Differential effect of nucleoside analog triphosphates on ribonucleotide reductases from uninfected and herpes simplex virus-infected HeLa cells

Effects of the triphosphates of eight pyrimidine nucleoside analogs (5-substituted, 2'-fluoroara-, and acyclonucleosides) and acycloguanosine were examined on the ribonucleotide reductases prepared from uninfected and herpes simplex virus (types 1 and 2)-infected HeLa cells. Of the analogs tested, E-5-propenyl- and E-5-(2-bromovinyl)-dUTP were more potent inhibitors than dTTP of the enzymes from virus-infected cells, whereas only the former compound showed this effect on the uninfected HeLa enzyme.

In vitro biological activity of 9-beta-D-arabinofuranosyl-2-fluoroadenine and the biochemical actions of its triphosphate on DNA polymerases and ribonucleotide reductase from HeLa cells

9-beta-D-Arabinofuranosyl-2-fluoroadenine (2-F-araA) inhibited the growth in vitro of HeLa cells by 50% at a concentration of 0.25 microM and depressed the replication of herpes simplex virus Types 1 and 2 by 99% at 25 microM. The analogue served as a substrate for cytoplasmic but not mitochondrial deoxycytidine (dCyd) kinase partially purified from human peripheral chronic lymphocytic leukemic blast cells. The Km values of dCyd and 2-F-araA for the cytoplasmic enzyme were 5 microM and 213 microM, respectively. However, at concentrations of 0.4 mM, the analogue was phosphorylated 2.9 times faster than dCyd. The 5'-triphosphate of 2-F-araA was examined for its biochemical effects on partially purified ribonucleotide reductase and highly purified DNA alpha- and beta-polymerases from HeLa cells. 2-F-araATP was a potent inhibitor of ribonucleotide reductase; the concentration required for 50% inhibition of ADP reduction (0.3 mM ADP; 5 mM GTP or dGTP) was 1 microM and for CDP reduction (0.15 mM CPD; 5 mM ATP) was 8.5 microM. Furthermore, 2-F-araATP was a competitive inhibition (Ki = 1.2 microM) with respect to dATP (Km = 3.8 microM) of DNA alpha-polymerase, whereas DNA beta-polymerase was relatively insensitive to the drug. The results suggest that the cytotoxic actions of 2-F-araA may be due, in part, to a "self-potentiating" inhibition of DNA synthesis. This is, by inhibiting the formation of competing dATP, 2-F-araATP may potentiate its inhibition of DNA synthesis.

Effect of methotrexate on dihydrofolate reductase activity in methotrexate-resistant human KB cells

A cloned subline of human cell variants derived from KB cells (KB/6b), 6500-fold resistant to methotrexate (MTX), exhibited a stable 40-fold elevation of the enzyme dihydrofolate reductase (EC 1.5.1.3., DHFR) in the absence of the drug. No differences were detected between the enzyme isolated from resistant and parental KB cells. After the culture medium was supplemented with MTX, the resistant cells were shown to have an additional 5-fold increase in DHFR levels. This increment was dependent upon the concentration of exogenous MTX and was freely reversible. This behavior differs from that of other DHFR-overproducing mammalian cell lines previously reported. The half-life of DHFR in these cells in the presence or absence of MTX was the same, thus eliminating stabilization of the enzyme by MTX as being responsible for the modulation or "induction" phenomenon. Furthermore, the effect was blocked by cycloheximide and was not affected by actinomycin D. These results suggest that modulation of DHFR specific activity by MTX occurs at either the translational level or by as yet undefined post-transcriptional mechanism(s).

Sequential high-dose cytosine arabinoside and asparaginase in refractory acute leukemia

The development of resistance to Ara-C by leukemia cells may be a multifactorial process. These include diminished rates of anabolism or increased rate of catabolism to Ara-C, competition for incorporation into DNA by higher pool size of the competing normal metabolite, dCTP and perhaps other mechanisms. Laboratory investigations have shown that cellular resistance to lower doses of Ara-C (LoDAC) may be overcome by a substantial increase in the extracellular concentration (dose-effect). Clinical extrapolation of these observations have shown that high dose Ara-C (HiDAC) is effective in re-inducing remission in patients with acute leukemia who have either failed to enter remission or who relapsed while being treated with LoDAC. Other laboratory investigations indicate significant schedule-dependent synergy between sequential HiDAC and asparaginase. Application of these observations to clinical trial has resulted in a 64% complete remission rate in patients with non-lymphocytic leukemia, including those who were previously treated with LoDAC or who had had an antecedent hematologic disorder. Toxicity from this regimen was not significantly different from those employing LoDAC. These preliminary data in patients with high risk disease would suggest that HiDAC/asparaginase might have significant utility in patients with previously untreated acute non-lymphocytic leukemia.

