Biological time and the effects of hydroxyurea on DNA synthetic activity of bone marrow and tumor cells in mice bearing the Ehrlich ascites carcinoma

The objective of this experiment was to attempt to induce, with hydroxyurea (HU), significant quantitative differences in the level of DNA-synthetic activity (DNA-SA) between a neoplastic cell population (the Ehrlich ascites carcinoma or EAC) and bone marrow in the same animal. Mice bearing a 5-day-old EAC were standardized to and kept on an LD 12:12 cycle (light 0600-1800 hr). They were treated with 500 mg/kg HU at 0500 hr (23 hr after lights on, or HALO) or at 1700 hr (11 HALO). DNA-SA was determined by liquid scintillation counting of 3H-thymidine incorporation into chemically isolated DNA. DNA-SA in bone marrow and EAC cells was monitored over the next 60 hr with subgroups of ten mice each killed every 3 hr beginning 3 hr after treatment with HU. The circadian system of the host influenced the response of the bone marrow to HU; i.e., the response to HU administered at 0500 hr was different both qualitatively and quantitatively from that for HU given at 1700 hr. Comparisons of DNA-SA in bone marrow and EAC from the same animal revealed time points after treatment with HU when DNA-SA in the EAC was high, but DNA-SA in bone marrow was low. These differences in the level of DNA-SA between a tumor cell population and bone marrow should be of therapeutic value; i.e., executor doses of anti-DNA-SA drugs such as cytosine arabinoside could be given at that point in time after treatment with HU when DNA-SA in the tumor was high, but DNA-SA in the bone marrow was low.     

Some inhibitory effects of (?)-emetine on growth of Ehrlich ascites carcinoma

(−)-Emetine has little or no effect on O₂ consumption of Ehrlich ascites-cell suspensions or on the viability of transplanted Ehrlich ascites-tumour cells exposed to, or incubated with, the drug in vitro before inoculation into new-host mice. (−)-Emetine administered as a single injection to mice bearing Ehrlich ascites-tumour cells slows the growth rate of the tumour. The subcutaneous or intraperitoneal injection of the drug depresses protein and DNA synthesis of the tumour cells in vivo in a reversible manner. Mice bearing ascitic sarcoma 180 or Ehrlich ascites-tumour cells when given a course of treatment with (−)-emetine or (−)-O-methyltubulosine have a substantially lower tumour load than untreated controls and correspondingly longer survival times.     

Dose-dependent cytokinetic changes following 1-beta-D-arabinofuranosylcytosine and hydroxyurea in L1210 and S-180 in vivo.

DNA synthesis inhibition and recovery in L1210 and S-180 ascites tumors following 1-beta-D-arabinofuranosylcytosine (Ara-C) and hydroxyurea (HU) were measured autoradiographically as a basis for optimizing drug schedules. Tumor bearing mice, 10(6) cells day 0, were treated on day 4 with 20, 200 or 2000 mg/kg Ara-C or 50, 300 or 1800 mg/kg HU. At various intervals following drug, [3H]thymidine was administered i.p. and mice were killed 1 hr later. Tumor cells were analyzed for labeling index (LI) and grain count (GC) to determine the percentage of cells in S phase and the distribution of DNA synthesis rates among the labeled cells, respectively. Following each dose of HU, DNA synthesis was inhibited completely. Recovery of LI was rapid and approached control values by 6 hr. Following each dose of Ara-C, DNA synthesis was inhibited completely for at least 6 hr. Recovery of LI was first noted 6 hr following 20 mg/kg Ara-C and 9 hr following 200 mg/kg. Following both doses the LI reached 100% of the control value by 26 hr. GC analysis indicated that following Ara-C treatment, DNA synthesis was reinitiated first with cells with low GC from 6 to 12 hr followed by cells with increasing GC from 12 to 20 hr. The labeling intensity reached control values by 20 hr and an 'overshoot' occurred by 26 hr. These data suggest that the recovery of DNA synthesis rate is a gradual process. Survival data for mice receiving two doses of Ara-C indicated that the optimal interval for retreatment following the lower dose of Ara-C occurred by 6 hr as compared to 12--16 hr for the higher dose. These times coincided in both instances with recovery of LI to 33--50% of control values. Early recovery of LI may be the best method currently available for estimating the optimal time for retreatment with an S phase specific drug.     

