Permeation and salvage of dideoxyadenosine in mammalian cells

Transmembrane equilibration of 2',3'-dideoxyadenosine (ddAdo) was measured by rapid kinetic techniques in deoxycoformycintreated P388 and L1210 mouse leukemia cells and human erythrocytes, at 25 degrees. It was only about 10% as rapid as that of other purine nucleosides that are known substrates for the nucleoside transporters of these cells. ddAdo entry was nonsaturable up to a concentration of 1 mM and was not inhibited by other nucleosides or two nucleoside transport inhibitors, dipyridamole and nitrobenzylthioinosine. Thus, ddAdo permeation was mainly nonmediated. It was relatively rapid because of the high lipid solubility of ddAdo. ddAdo entered the cells at least 100 times more rapidly than dideoxycytidine but less rapidly than trideoxythymidine, with an even greater lipophilicity than ddAdo. ddAdo was not phosphorylated in human erythrocytes, but there was some phosphorylation in deoxycoformycin-treated P388 and L1210 cells. In situ conversion of 10 microM ddAdo to ddATP, however, was slow and ceased after 5-10 min at 25 degrees or 37 degrees. Cessation of net uptake was not due to turnover of dideoxy-ATP or deamination of dideoxy-AMP. The results suggest that ddAdo salvage in the absence of deamination is limited by feedback inhibition of its phosphorylation, perhaps by deoxycytidine kinase. Permeation into the cells was not rate limiting to ddAdo salvage. In P388 and L1210 cells that had not been treated with deoxycoformycin, ddAdo was salvaged at least 100 times more efficiently than in deoxycoformycin-treated cells and converted to nucleoside triphosphates, but the end-products and pathways of salvage have not been resolved entirely. Salvage of ddAdo required deamination but was not primarily via dideoxyinosine----hypoxanthine----IMP, as is the case for 2'-deoxyadenosine salvage, because [3H]ddAdo salvage was only little inhibited by unlabeled hypoxanthine, whereas it was strongly inhibited by 2'-deoxyadenosine, adenosine, and adenine.

Comparative pharmacokinetics of new anti-HIV agents: 2',3'-dideoxyadenosine and 2',3'-dideoxyinosine

A number of 2',3'-dideoxynucleosides have been shown to inhibit the in vitro infectivity and cytopathic effect of the human immunodeficiency virus (HIV). These compounds, as their 5'-triphosphates, inhibit viral reverse transcriptase by competing with the natural substrate at the same binding site on the enzyme. Dideoxynucleoside triphosphates can also be incorporated into growing DNA chains which then blocks further DNA elongation because they lack the 3'-hydroxyl group required for further polymerization. Among these nucleosides, 2', 3'-dideoxyadenosine 2',3'-dideoxyadenosine (ddA) and 2',3'-dideoxyinosine (ddI) show promising in vitro activity. Because adenosine is rapidly converted to inosine by adenosine deaminase, the in vivo conversion of ddA to ddI was studied to determine suitability of measuring plasma levels of ddI and to assess the bioavailability and pharmacokinetics of ddA. This report describes and compares the pharmacokinetics of ddA and ddI in the mouse.

Inhibitory effect of azidothymidine, 2'-3'-dideoxyadenosine, and 2'-3'-dideoxycytidine on in vitro growth of hematopoietic progenitor cells from normal persons and from patients with AIDS

Therapy of patients with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) with azidothymidine (AZT) and 2'-3'-dideoxycytidine (ddC) is complicated by severe anemia, neutropenia, and thrombocytopenia, the cause of which is unknown. We therefore tested the effect of AZT, ddC, and an additional 2'-3'-dideoxynucleoside analogue, 2'-3'-dideoxyadenosine (ddA), on the hematopoietic progenitor cells derived from the bone marrow of normal persons and patients with AIDS/ARC. All three substances dose-dependently inhibited the in vitro colony formation of the pluripotent (CFU-GEMM), as well as the erythroid (BFU-E) and granulocyte-macrophage progenitor cells (CFU-GM). The 50% inhibition of normal progenitors by AZT occurred at 0.13 microM for CFU-GEMM, 0.32 microM for BFU-E, and 1.9 microM for CFU-GM, by ddA at 15 microM for CFU-GEMM, 40 microM for BFU-E, and 140 microM for CFU-GM. ddC was the most toxic agent and already inhibited 71% +/- 16% (mean +/- standard error of the mean [SEM]) of CFU-GEMM and 52% +/- 22% of BFU-E at 0.1 microM, whereas the 50% inhibition of CFU-GM was reached at 0.3 microM. Hematotoxicity occurred at concentrations lower than necessary to inhibit the human immunodeficiency virus (HIV), except for ddA, which is 100 times less toxic than AZT whereas its antiviral effect is only 10 times less. The inhibition of progenitor cells from AIDS patients by the 2'-3'-dideoxynucleosides was comparable to normal progenitors, except for a higher sensitivity of AIDS-derived CFU-GEMM and BFU-E to AZT.

