Insulin and IGF-1 mediated inhibition of apoptosis in CHO cells grown in suspension in a protein-free medium

When Chinese hamster ovary (CHO) cells were grown in suspension and deprived of serum, 40% of them became apoptotic after 72 hours, as determined by flow cytometry analysis of TUNEL-labelled cells. Cell viability, assessed by erythrocin B staining, decreased correspondingly. An increase in the total fraction of cells expressing interleukin converting enzyme (ICE; caspase 1), B-cell lymphoma 2 protein (Bcl-2,) and Bcl-2 associated x protein (Bax) was shown by antibody probing and subsequent flow cytometry. The p53 tumour suppressor gene product level remained low within the cell population. Insulin-like growth factor-1 (IGF-1) inhibited cell death in a concentration-dependent manner, and at 20 ng/ml, cell viability was maintained close to 100% and no apoptotic cells were detected. Also, insulin was shown to inhibit cell death - at 1.0 microg/ml, cell viability was 95%, whereas 10% of the cells stained for apoptosis. At the highest concentrations of IGF-1 and insulin, the expression of ICE, Bcl-2 and Bax was fully suppressed, whereas the p53 product level increased, despite still being detectable in a minority of cells. Under these conditions, IGF-1 may increase p53 expression to restrain abnormal cell proliferation. It is concluded that special attention should be paid to exposure and culture conditions that induce acquired susceptibility to a toxic insult, during the development and validation of cell-based assays.

Toxicological evaluation of cigarettes with two banded cigarette paper technologies

A tiered testing strategy has been employed to evaluate the potential of tobacco processes, ingredients, or technological developments to change the biological activity resulting from burning cigarette tobacco. The strategy is based on comparative chemical and biological testing. The introduction of banded cigarette papers in cigarettes to meet New York state "Fire Safety Standards for Cigarettes" constitutes an example of a technological development evaluated utilizing this tiered testing strategy that included a comparison of the chemical and biological effects of cigarettes with and without the banded cigarette paper technologies (BCPT) (representative of current marketed technologies). Specific testing included mainstream cigarette smoke chemistry studies; in vitro studies included genotoxicity (Ames and sister chromatid exchange) and cytotoxicity studies (neutral red); in vivo studies included a 13-week inhalation study in Sprague-Dawley rats and a 30-week dermal tumor promotion study in SENCAR mice. Collectively, data indicated that cigarettes with and without BCPT had a similar toxicological profile in this test battery.

Aven and Bcl-xL enhance protection against apoptosis for mammalian cells exposed to various culture conditions

A balance between proliferation and cell death is critical for achieving desirable high cell densities in mammalian cell culture. In this study, we evaluate a recently discovered anti-apoptotic gene, aven, and examine its effectiveness alone and in combination with a member of the Bcl-2 family, bcl-xL. The commercially popular cell line, Chinese hamster ovary (CHO), was genetically modified to constitutively express aven, bcl-xL, and the two genes in combination. Cells were exposed to several model insults that simulate severe bioreactor environments, including serum deprivation, spent medium, and Sindbis virus infection, as well as staurosporine, a known chemical inducer of apoptosis. CHO cells exhibited DNA fragmentation, a hallmark of apoptosis, after exposure to these model insults. After exposure to serum deprivation, 4- and 5-day spent medium, and staurosporine, cells expressing Aven provided limited protection against cell death when compared with the protection afforded by cells expressing Bcl-xL alone. However, the highest survival levels for all insults were achieved when Aven was expressed in combination with Bcl-xL. In fact, Aven appeared to act synergistically to enhance the protective function of Bcl-xL for several insults, because the protective function of the two genes expressed together in one cell line often exceeded the additive protective levels of each anti-apoptosis gene expressed alone. Surprisingly, Aven expression provided a mildly pro-apoptotic response in CHO isolates infected with Sindbis virus. However, CHO cells expressing both Bcl-xL and Aven showed protection against Sindbis virus infection due to the inhibitory properties of the bcl-xL anti-apoptosis gene. This study shows that combinatorial anti-apoptosis cell engineering strategies may be the most effective mechanisms for providing extended protection against cell death in mammalian cell culture.

Characterization of a haemolytic phospholipase A2 activity in clinical isolates of Campylobacter concisus

A membrane-bound, haemolytic phospholipase A(2) (PLA(2)) activity was detected in clinical strains of Campylobacter concisus isolated from children with gastroenteritis. The clinical strains were assigned into two molecular groups (genomospecies) based on PCR amplification of their 23S rDNA. This calcium-dependent, heat-stable, haemolytic PLA(2) activity was detected in strains from both genomospecies. A crude haemolysin extract (CHE) was initially prepared from cellular outer-membrane proteins of these isolates and was further fractionated by ultrafiltration. The haemolytic activity of the extracted fraction (R30) was retained by ultrafiltration using a 30 kDa molecular mass cut-off filter, and was designated haemolysin extract (HE). Both CHE and HE had PLA(2) activity and caused stable vacuolating and cytolytic effects on Chinese hamster ovary cells in tissue culture. Primers for the conserved region of pldA gene (phospholipase A gene) from Campylobacter coli amplified a gene region of 460 bp in all tested isolates, confirming the presence of a homologous PLA gene sequence in C. concisus. The detection of haemolytic PLA(2) activity in C. concisus indicates the presence of a potential virulence factor in this species and supports the hypothesis that C. concisus is a possible opportunistic pathogen.