Dose-Dependent Cytokinetic Changes Following 1-β-D-Arabinofuranosylcytosine and Hydroxyurea In L1210 and S-180 In Vivo

DNA synthesis inhibition and recovery in L1210 and S-180 ascites tumors following 1-β-D-arabinofuranosylcytosine (Ara-C) and hydroxyurea (HU) were measured autoradiographically as a basis for optimizing drug schedules. Tumor bearing mice, 10⁶ cells day O, were treated on day 4 with 20, 200 or 2000 mg/kg Ara-C or 50, 300 or 1800 mg/kg HU. At various intervals following drug, [³H]thymidine was administered i.p. and mice were killed 1 hr later. Tumor cells were analyzed for labeling index (LI) and grain count (GC) to determine the percentage of cells in S phase and the distribution of DNA synthesis rates among the labeled cells, respectively. Following each dose of HU, DNA synthesis was inhibited completely. Recovery of LI was rapid and approached control values by 6 hr. Following each dose of Ara-C, DNA synthesis was inhibited completely for at least 6 hr. Recovery of LI was first noted 6 hr following 20 mg/kg Ara-C and 9 hr following 200 mg/kg. Following both doses the LI reached 100% of the control value by 26 hr. GC analysis indicated that following Ara-C treatment, DNA synthesis was reinitiated first with cells with low GC from 6 to 12 hr followed by cells with increasing GC from 12 to 20 hr. the labeling intensity reached control values by 20 hr and an ‘overshoot’ occurred by 26 hr. These data suggest that the recovery of DNA synthesis rate is a gradual process. Survival data for mice receiving two doses of Ara-C indicated that the optimal interval for retreatment following the lower dose of Ara-C occurred by 6 hr as compared to 12–16 hr for the higher dose. These times coincided in both instances with recovery of LI to 33–50% of control values. Early recovery of LI may be the best method currently available for estimating the optimal time for retreatment with an S phase specific drug.     

Effect of the diabetic environment on the lipid metabolism of Ehrlich ascites cells

One strain of Ehrlich ascites cells lacking of insulin receptors, was grown into control and diabetic mice and cells harvested from diabetic mice reimplanted into control mice. The fatty acid composition of neutral and polar lipids was analyzed and several parameters calculated. Results showed that it is possible to produce similar changes in the lipid fatty acid unsaturation of Ehrlich cells to those observed in the liver of the diabetic bearing mice. These changes may be reverted by growing these cells into control mice. The diabetic environment also promoted a relative increase in the radioactivity from incorporated in vitro into neutral lipids of Ehrlich cells. This metabolic adjustment, probably due to an induction of the enzyme diglyceride acyltransferase, was completely reverted by transplanting these cells in control mice. The metabolic adaptation of Ehrlich ascites cells to the diabetic environment did not modify their biological behaviour as pointed out by their mean generation time. The evidence presented here, showing relatively normal growth of Ehrlich cells in association with changes in the lipid fatty acid pattern and in lipid metabolism, indicates the adaptation of these cells, lacking of insulin receptors, to the environment provided by the diabetic mice.     

