Acyclic Nucleotide Research Articles

Inhibition of human telomerase by diphosphates of acyclic nucleoside phosphonates

Diphosphates of the antiviral acyclic nucleoside phosphonates (ANPs) were evaluated in telomeric repeat amplification protocol (TRAP) for their ability to inhibit the extension of telomeres by human telomerase. Extracts from human leukaemia HL-60 cells were used as a source of the enzyme. Data show that the most effective compound studied was the guanine derivative PMEGpp (IC 50 12.7 ± 0.5 μmol L −1 at 125 μmol L −1 deoxynucleoside triphosphates (dNTPs)). The inhibitory effects of other PME, PMP and HPMP diphosphates on telomerase reverse transcriptase decreased in the order: ( R)-PMPGpp > ( R)-HPMPGpp > PMEDAPpp > ( S)-PMPGpp > ( S)-HPMPApp > PMEO-DAPypp > ( R)-6-cyprPMPDAPpp > ( R)-PMPApp > ( R)-PMPDAPpp ≥ PMEApp ≥ PMECpp > PMETpp > ( S)-PMPApp ∼ 6-Me 2PMEDAPpp. These results are consistent with the observed antineoplastic activities of the parental guanine (PMEG) and 2,6-diaminopurine (PMEDAP) PME-derivatives. Moreover, structure–activity relationship indicates enantioselectivity of some of these human telomerase inhibitors: ( R)-isomers of the PMP-derivatives possess stronger inhibitory potency towards the enzyme than ( S)-isomers. The data may contribute to the rational design of telomerase inhibitors based on the structure of acyclic nucleotide analogues.

Epstein–Barr virus infections: prospects for treatment

Epstein-Barr virus (EBV) causes infectious mononucleosis and oral hairy leucoplakia, and is associated with a number of malignancies. There are, however, no regulatory agency-approved treatments for EBV-related diseases. Several antiviral drugs inhibit replication of EBV in cell culture including acyclic nucleoside and nucleotide analogues and pyrophosphate analogues, all of which inhibit the EBV DNA polymerase. Despite their potency in vitro, these drugs have limited use in vivo for treatment of acute primary EBV infection as well as EBV-associated malignancies for several reasons. Here we discuss novel anti-EBV compounds, including maribavir, potentially useful for the treatment of acute EBV infections. A number of experimental approaches for treatment of EBV-related malignancies that are not susceptible to conventional antiviral drug treatment are also discussed.

Cross-Resistance Testing of Next-Generation Nucleoside and Nucleotide Analogues against Lamivudine-Resistant HBV

Several next-generation nucleoside and nucleotide analogues are currently in clinical development for the treatment of chronic hepatitis B. However, the efficacy of newer agents against lamivudine-resistant hepatitis B virus (HBV) has not been fully explored. To investigate this in vitro, we generated novel stable cell lines expressing HBV encoding the four major patterns of lamivudine resistance mutations (rtL180M+rtM204V, rtV173L+rtL180M+rtM204V, rtM204I and rtL180M+ rtM204I). Using these cell lines, we assessed the susceptibility of all four strains of lamivudine-resistant HBV to eleven nucleoside analogues in various stages of clinical development. Our studies indicate that lamivudine-resistant HBV remain sensitive to acyclic phosphonate nucleotides (adefovir, tenofovir, and alamifovir), have reduced susceptibility to entecavir, and have high-level cross-resistance to all L-nucleosides tested including emtricitabine, telbivudine, clevudine, and torcitabine.

