General enzymatic screens identify three new nucleotidases in Escherichia coli. Biochemical characterization of SurE, YfbR, and YjjG

To find proteins with nucleotidase activity in Escherichia coli, purified unknown proteins were screened for the presence of phosphatase activity using the general phosphatase substrate p-nitrophenyl phosphate. Proteins exhibiting catalytic activity were then assayed for nucleotidase activity against various nucleotides. These screens identified the presence of nucleotidase activity in three uncharacterized E. coli proteins, SurE, YfbR, and YjjG, that belong to different enzyme superfamilies: SurE-like family, HD domain family (YfbR), and haloacid dehalogenase (HAD)-like superfamily (YjjG). The phosphatase activity of these proteins had a neutral pH optimum (pH 7.0-8.0) and was strictly dependent on the presence of divalent metal cations (SurE: Mn(2+) > Co(2+) > Ni(2+) > Mg(2+); YfbR: Co(2+) > Mn(2+) > Cu(2+); YjjG: Mg(2+) > Mn(2+) > Co(2+)). Further biochemical characterization of SurE revealed that it has a broad substrate specificity and can dephosphorylate various ribo- and deoxyribonucleoside 5'-monophosphates and ribonucleoside 3'-monophosphates with highest affinity to 3'-AMP. SurE also hydrolyzed polyphosphate (exopolyphosphatase activity) with the preference for short-chain-length substrates (P(20-25)). YfbR was strictly specific to deoxyribonucleoside 5'-monophosphates, whereas YjjG showed narrow specificity to 5'-dTMP, 5'-dUMP, and 5'-UMP. The three enzymes also exhibited different sensitivities to inhibition by various nucleoside di- and triphosphates: YfbR was equally sensitive to both di- and triphosphates, SurE was inhibited only by triphosphates, and YjjG was insensitive to these effectors. The differences in their sensitivities to nucleotides and their varied substrate specificities suggest that these enzymes play unique functions in the intracellular nucleotide metabolism in E. coli.     

Nucleoside conjugates. 8. The preparation of 5-fluoro-2'-deoxyuridine conjugates of corticosteroids

Three 5'-(steroid-21-phosphoryl)-5-fluoro-2'-deoxyuridines (VI-VIII) have been prepared and characterized by uv, ir, 1H-nmr, elemental analysis, chemical and enzymatic hydrolyses. These new compounds are 5-fluoro-2'-deoxyuridine conjugates of cortisol (VI), cortico-sterone (VII), and prednisolone (VIII). Besides the physical and analytical data, all of the conjugates were demonstrated to be enzymatically hydrolyzed to the corresponding steroid and 5-fluoro-2'-deoxyuridine 5'-monophosphate (III), and the latter was further shown to be hydrolyzed to 5-fluoro-2'-deoxyuridine (II) by phosphodiesterase I, 5'-nucleotidase, and acid phosphatase. However, they were shown to be resistant to hydrolysis by bacterial alkaline phosphatase.     

Synthesis of 5-ethynyl-2'-deoxyuridine-5'-boranomono phosphate as a potential thymidylate synthase inhibitor

The 5-ethynyl-2'-deoxyuridine nucleoside and the 5'-boranomonophosphate nucleotide were synthesized as analogs of 5-fluoro-2'-deoxyuridine monophosphate (5-FdUMP), a widely used mechanism-based inhibitor of thymidylate synthase. Synthesis was carried out from protected 5-iodo-2'-deoxyuridine and trimethylsilylacetylene by Sonogashira palladium-catalyzed cross coupling reaction followed by selective phosphorylation and finally boronation.     

Assay of intracellular thymidylate synthetase activity and inhibition by 5-fluoro-2'-deoxyuridine in lymphocytes.

Thymidylate synthetase catalyses the formation of thymidine monophosphate from deoxyuridine monophosphate. Purified thymidylate synthetase can be assayed radiochemically using labelled deoxyuridine monophosphate as substrate, but cells are impervious to deoxyuridine monophosphate and so intracellular thymidylate synthetase activity cannot be assayed in this way. In this paper we describe the assay of intracellular thymidylate synthetase activity in intact cells using labelled 2'-deoxyuridine. The assay showed linear kinetics with respect to time, concentration of 2'-deoxyuridine, and cell concentration. 5-fluoro-2'-deoxyuridine inhibited intracellular thymidylate synthetase activity measured with this assay by 50% at 5 nM. Cell growth was inhibited by 50% at 6 nM 5-fluoro-2'-deoxyuridine. The assay was specific for thymidylate synthetase and enabled measurement of thymidylate synthetase activity in situ in intact cells.     

