Combinatorial synthesis of benzimidazolium dyes and its diversity directed application toward GTP-selective fluorescent chemosensors

Highly selective fluorescence turn-on GTP sensor, GTP Green, was discovered by a diversity directed sensor approach, combined by solid-phase combinatorial synthesis of a benzimidazolium library and high-throughput screening.

Benzo[a]pyrene-7,8-quinone-3'-mononucleotide adduct standards for 32P postlabeling analyses: detection of benzo[a]pyrene-7,8-quinone-calf thymus DNA adducts

Benzo[a]pyrene-7,8-quinone (BPQ) is one of the reactive metabolites of the widely distributed archetypal polycyclic aromatic hydrocarbon, benzo[a]pyrene (B[a]P). The formation of BPQ from B[a]P through trans-7,8-dihydroxy-7,8-dihydroB[a]P by the mediation of aldo-keto reductases and its role in the genotoxicity and carcinogenesis of B[a]P currently are under extensive investigation. Toxicity pathways related to BPQ are believed to include both stable and unstable (depurinating) DNA adduct formation as well as reactive oxygen species. We previously reported the complete characterization of four novel stable BPQ-deoxyguanosine (dG) and two BPQ-deoxyadenosine (dA) adducts (Balu et al., Chem. Res. Toxicol. 17 (2004) 827-838). However, the identification of BPQ-DNA adducts by 32P postlabeling methods from in vitro and in vivo exposures required 3'-monophosphate derivatives of BPQ-dG, BPQ-dA, and BPQ-deoxycytidine (dC) as standards. Therefore, in the current study, BPQ adducts of dGMP(3'), dAMP(3'), and dCMP(3') were prepared. The syntheses of the BPQ-3'-mononucleotide standards were carried out in a manner similar to that reported previously for the nucleoside analogs. Reaction products were characterized by UV, LC/MS analyses, and one- and two-dimensional NMR techniques. The spectral studies indicated that all adducts existed as diastereomeric mixtures. Furthermore, the structural identities of the novel BPQ-dGMP, BPQ-dAMP, and BPQ-dCMP adducts were confirmed by acid phosphatase dephosphorylation of the BPQ-nucleotide adducts to the corresponding known BPQ-nucleoside adduct standards. The BPQ-dGMP, BPQ-dAMP, and BPQ-dCMP adduct standards were used in 32P postlabeling studies to identify BPQ adducts formed in vitro with calf thymus DNA and DNA homopolymers. 32P postlabeling analysis revealed the formation of 8 major and at least 10 minor calf thymus DNA adducts. Of these BPQ-DNA adducts, the following were identified: 1 BPQ-dGMP adduct, 2 BPQ-dAMP adducts, and 3 BPQ-dCMP adducts. This study represents the first reported example of the characterization of stable BPQ-DNA adducts in isolated mammalian DNA and is expected to contribute significantly to the future BPQ-DNA adduct studies in vivo and thereby to the contribution of BPQ in B[a]P carcinogenesis.

Differences in oxidative stress dependence between gastric adenocarcinoma subtypes

AIM: To investigate the extent of oxidative stress in pre-neoplastic and neoplastic gastric mucosa in relation to their pathological criteria and histological subtypes.

METHODS: A total of 104 gastric adenocarcinomas from 98 patients (88 infiltrative and 16 intraepithelial tumors) were assessed immunohistochemically for expression of iNOS and occurrence of nitrotyrosine (NTYR)-containing proteins and 8-hydroxy-2’-deoxyguanosine (8-OH-dG)-containing DNA, as markers of NO production and damages to protein and DNA.

RESULTS: Tumor cells staining for iNOS, NTYR and 8-OH-dG were detected in 41%, 62% and 50% of infiltrative carcinoma, respectively. The three markers were shown for the first time in intraepithelial carcinoma. The expression of iNOS was significantly more frequent in tubular carcinoma (TC) compared to diffuse carcinoma (DC) (54% vs 18%; P = 0.008) or in polymorphous carcinoma (PolyC) (54% vs 21%; P = 0.04). NTYR staining was obviously more often found in TC than that in PolyC (72% vs 30%; P=0.03). There was a tendency towards a higher rate of iNOS staining when distant metastasis (pM) was present. In infiltrative TC, the presence of oxidative stress markers was not significantly correlated with histological grade, density of inflammation, the depth of infiltration (pT), lymph nodes dissemination (pN) and pathological stages (pTNM).

CONCLUSION: The iNOS-oxidative pathway may play an important role in TC, but moderately in PolyC and DC. DNA oxidation and protein nitration occur in the three subtypes. Based on the significant differences of NTYR levels, TC and PolyC appear as two distinct subtypes.

Capillary electrophoresis-ion trap mass spectrometry analysis of Ziagen and its phosphorylated metabolites

A capillary electrophoresis-ion trap mass spectrometry method with a time-segment program was developed to simultaneously analyze Ziagen and its phosphorylated metabolites such as carbovir monophosphate, carbovir diphosphate, and carbovir triphosphate. By using the time-segment program, the positively charged nucleoside analog and negatively charged nucleotides were separated and detected in a single electrophoretic run. The limits of detection were less than 2 micro M for all of the analytes. Calibration curves of the compounds showed excellent linearity over the range of 2-100 micro M. The capability of the method was demonstrated by analyzing Ziagen and its phosphorylated metabolites that were spiked in cellular extracts of human peripheral blood mononuclear cells at 20 micro M levels. Some endogenous nucleotides such as adenosine 5'-triphosphate, adenosine 5'-diphosphate, and adenosine 5'-monophosphate, were also detected in the cellular extracts.

Determination of the Capped Site Sequence of mRNA Based on the Detection of Cap-Dependent Nucleotide Addition Using an Anchor Ligation Method

The sequence analysis of the 5' ends of cDNAs prepared using the anchor ligation method has revealed that most of the full-length cDNAs have an additional dGMP at their 5' end that is absent in the corresponding genome sequence. Using model RNA transcripts with cap analogues possessing 7-methylguanosine and adenosine, the base of the added nucleotide has been shown to be complementary to the base of the cap analogue, suggesting that the cDNAs possessing an additional dGMP are derived from intact mRNAs with the cap structure. On the other hand, cap-free RNA did not produce cDNA with an extra dGMP. These findings suggest that we can determine whether or not the cDNA starts from the capped site sequence of mRNA based on the presence or absence of an additional dGMP at the 5' end of the cDNA synthesized using the anchor ligation method. This approach will be useful to determine the capped site sequence of mRNA, thus, to identify transcription start sites.