Improved Synthesis of 1,3‐Propanediol Derivatives Having a Diethoxyphosphoryldifluoroethyl Functional Group at the 2‐Position: Application to Chemoenzymatic Synthesis of Novel Acyclic Nucleotide Analogues of Adenosine Bisphosphates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Inhibition of thymidine phosphorylase (PD-ECGF) from SD-lymphoma by phosphonomethoxyalkyl thymines

A series of thymine phosphonomethoxyalkyl derivatives were evaluated for their ability to inhibit thymidine phosphorylase (dThdPase) purified from rat spontaneous T-cell lymphoma. A kinetic study of thymidine phosphorolysis catalyzed by dThdPase was performed with thymidine and/or inorganic phosphate as substrates. Data show that the substantial inhibitory effect of these acyclic nucleotide analogues is decreasing in the order of ( R)-FPMPT > ( S)-FPMPT ≥ ( R)-HPMPT > ( S)-PMPT > ( S)-HPMPT > PMET ≥ ( R)-PMPT. The inhibitory potency ( K i/ dThd K m) of the most efficient inhibitors from this series against T-cell lymphoma enzyme is 0.0026 for ( R)-FPMPT and 0.0048 for ( S)-FPMPT. The studied compounds do not inhibit Escherichia coli and human enzyme and possess lower inhibitory potency against rat liver thymidine phosphorylase.

Improved Synthesis of 1,3-Propanediol Derivatives Having a Diethoxyphosphoryldifluoroethyl Functional Group at the 2-Position: Application to Chemoenzymatic Synthesis of Novel Acyclic Nucleotide Analogues of Adenosine Bisphosphates

An alternative synthesis of 1,3-propanediol 1 having a diethoxyphosphoryldifluoroethyl group was examined. The method readily provided a multi-gram quantity of 1. The propanediol 1 was chemo-enzymatically transformed to acyclic nucleotide analogues for adenosine bisphosphates.

Adefovir dipivoxil in chronic hepatitis B infection

Adefovir dipivoxil, an acyclic nucleotide analogue, is effective for the treatment of chronic hepatitis B in both hepatitis B e antigen (HBeAg)-positive and -negative patients, with improvement in liver histology, hepatitis B virus (HBV) DNA levels, alanine aminotransferase levels, and HBeAg seroconversion (for HBeAg-positive patients). It is also effective against lamivudine-resistant strains of hepatitis B mutations. It has been studied in pre- and post-liver transplant patients. Compared to lamivudine, adefovir dipivoxil is associated with a much lower risk of emergence of drug-resistant HBV. Adefovir-associated resistant virus is susceptible to lamivudine therapy. The recommended dose of adefovir dipivoxil 10 mg is associated with low risk of nephrotoxicity. Adefovir dipivoxil can be recommended as a first-line treatment but can also be used in patients with chronic hepatitis B infection who are failing lamivudine therapy.

A New Approach to the Synthesis of Optically Active Alkylated Adenine Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Involvement of adenosine A 1 receptors in upregulation of nitric oxide by acyclic nucleotide analogues

Acyclic nucleoside phosphonates are a novel class of virostatics effective against replication of both DNA-viruses and retroviruses. They are synthetic analogues of natural nucleotide monophosphates, and purine derivatives thus represent counterparts of AMP. Mono- and di-phosphorylated species are analogues of natural ADP and ATP, respectively. A number of these compounds are endowed with immunostimulatory and immunomodulatory potential. We investigated whether their augmenting effect on the interferon-γ-primed production of nitric oxide (NO) by murine macrophages is mediated by purinoceptors. The test compounds comprise alterations at the N 6-group of the heterocyclic base, i.e., adenine or 2,6-diaminopurine, and at the N 9-side chain, represented by 9-[2-(phosphonomethoxy)ethyl] and 9-[2-(phosphonomethoxy)propyl] moieties: 9-[2-(phosphonomethoxy)propyl]adenine [( R)-PMPA; tenofovir], N 6-cyclopropyl-( R)-9-[2-(phosphonomethoxy)propyl]2,6-diaminopurine [ N 6-cyclopropyl-( R)-PMPDAP], N 6-cyclopentyl-( R)-9-[2-(phosphonomethoxy)propyl]2,6-diaminopurine [ N 6-cyclopentyl-( R)-PMPDAP], N 6-dimethylaminoethyl-( R)-9-[2-(phosphonomethoxy)propyl]2,6-diaminopurine [ N 6-dimethylaminoethyl-( R)-PMPDAP], N 6-isobutyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine ( N 6-isobutyl-PMEDAP), N 6-cyclopentyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine ( N 6-cyclopentyl-PMEDAP), N 6-cyclooctyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine ( N 6-cyclooctyl-PMEDAP), and N 6-cyclohexylmethyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine ( N 6-cyclohexylmethyl-PMEDAP). The cells were cultured in the presence of interferon-γ (5000 pg/ml) and test compounds (2–50 μM). Formation of nitrites was determined after 24 h using Griess reagent. It was inhibited by specific and nonspecific antagonists of adenosine A 1 receptors (IC 50 for 8-cyclopentyl-1,3-dipropylxanthine [CPX] was approximately 10 μM), while all other purine P 1 and purine P 2 receptor antagonists remained ineffective to suppress the NO-synergistic effect of acyclic nucleoside phosphonates.