Measurement of 5-fluoro-2'-deoxyuridine serum levels by gas chromatography chemical ionization mass spectrometry

Serum levels of 5-fluoro-2'-deoxyuridine in cancer treated patients were measured by gas chromatography mass spectrometry under chemical ionization conditions; 1-(2-deoxy-beta-D-lyxofuranosyl)-5-fluorouracil (3'-epi-5-fluoro-2'-deoxyuridine) was used as an internal standard. The drug and internal standard were quantitatively isolated from the serum sample by a mini-column anion exchange method and the extract permethylated using potassium-tert-butoxide in dimethylsulphoxide and methyl iodide. The derivatized nucleosides were then re-extracted from the reaction mixture and analysed on a glass capillary column coated with Superox-4. The column was coupled directly to the chemical ionization source of the mass spectrometer; NH3 was used as the reagent gas. The gas chromatographic effluent was monitored at m/z 289, the [MH]+ ion of the N,O-permethyl derivatives of 5-fluoro-2'-deoxyuridine and the internal standard. Recovery of 5-fluoro-2'-deoxyuridine from serum in the 0-1 microgram ml-1 concentration range averaged 93 +/- 2% (SD); a linear detector response was observed up to 50 ng 5-fluoro-2'-deoxyuridine ml-1. At the 10 ng ml-1 level, a within-run assay precision of 10% (CV) (n = 5) was found, while a detection limit of about 1 ng 5-fluoro-2'-deoxyuridine ml-1 of serum was attained. The method was applied to the measurement of disappearance curves of 5-fluoro-2'-deoxyuridine in the serum of treated patients.     

5-Fluorouracil derivatives. III. A simple method to prepare 5-fluoro-2'-deoxyuridine derivatives

3',5'-Diacyl-2'-bromo-5-fluoro-2'-deoxyuridine (4) was obtained by the reaction of 5, 6-dihydro-6-hydroxy-5-fluorouridine (2) and acyl bromide. Because the route from uridine (1) to 2, the route from 4 to 3',5'-diacyl-5-fluoro-2'-deoxyuridine (5), and the route from 5 to 5-fluoro-2'-deoxyuridine (FUDR, 6) are known reactions, the three step synthesis from uridine to 5 and four step synthesis from uridine to FUDR have been accomplished.     

Rapid quantitation of plasma 2'-deoxyuridine by high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry and its application to pharmacodynamic studies in cancer patients

A novel method employing high-performance liquid chromatograph-mass spectrometry (LC-MS) has been developed and validated for the quantitation of plasma 2'-deoxyuridine (UdR). It involves a plasma clean-up step with strong anion-exchange solid-phase extraction (SAX-SPE) followed by HPLC separation and atmospheric pressure chemical ionization mass spectrometry detection (APCI-MS) in a selected-ion monitoring (SIM) mode. The ionization conditions were optimised in negative ion mode to give the best intensity of the dominant formate adduct [M+HCOO]- at m/z 273. Retention times were 7.5 and 12.5 min for 2'-deoxyuridine and 5-iodo-2'-deoxyuridine, an iodinated analogue internal standard (IS), respectively. Peak area ratios of 2'-deoxyuridine to IS were used for regression analysis of the calibration curve. The latter was linear from 5 to 400 nmol/l using 1 ml sample volume of plasma. The average recovery was 81.5% and 78.6% for 2'-deoxyuridine and 5-iodo-deoxyuridine, respectively. The method provides sufficient sensitivity, precision, accuracy and selectivity for routine analysis of human plasma 2'-deoxyuridine concentration with the lowest limit of quantitation (LLOQ) of 5 nmol/l. Clinical studies in cancer patients treated with the new fluoropyrimidine analogue capecitabine (N4-pentoxycarbonyl-5'-5-fluorocytidine) have shown that plasma 2'-deoxyuridine was significantly elevated after 1 week of treatment, consistent with inhibition of thymidylate synthase (TS). These findings suggest that the mechanism of antiproliferative toxicity of capecitabine is at least partly due to TS inhibitory activity of its active metabolite 5-fluoro-2'-deoxyuridine monophosphate (FdUMP). Monitoring of plasma UdR concentrations have the potential to help clinicians to guide scheduling of capecitabine or other TS inhibitors in clinical trials. Marked differences of plasma 2'-deoxyuridine between human and rodents have also been confirmed. In conclusion, the LC-MS method developed is simple, highly selective and sensitive and permits pharmacodynamic studies of TS inhibitors in several species.     