An in vitro system for screening anti-hepatitis B virus drugs

A human hepatoblastoma cell line (HB 611) that continuously synthesizes hepatitis B viral (HBV) DNA was grown in the presence of various inhibitors of DNA synthesis, and the DNA from the cells was analyzed by the Southern blotting method to examine selective inhibition of the viral DNA synthesis. Among those that showed selective inhibition, and interferons alpha and beta, acyclovir, and dideoxy cytidine were effective. This system should be useful for screening new antiviral agents against HBV.

Production of 2',3'-dideoxyadenosine and 2',3'-dideoxyinosine from 2',3'-dideoxyuridine and the corresponding purine bases by resting cells of Escherichia coli AJ 2595

A novel microbial method for the production of 2',3'-dideoxynucleosides by transdideoxyribosylation has been developed. By screening microorganisms producing 2',3'-dideoxyadenosine (DDA) from 2',3'-dideoxyuridine (DDU) and adenine, Escherichia coli AJ 2595 was selected as the best producer. Optimal pH and temperature for the DDA-producing reaction were ca. 6.5 and 50 degrees C, respectively. Pi seemed to be an essential factor for the reaction, and its optimal concentration was ca. 25 mM. Moreover, polyethylene glycol had a notable effect on DDA production. Under the best conditions established, 52 mM DDA was obtained from 100 mM DDU and 100 mM adenine after 48 h of incubation from resting cells of E. coli AJ 2595. This strain could also produce 2',3'-dideoxynucleosides, such as 2',3'-dideoxyinosine (DDI), 2',3'-dideoxyguanosine, and 2',3'-dideoxythymidine, from DDU and the corresponding bases. In particular, this strain could produce DDI in high yield (ca. 32 mM from 100 mM DDU and 100 mM hypoxanthine) after 24 h of incubation. However, 2',3'-dideoxycytidine was not produced from DDU and cytosine by resting cells of E. coli AJ 2595.

Testing of nucleoside analogues in cats infected with feline leukemia virus: a model

In the present communication we evaluate the feline leukemia virus (FeLV) infection of cats as a model for antiretroviral chemotherapy studies. Additionally, we report the results of testing the antiviral effect of the compounds, 3'-azido-3'-deoxythymidine (AZT), 2',3'-dideoxycytidine, 2',3'-dideoxyinosine and 2',3'-dideoxyadenosine against FeLV replication in vitro. Cumulative data from experiments in which FeLV-infected cats were treated with AZT at different stages of experimental infection are also evaluated.

Studies on cholesterol esterase in rat adipose tissue: comparison of substrates and regulation of the activity

Efficiency of substrates for cholesterol esterase (EC 3.1.1.13) assay, and regulation of the activity were investigated in rat epididymal adipose tissue. The activity in the supernatant was activated by cyclic AMP-dependent protein kinase, cyclic AMP, ATP and Mg2+, both with micellar and liposomal substrates. However, the micellar substrate was more suitable for the assay than the liposomal with respect to Vmax and Km. Thus, the micellar substrate was employed. Pretreatment of the supernatant with exogenous cyclic AMP-dependent protein kinase enhanced the activity dose dependently, whereas that with cyclic AMP decreased the activity slightly. The cyclic AMP-dependent protein kinase activity in the assay mixture was within the range which can cause changes in cholesterol esterase activity. These results suggest that the amount of cyclic AMP-dependent protein kinase, rather than the cyclic AMP level, plays an important role in the regulation of cholesterol esterase in tissues with a high cholesterol esterase activity relative to the kinase activity, such as in adipose tissue.

Inhibition by forskolin of insulin-stimulated glucose transport in L6 muscle cells

The cardioactive diterpene forskolin is a known activator of adenylate cyclase, but recently a specific interaction of this compound with the glucose transporter has been identified that results in the inhibition of glucose transport in several human and rat cell types. We have compared the sensitivity of basal and insulin-stimulated hexose transport to inhibition by forskolin in skeletal muscle cells of the L6 line. Forskolin completely inhibited both basal and insulin-stimulated hexose transport when present during the transport assay. The inhibition of basal transport was completely reversible upon removal of the diterpene. In contrast, insulin-stimulated hexose transport did not recover, and basal transport levels were attained instead. This effect of inhibiting (or reversing) the insulin-stimulated fraction of transport is a novel effect of the diterpene. Forskolin treatment also inhibited the stimulated fraction of transport when the stimulus was by 4 beta-phorbol 12,13-dibutyrate, reversing back to basal levels. Half-maximal inhibition of the above-basal insulin-stimulated transport was achieved with 35-50 microM-forskolin, and maximal inhibition with 100 microM. Forskolin did not inhibit 125I-insulin binding under conditions where it caused significant inhibition of insulin-stimulated hexose transport. Forskolin significantly elevated the cyclic AMP levels in the cells; however its inhibitory effect on the above basal, insulin-stimulated fraction of hexose transport was not mediated by cyclic AMP since: (i) 8-bromo cyclic AMP and cholera toxin did not mimic this effect of the diterpene, (ii) significant decreases in cyclic AMP levels caused by 2',3'-dideoxyadenosine in the presence of forskolin did not prevent inhibition of insulin-stimulated hexose transport, (iii) isobutylmethylxanthine did not potentiate forskolin effects on glucose transport but did potentiate the elevation in cyclic AMP, and (iv) 1,9-dideoxyforskolin, which does not activate adenylate cyclase, inhibited hexose transport analogously to forskolin. We conclude that forskolin can selectively inhibit the insulin- and phorbol ester-stimulated fraction of hexose transport under conditions where basal transport is unimpaired. The results are compatible with the suggestions that glucose transporters operating in the stimulated state (insulin or phorbol ester-stimulated) differ in their sensitivity to forskolin from transporters operating in the basal state, or, alternatively, that a forskolin-sensitive signal maintains the stimulated transport rate.

