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Biomedical subjects

C Heidelberger

Publications and source records attributed to C Heidelberger.

At least 73 records · Page 4Linked to original sources
PubMed1977

Chemical carcinogenesis.

The field of chemical carcinogenesis is reviewed, with emphasis on three aspects: 1) environmental chemicals are a major cause of human cancer; 2) most chemical carcinogens require metabolic activation by mixed-function oxidases to electrophilic metabolites that form strong covalent chemical bonds with cellular macromolecules and thereby initiate the carcinogenic process; and 3) several systems are available in which normal cells can be transformed by chemical carcinogens into malignant cancer cells. Much has been learned about the cellular mechanisms of chemical carcinogenesis using these systems. They also have considerable potential to be used as prescreens for environmental carcinogens.

Animals↗
PubMed1977

Effects of promoters on DNA synthesis in C3H/10T1/2 mouse fibroblasts.

The synthesis of DNA has been studied by autoradiography and by measurements of tritiated thymidine ([3H]TdR) incorporation in cultured C3H/10T1/2 mouse embryo fibroblasts. The cells were first treated with 3-methylcholanthrene as an initiator and then with promoters according to schedules that produce oncogenic transformation. The levels of 3-methylcholanthrene used did not affect the growth or [3H]TdR incorporation of the cells. Treatment during the log phase of growth with 12-O-tetradecanoyl-phorbol-13-acetate, phorbol didecanoate, or 4alpha-phorbol didecanoate produced a transient inhibition of [3H]TdR incorporation with the maximum at 12 hr after treatment. This resulted in a temporary delay of growth followed by recovery of the normal cell-doubling time. Phorbol did not produce these effects, suggesting that the inhibition of DNA synthesis is associated with the process of promotion. Although treatment of the cells with 12-O-tetradecanoyl-phorbol-13-acetate during stationary phase resulted in a 2- to 3-fold stimulation of [3H]TdR incorporation, multiple treatments spanning log and stationary phases were found to be necessary for promotion.

Animals↗
PubMed1976

The effect of Raney nickel on the covalent thymidylate synthetase-5-fluoro-2'-deoxyuridylate-5,10-methylenetetrahydrofolate complex.

Raney nickel (Ni(H)) catalyzes a specific reductive cleavage of carbon-sulfur bonds and, therefore, can be used to determine whether compounds are covalently bound to proteins through a sulfide linkage. When the covalent thymidylate synthetase-[3H]5-fluoro-2'-deoxyuridylic acid-[14C]-5,10-CH2H4-folate complex (Langenbach et al. (1972a), Biochem, Biophys. Res. Commun. 48, 1565) was denatured and then shaken with Ni(H) at 25 degrees C, both isotopes were rapidly cleaved from the protein, with identical reaction halftimes of less than 10 min. The liberated radioactivity was filterable through nitro-cellulose filters and comigrated with small molecules on Sephadex G-25. Both labels migrated identically upon paper chromatography. A [3H]5-fluoro-2'-deoxyuridylic acid-[35S]thymidylate synthetase complex was formed with enzyme isolated from Lactobacillus casei grown in the presence of [35S]cysteine. This complex, upon Ni(H) treatment, released both tritium and sulfur-35 at identical rates. Control experiments on amino acids showed that only the sulfur-containing amino acids are degraded by Ni(H). Cysteine was rapidly converted to alanine and methionine to alpha-aminobutyric acid. 5-Carboxymethylcysteine and 5-uracilylcysteine, simple models for the tenary enzyme-5-fluoro-2'-deoxyuridylic acid-5,10-CH2H4-folate complex, were converted to alanine at the same rate that 5-fluoro-2'-deoxyuridylic acid (FdUrd-5'-P) was cleaved from the enzyme. Native ribonuclease, which has a tightly coiled structure, was not affected by the reagent, but carboxymethylated ribonuclease was desulfurized. Amino acid analysis of Ni(H)-treated thymidylate synthetase showed that cysteine was the only amino acid degraded. Gel electrophoresis of the proteins after exposure to Ni(H) showed no breakage of polypeptide chains. These results support a sulfide linkage between FdUrd-5'-P and thymidylate synthetase in the covalent complex.

Amino Acids↗
PubMed1976

Cytotoxicity, mutations and DNA damage produced in Chinese hamster cells treated with streptozotocin, its analogs, and N-methyl-N'-nitro-N-nitrosoguanidine.

The activities of streptozotocin (SZ), three structural analogs of SZ, and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in producing cytotoxicity, mutations to 8-azaguanine (8-AzG) resistance, and DNA damage (single-strand breaks) in V79 Chinese hamster cells have been examined. These three biological processes appear to be associated. MNNG was about 10(3) times more active on a molar basis than SZ, and the activities of the analogs fell within these extremes.

Cell Line↗
PubMed1976

The influence of serum components on the growth and mutation of Chinese hamster cells in medium containing 8-azaguanine.

