The 2',3'-dideoxyriboside of 2,6-diaminopurine selectively inhibits human immunodeficiency virus (HIV) replication in vitro

The 2',3'-dideoxyriboside of 2,6-diaminopurine(ddDAPR) is, like 2',3'-dideoxyadenosine (ddAdo), a potent and selective inhibitor of human immunodeficiency virus (HIV) in vitro. The ddDAPR compound inhibits HIV antigen expression and HIV-induced cytopathogenicity in MT4 cells at a 50% effective dose (ED50) of 2.5-3.6 microM, as compared to 3.1-6.4 microM for ddAdo. Both compounds are endowed with a high selectivity index: 112 for ddDAPR and 139 for ddAdo. The 2',3'-unsaturated derivatives of ddDAPR and ddAdo, i.e. ddeDAPR and ddeAdo, are considerably more cytotoxic and less effective against HIV than the parental compounds. Like ddAdo, ddDAPR is only weakly inhibitory to the proliferation and DNA and RNA synthesis of a series of human B-lymphoblast, T-lymphoblast and T-lymphocyte cell lines. In contrast to ddAdo, which is rapidly deaminated by beef intestine adenosine deaminase at an initial velocity (Vi) of 145 mumol/mg protein/min, ddDAPR and ddeDAPR are poor substrates for the enzyme (Vi: 8 and 0.7 mumol/mg protein/min, respectively), which further contributes to the potential of ddDAPR as a chemotherapeutic agent against AIDS.     

Dideoxynucleoside triphosphates inhibit a late stage of SV40 DNA replicationin vitro

Summary The role of DNA polymerases in the replication of SV40 DNA was studied using a T-antigen-dependent assay supplemented with a human KB cell extract. Inhibition of DNA polymerase α by addition of aphidicolin or monoclonal antibodies prevented DNA synthesis, confirming the requirement for this enzyme in replication. The replication process was unaffected by ddTTP at a concentration (5 μM) inhibitory to DNA polymerases β and γ, however, higher concentrations of ddTTP (200 μM) caused an apparent accumulation of relaxed circular plasmid with a concomitant decrease in DNA synthesis. An analysis of this replication intermediate indicated that it was formed during the replication reaction and that the replicative cycle was nearly complete. A kinetic study of ddTTP inhibition strongly suggested DNA polymerase ε (PCNA-independent DNA polymerase δ) was the target of the inhibitor and that this enzyme functions during the final stages of DNA replication.     

Effect of DNA polymerase inhibitors on DNA repair in intact and permeable human fibroblasts: evidence that DNA polymerases delta and beta are involved in DNA repair synthesis induced by N-methyl-N'-nitro-N-nitrosoguanidine

The involvement of DNA polymerases alpha, beta, and delta in DNA repair synthesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was investigated in human fibroblasts (HF). The effects of anti-(DNA polymerase alpha) monoclonal antibody, (p-n-butylphenyl)deoxyguanosine triphosphate (BuPdGTP), dideoxythymidine triphosphate (ddTTP), and aphidicolin on MNNG-induced DNA repair synthesis were investigated to dissect the roles of the different DNA polymerases. A subcellular system (permeable cells), in which DNA repair synthesis and DNA replication were differentiated by CsCl gradient centrifugation of BrdUMP density-labeled DNA, was used to examine the effects of the polymerase inhibitors. Another approach investigated the effects of several of these inhibitors on MNNG-induced DNA repair synthesis in intact cells by measuring the amount of [3H]thymidine incorporated into repaired DNA as determined by autoradiography and quantitation with an automated video image analysis system. In permeable cells, MNNG-induced DNA repair synthesis was inhibited 56% by 50 micrograms of aphidicolin/mL, 6% by 10 microM BuPdGTP, 13% by anti-(DNA polymerase alpha) monoclonal antibodies, and 29% by ddTTP. In intact cells, MNNG-induced DNA repair synthesis was inhibited 57% by 50 micrograms of aphidicolin/mL and was not significantly inhibited by microinjecting anti-(DNA polymerase alpha) antibodies into HF nuclei. These results indicate that both DNA polymerases delta and beta are involved in repairing DNA damage caused by MNNG.     