Metabolic pathways for the activation of the antiretroviral agent 2',3'-dideoxyadenosine in human lymphoid cells

The pathways of 2',3'-dideoxyadenosine (ddAdo) metabolism, a selective inhibitor of the replication of human immunodeficiency virus, were investigated with use of the human T-lymphoid cell line CCRF-CEM which is deficient in either deoxycytidine kinase or adenosine kinase activity, or both. At an extracellular concentration of 10 microM, which blocks the cytopathic effect of human immunodeficiency virus in vitro, ddAdo was found to be metabolized to its mono-, di-, and triphosphates and to dideoxyinosine monophosphate (ddIMP). The metabolism of ddAdo in the kinase-deficient mutants was found to be unchanged by comparison with that in parental cells; however, the inhibition of ddAdo deamination to 2',3'-dideoxyinosine (ddIno) by the adenosine deaminase inhibitor, 2'-deoxycoformycin, reduced ddAdo nucleotide formation in deoxycytidine kinase-deficient, adenosine kinase-deficient, and doubly kinase-deficient mutants by 42, 54, and 80%, respectively. Incubation of the CCRF-CEM cells with 20 microM L-alanosine, an amino acid antagonist that inhibits purine biosynthesis at the level of adenylosuccinate/lyase synthetase, resulted in 80% inhibition in the accumulation of ddAdo nucleotides in both wild-type and kinase-deficient mutants and also increased ddIMP accumulation 2- to 3-fold. These findings indicate that ddAdo activation in human T-lymphoblasts can occur by three metabolic pathways: directly, by phosphorylation to ddAMP by the action of either deoxycytidine kinase or adenosine kinase and, indirectly, through deamination to ddIno with consequent phosphorylation of ddIno to ddIMP, and reamination to ddAMP in a reaction catalyzed by adenylosuccinate synthetase/lyase. However, in the absence of 2'-deoxycoformycin, the activation of ddAdo to ddATP in T-lymphoid cells is primarily a function of the indirect route.

Antiviral effects of 3'-azido-3'-deoxythymidine, 2',3'-dideoxycytidine, and 2',3'-dideoxyadenosine against simian acquired immunodeficiency syndrome-associated type D retrovirus in vitro

The simian acquired immunodeficiency syndrome (SAIDS) in macaques at the Washington Regional Primate Research Center is associated with a type D retrovirus known as SAIDS-D/WA. We tested the ability of 3'-azido-3'-deoxythymidine (AZT), 2',3'-dideoxycytidine (ddC), and 2',3'-dideoxyadenosine (ddA) to inhibit the in vitro cytopathic effect (syncytium formation) and infectivity of the SAIDS-D/WA virus. Raji cell cultures were infected with virus and treated with various concentrations of AZT, ddC, and ddA. The ability of these drugs to inhibit replication of the SAIDS-D/WA virus in Raji cells was monitored by syncytium formation, expression of viral antigen, and reverse transcriptase assay. At concentrations of 4, 40, and 400 microM, AZT completely blocked the viral infectivity and inhibited the cytopathic effect of SAIDS-D/WA. Likewise, ddC was inhibitory at concentrations of 5 and 50 microM and ddA was inhibitory at 100 and 200 microM. AZT, ddC, and ddA became cytostatic to Raji cells with increasing drug concentrations. AZT also partially inhibited SAIDS-D/WA replication in previously infected Raji cell cultures, and viral inhibition increased in response to the concentration of AZT. These data indicate that AZT, ddC, and ddA are effective antiretroviral agents that merit further evaluation, including clinical trials, in animal models with AIDS-like diseases.

Synthesis of 2',3'-dideoxynucleosides by enzymatic trans-glycosylation

Recently, several pyrimidine and purine 2',3'-dideoxynucleosides have been shown to inhibit the replication of the human immunodeficiency virus-1 (HIV), the causative agent of the acquired immune deficiency syndrome (AIDS). These compounds are usually prepared by reduction of the corresponding 2'-deoxynucleosides. The present experiments demonstrate that 2',3'-dideoxynucleosides can also be made by enzymatic trans-glycosylation, using the trans-N-deoxyribosylase from Lactobacillus helveticus. The broad specificity of this enzyme makes it possible to synthesize for metabolic studies radiochemically pure 2',3'-dideoxynucleosides, using diverse purine and pyrimidine base acceptors.