Low concentrations (less than or equal 20 mug/ml) of 8-azaguanine are 1000 fold more toxic to V79 Chinese hamster cells in medium containing 10% dialyzed fetal calf serum than in medium containing 10% undialyzed serum. Serum enzyme activity that converts AG to nontoxic 8-azaxanthine degrades AG at the same rate, whether or not the serum is dialyzed. However, cytotoxicity results similar to those obtained with US were produced in medium containing DS and 2.5 mug of hypoxanthine (HX)/ml (DSH). Therefore, serum HX is considered to be responsible for the relatively low cytotoxicity of AG in medium containing US. Colonies that arose in medium containing AG were isolated and characterized. Those that remained resistant to AG (40 mug/ml) and sensitive to aminopterin in the presence of HX and thymidine (HAT) were considered mutants; non-mutants were sensitive to AG and resistant to HAT. Colonies isolated from medium containing DSH or US and low concentrations of AG were not mutants, but those from medium containing high concentrations (greater than or equal 30 mug/ml) of AG were mutants. Spontaneous and N-methyl-N-nitro-N-nitrosoguanidine induced mutants were detectable in medium containing DSH without replating the cells prior to adding AG (greater than or equal 30 mug/ml), but in order to detect MNNG induced mutations in medium containing DS replating was essential. In DS, the mutation frequency increased as an exponential function of the toxicity of MNNG, but remained two orders of magnitude lower than the induced mutation frequencies that occurred in DSH. HX, in DSH or US, produced profound effects, other than interference with AG toxicity, that distort the results of mutagenesis assays. To study mutation using AG resistance as the endpoint, it is essential to use dialyzed serum.

Azaguanine↗
PubMed1976

Synthesis and biological studies of 3-(beta-D-ribofuranosyl)-2,3,-dihydro-6H-1,3-oxazine-2,6-dione, a new pyrimidine nucleoside analog related to uridine.

Reaction of the trimethylsilyl derivative of 2,3-dihydro-6H-1,3-oxazine-2,6-dione (2, "uracil anhydride") with protected 1-O-acetylribofuranoses in the presence of stannic chloride gave the corresponding block nucleosides. 3-(2,3-5-Tri-O-2',2',2'-trichloroethoxycarbonyl-beta-d-ribofuranosyl)-2,3-dihydro-6H-1,3-oxazine-2,6-dione (4c) thus prepared from the protected sugar 3c, 1-O-acetyl-2,3,5-tri-O-(2,2,2-trichloroethoxycarbonyl)ribofuranose, gave, on removal of the protecting groups with zinc dust,3-(beta-d-ribofuranosyl)-2,3-dihydro-6H-1,3-oxazine-2,6-dione (1). The structure of 1 was confirmed by uv, ir, NMR, and CD spectral data and was shown to be an N nucleoside. Uracil anhydride, 2, and, to a lesser extent, its ribonucleoside 1 exert a moderate growth inhibition of mouse leukemia L5178Y, HeLa, and Novikoff hepatoma cells i- culture. Both compounds produce weak inhibition of vaccinia viral replication in HeLa cells.

Animals↗
PubMed1976

Growth inhibition of cells in cultures and of vaccinia virus infected HeLa cells by derivatives of trifluorothymidine.

The effects of 5-trifluoromethyluracil (F3Thy), 5-trifluoromethyl-2'-deoxyuridine (F3dThd), F3dThd-5'-P, and F3dThd-5'-methylphosphonate on the growth of HeLa cells, Novikoff hepatoma cells, L5178Y mouse leukemia cells, and on the replication of vaccinia virus in HeLa cells have been determined. F3Thy and F3dThd-5'-methylophosphonate were approximately 500-fold and 100-fold less effective, respectively, than F3dThd or F3dThd-5'-P in their inhibition of these cells. F3dThd and F3dThd-5'-P are potent inhibitors of vaccinia viral replication of HeLa cells. The nucleoside and nucleotide were 1,000-fold more inhibitory than the free base. F3dThd was nost inhibitory when added between 1 and 2 h post-infection; however, it was also somewhat inhibitory when added at later times.

Animals↗
PubMed1976

The effect of modifiers of microsomal enzymes on chemical oncogenesis in cultures of C3H mouse cell lines.