Inhibition of purified human and herpes simplex virus-induced DNA polymerases by 9-(2-hydroxyethoxymethyl)guanine triphosphate. Effects on primer-template function

The inhibition of highly purified herpes simplex virus (HSV)-induced and host cell DNA polymerases by the triphosphate form of 9-(2-hydroxyethoxymethyl)guanine (acyclovir; acycloguanosine) was examined. Acyclovir triphosphate (acyclo-GTP) competitively inhibited the incorporation of dGMP into DNA, catalyzed by HSV DNA polymerase; apparent Km and Ki values of dGTP and acyclo-GTP were 0.15 microM and 0.003 microM, respectively. HeLa DNA polymerase alpha was also competitively inhibited; Km and Ki values of dGTP and acyclo-GTP were 1.2 microM and 0.18 microM, respectively. In contrast, HeLa DNA polymerase beta was insensitive to the analogue. The "limited" DNA synthesis observed when dGTP was omitted from HSV or alpha DNA polymerase reactions was inhibited by acyclo-GTP in a concentration-dependent manner. Prior incubation of activated DNA, acyclo-GTP, and DNA polymerase (alpha or HSV resulted in a marked decrease in the utilization of the primer-template in subsequent DNA polymerase reactions. This decreased ability of preincubated primer-templates to support DNA synthesis was dependent on acyclo-GTP, enzyme concentration, and the time of prior incubation. Acyclo-GMP-terminated DNA was found to inhibit HSV DNA polymerase-catalyzed DNA synthesis. Kinetic experiments with variable concentrations of activated DNA and fixed concentrations of acyclo-GMP-terminated DNA revealed a noncompetitive inhibition of HSV-1 DNA polymerase. The apparent Km of 3'-hydroxyl termini was 1.1 X 10(-7) M, the Kii and Kis of acyclo-GMP termini in activated DNA were 8.8 X 10(-8) M and 2.1 X 10(-9) M, respectively. Finally, 14C-labeled acyclo-GMP residues incorporated into activated DNA by HSV-1 DNA polymerase could not be excised by the polymerase-associated 3',5'-exonuclease activity.

Induction of uracil-DNA glycosylase and dUTP nucleotidohydrolase activity in herpes simplex virus-infected human cells

HeLa BU cells infected with either the type 1 or the type 2 forms of herpes simplex virus show an increase in the activities of uracil-DNA glycosylase and dUTP nucleotidohydrolase. Under optimal conditions, uracil-DNA glycosylase activity increases approximately 40-fold in HSV type 2-infected cells. In herpes simplex virus (HSV) type 1-infected cells, uracil-DNA glycosylase activity increases only 6-fold. At a KCl concentration of 100 mM, uracil-DNA glycosylase derived from HSV type 2-infected cells is activated 2-fold, while the glycosylase extracted from mock infected HeLa BU cells is inhibited almost 90% at 100 mM KCl. dUTP nucleotidohydrolase activity increases 4-fold and 3-fold, respectively, in HSV type 1- and HSV type 2-infected HeLa BU cells. Nondenaturing polyacrylamide gel electrophoresis of extracts derived from the type 1- and type 2-infected cells indicates distinct electrophoretic mobilities from the host cell enzyme. dUTP nucleotidohydrolase RF values for the mock infected cells, HSV type 1, and HSV type 2 are 0.5, 0.25, and 0.33, respectively. Serum from rabbits immunized against cells infected with herpes simplex virus type 1 or type 2 specifically neutralizes the dUTPase and uracil-DNA glycosylase activities extracted from herpes simplex virus-infected cells. This serum does not neutralize dUTPase or uracil-DNA glycosylase activity derived from mock infected cells.

Differential activity of potential antiviral nucleoside analogs on herpes simplex virus-induced and human cellular thymidine kinases

Potential antiviral nucleoside analogs 1-beta-D-arabinofuranosylthymine, the 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-nucleosides of -5-methyluracil, -5-iodouracil, -5-methylcytosine, -5-iodocytosine, and -E-5-(2-bromovinyl)uracil, E-5-(2-bromovinyl)-2'-deoxyuridine, E-5-(2-bromovinyl)-1-beta-D-arabinofuranosyluracil, and 9-(2-hydroxyethyoxymethyl)guanine were studied to compare their phosphorylation rates relative to thymidine by purified thymidine kinases from human and herpes simplex virus sources. Most of these analogs are capable of being phosphorylated by both human and viral enzymes. On the assumption that inhibition constants (Ki) reflect binding affinity, Ki values were determined for these analogs with the same thymidine kinases. In general, these analogs have a greater affinity for the viral enzymes. The amount of the analogs phosphorylated to the monophosphate form, which is presumably necessary to produce cytotoxic effects, was determined by the combined effects of phosphorylation rates and binding affinities. All of these analogs act as preferential substrates for the viral thymidine kinases at low concentrations, which may be one of the main reasons for their selective antiviral action.