Inhibition of human immunodeficiency virus (HIV-1/HTLV-IIIBa-L) replication in fresh and cultured human peripheral blood monocytes/macrophages by azidothymidine and related 2',3'-dideoxynucleosides

Because of the probable role of HIV-infected monocyte/macrophages in the pathogenesis and progression of AIDS, it is essential that antiretroviral therapy address viral replication in cells of this lineage. Several dideoxynucleosides have been shown to have potent in vitro and, in the case of 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC), in vivo activity against HIV. However, because these compounds must be phosphorylated (activated) in target cells, and because monocyte/macrophages may have levels of kinases that differ from those in lymphocytes, we investigated the capacity of these drugs to suppress HIV replication in monocyte/macrophages using HIV-1/HTLV-IIIBa-L (a monocytotropic isolate). In the present study, we observed that HTLV-IIIBa-L replication in fresh human peripheral blood monocyte/macrophages was suppressed by each of three dideoxynucleosides: 3'-azido-2',3'-dideoxythymidine (AZT), 2',3'-dideoxycytidine (ddC), and 2',3'-dideoxyadenosine (ddA). Similar results were observed in 5-d-cultured monocyte/macrophages, although higher concentrations of the drugs were required. We then studied the metabolism of AZT and ddC in such cells. The phosphorylation of ddC to a triphosphate moiety was somewhat decreased in monocyte/macrophages as compared with H9 T cells. On the other hand, the phosphorylation of AZT in monocyte/macrophages was markedly decreased to 25% or less of the level in T cells. However, when we examined the level of the normal endogenous 2'-deoxynucleoside triphosphate pools, which compete with 2',3'-dideoxynucleoside triphosphate for viral reverse transcriptase, we found that the level of 2'-deoxycytidine-triphosphate (dCTP) was six- to eightfold reduced, and that of 2'-deoxythymidine-triphosphate (dTTP) was only a small fraction of that found in T cell lines. These results suggest that the ratio of dideoxynucleoside triphosphate to normal deoxynucleoside triphosphate is a crucial factor in determining the antiviral activity of dideoxynucleosides in HIV target cells, and that the lower levels of dTTP may account for the antiretroviral activity of AZT in the face of inefficient phosphorylation of this compound.

2',3'-Dideoxyadenosine is selectively toxic for TdT-positive cells

The 2',3'-dideoxynucleosides (ddNs) are currently undergoing clinical evaluation as antiretroviral agents in HIV-infected individuals. When phosphorylated, the ddNs (ddNTPs) function as chain-terminating substrate analogues with reverse transcriptase, thereby inhibiting HIV replication. These nucleoside analogues can also inhibit, by chain-terminating additions, the primitive lymphoid DNA polymerase, terminal deoxynucleotidyl transferase (TdT). To determine the effect of possible intracellular chain-terminating additions of ddNMPs by TdT, we exposed a series of TdT-positive and TdT-negative cell lines to 2',3'-dideoxyadenosine (ddA), a representative ddN. At ddA concentrations 25-fold higher than required for inhibition of HIV replication, progressive dose-related cytotoxicity was observed in the TdT-positive cell lines. This was accentuated by the adenosine deaminase inhibitor Coformycin (CF), presumably by enhancing the intracellular generation of ddATP from ddA. A central role of TdT in mediating the ddA/CF cytotoxicity was suggested by studies in a pre-B-cell line rendered TdT positive by infection with a TdT cDNA-containing retroviral vector. After a 48-hour continuous exposure period to 250 mumol/L ddA and 30 mumol/L CF, 30% cell death was observed in the TdT-negative parental line, whereas 90% cell death was observed in the TdT-positive daughter line. Exposure of fresh TdT-positive leukemic cells to ddA/CF for 72 hours ex vivo resulted in cytotoxicity (six cases of acute lymphocytic leukemia [ALL]) while not affecting TdT-negative acute leukemic cells (six cases). We conclude that ddA/CF selectively damages TdT-positive cells, presumably by chain-terminating additions of ddAMP, and that this may have therapeutic relevance in TdT-positive malignant disease.

Metabolism and anti-human immunodeficiency virus-1 activity of 2-halo-2',3'-dideoxyadenosine derivatives

Both 2',3'-dideoxyadenosine and 2',3'-dideoxyinosine have been shown (Mitsuya, H., and Broder, S. (1987) Nature 325, 773-778) to have in vitro activity against the human immunodeficiency virus-1 (HIV). However, these dideoxynucleosides may be catabolized by human T cells, even when adenosine deaminase is inhibited by deoxycoformycin. To overcome this problem, we have synthesized the 2-fluoro-, 2-chloro-, and 2-bromo-derivatives of 2',3'-dideoxyadenosine. The metabolism and anti-HIV activity of the 2-halo-2',3'-dideoxyadenosine derivatives and of 2',3'-dideoxyadenosine were compared. The 2-halo-2',3'-dideoxyadenosine derivatives were not deaminated significantly by cultured CEM T lymphoblasts. Experiments with 2-chloro-2',3'-dideoxyadenosine showed that the T cells converted the dideoxynucleoside to the 5'-monophosphate, 5'-diphosphate, and 5'-triphosphate metabolites. At concentrations lower than those producing cytotoxicity in uninfected cells (3-10 microM), the 2-halo-2',3-dideoxyadenosine derivatives inhibited the cytopathic effects of HIV toward MT-2 T lymphoblasts, and retarded viral replication in CEM T lymphoblasts. Experiments with a deoxycytidine kinase-deficient mutant CEM T cell line showed that this enzyme was necessary for the phosphorylation and anti-HIV activity of the 2-chloro-2',3'-dideoxyadenosine. In contrast, 2',3'-dideoxyadenosine was phosphorylated by the deoxycytidine kinase-deficient mutant and retained anti-HIV activity in this cell line. Thus, the 2-halo derivatives of 2',3'-dideoxyadenosine, in contrast to 2',3'-dideoxyadenosine itself, are not catabolized by T cells. Their anti-HIV and anti-proliferative activities are manifest only in cells expressing deoxycytidine kinase. The in vivo implications of these results for anti-HIV chemotherapy are discussed.