Deoxyribonucleotide pool imbalance stimulates deletions in HeLa cell mitochondrial DNA

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder associated with multiple mutations in mitochondrial DNA, both deletions and point mutations, and mutations in the nuclear gene for thymidine phosphorylase. Spinazzola et al. (Spinazzola, A., Marti, R., Nishino, I., Andreu, A., Naini, A., Tadesse, S., Pela, I., Zammarchi, E., Donati, M., Oliver, J., and Hirano, M. (2001) J. Biol. Chem. 277, 4128-4133) showed that MNGIE patients have elevated circulating thymidine levels and they hypothesized that this generates imbalanced mitochondrial deoxyribonucleoside triphosphate (dNTP) pools, which in turn are responsible for mitochondrial (mt) DNA mutagenesis. We tested this hypothesis by culturing HeLa cells in medium supplemented with 50 microM thymidine. After 8-month growth, mtDNA in the thymidine-treated culture, but not the control, showed multiple deletions, as detected both by Southern blotting and by long extension polymerase chain reaction. After 4-h growth in thymidine-supplemented medium, we found the mitochondrial dTTP and dGTP pools to expand significantly, the dCTP pool to drop significantly, and the dATP pool to drop slightly. In whole-cell extracts, dTTP and dGTP pools also expanded, but somewhat less than in mitochondria. The dCTP pool shrank by about 50%, and the dATP pool was essentially unchanged. These results are discussed in terms of the recent report by Nishigaki et al. (Nishigaki, Y., Marti, R., Copeland, W. C., and Hirano, M. (2003) J. Clin. Invest. 111, 1913-1921) that most mitochondrial point mutations in MNGIE patients involve T --> C transitions in sequences containing two As to the 5' side of a T residue. Our finding of dTTP and dGTP elevations and dATP depletion in mitochondrial dNTP pools are consistent with a mutagenic mechanism involving T-G mispairing followed by a next-nucleotide effect involving T insertion opposite A.

Applications of capillary electrophoresis with laser-induced fluorescence for analysis of dGMP-BPDE adduct

DNA adducts are thought to be crucial to the initiation of mutational and carcinogenic processes. Polycyclic aromatic hydrocarbons (PAHs) have been identified as one major source of carcinogenic risk since they can bind to DNA thus forming an adduct. Quantification of this adduct is important because it may correlate to the risk for cancer development. In this study, the adduct formed between 2'-deoxyguanosine 5'-monophosphate and benzo[ a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) was analyzed by capillary electrophoresis. Both capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) modes with laser-induced fluorescence detection were used for the separation and analysis of DNA adducts. The exploration of capillary electrophoresis in several modes provided different separation mechanisms in which the stereochemical forms of the adduct could be separated. The best result obtained was using a coated fused-silica capillary in Tris-TAPS buffer, which provided high sensitivity with a detection limit of 2.5x10(-9) mol L(-1). MECC separation of the BPDE adduct, although less sensitive, provided an efficient enantioselective separation option.

The addition of mycophenolate mofetil to antiretroviral therapy including abacavir is associated with depletion of intracellular deoxyguanosine triphosphate and a decrease in plasma HIV-1 RNA

Mycophenolic acid (MPA) enhances the in vitro activity of abacavir (ABC) and other nucleoside analog reverse transcriptase inhibitors (NRTIs) against sensitive and NRTI-resistant HIV-1. This may occur via depletion of intracellular deoxyguanosine triphosphate (dGTP). Mycophenolate mofetil (MMF) 500 mg twice daily was added as a single agent to the antiretroviral regimens of five patients failing maximal available therapy. Therapy included ABC, and in most cases didanosine (DDI) and tenofovir (TDF). At entry, mean plasma HIV-1 RNA (VL) was 5.02 log copies/mL (median 4.78, range 4.71-5.63) and mean CD4 count was 106/microL (median 117, range 11-174). MMF was well tolerated. CD4 cell counts did not change significantly from baseline for up to 60 weeks of follow-up. Three of five subjects had VL declines of >0.5 log copies/mL immediately after adding MMF; a fourth subject had a sustained decline of >0.5 log copies/mL after week 8. Declines of >0.5 log copies/mL were lost in two patients at 6 and 8 weeks, and persisted in two patients at 36 and 60 weeks of follow-up, respectively. An increase in the ratio of carbovir triphosphate (CBV-TP), the active antiviral metabolite of ABC, to dGTP was documented in 3 of 4 subjects in temporal association with decreased VL. Trough plasma MPA levels ranged from 0.26-1.67 microg/mL; peak levels 90 minutes after dosing from 1.20-7.77 microg/mL. AUC of MPA appeared little changed when measured over 28 weeks of therapy. Declines in VL were observed in association with measurable changes in the CBV-TP/dGTP ratio in some patients, whereas MPA AUC was below the 30-60 microg*hr/mL range targeted in organ transplantation. The possibility that MMF may enhance the effect of selected NRTIs and be tolerated in late stage HIV disease deserves careful randomized study.

Identification and characterization of (3",4"-dihydroxy)-1,N(2)-benzetheno-2'-deoxyguanosine 3'-monophosphate, a novel DNA adduct formed by benzene metabolites

Reaction of 2'-deoxyguanosine 3'-monophosphate with mixtures of the benzene metabolites p-benzoquinone (p-BQ) and hydroquinone (HQ) in an aqueous solution at pH 6.0 gave two main products which were isolated from the reaction mixture using reversed-phase HPLC and characterized using UV spectroscopy, negative ion electrospray mass spectrometry, and (1)H NMR. Variation of the ratio of p-BQ to HQ in the reaction mixture caused an increase in yield of one of the products. The two products were identified as (3"-hydroxy)-1,N(2)-benzetheno-2'-deoxyguanosine 3'-monophosphate and a new product, not previously characterized, (3",4"-dihydroxy)-1,N(2)-benzetheno-2'-deoxyguanosine 3'-monophosphate. Similar products were isolated from identical reactions with 2'-deoxyguanosine. Reaction of calf thymus DNA with HQ and p-BQ (1:1, w/w) resulted in four main products as identified by (32)P-postlabeling coupled with HPLC. The relative abundances of these adducts were 9%, 60%, 27%, and 4%, respectively. Co-chromatography of (32)P-postlabeled (3"-hydroxy)-1,N(2)-benzetheno-2'-deoxyguanosine 3'-monophosphate and (3",4"-dihydroxy)-1,N(2)-benzetheno-2'-deoxyguanosine 3'-monophosphate with the (32)P-postlabeled adducted calf thymus DNA identified these as the two minor products of the calf thymus DNA reaction.

Assessing the metabolic function of the MutT 8-oxodeoxyguanosine triphosphatase in Escherichia coli by nucleotide pool analysis

In Escherichia coli the mutT gene is one of several that acts to minimize mutagenesis by reactive oxygen species. The bacterial MutT protein and its mammalian homolog have been shown to catalyze in vitro the hydrolysis of the oxidized deoxyguanosine nucleotide, 8-oxo-dGTP, to its corresponding monophosphate. Thus, the protein is thought to "sanitize" the nucleotide pool by ridding the cell of a nucleotide whose incorporation into DNA would be intensely mutagenic. However, because others have shown mutT mutations to be mutagenic under some conditions of anaerobic growth, and have shown 8-oxo-dGTP to be a poor DNA polymerase substrate, there is reason to question this model. We have devised an assay for 8-oxo-dGTP in bacterial extracts. Using this assay, which involves reversed-phase high-performance liquid chromatography and electrochemical detection, we have been unable to detect 8-oxo-dGTP in extracts of three different mutT mutants of E. coli, even after growth of the bacteria in the presence of hydrogen peroxide. Our estimated upper limit for 8-oxo-dGTP content of these bacteria is about 200 molecules/cell, corresponding to a concentration of about 0.34 microm. When 8-oxo-dGTP was added at 0.34 microm to an in vitro DNA replication system primed with a DNA template that permits scoring of replication errors and with the four normal dNTPs at their estimated intracellular concentrations, there was no detectable effect upon the frequency of replication errors. These findings lead us to question the conclusion that 8-oxo-dGTP is the most significant physiological substrate for the MutT protein.

