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PubMed1988

Absence of pyrimidine salvage and prevention of thymineless radiosensitization in Escherichia coli thyA cells fed dihydrothymine or thymine glycol.

Little information is available concerning the metabolic fate of radiation-induced thymine base damage products once they have been excised from DNA. The present study was an attempt to determine whether or not thymine-requiring mutants of Escherichia coli could grow on dihydrothymine (DHT) and thymine glycol (TG) by "salvaging" the altered thymines. A second test of thymine product utilization was prevention of thymineless radiosensitization. Results showed that very low growth of Thy- cells on DHT or TG could be explained by the presence of less than or equal to 1% contaminating thymine in the mixtures. Radiation dose-modification factors (DMFs) for thyA cells fed DHT or TG for 3 h were 1.38 +/- 0.28 and 1.26 +/- 0.24, respectively, whereas the DMF for 3 h thymine-starved cells was 1.63 +/- 0.05. The small (approximately 25%) amelioration of thymineless radiosensitization observed in DHT- or TG-fed cells could probably be explained by contaminating thymine in the medium. Although DHT is a normal metabolite in some cells, neither DHT nor TG could be used efficiently by thymine-requiring cells in the protocol presented.

Dose-Response Relationship, Radiation↗
PubMed1983

Nonlinear pharmacokinetics of thymidine, thymine, and fluorouracil and their kinetic interactions in normal dogs.

We have investigated the pharmacokinetics of thymidine (dThd), thymine, and fluorouracil (FUra) over a range of doses in normal dogs. Evidence was obtained to show that the metabolic elimination of these pyrimidines is saturable, resulting in nonlinear pharmacokinetic behavior. Additionally, dThd and thymine were shown to inhibit the catabolism of FUra. Following i.v. infusion to low-microM steady-state plasma levels (Css = 7.6 to 12 microM), each compound alone demonstrated an elimination half-life (t1/2) between 2 and 20 min. When Css was increased to near 1000 microM, the elimination of dThd, thymine, and FUra was markedly slower and no longer followed first-order kinetics. Over the same concentration range, plasma clearance of each compound decreased about 90%, while urinary clearance was increased in each case. The relationship between infusion rate and Css was nonlinear. Using equations based on Michaelis-Menten kinetics, in vivo values of Km and Vmax were determined: Km (in microM): dThd, 45.5; thymine, 82.5; FUra, 39.8; Vmax (in mumol/min/kg): dThd, 2.45; Thymine, 2.55; FUra, 2.16. When FUra and thymine or FUra and dThd were infused simultaneously following a base-line infusion of FUra alone, the Css of FUra increased in proportion to the plasma level of thymine achieved. Plasma clearance and metabolism decreased markedly in a nonlinear manner with thymine concentration, while there was little effect on the urinary clearance of FUra. Assuming competitive enzymatic inhibition, in vivo Ki values for dThd and thymine effects on FUra metabolism were 24.2 and 17.4 microM, respectively.

Animals↗
PubMedDate not supplied

The trans-syn-I thymine dimer bends DNA by approximately 22 degrees and unwinds DNA by approximately 15 degrees.

Irradiation of DNA with ultraviolet light leads to the formation of two classes of cyclobutane dimers at adjacent thymines sites, of which the cis-syn is the major class and the trans-syn is the minor class. While the structure and properties of DNA containing cis-syn thymine dimers have been extensively studied, virtually nothing is known about DNA containing trans-syn thymine dimers. To investigate the bending and unwinding of DNA induced by the trans-syn-I thymine dimer, the electrophoretic properties of oligomers of trans-syn-I dimer-containing DNA duplexes were studied. Oligonucleotides 10, 11, and 12 bp in length containing a centrally located trans-syn-I thymine dimer were synthesized, polymerized, and analyzed by polyacrylamide gel electrophoresis. In contrast to the small bending angle (approximately 7 degrees) induced by the cis-syn thymine dimer, we found that trans-syn-I thymine dimer bends DNA significantly (approximately 22 degrees). Both dimers, however, are found to unwind DNA by the same amount (approximately 15 degrees). On the basis of previous NMR studies, it appears that the bend of the trans-syn-I dimer is localized at the 5'-side of the dimer. Gel electrophoretic analysis of multimers of two 11-mers containing a cis-syn thymine dimer at the 5'-end and at the center of a dT6.dA6 tract confirmed our previous estimates for the bending angles of thymine dimer-containing T6 tracts. The substrates reported may be useful in determining how general repair enzymes recognize DNA damage.