Inhibition of infectivity and replication of HIV-2 and SIV in helper T-cells by 2',3'-dideoxynucleosides in vitro

We have previously shown that 2',3'-dideoxynucleosides and their derivatives are potent inhibitors of the infectivity and cytopathic effect mediated by human immunodeficiency virus type-1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS). Recently a new group of retroviruses has been found in individuals originating from the western part of Africa. One member of this group is human immunodeficiency virus type-2 (HIV-2), previously designated lymphadenopathy-associated virus type-2 (LAV-2), found in patients with an AIDS-like illness. In this report, we show that 2',3'-dideoxynucleosides including 3'-azido-2',3'-dideoxythymidine (AZT) can significantly inhibit the infectivity and/or cytopathic effect of these retroviruses in vitro. Current data provide a rationale for considering 2',3'-dideoxynucleosides and their derivatives as experimental antiviral agents in individuals with illnesses caused by these new retroviruses.

Investigations on the anti-HIV activity of 2',3'-dideoxyadenosine analogues with modifications in either the pentose or purine moiety. Potent and selective anti-HIV activity of 2,6-diaminopurine 2',3'-dideoxyriboside

Several 2',3'-dideoxyadenosine analogues with modifications in either the ribose or purine moiety were evaluated for their inhibitory effects on the replication of human immunodeficiency virus (HIV) in MT-4 cell cultures. The 2',3'-dideoxyriboside of 2,6-diaminopurine (ddDAPR) inhibited HIV antigen expression and HIV-induced cytopathogenicity at a 50% effective dose of 2.4-3.8 microM, as compared to 3-6 microM for 2',3'-dideoxyadenosine (ddAdo), whereas 50% inhibition of MT-4 cell viability was noted only at a concentration of 477 and 889 microM, respectively. Both ddDAPR and ddAdo were only weakly inhibitory to the proliferation of a number of T-lymphoblast and T-lymphocyte cell lines, pointing to the selectivity of these compounds as anti-HIV agents. In contrast to ddAdo, ddDAPR was found to be a poor substrate for adenosine deaminase, which may be advantageous from a chemotherapeutic viewpoint. Substitution of an azido or fluoro group at the 2' and 3'-position of the ribose moiety in either "up" or "down" configurations resulted in a decrease of the anti-HIV potency and selectivity of ddAdo. In addition to ddDAPR other purine-modified ddAdo analogues, i.e. several pyrrolo[2,3-d]pyrimidine 2',3'-dideoxynucleosides, were investigated for their anti-HIV activity, but none of these derivatives proved as potent or selective as ddDAPR.

Biochemical genetic analysis of 2',3'-dideoxyadenosine metabolism in human T lymphocytes

2',3'-dideoxyadenosine (ddAdo) has been shown to inhibit the infection of cultured human T lymphoblasts with the human immunodeficiency virus-1 (HIV-1). However, the pathways of ddAdo metabolism in T lymphocytes have not been well defined. We have studied the uptake and degradation of ddAdo in human CEM T lymphoblasts, in mutant CEM T cells deficient in adenosine kinase or deoxycytidine kinase, and in normal lymphocytes and monocytes. The results indicate that ddAdo may be phosphorylated in T cells by several different enzymes, although deoxycytidine kinase predominates. However, 99% of the ddAMP formed is deaminated by AMP deaminase and subsequently dephosphorylated. Thus, the ability of ddAdo to prevent HIV-1 infection may be limited in cells with high AMP deaminase activity.

Structures of two dideoxynucleosides: 2',3'-dideoxyadenosine and 2',3'-dideoxycytidine

2',3'-Dideoxyadenosine, C10H13N5O2, Mr = 235.24, orthorhombic, P2(1)2(1)2(1), a = 7.7404(4), b = 9.9843(9), c = 14.0842(10) A, V = 1088.46 A3, Z = 4, Dx = 1.435 Mg m-3, lambda(CuK alpha) = 1.5418 A, mu = 0.8326 mm-1, F(000) = 496, T = 296 K, final R = 0.032 for 1088 observed reflections. 2',3'-Dideoxycytidine, C9H13N3O3, Mr = 211.21, tetragonal, P4(1)2(1)2, a = 8.6802(4), c = 26.1386(14) A, V = 1969.44 A3, Z = 8, Dx = 1.424 Mg m-3, lambda(CuKa) = 1.5418 A, mu = 0.8701 mm-1, F(000) = 896, T = 296 K, final R = 0.050 for 1116 observed reflections. In both compounds the sugar rings have conformations intermediate between envelope and half chair but somewhat different pseudorotations. The relative orientations of the sugar and base are different in the two molecules with dideoxyadenosine being at the boundary of syn and anti and deoxycytidine being anti.

