Prostaglandin biosynthetic capacity of hepatomas with different growth rates

1. Prostaglandin synthesis from [14C]arachidonate by microsomal fractions was measured with preparations from rat liver and from hepatomas of different growth rates. The highest rates of synthesis were observed with microsomal preparations from the rapidly growing hepatoma HTC. 2. Assay of endogenous levels of prostaglandins E2, F2 alpha and thromboxane B2 also indicated high levels in solid tumors of the HTC line. 3. With HTC cells in culture it was necessary to incubate in the absence of serum in order to detect prostaglandin synthesis. 4. The data indicated that, while prostaglandin synthesis was elevated in HTC cells, the synthesis of prostaglandins by a series of hepatomas was not closely correlated with the growth rates of the tumors.

pH-related effects of sodium cyanate on macromolecular synthesis and tumor cell division

In past work, the selective effects of sodium cyanate on macromolecular synthesis in tumors have not been seen with cells in culture. We have explored the possibility that differences in the response of tumor cells to cyanate in vivo and in vitro may be related to the pH in the environment to which cells are exposed. When rat hepatoma (HTC) cells were incubated with sodium cyanate (0.25 mg/ml), there was a greater inhibition of precursor incorporation into RNA and DNA with a decrease in pH from 7.4 to 6.6. At pH 7.4 there was no significant effect of sodium cyanate on the incorporation of [3H]leucine into protein of rat hepatocytes and HTC cells, but at pH 6.6 there were decreases of 50% or greater. The time of response and the reversibility of the inhibitory effects of sodium cyanate were not those anticipated from carbamoylation of amino groups but were compatible with modification of sulfhydryl groups. The uptake of [14C]sodium cyanate in HTC cells and human colon cancer (HT29) cells was greater at pH 6.6 than at 7.4. Over a period of 4 days there was a slower rate of cell division by HTC and HT29 at pH 6.6 than at pH 7.4. The addition of sodium cyanate caused a further reduction in the rate of proliferation, and at a concentration of 0.25 mg sodium cyanate/ml there were decreases in cell numbers. The data suggested that a lower interstitial pH in tumors than normal tissues would result in greater sensitivity to inhibitory effects of sodium cyanate on macromolecular synthesis.

Selective modulation of nucleotide levels in rat liver and hepatomas by high-orotate or arginine-deficient diets and by carbamoylating agents

Transplanted Morris hepatomas in Buffalo-strain rats were found to be resistant to the changes in ribonucleotide levels in rat liver caused by a high-orotate diet or an arginine-deficient diet. The increase in UTP levels and decrease in ATP levels seen in the livers of rats on a 1%-orotate diet were less marked in the livers of BUB- and DBA-strain mice on this diet. Although the changes were less than in rat liver, there was a 2-3-fold increase in UTP concentration in the livers of mice on the high-orotate diet. However, there was a similar response in nucleotide levels in the two species when the animals were maintained on an arginine-deficient diet, and there was a greater than 10-fold increase in the UTP level in the livers of both rats and mice. These diets had much less effect on the levels of deoxyribonucleotides than of ribonucleotides. In contrast to the insensitivity of hepatomas to dietary modulation of nucleotide levels, treatment of hepatoma-bearing rats with carbamoylating agents (sodium cyanate and 2-chloroethyl isocyanate) caused decreases in the levels of nucleotides in the tumors which were generally greater than in host livers. For example, 2-chloroethyl isocyanate depressed ATP levels in the Morris hepatomas 5123C and 20 under conditions in which there was no significant effect on host liver ATP. The data revealed selective modulation of nucleotide levels in normal and neoplastic liver which may be achieved by either dietary modification or drug treatment.

Chromatin solubilization in rapidly growing hepatomas

The presence of substantial amounts of DNA in the cytosol fractions prepared from rapidly growing transplanted rat hepatomas was confirmed. Agarose gel electrophoresis of this DNA from the Morris hepatomas 7288CTC, 7777, and 7800 suggested that it corresponds primarily to nucleosome monomers with smaller amounts of nucleosome dimers and trimers. Despite the evidence for solubilization of chromatin in rapidly growing hepatomas the potential DNA endonuclease activity was less in nuclei from these tumors than in nuclei from more slowly growing hepatomas or host livers. It was suggested that focal necrosis in rapidly growing solid tumors may be associated with the influx of divalent cations and the activation of DNA endonuclease activity.