Identification of nucleotides with identical fluorescent labels based on fluorescence polarization in surfactant solutions

A solution-phase steady-state polarization-based method for discriminating among the four DNA nucleotides labeled identically with tetramethylrhodamine is described and demonstrated. Labeled nucleotides were dissolved in buffered surfactant solutions. In room temperature 4.5 mM Triton X-100 solutions at neutral pH, the measured steady-state polarizations of tetramethylrhodamine-labeled dATP, dCTP, dGTP and dUTP were 0.261 +/- 0.003, 0.112 +/- 0.003, 0.288 +/- 0.003, and 0.147 +/- 0.003, respectively. A blind test of 40 samples showed no errors in classification based on polarization. The reproducibility obtained during this study demonstrates that the four dye-labeled nucleotides can be discriminated with more than 99.8% confidence.

Simultaneous determination of Ziagen and its phosphorylated metabolites by ion-pairing high-performance liquid chromatography-tandem mass spectrometry

An ion-paring HPLC-MS-MS method with positive ion mode electrospray ionization has been developed to simultaneously quantify Ziagen, carbovir monophosphate, carbovir diphosphate and carbovir triphosphate. N',N'-Dimethylhexylamine was used as the ion-pairing agent. The presence of this ion-pairing agent allowed the retention and separation of the four compounds on a reversed-phase HPLC column as well as the detection of the nucleotides with positive ion mode electrospray ionization. The limits of detection were found to be better than 25 nM for all the analytes. Calibration curves of the analytes showed excellent linearity over the range of 25 nM to 5 microM. The relative standard deviations and accuracies for replicate analyses of quality control samples were less than 15%. The method has been successfully applied to the analysis of these compounds in human liver cells treated with Ziagen.

Development of a (32)P-postlabeling/HPLC method for detection of dehydroretronecine-derived DNA adducts in vivo and in vitro

Pyrrolizidine alkaloids are naturally occurring genotoxic chemicals produced by a large number of plants. Metabolism of pyrrolizidine alkaloids in vivo and in vitro generates dehydroretronecine (DHR) as a common reactive metabolite. In this study, we report the development of a (32)P-postlabeling/HPLC method for detection of (i) two DHR-3'-dGMP and four DHR-3'-dAMP adducts and (ii) a set of eight DHR-derived DNA adducts in vitro and in vivo. The approach involves (1) synthesis of DHR-3'-dGMP, DHR-3'-dAMP, and DHR-3',5'-dG-bisphosphate standards and characterization of their structures by mass and (1)H NMR spectral analyses, (2) development of optimal conditions for enzymatic DNA digestion, adduct enrichment, and (32)P-postlabeling, and (3) development of optimal HPLC conditions. Using this methodology, we have detected eight DHR-derived DNA adducts, including the two epimeric DHR-3',5'-dG-bisphosphate adducts both in vitro and in vivo.

Development of a quality control material for the measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an in vivo marker of oxidative stress, and comparison of results from different laboratories

The measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine is an increasingly popular marker of in vivo oxidative damage to DNA. A random-sequence 21-mer oligonucleotide 5'-TCA GXC GTA CGT GAT CTC AGT-3' in which X was 8-oxo-guanine (8-oxo-G) was purified and accurate determination of the oxidised base was confirmed by a 32P-end labelling strategy. The lyophilised material was analysed for its absolute content of 8-oxo-dG by several major laboratories in Europe and one in Japan. Most laboratories using HPLC-ECD underestimated, while GC-MS-SIM overestimated the level of the lesion. HPLC-ECD measured the target value with greatest accuracy. The results also suggest that none of the procedures can accurately quantitate levels of 1 in 10(6) 8-oxo-(d)G in DNA.

Analysis of melphalan adducts of 2'-deoxynucleotides in calf thymus DNA hydrolysates by capillary high-performance liquid chromatography-electrospray tandem mass spectrometry

Melphalan is a bifunctional alkylating agent that covalently binds with intracellular nucleophilic sites. A methodology using electrospray mass spectrometry was developed to detect and identify DNA adducts. Alkylation sites within a particular nucleotide were examined using electrospray tandem mass spectrometry hyphenated to capillary liquid chromatography in combination with a column switching system. In the reaction mixtures resulting from the interaction of 2'-deoxynucleotides and melphalan several base-aklylated adducts were found. In the case of 2'-deoxyadenosine monophosphate, thymidine monophosphate and 2'-deoxyguanosine phosphate alkylation was observed in the mononucleotide reaction mixtures but not in the DNA-hydrolysates. Calf thymus DNA was reacted in vitro with melphalan. The DNA pellet was isolated and enzymatically hydrolyzed with the aid of Nuclease P1. In this hydrolysate both mono-alkylated 2'-deoxynucleotides and dinucleotides were found. The most important adduct found was identified as the N-7 alklylated dGMP adduct. The alkylated dinucleotides were identified as a pdApdT/melphalan and pdGpdC/melphalan the latter being the most important.

The ribonucleoside diphosphate reductase inhibitor (E)-2'-deoxy-(fluoromethylene)cytidine as a cytotoxic radiosensitizer in vitro

(E)-2'-Deoxy-(fluoromethylene)cytidine (FMdC) is known as an inhibitor of ribonucleoside diphosphate reductase, a key enzyme in the de novo pathway of DNA synthesis. FMdC was tested as a modifier of radiation response in vitro on a human colon carcinoma cell line (WiDr), and the observed radiosensitization was confirmed on two human cervix cancer cell lines (C33-A and SiHa). Using the clonogenic assay, the effect ratio (ER) at a clinically relevant dose level of 2 Gy was 2.10 (50 nM FMdC), 1.70 (30 nM FMdC), and 1.71 (40 nM FMdC) for the three cell lines WiDr, C33-A, and SiHa, respectively. A more detailed analysis of the importance of timing and concentration of FMdC was done on the WiDr cell line alone, yielding an increased ER(2Gy) with increasing concentration and duration of exposure to the drug, ranging from 1.0 (6 h) to 1.8 (72 h) at 30 nM FMdC and from 1.2 (6 h) to 3.5 (24 h) at 300 nM. We investigated the effect of FMdC on the cellular deoxynucleotide triphosphate pool in WiDr cells and demonstrated a marked depletion of dATP and a significant rise of TTP levels. Cell cycle analysis showed early S-phase accumulation induced by FMdC alone, G2-M block induced by irradiation alone, and an increased accumulation of cells in G2-M if both modalities are used. Our data suggest that FMdC is a radiation response modifier in vitro on different cancer cell lines. The observed radiosensitization may in part be explained by alteration of the deoxynucleotide triphosphate pool, which is consistent with the effect of FMdC on ribonucleoside diphosphate reductase.