2',3'-Dideoxynucleoside phosphorylation by deoxycytidine kinase from normal human thymus extracts: activation of potential drugs for AIDS therapy

As a first step toward improving dideoxynucleoside inhibition of human immunodeficiency virus replication in human lymphocytes, we examined the kinetics of 5'-phosphorylation of a series of 2',3'-dideoxynucleosides, using deoxycytidine kinase purified from human thymus extracts. Nucleosides with the 2'-deoxyribose moiety were activated 30 times faster than were 2',3'-dideoxynucleosides. The adenosine deaminase inhibitor, 2'-deoxycoformycin, showed an unexpected ability to inhibit purine and pyrimidine dideoxynucleoside phosphorylation; such inhibition was not competitive and was not observed when 2'-deoxycytidine was the substrate. 2'-Deoxycytidine, the natural substrate, inhibited dideoxynucleoside phosphorylation in a manner similar to that observed with 2'-deoxycoformycin. Thus, dideoxynucleosides are activated by deoxycytidine kinase through a different catalytic interaction than occurs in 5'-activation of 3'-hydroxynucleosides by this enzyme.

Synthesis and anti-HIV activity of various 2'- and 3'-substituted 2',3'-dideoxyadenosines: a structure-activity analysis

A systematic synthesis was undertaken of 2',3'-dideoxyadenosine analogues with either an azido, fluorine, or hydroxyl group substituted in the "up" or "down" position of C-2 or C-3 of the sugar moiety. The compounds were evaluated against the cytopathogenicity of human immunodeficiency virus (HIV) for MT-4 cells. The four azido derivatives 6, 7, 8, and 9 were synthesized by a nucleophilic displacement reaction with lithium azide on the mesylates 3, 2, 5, and 4. (Diethylamido)sulfur trifluoride was used for the synthesis of 10-12. The compound 13 was obtained by 2'-deoxygenation of 9-(3-fluoro-3-deoxy-beta-D-xylofuranosyl)adenine. Among the azido derivatives, compound 8 with the 3'-azido "down" was slightly more active than 2',3'-dideoxyadenosine (1) but considerably more toxic, and, of the fluorine series, compound 11, with the 2'-fluoro "up", was the most selective inhibitor of HIV, although it was less active than 1. Hence, none of the newly synthesized compounds proved more selective in their anti-HIV activity than the parent compound, 1.

Failure of dideoxynucleosides to inhibit human immunodeficiency virus replication in cultured human macrophages

Primary human monocyte-derived macrophages (MDM) were shown to have diminished deoxynucleoside kinase activities compared to T lymphoblasts, and a reduced ability to phosphorylate dideoxynucleosides with anti-human immunodeficiency virus (HIV) activity. These drugs, azidothymidine (AZT), dideoxycytidine (ddC), and dideoxyadenosine (ddA), which are potent anti-HIV agents in CD4 lymphocytes, did not inhibit HIV replication in MDM, even at concentrations of 100 microM. This drug concentration of AZT is approximately 100-fold higher than the levels attained in the serum of treated patients and the levels required to inhibit HIV replication in lymphocytes. These observations may explain the failure of AZT therapy to clear viremia, consistent with the presence of a drug-resistant reservoir of infected cells in vivo. New therapeutic approaches to inhibit the replication of HIV in MDM may be needed.

Application of high-performance liquid chromatography and thermospray high-performance liquid chromatography-mass spectrometry to the analysis and identification of 2',3'-dideoxyadenosine and its metabolite in biological media

Reversed-phase high-performance liquid chromatographic (HPLC) procedures are described for determining the stability of 2',3'-dideoxyadenosine (DDA) in biological fluids at therapeutic dosages. The validated methodology uses both direct injection and solid-phase extraction techniques. Deamination of DDA to 2',3'-dideoxyinosine (DDI) in plasma by adenosine deaminase was monitored by HPLC, and the identification of DDI verified by thermospray HPLC-mass spectrometry. This methodology should prove useful in future studies concerning the stability and metabolism of dideoxynucleosides.

The 2',3'-dideoxyriboside of 2,6-diaminopurine and its 2',3'-didehydro derivative inhibit the deamination of 2',3'-dideoxyadenosine, an inhibitor of human immunodeficiency virus (HIV) replication

The 2',3'-dideoxyriboside of 2,6-diaminopurine (ddDAPR) and its 2',3'-didehydro derivative (ddeDAPR) are poor substrates for adenosine deaminase (ADA) but potent inhibitors of the enzyme. Their Km values for ADA are of the same order of magnitude as those of the natural adenosine (Ado) and 2'-deoxyadenosine (dAdo), but their Vmax values are 35-fold (ddDAPR) to 350-fold (ddeDAPR) lower than those of Ado and dAdo. The Ki/K values of ADA for ddeDAPR (as inhibitor) and Ado, 2',3'-dideoxyadenosine (ddAdo) and 9-beta-D-arabinofuranosyladenine (araA) as the substrates are 0.17, 0.05 and 0.06, respectively. ddDAPR is about 3-fold less potent as an inhibitor of ADA than ddeDAPR. The 2,6-diaminopurine derivatives ddeDAPR and ddDAPR [which is also a potent inhibitor of human immunodeficiency virus (HIV)], may hold great promise, from a chemotherapeutic viewpoint, in combination with other adenosine analogues such as ddAdo and araA, which have been recognized and/or being pursued as either anti-retrovirus or anti-herpesvirus agents.