Herpes simplex virus type I DNA polymerase. Kinetic properties of the associated 3'-5' exonuclease activity and its role in araAMP incorporation

An exonuclease activity copurified with herpes simplex virus type I (HSV-1) DNA polymerase through DNA-cellulose column chromatography and comigrated with DNA polymerase activity on nondenaturing gel electrophoresis at varied polyacrylamide concentrations. A gapped duplex DNA was the preferred substrate for this exonuclease activity since the hydrolytic activity on this type of DNA was much greater than the hydrolysis of either native or heat-denatured DNA. Using 3'-terminally labeled activated calf thymus DNA as substrate, the exonuclease activity was found to be activated by salt and spermidine in a manner identical with HSV-1 DNA polymerase. This activation was accompanied by increases in apparent Km and Vmax values of the activated DNA substrate. Phosphonoformic acid inhibited both DNA polymerase and exonuclease activities uncompetitively with respect to activated DNA and had a Ki of 2.4 microM at an ionic strength of 0.25 mu. Of the nucleoside 5'-monophosphates tested only the purine ribonucleotides inhibited the exonuclease activity. The inhibition was noncompetitive with respect to DNA, and GMP was about twice as potent as AMP or IMP. 9-beta-D-arabinosyladenine 5'-monophosphate (araAMP) could be incorporated into DNA by HSV-1 DNA polymerase; however, 9-beta-D-arabinosyladenine 5'-triphosphate would not replace dATP in supporting in vitro HSV-1 DNA synthesis. AraAMP incorporated into primer termini caused a significant decrease in the rate of subsequent primer elongation. These 3'-terminal araAMP residues could be removed by the HSV-1 DNA polymerase-associated exonuclease activity in a manner dependent on GMP concentration.

Biological and biochemical effects of 2'-azido-2'-deoxyarabinofuranosylcytosine on human tumor cells in vitro

2-azido-2'-deoxyarabinofuranosylcytosine (Cytarazid), recently synthesized, was found to inhibit the in vitro growth of several human cell lines by 50% at concentrations ranging from 0.06 to 0.2 microM and to prevent the replication of herpes simplex virus types 1 and 2 by 98% at 50 microM. As determined with HeLa cells, the inhibition of cell growth was partially prevented by 2'-deoxycytidine (dCyd) and cytidine but not by uridine or thymidine. Cytarazid proved resistant to deamination by human cytidine/dCyd deaminases purified from acute myelocytic leukemia blast cells and from liver, a property reflected in the inability of tetrahydrouridine to enhance the cytotoxicity of the compound. Cytarazid served as a substrate for cytoplasmic dCyd kinase partially purified from human peripheral chronic lymphocytic leukemia blast cells. At a concentration of 0.4 mM, the nucleoside analog was phosphorylated 2.6 times more effectively by this enzyme than was dCyd, the Km for Cytarazid being 250 microM. In intact HeLa cells, the triphosphate derivative of Cytarazid was the major drug metabolite formed. In these cells, the analog interfered with the incorporation of radiolabeled thymidine into DNA at a concentration and a time interval at which the incorporation of uridine into RNA and amino acids into protein was not inhibited, suggesting that interference with DNA synthesis is a primary drug effect. Further analysis showed that Cytarazid triphosphate interferes with DNA synthesis in intact HeLa cell nuclei and that it inhibits both the alpha- and beta-DNA polymerases purified from HeLa cells in a manner competitive with deoxycytidine triphosphate, with Ki's of 0.6 and 0.7 microM, respectively. Cytarazid triphosphate was not able to replace deoxycytidine triphosphate for the synthesis of DNA in either intact nuclei or in cell-free preparations; but, in the cell-free assay system, the compound was found to interfere with primer-template activity.

Mode of action of phosphonoformate as an anti-herpes simplex virus agent

Phosphonoformate inhibited the replication of Herpes simplex virus (HSV) type 1 and type 2 in culture. The concentration required to inhibit the replication of both types of virus by 2 logs at 28 h post-infection was approximately 150 microM. It was more potent than phosphonoacetate against the growth of both virus types. A virus mutant which is resistant to phosphonoacetate was cross-resistant to phosphonoformate. Arsonoacetate, at 300 microM, had no antivirus activity. Phosphonoformate also inhibited HeLa and KB cell growth; at a concentration of about 500 microM, cell growth was inhibited by 50%. The anti-cell growth effects of the drug were completely reversible. The antivirus effect of phosphonoformate was partially reversible, depending on the time and duration of exposure of infected cultures to the drug. To obtain the maximum antivirus effect, phosphonoformate had to be added within the first 3 h post-virus-infection and be continuously present for at least 18 h. Phosphonoformate, added at 0 h post-infection, suppressed the induction of virus-specific DNA polymerase and DNAase activities. dTMP incorporation into DNA was preferentially inhibited in nuclei isolated from infected cells compared to uninfected cells, and the degree of inhibition varied with the ionic strength of the assay. Phosphonoformate was a potent inhibitor of the purified HSV-1 and HSV-2 DNA polymerases, inhibiting DNA polymerase activity by 50% at a concentration of 3 microM and ionic strength of 0.2.

Synthesis and antiviral activity of 1-(2-deoxy-beta-D-ribofuranosyl)-5-(methylmercapto)-2-pyrimidinone

1-(2-Deoxy-beta-D-ribofuranosyl)-5-(methylmercapto)-2-pyrimidinone (1b) was synthesized via modification of the silyl method. 1b inhibits the Herpes simplex virus type 1 (98%) and type 2 (97%) at a concentration which is nontoxic to human HeLa cells. The compound shows 50 times greater binding affinity (lower Ki) to the virus-specific thymidine kinase than to the thymidine kinase of uninfected HeLa cells.