APOPTOSIS OF EHRLICH MOUSE ASCITES CELLS INDUCED BY LONG-TERM EXPOSURE OF WEAK ELECTROMAGNETIC FIELDS IN VIVO

To study the possibility of apoptosis of tumor cells induced by weak electromagnetic fields (EMFs) in vivo, mice were inoculated with Ehrlich ascites cells and exposed to a long-term electromagnetic field (1 mT, 700 KHz). During the treatment, growth curves of mice were measured and compared between exposed and sham-exposed mice. The results show that the growth curves of healthy controls agree well with the ideal curve of logistic growth, but the growth curves of cancer mice deviate from the ideal curve. There is no difference in growth curves between exposed, and sham-exposed healthy mice, and they both agree with the ideal curve. However, a notable difference in growth curves between exposed and sham-exposed cancer mice was obtained. Moreover, the curves of sham-exposed mice deviate even more than those of the exposed mice; in other words, the growth curves of Ehrlich ascites mice deviate from the ideal curve of healthy mice but are shifted toward it by the EMF treatments. After the treatment, apoptosis of Ehrlich ascites cells from inoculated mice was analyzed by several methods, including flow cytometry, fluorescence microscopy, and DNA gel electrophoresis. Statistical analysis from flow cytometry shows that the apoptotic ratio of cells from exposed Ehrlich ascites mice was significantly higher than that from sham-exposed treated mice. Microscopic observation of Ehrlich ascites cells stained with acridine orange (AO) and propidium iodide (PI) showed typical apoptotic changes in exposed animals whose cell nuclei were highly condensed or fragmented and uniformly stained green by the AO, whereas cell nuclei from sham-exposed mice were stained green and showed a fine reticular pattern. Agarose gel electrophoresis of DNA from exposed mice showed that the chromatin DNA exhibited ladders, a characteristic feature of internucleosomal degradation of DNA by EMF treatments. For interactions between external electromagnetic fields and DNA, the mechanism of apoptosis of tumor cells induced by weak EMFs is discussed.     

CELL PROLIFERATION IN NEWLY TRANSPLANTED EHRLICH ASCITES TUMOR CELLS

• 1 Ehrlich ascites tumor cells collected from donor mice on the 5th day after inoculation were injected into the peritoneal cavity of new recipient mice.
• 2 Cell cycle times were drastically shortened by transplantation, for instance, the length of the cell cycle from 47 to 21.5 hr, and the duration of S from 26.5 to 16.5 hr.
• 3 Transplantation also caused a transient delay of cells in G₂ followed by a rapid acceleration and produced an immediate increase in the number of cells in DNA synthesis by about 5–8%.

     

Selective inhibition of thymidine transport at low doses of the alkylating agents triethyleneiminobenzoquinone (Trenimon)

The alkylating antitumor agent triethyleneiminobenzoquinone (Trenimon) causes a rapid decrease in the incorporation of labeled thymidine into the DNA of Yoshida or Ehrlich ascites tumor cells. The effect is expressed 4 h after administration of 6 × 10⁻⁸ moles/kg of the drug to mice bearing Yoshida ascites tumors or of 6 × 10⁻⁷ moles/kg to Ehrlich ascites tumor-bearing animals, respectively. The reduced incorporation of labeled thymidine which is observed under these conditions is not due to an inhibition of DNA synthesis. DNA synthesis was measured by an isotope dilution assay after pulse-labeling with ³H-thymidine and by monitoring the increase in the total amount of DNA of the cell populations. The data demonstrate that DNA synthesis is not affected during the first 8 h after exposure to the drug. This conclusion is supported by cell kinetic measurements which indicate that the alkylating agent does not interfere with the progression of cells into the S phase, but exerts a block at the G 2 stage of the cell cycle. The reduced incorporation of thymidine into DNA is explained by a decreased transport of the nucleoside into the cells.     

Absence of anthracycline-induced degradation of nuclear DNA in Ehrlich ascites tumour cells

The in vivo effects of anthracycline antibiotics on the integrity of Ehrlich ascites tumour cell DNA have been studied by sedimentation analysis of nuclear structures containing superhelical DNA in neutral sucrose gradients. These fast-sedimenting protein-DNA complexes may be released by gently lysing cells in solution containing non-ionic detergents and high NaCl concentrations (1.95 M). The supercoiled structure of DNA in these protein-DNA complexes is suggested by the characteristic sedimentation in the presence of intercalating agents. Apparently, no DNA damage could be detected in Ehrlich cells from 7-day-old tumours within 3 h after various doses of daunomycin (0.5–10 mg/kg of body wt.) were administered i.p. to mice. Sedimentation anomalies could not be observed even 15 or 30 h after administration of therapeutic doses of daunomycin or adriamycin. In contrast, at 30 min after administration to mice, therapeutic doses of bleomycin (2–8 mg/kg) caused extensive fragmentation of tumour cell DNA, which could be monitored as slowly sedimenting DNA structures (compared with the control). Similarly, DNA damage could be induced by procarbazine at therapeutic doses. Exposure to bleomycin or procarbazine abolished the characteristic biphasic response to ethidium bromide. The absence of anthra-cycline-induced degradation of Ehrlich ascites tumour cell DNA is apparently in contrast with the DNA damage observed in L1210 tumour cells. These observations suggest that DNA damage is not a necessary condition for antitumour activity.     

