Extracellular matrix-specific induction of elastogenic differentiation and maintenance of phenotypic stability in bovine ligament fibroblasts

We studied the process of elastogenic differentiation in the bovine ligamentum nuchae to assess the mechanisms that regulate elastin gene expression during development. Undifferentiated ( nonelastin -producing) ligament cells from early gestation animals initiate elastin synthesis when grown on an extracellular matrix (ECM) substratum prepared from late gestation ligamentum nuchae. ECM from ligaments of fetal calves younger than the time when elastin production occurs spontaneously in situ (i.e., beginning the last developmental trimester at approximately 180 d of gestation) does not stimulate elastin production in undifferentiated cells. Matrix-induced differentiation requires direct cell matrix interaction, is dependent upon cell proliferation after cell-matrix contact, and can be blocked selectively by incorporation of bromodeoxyuridine into the DNA of undifferentiated cells before (but not after) contact with inducing matrix. Quantitative analysis of elastin synthesis in young cells after matrix-induced differentiation indicates that the entire cell population is competent to respond to the matrix inducer, and continued synthesis of elastin after young cells are removed from the ECM substratum indicates that the phenotypic transition to elastin synthesis is stable and heritable. Although ligament cells do not require continuous contact with ECM to express the elastin phenotype, elastin synthesis is increased substantially when elastin-producing cells are grown on ligament matrix, suggesting that elastogenic differentiation is stabilized by ECM. The matrix substratum was also found to alter the distribution of tropoelastin between the medium and matrix cell layer. When grown on tissue culture plastic, ligament cells secrete greater than 80% of newly synthesized tropoelastin into the culture medium. When cultured on ECM, however, 50-70% of the newly synthesized tropoelastin remains associated with the cell layer and is cross-linked to form insoluble elastin as shown by the incorporation of radiolabeled lysine into desmosine.

A study of the proliferative response of rabbit T cells using the BrdU-Hoechst method

Con-A- and PHA-induced proliferation of cells from rabbit thymus, spleen and mesenteric lymph node was studied with the DNA-fluorescent probe 33258 Hoechst. The fluorescence of this probe is quenched when 5-bromo-2'-deoxy-uridine is incorporated into nascent DNA during the S phase. Fluorescence decreased with increasing content of newly formed DNA per cell. Proliferation kinetics and the number of Con-A- and PHA-reactive cells (C+ and P+ cells) were determined cytofluorometrically . Lymphocytes from control and dexamethasone (DX)-treated animals start their proliferation early: after 42 hr about 25% of the control and the majority of the DX-resistant cells finished their second cell division. Small numbers of C+ (12.0%) and P+ (3.5%) cells were found in control thymus, while these percentages were enhanced in DX thymus: 32.5 and 27.0% respectively; 50% of the spleen T cells in control and DX animals are C+ or P+ and 75% of the lymph-node T cells are C+ (after DX 45%) and 50% are P+ (after DX also 50%). It is concluded that in thymus and lymph nodes, a steroid sensitive (Ss) C+P-, and in lymph nodes a Ss C+P+ cell pool is present. A mitogen non-proliferative cell pool (C-P-) is present in control and DX thymus.

Appearance of chemotactic responsiveness to elastin peptides by developing fetal bovine ligament fibroblasts parallels the onset of elastin production

We studied chemotaxis to elastin peptides by bovine ligamentum nuchae fibroblasts to determine whether there is a developmental association between chemotactic responsiveness to elastin and expression of the elastin phenotype. Undifferentiated ligament cells demonstrate chemotactic responsiveness to platelet-derived growth factor and fibronectin, known chemoattractants for fibroblasts, but do not show chemotaxis to elastin peptides. After matrix-induced differentiation, however, young cells display a positive chemotactic response to elastin that persists even after the cells are removed from the matrix substratum. Matrix-induced chemotaxis to elastin could be inhibited selectively by incorporation of bromodeoxyuridine into DNA of undifferentiated cells before (but not after) contact with inducing matrix. These results show that the appearance of chemotaxis to elastin peptides parallels the onset of elastin synthesis and suggests that the acquisition of chemotactic responsiveness to elastin and expression of the elastin phenotype are affected by the same inducing elements or processes and may be closely coupled in development.

