentiation, and the carcinogenic process. These technologies have provided new experimental approaches to genetic toxicology assessments, including transgenic cell and animal models, human monitoring, and analysis of macromolecular interactions at environmentally relevant exposures. The potential exists for the development of more efficient and more relevant genetic toxicology testing schemes for use assessing human safety. A delineation of contemporary needs, a modern view of the elements of cancer induction, and an examination of new assays and technologies may provide a framework for integrating new approaches into current schemes for evaluating the potential genetic and carcinogenic risk of environmental chemicals.