Gas-liquid chromatographic analysis of fluoropyrimidine nucleosides and fluorouracil in plasma and urine

A gas-liquid chromatographic method employing on-column alkylation and a nitrogen-sensitive detector was developed for the analysis of 5-fluoro-2'-deoxyuridine, 5-fluorouridine, and 5-fluorouracil in plasma and urine. Samples (0.72 ml) containing the fluoropyrimidine and internal standard (5-chloro-2'-deoxyuridine for nucleoside analyses and 6-methyluracil for 5-fluorouracil analyses) were prepared for gas-liquid chromatography by sequential cation-exchange and anion-exchange column chromatography. Recoveries of fluoropyrimidines were 71-95% over the concentration ranges studied. The dried eluate from the anion-exchange column was dissolved in p-tolyltrimethylammonium hydroxide in methanol before gas-liquid chromatographic analysis. Columns packed with either 3% SP-2100 on Supelcoport or 3% OV-1 on Gas-Chrom Q were suitable for nucleoside analyses; a column packed with 0.75% Carbowax 20M-5% KOH on Chromsorb G was used for 5-fluorouracil analyses. The fluoropyrimidine nucleosides were well separated from each other and from the potentially interfering endogenous compounds 2'-deoxyuridine and uridine; 5-fluorouracil was well separated from uracil. Linear standard curves (peak area ratio method) were obtained for plasma containing 0.025 to 20 micrograms FdUrd (0.1 to 81 microM) or 0.05 to 1.0 microgram FUrd (0.2 to 3.8 microM), and for urine containing 0.2 to 1.0 microgram (0.8 to about 4 microM) of the nucleosides. Standard curves for 5-fluorouracil (1.5 to 7.9 microM) and 2'-deoxyuridine (0.9 to 4.4 microM) were also linear. A measurable amount of 5-fluorouracil, equivalent to 4 to 7% of the 5-fluoro-2'-deoxyuridine injected, was formed from the nucleoside on the gas-liquid chromatographic column, requiring correction of 5-fluorouracil concentrations measured in the presence of 5-fluoro-2'-deoxyuridine.     

Amino acid phosphoramidate nucleosides: potential ADEPT/GDEPT substrates

A series of aromatic, serum-stable, water soluble and nontoxic amino acid phosphoramidate monoesters of 5-fluoro-2'-deoxyuridine (FUdR) and 1-beta-arabinofuranosylcytosine (Ara-C) was shown to inhibit the cellular growth of the human leukemia cell line CCRF-CEM in the presence of human prostatic acid phosphatase (hPAP).     

Delivery of floxuridine derivatives to cancer cells by water-soluble organometallic cages

The self-assembly of 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine (tpt) triangular panels with p-cymene (pPr(i)C(6)H(4)Me) ruthenium building blocks and 2,5-dioxydo-1,4-benzoquinonato (dobq) or 5,8-dioxydo-1,4-naphthoquinonato (donq) bridges, in the presence of a pyrenyl-nucleoside derivatives (pyreneR), affords the triangular prismatic host-guest compounds [(pyrene-R)?Ru(6)(pPr(i)C(6)H(4)Me)(6)(tpt)(2)(dobq)(3)](6+) ([(pyrene-R)?1](6+)) and [(pyrene-R)?Ru(6)(pPr(i)C(6)H(4)Me)(6)(tpt)(2)(donq)(3)](6+) ([(pyrene-R)?2](6+)), respectively. The inclusion of six monosubstitutedpyrenyl-nucleosides (pyrene-R1 = 5'-(1-pyrenyl butanoate)-2'-deoxyuridine, pyrene-R2 = 5-fluoro-5'-(1-pyrenyl butanoate)-2'-deoxyuridine, pyrene-R3 = 5'-{N-[1-oxo-4-(1-pyrenyl)butyl]-glycyl}-2'-deoxyuridine, pyrene-R4 = 5-fluoro-5'-{N-[1-oxo-4-(1-pyrenyl)butyl]-glycyl}-2'-deoxyuridine, pyrene-R5 = 5-fluoro-5'-{N-[1-oxo-4-(1-pyrenyl)butyl]-phenylalanyl}-2'-deoxyvuridine, pyrene-R6 = 5-fluoro-5'-{N-[1-oxo-4-(1-pyrenyl)butyl]-phenylalanyl}-2'-deoxyuridine) has been accomplished. The carceplex nature of [(pyrene-R)?1](6+) with the pyrenyl moiety firmly encapsulated in the hydrophobic cavity of the cage with the nucleoside groups pointing outward was confirmed by NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS), while the host-guest nature of [(pyrene-R)?2](6+) was studied in solution by NMR techniques. In contrast to the floxuridine compounds used in the clinic, the host-guest complexes are highly water-soluble. Consequently, the cytotoxicities of these water-soluble compounds have been established using human ovarian A2780 and A2780cisR cancer cells. All the host-guest systems are more cytotoxic than the empty cages alone [1][CF(3)SO(3)](6) (IC(50) = 23 μM) and [2][CF(3)SO(3)](6) (IC(50) = 10 μM), the most active compound [pyrene-R4?1][CF(3)SO(3)](6)being 2 orders of magnitude more cytotoxic (IC(50) = 0.3 μM) on these human ovarian cancer cell lines (A2780 and A2780cisR).     