A novel method for the isolation and identification of stable DNA adducts formed by Dibenzo[a,l]pyrene and Dibenzo[a,l]pyrene 11, 12-dihydrodiol 13,14-epoxides in vitro

Our laboratory previously reported the identification and quantification of depurinating DNA adducts of dibenzo[a,l]pyrene (DB[a,l]P) in vitro, which comprise about 84% of all the DNA adducts that are formed [Li, K.-M., et al. (1995) Biochemistry 34, 8043-8049]. To determine a complete adduct profile and identify both stable and depurinating DNA adducts, we have developed a relatively simple, nonradioactive method for the identification of stable DNA adducts by combining enzymatic digestion, HPLC, and fluorescence line-narrowing spectroscopy (FLNS) techniques. Calf thymus DNA, bound to either (+/-)-anti- or (+/-)-syn-DB[a,l]PDE or rat liver microsome-activated DB[a,l]P, was first digested to 3'-mononucleotides with micrococcal nuclease and spleen phosphodiesterase. The adducts were then separated by HPLC with an ion-pair column and identified by FLNS by using the spectra of standards for comparison. In reactions with (+/-)-anti-DB[a,l]PDE, three adducts, an anti-cis-DB[a,l]PDE-dGMP, an anti-trans-DB[a, l]PDE-dAMP, and an anti-cis-DB[a,l]PDE-dAMP, were identified by HPLC and FLNS. In reactions with (+/-)-syn-DB[a,l]PDE, a pair of syn-trans-DB[a,l]PDE-dGMP adducts as well as a syn-cis-DB[a, l]PDE-dGMP, a syn-cis-DB[a,l]PDE-dAMP, and a pair of syn-trans-DB[a, l]PDE-dAMP adducts were identified. From the digest of microsome-activated DB[a,l]P-bound DNA, a syn-trans-DB[a,l]PDE-dGMP, an anti-cis-DB[a,l]PDE-dGMP, a syn-trans-DB[a,l]PDE-dAMP, and a syn-cis-DB[a,l]PDE-dAMP adduct were identified. An anti-cis-DB[a, l]PDE-dAMP adduct was identified only by (32)P-postlabeling. A total of five of the stable adducts formed by DB[a,l]P and nine of the stable adducts formed by DB[a,l]PDE in vitro have been identified. These adducts were also correlated to adduct spots in the (32)P-postlabeling method by cochromatography with standards. Approximately 93% of the stable adducts formed in reactions with (+/-)-anti-DB[a,l]PDE, 90% of adducts with (+/-)-syn-DB[a,l]PDE, and 85% of adducts formed with microsome-activated DB[a,l]P have been identified as Gua or Ade adducts. Equal amounts of stable Gua and Ade adducts were observed in the microsome-catalyzed binding of DB[a, l]P to calf thymus DNA, while 1.4 times more Gua adducts than Ade adducts were obtained in reactions with (+/-)-anti- or (+/-)-syn-DB[a,l]PDE.

Accurate and sensitive quantitation of N7-methyldeoxyguanosine-3'-monophosphate by 32P-postlabeling and storage-phosphor imaging

As N7-methyldeoxyguanosine-3'-monophosphate (N7-MedGp) is the major, persistent DNA lesion generated by methylating agents, a combined HPLC/32P-postlabeling assay has been developed to quantitate this adduct in human DNA. N7-MedGp was purified from normal nucleotides by anion-exchange chromatography followed by reverse-phase HPLC procedures. The adduct was then 32P-postlabeled and resolved by two-dimensional TLC for detection and quantitation by storage-phosphor imaging. The effect of conditions used for DNA purification and digestion on the recovery of N7-MedGp has been investigated. Extended, raised temperature incubations normally employed during DNA purification were demonstrated to result in considerable loss of adduct through depurination after 22 h at 65 and 37 degrees C (82% and 20% loss, respectively), but depurination was reduced to 5% if the incubation was performed at either 4 or 22 degrees C. Similarly, close to optical recovery (83%) of N7-MedGp was achieved after DNA digestion by incubating at 4 degrees C, pH 7.4, for 18 h in the presence of micrococcal nuclease and calf spleen phosphodiesterase from Sigma and Boehringer Mannheim, respectively. Overall, the recovery of N7-MedGp was 40%, resulting in a detection limit of 1.3 fmol which is equivalent to 0.16 mumol of adduct/mol of 2'-deoxyguanosine-3'-monophosphate (dGp) when analyzing 10 micrograms of DNA. The N7-MedGp content of DNA that had been methylated in vitro using 0, 16, and 80 microM N-methyl-N-nitrosourea (NMU) was determined by 32P-postlabeling to be 12, 112, and 671 mumol of N7-MedGp/mol of dGp. Electrochemical detection of N7-methylguanine (N7-MeG) after HPLC purification measured approximately 2-fold higher levels, i.e., 25, 225, and 1080 mumol of N7-MeG/mol of Gua, at each NMU concentration, respectively. The levels of N7-MedGp in the white blood cell (WBC) DNA of patients receiving a single dose of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC) chemotherapy were determined by 32P-postlabeling. Maximum levels were found 4-6 h after treatment, and in two out of four individuals adduct levels were decreased by 21 h. Prior to treatment, N7-MedGp was detectable in WBC DNA in two out of the four individuals indicating that nontherapeutic exposure to methylating agents had occurred.

Detection and characterization of two major ethylated deoxyguanosine adducts by high performance liquid chromatography, electrospray mass spectrometry, and 32P-postlabeling. Development of an approach for detection of phosphotriesters

Postlabeling can be one of the most sensitive methods for the measurement of DNA adducts. However, for the determination of alkylated adducts, essential requirements are standards which must be fully chemically characterized. In order to develop a postlabeling assay for monitoring exposure to genotoxic ethylating agents, the reaction of diethyl sulfate with 2'-deoxynucleoside 3'- and 5'-monophosphates was examined. The adducts generated were fully characterized using HPLC, electrospray tandem mass spectrometry, UV, and postlabeling. The major product was the phosphodiester derived from alkylation of the phosphate, and alkylation of the base occurred to a lesser extent. The phosphodiester standard, 2'-deoxyguanosine 3'-(mono-O-ethyl phosphate) (3'Et-pdG), was used to develop a postlabeling assay for the detection of this adduct in DNA samples. Since alkylated phosphodiesters in DNA are not susceptible to the actions of micrococcal nuclease and calf spleen phosphodiesterase, they can be obtained as alkylated phosphodiester dinucleosides from DNA. Nuclease P1 was used as enhancement step which allowed the separation of these adducted phosphotriesters from the unmodified nucleotides by HPLC. Subsequent hydrolysis of the phosphotriester dinucleosides in alkali yielded phosphodiesters, including 3'Et-pdG, which was efficiently postlabeled. This approach was shown to be capable of detecting this adduct in liver DNA from mice treated intraperitoneally with N-nitrosodiethylamine.