Action of carbamoylating agents on the uptake of metabolites in hepatomas and liver

The effects of 2-chloroethylisocyanate, ethylisocyanate and sodium cyanate on the uptake of isotope-labeled thymidine, leucine and H2O were compared in rat liver and hepatomas. The data suggested that carbamoylating agents may have a common property of inhibiting uptake of compounds in hepatomas under conditions in which there is a smaller effect or no action in the liver of tumor-bearing rats. The distinction between tissues may have been mediated, in part, through effects on tumor circulation and was less apparent when isolated cells were studied in vitro. Preferential inhibitory effects of carbamoylating agents on the uptake of leucine and H2O were also observed with a murine hepatoma, but they were not as great as with rat hepatomas.

Effects of carbamoylation with alkyl isocyanates on the assay of proteins by dye binding

The effect of carbamoylation with alkyl isocyanate was used both to monitor the stability of the isocyanates and to study the influence of charge modification on protein assay. Carbamoylation of poly (L-lysine) with methyl isocyanate, ethyl isocyanate and 2-chloroethyl isocyanate was observed to decrease binding of methyl orange. The data emphasized the lability of alkyl isocyanates and indicated the importance of preparing aqueous solutions at low temperatures for studies on protein carbamoylation. After carbamoylation of several proteins, there was decreased metachromasia on binding to Coomassie Blue G. Poly (L-lysine) and H1 histone showed anomalous behavior in that with low concentrations of Coomassie Blue G the metachromasia was increased by carbamoylation, but at high concentrations of the dye the metachromasia was decreased by carbamoylation. In contrast to some reports in the literature, the data indicated that there is not always a simple relationship between the positive charge on a protein and the interaction with anionic dyes.

Effects of carbamoylating agents on tumor metabolism

Carbamoylation of macromolecules occurs by the displacement of hydrogen on several groups, but the most stable addition at neutral pH is on amino groups. This reaction occurs predominantly with proteins and results from the administration in vivo of inorganic cyanate or organic isocyanates. The latter act more rapidly, but also are more rapidly hydrolyzed in aqueous solution. This instability has been a factor limiting study of the pharmacological properties of organic isocyanates. However, organic isocyanates are released from some nitrosoureas of value in cancer therapy such as 1,3-bis(2-chlorethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU). The carbamoylating activities of BCNU and CCNU are generally considered less significant than their alkylating activity in the action of these drugs on tumors, but carbamoylation may serve to inhibit DNA repair. There is evidence that carbamoylating agents can exert selective inhibitory effects on metabolite uptake and macromolecular synthesis in neoplastic tissues. Such selectivity is much more notable in vivo than in vitro. In the case of cyanate, the selectivity in vivo has been variously attributed to a requirement for metabolic activation, to selective effects on circulation in solid tumors, and to diminished pH in tumors. It is the distinction between such factors and the identification of critical cellular targets which provide major challenges in present studies on the effects of carbamoylating agents on tumor metabolism.

Orotate uptake and metabolism in normal and neoplastic tissues

The uptake of [3H]orotate was greater in mouse liver than in hepatoma but the difference was less marked than in the rat. Of the tissues examined, a high uptake of [3H]orotate was restricted to the liver and kidney in rat, mouse and guinea-pig. We confirmed that a high orotate diet greatly increases the ratio of UTP to ATP concentration in rat liver but we observed that there is little change of this nucleotide ratio in kidney. Evidence was obtained for a different pattern of orotate metabolism in rat liver and kidney.

Effects of sodium cyanate in mice bearing B16 melanoma

Sodium cyanate injected IP at a dose level of 200 or 250 mg/kg caused a 90% or greater inhibition of the incorporation of [3H]thymidine into DNA of B16 melanoma transplanted SC in mice. Despite the inhibitory effect of sodium cyanate on precursor incorporation into DNA, no significant effect on host survival was observed when sodium cyanate was administered as a single agent in the diet, in drinking water, or by IP injection to mice that had received IP transplants of B16 melanoma. The action of melphalan and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in prolonging the survival time of melanoma-bearing mice was not enhanced by combined treatment with sodium cyanate. However, combined injections of sodium cyanate and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) increased the survival of tumor-bearing mice significantly more than injections of BCNU alone at a lower dose than the maximum tolerated one. These data and other studies suggest that B16 melanoma may be less responsive to the action of sodium cyanate than are murine leukemic cells or rat hepatomas.