SCEs are induced by replication of BrdU-substituted DNA templates, but not by incorporation of BrdU into nascent DNA

After 3 rounds of DNA replication in the presence of BrdU, third-division metaphase cells can be scored for the frequencies of SCEs that occurred during cycles 1 and 2, and also for the frequency of SCE during cycle 3. This procedure was used to resolve the issue of SCE induction by replication of BrdU-substituted DNA templates versus induction by BrdU incorporation into nascent DNA. It was observed that third-cycle SCE frequencies in CHO are dependent upon the amount of BrdU that was present during cycles 1 and 2 and are independent of the BrdU concentration during the third cycle. It is therefore BrdU serving as a template, rather than BrdU being incorporated, that initiates the SCE event. A model is proposed that produces reasonable fits to the observed data. It also predicts a true background or spontaneous SCE frequency of 3 per cell per cycle as previously reported by Heartlein et al. (Mutation Res., 107 (1983) (103-109). The predicted single twin ratio is higher than that reported by Wolff and Perry (Exp. Cell Res., 93 (1975) 23-30), and possible explanations for this discrepancy are discussed.

Effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine on synthesis of herpes simplex virus type 1-specific polypeptides

The antiherpesvirus agent (E)-5-(2-bromovinyl)-2'-deoxyuridine caused marked alterations in the synthesis and processing of several herpes simplex virus type 1 (HSV-1)-infected-cell polypeptides. Analogous to other thymidine analogs, there was a dose-dependent decrease in several beta and gamma polypeptides and an accumulation of HSV-1 thymidine kinase. In contrast to the action of other thymidine analogs, there were alterations in alpha polypeptides, including an increase in the synthesis and phosphorylation of infected-cell polypeptide 4b and a decrease in the synthesis of infected-cell polypeptide 27. The phosphorylation of several other HSV-1 phosphoproteins was mildly inhibited. (E)-5-(2-Bromovinyl)-2'-deoxyuridine inhibited the glycosylation of the major HSV-1 glycoproteins, and this activity appeared to be independent of the incorporation of the drug into the viral DNA. Thus, the alterations in HSV-1 polypeptide expression appear to be due to the presence of the drug in a low-molecular-weight form as well as its presence in the viral DNA. This suggests that this analog or a phosphorylated derivative might act as an inhibitor of an enzyme(s) responsible for posttranslational modification of polypeptides.

Studies by means of the SCE assay in V79-E Chinese hamster cells on the mode of action of tri-substituted nitrosoureas

The genotoxic activity of 3,3-diethyl-1-methyl-1-nitrosourea ( DEMNU ), 1,3-dimethyl-3-phenyl-1-nitrosourea ( DMPNU ) and 1-chloroethyl-3-methyl-3-phenyl-1-nitrosourea ( CEMPNU ) was studied in the SCE assay in V79-E cells in vitro. These compounds are very stable in aqueous solutions, but are directly acting genotoxins . The SCE rates increase linearly with the length of the incubation period. This direct activity is presumably due to an intracellular catalytic decomposition. Whereas the SCE-inducing effect of DMPNU and CEMPNU is not influenced by addition of S9 mix, that of DEMNU is strongly potentiated by rat and Syrian hamster S9 mix. This DEMNU activation is an NADPH-dependent enzymatic reaction and is inducible by phenobarbital. The absence of a direct mutagenic effect of DEMNU in the Ames test, as reported by other authors, is probably caused by a striking insensitivity to tri-substituted nitrosoureas of the Salmonella assay. This assumption was substantiated by long-term application of very low DMPNU doses to V79-E. Long-term simultaneous treatment with DMPNU and bromodeoxyuridine (BUdR) significantly diminished the rate of SCE induction.