Selective potentiation of lometrexol growth inhibition by dipyridamole through cell-specific inhibition of hypoxanthine salvage

The novel antifolate lometrexol (5,10-dideazatetrahydrofolate) inhibits de novo purine biosynthesis, and co-incubation with hypoxanthine abolishes its cytotoxicity. The prevention of hypoxanthine rescue from an antipurine antifolate by the nucleoside transport inhibitor dipyridamole was investigated for the first time in nine human and rodent cell lines from seven different tissues of origin. In A549, HeLa and CHO cells, dipyridamole prevented hypoxanthine rescue and so growth was inhibited by the combination of lometrexol, dipyridamole and hypoxanthine, but in HT29, HCT116, KK47, MDA231, CCRF CEM and L1210 cells dipyridamole had no effect and the combination did not inhibit growth. Dipyridamole inhibited hypoxanthine uptake in A549 but not in CCRF CEM cells. Dipyridamole prevented the hypoxanthine-induced repletion of dGTP pools, depleted by lometrexol, in A549 but not in CCRF CEM cells. Thus, the selective growth-inhibitory effect of the combination of lometrexol, dipyridamole and hypoxanthine is apparently due to the dipyridamole sensitivity (ds) or insensitivity (di) of hypoxanthine transport. Both the human and murine leukaemic cells are of the di phenotype. If this reflects the transport phenotype of normal bone marrow it would suggest that the combination of lometrexol, dipyridamole and hypoxanthine might be selectively toxic to certain tumour types and have reduced toxicity to the bone marrow.

Electrospray interface for capillary electrophoresis-mass spectrometry with fiber-optic UV detection close to the electrospray tip

A miniaturized, integrated capillary electrophoresis-ultraviolet detection-electrospray ionization-mass spectrometry (CE-UV-ESI-MS) interface has been constructed and evaluated. The device incorporates a fiber optic detection cell close to the electrospray tip to allow UV monitoring of separated zones just prior to their admittance into the mass spectrometer. This configuration provides precise information about the time when UV-active zones enter the electrospray and allows easy location of analyte mass information in the ion current profile. The miniaturized dimensions of the interface allow the use of short capillaries for fast separations.

Detection of N7-methyldeoxyguanosine adducts in human pulmonary alveolar cells

Alkylating agents may cause DNA damage in different human cells and tissues, including lungs. For instance, tobacco-specific N-nitrosamines are known to produce methyl-DNA adducts, such as N7-methyldeoxyguanosine, and to induce lung tumors. We applied a combined high-performance liquid chromatography (HPLC)/32P-postlabeling technique for measurement of N7-methyldeoxyguanosine in human pulmonary alveolar cells (HPAC). Thirty patients (13 males, 17 females; mean age 51 +/- 17 yr) undergoing bronchoalveolar lavage for diagnosis of nonmalignant lung diseases were studied. DNA was extracted from HPAC, digested to 2'-deoxyribonucleotide 3'-monophosphates and HPLC separated to obtain deoxyguanosine (dGp) and N7-methyldeoxyguanosine (N7-MedGp) monophosphates. Fractions corresponding to normal (1:10,000) and N7-methylated dGp were subsequently 32P-postlabeled by T4 polynucleotide kinase with high specific activity 32P-ATP, resolved by two-dimensional thin-layer chromatography (TLC) and autoradiographed after 3 to 18 h exposure. Spots corresponding to dGp and N7-MedGp were scraped off the plates and quantitated by liquid scintillation counting to calculate direct molar ratios. Recovered HPAC (14.4 +/- 10.0 x 10(6)) were predominantly macrophages (73.8 +/- 16.4%) and lymphocytes (9.8 +/- 11.6%). N7-MedGp was detected in 11 patients, the level ranging from 0.10 to 48.03 fmol/micrograms DNA which corresponded to 0.31-79.00 x 10(-6) N7-MedGp/dGp ratios. Detection of N7-MedGp in HPAC was associated with the smoking habit of patients: N7-MedGp was present in 7 of 10 smokers, 2 of 10 ex-smokers, and 2 of 10 nonsmokers (P < 0.05). These results show that HPAC may be used for molecular dosimetry of DNA damage by alkylating agents, including tobacco-specific N-nitrosamines, in cigarette smokers and thus used for cancer risk assessment.

Optimization of 32P-postlabelling assays for the quantitation of O6-methyl and N7-methyldeoxyguanosine-3'-monophosphates in human DNA

The 3' and 5'-monophosphates of O6-methyldeoxyguanosine and N7-methyldeoxyguanosine were chemically synthesized. Using these standards with deoxyguanosine-3'-monophosphate (dGp) as an internal standard, conditions were optimized to quantify O6-methyldeoxyguanosine-3'-monophosphate (O6-MedGp) and N7-methyldeoxyguanosine-3'-monophosphate (N7-MedGp) by 32P-postlabelling. Under optimal conditions, the labelling efficiencies of O6-MedGp and N7-MedGp were respectively approximately 100 and approximately 15%, with detection limits of approximately 1.1 and approximately 6.0 fmol respectively using 10 pmol dGp or 0.8 fmol of O6-MedGp if 2 pmol of dGp was used. The assay developed for O6-MedGp was then applied to the quantitation of [3H]-O6-MedGp and O6-MedGp isolated from DNA digests by immunoaffinity separation. The standard curve generated from the use of [3H]-O6-MedGp, thus isolated, was identical to that generated previously using the chemically synthesized O6-MedGp, indicating that no inhibitory factors co-eluted with the O6-MedGp. After passage through two immunocolumns, recovery of 4 and 40 fmol of O6-MedGp was approximately 30%. Four human stomach samples were analysed by combining this immunoaffinity purification with 32P-post-labelling: levels ranged from 0.21 to 0.86 mumol O6-MedGp/mol dG. Further DNA samples, isolated from the human colon, were fractionated by anion-exchange HPLC and the N7-MedGp and O6-MedGp containing fractions were purified by reverse-phase HPLC and immunoaffinity chromatography respectively. Adduct-containing fractions were dried and 32P-postlabelled. Whereas O6-MedGp was detected at levels between 0.3 and 3.4 mumol O6-MedGp/mol dG, no N7-MedGp was detected in these samples, probably due to depurination of N7-MedGp to N7-methylguanine or reduced assay sensitivity resulting from contaminating nucleotides and/or unidentified radioactivity eluting close to the N7-methyldeoxyguanosine-5'-monophosphate.

Molecular effects of 2',2'-difluorodeoxycytidine (Gemcitabine) on DNA replication in intact HL-60 cells

The ability of pH-step alkaline elution to isolate different size species of nascent DNA (nDNA) from intact cells was utilized to study the effects of 2',2'-difluorodeoxycytidine (dFdC) on DNA replication in HL-60 cells. Preincubation with dFdC caused a concentration-dependent decrease in overall [3H]thymidine incorporation into DNA, accompanied by an increase in the proportion of radiolabel accumulated in small nDNA fragments. Twenty-four hours following removal of dFdC, radiolabel progressed from smaller to larger fragments and into genomic-length DNA. At initial concentrations of exposures to dFdC or cytosine arabinoside (ara-C) that caused 50% lethality (LC50) to HL-60 cells (40 and 50 nM, respectively), slower and less complete transit of nDNA from small subreplicon-length fragments through larger intermediates to genomic-length DNA was observed for nDNA fragments containing incorporated [3H]dFdC than for fragments containing [3H]ara-C. This was accomplished with less [3H]dFdC incorporated into DNA than [3H]ara-C at these extracellular concentrations of drug. Pulse-chase studies, using higher concentrations of radiolabeled drug, similarly revealed that nDNA fragments containing incorporated dFdC, like those containing ara-C, progressed with respect to time into larger nDNA intermediates and ultimately into genomic-length DNA; however, such progression for nDNA fragments containing dFdC was less complete than for fragments containing ara-C. The radioactivity incorporated into DNA represented authentic dFdC, as determined by DNA degradation studies, and was stable in DNA for at least 48 hr after removal of extracellular [3H]dFdC. Some of the effects of dFdC on ribonucleotide reduction in HL-60 cells were assessed by measurement of the intracellular pools of dCTP and dGTP. The drug had a greater effect on pools of dGTP than of dCTP, with transient reductions in dGTP observed at concentrations that encompass the LC50 for dFdC. These studies suggest that the interaction with DNA synthesis is an important component of the cytotoxicity of dFdC in HL-60 cells. Because it is incorporated progressively through nDNA compartments and ultimately into genomic-length DNA, dFdC should be categorized as an agent that slows DNA elongation in the intact cell, and not as a chain terminator in the absolute sense.

