Chemotherapeutic agents for herpesvirus infections

5-Substituted-2′-deoxyuridines as anti-HSV-1 Agents: Synthesis and Structure Activity Relationship

Nucleoside and pyrophosphate analogues are currently in use to treat infection with Human herpesvirus 1 (HSV-1). Both series of compounds exert their activity by inhibition of the viral DNA polymerase either directly, or after anabolic phosphorylation. As the X-ray structure of the viral-specific DNA polymerase is not known, it is difficult to design a nucleoside or non-nucleoside antiviral agent which specifically inhibits this enzyme. Therefore, alternative strategies have relied on extensive structure activity relationship studies of anti-HSV-1 agents in an endeavour to understand the essential structural requirements for activity and hence the design of drugs with increased selectivity. A virus-specific enzyme which plays a crucial role in the selective activation of nucleoside analogues is thymidine kinase. Present knowledge regarding the specificity of herpesvirus thymidine kinase for its 5-substituted-2′-deoxyuridine substrates is reviewed herein.

Novel bicyclic sugar modified nucleosides: synthesis, conformational analysis and antiviral evaluation

Methodology previously described by us was applied to the formation of novel conformationally restrained bicyclic sugar modified nucleosides, with introduction of an oxazole and a thiocarbamate ring at the 2('),3(')-positions of the ribonucleosides. Two novel alkyl derivatives of 2('),3(')-dideoxy-2('),3(')-oxazole-beta-d-uridine and a novel uridine 2('),3(')-thiocarbamate were successfully synthesised. Conformational evaluation of all the synthesised compounds was conducted using the theoretical potential energy calculation via the macromodel v.6.0 molecular modelling programme. The conformationally restrained nucleosides described were evaluated against a wide range of DNA and RNA viruses. None of the compounds showed specific antiviral effects at subtoxic concentrations.

Novel 6-azapyrimidine-2'-deoxy-4'-thionucleosides: synthesis, biological evaluation and conformational analysis

We report the synthesis of novel 1-(2'-deoxy-4'-thio-beta-D-erythro-pentofuranosyl)-(6-azapyrimidine) nucleosides and the subsequent preparation of a series of N3-substituted analogues. All the novel compounds were evaluated against a range of viruses, however they lacked any measurable activity. The lack of anti-herpetic activity may be a result of the parent nucleoside having poor affinity for herpes simplex virus type 1 thymidine kinase. Conformational analysis of the parent nucleoside showed a twist (3T2) sugar conformation commonly displayed by 2'-deoxy-4'-thionucleosides and the anti-human immunodeficiency virus type 1 agents zidovudine and 3'-fluoro-ddT.

Anterior nongranulomatous uveitis after intravitreal HPMPC (cidofovir) for the treatment of cytomegalovirus retinitis. Analysis and prevention

BACKGROUND AND OBJECTIVE

The authors characterize and analyze the incidence of a previously reported mild anterior nongranulomatous uveitis associated with intravitreal injections of (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC), also termed cidofovir (Vistide, Gilead Sciences, Foster City, CA). This is an acyclic nucleoside phosphonate analogue with a potent anticytomegalovirus effect. The authors also analyzed the effects of probenecid therapy, as well as prophylaxis with probenecid plus topical corticosteroids and cycloplegics on the course and outcome of the uveitis.

METHODS

Prospective case series from a tertiary referral center, which included 46 consecutive patients with acquired immune deficiency syndrome (AIDS) and cytomegalovirus (CMV) retinitis. There was a total of 130 injections in 69 eyes treated with 20 micrograms of intravitreal HPMPC. Forty-one patients (119 injections) received oral probenecid, 5 patients (11 injections) did not, and 21 patients (53 injections) received topical corticosteroids and cycloplegics as an adjuvant to probenecid in the prophylaxis of iritis.