DNA polymerase requirements for parvovirus H-1 DNA replication in vitro.

An in vitro system using nuclei from parvovirus H-1-infected cells was used to characterize the influence of inhibitors of mammalian DNA polymerases on viral DNA synthesis. The experiments tested the effects of aphidicolin, which is highly specific for DNA polymerase alpha, and 2',3'-dideoxythymidine-5'-triphosphate (ddTTP), which inhibits cellular DNA polymerases in the order gamma greater than beta greater than alpha. Both aphidicolin and ddTTP were inhibitory, indicating that both polymerase alpha and a ddttp-sensitive enzyme are required for viral DNA synthesis. This was seen more clearly in kinetic measurements, which indicated an initial period of rapid DNA synthesis with the participation of polymerase alpha, followed by a period of less rapid, but more sustained, rate of DNA synthesis carried out by a ddTTP-sensitive enzyme, probably polymerase gamma. One interpretation of the results is that polymerase alpha functions in a strand displacement stage of the viral DNA replication mechanism, whereas polymerase gamma serves to convert the displaced single strands back to double-strand replicative form.     

2',3'-Dideoxythymidine 5'-triphosphate inhibition of DNA replication and ultraviolet-induced DNA repair synthesis in human cells: evidence for involvement of DNA polymerase delta

It is well established that DNA replication and ultraviolet-induced DNA repair synthesis in mammalian cells are aphidicolin-sensitive and thus are mediated by one or both of the aphidicolin-sensitive DNA polymerases, alpha and/or delta. Recently, it has been shown that DNA polymerase delta is much more sensitive to inhibition by the nucleotide analogue 2',3'-dideoxythymidine 5'-triphosphate (ddTTP) than DNA polymerase alpha but is less sensitive than DNA polymerase beta [Wahl, A. F., Crute, J. J., Sabatino, R. D., Bodner, J. B., Marraccino, R. L., Harwell, L. W., Lord, E. M., & Bambara, R. A. (1986) Biochemistry 25, 7821-7827]. We find that DNA replication and ultraviolet-induced DNA repair synthesis in permeable human fibroblasts are also more sensitive to inhibition by ddTTP than polymerase alpha and less sensitive than polymerase beta. The Ki for ddTTP of replication is about 40 microM and that of repair synthesis is about 25 microM. These are both much less than the Ki of polymerase alpha (which is greater than 200 microM) but greater than the Ki of polymerase beta (which is less than 2 microM). These data suggest that DNA polymerase delta participates in DNA replication and ultraviolet-induced DNA repair synthesis in human cells.     

The role of DNA polymerases alpha, beta and gamma in nuclear DNA synthesis.

The effects of the inhibitors 2'3' dideoxythymidine triphosphate (ddTTP) and 1-beta-D-arabinofuranosyl cytosine triphosphate (araCTP) on DNA synthesis in isolated S-phase HeLa S3 nuclei have been examined. These effects are compared with the effects of the same inhibitors in partially purified preparations of DNA polymerases alpha and beta. The effect of ddTTP on partially purified DNA polymerase gamma was also tested. DNA polymerases beta and gamma were very sensitive to ddTTP whereas DNA polymerase alpha and DNA synthesis in isolated nuclei were quite resistant. The synthesis and subsequent ligation of primary DNA pieces ('Okazaki fragments') were not affected by the presence of this inhibitor. DNA synthesis in isolated nuclei and DNA polymerase alpha activity were very sensitive to araCTP whereas DNA polymerase beta was almost totally resistant to the inhibitor. The results indicate a major role for DNA polymerase alpha in DNA replication.     

Selective inhibition of human immunodeficiency virus (HIV) by 3'-azido-2', 3'-dideoxyguanosine in vitro

3'-Azido-2',3'-dideoxyguanosine (AzddGuo) is a potent and selective inhibitor of human immunodeficiency virus (HIV) in vitro. AzddGuo completely inhibits HIV-induced cytopathogenicity and viral antigen expression in MT-4 cells at a concentration of 5.0 microM. Its 50% effective dose for inhibiting HIV-induced cytopathogenicity is 1.4 microM, as compared to 6.4 microM for 2',3'-dideoxyadenosine (ddAdo). Thus, AzddGuo is approximately 4.6-fold more potent as an anti-HIV agent than ddAdo, one of the most promising compounds for the treatment of AIDS. However, AzddGuo is about 4.7 times more cytotoxic than ddAdo, so that its selectivity index, as based on the ratio of the 50% cytotoxic dose to the 50% antiviral effective dose, is almost the same as that of ddAdo (136 and 139, respectively).     