Cytogenetic investigations in mentally retarded and normal males from 14 families with the fragile site at Xq28. Results of folic acid treatment on fra(X) expression

Lymphocyte cultures from 27 mentally retarded males aged 1 year to 77 years, and from 11 normal brothers from a total of 14 families with the fragile X segregating have been examined cytogenetically employing three different culture methods including methods for induction of fra(X) by FUdR (flourodeoxyuridine) or MTX (methotrexate). All mentally retarded males showed unequivocal fra(X) expression. No statistically significant correlation between fra(X) expression and age could be demonstrated. No enhancement with FUdR was observed. Fibroblast cultures from 10 retarded males expressed fra(X) in a dose-response relationship to increasing concentrations of FUdR. None of the normal males showed fra(X). In vivo folic acid treatment of seven mentally retarded males resulted in marked reduction in fra(X) expression in lymphocyte cultures grown in medium 199. However, reinduction was achieved by FUdR or MTX, except in one case who temporarily received very high doses of folic acid.

In vitro effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine, 5'-amino-5-iodo-2',5'-dideoxyuridine and 2-deoxy-D-glucose on latent ganglionic herpes simplex virus infection

(E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVDU) and 5'-amino-5-iodo-2',5'-dideoxy-uridine AIdUrd, blocked the reactivation of latent ganglionic herpes simplex virus in vitro. Furthermore, BVDU, but not AIdUrd, blocked the multiplication of reactivated latent virus and transiently suppressed emergence of reactivated virus from the sensory ganglia after removal of drug from the medium. 2-Deoxy-D-glucose (2-DG) neither prevented the in vitro reactivation of latent virus nor blocked the further multiplication of reactivated latent virus.

Synergistic antiviral effects of antiherpes compounds and human leukocyte interferon on varicella-zoster virus in vitro

The four antiherpes compounds acyclovir, adenine arabinoside, bromovinyldeoxyuridine, and phosphonoformic acid showed an additive to synergistic effect with human leukocyte interferon in inhibiting focus formation by three different strains of varicella-zoster virus in human embryonic fibroblasts.

Distribution of sister chromatid exchanges on the mouse chromosomes in vivo with reference to the replication properties of the X chromosome

Frequency of sister chromatid exchanges (SCE) were recorded separately for different chromosomes from bone marrow cells of female mice of the two genetic strains (C3H/S and C57BL/6J). SCEs were evaluated following different doses of 5-bromo-2'-deoxyuridine (BrdU) as nine hourly i.p. injections. The SCE per cell increased with increasing BrdU doses which was slightly higher in C3H/S than in the C57BL/6J. SCEs per cell were variable at every treatment-strain combination, possibly reflecting the heterogeneous nature of the bone marrow cells. In general, there is a positive correlation between SCE per chromosome and the relative chromosome length. Total SCEs on one of the large chromosomes (most likely the X chromosome), however, are significantly higher than expected on the basis of relative length alone. Most of this increase is attributable to one of the homologues of this chromosome, which is not in synchrony with the rest of the chromosomes and may represent the late-replicating X. These results when viewed in the light of replication properties of the heterochromatinized X, suggest a direct involvement of DNA replication in SCE formation and may argue against the replication point as the sole site for the SCEs.

Genotoxicity of quercetin in cultured mammalian cells

The naturally occurring flavonol, quercetin, was investigated concerning its ability to induce SCEs and HGPRT-deficient mutants in V79 Chinese hamster cells, and HGPRT- and TK-deficient mutants in mouse lymphoma L5178Y cells. V79 cells were exposed to quercetin in monolayer, under exponential growing condition, in suspension in the presence of liver homogenate, and in co-cultivation with primary chick embryo hepatocytes. No induction of HGPRT-deficient mutants was observed. Furthermore, under standard conditions, no relevant increase in the number of SCEs could be detected. If, however, the cells were exposed simultaneously to quercetin and BrdUrd, a greater than 3-fold increase in the number of SCEs was observed. This induction was dose-related for both quercetin and BrdUrd. Treatment of L5178Y cells with quercetin did not result in an increase in HGPRT-deficient mutants. At the TK locus a weak increase in the number of TK-deficient mutants was found. Addition of liver homogenate abolished this effect. The inability of quercetin to induce SCEs and point mutations in mammalian cells, and the fact that the clastogenic effect of quercetin, whereby it induces TK-deficient mutants in mouse lymphoma L5178Y cells, is abolished by the addition of liver homogenate, may explain the negative outcome of the majority of carcinogenicity studies on quercetin in mammals.