Two cell lines, both derived from the C3H mouse and each having different responses (oncogenic and cytotoxic) to polycyclic aromatic hydrocarbon oncogens, were studied with respect to their drug-metabolizing enzymes. The 10T1/2CL8 cells (a C3H mouse embryo fibroblastic cell line) were much more effective in converting 3-methylcholanthrene (3-MC) to 3-MC water-soluble metabolites, 3-MC phenols, and 3-MC-bound cellular macromolecules than were CVP3SC6 cells (a new line of C3H mouse adult ventral prostate fibroblasts). Basal aryl hydrocarbon hydroxylase activity was higher in 10T1/2CL8 cells than in CVP3SC6 cells, while the reverse was found for epoxide hydrase activity (using 3-methylcholanthrene-11, 12-oxide as substrate. 3-MC or benz(a)anthracene induced epoxide hydrase activity in both cell lines to about the same extent. 3-MC did not induce aryl hydrocarbon hydroxylase activity in CVP3SC6 cells. Aryl hydrocarbon hydroxylase activity was markedly induced in both cell lines by benz(a)anthracene and was slightly induced in 10T1/2CL8 cells by 3-MC. In a chemical oncogenesis cell culture system, transformation of 10T1/2CL8 cells mediated by 3-MC could be increased two- to threefold by treating the cell cultures with: either benz(a)anthracene, styrene oxide, cyclohexene oxide, or 1,2,3,4-tetrahydrona=phthalene-1,2-oxide; or with cyclohexene or 1,2-dihydrona-phthalene, alkene precursors of cyclohexene oxide and 1,2,3,4-tetrahydronaphthalene-1,2-oxide, respectively. When 10T1/2CL8 cells were treated with a combination of benz(a)anthracene and cyclohexene, 3-MC-mediated transformation was increased 7.8-fold. CVP3SC6 cells that were not transformed by 3-MC or other hydrocarbon oncogens were transformed by a combined treatment with benz(a)anthracene, 1,2-dihydronaphthalene, and 3-MC.

Aryl Hydrocarbon Hydroxylases↗
PubMed1976

Oncogenic transformation of C3H/10T1/2 clone 8 mouse embryo cells by halogenated pyrimidine nucleosides.

Oncogenic transformation has been induced in vitro in the C3H/10T1/2 clone 8 line of mouse cells by exposure to 5-fluoro-2'-deoxyuridine (FUdR) or 5-fluorouracil. This transformation is both dose and time dependent and can be markedly decreased by simultaneous exposure of the cells to thymidine. The transformation induced by 5-fluorouracil is probably due to its intracellular conversion to FUdR or its monophosphate. Transformation by FUdR was found to be cell cycle dependent with maximum sensitivity to transformation occurring in early S phase. Cell lines that produced sarcomas in antithymocyte-treated syngeneic mice were isolated from FUdR-transformed cultures. Trifluorothymidine, 5-bromo-2'-deoxyuridine, and 5-iodo-2'-deoxyuridine induced no transformed foci in the C3H/10T1/2 clone 8 cell line. Thus, not all mutagens produce oncogenic transformation nor does the lack of mutagenicity, as classically measured, completely exclude the possibility that a given agent is oncogenic. Also, there was no evidence of the "switch on" of oncornaviral information in the FUdR-transformed cell lines.

Animals↗
PubMed1976

Two-stage chemical oncogenesis in cultures of C3H/10T1/2 cells.

The initiation and promotion stages of chemical oncogenesis have been demonstrated in cultured C3H/10T1/2 mouse embryo cells. Treatment of the cells with a subeffective concentration of 3-methylcholanthrene, benzo(a)pyrene, or 7,12-dimethylbenz(a)anthracene, followed 4 days later by a nontransforming amount of tetradecanoylphorbol acetate (TPA), phorbol didecanoate, or 4-alpha-phorbol didecanoate, produced transformation. Phorbol was ineffective. TPA did not select for transformed cells. When TPA treatment preceded 3-methylcholanthrene, no enhancement of transformation was observed. When TPA was added immediately after hydrocarbon treatment, there was a significant inhibition of transformation. TPA did not exert promoting activity when the hydrocarbons were in high enough concentrations to produce appreciable transformation. The promoting action of TPA cannot be attributed only to a stimulation of cell division.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1975

Increased thymidine uptake by methylcholanthrene-treated C3H/10T1/2 cells.

The uptake of 3H-thymidine in post-confluent cultures of methylcholanthrene-transformed C3H/10T1/I mouse embryo cells was markedly higher than in their non-transformed counterparts. In a reconstruction experiment as few as 2% transformed cells could be detected by increased thymidine uptake. Measurements made at various times up to 110 days in multi-chambered plates revealed that after 25 days methylcholanthrene-treated cultures incorporated significantly more thymidine than the acetone-treated controls. This increased uptake correlated with the appearance of Type III transformed foci.

Animals↗
PubMed1975

Lack of direct correlation among repair, oncogenesis, and lethality in cultured synchronized mouse fibroblasts treated with N-methyl-N'-nitro-N-nitrosoguanidine.

The repair of single-strand breaks induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in mouse embryo fibroblast DNA was studied using an alkaline sucrose sedimentation procedure with cells synchronized by arginine deprivation. Parallel studies in synchronized cells examined the effects of MNNG on malignant transformation and cell death. Cells in late G1 were maximally transformed, while cells in S-phase were maximally killed; by contrast, the repair capacity in both cases was similarly rapid. Arginine-deprived cells showed a low level of DNA repair, but the extent of cell death and transformation was comparable to that in rapidly repairing cells in G1 and S, respectively. Thus, in this system there is no direct correlation among DNA repair, cell transformation, and lethality.

Animals↗