Effect of 2'',3''-dideoxythymidine-5''-triphosphate on HeLa cell in vitro DNA synthesis: evidence that DNA polymerase alpha is the only polymerase required for cellular DNA replication.

We have studied the effects of the nucleotide analogue, 2',3'-dideoxythymidine-5'-triphosphate (ddTTP) on replicative DNA synthesis in HeLa cell lysates. As previously demonstrated (1), such lysates carry out extensive DNA synthesis in vitro, at rates and in a fashion similar to in vivo DNA replication. We report here that all aspects of DNA synthesis in such lysates (total dNTP incorporation, elongation of continuous nascent strands, and the initiation, elongation, and joining of Okazaki pieces) are only slightly inhibited by concentrations of ddTTP as high as 100-500 micrometer when the dTTP concentration is maintained at 10 micrometer. This finding is consistent with the report by Edenberg, Anderson, and DePamphilis (2) that all aspects of replicative in vitro simian virus 40 DNA synthesis are also resistant to ddTTP. We also find, in agreement with Edenberg, Anderson, and DePamphilis (2), that DNA synthesis catalyzed by DNA polymerases beta or gamma is easily inhibited by ddTTP, while synthesis catalyzed by DNA polymerase alpha is very resistant. These observations suggest that DNA polymerase alpha may be the only DNA polymerase required for all aspects of cellular DNA synthesis.     

Both 2',3'-dideoxythymidine and its 2',3'-unsaturated derivative (2',3'-dideoxythymidinene) are potent and selective inhibitors of human immunodeficiency virus replication in vitro

2',3'-Dideoxythymidine (ddThd) and its 2',3'-unsaturated derivative 2',3'-dideoxythymidinene (ddeThd) are potent and selective inhibitors of human immunodeficiency virus (HIV) in vitro. When evaluated for their inhibitory effects on the cytopathogenicity of HIV in MT-4 cells, ddThd and ddeThd completely protected the cells against destruction by the virus at a concentration of 1 microM and 0.04 microM, respectively. In this aspect, ddeThd was about 5 times more potent than 2',3'-dideoxycytidine (ddCyd), one of the most potent and selective anti-HIV compounds now pursued for its therapeutic potential in the treatment of AIDS. ddThd and ddeThd also suppressed HIV antigen expression at 1 microM and 0.04 microM, respectively. Their selectivity indexes, as based on the ratio of the 50% cytotoxic dose to the 50% antiviral effective dose, were 120 (ddeThd) and greater than 625 (ddThd).     

Effects of the PAF-analog and -antagonist CV-6209 on cultured human glioma cell lines

Cell lines of human glioma (U-343 MGa and U-251 MG) and human glia (U-533 CG) origin were cultured as monolayers and exposed to CV-6209, an alkyl-phospholipid analog and antagonist of platelet activating factor. This drug had very potent antiproliferative effects on the studied human glioma cell lines; IC50 was 0.9 microM after 48 h treatment and 0.2 microM after 2 weeks treatment. At these doses no growth inhibitory effect was noted on the normal glia cells. The effects on the glioma cells were reversible in the dose intervals, where cell proliferation, 3H-thymidine and 14C-methionine uptakes were greatly inhibited. The simultaneous administration of platelet activating factor [(R)PAF] did not influence the antiproliferative effects of CV-6209 on the cells cultured as monolayers. The structurally similar analog CV-3988 also had antiproliferative effects, although at 10 times higher concentration than CV-6209. Two other, structurally unrelated, PAF-antagonists (WEB-2086 and TCV-309) gave effects only at very high concentrations. The U-343 MGa cell line was also exposed to CV-6209 when growing as multicellular spheroids. The studies on the spheroid cultures also demonstrated good antitumoral effects with decreases of both the volume growth and the thymidine uptake. The simultaneous administration of (R)PAF reversed the inhibitory effect of CV-6209 on thymidine incorporation. This study demonstrates a strong antitumoral effect at low concentrations of CV-6209. The antiproliferative effects were probably primarily related to the ether-lipid structure and not to the PAF-antagonistic properties. The good antitumoral effect of CV-6209 on both monolayer and spheroid cultures and the possible PAF-antagonistic properties are discussed.     