Autoradiography↗
PubMed1993

Thymine ring saturation and fragmentation products: lesion bypass, misinsertion and implications for mutagenesis.

We have used thymine glycol and dihydrothymine as representative ring saturation products resulting from free-radical interaction with DNA pyrimidines, and urea glycosides and beta-ureidoisobutyric acid (UBA) as models for pyrimidine-ring fragmentation products. We have shown that thymine glycol and the ring-fragmentation products urea and beta-ureidoisobutyric acid, as well as abasic sites, are strong blocks to DNA polymerases in vitro. In contrast, dihydrothymine is not a block to any of the polymerases tested. For thymine glycol, termination sites were observed opposite the putative lesions, whereas for the ring-fragmentation products, the termination sites were primarily one base prior to the lesion. These and other data have suggested that thymine glycol codes for an A, and that a base is stably inserted opposite the damage, whereas when a base is inserted opposite the non-coding lesions, it is removed by the 3-->5 exonuclease activity of DNA polymerase I. Despite their efficiency as blocking lesions, thymine glycol, urea and UBA can be bypassed at low frequency in certain specific sequence contexts. When the model lesions were introduced individually into single-stranded biologically active DNA, we found that thymine glycol, urea, beta-ureidoisobutyric acid, and abasic sites were all lethal lesions having an activation efficiency of 1, whereas dihydrothymine was not. Thus the in vitro studies predicted the in vivo results. When the survival of biologically active single-stranded DNA was examined in UV-induced Escherichia coli cells where the block to replication was released, no increase in survival was observed for DNA containing urea or abasic sites, suggesting inefficient bypass of these lesions. In contrast, beta-ureidoisobutyric acid survival was slightly enhanced, and transfecting DNA containing thymine glycols was significantly reactivated. When mutation induction by unique lesions was measured using f1-K12 hybrid DNA containing an E. coli target gene, thymine glycols and dihydrothymine were found to be inefficient as premutagenic lesions, suggesting that in vivo, as in vitro, they primarily code for A. In contrast, urea and beta-ureidoisobutyric acid were efficient premutagenic lesions, with beta-ureidoisobutyric acid being about 4-5-fold more effective than urea glycosides, which have approximately the same rate of mutation induction as abasic sites from purines. Sequence analysis of the mutations resulting from these ring-fragmentation products shows that the mutations produced are both lesion and sequence context dependent. The possible roles that bypass efficiency and lesion-directed misinsertion might play in mutagenesis are discussed.

Base Sequence↗
PubMed1991

Thymine glycols and pyrimidine dimers in brain DNA during post-ischemic reperfusion.