Phospholipid metabolism in Ehrlich ascites tumor cells. I. Turnover rate of phosphatidylinositol.

1. Radioactive precursors, 32 PI, [1-14C]glycerol, and [1-14C]acetate, were individually injected into the peritoneal cavity of mice bearing Ehrlich ascites tumor, and the rates of incorporation into phospholipid fraction of Ehrlich ascites tumor cells were estimated. Although no distinct difference in specific activities was observed between phosphatidylinositol and other phospholipid classes as regards the incorporation of [1-14C]acetate of [1-14C]glycerol, a higher rate of incorporation of 32Pi into phosphatidylinositol was observed. The specific activity of phosphatidylinositol reached more than ten times that of phosphatidylcholine in the first hour. 2. The radioactivities incorporated into the phospholipids of Ehrlich ascites tumor cells and liver were estimated after simultaneous injection 32Pi and [2-3H]inositol. The incorporation of 32Pi into phosphatidylinositol of liver was similar in specific activity to those of other phospholipids. The ratio (3H/32Pi) of phosphatidylinositol only slightly in the ascites tumor cells, while an appreciable decrease of the ratio was observed in the liver during the first 3 hr. 3. These results suggest that phosphatidylinositol synthesis through pathways other than de novo synthesis is rapid in ascites tumor cells.     

Mitoxantrone toxicity on Ehrlich ascites tumour cells: inhibition of the transplasma membrane redox activity

This study focused on the potent cytotoxic effect that mitoxantrone produces on Ehrlich ascites tumour cells. Host mice treated with mitoxantrone showed a life span three times higher than control non-treated host mice. Mitoxantrone also showed a potent cytotoxic effect on Ehrlich cells incubated in vitro for only a few hours. Studies on the effect of mitoxantrone on a plasma membrane redox system showed that mitoxantrone inhibits this activity, which is apparently related to cell proliferation.     

Cell cycle phase-dependent induction of ornithine decarboxylase-antizyme

The activities of ornithine decarboxylase (ODC) and ODC inhibitory protein (ODC-antizyme) were studied in Ehrlich ascites tumor cells, separated according to their position in the cell cycle by centrifugal elutriation. Release and/or synthesis of ODC-antizyme was induced by putrescine treatment. Each mouse received an intraperitoneal injection of 25 mumoles of putrescine at 0, 1, 2, and 3 hr after tumor transplantation. Tumor cells obtained from putrescine-treated and control mice at 4 hr after transplantation were separated into fractions representing all phases of the cell cycle. The cell cycle distribution of the tumor cells in each fraction was determined by flow cytometry. In control tumor cells the ODC activity exhibited two maxima; in late-G1/early-S and in late-S/G2. A marked decrease in ODC activity was observed in mid-S phase. This decrease coincided with maximum ODC-antizyme activity (revealed by putrescine treatment), suggesting that ODC-antizyme is involved in the regulation of ODC activity during the cell cycle.     

Effect of thioacetamide on the incorporation of [3H]-thymidine into DNA of 13 tissues and on the mitotic index of the corneal epithelium of BD2F1 in male mice while taking into consideration circadian variation