Thermal sensitivity and radiosensitization in V79 cells after BrdUrd or IdUrd incorporation

Chinese hamster V79 cells were exposed to 10(-5) moles/liter bromodeoxyuridine (BrdUrd) or iododeoxyuridine (IdUrd) for 16 or 29 hr and then tested for thermal sensitivity, radiosensitivity, and sensitivity to the combined treatments of heat and radiation. BrdUrd and IdUrd treatment of cells resulted in enhanced radiosensitivity which increased with exposure time but had little or no effect on thermal sensitivity. For 42.0 degrees C heating, no effect was observed, while for 45.0 degrees C heating, a small decrease in thermal sensitivity occurred for both 16- and 29-hr exposure times, in the combined treatment of heat and radiation, the presence of BrdUrd or IdUrd resulted in about the same thermal enhancement in radiosensitivity. BrdUrd and IdUrd uptake into cellular DNA were measured using high-pressure liquid chromatography and, after a 29-hr exposure to 10(-5) moles/liter of BrdUrd or IdUrd, approximately 40% of the thymidine was substituted.

Inhibition of cell proliferation by interferons. 2. Changes in processing and stability of newly synthesized DNA in human lymphoblastoid (Daudi) cells

The inhibition of proliferation of Daudi cells in culture by human interferons is characterized by a change in the kinetics of labelling of different size classes of newly synthesized DNA. Initially, labelled precursors are incorporated exclusively into small DNA (Okazaki fragments) in both control and interferon-treated cells, as revealed by alkaline sucrose gradient centrifugation. In the interferon-treated cells, there is enhanced labelling of this small DNA after short periods of incorporation and slower conversion to larger DNA size classes, in comparison with the DNA of control cells. This effect is apparent after 12 h of interferon treatment, coincident with the onset of the inhibition of cell proliferation. It becomes progressively more marked up to 4 days, by which time cell growth has ceased completely. Experiments using bromodeoxyuridine as a density label and analysis of radioactive DNA on caesium chloride/caesium sulphate gradients also reveal that some newly replicated DNA may be unstable and may turn over within a few hours of its synthesis. The label derived from DNA breakdown is efficiently reincorporated into newly synthesized molecules. It is suggested that interferon treatment inhibits DNA replication by activating DNA turnover rather than by directly inhibiting synthesis. This effect, together with the progressive retardation of conversion of Okazaki fragments to larger DNA, may lead to the eventual failure of cell proliferation.

Developmental regulation of neuraminidase-sensitive lectin-binding glycoproteins during myogenesis of rat L6 myoblasts

Intact monolayers of L6 myoblasts were treated with neuraminidase, with the aim of selectively removing sialic acid residues of cell-surface glycoproteins. Neuraminidase treatment unmasked binding sites for Ricinus communis agglutinin I and peanut agglutinin, thus allowing the identification of the major binding proteins for these lectins. For Ricinus communis agglutinin I these neuraminidase-sensitive glycoproteins had apparent Mr values of 136000, 115000, 87000, 83000 and 49000. For peanut agglutinin the major neuraminidase-sensitive glycoproteins had apparent Mr values of 200000, 136000, 87000 and 83000. We found highly reproducible, developmentally regulated, changes in the lectin-binding capacity of certain of these glycoproteins as L6 myoblasts differentiated into myotubes. Coincident with myoblast fusion there was a co-ordinate decrease in Ricinus communis agglutinin I binding by glycoproteins of apparent Mr of 136000 and 49000. There was also a co-ordinate shift in mobility of the broad band of glycoprotein, centred at an apparent Mr of 115000 in myoblasts, to a new average apparent Mr of 107000 in mid-fusion cultures and myotube cultures. Peanut agglutinin binding by the major protein of apparent Mr 136000 also decreased at the mid-fusion stage of myogenesis, and was barely detectable in 7-day-old fused cultures. These developmentally regulated changes in neuraminidase-sensitive glycoproteins were all inhibited by growth of myoblasts in 6.4 microM-5-bromo-2'-deoxyuridine, indicating that they are associated with myoblast differentiation. In contrast, an increase in fibronectin was seen in mid-fusion cultures, which was not inhibited by growth of myoblasts in 5-bromo-2'-deoxyuridine. This initial increase in fibronectin is, therefore, unlikely to be directly related to myoblast fusion or differentiation.