Involvement of eucaryotic deoxyribonucleic acid polymerases alpha and gamma in the replication of cellular and viral deoxyribonucleic acid.

In an effort to identify the deoxyribonucleic acid (DNA) polymerase activities responsible for mammalian viral and cellular DNA replication, the effect of DNA synthesis inhibitors on isolated DNA polymerases was compared with their effects on viral and cellular DNA replication in vitro. DNA polymerase alpha, simian virus 40 (SV40) DNA replication in nuclear extracts, and CV-1 cell (the host for SV40) DNA replication in isolated nuclei all responded to DNA synthesis inhibitors in a quantitatively similar manner: they were relatively insensitive to 2',3'-dideoxythymidine 5'-triphosphate (d2TTP), but completely inhibited by aphidicolin, 1-beta-D-arabinofuranosylcytosine 5'-triphosphate (araCTP), and N-ethylmaleimide. In comparison, DNA polymerases beta and gamma were inhibited by d2TTP but insensitive to aphidicolin and 20--30 times less sensitive to araCTP than DNA polymerase alpha. Herpes simplex virus type 1 (HSV-1) DNA polymerase and DNA polymerase alpha were the only enzymes tested that were relatively insensitive to d2TTP; DNA polymerases beta and gamma, phage T4 and T7 DNA polymerases, and Escherichia coli DNA polymerase I were 100--250 times more sensitive. The results with d2TTP were independent of enzyme concentration, primer-template concentration, primer-template choice, and the labeled dNTP. A specific requirement for DNA polymerase alpha in the replication of SV40 DNA was demonstrated by the fact that DNA polymerase alpha was required, in addition to other cytosol proteins, to reconstitute SV40 DNA replication activity in N-ethylmaleimide-inactivated nuclear extracts containing replicating SV40 chromosomes. DNA polymerases beta and gamma did not substitute for DNA polymerase alpha. In contrast to SV40 and CV-1 DNA replication, adenovirus type 2 (Ad-2) DNA replication in isolated nuclei was inhibited by d2TTP to the same extent as gamma-polymerase. Ad-2 DNA replication was also inhibited by aphidicolin to the same extent as alpha-polymerase. Synthesis of CV-1 DNA, SV40 DNA, and HSV-1 DNA in intact CV-1 cells was inhibited by aphidicolin. Ad-2 DNA replication was also inhibited, but only at a 100-fold higher concentration. We found no effect of 2'-3'-dideoxythymidine (d2Thd) on cellular or viral DNA replication in spite of the fact that Ad-2 DNA replication in isolated nuclei was inhibited 50% by a ratio of d2TTP/dTTP of 0.02. This was due to the inability of CV-1 and Hela cells to phosphorylate d2Thd to d2TTP. These data are consistent with the hypothesis that DNA polymerase alpha is the only DNA polymerase involved in replicating SV40 DNA and CV-1 DNA and that Ad-2 DNA replication involves both DNA polymerases gamma and alpha.     

Increased sensitivity for detection of carcinogen-induced DNA repair with the chain terminator dideoxythymidine.

The sensitivity for quantitation of DNA excision repair caused by a carcinogen is increased when the resynthesis of DNA is inhibited with dideoxythymidine (ddThd), a chain terminator. Incorporation of ddThd in primary liver cell cultures leaves discontinuities in the DNA chain at sites of reparative synthesis in response to benzo(a)pyrene [B(a)P] treatment. This is detectable by the accumulation of cellular DNA with reduced molecular weight on alkaline sucrose gradients. Up to 78 percent of the DNA in cells incubated with B(a)P and ddThd had greatly reduced molecular weight compared to control cells, whereas only 32 percent of the DNA in cells treated with B(a)P but not incubated with ddThd was affected similarly.     