Fluorination of 6-methyluracil and its nlcleosides.

6-Methyluracil and its perbenzoylated 1-(beta-D-ribofuranosyl) and 1-(2-deoxy-beta-D-ribofuranosyl) derivatives afford on treatment with elemental fluorine in acetic acid solutions, the corresponding derivatives of 5-fluoro-6-methyluracil and 5-fluoro-6-fluoromethyluracil. The free nucleosides have been obtained from the protected derivatives by methanolysis. The CH2F linkage in 5-fluoro-6-fluoromethyluracil derivatives is stable towards hydrolysis and nucleophilic agents.     

The incorporation of deoxyuridine monophosphate into DNA increases the sister-chromatid exchange yield

The effect of a treatment with 5-fluoro-2'-deoxyuridine (FdUrd) in combination with 2'-deoxyuridine (dUrd) on cell proliferation, incorporation of DNA precursors into DNA and sister-chromatid exchanges (SCEs) has been analyzed in Allium cepa meristem cells. FdUrd in the range 10(-9)-5 X 10(-7) M produced a dose- and time-dependent decrease in the amount of cells in mitosis. This inhibitory effect could be reversed by 70-80% in short-term (6 h) experiments, by exogenously supplied dUrd at a concentration of 10(-4) M. However, at the highest FdUrd dose tested (10(-7) M), 10(-4) M dUrd could not reverse the FdUrd effect in long-term experiments (20 h, about one cell cycle interval), as shown by analyzing the kinetics of synchronous cell populations. DNA extracted from cells pulsed with [6-3H]dUrd in the presence of FdUrd and 6-amino-uracil (6-AU), an inhibitor of uracil-DNA glycosylase, contained a small amount of label (at least 3% of the total radioactivity incorporated into DNA) in the form of [6-3H]dUMP. Thus, we conclude that, under our experimental conditions, exogenously supplied dUrd may be metabolized intracellularly to 2'-deoxyuridine triphosphate (dUTP) and that this deoxynucleotide may eventually be mis-incorporated into DNA. As far as the formation of SCEs is concerned, analysis of second division chromosomes showed that 2'-deoxyuridine monophosphate (dUMP) residues present in newly-synthesized DNA strands are probably not relevant to SCE formation. However, by analyzing SCE levels in third division chromosomes of cells treated with FdUrd and dUrd during their second cycle, we have scored a 6-fold increase in the reciprocal SCE level which demonstrates that the replication of a dUMP-containing DNA template leads to a higher SCE yield.     