Bromodeoxyuridine resistance: thymidine transport and phosphorylation in Friend leukemia cells

We have studied multiple step bromodeoxyuridine (BrdU) resistance in Friend leukemia cells. The mutation rate to 30 micrograms/ml resistance was 5.1 X 10(-5) per cell per generation, and to 100 micrograms/ml was 3.7 X 10(-7) per cell per generation. Resistant variants could not be obtained in a single step using BrdU concentrations higher than 100 micrograms/ml. Three clones isolated through multiple step selection were resistant to 640 micrograms/ml of BrdU and deficient in thymidine kinase, although their ability to transport radiolabeled thymidine was unimpaired relative to wild type. All three clones had low reversion frequencies, as judged by plating efficiencies in couterselective HAT medium. Two such revertant clones were isolated and tested for their forward mutation frequency in BrdU. No resistant clones were obtained when as many as 5 X 10(7) cells were tested. This observation argues against the hypothesis that the Friend cells possess two functional thymidine kinase loci and that the revertants represent a heterozygous condition. We conclude that the hypothesis of null mutations within a hemizygous or heterozygous thymidine kinase locus is sufficient to account for high-level BrdU resistance in Friend leukemia cells.

Changes in the synthesis of minor cartilage collagens after growth of chick chondrocytes in 5-bromo-2'-deoxyuridine or to senescence

Analyses were made of the minor collagens synthesized by cultures of chondrocytes derived from 14-day chick embryo sterna. Comparisons were made between control cultures, cultures grown for 9 days in 5-bromo-2'-deoxyuridine (BrdU) and clones of chondrocytes grown to senescence. Separation of minor collagens from interstitial collagens was achieved by differential salt precipitation in the presence of carrier collagens in acid conditions. The precipitate at 0.9 M NaCl 0.5 M acetic acid from control cultures was shown by CNBr peptide analysis to contain only the alpha 1(II) chain of type II collagen, whereas after BrdU treatment or growth to senescence synthesis of only alpha 1(I) and alpha 2(I) chains occurred. The synthesis of type III collagen was not detected. Analysis of the precipitate at 2.0 M NaCl, 0.5 M HAc from control cultures demonstrated the synthesis of 1 alpha, 2 alpha and 3 alpha chains together with the synthesis of short chain (SC) collagen of Mr 43000 after pepsin digestion. After BrdU treatment or growth to senescence alpha chains were isolated which possessed the migration positions on polyacrylamide gel electrophoresis (PAGE), or the elution positions on CM-cellulose chromatography, of the alpha 1(V) and alpha 2(V) chains of type V collagen. In addition, for BrdU-treated but not for control cultures, intracellular immunofluorescent staining was observed with a monoclonal antibody which specifically recognizes an epitope present in the triple helix of type V collagen. Synthesis of short chain (SC) collagen was not detected after BrdU treatment or growth to senescence. These results suggest that chick chondrocytes grown in conditions known to cause switching of collagen synthesis from type II to type I collagen also undergo a switch from the synthesis of 1 alpha, 2 alpha and 3 alpha chains to the synthesis of the alpha 1(V) and alpha 2(V) chains of type V collagen. It appears that there are several cartilage-specific collagens which together undergo a regulatory control to the synthesis of collagens typical of other connective tissues.