RESULTS

Mild to moderate nongranulomatous iritis was seen in 26% of patients after their first injection (n = 12). Patients receiving probenecid prophylaxis after first injection had a significantly lower frequency of iritis versus patients who did not receive probenecid at the time of first injection (P = 0.0089). In contrast, treatment with topical corticosteroid and cycloplegics after injection did not statistically significantly affect the frequency of iritis in patients (P = 0.44). The development of iritis after a second injection of HPMPC was more likely if it had occurred after the initial injection (P = 0.015; Fisher's exact test). All cases of iritis were treated with topical corticosteroids and cycloplegics, and there was no permanent impairment of vision secondary to iritis after HPMPC injection in any eyes.

CONCLUSIONS

Anterior uveitis was seen in 26% of patients after first-time HPMPC injection. Concomitant use of probenecid appears to decrease the frequency of the iritis from 71% to 18% in patients with AIDS and CMV retinitis after the first intravitreal injection of HPMPC. Topical corticosteroid administration after injection (before iritis) was ineffective in preventing iritis treatment with topical corticosteroids and cycloplegics resulted in resolution of all iritis cases.

Accumulation of 5-ethyl-2'-deoxyuridine and its 5,6-dihydro prodrugs in murine lung and its potential clinical application

The accumulation of 5-ethyl-2'-deoxyuridine (EDU), (--)-trans-(5S,6S)-5-bromo-5-ethyl-6-methoxy-5,6- dihydro-2'-deoxyuridine [(5S,6S)-BMEDU], (+)-trans-(5R,6R) -5-bromo-ethyl-6-methoxy-5,6-dihydro- 2'-deoxyuridine [(5R,6R)-BMEDU], (+)-trans-(5R,6R)-5-bromo- 5-ethyl-6-ethoxy-5,6-dihydro-2'-deoxy- uridine (BEEDU), (+)-trans-(5R,6R)-5-bromo-5-ethyl-6-ethoxy -5,6-dihydro-5'-O-valeryl-2'deoxyuridine (VBEEDU) [formula: see text] and (+)-trans-(5R,6R)-5-bromo-5-ethyl-6-ethoxy-5, 6-dihydro-3'-5'-di-O-valeryl-2'-deoxyuridine [formula: see text] (DVBEEDU) in lung and other tissues was investigated in male Balb-C mice following intravenous injection of the corresponding 4-(14)C-labelled compounds. EDU showed a rapid distribution into liver and lung immediately after injection, and the overall levels of radioactivity in blood, liver and lung were similar. The distribution of radioactivity in lung after injection of [4-(14)C](5S,6S)-BMEDU and [4-(14)C]5R,6R)-BMEDU were substantially different from one another and also from that of[4(-14)C]EDU. The radioactivity level present in lung samples after injection of both (4-(14C](5S,6S)-BMEDU and [4-(14)C](5R,6R)-BMEDU was substantially higher than that in blood samples. Radioactivity levels present in lung samples taken at 18 min after injection of [4-(14)C]BEEDU were significantly higher (P < 0.05) than those for liver and blood samples. Although the radioactivity present in lung samples after injection of [4-(14)C]BEEDU did not provide a higher radioactivity level in lung samples than did [4-(14)C]BEEDU.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioavailability and pharmacokinetic parameters for 5-ethyl-2'-deoxyuridine

Pharmacokinetic parameters for 5-ethyl-2'-deoxyuridine (EDU) were determined following intravenous (iv) and oral (po) dosing in male Balb-C mice and iv dosing in male Sprague-Dawley rats. The concentrations of EDU in blood after 100 mg/kg iv bolus injections into mice and rats were consistent with a two compartment kinetic model. Based on this kinetic model, EDU showed a very short distribution half-life of 1.4 +/- 0.7 min in mice and 1.3 +/- 0.1 min in rats. The elimination half-life of EDU in rats following iv bolus injection, was substantially (18.5 +/- 1.0 min) shorter than that in mice (24.1 +/- 2.9 min). The mean residence time (MRT) of EDU was also substantially longer in mice (25.8 +/- 4.9 min) compared to rats (11.0 +/- 2.9 min). However, clearance of EDU was similar in both rats and mice. Although the biotransformation of EDU was similar in mice and rats, cleavage of the EDU glycoside bond was less extensive in mice than in rats. EDU showed a 49% bioavailability in mice after a 100 mg/kg po dose. The concentration of EDU in blood after a po dose provided the best fit to a one compartment model. The maximum blood concentration of EDU (Cmax) was 2.4 +/- 0.2 micrograms/g of blood which attained 31.1 +/- 1.2 min (Tmax) after a 100 mg/kg po dose. The AUC of 5-ethyluracil (EU) after a po dose of EDU was significantly higher (P < 0.05) than after an iv dose of EDU. This observation indicates that EDU undergoes degradation by phosphorylases present in the gastrointestinal tract and/or by presystemic metabolism.