Influence of carbamoylation on some analytical properties of basic polypeptides

The effect of carbamoylation on the assay or identification of histones and polylysine was investigated. Incubation with sodium cyanate decreased the positive charge on these polypeptides as judged by changes in the binding of methyl orange or the electrophoretic mobility. Histones in chromatin appeared less accessible to carbamoylation than isolated histones. Carbamoylation of proteins under conditions in which there was little or no effect on the Lowry procedure could affect their assay by methods utilizing metachromasia with Coomassie Blue G. The Bradford assay has low sensitivity for Hl histone and polylysine but this can be increased by preincubation with sodium cyanate. More extensive carbamoylation of polylysine caused decreased sensitivity which was the only response seen with core nucleosomal histones and bovine serum albumin when preincubated with sodium cyanate. It was concluded that the sensitivity for Hl histone and polylysine in assays dependent on metachromasia with Coomassie Blue G may be changed by factors which decrease the positive charge on these polypeptides.

Plasma protein alterations in AIDS and hemophilia A

Plasma proteins of patients with AIDS, ARC, hemophilia A, and some viral infections were studied using various electrophoretic techniques, and compared to healthy control subjects. On isoelectric focusing (IEF) gels the most prominent and consistent finding was a marked increase in a basic protein band (AABP) at pI approximately equal to 9.0 in plasma samples derived from AIDS and hemophilia A patients. Using SDS gels, we noted an increased amount of protein in the 90 KD region in AIDS patients as compared to control subjects. On two dimensional gels (2D gels) basic protein(s) with pI congruent to 8.1-9.0 and molecular weight of approximately 90 KD were noted to be increased. In addition, a basic protein of 27 KD along with two acidic proteins in the low molecular weight region were also elevated in AIDS plasma. Although a limited number of samples were analyzed, it seems probable that a number of proteins are altered in AIDS plasma. AABP stained positive with periodic acid Schiff (PAS) reagent, indicating that it is a glycoprotein. This protein did not bind to an anti-IgG sepharose column, suggesting that it is not an immunoglobulin. The purified protein also did not react with antibody to fibrinogen and hemoglobin beta-chain. There are many changes in the plasma protein pattern of AIDS and hemophilia A patients as compared to normal controls.

Disparity in the effects of two N-methyl nicotinamides on poly(ADP-ribose) synthetase and macromolecular synthesis in hepatomas

The inhibitory effects of nicotinamide analogs on the activity of poly(ADP-ribose)) synthetase were compared to effects on precursor incorporation into macromolecules in three lines of hepatoma cells (Morris hepatomas 5123C, 7777 and HTC). N'-methylnicotinamide was a less effective inhibitor of poly (ADP-ribose) synthetase than was 1-methylnicotinamide while both these compounds had smaller inhibitory effects on the enzyme than were seen with nicotinamide or 3-aminobenzamide. On the other hand, the incorporation of [3H]thymidine into DNA and of [3H]uridine into RNA were inhibited by N'-methylnicotinamide in the concentration range 2-20 mM but not by 1-methylnicotinamide. Under the conditions examined there were no significant effects on the incorporation of [14C]lysine and [3H]leucine in hepatoma cells. The data indicated that the inhibitory effect of N'-methylnicotinamide on nucleic acid synthesis may be unrelated to action on poly (ADP-ribose) synthetase.

Effects of nicotinamide and structural analogs on DNA synthesis and cellular replication of rat hepatoma cells

The effects of nicotinamide and structural analogs on DNA synthesis were studied in rat hepatoma (HTC) cells. Inhibitory effects of these compounds were observed on DNA synthesis as judged by the incorporation of [3H]-thymidine into DNA. Evidence for a marked effect on DNA integrity after preincubation with 1 mM methyl methanesulfonate was provided by a fluorometric technique with ethidium bromide. There was only a small or insignificant enhancement of this effect when hepatoma cells were incubated with nicotinamide. At concentrations of 2-20 mM, 3-aminobenzamide was observed to cause greater effects than nicotinamide on DNA synthesis and integrity and on cellular proliferation in HTC cells. Comparison of the effects of nicotinamide and 3-aminobenzamide with those of N'-methylnicotinamide suggested that some of the effects on DNA synthesis may not be mediated through inhibition of poly(ADP-ribose) synthetase. Inhibition of HTC cell proliferation was observed at a concentration of 3-aminobenzamide, 2 mM, which has been reported to be nontoxic for other cell types.