An investigation was done to assess the effect of a single intraperitoneal (ip) injection of thioacetamide on the incorporation of [3H]TdR into DNA of 13 different tissues and on the mitotic index of the corneal epithelium of mice. Seven-week-old CD2F1 mice, who had been standardized to 12 hours (hr) of light alternating with 12 hr of darkness, and fed ad libitum were used. The experimental design took into consideration the circadian variation that characterizes cell proliferation in all of the tissues studied. This was done by killing subgroups of seven animals every 6 hr for 96 hr. Thirty minutes prior to killing all mice were injected ip with 25 mu Ci of [3H]-thymidine and its incorporation into DNA was determined. The tissues of all thioacetamide and saline treated mice showed marked circadian variation in DNA synthesis. Thioacetamide treatment brought about significant (P less than 0.05) stimulation of DNA synthesis in the liver and kidney thus confirming, but extending an earlier finding. Moreover, the data showed for the first time that DNA synthesis in the bone marrow and spleen and colon were markedly statistically significantly stimulated at specific times after treatment. Synthesis of DNA in the thymus, lung, testes, tongue, esophagus, duodenum, rectum and the mitotic index in the corneal epithelium were not statistically significantly altered by thioacetamide treatment. A preliminary study also was carried out to explore what effect multiple treatment with epidermal growth factor (EGF) had on DNA synthesis in thioacetamide treated mice. Mice were killed 36 hr after thioacetamide treatment, but were treated with EGF which began 15 hr after the thioacetamide was administered and this was repeated at 18, 21 and 24 hr (50 micrograms/mouse/treatment). Under the conditions of this study EGF significantly (P less than 0.05) depressed DNA synthesis 76% in the liver, 64% in the thymus, 22% in the spleen, 30% in the duodenum and 24% in the esophagus. A histological analysis of the livers of four EGF treated and four non-EGF treated mice was done, but no consistent differences in terms of necrosis, inflammation or regeneration were observed between the two groups.     

Effects of cycloheximide on virus RNA replication in an inducible line of polyoma-transformed rat cells.

In this article, we describe two distinct effects of cycloheximide (CH), a potent inhibitior of protein synthesis, on the replication of polyoma virus (PV) DNA in an inducible line of PV-transformed rat cells (LPT cells). Exposure of LPT cells to CH causes up to an 8 fold increase in the cellular concentration of PV DNA determined by molecular hybridization. The same treatment inhibits cell division and chromosomal DNA replication. However, the amount of chromosomal DNA per cell is not affected by the drug. In LPT cells treated with mitomycin C (MMC), PV DNA replication is enhanced after 7 hr. During the period extending from 7 hr to 24 hr, the concentration of virus DNA increases at least 100 fold. CH added to the cells 0-7 hr after treatment with MMC inhibits the replication of PV DNA by 90-100%. The inhibition is less effective in cells exposed to CH from 7 hr and on. The inhibitory effect is reversible: virus DNA synthesis is resumed after removal of CH from the growth medium. Thus CH acts as an inducer of virus DNA synthesis in cells whose resident viral genome is repressed, but inhibits the autonomous replication of the activated genome following induction with MMC.     

Chalone-like inhibition of Ehrlich ascites cell proliferation in vitro by an ultrafiltrate obtained from the ascitic fluid.

An aqueous ultrafiltrate (10 000-50 000 dalton) prepared from the cell-free ascitic fluid of mice bearing Ehrlich ascites tumour (EAT) in the plateau phase of growth (12-16 days after transplantation) was investigated with regard to its inhibitory effects on the proliferation of EAT cells in a 24-hr suspension culture. The following results were obtained: (1) The in vitro proliferation of cells obtained from the plateau phase of in vivo growth was reversibly inhibited. (2) The dose-response curves show a plateau with a maximum inhibition of about 50%, which suggests that not all cells can be affected. (3) Young cells (4-6 days after transplantation) were not inhibited. (4) Preincubation of plateau phase cells in the culture medium before treatment abolishes the inhibitory effect of the ultrafiltrate. This effect of preincubation is dependent on time and serum concentration. It provides the possibility to differentiate between true "chalone-like" and cytotoxic effects. (5) the inhibitory properties of the ultrafiltrate are destroyed by heating or trypsin treatment. (6) Extracts prepared in the same way from ascitic fluid of mice bearing lymphocytic leukemia L1210 do not inhibit the proliferation of EAT cells. Corresponding extracts from ascitic fluid of mice bearing myelocytic leukemia YM were found to be inhibitory; however, the inhibitory effect was also found on preincubated cells and is therefore considered to be due to an unspecific cytotoxicity. In conclusion, evidence was obtained for a factor from the ascitic fluid of mice bearing EAT, which prevents EAT cells from entering the proliferating state.     