Long-term inhibition of human T-lymphotropic virus type III/lymphadenopathy-associated virus (human immunodeficiency virus) DNA synthesis and RNA expression in T cells protected by 2',3'-dideoxynucleosides in vitro

We report that 2',3'-dideoxyadenosine and 2',3'-dideoxycytidine inhibit retroviral DNA synthesis and mRNA expression in T cells exposed to the virus that causes acquired immunodeficiency syndrome, and afford such cells long-term protection in vitro under conditions of substantial viral excess. Both 2',3'-dideoxyadenosine and 2',3'-dideoxycytidine appear to completely block reverse transcription from viral RNA to viral DNA. Viral mRNA expression is also not detected in cells protected by the drugs throughout 30 days of culture following exposure to the virus. Purine and pyrimidine analogues as 2',3'-dideoxynucleoside-5'-triphosphate serve as substrates for the human T-lymphotropic virus type III/lymphadenopathy-associated virus reverse transcriptase to elongate a DNA chain by one residue, after which the chain is terminated. Cloned normal helper/inducer T cells exposed to a cytopathic dose of the virus, but protected by the drugs, respond normally to specific antigen in vitro. These results suggest that the drugs could be promising agents for further studies in the experimental treatment of patients infected with retroviruses.

The effect of thyrotropin and cAMP on DNA synthesis and cell growth of human thyrocytes in monolayer culture

Monolayer cultures of human thyrocytes from normal tissue (n = 10), and adenomas (n = 7), differentiated (n = 4), poorly differentiated (n = 2), and undifferentiated (n = 3) thyroid cancers were established to assess the significance of thyrotropin (TSH) and cAMP (adenosine 3',5'-cyclic monophosphate) on cell growth and DNA (deoxyribonucleic acid) synthesis. Cell growth of thyrocytes from normal and adenomatous tissues increased more rapidly (p less than 0.01) after TSH (0.1 IU/ml) was added but was unaffected by cAMP (10(-4) mol/L). In these cells, TSH also enhanced DNA synthesis twofold to twelvefold (p less than 0.01). The adenylate cyclase (AC) inhibitor, 2',3' dideoxyadenosine (ddA), increased DNA synthesis 1.3 to 6 times at a concentration of 2 X 10(-4) mol, whereas the membrane/passable cAMP analogue, dibutyryl-cAMP, and the AC stimulator, forskolin, failed to show any effect on DNA synthesis up to a concentration of 10(-5) mol/L (p less than NS). When administered simultaneously, TSH (1/2 maximum) and ddA (20 mumol) had no cumulative effect on DNA synthesis (p = NS). TSH stimulation in cancerous thyroid tissue (n = 11) demonstrated a lack of TSH response in seven of 11 monolayer cultures with no apparent correlation to cancer differentiation, patient age, or sex. Thus TSH was demonstrated to stimulate DNA synthesis and cell growth of human thyrocytes in monolayer cultures independent of the AC system. However, the TSH effect on cell growth and DNA synthesis was unpredictable in thyrocytes from cancerous tissues.

Effect of prostaglandin E1 on DNA synthesis in vascular smooth muscle cells

The effect of prostaglandin E1 (PGE1) on DNA synthesis was determined using cultured vascular smooth muscle cells. It was found that when PGE1 was added to synchronous, quiescent (growth-arrested) cells, it enhanced DNA synthesis. This was in contrast to the effects of PGE1 on asynchronous, cycling (growing) cells. In these cells, when PGE1 was added, it functioned as an antiproliferative agent. In both cases the effects of PGE1 could be mimicked by 6 alpha-carbaprostacyclin (stable prostacyclin analogue) or by 8-bromo adenosine 3',5'-cyclic monophosphate [a permeable adenosine 3',5'-cyclic monophosphate (cAMP) analogue]. In addition PGE1 was shown to cause an elevation in cellular cAMP levels. On the basis of these studies it is hypothesized that the ultimate effect of addition of PGE1 to vascular smooth muscle cells is dependent on the phase of the cell cycle in which it is added.

Inhibition of the in vitro infectivity and cytopathic effect of human T-lymphotrophic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV) by 2',3'-dideoxynucleosides

Human T-lymphotropic virus type III (HTLV-III)/lymphadenopathy-associated virus (LAV) is a a newly discovered lymphotropic retrovirus that is cytopathic for helper/inducer T cells in vitro. This virus is the etiologic agent of the acquired immunodeficiency syndrome and related diseases. In the current study, we tested the capacity of purine and pyrimidine nucleoside derivatives to inhibit the infectivity and cytopathic effect of human T-lymphotropic virus type III in vitro. With the ribose moiety of the molecule in a 2',3'-dideoxy configuration, every purine (adenosine, guanosine, and inosine) and pyrimidine (cytidine and thymidine) nucleoside tested suppressed the virus, although the thymidine derivative seemed to have substantially less activity in our system than the others. In general, we observed essentially complete suppression of the virus at doses that were lower by a factor of 10 to 20 than those needed to inhibit the proliferation of the target T cells and the immune reactivity of normal T cells in vitro. An analysis of five adenosine congeners, which differed only in the sugar moiety, revealed that reduction (an absence of hydroxyl determinants) at both the 2' and 3' carbons of the ribose was necessary for an anti-viral effect, and an additional reduction at the 5' carbon nullified the anti-viral activity. These observations may be of value in developing a new class of experimental drugs for the therapy of human T-lymphotropic virus type III infections.