Apoptosis induced by different doses of caffeine on Chinese hamster ovary cells

Caffeine has been investigated for its potential mutagenic activity to bacteria, fungi and mammalian cells in culture, and at high concentrations it is also an inducer of apoptosis. Caffeine can exert acute cellular toxicity, including inhibition of cell growth and cell death, in Chinese hamster ovary cells. The aim of this study was to evaluate the cell survival and apoptotic or non-apoptotic effects of caffeine to different concentrations in Chinese hamster ovary cells (CHO-K1). These effects were evaluated by measuring cell viability, caspase 8 activity and fragmented DNA. This study suggests that the concentration of caffeine is of critical importance because high doses of caffeine induce apoptosis and low concentrations can act as an antioxidant. Previously, the cytotoxicity of caffeine was evaluated using a wide range of concentrations by the neutral red test. From this screening, adequate doses were selected to perform the caspase activity and fragmentation DNA studies. The potential antioxidant effect of caffeine was studied using tert-butyl-hydroperoxide as a free-radical generator. The repeatability was checked through three separate tests with the same concentration.

Characterization of cytotoxic and genotoxic effects of different compounds in CHO K5 cells with the comet assay (single-cell gel electrophoresis assay)

Different variants of the comet assay were used to study the genotoxic and cytotoxic properties of the following eight compounds: chloral hydrate, colchicine, hydroquinone, DL-menthol, mitomycin C, sodium iodoacetate, thimerosal and valinomycin. Colchicine, mitomycin C, sodium iodoacetate and thimerosal induced genotoxic effects. The other compounds were found to be inactive. The compounds were tested in the standard comet assay as well as in the all cell comet assay (recovery of floating cells after treatment), designed in our laboratory for adherently-growing cells. This latter procedure proved to be more adequate for the assessment of the cytotoxicity for some of the compounds tested (hydroquinone, DL-menthol, thimerosal, valinomycin). Colchicine was positive in the standard comet assay (3h treatment) and in the all cell comet assay (24h treatment). Sodium iodoacetate and thimerosal were positive in the standard and/or the all cell comet assay. Chloral hydrate, hydroquinone, sodium iodoacetate, mitomycin C and thimerosal were also tested in the modified comet assay using lysed cells. Mitomycin C and thimerosal showed effects in this assay, whereas sodium iodoacetate was inactive. This indicates that it does not induce direct DNA damage. Compounds that are known or suspected to form DNA-DNA cross-links or DNA-protein cross-links (chloral hydrate, hydroquinone, mitomycin C and thimerosal) were checked for their ability to reduce ethyl methanesulfonate (EMS)-induced DNA damage. This mode of action could be demonstrated for mitomycin C only.

Application of the biotin-dUTP chromosome labelling technique to study the role of 5-bromo-2'-deoxyuridine in the formation of UV-induced sister chromatid exchanges in CHO cells

The role of 5-bromo-2'-deoxyuridine (BrdU) in the formation of sister chromatid exchanges (SCEs) in cells exposed to UV radiation was studied. Cells were unifilarily labelled (labelling of one strand of chromosomal DNA) with BrdU or biotin-16-2'-deoxyuridine (biotin-dU) and irradiated in G(1) phase of the cell cycle either with 254 nm, which is absorbed by all nucleobases including bromouracil (BrU) or with 313 nm radiation, which is predominantly absorbed by the BrU moiety. Elevated SCE frequencies were observed in cells irradiated at 254 nm (1.2 and 3.0 J m(-2)) which were pre-labelled with BrdU or biotin-dU. Following irradiation at 313 nm (38 and 96 J m(-2)) a statistically elevated SCE frequency was observed in cells pre-labelled with BrdU but not with biotin-dU. In cells pre-labelled with BrdU, UV-radiation at 254 nm was 50-80 times more effective in inducing SCEs than that at 313 nm. This result can be accounted for by the fact that in BrdU-DNA the cross-section for uracilyl radical and bromine atom formation is approximately 100-fold higher at 254 nm than that at 313 nm. Upon irradiation at 254 nm, BrdU had a strong sensitising effect on SCE induction: the SCE frequencies observed in cells pre-labelled with BrdU are approximately 6 times higher than in cells pre-labelled with biotin-dU. From this it follows that BrdU-induced damage is responsible for more than 80% of the SCEs formed in UV irradiated cells unifilarily labelled with BrdU. Based on photochemical considerations and the fact that chemical agents which form DNA interstrand cross-links are among the most potent inducers of SCEs, we propose that an interstrand cross-link may be the major lesion leading to SCEs in BrdU-labelled cells.