Anti-herpes simplex virus and anti-human cell growth activity of E-5-propenyl-2'-deoxyuridine and the concept of selective protection in antivirus chemotherapy

E-5-Propenyl-2'-deoxyuridine (E-5-propenyl-dUrd) inhibited the growth of herpes simplex virus (HSV) types 1 (HSV-1) and 2 in culture. The concentration of drug required to give a 2-log reduction in virus titer was 5 microM for HSV-1 and 23 microM for HSV-2. The anti-HSV-1 activity of this agent was more potent than 5-propyl-dUrd, equivalent to E-5(3,3,3-trifluoropropenyl)-dUrd, and less potent than E-5-bromovinyl-dUrd. The HSV-1 mutant (B2006) lacking the ability to induce virus-specific thymidine kinase could not be inhibited by E-5-propenyl-dUrd. The binding constants of E-5-propenyl-dUrd to HSV-1, HSV-2, varicella-zoster virus, and human mitochondrial thymidine kinases were established to be 0.2, 6.2, 0.3, and 0.8 microM, respectively. Thymidine phosphorylation catalyzed by human cytosol thymidine kinase could not be inhibited by E-5-propenyl-dUrd at a concentration 10-fold higher than the thymidine in the assay. When thymidine and E-5-propenyl-dUrd were added concomitantly at equal concentrations to virus-infected cells, the antiviral activity was not reversed in HSV-1 and only partially reversed in HSV-2. E-5-Propenyl-dUrd also inhibited the growth of human cells in culture with 50% inhibitory dose of 50 microM. Since this inhibition could be readily reversed by a lower concentration of thymidine, the idea of selective protection is proposed. This approach could avoid the cytotoxic effect of an antiviral agent with properties similar to E-5-propenyl-dUrd without sacrificing antiviral activity.

Metabolism and chemotherapeutic activity of 9-beta-D-arabinofuranosyl-2-fluoroadenine against murine leukemia L1210 and evidence for its phosphorylation by deoxycytidine kinase

The 2-fluoro derivative of 9-beta-D-arabinofuranosyladenine (2-F-ara-A) and its soluble 5'-formate and 5'-phosphate derivatives were therapeutically effective against the parent leukemia L1210 (L1210/0). 2-F-ara-A and 9-beta-D-arabinofuranosyladenine 5'-formate were inactive aginst a 1-beta-D-arabinofuranosylcytosine-resistant subline (L1210/ara-C) that was deficient in deoxycytidine kinase. Deoxycytidine prevented 2-F-ara-A-induced inhibition of proliferation of L1210/0 cells in culture and alleviated 2-F-ara-a inhibition of DNA synthesis. After treatment of mice with 9-beta-D-arabinofuranosyladenine 5'-formate, intracellular levels of the 5'-triphosphate of 9-beta-D-arabinofuranosylfluoroadenine in leukemia cells were more than 10 times higher in L1210/0 cells than in L1210/ara-C cells. Similar results were obtained in this line of leukemia cells from mice treated with the 5'-monophosphate of 9-beta-D-arabinofuranosyl-2-fluoroadenine. Thus, L1210/ara-C cells deficient in deoxycytidine kinase activity were also deficient in capacity to phosphorylate 2-F-ara-A. Kinase activity from L1210/0 cells for deoxycytidine and for 2-F-ara-A coeluted from calcium phosphate cellulose and from diethylaminoethyl cellulose columns and had similar mobility on gel electrophoresis. Deoxyadenosine kinase was clearly separated from deoxycytidine kinase. Deoxycytidine competed with 2-F-ara-A for phosphorylation by the partially purified enzyme from L1210 cells. These results indicate that 2-F-ara-A is phosphorylated to the 5'-monophosphate by deoxycytidine kinase of leukemia L1210 cells.

Effects of deoxyadenosine triphosphate and 9-beta-D-arabinofuranosyl-adenine 5'-triphosphate on human ribonucleotide reductase from Molt-4F cells and the concept of "self-potentiation"

Deoxyadenosine triphosphate (dATP) acted as a noncompetitive inhibitor with respect to the specific nucleoside triphosphate activator for the reduction of all four common ribonucleoside diphosphates catalyzed by the reductase derived from human Molt-4F (T-type lymphoblast) cells. The inhibition constant of dATP for different ribonucleotide reduction reactions was different, indicating that the binding of the nucleoside triphosphate activator or substrate could modify the binding affinity of dATP to the enzyme. dATP also acted as a noncompetitive inhibitor with respect to cytidine diphosphate (CDP) for reductase-catalyzed CDP reduction. 9-beta-D-Arabinofuranosyl-adenine 5'-triphosphate acted as a competitive inhibitor with respect to either adenosine triphosphate or guanosine triphosphate for CDP or for adenosine diphosphate reduction, respectively. The inhibition constant was 15 microM for CDP reduction and 4 microM for adenosine diphosphate reduction. 1-beta-D-Arabinofuranosyladenine 5'-triphosphate could not substitute for adenosine triphosphate or guanosine triphosphate as the activator for CDP or adenosine diphosphate reduction, respectively. The effects of 9-beta-D-arabinofuranosylcytosine 5'-triphosphate and 5-iodo-2'-deoxyuridine 5'-triphosphate on ribonucleotide reductase were also included for comparison. The "self-potentiation" mechanism of the action of 9-beta-D-arabinofuranosyladenine and 5-iodo-2'-deoxyuridine is discussed.