Butachlor is cytotoxic and clastogenic and induces apoptosis in mammalian cells

The ability of butachlor to induce cytotoxicity, clastogenicity and DNA damage was assessed using Chinese hamster ovary cells (CHO), Swiss mouse embryo fibroblasts (MEF) and human peripheral blood lymphocytes. A dose and time dependent loss of viability was evident upon treatment of CHO cells with butachlor. Cell killing to an extent of 50% was observed when cells were treated with 16.2 micrograms/ml of butachlor for 24 hr or with 11.5 micrograms/ml for 48 hr. The herbicide induced micronuclei significantly in cultured lymphocytes at 24 and 48 hr of treatment suggesting that it is clastogenic. To understand the mechanism of cell death caused by butachlor, its effect on DNA strand breaks was studied in MEF. A concomitant decrease in cell viability was observed with increase in DNA strand breaks. Agarose gel electrophoresis of DNA from herbicide treated CHO cells and cytochemical staining indicate the induction of apoptosis by butachlor.     

Increases in mRNA levels of glucose transporters types 1 and 3 in Ehrlich ascites tumor cells during tumor development

A common feature of many tumors is an increase in glucose catabolism during tumor growth. We studied the mechanism of this phenomenon by using Ehrlich ascites tumor bearing mice as the animal model. We found that Ehrlich ascites tumor cells possess only glucose transporter 1 (GLUT1) and GLUT3 but no GLUT2, GLUT4, or GLUT5. The mRNA levels of GLUT1 and GLUT3 increased progressively in the tumour during development; however, there were no changes observable in mRNA levels of glucose transporters of all types in brain, liver, and heart of the host mice. These findings suggest that Ehrlich ascites tumor augments its glucose transport mechanism relative to other tissues in response to its unique growth needs. J. Cell. Biochem. 67:131–135, 1997. © 1997 Wiley-Liss, Inc.     

Reaction of 3-ethoxy-2-oxobutyraldehyde bis(thiosemicarbazonato) Cu(II) with Ehrlich cells. Binding of copper to metallothionein and its relationship to zinc metabolism and cell proliferation

The copper complex of 3-ethoxy-2-oxobutyraldehyde bis(thiosemicarbazone) or CuKTS is reduced and dissociated upon reaction with Ehrlich cells. Titration of the cells with the complex leads to the specific binding of copper to metallothionein with 1 to 1 displacement of its complement of zinc. Under conditions of complete titration of metallothionein, 1.25-2.5 nmol CuKTS/10(7) cells, cellular DNA synthesis is rapidly inhibited but no long term effects on cell proliferation are observed. The kinetics of redistribution of Cu and Zn in Ehrlich cells in culture and in animals were studied after pulse reaction of CuKTS with cells. After exposure of cells to the noncytotoxic concentration of 2.5 nmol of CuKTS/10(7) cells, nonmetallothionein bound copper is lost rapidly from the cells, after which copper in metallothionein decays. New zinc metallothionein is made as soon as exposed cells are placed in culture. New synthesis stops when the level of zinc in metallothionein reaches control levels. A second pulse treatment of cells with CuKTS to displace zinc from metallothionein again stimulates new synthesis of the protein to restore its normal concentration. The kinetics of metal metabolism in Ehrlich cells exposed to 5.5 nmol of CuKTS/10(7) cells, which inhibits cell proliferation, are qualitatively similar except there is a pronounced lag before new zinc metallothionein is synthesized. The Ehrlich ascites tumor in mice responds to CuKTS similarly to cells in culture. It is also shown that cultured Ehrlich cells do not make extra zinc metallothionein in the presence of high levels of ZnCl2, and fail to accumulate copper in the presence of large concentrations of CuCl2.     

艾氏腹水癌患鼠腹水中一种高分子量DNA结合蛋白的分离

 本文利用免疫吸收法和免疫亲和层析法,从艾氏腹水癌患鼠腹水DNA结合蛋白中,分离得到了一种高分子量DNA结合蛋白。在免疫双扩散反应中,它与抗艾氏腹水癌患鼠血清DNA结合蛋白的兎抗血清反应形成一条沉淀线,但与正常小鼠血清DNA结合蛋白的兎抗血清不形成沉淀线。该DNA结合蛋白样品用2-巯基乙醇还原后,经SDC-PAGE分析,测得其分子量约为41000。