An inhibitory factor for cell-free protein synthesis from Salmonella enteritidis exhibits cytopathic activity against Chinese hamster ovary cells

A factor inhibiting cell-free protein synthesis was purified from Salmonella enteritidis cell lysate by sequential ammonium sulfate precipitation, chromatography on anion exchange and hydrophobic interaction columns, and polyacrylamide disc gel electrophoresis. The purified factor, which was named SIPS (Salmonella inhibitor of protein synthesis), inhibited in vitro protein synthesis in rabbit reticulocyte lysate and had a molecular mass of 38 kDa, estimated by PAGE under denaturing conditions. SIPS was also cytopathic for Chinese hamster ovary cells. The N-terminal amino acid sequence (20 residues) of SIPS was found to be identical to that of mature L-asparaginase II of Escherichia coli. Indeed, the purified SIPS exhibited asparaginase activity, E. coli L-asparaginase II had cytopathic activity and inhibited in vitro protein synthesis. The results suggest that at least a part of cytotoxicity and inhibition of cell-free protein synthesis caused by S. enteritidis is a property of the bacterial L-asparaginase.

Effect of O6-benzylguanine on nitrogen mustard-induced toxicity, apoptosis, and mutagenicity in Chinese hamster ovary cells

O6-Benzylguanine (BG) inactivates O6-alkylguanine-DNA alkyltransferase (AGT), resulting in an increase in the sensitivity of cells to the toxic effects of O6-alkylating agents. BG significantly enhances the cytotoxicity and decreases the mutagenicity of nitrogen mustards [i.e., phosphoramide mustard (PM), melphalan, and chlorambucil], a group of alkylating agents not known to produce O6-adducts in DNA. The enhancement is observed in cells irrespective of AGT activity. Exposure of Chinese hamster ovary cells to 100 microM BG results in enhancement in the cytotoxicity of PM (300 microM), chlorambucil (40 microM), and melphalan (10 microM) by 9-, 7-, and 18-fold, respectively. In contrast, mutation frequency after treatment with 300 microM PM is decreased from 259 mutants/10(6) cells to 22 mutants/10(6) cells when cells are pretreated with BG. The enhancement of toxicity of these bis-alkylating agents appears to involve cross-link formation, because neither cytotoxicity nor mutagenicity of a monoalkylating PM analogue is significantly altered when combined with BG. Enhanced cytotoxicity and decreased mutagenicity is concomitant with a dramatic increase in the number of cells undergoing apoptosis when BG is combined with PM, melphalan, or chlorambucil at 72-94 h after treatment. Cell cycle analysis demonstrates that BG alone or combined with nitrogen mustards arrests cells in G1 phase of the cell cycle. At 16 h after treatment, 11 and 57% of cells treated with PM alone or with BG plus PM are in G1 phase, respectively. Our data suggest that treatment with BG causes G1 arrest and drives noncycling cells treated with nitrogen mustards into apoptosis, thus protecting against mutagenic DNA damage introduced by nitrogen mustards.

Amine oxidase, spermine, and hyperthermia induce cytotoxicity in P-glycoprotein overexpressing multidrug resistant Chinese hamster ovary cells

Multidrug resistance is a major obstacle for the successful use of chemotherapy. The multidrug resistance phenotype is often attributed to overexpression of P-glycoprotein, which is an energy-dependent drug efflux pump. We investigated a new strategy to overcome multidrug resistance, using purified bovine serum amine oxidase, which generates two major toxic products from the polyamine spermine. The cytotoxicity of the aldehyde(s) and H2O2, produced by the enzymatic oxidation of micromolar concentrations of spermine, was evaluated in multidrug resistant Chinese hamster ovary cells CHRC5 with overexpression of P-glycoprotein, using a clonogenic cell survival assay. We examined the ability of hyperthermia (42 degrees C), and inhibition of cellular detoxification systems, to sensitize multidrug resistant cells to spermine oxidation products. Severe depletion of intracellular glutathione was achieved using L-buthionine sulfoximine and inhibition of glutathione S-transferase by ethacrynic acid. CH(R)C5 cells showed no resistance to the toxic oxidation products of spermine, relative to drug-sensitive AuxB1 cells. Exogenous catalase protected cells against cytotoxicity of H2O2, but spermine-derived aldehyde(s) still caused some cytotoxicity. Hyperthermia (42 degrees C) enhanced cytotoxicity of spermine oxidation products. Cytotoxic responses in CH(R)C5 cells were compared to the drug-sensitive cells, to determine whether there are differential responses. CH(R)C5 cells were more sensitive to the cytotoxic effect of spermine oxidation products under more extreme conditions (higher temperature, higher spermine concentration, and longer exposure time). Glutathione depletion or glutathione S-transferase inhibition also led to enhanced cytotoxicity of spermine oxidation products in CH(R)C5 and AuxB1 cells. Our findings suggest that hyperthermia, combined with toxic oxidation products generated from spermine and amine oxidase, could be useful for eliminating drug-sensitive and multidrug resistant cells.