Frequency and levels of antibodies to Epstein-Barr virus-specific DNase are elevated in patients with nasopharyngeal carcinoma

Sera from healthy individuals and patients with infectious mononucleosis, Burkitt lymphoma, nasopharyngeal carcinoma, or other malignancies were examined for their capacity to neutralize Epstein-Barr virus (EBV)-induced DNase activity. Sera were found that neutralized the EBV DNase but not herpes simplex virus type 1 or type 2 DNases, and vice versa. Sera from 46 of the 49 patients with nasopharyngeal carcinoma examined (94%) neutralized > 6 units of EBV DNase per ml of serum. In contrast, only 19% of 47 patients with Burkitt lymphoma, 12% of 183 patient with other malignancies, 4% of 58 patients with infectious mononucleosis, and none of 101 healthy individuals had such levels of neutralizing activity. The neutralizing factor was found in the IgG fraction derived from nasopharyngeal carcinoma sera. There was no correlation between the concentration of these antibodie and the titers of IgG ad IgA antibodies to the EBV capsid antigen, the early antigen complex, or the EBV-associated nuclear antigen.

Properties of herpes simplex virus type 1 and type 2 DNA polymerase

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) DNA polymerases were highly purified from infected HeLa BU cells by DEAE cellulose, phosphocellulose and DNA cellulose column chromatography. DNA exonuclease activity but not endonuclease activity was found associated with both types of DNA polymerase. Both DNA polymerase activities could be activated by salt in a similar fashion with the optimal activity in the range of ionic strength between 0.22 and 0.29 alpha. At an ionic strength of 0.14, spermidine and putrescine in the concentration range (0--5 mM) studied could mimic the action of KCI in stimulating DNA polymerase activity. Spermine, in the same concentration range, had a biphasic effect. At an ionic strength of 0.29 all three polyamines were inhibitory. HSV-1 and HSV-2 DNA polymerase are similar in their column chromatographic behavior, sedimentation rate in sucrose gradient centrifugation, and activation energy, but they differ in their heat stability at 45 degrees C with the HSV-2 enzyme more stable than the HSV-1 enzyme. Kinetic behavior of both enzymes is similar, with Km values for deoxyribonucleoside triphosphates in the range of 5 . 10(-7) to 1.8 . 10(-8) M. IdUTP and dUTP served as apparent competitive inhibitors with respect to dTTP, and AraATP acted as an apparent competitive inhibitor with respect to dATP. AraATP could not replace dATP in the DNA polymerization reaction; in contrast, IdUTP could replace TTP. Phosphonoformic acid behaved as an uncompetitive inhibitor with respect to DNA. The ID(50) value estimated was foind to be dependent on the purity of the DNA polymerase used and the ionic strength of the assay condition. Each DNA-polymerase associated DNA exonuclease had the same stability at 45 degrees C as its DNA polymerase. The associated DNAase activity was inhibited by phosphonoformic acid and high ionic strength of the assay condition.

Uracil DNA-glycosylase. Purification and properties of this enzyme isolated from blast cells of acute myelocytic leukemia patients

The enzyme uracil DNA-glycosylase has been purified from blast cells of patients with acute myelocytic leukemia. A 1000-fold purification has been achieved and the enzyme appears highly enriched for the uracil glycosylase activity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The apparent molecular weight of the purified enzyme is 30,000. Uracil DNA-glycosylase exhibits activity in the absence of any added metal and the addition of MgCl2, MnCl2, CaCl2, NaCl, or KCl causes inhibition. EDTA as well as EGTA can inhibit enzyme activity. An interesting finding is the biphasic effect of spermine. At a concentration of 25 microM, spermine will cause a 2.5-fold activation of enzyme activity, whereas at concentrations of 100 microM and higher, spermine will inhibit enzyme activity. An Arrhenius plot of glycosylase activity in the presence of 25 microM spermine shows a biphasic curve with the transition temperature being 36 degrees C. Initial velocity studies in the presence of varying concentrations of spermine indicate a change in both the apparent Km and Vmax of the enzyme. Various uracil analogs were tested to establish a structure-activity relationship for this enzyme. It appears from this data that uracil DNA-glycosylase is very specific for uracil moieties. Uracil, acting as a product inhibitor, gives a Ki value of 220 microM.