Factors affecting the assay of histone H1 and polylysine by binding of Coomassie blue G

Although a mixture of calf thymus histones or the H2B and H4 fractions gave values in the Bradford assay that were similar to those for bovine serum albumin, low values were obtained with histone H1 and polylysine. The assay was found to be more sensitive for histone H1 and polylysine if the phosphoric acid concentration in the reagent was decreased or the polypeptide solutions contained low concentrations of nonionic detergents. Substitution of perchloric acid or hydrochloric acid for phosphoric acid and alcohol in the Coomassie blue G reagent provided an assay that was similar in sensitivity for histone H1 and a total histone mixture. It was suggested that the degree of metachromasia with Coomassie blue G may serve as a probe of conformational changes in histone H1.

DNA in cytosol fractions obtained by differential centrifugation of homogenates of rapidly growing liver tumors

Preliminary work revealed that the cytosol fractions obtained by differential centrifugation of homogenates of the rapidly growing Morris hepatomas 7777 and 7288CTC contained substantially more DNA than could be detected with the more slowly growing hepatoma 5123C or the liver of tumor-bearing rats. The amount of DNA in the cytosol fractions of the rapidly growing hepatomas was decreased by concentrations of cations which are known to promote precipitation of solubilized chromatin. Data on the incorporation of [3H]thymidine into DNA of nuclear and cytosol fractions and the time-dependent effects of hydroxyurea were compatible with initial nuclear synthesis and later release of the DNA seen in the cytosol fractions. The amount of this DNA was increased in larger tumors and was less in isolated cells than in solid tumors. Postmortem changes in the liver and hepatoma 5123C, but not in hepatomas 7777 and 7288CTC, resulted in a large increase in DNA appearing in the cytosol fraction. The results indicated that the measurement of DNA in cytosol fractions may serve as a guide to the existence of necrosis in tumors, but is not always proportional to the degree of necrosis.

Decreased sensitivity to colchicine-mediated inhibition of metabolite uptake in isolated hepatoma cells

The effects of colchicine on the incorporation of [3H]-leucine and [3H]thymidine were studied in inbred BUF rats bearing Morris hepatomas and in isolated hepatoma cells and hepatocytes. The results confirmed previous work by other investigators that uptake of amino acids in hepatomas can be inhibited by colchicine (250 micrograms/100 body wt) under conditions in which uptake is not impeded in host liver. Uptake and incorporation of [3H]thymidine in hepatomas were also more sensitive to inhibition by colchicine. Evidence was obtained that these inhibitory effects on incorporation were diminished in isolated cells and were similar for isolated hepatoma cells and hepatocytes. The data did not exclude alternative mechanisms, but they were compatible with a previous suggestion that an effect of colchicine on circulation in hepatomas may be a factor in the inhibitory action on metabolite uptake.

Increased fraction of acid-soluble proteins in 0.35 M NaCl extracts of nuclei from rat liver tumors

1. The fraction of proteins extracted from nuclei with 0.35 M NaCl and soluble in 2% trichloroacetic acid was examined in five Morris hepatomas and rat liver. 2. This fraction was a much greater percentage of the total 0.35 M NaCl soluble proteins in the tumors than in normal or regenerating liver. 3. In part, this difference was due to proteins with molecular weights greater than high mobility group proteins. 4. The conditions for precipitation of high mobility group proteins 1 and 2 with trichloroacetic acid were found to differ in hepatoma and liver fractions.