Enhanced inhibition of thymidylate synthase by methotrexate polyglutamates

We have studied the effects of methotrexate (MTX-Glu1) and the polyglutamate derivatives of methotrexate (MTXPGs) with 2, 3, 4, and 5 glutamyl residues on the catalytic activity of thymidylate synthase purified from MCF-7 human breast cancer cells and on the kinetics of the ternary complex formation by 5-fluoro-2'-deoxyuridine 5'-monophosphate, folate cofactor, and thymidylate synthase. MTX-Glu1 exhibited uncompetitive inhibition of thymidylate synthase when reaction kinetics were analyzed by either double reciprocal plots or a computerized mathematical model based on nonlinear least-squares curve fitting. The Ki for MTX-Glu1 inhibition was 13 microM and the I50 was 22 microM, irrespective of the degree of polyglutamation of the folate. In contrast, the polyglutamated derivatives of MTX all acted as noncompetitive inhibitors. The MTXPGs had 75-300-fold greater potency than MTX-Glu1 as inhibitors of thymidylate synthase catalytic activity, with Ki values from 0.17 to 0.047 microM for MTX-Glu2 to MTX-Glu5, respectively. Neither MTX-Glu1 nor MTXPGs promoted the formation of a charcoal-stable ternary complex with thymidylate synthase and 5-fluoro-2'-deoxyuridine 5'-monophosphate. CH2-H4PteGlu5 (where PteGlu represents pteroylglutamic acid) was found to be 40-fold more potent than CH2-H4PteGlu1 in participating in the formation of a ternary complex, and 10 microM MTX-Glu5 significantly inhibited the formation of a ternary complex containing this folate as cofactor. The inhibition was determined to be due to a reduction in the kon. The potency of this inhibition was markedly greater in the presence of CH2-H4PteGlu1 as compared to CH2-H4PteGlu5. This finding suggests that the degree of interference with complex formation in intact cells would depend on the state of polyglutamation of available folate cofactor. Ternary complex formation with H2PteGlu5 as the folate cofactor was also investigated, and a 50% reduction in complex formation was found in the presence of a 2 microM concentration of MTX-Glu5. These findings have significant implications regarding the mechanism of action of MTX-Glu1 and contribute to an understanding of the complex interactions of MTX-Glu1 and 5-fluorouracil.     

Synthesis and evaluation of 6-aza-2'-deoxyuridine monophosphate analogs as inhibitors of thymidylate synthases, and as substrates or inhibitors of thymidine monophosphate kinase in Mycobacterium tuberculosis

A series of 5-substituted analogs of 6-aza-2'-deoxyuridine 5'-monophosphate, 6-aza-dUMP, has been synthesized and evaluated as potential inhibitors of the two mycobacterial thymidylate synthases (i.e., a flavin-dependent thymidylate synthase, ThyX, and a classical thymidylate synthase, ThyA). Replacement of C(6) of the natural substrate dUMP by a N-atom in 6-aza-dUMP 1a led to a derivative with weak ThyX inhibitory activity (33% inhibition at 50?μM). Introduction of alkyl and aryl groups at C(5) of 1a resulted in complete loss of inhibitory activity, whereas the attachment of a 3-(octanamido)prop-1-ynyl side chain in derivative 3 retained the weak level of mycobacterial ThyX inhibition (40% inhibition at 50?μM). None of the synthesized derivatives displayed any significant inhibitory activity against mycobacterial ThyA. The compounds have also been evaluated as potential inhibitors of mycobacterial thymidine monophosphate kinase (TMPKmt). None of the derivatives showed any significant TMPKmt inhibition. However, replacement of C(6) of the natural substrate (dTMP) by a N-atom furnished 6-aza-dTMP (1b), which still was recognized as a substrate by TMPKmt.     

Synthesis and study of cyclic pronucleotides of 5-fluoro-2'-deoxyuridine

A one-step method for the synthesis of cyclic pronucleotide (cProTide) derivatives of 5-fluoro-2'-deoxyuridine (FdUrd), utilizing a novel phosphoramidating reagent, is described. Stereochemistry at phosphorus was established by NMR studies and modeling. Cytotoxicity data of representative cProTide derivatives of FdUrd are presented. The observed cell-to-cell variations in activity suggests that it is feasible to screen for structural variations in the cProTide moiety favoring metabolic activation in cancer cells, which may lead to an increase in the therapeutic effectiveness of FdUrd. The method described is applicable to all anticancer and antiviral nucleoside analogs having both the 5'- and the 3'-OH groups available for modification, forming cProTide derivatives capable of delivering the 5'-monophosphates to cells.     

Phosphorolysis of 5-Fluoro-2′-Deoxyuridine in Escherichia coli and Its Inhibition by Nucleosides

The effect of ribonucleosides and deoxyribonucleosides on the phosphorolysis of 5-fluoro-2'-deoxyuridine (FUdR) was examined in cells of Escherichia coli. All nucleosides tested except guanosine and deoxyguanosine inhibited phosphorolysis. By using genetically marked strains it was found that in vivo FUdR is a specific substrate of thymidine phosphorylase.     