Effects of ammonia on CHO cell growth, erythropoietin production, and glycosylation

The effect of ammonium chloride was determined on a culture of CHO cells transfected with the human erythropoietin (EPO) gene. Cell growth was inhibited above a culture concentration of 5 mM NH(4)Cl with an IC-50 determined to be 33 mM. The specific production of EPO increased with the addition of NH(4)Cl above 5 mM. At 10 mM NH(4)Cl, the final cell density after 4 days in culture was significantly lower but the final yield of EPO was significantly higher. This appeared to be due to continued protein production after cell growth had ceased. The metabolic effects of added NH(4)Cl included higher specific consumption rates of glucose and glutamine and an increased rate of production of alanine, glycine, and glutamate. The EPO analyzed from control cultures had a molecular weight range of 33-39 kDa and an isoelectric point range of 4.06-4.67. Seven distinct isoforms of the molecule were identified by two-dimensional electrophoresis. This molecular heterogeneity was ascribed to variable glycosylation. Complete enzymatic de-glycosylation resulted in a single molecular form with a molecular mass of 18 kDa. Addition of NH(4)Cl to the cultures caused a significant increase in the heterogeneity of the glycoforms as shown by an increased molecular weight and pI range. Enzymatic de-sialylation of the EPO from the ammonia-treated and control cultures resulted in identical electrophoretic patterns. This indicated that the effect of ammonia was in the reduction of terminal sialylation of the glycan structures which accounted for the increased pI. Selective removal of the N-glycan structures by PNGase F resulted in two bands identified as the O-glycan linked structure (19 kDa) and the completely de-glycosylated structure (18 kDa). The proportion of the O-linked glycan structure was reduced, and its pI increased in cultures to which ammonia was added. Thus, the glycosylation pattern altered by the presence of ammonia included a reduction in terminal sialylation of all the glycans and a reduction in the content of the O-linked glycan. The addition of a sialidase inhibitor to the cultures had no effect on the ammonia-induced increase in EPO heterogeneity. Also, the effect of ammonia on glycosylation could not be mimicked using the weak base chloroquine in our system.

Class A type II scavenger receptor mediates silica-induced apoptosis in Chinese hamster ovary cell line

Macrophage scavenger receptors are known to bind endotoxins, oxidized low-density lipoproteins (Ox-LDL), and other proteins with clustered negative charges. Recent evidence indicates some particulates may also bind to the scavenger receptor and initiate apoptosis. In this study, chinese hamster ovary (CHO) cells stabily transfected with the murine class A type II scavenger receptor (SR-A II) were exposed to crystalline silica to examine the role of this receptor in apoptosis. In a 24-h culture, silica (250 microg/ml) induced significant cell injury (necrosis and apoptosis) in transfected cells (MSR II) but not in the control cells (KA-7). This effect was specific to silica, as a control particle titanium dioxide had no cytotoxic effects on the MSR II cells at equal particle mass concentrations. Furthermore, silica-induced apoptosis in the MSR II cells could be eliminated by preincubating the cells with SR-A II antagonists: polyinosinic acid or maleylated bovine serum albumin. This study further supports the hypothesis that the SR-A II is directly involved with silica toxicity and that certain scavenger receptor ligands may have an important role in regulating macrophage apoptosis.

Opposing effects of protein kinase C delta and protein kinase B alpha on H(2)O(2)-induced apoptosis in CHO cells

H(2)O(2)-induced apoptosis was enhanced in the CHO cell line overproducing protein kinase C delta (PKCdelta) as judged by DNA fragmentation. In response to the H(2)O(2) treatment, PKCdelta was tyrosine phosphorylated and recovered as a constitutively active form, but its proteolytic fragment was not generated. In contrast, H(2)O(2)-induced apoptosis was suppressed in the CHO cell line overexpressing protein kinase B alpha (PKBalpha). Consistently, phosphorylation of BAD, a pro-apoptotic protein negatively regulated by PKBalpha, was sustained in the cells overproducing PKBalpha, but was not changed in the cells overexpressing PKCdelta. In the CHO cell line overproducing both PKCdelta and PKBalpha, H(2)O(2)-induced tyrosine phosphorylation of PKCdelta was suppressed, and DNA fragmentation was diminished concomitantly. These results suggest that PKCdelta contributes to H(2)O(2)-induced apoptosis by a mechanism independent of BAD and that PKCdelta is a target of PKB for the regulation of cell survival.

Multi-organ metastatic capability of Chinese hamster ovary cells revealed by green fluorescent protein (GFP) expression

Stable high-level green fluorescent protein (GFP)-expressing Chinese hamster ovary cells (CHO) were used to visualize the degree of metastatic behavior of this cell line in nude and SCID mice. A stable GFP high-expression CHO clone, selected in 1.5 microM methotrexate, was injected subcutaneously in nude and severe combined immunodeficient (SCID) mice and implanted orthotopically in the ovary of nude mice. CHO proved to be highly metastatic from both the subcutaneous and orthotopic sites as brightly visualized by GFP fluorescence. High-level GFP-expression allowed the visualization of metastatic tumor in fresh live host tissue in great detail. Metastases were visualized by GFP expression in the lung, pleural membrane, spleen, kidney, ovary, adrenal gland, and peritoneum after orthotopic implantation in nude mice. Metastases were visualized by GFP expression mainly in the lung, pleural membrane after subcutaneous implantation in nude mice. Metastases were visualized in the lung and pleural membrane, liver, kidney, and ovary after subcutaneous implantation in SCID mice. The construction of highly fluorescent stable GFP transfectants of CHO has revealed the multi-organ metastatic capability of CHO cells. CHO has such a high degree of malignancy that it is metastatic from both the orthotopic and subcutaneous transplant sites. This highly malignant GFP-expressing cell-line with multi-organ metastatic affinity should serve as a powerful tool to study tumor-host interaction.