Effects of nicotinamide, isonicotinamide, and bleomycin on DNA synthesis and repair in rat hepatocytes and hepatoma cells

Because inhibitors of poly (ADP-ribose) synthetase have been found to influence DNA synthesis in some systems, the possibility that nicotinamide or isonicotinamide might potentiate the effect of bleomycin on DNA replication and repair was examined. After a 30-minute incubation with bleomycin (200 micrograms/ml), tritiated thymidine ([3H]dThd) incorporation into DNA was stimulated during a subsequent 30-minute incubation with hepatocytes of inbred BUF rats but was decreased in HTC cells of BUF rats. When unscheduled DNA synthesis was measured in the presence of 10 mM hydroxyurea, bleomycin (200 micrograms/ml) increased [3H]dThd incorporation in both cell types. A dose of 20 mM nicotinamide and isonicotinamide caused an approximately 50% inhibition of total [3H]dThd incorporation in HTC cells. Significant inhibitory effects of 20 mM nicotinamide and isonicotinamide on unscheduled DNA synthesis were observed after preincubation of hepatocytes and HTC cells with bleomycin. When the effects of bleomycin on DNA structure were assessed fluorometrically with ethidium bromide after mild alkaline incubation, nicotinamide and isonicotinamide did not significantly affect the damage revealed with bleomycin alone. When HTC cells were incubated for 48 hours with bleomycin (20 micrograms/ml), the increase in cell numbers was about 50% of that in control cultures. Nicotinamide and isonicotinamide also inhibited the proliferation of HTC cells, but the effects were not additive with the effect of bleomycin.

Effects of cyanate on the distribution of isotope-labeled H2O and extracellular markers in rat liver and tumors

Previous work has shown that administration of sodium cyanate inhibits the uptake of several metabolites in tumors under conditions in which there is generally no inhibition in normal tissues of the rat. In the present work, it was found that cyanate treatment inhibits the distribution of 3H2O, [3H]methoxyinulin, and [14C]sucrose in rats with greater effects in the tumors than the normal tissues examined. Tumor-bearing rats received i.p. injections of sodium cyanate (250 mg/kg body weight). After 60 min, the rats received s.c. injections of 3H2O. Treatment with cyanate decreased the radioactivity in blood and liver, but greater effects were seen in five transplanted tumors (LK1 colon tumor and Morris hepatomas 5123C, 7288CTC, 7777, and 9618A2). At 10 min after injection of 3H2O, the mean radioactivities in tumors of cyanate-treated rats were 11 to 23% of control values and in some tumors were still less than in controls at 60 min after isotope injection. Evidence was obtained that the action of cyanate was not due to osmotic effects or loss of water from the tissues. The distribution of the extracellular markers [3H]methoxyinulin and [14C]sucrose was also decreased in hepatomas in cyanate-treated rats. The data do not exclude effects on membrane permeability but suggested that cyanate decreased circulation in the tumors.

Colchicine affects the distribution of isotope-labeled H2O and extracellular markers in rat liver and hepatomas

Treatment of hepatoma-bearing rats with colchicine (175 or 250 micrograms/100 g body wt) greatly diminished the radioactivity in tumors when measured 10 min after subcutaneous injection of 3H2O. There were relatively small effects of colchicine treatment on the level of radioactivity in blood and little change in the ratio of radioactivity in blood and liver. Inhibitory effects of colchicine were also observed for the distribution in hepatomas of the extracellular markers [3H] methoxy-inulin and [14C] sucrose. An effect of colchicine on circulation in hepatomas may be a factor in the previously reported inhibitory action on metabolite uptake.

Uptake of 14C-labeled dicarboxylic amino acids in hepatocytes and hepatoma cells

In previous studies, we observed decreased uptake of 14C-labeled L-aspartate and L-glutamate in s.c. transplants of several rapidly growing hepatomas relative to that in normal liver. The present report extends these observations to isolated cells and indicates that circulation differences cannot be the major factor. Mean net uptakes for the two dicarboxylic amino acids in cells from the rapidly growing Morris Hepatomas 7288ctc and 7777 were 5 to 26% of corresponding values for normal hepatocytes. Rates for net uptake in Hepatoma 7787 cells were intermediate between those of the rapidly growing hepatomas and hepatocytes, while the rates for Hepatoma 5123C cells and hepatocytes were similar. The contribution of sodium-dependent uptake to the mean total net uptake of [14C]aspartate and [14C]glutamate tended to be higher in hepatoma cells than in hepatocytes. Studies with isolated hepatocytes and Hepatoma 5123C cells showed no significant effect on uptake by 10 mM alpha-(methylamino)isobutyric acid and 10 mM 2-amino-2-carboxybicyclo[2.2.1]heptane. On the other hand, L-cysteic acid, L-alanosine, and N-phosphonacetyl-L-aspartic acid were shown to be effective inhibitors of sodium-dependent uptake in Hepatoma 5123C cells. The data suggest that the A and L systems are not major contributors to the uptake of dicarboxylic amino acids in hepatic cells. It was concluded that decreased uptake of dicarboxylic amino acids in rapidly growing hepatomas may accompany decreased metabolism of these dietary nonessential amino acids.