Synthesis, biologic effects, and biochemical properties of some 2'-azido- and 2'-amino-2'-deoxyarabinofuranosyl pyrimidines and purines

Various 2'-azido- and 2'-aminoarabinofuranosyl purine and pyrimidine nucleosides have been synthesized. Among these, the derivatives of cytosine and of adenine inhibit the growth of some tumor cell lines in vitro and in vivo. 2'-Azidoarabinofuranosyl cytosine also interferes with the replication of herpes simplex virus types I and II. Whereas 2'-azidoara-C is resistant to deamination by a partially purified CdR deaminase from KB cells, the adenine derivatives are substrates for aminohydrolases partially purified from calf and mouse intestines. Both azido- and aminoara-C are phosphorylated by partially purified CdR kinases from leukemia L1210 and from human AML blast cells. The accumulated data encourage exploration of the clinical utility of the more potent of these analogues.

Substrate specificity of human ribonucleotide reductase from Molt-4F cells

Nucleoside triphosphates were examined as the activator for various nucleoside diphosphate reductions catalyzed by a highly purified ribonucleotide reductase obtained from Molt-4F cultured human cells. It was found that cytidine 5'-diphosphate and uridine diphosphate reductions are activated by adenosine 5'-triphosphate with apparent Ka's of 0.63 +/- 0.03 (S.E.) and 1.25 +/- 0.10 mM, respectively. Guanosine 5' diphosphate reduction is activated by deoxythymidine 5'-triphosphate with an apparent Ka of 1.25 +/- 0.11 microM, and adenosine 5'-diphosphate reduction is activated by guanosine 5'-triphosphate or deoxyguanosine 5'-triphosphate with an apparent Ka of 1.1 +/- 0.09 or 1.1 +/- 0.08 mM, respectively. In the presence of saturating amounts of their best activating nucleoside triphosphates, the Km's of various nucleotide diphosphates for this purified enzyme were studied. Double reciprocal plots of velocity against substrate concentration were found to be linear for all four substrates in the concentration range tested and yielded apparent Km's of 7 +/- 0.3 microM for cytidine 5'-diphosphate, 80 +/- 6.5 microM for adenosine 5'-diphosphate, 33 +/- 3.1 microM for guanosine 5'-diphosphate, 50 +/- 2.0 microM for uridine 5'-diphosphate. The reduction of one ribonucleoside diphosphate could be inhibited by other ribonucleoside diphosphates in a noncompetitive manner.

DNase induced after infection of KB cells by herpes simplex virus type 1 or type 2. II. Characterization of an associated endonuclease activity

Purified preparations of the "exonuclease" specified by herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) possess an endonuclease activity. The exonuclease and endonuclease activities copurify and cosediment in a sucrose density gradient. Endonuclease activity is only observed in the presence of a divalent cation, and Mg(2+) or Mn(2+) is equally effective as a cofactor with an optimal concentration of 2 mM. A slight amount of endonuclease activity is observed in the presence of Ca(2+), whereas no activity occurs in the presence of Zn(2+). In the presence of Mg(2+), Ca(2+) and Zn(2+) are inhibitory. Comparison of exonuclease and endonuclease activity in the presence of various divalent cations revealed that, at concentrations of Mn(2+) greater than 1 mM, only endonuclease activity occurs whereas endonuclease and exonuclease activity occur at all concentrations of Mg(2+). The endonuclease was affected by putrescine and spermidine to the same extent as the exonuclease activity, but in marked contrast the endonuclease was inhibited by a 10-fold-lower concentration of spermine compared to the exonuclease. The activity specified by HSV-1 and HSV-2 has very similar properties. HSV-1 and HSV-2 endonuclease cleave covalently closed circular DNA to yield, firstly, nicked circles and then linear DNA which is subsequently hydrolyzed to small oligonucleotides. Cleavage does not appear to be base sequence specific. Conversion of nicked circles to linear DNA and subsequent degradation of linear DNA occurs more rapidly in the presence of Mg(2+) than Mn(2+) presumably by virtue of the presence of the exonuclease activity. Nonsuperhelical covalently closed circular duplex DNA is cleaved by the endonucleases at a rate 60 times slower than the rate observed on the supercoiled form. These data indicate that the HSV-1 and HSV-2 endonuclease preferentially recognize single-stranded DNA regions.

Induction of thymidine kinase and DNase in varicella-zoster virus-infected cells and kinetic properties of the virus-induced thymidine kinase

Thymidine kinase (TK), DNA polymerase, and DNase activities were induced in human foreskin fibroblasts after varicella-zoster virus infection. The induced TK and DNase activities have electrophoretic mobilities different from the corresponding host enzymes. Varicella-zoster virus-induced TK was purified and separated from the host enzyme by affinity column chromatography. This enzyme has been shown to have a broader substrate specificity with respect to either the phosphate donor or acceptor as compared with human cytoplasmic and mitochondrial TKs. The best phosphate donor is ATP, with a Km of 16 microM. The Km values of thymidine, deoxycytidine, and 5-propyl deoxyuridine were estimated to be 0.4, 180, and 0.8 microM, respectively. The Ki values for several analogs of thymidine such as 5-iododeoxyuridine, arabinofuranosylthymine, 5-ethyl deoxyuridine, and 5-cyanodeoxyuridine were also examined. TTP acted as a noncompetitive inhibitor with respect to thymidine with a Ki of 5 microM. The kinetic behavior of varicella-zoster virus-induced TK is different from human cytoplasmic, human mitochondrial, and herpes simplex virus type 1- and 2-induced TKs.