Apoptosis in batch cultures of Chinese hamster ovary cells

One of the main problems in the culture of Chinese Hamster Ovary (CHO) cells continues to be the inability to maintain the viability of the cultures over an extended period of time. The rapid decline in viability at the end of the culture is exacerbated by the absence of serum. In trying to reduce the extent of death in these cultures, we first tried to determine the mode of death. We found that more than 80% of the cells in a standard serum-free batch culture of CHO cells in suspension died via apoptosis--as evidenced by condensed chromatin and the appearance of a characteristic DNA ladder. Furthermore, when protein synthesis was inhibited using cycloheximide, the cells underwent rapid apoptosis indicating that death proteins were present in greater abundance than survival proteins in our CHO cells. Cell lysate from CHO cells showed evidence of cysteine protease (caspase) activity. Caspases of the Interleukin-1-beta-Converting Enzyme (ICE) family, e.g., CPP32, Mch-1, etc., have been implicated in the apoptotic process. Surprisingly, a caspase peptide inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoro-methyl-ketone (z-VAD.fmk), was unable to substantially extend the life of a serum-free batch culture of CHO cells. In addition, z-VAD.fmk was only marginally able to extend viability in response to withdrawal of growth and survival factors, insulin and transferrin. In both these instances, z-VAD.fmk was able to prevent cleavage of caspase substrates, but not protect cells from death. However, we found that bcl-2 expression was able to significantly extend viabilities in CHO batch culture. Bcl-2 expression also substantially extended the viability of cultures in response to insulin and transferrin withdrawal. These results provide interesting insights into the pathways of death in a CHO cell.

A functional link between N-linked glycosylation and apoptosis in Chinese hamster ovary cells

Seven different Chinese hamster ovary (CHO) cell mutants, isolated in different ways and having biochemical defects that were expressed at 34 degrees C, were found to be temperature sensitive for growth at 40.5 degrees C. Six of the mutants had five different lesions in N-linked glycosylation; two mutants were in the same complementation group. The temperature-sensitive phenotype in three mutants appeared by cell fusion studies to be linked to the glycosylation phenotype. In some of the glycosylation mutants [B4-2-1 (Lec15.1), Lec9, Lec1, and Lec24], but not in all of them (MI5-4 and MI8-5), incubation at 40.5 degrees C induced apoptosis, as determined by appearance of DNA fragmentation. Tunicamycin (TM) also induced apoptosis in both parental and Lec9 cells. There was a direct correlation between inhibition of glycosylation by TM treatment and induction of apoptosis. Induction of apoptosis by TM was inhibited by cycloheximide. These studies suggest that specific alterations in N-linked glycosylation in CHO cells are endogenous inducers of apoptosis.

Cytopathic effects of Blastocystis hominis on Chinese hamster ovary (CHO) and adeno carcinoma HT29 cell cultures

Blastocystis hominis isolates from asymptomatic carriers and symptomatic patients were cultured in vitro, purified from the co-cultivated bacterial flora and tested for cytopathic effects on monolayers of Chinese Hamster Ovary (CHO) cells and Adeno Carcinoma HT29 cells. In the case of the CHO cells, living B. hominis cells and B. hominis cell lysates were able to cause significant cytopathic effects, which were dependent on the concentration of cells employed. Destruction of the cell monolayers was observed to the same extent with patient isolates derived from healthy or symptomatic B. hominis carriers. HT29 cells were less susceptible: B. hominis cells and cell lysates caused only minor effects which were not statistically significant. Culture filtrates of B. hominis exhibited cytopathic potential on CHO and HT29 cells; however, the control which consisted of filtrates from Robinson's cultures in which B. hominis failed to grow showed similar effects, too. Therefore the culture supernatants could not be proven to produce a specific cytopathic effect on CHO and HT29 cells.