Development of a 32P-postlabelling method for the analysis of 2'-deoxyguanosine-3'-monophosphate and DNA adducts of methylglyoxal

A 32P-postlabelling assay was developed for the analysis of adducts arising from the reaction of 2'-deoxyguanosine-3'-monophosphate with the 1,2-dicarbonyl compound methylglyoxal, a major mutagen in several foodstuffs, in particular, instant and brewed coffee. The 32P-postlabelling reaction was optimized by testing various parameters such as the kinetics of phosphorylation by T4 polynucleotide kinase, substrate concentration-dependent labelling efficiency and the concentration of the various ingredients of the phosphorylation reaction. The sensitivity to the 3'-monophosphate dephosphorylation activity of nuclease P1 was also studied. Four isomeric reaction products were separated by HPLC, structurally characterized and identified as 3-(2'-deoxy-beta-D-erythro-pentafuranosyl)-6,7-dihydro-6,7-dihydro xy-6- methylimidazo[2,3-b]purine-9(8H)one. The same adducts could be detected from calf thymus DNA that had been reacted in vitro with methylglyoxal. DNA adducts were isolated after enzymatic digestion to mononucleotides followed by nuclease P1 digestion of normal nucleotides. The total level of methylglyoxal-DNA adducts obtained was 5.7 +/- 1.7 (n = 15) adducts/10(6) nucleotides. The 32P-postlabelling method was further validated by the detection of adducts of methylglyoxal in DNA from freshly isolated and stimulated human lymphocytes exposed in vitro. The concentrations of the adducts detected in these samples were 8.2 +/- 0.9 (n = 3) adducts/10(7) nucleotides and 1.5 +/- 0.1 (n = 3) adducts/10(6) nucleotides after treatment with 1.5 and 3.0 mM methylglyoxal respectively.

Identification and characterization of deoxyguanosine adducts of mutagenic beta-alkyl-substituted acrolein congeners

The reaction of the mutagenic beta-alkyl-substituted acroleins (E)-2-pentenal, (E)-2-hexenal, (E,E)-2,4-hexadienal, and 3,3-dimethylacrolein with nucleosides and 5'-mononucleotides was studied. We found two different types of adducts with deoxyguanosine and 2'-deoxyguanosine 5'-monophosphate. No adducts could be isolated with either nucleosides other than deoxyguanosine or nucleotides other than 2'-deoxyguanosine 5'-monophosphate. With pentenal, hexenal, and 3,3-dimethylacrolein, we identified and characterized 1,N2-cyclic adducts and 7,8-cyclic adducts. The 1,N2-adducts of pentenal and hexenal were mixtures of diastereomers, one pair in which the substituents in the newly formed ring were trans (6S,8S and 6R,8R) and another in which they were cis. The cis isomers were formed to a much lesser extent. In all cases, the regioisomer is formed in which the OH group is vicinal to the N-1 atom of the guanine moiety. In the case of the 7,8 adducts, the ribose cleaved spontaneously during the reaction, and a mixture of isomers in which the substituents were cis and trans in the newly formed tetrahydropyrrole ring was observed. Since these compounds form adducts in a similar way to crotonaldehyde and are also mutagenic like crotonaldehyde, it was proposed to regard them as carcinogenic, like crotonaldehyde, unless experimental examination demonstrates nonmutagenicity.

A simplified HPLC method for simultaneously quantifying ribonucleotides and deoxyribonucleotides in cell extracts or frozen tissues

Agents and conditions that induce alterations in deoxyribonucleotide pools can have important regulatory effects on the rate of DNA synthesis as well as cell cycle progression. A simplified procedure for the separation of both ribonucleoside triphosphates (NTP) and deoxyribonucleoside triphosphates (dNTP) is presented which utilizes reversed phase high-performance liquid chromatography coupled with diode array detection. The simultaneous resolution of NTP and dNTP peaks within the same cell extract effectively eliminates the need for post-extraction steps such as periodate oxidation and/or boronate affinity chromatography previously used to degrade or isolate co-eluting NTP from dNTP. The resolution of two nucleotides, dGTP and ADP, was found empirically to vary with the efficiency of the C18 column. High efficiency columns (> 90,000 plates/m) provided good separation; however, less efficient columns resulted in co-elution of dGTP and ADP. These co-eluting nucleotides can be accurately quantified, if necessary, using diode array technology and a mathematical expression which incorporates molar peak coefficients and peak areas obtained by monitoring at dual wave-lengths. Tissue samples or single cell suspensions were extracted with trichloroacetic acid and the neutralized extract was injected directly into the column without prior lyophilization. The per cent recovery of standards was > or = 99% and replicate extractions within or between samples were highly reproducible (SD < 5%). The single step method described minimizes potential losses associated with post-extraction manipulation and provides the capability to examine alterations in nucleotide precursor-product metabolism under various physiological and pharmacological conditions.

Absence of 2'-deoxy-GTP in adult brain tubulin

Nerve growth factor can stimulate incorporation of 2'-deoxy-GTP into the non-exchangeable nucleotide sites in tubulin and cytoskeletal microtubules of PC12 pheochromocytoma cells and embryonic chick dorsal root ganglion neurons [J. M. Angelastro and D. L. Purich (1992) J. Biol. Chem. 267, 25685-25689]. We replaced and hydrolyzed exchangeable-site GTP and GDP in adult bovine brain tubulin by incubation with the non-hydrolyzable nucleotide analogue 5'-guanylyl-methylenediphosphonate and alkaline phosphatase, thereby allowing us to analyze the non-exchangeable guanine nucleotides for GTP and dGTP. HPLC analysis reveals no evidence of dGTP in adult tubulin, suggesting further that the appearance of dGTP in tubulin and microtubules may be a characteristic of recently dividing neurons in response to nerve growth factor.