Regulation of depolarization-dependent release of neurotransmitters by adenosine: cyclic AMP-dependent enhancement of release from PC12 cells

We have used pheochromocytoma cells, clone PC12, as a model system for studying the effects of adenosine on neurosecretion. Exposure of the cells to adenosine or 2-chloroadenosine caused immediate activation of adenylate cyclase, increases in cellular cyclic AMP content, and inhibition of SAM-dependent phospholipid N-methylation and protein carboxymethylation. However, the effects on methylation were only observed with concentrations of adenosine 100 times greater than those that elevated cyclic AMP. Exposure of the cells to adenosine and 2-chloroadenosine did not alter the release of [3H]norepinephrine [(3H]NE) in the absence of depolarization. However, depolarization-dependent release of [3H]NE was markedly elevated by short (1-20 min) pretreatments with adenosine or 2-chloroadenosine. The enhancement of release was observed irrespective of the nature of the depolarizing stimulus (elevated K+, carbamylcholine, or veratridine). Release of [3H]acetylcholine in response to elevated K+ also was increased by adenosine pretreatment. These effects of adenosine and 2-chloroadenosine on neurotransmitter release closely paralleled elevation of cellular cyclic AMP but not inhibition of methylation. Taken together, the results show that adenosine, probably acting through adenosine receptors coupled to stimulation of adenylate cyclase, is able to modulate the neurosecretory process in PC12 cells. Furthermore, the enhancement of release occurred even though the extent of depolarization (measured as 86Rb+ flux through the acetylcholine receptor channel) and the amount of 45Ca2+ which entered upon depolarization were unchanged. Therefore, the enhancement of release produced by elevated cyclic AMP appeared to reflect increased efficiency of the stimulus-secretion coupling process.

Chromosomal location of the gene encoding phosphoribosylpyrophosphate synthetase in Escherichia coli

A mutant of Escherichia coli with a partially defective phosphoribosylpyrophosphate synthetase (ribosephosphate pyrophosphokinase) has been characterized genetically. The genetic lesion causing the altered phosphoribosylpyrophosphate synthetase, prs, was mapped at 26 min on the linkage map by conjugation. Transductional analysis of the prs region established the gene order as purB-fadR-dadR-tre-pth-prs-hemA-trp. Two additional mutations were identified in the mutant: one in gsk, the gene encoding guanosine kinase, and one in lon, conferring a mucoid colony morphology. The contribution of each mutation to the phenotype of the mutant has been evaluated.

Inhibition of the cyclic AMP-adenylate cyclase system and of secretion by high concentrations of adenosine in the dog thyroid

Adenosine inhibits cyclic AMP accumulation in stimulated slices and adenylate cyclase in acellular preparations of dog thyroid. The onset of this inhibition is rapid, requires relatively high adenosine concentrations (greater than or equal to 10 microM) and occurs with all activators tested (TSH, PGE1, forskolin and cholera toxin). The manganous ion, which uncouples receptor and cyclase, enhances the inhibition by adenosine. The effect of 2',5'-dideoxyadenosine, the high concentration of adenosine needed, the Mn2- effect and the lack of reversal by methylxanthines all suggest that this effect bears on the "P"-site, i.e. on the cyclase itself. Adenosine also inhibits thyroid secretion, which shows that its effect bears on the follicular cells. However the fact that cyclic AMP and DB cyclic AMP induced secretion are also reduced by adenosine suggests that adenosine also inhibits cyclic AMP action.

Antibacterial activity of 2',3'-dideoxyadenosine in vivo and in vitro

2',3'-Dideoxyadenosine (DDA) was shown not only to possess antibacterial activity in vitro against a variety of Enterobacteriaceae, but also to be effective in vivo, DDA was active in experimental mouse infections by the oral route against 5 Salmonella strains, 2 of 3 Arizona strains, 5 of 7 Citrobacter strains, 3 of 8 Klebsiella strains, 3 of 5 Escherichia strains, 1 of 3 Shigella strains, and 3 of 15 Serratia strains at concentrations generally well below the toxic level. Closely related compounds, with the exception of 2',3'-dideoxyinosine, were found to be inactive in vivo, indicating that a high degree of structural specificity was required for activity. The synthesis of deoxyribonucleic acid was inhibited by DDA in those strains susceptible in vitro to DDA, whereas ribonucleic acid and protein syntheses were not affected. The concentration of DDA which inhibited bacterial deoxyribonucleic acid synthesis by 50% was calculated based on the relative rates of deoxyribonucleic acid synthesis in ;the absence and in the presence of DDA. This value correlated well with the minimal inhibitory concentration determined by the in vitro broth dilution assay but not always with in vivo activity determined by the mouse protection test.