Free-radical reactions, known to occur in the reperfused brain, damage DNA in vitro. We therefore examined the hypothesis that thymine glycols and thymine dimers, which are known to block transcription and are formed by free radical mechanisms, are formed in brain DNA during reoxygenation following ischemia. Such biochemical lesions could account for the failure of protein synthesis that occurs following an ischemic insult. Large dogs were anesthetized, instrumented, and divided into four groups: (1) non-ischemic controls; (2) 20-min cardiac arrest without resuscitation; (3) 20-min cardiac arrest, resuscitation and 2 h reperfusion; and (4) 20-min cardiac arrest, resuscitation and 8 h reperfusion. Genomic DNA was isolated from the cerebral cortex. Thymine glycols were labeled by reduction with [3H]NaBH4. Pyrimidine dimers were determined by ELISA using antibody prepared against ultraviolet irradiated DNA. The data was evaluated by Kruskal-Wallis ANOVA with alpha = 0.05. The rabbit antibodies detected the thymine dimer content in 10 pg UV irradiated DNA but did not react with normal DNA. Borohydride labeling qualitatively detected thymine glycols generated by treatment of DNA with osmium tetroxide. There was no difference between the DNAs from the experimental groups in the content of thymine glycols or pyrimidine dimers (P = 0.608 and P = 0.219, respectively). We conclude that significant quantities of thymine glycols and thymine dimers are not formed in brain DNA during post-ischemic reperfusion. Therefore, the inhibition of brain protein synthesis during reperfusion, observed by other investigators, is unlikely to be caused by interruption of transcription by these species.

Animals↗
PubMed1992

Synthesis and antiviral activity of deoxy analogs of 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) as potent and selective anti-HIV-1 agents.

The effect of substitution in the acyclic structure of 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)-thymine (HEPT) on anti-HIV-1 activity was investigated by synthesizing a series of deoxy analogs and related compounds. Preparation of 1-[(2-alkyloxyethoxy)methyl]-6- (phenylthio)thymine (2-4) derivatives was carried out based on alkylation of HEPT with primary alkyl halides. Preparation of the 1-[(alkyloxy)methyl]-6-(phenylthio)thymine (26-31) and 1-[(alkyloxy)methyl]-6-(arylthio)-2-thiouracil (32-45) derivatives was carried out on the basis of LDA lithiation of 1-[(alkyloxy)-methyl]thymine (9-14) and 1-[(alkyloxy)methyl]-2-thiouracil (15-25) followed by reaction with diaryl disulfides. The oxidative hydrolysis of the 2-thiouracil derivatives gave 1-[(alkyloxy)methyl]-6-(arylthio)uracil derivatives (46-57). 1-Alkyl-6-(phenylthio)thymine (59-61) derivatives were prepared on the basis of alkylation of 6-(phenylthio)thymine (58). Methylation of the hydroxyl group of HEPT did not affect the anti-HIV-1 activity of HEPT. Substitution of the 1-(2-hydroxyethoxy)methyl group by ethyl, butyl, methoxymethyl, (propyloxy)methyl, and (butyloxy)-methyl groups somewhat improved the original anti-HIV-1 activity of HEPT. Substitution with ethoxymethyl and (benzyloxy)methyl groups further potentiated the activity [EC50: 1-(ethoxy-methyl)-6-(phenylthio)thymine (27), 0.33 microM; 1-[(benzyloxy)methyl]-6-(phenylthio)thymine (31), 0.088 microM]. When the 5-methyl group of 27 and 31 was replaced by an ethyl or an isopropyl group, the anti-HIV-1 activity was improved remarkably [EC50: 5-ethyl-1-(ethoxymethyl)-6-(phenylthio)-uracil (46), 0.019 microM; 5-ethyl-1-[(benzyloxy)methyl]-6-(phenylthio)uracil (52), 0.0059 microM; 5-isopropyl-1-(ethoxymethyl)-6-(phenylthio)uracil (55), 0.012 microM; 5-isopropyl-1-[(benzyloxy)methyl]-6-(phenylthio)uracil (56), 0.0027 microM]. Introduction of two m-methyl groups into the phenylthio ring also potentiated the activity.

Antiviral Agents↗
PubMed2005

The influence of microhydration on the ionization energy thresholds of uracil and thymine.