5'-O-Palmitoyl- and 3',5'-O-dipalmitoyl-5-fluoro-2'-deoxyuridine--novel lipophilic analogues of 5'-fluoro-2'-deoxyuridine: synthesis, incorporation into liposomes and preliminary biological results

5'-O-palmitoyl- and 3',5'-O-dipalmitoyl-5-fluoro-2'-deoxyuridine were prepared by the reaction of 5-fluoro-2'-deoxyuridine in dimethylacetamide with palmitic acid chloride. The incorporation of the synthesized prodrugs into liposomes composed of egg phosphatidylcholine/stearylamine/cholesterol/alpha-tocopherol at a molar ratio of 10:1:2:0.05 was nearly quantitative; homogeneous bilayer vesicles (75 nm diameter) were obtained. Preliminary tolerance studies revealed that the prodrug-liposome preparations are about 20-60 times more toxic than the parent drug. The prodrugs incorporated into liposomes were 10 to 30 times more active against murine colon 38 carcinoma compared to the free drug. In comparison to the administration of the prodrugs in peanut oil the liposomal preparations seem to exert improved effects and represent a valuable drug delivery system for parenteral applications.     

Mechanism of the cytotoxic synergism of fluoropyrimidines and folinic acid in mouse leukemic cells

We have investigated the mechanism by which reduced folates, such as folinic acid, enhance the cytotoxicity of fluoropyrimidines in L1210 mouse leukemic cells. Exposure of L1210 cells to folinic acid resulted in expansion of intracellular pools of 5,10-CH2-H4PteGlun, delayed the reappearance of catalytically active thymidylate synthase (TS) following 5-fluoro-2'-deoxyuridine exposure, and stabilized inhibited TS complexes over the same concentration range that augmented the cytotoxic effects of fluorodeoxyuridine and 5-fluorouracil. The data showed that, in intact L1210 cells, fluorodeoxyridylate behaves as an inhibitor whose complexes with TS dissociated with a biologically significant rate. However, these complexes become functionally irreversible in cells incubated with high levels of folinic acid. It was also found that bound and total TS levels increased in cells treated with fluorodeoxyuridine to an extent that substantially exceeded the increase in protein content per cell under the same conditions. These results are in accord with the concept that folinic acid augments the effects of the fluoropyrimidines by expansion of cellular 5,10-CH2-H4PteGlun pools with subsequent stabilization of ternary complexes among 5-fluoro-2'-deoxyuridine 5'-monophosphate, TS, and 5,10-CH2-H4PteGlun. In light of the accumulation of TS that occurs following exposure to fluoropyrimidines, this stabilization may be needed for efficient tumor cell killing by these agents.     

Antisense oligodeoxynucleotides: synthesis, biophysical and biological evaluation of oligodeoxynucleotides containing modified pyrimidines.

6-Azathymidine, 6-aza-2'-deoxycytidine, 6-methyl-2'-deoxyuridine, and 5,6-dimethyl-2'-deoxyuridine nucleosides have been converted to phosphoramidite synthons and incorporated into oligodeoxynucleotides (ODNs). ODNs containing from 1 to 5 of these modified pyrimidines were compared with known 2'-deoxyuridine, 5-iodo-2'-deoxyuridine, 5-bromo-2'-deoxyuridine, 5-fluoro-2'-deoxyuridine, 5-bromo-2'-deoxycytidine, and 5-methyl-2'-deoxycytidine nucleoside modifications. Stability in 10% heat inactivated fetal calf serum, binding affinities to RNA and DNA complements, and ability to support RNase H degradation of targeted RNA in DNA-RNA heteroduplexes were measured to determine structure-activity relationships. 6-Azathymidine capped ODNs show an enhanced stability in serum (7- to 12-fold increase over unmodified ODN) while maintaining hybridization properties similar to the unmodified ODNs. A 22-mer ODN having its eight thymine bases replaced by eight 6-azathymines or 5-bromouracils hybridized to a target RNA and did not inhibit RNase H mediated degradation.     

5-Fluoro-2'-deoxyuridine has effects on mitochondria in CEM T-lymphoblast cells

Fluoropyrimidines are useful anticancer agents and the compound 5-fluoro-2'-deoxyuridine (FdUrd) plays an important role in chemotherapy of colon cancers. Several nucleoside analogs, such as 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC), can be incorporated into and cause depletion of mitochondrial DNA (mtDNA). These drugs are known to cause mitochondrial toxicity after prolonged treatment in patients. In this study we demonstrate that FdUrd reduces the mtDNA content and the expression level of the mtDNA encoded cytochrome c oxidase (COX II) in a CEM T-lymphoblastic cell line.