Antiaggregatory activity in human platelets of potent antagonists of the P2Y 1 receptor

Activation of the P2Y 1 nucleotide receptor in platelets by ADP causes changes in shape and aggregation, mediated by activation of phospholipase C (PLC). Recently, MRS2500 (2-iodo- N 6-methyl-(N)-methanocarba-2′-deoxyadenosine-3′,5′-bisphosphate) was introduced as a highly potent and selective antagonist for this receptor. We have studied the actions of MRS2500 in human platelets and compared these effects with the effects of two acyclic nucleotide analogues, a bisphosphate MRS2298 and a bisphosphonate derivative MRS2496, which act as P2Y 1 receptor antagonists, although less potently than MRS2500. Improved synthetic methods for MRS2500 and MRS2496 were devised. The bisphosphonate is predicted to be more stable in general in biological systems than phosphate antagonists due to the non-hydrolyzable C P bond. MRS2500 inhibited the ADP-induced aggregation of human platelets with an IC 50 value of 0.95 nM. MRS2298 and MRS2496 also both inhibited the ADP-induced aggregation of human platelets with IC 50 values of 62.8 nM and 1.5 μM, respectively. A similar order of potency was observed for the three antagonists in binding to the recombinant human P2Y 1 receptor and in inhibition of ADP-induced shape change and ADP-induced rise in intracellular Ca 2+. No substantial antagonism of the pathway linked to the inhibition of cyclic AMP was observed for the nucleotide derivatives, indicating no interaction of these three P2Y 1 receptor antagonists with the proaggregatory P2Y 12 receptor, which is also activated by ADP. Thus, all three of the bisphosphate derivatives are highly selective antagonists of the platelet P2Y 1 receptor, and MRS2500 is the most potent such antagonist yet reported.

434 The interactions of acyclic nucleotide analogues with human telomerase

434 The interactions of acyclic nucleotide analogues with human telomerase

A new approach to the synthesis of optically active alkylated adenine derivatives

A new synthesis of chiral acyclic nucleoside and nucleotide analogues starting from d(−)- or l(+)-riboses was proposed. Antiviral properties of the synthesized compounds towards the pox virus family were evaluated.

A new approach to the synthesis of optically active alkylated adenine derivatives

A new synthesis of chiral acyclic nucleoside and nucleotide analogues starting from d(−)- or l(+)-riboses was proposed. Antiviral properties of the synthesized compounds towards the pox virus family were evaluated.

Adefovir dipivoxil in the treatment of chronic hepatitis B.