Decreased uptake of 14C-labeled dicarboxylic amino acids in rapidly growing hepatomas

In contrast to the increased uptake of amino acids which has been found in many neoplastic cells, we have observed a decrease in the net uptake of [14C]aspartate and [14C]glutamate in rapidly growing hepatomas relative to rat host liver. When measured 10 min after s.c. injection, the radioactivity from 14C-labeled dicarboxylic amino acids was greater in liver than in all other tissues examined (blood, skeletal, muscle, heart, spleen, lung, and brain) except kidney, where there was an approximately 2-fold greater uptake of aspartate and 10-fold greater uptake of glutamate. Mean uptakes in the rapidly growing Morris hepatomas 7288CTC and 7777 were 19 to 26% of corresponding values for the host livers. Comparison with uptake of 3H2O indicated that these low values were not solely due to differences in circulation. Decreased uptake was not accompanied by equivalent decreases in the concentration of aspartate and glutamate in the tumors. There were small changes in the net uptake of these amino acids in the slowly growing hepatoma 7787 and no significant differences in regenerating liver and hepatoma 5123C, a tumor of intermediate growth rate. The net uptake of [14C]arginine and [14C]lysine in the hepatomas was similar to that in host livers, except for a 250% increase in uptake of [14C]lysine in hepatoma 5123C. A decreased uptake of the magnitude seen with dicarboxylic amino acids in rapidly growing hepatomas has not been observed with other amino acids.

Effects of cyanate, thiocyanate, and amygdalin on metabolite uptake in normal and neoplastic tissues of the rat

Thiocyanate was found to resemble cyanate in its inhibitory effects on [3H]thymidine incorporation and the uptake of [32P]phosphate and [3H]amino acids in transplanted tumors of the BUF rat. The capacity to inhibit metabolite uptake in hepatomas and a colon tumor under conditions in which uptake was unchanged or increased in host liver was concluded to be a common feature of the action of cyanate and thiocyanate. Inhibition of [32P]phosphate uptake and [3H]thymidine incorporation into DNA of tumors was also observed after treatment of rats with amygdalin. With this drug, however, the action on tumors and livers of host rats was similar.

Soluble factors from liver and hepatomas which inhibit [3H]thymidine incorporation into DNA of Novikoff hepatoma cells

The nature of soluble factors from liver and hepatomas which inhibit [3H]thymidine incorporation into DNA was studied in Novikoff hepatoma cells. The decreased activity in hepatoma preparations was due to loss of a high-molecular-weight heat-labile factor. Although this factor cochromatographed with arginase activity on Sephadex G-150, it does not appear to result from this activity as judged by the failure of arginine to prevent the inhibitory effect on [3H]thymidine incorporation. Both liver and hepatomas contained a heat-stable factor with inhibitory activity. Studies with ethanol-soluble material suggested that the action was not solely attributable to the presence of unlabeled thymidine, since the apparent molecular weight was too high and since the factor(s) inhibited [3H]leucine incorporation into protein in addition to inhibiting [3H]thymidine incorporation in DNA.

Spermine-induced variations in the adenosine 5'-diphosphate ribosylation patterns of nuclear proteins from rat liver and hepatoma

Rat liver and hepatoma nuclei were incubated in vitro with [3H]nicotinamide adenine dinucleotide to allow synthesis of a polymer of adenosine diphosphoribose subunits joined in an 1',2' ribose-ribose linkage. The addition of 1 mM spermine altered the adenosine 5'-diphosphate (ADP) ribosylation patterns of nuclear proteins in hepatoma, host liver, and regenerating liver. Spermine-treated nuclei showed a greater incorporation of ADP-ribose into H1 histones and nonhistone nuclear proteins with isoelectric points between pH 3.0 and 6.0 when separated on polyacrylamide gels. Conversely, a large reduction in ADP ribosylation was seen in core histones (H2A, H2B, and H3) from the same nuclei. The proportion of ADP-ribose incorporated into histones was reduced in the nuclei from proliferating cells relative to their respective control livers. These results imply that polyamines, which are higher in concentration in rapidly dividing cells, may elicit a regulatory function by causing the preferential ADP ribosylation of H1 histones, as well as the more acidic of the nuclear proteins.