7-Alkyldeoxyguanosine adduct detection by two-step HPLC and the 32P-postlabeling assay

7-Alkyldeoxyguanosine DNA adducts may be a marker for some N-nitroso compound exposures and subsequent human cancer risk. A sensitive and highly specific assay for the detection of 7-methyl-2'-deoxyguanosine-3'-monophosphate (7-methyldGp) and 7-ethyl-2'-deoxyguanosine-3'-monophosphate (7-ethyldGp) has been developed by combining two different HPLC purification steps with the 32P-postlabeling assay. We previously reported that ion-pair reverse-phase (IP) chromatography coupled with the 32P-postlabeling assay detects 7-methyldGp in human lung, but have found that other nucleotides and unknown adducts co-elute. Thus, weak anion exchange (AE) HPLC was added in tandem with IP HPLC prior to the 32P-postlabeling assay. 2'-Deoxyguanosine-3'-monophosphate (dGp) is incorporated into the assay as an internal standard for the assessment of enzyme labeling efficiency and adduct recovery. The methodology was validated using radiolabeled DNA and liquid scintillation counting, which accounts for adduct loss from enzymatic digestion to detection. Levels of 7-ethyldGp also were correlated with accelerator mass spectrometry. The overall adduct recovery with this method was 58% for 7-methyldGp and 98% for 7-ethyldGp. The detection limit for both assays using 100 micrograms of DNA was one adduct in 10(8) unmodified dGp. 7-MethyldGp and 7-ethyldGp levels were determined in ten human lung samples at levels of 1.4-5.4 and 0.6-3.1 adducts per 10(7) dGp respectively, and in five human lymphocyte samples at levels of 5.0-8.3 and 0.3-1.4 adducts per 10(7) dGp respectively. Combining the two HPLC purification steps and the 32P-postlabeling assay attains chemical specificity, retains sufficient quantitative sensitivity and should be useful in human biomonitoring studies.

Comparative in vitro and in vivo activities of two 9-deazaguanine analog inhibitors of purine nucleoside phosphorylase, CI-972 and PD 141955

An in-parallel comparison is presented of the in vitro and in vivo properties of two 9-deazaguanine analog inhibitors of purine nucleoside phosphorylase (PNP), CI-972 [8-amino-9-deaza-9-(3-thienylmethyl)guanine] and PD 141955 [9-deaza-9-(3-thienylmethyl)guanine] (published Ki values of 0.83-8.0 and 0.08 microM, respectively). Despite structural similarities, PD 141955 was considerably more potent and active in all systems studied. The respective IC50 values for inhibition of MOLT-4 cell growth in the absence and presence of 10 microM 2'-deoxyguanosine (GdR) were greater than 50 and 5.06 microM for CI-972 and 15.4 and 0.061 microM for PD 141955. PD 141955 induced accumulation of dGTP in GdR-treated MOLT-4 and CEM cells at log-lower concentrations than were required of CI-972, and the magnitude of dGTP accumulation in PD 141955-treated T cell cultures was markedly greater (e.g. 366 vs 100 pmol/10(6) CEM cells at 10 microM). PD 141955 administered orally produced a dose-dependent elevation of plasma inosine and guanosine in rats over a broad concentration range. Mean plasma inosine concentrations following a 150 mg/kg p.o. dose peaked at 6.21 and 13.2 microM in CI-972 and PD 141955-treated rats, respectively. Low levels of inosine were detectable at 50 micrograms/kg following oral administration of PD 141955.

Enzymatic assay for deoxyribonucleoside triphosphates using synthetic oligonucleotides as template primers

The enzymatic assay for deoxyribonucleoside triphosphates has been improved by using synthetic oligonucleotides of a carefully defined sequence as template primers for DNA polymerase. High backgrounds, which limit the sensitivity of the assay when calf thymus DNA or alternating copolymers are used as template primers, were eliminated with these oligonucleotide template primers. Sensitivity was further increased by designing the template primer to incorporate multiple labeled deoxyribonucleotides per limiting unlabeled deoxyribonucleotide. Each of several DNA polymerases exhibited unique reaction characteristics with the oligonucleotide template primers, which was attributed to the differing exonuclease activities associated with these various enzymes. Assay optimization therefore included matching the polymerase with the template primer to obtain the lowest background reaction and highest sensitivity. This modified assay is particularly well suited for keeping cell sample size to a minimum in experimental protocols which generate large numbers of data points or require careful timing of sampling. With this technique, we measured the levels of all four deoxyribonucleoside triphosphates in extracts from as few as 2 x 10(4) cultured cells.

Alterations in the d(CpGpT) structure in solution as a result of [PtCl(diethylenetriamine)]+ binding

The trinucleotide d(CpGpT) reacts with [PtCl(dien)]Cl (dien = diethylenetriamine) to yield as a single adduct Pt(dien)[d(CpGpT)-N7(2)]. The structure of this adduct in solution has been analysed with the aid of NMR spectroscopy and compared with that of the unmodified trinucleotide. A change in the population of the S conformer of the guanosine deoxyribose ring and a syn preference of the guanine residue are the most important changes occurring upon platination. As a result the dC-dG stack disappears, whereas the dG-dT stack is hardly affected. The CD spectra of both platinated and free d(CpGpT) confirm the different nature of the two molecules.

Effects of methotrexate on purine and pyrimidine metabolism and cell-kinetic parameters in human malignant lymphoblasts of different lineages

MOLT-4 (T-), RAJI (B-), and KM-3 (non-B-non-T-, common ALL) malignant lymphoblasts demonstrated significant differences in their activities of purine de novo synthesis (PDNS) and purine salvage pathway and in their cell-kinetic parameters. Incubations with concentrations of methotrexate (0.02 and 0.2 microM), which can be maintained during many hours in the oral maintenance therapy of acute lymphoblastic leukemia, indicated large differences between the three cell lines with respect to the inhibition of PDNS, depending on the concentration of methotrexate (MTX) and on the activities of the two pathways. These dose- and cell line-dependent differences corresponded to the perturbations of cell-kinetics and purine and pyrimidine (deoxy)ribonucleotide pools in the three cell lines. Exposure of MOLT-4 cells to 0.02 microM MTX resulted in an incomplete inhibition of DNA synthesis in early S phase, as shown by DNA-flow cytometry and increase of dCTP levels, which recovered spontaneously after 48 hr. Almost no impairment of RNA synthesis occurred (unbalanced growth). In RAJI cells, exposed to 0.02 microM MTX, DNA synthesis was delayed in the S phase, not arrested, and RNA synthesis was not impaired, also indicating an unbalanced growth pattern, which, however, did not recover in time. KM-3 cells were arrested in G1 phase and subsequently in early S phase after incubation with 0.02 microM MTX, and perturbations of ribonucleotides indicated a complete inhibition of RNA synthesis, resulting in a balanced growth pattern. Cytotoxicity was more pronounced in KM-3 cells. The reliability of the soft agar colony forming assay after low dose MTX treatment is discussed. Exposure of MOLT-4 and KM-3 cells to 0.2 microM MTX resulted in a complete inhibition of DNA synthesis, with cessation of cell progression through all parts of the cell cycle and arrest in G1 phase. RAJI cells showed an increasing accumulation of cells in G1 phase without complete cessation of cell cycle progression. Perturbations of ribonucleotide pools suggested an inhibition of RNA synthesis in all cell lines, indicating a balanced growth pattern in KM-3 cells and MOLT-4 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation of thymidylate biosynthesis from DNA biosynthesis by 5-fluoro-2'-deoxyuridine and 5,8-dideazaisofolic acid