To evaluate properties of the new acyclic nucleotide analog adefovir dipivoxil in the treatment of chronic hepatitis B (CHB). MEDLINE and PubMed searches from 1966 to December 2003 were performed with the headings chronic hepatitis B, interferon alfa-2b, lamivudine, liver transplant, and adefovir dipivoxil. Randomized controlled studies and meta-analyses were evaluated in detail. A manual search was performed using references from retrieved primary literature, review articles, editorials, postgraduate course syllabi from national meetings, and textbooks. Emphasis was placed on controlled, prospective, randomized trials. National meeting abstract presentations were included if the information offered was original. CHB is a major viral infection with an estimated 400 million carriers worldwide. Medications available to treat CHB include interferon alfa-2b and lamivudine, both agents having significant limitations. Adefovir dipivoxil is a novel nucleotide analog which, when given at 10 mg/day for 48 weeks, improved liver histology in 28% more patients with hepatitis B e antigen (HBeAg)-positive CHB, and in 31% more patients with HBeAg-negative CHB compared with placebo (p < 0.001). Additionally, adefovir dipivoxil therapy significantly improved virologic and biochemical parameters in both HBeAg-positive and -negative CHB patients. Adefovir dipivoxil offers important advantages over other CHB treatment options: it maintains activity against lamivudine-resistant CHB, has good efficacy against HBeAg-negative CHB, and has minimal adverse effects at the 10-mg/day Food and Drug Administration-approved dose. Approved medications for the treatment of CHB have many limitations, and adefovir dipivoxil provides a new important option as an initial treatment, as well as treatment in lamivudine-resistant patients.

Role of purine nucleoside phosphorylase in interactions between 2',3'-dideoxyinosine and allopurinol, ganciclovir, or tenofovir.

The level of systemic exposure to 2',3'-dideoxyinosine (ddI) is increased 40 to 300% when it is coadministered with allopurinol (Allo), ganciclovir (GCV), or tenofovir. However, the mechanism for these drug interactions remains undefined. A metabolic route for ddI clearance is its breakdown by purine nucleoside phosphorylase (PNP). Consistent with previous reports, enzymatic inhibition assays showed that acyclic nucleotide analogs can inhibit the phosphorolysis of inosine. It was further established that the mono- and diphosphate forms of tenofovir were inhibitors of PNP-dependent degradation of ddI (K(i)s, 38 nM and 1.3 microM, respectively). Allo and its metabolites were found to be relatively weak inhibitors of PNP (K(i)s, >100 microM). Coadministration of tenofovir, GCV, or Allo decreased the amounts of intracellular ddI breakdown products in CEM cells, while they increased the ddI concentrations (twofold increase with each drug at approximately 20 microM). While inhibition of the physiological function of PNP is unlikely due to the ubiquitous presence of high levels of enzymatic activity, phosphorylated metabolites of GCV and tenofovir may cause the increased level of exposure to ddI by direct inhibition of its phosphorolysis by PNP. The discrepancy between the cellular activity of Allo and the weak enzyme inhibition by Allo and its metabolites may be explained by an indirect mechanism of PNP inhibition. This mechanism may be facilitated by the unfavorable equilibrium of PNP and the buildup of one of its products (hypoxanthine) through the inhibition of xanthine oxidase by Allo. These findings support the inhibition of PNP-dependent ddI degradation as the molecular mechanism of these drug interactions.

Synthesis and Molecular Structure of New Acyclic Analogues of Nucleotides with a 1,2‐Alkadienic Skeleton.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Hepatology highlights

Hepatology highlights

Nickel(II), Copper(II) and Zinc(II) Complexes of 9-[2- (Phosphonomethoxy)ethyl]-8-azaadenine (9,8aPMEA), the 8-Aza Derivative of the Antiviral Nucleotide Analogue 9-[2-(Phosphonomethoxy)ethyl] adenine (PMEA). Quantification of Four Isomeric Species in Aqueous Solution