The DNA polymerases associated with the adenovirus type 2 replication complex: effect of 2''-3''-dideoxythymidine-5''-triphosphate on viral DNA synthesis.

An adenovirus (Ad) DNA replication complex extracted from infected HeLa nuclei could be purified free of the bulk of intracellular DNA polymerase activity by sedimetation in neutral sucrose gradients. However, the replication complex still retained some alpha and gamma DNA-polymerase activity. Since this complex is inhibited by 2', 3' dideoxythymidine-5'-triphosphate (ddTTP), an inhibitor of DNA polymerase gamma, a functional role for this enzyme in Ad DNA replication is suggested. Similar inhibition by ddTTP in intact Ad infected nuclei and comparable inhibition of Ad DNA synthesis in whole cells by dideoxythymidine (ddThy) are consistent with a role for DNA polymerase gamma. Uninfected HeLa nuclei or whole cells are not similarly inhibited by ddTTP or DDThy respectively. Such data does not rule out an additional functional role for other DNA polymerases, and recent experiments from this laboratory (1) suggest that DNA polymerase alpha is also involved in Ad DNA synthesis.     

Studies on a novel DNA polymerase inhibitor group, synthetic sulfoquinovosylacylglycerols: inhibitory action on cell proliferation

Some chemically synthesized sulfoquinovosylmonoacylglycerols (SQMG)-sulfoquinovosyldiacylglycerols (SQDG) have been reported to selectively and strongly inhibit the activities of mammalian DNA polymerases alpha and beta in vitro. In this study, using human cancer cell lines, we investigated the effects of SQMG-SQDG on the DNA polymerase in the cells. In the presence of n-decane, the IC(50) values on cell growth were approximately 1-5 microM for SQMG and about 0.3-1 microM for SQDG. The values were almost the same as the in vitro enzyme inhibitory levels. The cell lines were arrested in early S-phase by SQMG-SQDG at the concentrations of 0.1-4.7 microM in a manner dependent on incubation time, suggesting that SQMG-SQDG blocked the primary step of DNA replication by inhibiting DNA polymerase, possibly alpha-type. We also demonstrated the localization of SQMG in the cell using the fluorescent SQMG analog, SQMGalpha-NBDD, which was synthesized in our laboratory. SQMGalpha-NBDD was localized in the nucleus and on the nuclear surface, but the binding site seemed not to be the DNA/chromatin, suggesting that the SQMG-SQDG might interact with molecules located close to the DNA/chromatin and on the nuclear surface. These results suggested a correlation between the in vitro biochemical action of the SQMG-SQDGs and their intracellular mode of action.     

Inhibitory effect of interferon on the genetic and oncogenic transformation by viral and cellular genes.

The rodent established cell lines LTk- and NIH 3T3 have been used as recipients in gene transfer experiments to study the effect of interferon treatment on the genetic and oncogenic transformation by several genes of viral and cellular origin. Our results show that interferon severely inhibits, to a similar extent, the stable transformation of Ltk- and NIH 3T3 cells by the chicken thymidine kinase (tk) gene, Ecogpt gene, simian virus 40, v-Ha-ras, and human c-Ha-ras and c-Ki-ras oncogenes. These results are consistent with an inhibition by interferon at the level of stabilization or integration, or both, of exogenous DNA sequences in the recipient cells, with an apparent effect on gene expression.     

Contribution of DNA polymerase delta to DNA replication in permeable CHO cells synchronized in S phase.

To evaluate the relative contributions of DNA polymerase alpha and DNA polymerase delta in chromosome replication during the S phase of the cell cycle, we have used the permeable cell system for replication as a functional assay. We carried out the analysis of DNA polymerases both in quiescent cells stimulated to proliferate and progress through the cell cycle (monolayers) and in actively growing cells separated into progressive stages of the cell cycle by centrifugal elutriation (suspension cultures). DNA polymerase alpha was measured by using the inhibitor butylphenyl dGTP at low concentrations. Using several inhibitors such as aphidicolin, ddTTP and butylphenyl dGTP, we found that DNA polymerase alpha and delta activity were coordinately increased during S phase and declined at the end. However, DNA polymerase delta was performing about 80% of the total replication and DNA polymerase alpha performed only 20%. This high ratio of DNA polymerase delta to DNA polymerase alpha replication activity was maintained throughout S phase in two entirely different experimental approaches.     