In the present study the ionization energy thresholds (IET's) of uracil and thymine have been calculated (with the B3LYP, PMP2, and P3 levels of theory using the standard 6-31++G(d,p) basis set) with one to three water molecules placed in the first hydration shell. Then (B3LYP) polarizable continuum model (PCM) calculations were performed with one to three waters of the hydration shell included. Calculations show there is a distinct effect of microhydration on uracil and thymine. For uracil, one added water results in a decrease in the IET of about 0.15 eV. The second and third water molecules cause a further decrease by about 0.07 eV each. For thymine, the first water molecule is seen to decrease the IET by about 0.1 eV, while the second and third water molecules cause a further decrease of less than 0.1 eV each. The changes in IET calculated here for thymine with one to three waters of hydration are smaller than the experimental values determined by Kim et al. (Kim, S. K.; Lee, W.; Herschbach, D. R. J. Phys. Chem. 1996, 100, 7933). Preliminary results presented here indicate that the experimental results may involve keto-enol tautomers of thymine. The results of placing the microhydrated structures of uracil and thymine in a PCM cavity was seen to make very little difference in the IET when compared to the IET of ordinary uracil or thymine in a PCM cavity. The implications are that accurate calculations of the IET's of uracil and thymine can be obtained by simply considering long-range solvation effects.

Ions↗
PubMed2006

Influence of microhydration on the ionization energy thresholds of thymine: comparisons of theoretical calculations with experimental values.

In the present study the ionization energy thresholds (IETs) of thymine, and thymine keto-enol tautomers, have been calculated (with the B3LYP, and P3 levels of theory using the standard 6-31++G(d,p) basis set) with 1-3 water molecules placed in the first hydration shell. Calculations show there is a distinct effect of microhydration on the IET of thymine. The first water molecule is seen to decrease the IET by about 0.1 eV, whereas the second and third water molecules cause a further decrease of less than 0.1 eV each. The changes in IET calculated here for thymine with 1-3 waters of hydration are smaller than the experimental values determined by Kim et al. (J. Phys. Chem. 1996, 100, 7933). Therefore calculations have been performed on the microhydrated keto-enol tautomers of thymine. The calculated results on the keto-enol tautomers are seen to be in better agreement with the experimental results. However, the keto-enol thymine tautomers are considerably higher in energy than the canonical form of thymine, and there is presently no good evidence that these thymine tautomers are actually present in a supersonic jet-cooled experiment.

Computer Simulation↗
PubMed1981

Alternative metabolic fates of thymine nucleotides in human cells.

Three types of experiments have been used to study the metabolism of thymine nucleotides by human cells. (1) Cells were labelled continuously with [3H]thymidine and the incorporation of label into DNA compared with the specific radioactivities of pools of individual thymine nucleotides separated by chromatography on polyethylene-imine-cellulose. (2) Cellular thymine nucleotides were labelled with [3H]thymidine at 13 degrees C, followed by incubation at 37 degrees C in unlabelled medium. Incorporation of label into DNA and loss of label from the nucleotide pools were monitored during the 'chase' period at 37 degrees C. (3) The experiments described in (2) above were repeated in the presence of the DNA-synthesis inhibitor cytosine arabinoside, in order to demonstrate more clearly and to quantify degradative pathways for thymine nucleotides. In phytohaemagglutinin-stimulated lymphocytes and in bone-marrow cells, only a proportion (25-60%) of labelled thymine nucleotide was incorporated into DNA, the rest being rapidly degraded and lost from the cell. In contrast, an established cell line (HPB-ALL) from a patient with acute lymphoblastic leukaemia of thymic origin incorporated 100% of its exogenously labelled thymine nucleotides into DNA. These results indicated that alternative metabolic routes are open to thymine nucleotides in human cells. In lymphocytes from patients with megaloblastic anaemia and in normal lymphocytes treated with methotrexate, the utilization of labelled thymine nucleotides for DNA synthesis was more efficient than in controls. These results offer an explanation for the observation of a normal pool of thymidine triphosphate in the cells of patients with untreated megaloblastic anaemia even though the amount of this compound available for DNA synthesis appears to be decreased.

Anemia, Megaloblastic↗
PubMed2002

Human DNA polymerase kappa bypasses and extends beyond thymine glycols during translesion synthesis in vitro, preferentially incorporating correct nucleotides.