An enzymatic method for distinguishing deoxyuridine and deoxythymidine nucleotide pools and its application for determining ribonucleotide reductase activity

A method is described for distinguishing deoxyuridine and deoxythymidine di- and triphosphate pools. The method utilizes a DNA polymerase assay for triphosphate determination and a coupled assay in which the disphosphate is converted to its corresponding triphosphate by nucleoside-diphosphate kinase and the triphosphate is measured by the DNA polymerase assay. By including deoxyruidine-triphosphate nucleotidohydrolase in the reaction mixture, dUTP is removed as a substrate for the polymerase. By determining differences in labelled acid-insoluble product formed in the reaction it is possible to determine dUTP, dUDP, dTDP and dTTP pools. Ribonucleotide reductase activity was determined by converting either CDP or ADP to its corresponding deoxyribonucleoside disphosphate and then using the diphosphate assay described for deoxyribonucleoside pools.

Optical properties of particle migration imaging film

The optical properties of an electrophotographic film comprised of closely packed submicron selenium spheres embedded in a polymer matrix were investigated. In one case the spheres were arranged in a monolayer; in a second the particles were dispersed throughout the polymer matrix. The optical transmission of these structures was measured as a function of wavelength and particle size and compared with physical models based on Mie theory.

The deoxyribonuclease induced after infection of KB cells by herpes simplex virus type 1 or type 2. I. Purification and characterization of the enzyme

The deoxyribonuclease induced in KB cells by herpes simplex virus (HSV) type 1 and type 2 has been purified. Both enzymes are able to completely degrade single- and double-stranded DNA yielding 5'-monophosphonucleotides as the sole products. A divalent cation, either Mg2+ or Mn2+, is an absolute requirement for catalysis and a reducing agent is necessary for enzyme stability. The maximum rate of reaction is achieved with 5 mM MgCl2 for both HSV-1 and HSV-2 DNase. The optimum concentration for Mn2+ is 0.1 to 0.2 mM and no exonuclease activity is observed when the concentration of Mn2+ is greater than 1 mM. The rate of reaction at the optimal Mg2+ concentration is 3- to 5-fold greater than that at the optimal Mn2+ concentration. In the presence of Mg2+, the enzymes are inhibited upon the addition of Mn2+, Ca2+, and Zn2+. The enzymatic reaction is also inhibited by spermine and spermidine, but not by putrescine. Crude and purified HSV-1 and HSV-2 DNase can degrade both HSV-1 and HSV-2 DNA, but native HSV-1 DNA is hydrolyzed at only 22% of the rate and HSV-2 DNA at only 32% of the rate of Escherichia coli DNA. Although HSV-1 and HSV-2 DNase were similar, minor differences were observed in most other properties such as pH optimum, inhibition by high ionic strength, activation energy, and sedimentation coefficient. However, the enzymes differ immunologically.

Demonstration, in leukemia L-1210 cells, of a phosphodiesterase acting on 3':5'-cyclic CMP but not on 3':5'-cyclic AMP or 3':5'-cyclic GMP

cCMP-specific phosphodiesterase activity was demonstrated in the 80 to 100% ammonium sulfate fraction obtained from disrupted leukemia L-1210 cells. The activity was linear with time (up to 60 min), was a function of protein concentration, and was markedly stimulated by Mg2+ and by ammonium sulfate. Under identical assay conditions, no significant hydrolysis of cAMP or cGMP was observed, although these cyclic nucleotides served as substrates for phosphodiesterase(s) present in all the fractions obtained by less than 80% ammonium sulfate saturation. This is the first demonstration of a cCMP-specific phosphodiesterase.

Effects of methylglyoxal bis(ganylhydrazone) on trypanosomatid flagellates: inhibition of growth and nucleoside incorporation in Trypanosoma brucei

Methyglyoxal bis (guanylhydrazone) (MGBG) at 0.5 mM had little effect in vitro on Blastocrithidia culicis, Crithidia oncopelti, and Leishmania spp., but completely inhibited growth of Trypanosoma brucei. Inhibition became irreversible after a 3-h exposure of T. brucei culture procyclics. Treated organisms remained motile, but failed to divide. Polyamines, spermidine, and spermine, did not reverse the anti-trypanosome action of MGBG (preloading of cells or concurrent administration). Two intraperitoneal injections of the drug at a concentration of 50 mg/kg body weight at a 1-day interval greatly reduced the parasitemia of T. brucei and T. congolense in rats. Trypanosome infections, however, relapsed and killed the animals in 6 days after treatment. It was evident from the results of tracer experiments with T brucei that MGBF significantly lowered incorporation of [3H]thymidine by culture pocyclics and of [3H]uridine by bloodstream forms; in both stages [3H]leucine incorporation was only slightly inhibited. It is suggested that MGBG interferes with nucleoside incorporation by Trypanosoma and that its mode of action is different in bloodstream and culture procyclics.