Selective effects of two chloromethyl ketones on amino acid and phosphate uptake in rat liver and tumors

Injection of L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK) at a level of 10 mg/100 g body weight inhibited the incorporation of 3H-labeled amino acids into protein in Morris hepatomas 7777and 9618A2. The degree of inhibition was similar in cytoplasmic proteins and in histone and nonhistone nuclear protein fractions. There was no inhibitory effect on 3H-labeled amino acid incorporation in the livers of the tumor-bearing rats. The inhibitory effect of N-tosyl-L-lysine chloromethyl ketone (TLCK) on incorporation of 3H-labeled amino acids was observed in both the slowly growing hepatoma 7787 and the rapidly growing hepatoma 7777. In hepatoma 7777, TLCK (2.5 mg/100 g body wt) exerted a greater inhibitory effect on incorporation when administered 60 minutes before [3H]leucine injection than when injected simultaneously. Studies on tissue uptake of amino acids, thymidine, and phosphate indicated that inhibitory effects of TPCK and TLCK on active transport may be a major factor in the action of these drugs on macromolecular synthesis. The inhibitory effects of TPCK and TLCK seen in transplanted hepatomas and a colon tumor were not generally seen in normal tissues of the tumor-bearing rats.

Regulation of macromolecular synthesis in Morris hepatomas

In this review, some studies are discussed in which an attempt has been made to determine the nature of changes in macromolecular synthesis in Morris hepatomas. The incorporation of isotope labeled precursors into nucleic acids and proteins has suggested greatly increased rates of DNA synthesis in comparison with rat liver of normal and tumor bearing rats, but for RNA and proteins the changes may be impressive for individual macromolecular species but total synthesis is not greatly changed. Fractionation of nuclear proteins has indicated altered patterns of synthesis which are related to the growth rates of the tumors and are much more pronounced than in regenerating liver despite a growth rate similar to that of the most rapidly growing hepatomas. Investigations with drugs which inhibit synthesis of macromolecules has suggested that liver neoplasia may be accompanied by changes in response which may make the tumor less sensitive or more sensitive to regulation than the tissue of origin.

Divergent effects of cyanate on amino acid and phosphate uptake by liver and hepatoma

The uptake of alpha-aminoiso[3H]butyric acid and 32Pi was observed to be inhibited by sodium cyanate in transplanted hepatomas but was increased in the livers of the tumor bearing rats. Incorporation of 32Pi into macromolecules in hepatomas was also inhibited by cyanate. Treatment with this drug did not influence circulating concentrations of isotope-labeled materials. There were relatively small effects on uptake of 36Cl- in cyanate-treated rats and the action was not tissue specific. The data were compatible with an inhibitory effect of cyanate on active transport in hepatomas which was not seen under the same conditions in host liver.

Binding of metabolically activated benzo(a)pyrene to nuclear macromolecules

The binding of metabolically activated [3H]benzo(a)pyrene ([3H]BP) to the DNA, RNA, histones, and nonhistones of isolated rat liver and lung nuclei was studied. Conditions for optimal binding to the nuclear components were determined. Upon incubation with isolated liver nuclei and reduced nicotinamide adenine dinucleotide phosphate, [3H]BP was able to bind to nuclear components. The binding appeared to be covalent in nature. Treatment of the rats with 3-methylcholanthrene induced the nuclear aryl hydrocarbon hydroxylase (AHH) activity and also increased the level of carcinogen binding. The addition of rat liver microsomes to the incubation systems greatly enhanced the level of [3H]BP binding to the macromolecules in the nuclei from both the control and 3-methylcholanthrene-treated rats, and the maximal levels of binding obtained with these two types of nuclei were similar. The binding was inhibited by 7,8-benzoflavone or glutathione. Lung nuclei from control rats had very low AHH activity and did not exhibit appreciable carcinogen binding, whereas those from 3-methylcholanthrene-pretreated animals had slightly higher AHH activity and caused low levels of binding. The binding of [3H]BP to lung nuclei was greatly enhanced by liver microsomes but only slightly by lung microsomes, which had rather low AHH activity. Several lines of evidence indicate that, in the control experiments (no reduced nicotinamide adenine dinucleotide phosphate added), the radioactivity associated with the macromolecule fractions is probably a background value rather than due to the binding caused by a specific interaction between benzo(a)pyrene and cytochrome P-450. The present study clearly demonstrates that a carcinogen activated at the microsomes can enter into the nucleus and react with its macromolecules; the carcinogen can also be activated by the monoxygenase system of the nuclear envelope. It appears that both the endoplasmic reticulum and the nuclear envelope are potentially important sites of carcinogen activation.