Human polymerase kappa (polkappa), the product of the human POLK (DINB1) gene, is a member of the Y superfamily of DNA polymerases that support replicative bypass of chemically modified DNA bases (Ohmori, H., Friedberg, E. C., Fuchs, R. P., Goodman, M. F., Hanaoka, F., Hinkle, D., Kunkel, T. A., Lawrence, C. W., Livneh, Z., Nohmi, T., Prakash, L., Prakash, S., Todo, T., Walker, G. C., Wang, Z., and Woodgate, R. (2001) Mol. Cell 8, 7-8; Gerlach, V. L., Aravind, L., Gotway, G., Schultz, R. A., Koonin, E. V., and Friedberg, E. C. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 11922-11927). Polkappa is shown here to bypass 5,6-dihydro-5,6-dihydroxythymine (thymine glycol) generated in two different DNA substrate preparations. Polkappa inserts the correct base adenine opposite thymine glycol in preference to the other three bases. Additionally, the enzyme correctly extends beyond the site of the thymine glycol lesion when presented with adenine opposite thymine glycol at the primer terminus. However, steady state kinetic analysis of nucleotides incorporated opposite thymine glycol demonstrates different misincorporation rates for guanine with each of the two DNA substrates. The two substrates differ only in the relative proportions of thymine glycol stereoisomers, suggesting that polkappa distinguishes among stereoisomers and exhibits reduced discrimination between purines when incorporating a base opposite a 5R thymine glycol stereoisomer. When extending beyond the site of the lesion, the misincorporation rate of polkappa for each of the three incorrect nucleotides (adenine, guanine, and thymine) is dramatically increased. Our findings suggest a role for polkappa in both nonmutagenic and mutagenic bypass of oxidative damage.

Adenine↗
PubMed1991

Stability of DNA thymine hydrates.

Pyrimidine hydrates are products of ultraviolet irradiation of DNA. We have already demonstrated the formation of both cis-thymine hydrate and trans-thymine hydrate (6-hydroxy-5,6-dihydrothymine) in irradiated poly(dA-dT):poly(dA-dT). These are released from DNA as free bases by bacterial or human glycosylases. Thymine hydrate stabilities were studied in irradiated DNA substrates using purified E. coli endonuclease III as a reagent for their removal. After irradiation, substrate poly(dA-dT):poly(dA-dT), radiolabeled in thymine, was incubated at 50, 60, 70 or 80 degrees C, cooled, and then reacted with the enzyme under standard conditions. Thymine hydrates were assayed by enzymic release of labeled material into the ethanol-soluble fraction. Their identities were confirmed by high performance liquid chromatography. The decay of thymine hydrates in heated DNA followed first-order kinetics with a k = 2.8 x 10(-5)/sec at 80 degrees C. These hydrates were also detected in lesser quantities in the unirradiated, control substrate. Extrapolation from an Arrhenius plot yields an estimated half-life of 33.3 hours at 37 degrees C for DNA thymine hydrates. Such stability, together with their formation in unirradiated DNA, suggest thymine hydrates to be formed under physiological conditions and to be sufficiently stable in DNA to be potentially genotoxic. This necessitates their constant removal from DNA by the excision-repair system.

Chromatography, High Pressure Liquid↗
PubMed2004

A thymine tetrad in d(TGGGGT) quadruplexes stabilized with Tl+/Na+ ions.