Induction of apoptotic cell death by particulate lead chromate: differential effects of vitamins C and E on genotoxicity and survival

Certain hexavalent chromium compounds are documented human carcinogens. Exposure of cells to particulate forms of chromium results in cell-enhanced dissolution of particles in the extracellular microenvironment and chronic production of chromium oxyanions, which are taken up by the cell through an anion transport system and are genotoxic and clastogenic. It was previously shown that apoptosis is the mode of cell death of nearly all of the Chinese hamster ovary cells (CHO-AA8 cell line), which die after high-dose, short-term treatments with soluble sodium chromate. In this report the mode of cell killing by particulate lead chromate and of low-dose continuous treaments of soluble sodium chromate designed to mimic conditions of ionic chromate uptake after lead chromate exposure was examined. CHO-AA8 cells were treated for 24 hr with doses of sodium chromate or lead chromate which cause a 50% decrease in survival in colony-forming effeciency assays. Longer treatments (up to 72 hr) at the same doses did not decrease survival further than the 24-hr exposure. Morphological changes indicative of apoptosis, as well as internucleosomal DNA fragmentation, were detectable by 24 hr after treatment with lead chromate or soluble sodium chromate. All of the cells killed by treatments with lead chromate particles underwent apoptosis as the mode of cell death and this was accurately modeled in cell culture by continuous treatments with low-dose soluble sodium chromate. Exposure of cells to hexavalent chromium compounds causes a spectrum of DNA damage which can be selectively altered by pretreatment of cells with antioxidant vitamins prior to chromium exposure. Here we show that ascorbate and alpha-tocopherol markedly inhibited the chromosomal aberrations induced by both particulate and soluble chromate compounds, even though chromium adduct levels were not decreased by either vitamin pretreatment. Cell survival assays showed that ascorbate, but not alpha-tocopherol, protected cells from apoptosis induced by sodium chromate. The results differentiate chromium-induced apoptosis from both chromosomal damage and adduct levels and suggest that other lesions sensitive to ascorbate but not tocopherol are the proximal inducing signal for chromium-induced apoptosis.

In vitro cytotoxicity of guanylhydrazones (MGBG and PGBG) on cultured Chinese hamster ovary cells

Guanylhydrazones, methylglyoxal bis(guanylhydrazone) (MGBG) and a new compound, phenylglyoxal bis(guanylhydrazone) (PGBG), interfering with polyamine biosynthesis have considerable potential for the use as antiparasitic and antitumor agents. The effect of these drugs on the cellular viability of Chinese hamster ovary cells was examined by in vitro neutral red assay. The time exposure and metabolic influence was studied. These compounds have a dose- and time-dependent cytotoxicity. The IC50 values were of 597.22 micrograms/ml and 1.77 micrograms/ml for MGBG after 3 and 24 h of incubation, respectively, and 380.50 micrograms/ml for PGBG after 24 h of incubation. The PGBG treatment during 3 h had no cytotoxic effect when the concentrations were lower than 3000 micrograms/ml. With the cytotoxicity assay used, we observed that the presence of S9 in cultured medium did not influence the cytotoxicity of these compounds.

Apoptosis and 1-methyl-2-nitroimidazole toxicity in CHO cells

The time course and characteristics of the selective hypoxic cytotoxicity of the 2-nitroimidazole model compound 1-methyl-2-nitroimidazole (INO2) were analysed during prolonged time periods (up to 5 days post treatment). When control populations were seeded at the same cell density as drug-treated cells, they entered confluency at day 3 and underwent apoptosis at day 5, which appeared to be mediated by an autocrine mechanism. In subsequent studies of drug-treated cells, the seeding density of treated cells was adjusted to avoid this cell confluency effect. Treatment with a low INO2 concentration (2.5 mM) resulted in apoptotic DNA fragmentation (ladders), which was observed 4-5 days after an acute 6-h hypoxic drug exposure. In contrast, at a high INO2 concentration (40 mM) for 2 h, which was equitoxic to the low concentration, no characteristic DNA ladders were observed. Fluorescence microscopy revealed apoptotic bodies and pyknotic nuclei 5 days following hypoxic 2.5 mM INO2 exposure, whereas 40 mM INO2 hypoxic treatment produced cellular ghosts devoid of DNA 5 days after exposure, consistent with the DNA ladder results. However, characteristic apoptotic morphology was previously observed immediately after the acute hypoxic exposure of 40 mM INO2. Cell cycle analysis and DNA fragmentation as measured by the TdT assay suggested that dose-dependent differences in the apoptotic response occur post exposure after an equitoxic acute hypoxic exposure to either the low or the high INO2 concentration. This dose-dependent differential in response may be attributed to the degree of initial DNA damage as measured by the comet assay.

A new complementation group of mitomycin C-hypersensitive Chinese hamster cell mutants that closely resembles the phenotype of fanconi anemia cells