The effects of 5-fluoro-2'-deoxyuridine (FdUrd) and 5,8-dideazaisofolic acid on the coordination of thymidylate synthase activity and DNA synthesis were examined in human CCRF-CEM leukemic cells following a continuous exposure to these agents. In logarithmically growing control tumor cells, the rate of in situ thymidylate synthase activity equaled the rate of DNA synthesis. However, in tumor cells incubated with growth-inhibitory concentrations of either FdUrd or 5,8-dideazaisofolic acid for 48 h, the rate of thymidylate synthase activity was between 15- and 17-fold greater than the rate of DNA synthesis. The loss in tumor cell viability of FdUrd-treated cells was temporally related to this prolonged dissociation of thymidylate biosynthesis from DNA biosynthesis. The dissociation of thymidylate from DNA biosynthesis in cells incubated with FdUrd was not closely related to thymidylate depletion. The intracellular concentrations and activities of thymidylate synthase were comparable in tumor cells incubated for 24 or 48 h with either a growth-inhibitory or non-growth-inhibitory concentration of FdUrd, indicating no direct relationship among these parameters. Indirect thymidylate depletion induced by the combination of 2,4-diamino-5-(3',4'-dichlorophenyl)-6-methylpyrimidine, hypoxanthine, and glycine inhibited in situ thymidylate synthase activity and DNA synthesis to an equal extent. In addition, the intracellular concentrations of all four deoxyribonucleoside 5'-triphosphates in tumor cells incubated with FdUrd for 48 h were between 1.3- and 3.1-fold greater than their respective concentrations in control cells, reflecting their decreased utilization in DNA synthesis in FdUrd-treated cells. These data indicated that inhibition of CCRF-CEM cell growth and DNA synthesis following a continuous exposure to cytostatic concentrations of either FdUrd or 5,8-dideazaisofolic acid resulted primarily from interference with thymidylate incorporation into DNA, and not simple blockade of thymidylate synthase.

[Directions of alkylation of deoxyguanosine and deoxyguanylic acid by thio-TEPA]

As exemplified with the reaction of well-known anticancer agent thio-TEPA with dGMP, the ability of ethylenimine derivatives to modify this DNA component under the conditions approaching the biological ones was demonstrated for the first time. Modification involves mainly the phosphate group alkylation. In addition, thio-TEPA alkylates the base in dGMP at position 7. The formation of dGMP 7-alkyl derivatives was confirmed by detecting the luminescent products generated in the course of this reaction.

Normal coordinate analysis of 5'-dGMP and its deuterated derivatives. A calculated approach to designate the guanine-residue vibration modes in B and Z forms of DNA

By calculations based on the Wilson GF-method and using a valence force field, the vibration modes of 5'-dGMP have been assigned. Good agreement was obtained between the calculated and experimental results corresponding to the Raman and infrared spectra of 5'-dGMP. The calculations can also predict the displacement of infrared bands observed upon selective deuteration on C8 and simultaneously on the C8, N1 and N2 atoms of the guanine ring. In order to preserve the harmonic approximation of the potential field, the redundancy between the internal coordinates is entirely removed using a B X B matrix-product diagonalization procedure. In this treatment the local symmetry of different constituents of the molecule is taken into consideration, thus avoiding extensive linear combinations of internal coordinates. The extension of these calculations to the guanosine-moiety involved in the double helix structures of DNAs allowed us to reproduce a certain number of the characteristic guanine vibration modes altered by the B----Z transitions of poly(dG-dC).poly(dG-dC) and d(CG)3.d(CG)3.

An improved method for the quantitative determination of deoxyribonucleoside triphosphates in cell extracts

The analysis of deoxyribonucleoside 5'-triphosphates (dNTPs) in cell extracts by high-pressure liquid chromatography [C. Garrett , and D.V. Santi (1979) Anal. Biochem. 99, 268-273] requires the prior, selective degradation of ribonucleoside 5'-triphosphates ( rNTPs ) that are present in the extracts in large quantities. When this method was used for quantifying the dNTPs in mammalian cell extracts, the presence of an interfering peak in the HPLC between the peaks for dTTP and dATP was observed. This unwanted peak sometimes overlapped with that of dATP, depending on the pH of the eluant. It was found that the material which gave this peak was formed during the periodate oxidation of rNTPs in the presence of methylamine, and that it could be removed by changing the order of addition of the reagents in the procedure, i.e., the methylamine was added only after the excess periodate was decomposed, instead of adding it together with periodate, as given in the original procedure. Furthermore, an addition of deoxyguanosine to the reaction mixture was found to be effective in preventing the partial loss of dGTP in the oxidation procedure. By using this improved method, the dNTP contents of the extracts of Ehrlich ascites tumor cells have been measured in an accurate and reproducible manner. The analysis requires about 10(6) cells, and all four dNTPs can be quantified in 2.5 h, starting from the harvest of the cells.

Deoxyribonucleoside triphosphate pools in human diploid fibroblasts and their modulation by hydroxyurea and deoxynucleosides

Deoxyribonucleoside triphosphate (dNTP) pool levels were examined in synchronized and unsynchronized log phase cultures and in quiescent cultures of human diploid foreskin fibroblasts. dNTP levels were in good agreement with those previously published for human HeLa and lymphoblastic leukemia cells. dCTP and dGTP levels showed only a modest lowering in quiescent as compared to log-phase cells, but dATP and dTTP levels were reduced dramatically in quiescent cultures. Cells synchronized by serum starvation and assayed at the peak DNA synthetic phase (18-21 hr post release) showed substantially higher pools of all four dNTPs. Hydroxyurea treatment reduced only purine dNTPs in both log phase and confluent cells while increasing dTTP and dCTP pools. The effects of deoxynucleosides on dNTP pools were also examined and are discussed in light of current models regarding regulation of purified ribonucleotide reductase formulated from in vitro studies.

gamma Ray induced deoxyribonucleic acid strand breaks. 3' Glycolate termini

Gamma irradiation of DNA in aqueous solution produces single strand breaks with two types of 3'-termini. These termini have been identified as a simple phosphoryl group and a glycolate moiety attached to the 3'-phosphoryl group via the 2"-OH of glycolic acid. Irradiation of 5'-end labeled poly(dG) produces compounds that comigrate with authentic 3',5'-dGDP and 2'-deoxyguanosine-3'-(phospho-2"-O-glycolic acid-5'-monophosphate by thin layer chromatography and polyacrylamide gel electrophoresis. Irradiation of poly(dGdC) followed by digestion to 3'-nucleotides produces 2'-deoxyguanosine-3'-(phospho-2"-O-glycolic acid). The presence of glycolate termini at some strand breaks may affect intracellular repair of these lesions.

On the presence of reverse transcriptase in myelo- and lymphoproliferative disorders

Buffy coats from 31 patients with a diagnosis of leukemia and 16 normal donors were tested for the presence of a viral-like reverse transcriptase. Eighty-five percent of fresh leukemic buffy coats were positive. Also tested were spleens from 16 patients with hematological disorders and 5 spleens from patients without history of hematological malignancy. The 5 normal spleens were negative. Also negative were 4 spleens from patients with Hairy cell leukemia. From the remaining 12 spleens 7 were positive. Reverse transcriptase measurements can be used to distinguish leukemic from normal buffy coats.

Nucleoside triphosphate pools in minicells of Escherichia coli

The nucleoside triphosphate pools of Escherichia coli minicells are different from those in parental cells. The growth phase in which minicells accumulate significantly affects the pool sizes.