干细胞因子逆转录病毒表达载体的构建及体外性质研究

目的通过逆转录病毒介导两种类型人干细胞因子在NIH3T3细胞中稳定表达,并研究它们对白血病细胞的作用。方法用DNA重组技术构建并鉴定可溶型及膜结合型干细胞因子的重组逆转录病毒表达载体MSCV—PGK—GFP—sSCF、MSCV—PGK—GFP—mSCF,与空载体对照MSCV—PGK—GFP分别转染Phoenix细胞包装病毒,并感染NIH3T3细胞,流式分选术获得3种阳性细胞,CCK8法分别检测与其共培养的K562细胞的增殖情况。结果成功构建了sSCF、mSCF逆转录病毒表达载体;经Phoenix包装的重组及对照逆转录病毒成功感染NIH3T3细胞,获得了稳定表达细胞株NIH3T3-S、NIH3T3-M和对照细胞株NIH3T3-V。共培养中NIH3T3-S、NIH3T3-M均可促进K562细胞的增殖,且在低血清条件下,NIH3T3-M的作用高于NIH3T3-S。结论可溶性及膜结合SCF分别通过旁分泌和并置性作用促进白血病细胞的增殖。     

Growth-Inhibitory Functions of a Mutated Gelsolin (His321) in NIH/3T3 Mouse Fibroblasts

We have previously established a murine flat revertant cell line R1 from an activated H-ras transformant EJ-NIH/3T3 by subjecting it to ethyl methanesulfonate. From the R1 cells, we cloned a mutated gelsolin gene His321 and have shown the inhibitory activity of His321 against EJ-NIH/3T3 tumors. Our present experiments were conducted to find out whether the His321 gene has any effects on untransformed NIH/3T3 fibroblasts. Rhodamine-phalloidin staining revealed that two NIH/3T3 clones expressing His321 (NIH/λ2S-3 and NIH/λ2S-6) form organized actin stress fibers as two clones transfected with the vector alone (NIH/neo-3 and NIH/neo-5). We also found that in a liquid medium, NIH/λ2S-3 and NIH/λ2S-6 grew more slowly than NIH/neo-3 and NIH/neo-5 and that the doubling times of the former were about 10 h slower than those of the latter. To investigate the effects of His321 on the signal transduction pathway necessary for cell growth, we stimulated the cell lines by prostaglandin E1 (PGE1), a platelet-derived growth factor (PDGF), or the epidermal growth factor (EGF). Although stimulation by PGE1 increased intercellular cyclic AMP in R1 cells, it did not do so in NIH/λ2S-3 and NIH/λ2S-6 cells. On the other hand, stimulation by PDGF or EGF induced far less DNA synthesis in NIH/λ2S-3 and NIH/λ2S-6 than in NIH/neo-3 and NIH/neo5. These results suggest that through the effects on the signal transduction pathway of PDGF and/or EGF His321-mutated gelsolin inhibits the growth of NIH/3T3.     

Inhibition by aphidicolin and dideoxythymidine triphosphate of a multienzyme complex of DNA synthesis from human cells

A multienzyme complex consisting of DNA polymerase and several DNA precursor-synthesizing enzymes was solubilized by gentle lysis of cultured human cells. This complex channelled the distal precursor [3H]dTMP into DNA. The patterns of inhibition of the complex by aphidicolin and dideoxythymidine triphosphate (ddTTP) suggested that the complex contained the replicative DNA polymerase, polymerase alpha. Inhibition by ddTTP was competitive with dTTP. This was exploited to estimate the effective concentration of [3H]dTTP at the site of DNA synthesis during channelling of [3H]dTMP into DNA. The estimated concentration (about 50 microM) was so high as to suggest that the solubilized complex was able to functionally compartmentalize DNA precursors.