Three Mitomycin C (MMC)-hypersensitive mutants (CL-V1B, CL-V5B, and CL-V101B) were isolated from Chinese hamster V79B cells by the replica plating technique. In comparison to the parental cell line, CL-V1B, CL-V5B, and CL-V101B show about a 22-, 32-, and 13-fold increased sensitivity to MMC, respectively (judged by the D10). These mutants are also sensitive to other DNA cross-linking agents, such as 1,2,3,4-diepoxybutane (9-, 19-, and 12-fold, respectively) and cis-diamminedichloroplatinum(II) (17-, 12-, and 6-fold, respectively). CL-V5B and CL-V101B display an exclusive sensitivity to DNA cross-linking agents, whereas CL-V1B also shows an increased sensitivity to monofunctional alkylating agents, such as methyl methanesulfonate (3-fold) and ethyl methanesulfonate (2-fold), and UV254mm (2-fold). Approximately 2-3-fold higher levels of spontaneous chromosomal aberrations are found in these three mutants in comparison to wild-type V79B cells. At a MMC survival level of 80%, CL-V5B demonstrates a 16-fold higher level of MMC-induced chromosomal damage than V79B. Despite phenotypical heterogeneity within this group of mutants, hybrid clones derived after fusion remained MMC sensitive, indicating that these mutants belong to the same complementation group. To determine whether the mutants represent a new complementation group among other Chinese hamster cell mutants that also display hypersensitivity to MMC, CL-V1B cells were fused with mutants representing different complementation groups i.e., irs1, irs3, irs1SF, UV20, UV41, V-H4, and V-C8 cells. In all cases, the derived hybrids regained MMC sensitivity similar to wild-type cells, indicating that the CL-V1B mutant represents a new complementation group. The phenotype of CL-V1B, CL-V5B, and CL-V101B cells closely resembles the phenotype of Fanconi anemia cells, suggesting that these hamster mutants could be defective in a gene that is involved in this disorder.

K252a, KT5720, KT5926, and U98017 support paclitaxel (taxol)-dependent cells and synergize with paclitaxel

We have used paclitaxel-dependent Tax 2-4 cells to screen for compounds that have paclitaxel-like functional activity. The indolocarbazole serine/threonine kinase inhibitor K252a and analogues such as KT5926, KT5720, and K252b partially support the growth of the paclitaxel-dependent cells in the absence of paclitaxel. A novel kinase inhibitor of similar structure, U98017, supports the growth of the dependent cells to 48% of that seen with paclitaxel. Used in combination with paclitaxel, these compounds reduce the amount of paclitaxel required for maximum growth of the dependent cells. Isobologram analysis demonstrates that these compounds also act synergistically with paclitaxel to promote toxicity in wild-type Chinese hamster ovary cells. These selected indolocarbazoles may act at sites distinct from that of paclitaxel and may specifically inhibit kinases that contribute to the destabilization of microtubules. Other indolocarbazoles such as staurosporine and rebeccamycin do not support paclitaxel-dependent cell growth. Structurally unrelated serine/threonine kinase inhibitors such as H-9 and H-7 or tyrosine kinase inhibitors such as lavendustin do not support the growth of these cells. These results define a screen for functional paclitaxel analogues and suggest that it may be useful to investigate the possible synergy of selected indolocarbazoles and paclitaxel in vivo.

Hyperthermia can reduce cytotoxicity from etoposide without a corresponding reduction in the number of topoisomerase II-DNA cleavable complexes

The chemotherapeutic drug etoposide (VP-16) causes the equilibrium reaction between noncleavable and cleavable topoisomerase II-DNA complexes to shift in favor of the cleavabel complex [H. Zang, P. D'Arpa, and L.F. Liu, Cancer Cells (Cold Spring Harbor), 2:23-27, 1990]. Pulsed-field gel electrophoresis was used to study induction and removal of cleavable complexes in cells heated before, during, or after VP-16 treatment. Pulsed-field gel electrophoresis results were evaluated both as the fraction of activity (DNA) released from the plug and as the number of double-strand breaks (DSBs) calculated from molecular weight distributions; both end points led to the same conclusions. When cells were heated at 42 degrees C during treatment with VP-16 (12 micrograms/ml up to 60 min), a slight decrease in cleavable complexes (from 30 to 20 DSBs/100 megabase pairs) was detected immediately after treatment when compared with cells treated with the drug at 37 degree C. Furthermore, heating at 42 degrees C caused a slight decrease in drug cytotoxicity as measured by less than a 2-fold increase in clonogenic survival. When cells were heated for 10 min at 45.5 degrees C prior to or after treatment with the drug, there was a reduction (approximately 50%) immediately after treatment in the number of DSBs/100 megabase pairs compared with unheated cells. The rate of removal of cleavable complexes was decreased slightly by heat. After 120 min at 37 degrees C, the number of DSB/100 megabase pairs decreased to approximately 6 for both unheated cells and those heated prior to drug treatment and to approximately 8 for cells heated after drug treatment. In agreement with a low effect of heat on the number of cleavable complexes after drug treatment, there was no significant effect of this heating protocol on drug cytotoxicity. However, heating at 45.5 degrees C prior to drug treatment at 37 degrees C protected cells from drug cytotoxicity (e.g., increased survival after 12 micrograms/ml for 60 min by approximately 100-fold) despite the similarity in the induction and rate of removal of cleavable complexes when compared with nonheated cells. Thus, when cells are heated prior to administration of VP-16, drug cytotoxicity does not correlate with the number of cleavable complexes measured either immediately after treatment or 180 min later when approximately 75% of the initial number have been removed. Finally, since hyperthermia can actually decrease drug cytotoxicity, the use of hyperthermia as an adjuvant to chemotherapy involving topoisomerase II poisons, such as VP-16, should be approached with caution.