We report two new structures of the quadruplex d(TGGGGT)4 obtained by single crystal X-ray diffraction. In one of them a thymine tetrad is found. Thus the yeast telomere sequences d(TG1-3) might be able to form continuous quadruplex structures, involving both guanine and thymine tetrads. Our study also shows substantial differences in the arrangement of thymines when compared with previous studies. We find five different types of organization: (i) groove binding with hydrogen bonds to guanines from a neighbour quadruplex; (ii) partially ordered groove binding, without any hydrogen bond; (iii) stacked thymine triads, formed at the 3'ends of the quadruplexes; (iv) a thymine tetrad between two guanine tetrads. Thymines are stabilized in pairs by single hydrogen bonds. A central sodium ion interacts with two thymines and contributes to the tetrad structure. (v) Completely disordered thymines which do not show any clear location in the crystal. The tetrads are stabilized by either Na+ or Tl+ ions. We show that by using MAD methods, Tl+ can be unambiguously located and distinguished from Na+. We can thus determine the preference for either ion in each ionic site of the structure under the conditions used by us.

Base Sequence↗
PubMed1970

Thymine and thymidine uptake by Haemophilus influenzae and the labeling of deoxyribonucleic acid.

The influence of ribo- and deoxyribonucleosides and ribo- and deoxyribonucleotides on the uptake of radiolabeled thymidine and thymine by Haemophilus influenzae during growth was investigated. A nucleoside-degrading enzyme similar to that reported in Escherichia coli was found to break down thymidine unless other nucleosides were present to divert its action. The presence of other nucleosides permitted a nearly quantitative uptake of even low levels of thymidine. This quantitative uptake of thymidine in the presence of an excess of other nucleosides suggests that the uptake mechanism for thymidine is specific in this organism. Under optimal conditions, as much as 50% of the deoxyribonucleic acid (DNA) thymine was derived from exogenous thymidine. Thymine was not taken up by H. influenzae but, in the presence of purine deoxynucleosides, labeled thymine entered the cells, presumably as thymidine. Ribonucleosides or ribonucleotides inhibited thymine conversion to thymidine, but, as noted above, they were degraded by a cellular enzyme. Thus, unless the ribonucleoside level was excessively high, a cell level of growth was reached at which the inhibiting ribonucleoside was broken down and labeled thymine appeared in the cells at an increasing rate. Twenty-five per cent of the DNA thymine of this organism was labeled with exogenous thymine. The information noted above serves as the basis for isotopically labeling the DNA.

Carbon Isotopes↗
PubMed1972

Effect of thymine limitation of chromosomal deoxyribonucleic acid synthesis in Proteus mirabilis.

The effects of thymine limitation on the rates of growth, deoxyribonucleic acid (DNA) synthesis, and increase in viable cell number for a thymine auxotroph of Proteus mirabilis were investigated. At thymine concentrations of 1.0 mug/ml and below, these rates were markedly decreased. After a reduction in thymine concentration from 10 mug/ml to 0.2 mug/ml, mass synthesis continued at the preshift rate for several hours. In contrast, the rate of DNA synthesis immediately decreased, resulting in a decrease in the DNA to mass ratio to about one-half of its normal level. Viable counts remained constant for several hours after the reduction in thymine concentration, and enlarged cells and multicellular "snakes" were formed. The rate of DNA synthesis was reduced at thymine concentrations below approximately 1.7 mug/ml. The addition of thymine to cultures which had been completely starved for thymine increased the rate of DNA synthesis to at least twice its normal value; this suggests that extra rounds of chromosome replication can be induced in P. mirabilis as previously observed in Escherichia coli.

Chromosomes, Bacterial↗
PubMed1962

Microbiological assay for thymine using a mutant of Streptococcus faecalis.

Doctor, V. M. (University of Texas, Houston). Microbiological assay for thymine using a mutant of Streptococcus faecalis. J. Bacteriol. 84:17-22. 1962.-A rapid microbiological assay procedure for the determination of thymine was devised. The test organism, Streptococcus faecalis Akt, a mutant of S. faecalis ATCC 8043, gives one-half the maximal growth response to 1.6 mug of thymine (assay range 0.5 to 2.5 mug) or to a molar equivalent (3.2 mug) of thymidine. Under these experimental conditions, 80 mug of 5-methylcytosine or 150 mug of thymidylic acid replace the thymine or thymidine requirement of the test organism. Addition of a mixture of adenine, guanine, and xanthine at a level of 40 mug/ml of each or higher to the basal medium, or addition of a mixture of deoxyadenosine and deoxyguanosine at a level of 80 mug/ml of each or higher to the basal medium, inhibited the thymine or thymidine growth response of the organism. Thymine activities of rat and chick tissues were determined by this procedure. The data on the recovery of added thymine to tissues gave 84 to 103% recovery. Thymus, spleen, small intestine, and ventral prostate were higher in thymine activities as compared with other tissues.