Inhibition of glycolytic enzymes of rat liver and hepatomas by free fatty acids

The action of free fatty acids on glycolytic enzymes was compared in normal and neoplastic tissues. Preincubation of tissue supernatant fractions with octanoate or laurate caused an inhibition of the activities of hexokinase and phosphofructokinase. An inhibition was also observed of lactate production with either glucose or glucose 6-phosphate as substrate. A similar degree of inhibition was observed for actions on normal liver and kidney, on the 7800 and 3924-A hepatomas and on the MK-3 renal cortical tumor. The possible relationship between the inhibition of glycolytic enzymes by fatty acids and anti-tumor activity previously observed with these compounds was noted.

Fractionation of nuclei and analysis of nuclear proteins of rat liver and Morris hepatoma 7777

The contributions of nuclear populations to the total profile of nuclear proteins in a tissue were examined in normal rat liver and Morris hepatoma 7777. Comparison by sodium dodecyl sulfate polyacrylamide gel electrophoresis of phenol-soluble nuclear proteins from tumor and control liver revealed additional proteins of molecular weight 60,000, 100,00, and 135,000 and the loss of proteins of about 45,000 and 55,000 in the tumor. Subfractionation of liver nuclei on a 30 to 50% sucrose gradient yielded three nuclear classes with nearly identical complements of the phenol-soluble proteins. Similar fractionation performed on the hepatoma nuclei also produced three nuclear populations. In the hepatoma nuclei, several differences in the phenol-soluble proteins were found between the minor, slowly sedimenting nuclear fraction, and the two major fractions, while the two latter fractions were very similar in their protein composition. Histones derived from both tissues were also compared electrophoretically, indicating a decrease in the concentration of histone H1(0)in all nuclear classes derived from the tumor.

Tumor-selective inhibition of the incorporation of 3H-labeled amino acids into protein by cyanate

Sodium cyanate at a dose level of 125 or 250 mg/kg i.p. caused an inhibition of incorporation of 3H-labeled amino acids into cytoplasmic and nuclear proteins of the rapidly growing hepatoma 7777 and the slowly growing hepatoma 9618A. There was no inhibitory effect on 3H-labeled amino acid incorporation into protein in the livers of rats bearing these tumors. Studies on the effects of sodium cyanate on incorporation of 3H-labeled amino acids into total acid-insoluble material indicated that a greater than 85% inhibition could be achieved in hepatoma 5123C, hepatoma 9618A2, and the MK3 kidney tumor with either little or no effect in host liver, kidneys, brain, skeletal muscle, intestinal mucosa, and regenerating liver after partial hepatectomy.

Nuclear protein changes in rat hepatomas correlating with growth rate

The nature of nuclear proteins that are soluble in 8 M urea-50 mM phosphate, pH 7.6, was compared in rat liver and Morris hepatomas, Isoelectric focusing, using carrier ampholytes for a pH gradient of 3.5 to 10, indicated that with increasing growth rate of the hepatomas there was a progressive tendency for a decrease in nonhistone nuclear proteins with isoelectric points in the range 7.5 to 8.9 and an increase in the range 5.1 to 6.7. Studies on the influence of time on the pH gradient revealed that a nonuniform drift provided a better resolution of the pH range 7.5 to 8.9 at 7 hr than at 24 hr, while the latter time for electrofocusing gave an improved resolution of the pH range 5.1 to 6.7 Polyarcylamide gel electrophoresis in a urea-acetic acid system showed that 8 M urea-50 mM phosphate; pH 7.6 extracted a small part of the histones from nuclei of both liver and hepatomas. There was less extraction of histones from the hepatoma nuclei, especially in two rapidly growing hepatomas with the most notable difference being seen in the lysine-rich H1 histone. The results suggested that in addition to qualitative or quantitative changes in nonhistone nuclear proteins in liver cancer there are alterations in the binding of histones to chromatin.