Overexpression of the RI alpha subunit of protein kinase A confers hypersensitivity to topoisomerase II inhibitors and 8-chloro-cyclic adenosine 3'5'-monophosphate in Chinese hamster ovary cells

We have shown that a mutant derivative of Chinese hamster ovary CHO-K1 cells, ADR-5, which shows hypersensitivity to topoisomerase II (topo II)-inhibitory drugs, is cross-sensitive to the site-selective cyclic AMP analogue 8-chloro-cyclic AMP. We tested the hypothesis that overexpression of the type I alpha regulatory subunit of protein kinase A may represent a common element conferring hypersensitivity to both topo II inhibitors and 8-chloro-cyclic AMP in ADR-5 cells. We have demonstrated that ADR-5 cells overexpress RI alpha protein, compared to parental CHO-K1 cells. Moreover, retroviral vector-mediated transfer of the RI alpha gene into CHO-K1 cells was able to confer a drug-hypersensitive phenotype similar to that exhibited by ADR-5 cells. Analysis of topo II protein levels and activity revealed no differences between parental and infected cells, suggesting that protein kinase A may be involved in the downstream processing of topo II-mediated events.

Gamma-glutamyltranspeptidase expression regulates the growth-inhibitory activity of the anti-tumor prodrug gamma-L-glutaminyl-4-hydroxy-3-iodobenzene

gamma-L-glutaminyl-4-hydroxy-3-iodobenzene (I-GHB), a novel iodinated analog of gamma-L-glutaminyl-4-hydroxybenzene (GHB), demonstrates greater anti-tumor activity in human and in murine melanoma cell lines. These phenolic amides are substrates for gamma-glutamyltranspeptidase (GGTP; E.C. 2.3.2.2), a cell-membrane-associated ecto-enzyme which is elevated in a number of tumor systems. We now present data to show that the growth-inhibitory activity of I-GHB and GHB may be mediated via GGTP-catalyzed reactions. The growth-inhibitory activity of I-GHB and GHB in pigmented B16-BL6 melanoma cells was blocked significantly by rabbit anti-rat GGTP polyclonal antibodies. The combination of L-serine and sodium borate, a specific transition-state inhibitor of GGTP, as well as acivicin, a glutamine antagonist and irreversible GGTP inhibitor, inhibited the killing of BL6 cells by GHB and I-GHB. To further define the role of GGTP expression in the regulation of phenolic amide cytotoxicity, GGTP-negative Chinese hamster ovary cells (CHO-K1) were transfected with a functional rat renal cDNA representing the full-length GGTP transcript. I-GHB and GHB were significantly more cytotoxic in GGTP cDNA transfected Chinese hamster ovary (CHO-K1-GGTP) cells than in non-transfected CHO-K1 cells. The combination of L-serine and sodium borate blocked the cytotoxic activity of these pro-drugs and also inhibited GGTP-catalyzed formation of polymerized products from these phenolic amides in intact BL6 melanoma and CHO-K1-GGTP cells. Furthermore, melanin formation from GHB was not observed in non-transfected CHO-K1 cells lacking GGTP expression. The combined data strongly suggest that GGTP-catalyzed hydrolysis of the anti-tumor pro-drugs I-GHB and GHB to 4-aminophenols mediates the expression of antitumor activity.

Malignancy-related characteristics of wild type and drug-resistant Chinese hamster ovary cells

Chinese hamster ovary (CHO) cell lines are a very popular cell model for a wide range of studies but are often misused experimentally as a substitute for normal cells. Although CHO was originally derived from normal tissue, the cell lines studied here, including the parental wild type, have many characteristics which indicate that they have undergone malignant transformation. Biological properties associated with malignancy were investigated in this study on wild type CHO cells and 4 drug resistant sublines, EOT, Col R-22, Pod R11-6, and Vin R-1. We report evidence of tumorigenicity in experimental animals, invasive capacity, in vivo and in vitro, protease release by 2 of the cell lines, features related to drug resistance in the mutant sublines, and numerical and structural chromosomal abnormalities.

Development of acute thermotolerance in L929 cells: lack of HSP28 synthesis and phosphorylation

We investigated the correlation between the development of acute thermotolerance and the phosphorylation, synthesis, and expression of the HSP28 family in murine L929 cells. Following heating at 43 degrees C for 30 min, thermotolerance developed rapidly in exponential-phase cells and reached its maximum 4-9 h after heat shock. Maximal thermal resistance was maintained for 24 h and then gradually decayed. However, heat-induced phosphorylation of HSP28 was not detected. Furthermore, HSP28 synthesis during incubation at 37 degrees C for 12 h following heat shock was not detected by [3H]-leucine labeling followed by two-dimensional polyacrylamide gel electrophoresis. In addition, Northern blots failed to demonstrate expression of the HSP28 gene. Unlike HSP28, the expression of constitutive and inducible HSP70 genes, along with the synthesis of their proteins, was observed during incubation at 37 degrees C after heat shock. These results demonstrate that HSP28 synthesis and its phosphorylation are not required to develop acute thermotolerance in L929 cells.