Adenine↗
PubMed1999

[Analysis of products of thymine irradiated by heavy ion beam with capillary gas chromatography].

In this study some chromatographic methods with capillary column, such as GC, GC-MS, GC-FTIR, were used to analyze the products of thymine irradiated by 18O8+ ion beam in N2O saturated aqueous solution. Because of the complexity and small amounts of the products after irradiation by heavy ion beams, it is very difficult to separate them, while with the methods of capillary gas chromatography this problem can be overcome. From the results of GC-MS analysis we can determine the molecular weight of the product, and from the results of GC-FTIR analysis we can get structure information of the product. By this way the products such as 5,6-dihydrothymine, 5-hydroxyl-5-methylhydantoin, 5-hydroxyl-6-hydrothymine, 5-hydro-6-hydroxylthymine, 5-hydroxymethyluracil, trans-thymine glycol, cis-thymine glycol and dimers were determined. Though these products are the same as those from thymine irradiated by gamma ray in N2O saturated aqueous solution, the mechanism of heavy ion beam interact ion with thymine aqueous solution is different from that of gamma ray. The main products from thymine irradiated by 18O8+ ion beam in N2O saturated aqueous solution are formed by hydroxyl additions between 5-6 band of thymine, while those by gamma ray are dimers of thymine.

Electrophoresis, Capillary↗
PubMed1980

Effect of coadministration of thymine or thymidine on the antitumor activity of 1-(2-tetrahydrofuryl)-5-fluorouracil and 5-fluorouracil.

The antitumor activity of 1-(2-tetrahydrofuryl)-5-fluorouracil (FT-207) on sarcoma was enhanced by oral coadministration of uracil, thymine, or thymidine. The activity was enhanced equally by thymine and by uracil than by thymidine, but thymine caused loss in body weight. The antitumor activity of 5-fluorouracil (5-FU) was also enhanced by thymine or uracil, but both caused loss in body weight. Degradation of 5-FU in vitro was inhibited more by thymine than by uracil. Phosphorylation of 5-FU, however, was not inhibited by uracil, thymine, or thymidine, even at 100 times the concentration of 5-FU. These results suggest that the mechanism of enhancement of the antitumor activity of FT-207 by thymine or thymidine was similar to that by uracil, and that uracil had more effect than thymine or thymidine in enhancing antitumor effect of these drugs to FT-207 without toxicity.

Administration, Oral↗
PubMed1997

Repair effect of phenylpropanoid glycosides on thymine radical anion induced by pulse radiolysis.

Repair effects on thymine radical anion by six phenylpropanoid glycosides (PPGs), isolated from Pedicularis species, were studied using pulse radiolysis method. The thymine radical anion was produced by the reaction of hydrated electron with thymine. PPGs were added into the thymine solution saturated with N(2). Kinetic analysis showed that transient absorption spectrum of thymine radical anion formed at first, and then after several microseconds of pulse radiolysis changed to that of PPG radical anion. The evidence indicated that thymine radical anion was repaired through one-electron transfer between the radical anion and PPG. Electrophilic phenyl-substituted unsaturated carboxylic group containing in PPGs' structure was able to capture electron from thymine radical anion before it undergo reversible protonation. The reaction rate constants of electron transfer from thymine radical anion to PPGs were within 1.16-2.29 x 10(9) dm(3) mol(-1) s(-1).

Journal Article↗