Biochemical and immunological characterization of deoxythymidine kinase of thymidine kinaseless HeLa cells biochemically transformed by herpes simplex virus type

Thymidine kinase (TK) from herpes simplex virus type 1 (HSV-1) biochemically transformed HeLa cells, purified by affinity chromatography, has been characterized with respect to its electrophoretic mobility, molecular weight, activation energy, substrate specificity, and immunological specificity. TK purified from HSV-1-transformed HeLa cells has the same electrophoretic mobility as TK purified from HeLa cells lytically infected with HSV-1. The sedimentation velocity of purified TK from transformed cells was similar to that previously reported for the lytic enzyme, and its molecular weight was estimated to be 70,000. The activation energy of purified transformed-cell TK was 18.3 kcal/mol. Antiserum prepared against purified HSV-1 TK, although it showed some cross-reactivity, preferentially neutralized homologous TK. The transformed-cell TK antiserum also neutralized the deoxycytidine kinase activity of HSV-1-infected cell extracts but had no effect on deoxycytidine kinase activity of HSV-2-infected cell extract. These results further support the notion that TK acquired by HeLa cells transformed by HSV-1 is of viral and not of cellular origin.

Human deoxycytidine kinase. Purification and characterization of the cytoplasmic and mitochondrial isozymes derived from blast cells of acute myelocytic leukemia patients

A procedure for purifying human cytoplasmic and mitochondrial deoxycytidine kinase (NTP:deoxycytidine 5'-phosphotransferase, EC 2.7.1.74) was developed. Both purified isozymes have a similar molecular weight, activation energy and catalyze the reaction by a sequential mechanism. These two isozymes differ with respect to their substrate specificities. With cytoplasmic deoxycytidine kinase, ATP, GTP and TTP have the highest reaction velocity. Pyrimidine nucleoside triphosphates have higher affinity but lower V than purine nucleoside triphosphates. Cytidine and arabinosylcytidine can serve as substrates. With mitochondrial isozyme only ATP gives the highest reaction velocity. ATP and dATP have the same Km but different V values. Besides deoxycytidine, also deoxythymidine but not cytidine or arabinosylcytidine can serve as substrates. There are also differences between these two isozymes with respect to their sensitivity to inhibition. For cytoplasmic enzyme, Br5dCyd and Iodo5dCyd are not inhibitory. Both dCTP and UTP are competitive inhibitors (Ki 0.25 and 0.5 micronM, respectively) with respect to ATP. For mitochondrial isozyme both Br5dCyd and Iodo5dCyd are inhibitory and dCTP and TTP are competitive inhibitors (Ki 2 and 10 micronM, respectively) with respect to ATP.

Deoxythymidine kinase induced in the HELA TK- cells by herpes simplex virus type I and type II. Substrate specificity and kinetic behavior

Deoxythymidine kinases (EC 2.7.1.--) induced in HeLa TK- cells by Herpes simplex Type I and Type II viruses both had a requirement for divalent cations. The enzymes had the highest activities in the presence of Mg2+, followed by Mn2+, Ca2+, Fe2+, and in that order, whereas they were inactive in the presence of Zn2+ and Cu2+. The amount of Mg2+ required for optimal activity was dependent on the amount of ATP present, so that optimal activities were found when the concentration of Mg2+ was equal to that of ATP; an excess of Mg2+ inhibited the reaction. The activities of various nucleoside triphosphates as phosphate donors for Herpes simplex virus Type I deoxythymidine kinase were in the order: ATP = dATP = ara ATP greater than CTP greater than dCTP greater than UTP greater than dUTP greater than GTP greater than dGTP. Those for Herpes simplex virus Type II deoxythymidine kinase were in the order: CTP greater than dCTP = ara CTP greater than dATP greater than ATP greater than UTP greater than GTP greater than dUTP = dGTP. For both deoxythymidine kinases induced by Herpes simplex virus, the nucleoside triphosphates tested exerted cooperative effects. The Km values of ATP and CTP for the Herpes simplex virus Type I enzyme were 30 and 70 muM respectively; whereas those for the Herpes simplex virus Typr II enzyme were 140 and 450 muM. Studies on binding of various thymidine analogs with free 5'-OH to these deoxythymidine kinases indicated that 5-substituted ethyl-, vinyl-, allyl-, propyl-, iodo- and bromo-dUrd as well as iodo5 dCyd and bromo5 dCyd had good affinity to both enzymes. In contrast, vinyl5 Urd, iodo5 Urd and arabinosylthymidine had good affinity only to the Herpes simplex virus Type I enzyme but not to the Herpes simplex virus Type II deoxythymidine kinase. All of these thymidine analogs were competitive inhibitors, with KI values in the range of 0.25 to 1.5 muM. Herpes simplex virus Type I deoxythymidine kinase was less sensitive to either dTTP or iodo dUTP inhibition than Herpes simplex virus Type II. Both dThd and dCyd could serve as substrates and competed with each other for Herpes simplex viruses Type I and Type II induced kinases, but they differed in their Km values for these enzymes. The Km values of dThd and dCyd were 0.59 muM and 25 muM for Herpes simplex virus Type I deoxythymidine kinase; while they were 0.36 muM and 88 muM respectively for the Herpes simplex virus Type II enzyme.