Effects of dibutyryl adenosine 3':5'-cyclic monophosphate and other agents on induction of alkaline phosphatase activity in monkey kidney cells

The induction of alkaline phosphatase (ALP) by dibutyryl adenosine 3':5'-cyclic monophosphate (Bt2cAMP) was investigated in strain JTC-12 . P3 cells derived from monkey (Maccaca irus) kidney cortex. ALP activity was increased by Bt2cAMP in a dose-dependent manner, reaching a plateau at concentrations higher than 5 mM with the activity being about 4 times that of the controls. The concentration of Bt2cAMP required for half-maximal induction of ALP activity was about 0.8 mM. ALP activity was increased rapidly by Bt2cAMP for the first 5 days and then continued to increase gradually towards a plateau level. Removal of Bt2cAMP from the medium caused a rapid decrease in the activity, suggesting that the induction of ALP activity by Bt2cAMP is reversible. ALP activity was induced synergistically in the presence of 1 mM sodium butyrate together with Bt2cAMP at concentrations from 0.01 to 1 mM. It was also found that in the presence of 1 mM Bt2cAMP, sodium butyrate increased ALP activity in the same manner as Bt2cAMP did in the presence of 1 mM sodium butyrate. Although dexamethasone, a potent glucocorticoid, had no effect on ALP activity in control cells, the hormone suppressed the ALP activity induced by Bt2cAMP in a dose-dependent manner. At concentrations above 0.2 mM, two xanthine derivatives, theophylline and 3-isobutyl-1-methyl-xanthine (IBMX), also inhibited the induction of ALP activity by 1 mM Bt2cAMP. Inhibitors of protein synthesis, cycloheximide (1.5 micrograms/ml) and pactamycin (10 micrograms/ml), as well as inhibitors of RNA synthesis, actinomycin D (2 micrograms/ml) and alpha-amanitin (50 micrograms/ml), suppressed the induction of ALP activity.

Phenotypic mixing of retroviruses in mitogen-stimulated lymphocytes: analysis of xenotropic and defective endogenous mouse viruses

In addition to the known induction of xenotropic endogenous virus in B-mitogen-stimulated murine lymphocyte cultures, distinguishable defective viruses were also induced in different mouse strains (NFS/N, 129, BALB/c). AKR cells produced xenotropic virus and also, in contrast to BALB/c, ecotropic virus. The drug bromodeoxyuridine appeared to have differential effects on virus expression, amplifying xenotropic virus induction but inhibiting the spontaneous production of the ecotropic virus in AKR cultures and of the defective virus in NFS/N cells. Infecting stimulated BALB/c or AKR cultures with Friend leukaemia virus resulted in the production of ecotropic-xenotropic pseudotype viruses, indicating that the infecting ecotropic virus replicates in the cells in which xenotropic virus is induced. No pseudotypes or recombinants were observed following infection of spleen cells releasing defective viruses. Friend leukaemia virus and xenotropic virus with an ecotropic envelope replicated equally well in stimulated lymphocytes from the different strains examined. Taken together, these findings indicate that the non-infectious viruses are encoded by defective proviruses, rather than resulting from faulty, host cell-controlled, virus maturation.

Chromosome breakage induced by thymidylate stress in thymidylate synthase-negative mutants of mouse FM3A cells

In thymidylate synthase-negative mutants of mouse FM3A cells, thymidine starvation rapidly decreased mitotic activity and resulted in cell death (thymineless death). When the thymidine starvation was reversed by an addition of thymidine, mitotic activity was recovered, but the majority of mitotic cells exhibited extensive chromosome aberrations, including chromatid breaks, chromatid exchanges, and pulverizations. Autoradiographic examination revealed that chromosome instability was induced only in cells arrested in the S phase during thymidine starvation. Furthermore, the most sensitive sites to the chromosome-damaging effect appeared to be sites which had replicated just prior to thymidine starvation. During thymidine starvation, cells at other stages in the cell cycle were accumulated at the G1-S boundary, and they were insensitive to the chromosome-damaging effect. Thymidine starvation was also found to be recombinagenic. Complete removal from the medium of a thymidine analogue, 5-bromo-2'-deoxyuridine, resulted in a dramatic increase in the frequency of sister chromatid exchanges. These results support the view that thymidine starvation in mammalian cells results in thymineless death via induction of DNA double-strand breaks, leading to chromosome fragmentation as well as rearrangements in the cells synthesizing DNA.