Nucleoside and nucleotide transport through a model liquid membrane. Periodic-catastrophic transport of a novel amantadine phosphoramidate conjugate of 5'-AMP

Adenosine 5'-phosphor(adamantyl)amidate (5), an analog derived by linking the antiviral drug amantadine to 5'-AMP is transported through a model membrane system in a discontinuous periodic-catastrophic fashion. The system was composed of a glass cell containing two aqueous buffer phases separated by a chloroform layer. A more lipophilic, but structurally related derivative, adenosine 5'-phosphor(n-decyl)amidate (3) showed linear transport in the same system. Less lipophilic substances, including 5'-AMP and adenosine 5'-phosphor(morpholidyl)amidate (2), did not show transport. It is hypothesized that the periodic-catastrophic transport is a result of the collective activity of amidate 5 at the interface between the first aqueous interface and the chloroform layer. The time between catastrophic events is thought to be a reflection of the time necessary for molecular organization at the interface. The phenomenon is a new example of molecular organization in a system far from equilibrium leading to a repetitive dynamic process.

Mechanism of inhibition of adenovirus DNA replication by the acyclic nucleoside triphosphate analogue (S)-HPMPApp: influence of the adenovirus DNA binding protein

The acyclic adenosine analogue (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine [S]-HPMPA) is a potent and selective inhibitor of adenovirus (Ad) replication in cell culture. We studied the mechanism of inhibition using a reconstituted in vitro DNA replication system. The diphosphoryl derivative (S)-HPMPApp, but not (S)-HPMPA, inhibited the DNA replication of origin containing fragments strongly. The inhibitory effect was exerted at the level of elongation, while initiation was resistant to the drug. Remarkably, the elongation of short strands was only slightly impaired, while inhibition was maximal upon synthesis of long DNA fragments. (S)-HPMPApp appeared to be competitive with dATP, suggesting that the Ad DNA polymerase is the prime target for the drug. We purified the Ad DNA polymerase in complex to the precursor terminal protein to homogeneity from cells infected with overproducing recombinant vaccinia viruses. Employing gapped DNA or poly(dT).oligo(dA) templates, only a weak inhibition was observed. However, inhibition was strongly enhanced in the presence of the adenovirus DNA binding protein (DBP). We interpret this to mean that the increased processivity of the polymerization reaction in the presence of DBP leads to increased drug sensitivity.

A comparison of the conformations adopted by some 5-bromovinyl-2'-deoxyuridines and a correlation with their antiviral properties: an X-ray study

Crystal structures of (Z)-5-(2-bromovinyl)-2'-deoxyuridine, 3',5'-di-O-acetyl-(E)-5-(2-bromovinyl)-2'-deoxyuridine and 3',5'-di-O-p-chlorobenzoyl-5-(2-dibromovinyl)-2'-deoxyuridine are compared with each other and with that of the most potent antiviral agent (E)-5-(2-bromovinyl)-2'-deoxyuridine (E-BVDU) reported earlier. A comparison of the conformation of 3',5'-di-O-acetyl-pyrimidine nucleoside structures in which intermolecular hydrogen bond network formation is minimized, with those of their parent compounds has shown that the greatest change in rotation about the glycosyl bond and in the sugar ring pucker is exhibited by E-BVDU. Upon acylation this molecule changes from C2'-endo/C3'-exo conformation to C3'-endo/C4'-exo conformation. The relevance of these structures upon the biological activity of the nucleosides and in particular to their ability to be a substrate for thymidine kinase is discussed.