The acidity constants of the twofold protonated acyclic nucleotide analogue 9-[2-(phosphonomethoxy)- ethyl]-8-azaadenine, H2(9,8aPMEA)±, as well as the stability constants of the M(H;9,8aPMEA)+ and M(9,8aPMEA) complexes with the metal ions M2+ =Ni2+, Cu2+ or Zn2+, have been determined by potentiometric pH titrations in aqueous solution at I=0.1 M (NaNO3) and 25℃. The result for the release of the first proton from H2(9,8aPMEA)+ (pKa= 2.73), which originates from the (N1)H+ site, was confirmed by UV-spectrophotometric measurements. Application of previously determined straight-line plots of log KMM(R-PO3) versus PKH3(R-HPO3)' for simple phosph(on)ate ligands, R- PO-, where R represents a residue without an affinity for metal ions, proves that the primary binding site of 9,8aPMEA2- is the phosphonate group for all three metal ions studied. By stability constant comparisons with related ligands it is shown, in agreement with conclusions reached earlier for the Cu(PMEA) system [PMEA2-=dianion of 9-[2- (phosphonomethoxy)ethyl]adenine], that in total four different isomers are in equilibrium with each other, i.e. (i) an open isomer with a sole phosphonate coordination, M(PA)op, where PA2-=PMEA2-or 9,8aPMEA2-, (ii) an isomer with a 5-membered chelate involving the ether oxygen, M(PA)cl/o, (iii) an isomer which contains 5- and 7-membered chelates formed by coordination of the phosphonate group, the ether oxygen and the N3 site of the adenine residue, M(PA)cl/O/N3, and finally (iv) a macrochelated isomer involving N7, M(PA)cl/]N7. The Cu2+ systems of PMEA2- and 9,8aPMEA2- behave quite alike; the formation degrees for Cu(PA)op, CuM(PA)cl/O, Cu(PA)cl/O/N3 and Cu(PA)cl/N3 are approximately 16, 32, 45 and 7%, respectively, which shows that Cu(PA)cl/N7 is a minority species. In the Ni2+ and Zn2+ systems the open isomer is the dominating one followed by M(PA)cl/O, but there are indications that the other two isomers also occur to some extent.

Adefovir dipivoxil: A new antiviral agent for the treatment of hepatitis B virus infection

Background: Hepatitis B virus (HBV) infection is a major problem worldwide and an important cause of chronic liver disease and cirrhosis. Currently available treatments include interferon alfa-2b, lamivudine, and adefovir dipivoxil. Adefovir dipivoxil is an acyclic nucleotide analogue that was developed in part to improve on the limitations of earlier therapies.Objective: This article is a review of available data on the clinical pharmacology, virology, efficacy, tolerability, and clinical use of adefovir dipivoxil.Methods: A search of the English-language literature indexed on MEDLINE from 1966 to July 2003 was performed using the terms adefovir, PMEA, and Bis-POM PMEA. Pertinent abstracts from scientific meetings on infectious diseases and hepatology were also included. The manufacturer of adefovir dipivoxil provided additional information. These materials were supplemented by US Food and Drug Administration briefing documents and other unpublished materials. In vitro and preclinical studies were included in the review, as were Phase II and III clinical trials.Results: In vitro, adefovir dipivoxil concentrations exceed those necessary to inhibit both wild-type and lamivudine-resistant isolates of HBV. In clinical trials, adefovir dipivoxil was clinically and virologically effective in patients in whom lamivudine therapy had failed due to the presence of lamivudine-resistant HBV. The drug was generally well tolerated. The risk of nephrotoxicity, the most notable adverse effect of adefovir dipivoxil at previously used higher doses, has been substantially reduced at the currently recommended dosage of 10 mg/d.Conclusion: Based on the data reviewed adefovir dipivoxil is an effective and well-tolerated alternative for the treatment of HBV infection, including disease that is lamivudine resistant.

Activity of 9-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine against Schistosomiasis mansoni in mice.

The activity of the acyclic nucleotide analogue 9-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine [(S)-HPMPA] against Schistosoma mansoni was investigated in mice. The compound was injected intraperitoneally, usually on two or five consecutive days, at 10 to 20 mg/kg of body weight/day. The treatment started before, at the time of, and after the onset of egg laying (oviposition) by S. mansoni. The animals were killed from 7 to 40 days after the cessation of treatment. Significant reductions in the total numbers of female and coupled worms were found. Female fecundity and both hepatic and intestinal egg loads were suppressed. These effects were more pronounced with dosing regimens launched before the time of oviposition. The complete disappearance of immature eggs and a significant reduction to the complete absence of mature eggs, with 99 to 100% of the eggs being dead, were produced. No hepatic egg-induced granulomas were present in mice treated at the time of oviposition, and the granulomas were smaller in mice treated before S. mansoni oviposition. These preliminary findings extend the knowledge of the antiparasitic properties of (S)-HPMPA.