[Effect of mouse age and genotype on the frequency of sister chromatid exchange in bone marrow cells]

No differences were found in both the baseline and mitomycin C induced levels of sister chromatid exchanges (SCE) between 101/H and C57BL/6J mice differing in chromosome mutability. An increase with the age of the spontaneous and mutagen induced SCE rates was similar in the strains compared, though instability of chromosomes was much higher in old 101/H than in C57BL/6J mice. Thus, no correlation was observed between chromosomal aberration and SCE levels in these strains. As 101/H mice were recently found to be DNA repair-deficient, possible connection of SCE and repair is discussed.

Synthesis and antiviral properties of 5-vinylpyrimidine nucleoside analogs

5-Vinylpyrimidine nucleosides can be readily synthesized via organometallic intermediates from commercially available nucleosides. Highly potent and selective inhibitors of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) are (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and some related analogs such as (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU), 1-beta-D-arabinofuranosyl-(E)-5-(2-bromovinyl)uracil (BVaraU) and (E)-5-(2-bromovinyl)-2'-deoxycytidine (BVDC). The selective antiviral action of BVDU is based upon a specific phosphorylation by the virus-encoded deoxythymidine kinase (TK), inhibition of the viral DNA polymerase and/or incorporation into viral DNA. The efficacy of BVDU against HSV-1 and VZV infections has been demonstrated in animal models and phase I clinical trials. Possible limitations in the clinical usefulness of 5-vinylpyrimidine nucleosides in general and BVDU in particular are discussed.

Effect of bromodeoxyuridine on induced sister chromatid exchanges

Analysis of sister chromatid exchanges (SCEs) is widely used as an assay for mutagenic carcinogens. Visualization of SCEs generally requires that the cells be cultured for 2 cycles of replication with the thymidine analog bromodeoxyuridine (BrdUrd). To see if incorporation of BrdUrd into chromosomal DNA influences the SCE response after treatment with chemical compounds, we have studied the effect of BrdUrd incorporation on SCEs induced by 5 different chemicals: bleomycin (BLM), which causes DNA single- and double-strand breakage; proflavine (PF), which intercalates into DNA; mitomycin C (MMC), a polyfunctional alkylating agent that cross-links DNA and also forms monoadducts; and 2 chemicals that do not appear to interact with DNA directly, aphidicolin (APC), an inhibitor of DNA polymerase alpha; and 3-aminobenzamide (3AMB), an inhibitor of poly-(ADP-ribose)-polymerase. Chemical treatment was for the first, second, or both cell cycles, and BrdUrd was present for the first or both cell cycles. All treatments with BLM, PF, or MMC increased the SCE frequency independently of the BrdUrd labeling protocol. With APC and 3AMB, on the other hand, only small increases in SCE frequency were observed when treatment was for the first cell cycle, but there were far greater increases when the chemical was present for the second or for both successive cell cycles. To further determine at which cycle SCEs were formed after continuous treatment of cells with BrdUrd and a test chemical, we also examined the induction of SCEs in the first cell cycle (twins) and in the second cell cycle (singles) in tetraploid cells. Bleomycin, PF, and APC induced almost equal numbers of SCEs in both cell cycles, but MMC appeared to induce more SCEs in the second cycle than in the first. This is probably caused by long-lived lesions that induce SCEs. 3-Aminobenzamide, which does not form persisting lesions, also induced more single than twin SCEs, suggesting that this compound affects BrdUrd-substituted DNA differently than it does unsubstituted DNA. This type of interaction between a chemical and BrdUrdsubstituted DNA should be taken into consideration when SCE analysis is used as an assay system.