Evaluation of anti-herpesvirus activity of (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]- guanine (A-5021) in mice

Pluronic F127-tailored lecithin organogel of acyclovir: preclinical evidence of antiviral activity using BALB/c murine model of cutaneous HSV-1 infection

Herpes is a well-known contagious infection equally affecting both sexes. Among many antiviral drugs employed for its treatment, acyclovir (ACY) is the drug of choice. The currently available therapies of ACY suffer from limitations like poor oral bioavailability (10-15%) and high-dose requirement. The present scientific study aims to explore pluronic lecithin organogel (PLO) as a novel drug delivery platform for ACY to bring an improvement in its delivery through topical route. The properties of organogel like biocompatibility and amphiphilic nature which facilitates dissolution of various drugs of different solubility characteristics along with enhancing the permeation potential of active molecules make it a favorable drug delivery platform for the management of topical diseases. The developed PLO formulations were characterized for micromeritic characteristics, viz., zeta potential, percentage drug content, organogel morphology, skin permeation, retention, and stability studies. The selected topical formulation was further compared with the marketed one for its therapeutic efficacy by inducing cutaneous Herpes simplex virus type 1 infection followed by confirmation of viral load by immunofluorescence and PCR analyses. The developed formulation showed significant improvement over the marketed product as reflected in lesion scoring index and PCR analysis. Further, it proved better to the marketed formulation in t.i.d. treatment regimen in comparison to control. The improvement in overall performance leading to enhanced bioavailability and safety is attributed to the synergism between excipient properties and formulation characteristics. The drug ACY in this micro environment not only finds an improved delivery vehicle but it also offers enhanced drug-target interactions.

In vitro and in vivo assessment of eprociclovir as antiviral treatment against testudinid herpesvirus 3 in Hermann's tortoise (Testudo hermanni)

Tortoises belonging to the Testudinidae family are infected by Testudinid herpesviruses. Testudinid herpesvirus 3 (TeHV-3) is considered the most pathogenic and affects several tortoise species, particularly those from the Testudo genus. As most species of this genus are endangered contribute to ecological concerns over this virus. Here, we aimed to explore the rational development of an antiviral treatment against TeHV-3 using Hermann's tortoise (Testudo hermanni) as a host model. Ten antiviral compounds were tested in cell culture for their toxicity and their activity against TeHV-3. Eight compounds exhibited different levels of activity against TeHV-3 with either no or only minor cytotoxic effects on cells. Next, eprociclovir (EPV, ciprovir) was selected for further investigations in vivo. Its pharmacokinetic properties were investigated after a single sub-cutaneous administration at 5 or 10 mg/kg. Plasma concentrations remained above half maximal effective concentration (EC₅₀) for 2.2 and 4.4 h after administration at 5 and 10 mg/kg, respectively. Finally, EPV toxicity was investigated after administration at the dose of 10 mg/kg, BID for seven consecutive days. As early as one day after initiation of the treatment up to its end, EPV plasma concentration remained under the EC_50. Apathy and anorexia developed after 7 days. Biochemical and anatomopathological examinations revealed nephrotoxic effects of EPV. Altogether, these data suggest that EPV is not a suitable molecule for the treatment of TeHV-3. Further studies are required to determine whether the other molecules identified here for their anti-TeHV-3 activity represent potential candidates for the development of efficacious treatments.

Evaluation of the antiviral activity of (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]guanine (A-5021) against equine herpesvirus type 1 in cell monolayers and equine nasal mucosal explants

Equine herpesvirus 1 (EHV1) is a ubiquitous equine alphaherpesvirus that causes respiratory disease, neurological symptoms and abortions. Current vaccines are not fully protective and effective therapeutics are lacking. A-5021 [(1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]guanine], previously shown to possess potent anti-herpetic activity against most human herpesviruses, was evaluated for its potential to inhibit EHV1 replication. In equine embryonic lung (EEL) cells, infected with either a non-neurovirulent (97P70) or a neurovirulent (03P37) EHV1 isolate, A-5021 proved to be about 15-fold more potent than acyclovir in inhibiting viral replication. Moreover, in equine nasal mucosal explants, A-5021 (at 8 and 32μM) was able to completely inhibit viral plaque formation whereas acyclovir did not exert an antiviral effect at these concentrations. Our data demonstrate that A-5021 is a potent inhibitor of EHV1 replication and may have potential for the treatment and/or prophylaxis of infections with this virus.

Novel 1,2,4-triazole and purine acyclic cyclopropane nucleoside analogues: synthesis, antiviral and cytostatic activity evaluations

BACKGROUND

Several published studies indicate that the acyclic guanine nucleoside analogues possessing bis(1,2-hydroxymethyl) substituted cyclopropane rings mimicking the sugar moiety are potent inhibitors of replication of several herpes viruses.

METHODS

Established synthetic methods and antiviral and cytostatic activity assays were used for the evaluation of new 1,2,4-triazole and purine acyclic nucleoside analogues.

RESULTS

The synthesis of new types of acyclic nucleoside analogues which incorporate 1,2,4-triazole or purine moiety bound via flexible methylenic spacer to the bis(1,2-hydroxymethyl) cyclopropane ring. None of the new compounds showed pronounced antiviral activities at subtoxic concentrations on a broad panel of DNA and RNA viruses. Evaluation of their affinity for herpes simplex type 1 (HSV-1) and varicella-zoster virus-encoded thymidine kinases (VZV TK) also showed that none of the compounds was able to significantly inhibit 1 μM deoxythymidine phosphorylation by HSV-1 and VZV TK at 500 μM concentrations. The in vitro cytostatic activity evaluation results indicated a weak antiproliferative activity for all tested compounds. Only 6-pyrrolylpurine derivative bearing a carboxylic group substituted cyclopropane ring produced a rather slight inhibitory effect at higher micromolar concentrations on a breast carcinoma cell line (MCF-7) and no cytotoxic effect on human normal fibroblasts (WI 38).

CONCLUSIONS

The lack of antiherpetic activity may be due to poor, if any, recognition of the compounds by virus-induced nucleoside kinases as an alternative substrate to become metabolically activated.

A-5021: a new acyclovir analogue inhibits murine herpetic keratitis

PURPOSE

To determine the efficacy of A-5021, a new analogue of acyclovir, on murine herpetic keratitis.

METHODS

Herpes simplex virus type 1 (strain CHR3) was inoculated onto bilateral scarified BALB/c corneas. Clinical scores on the corneas treated with A-5021 eyedrops were compared with those obtained from the treatment with 3% acyclovir eye ointment by slit lamp microscopy. Virus titers of the trigeminal ganglia and eyeballs were quantitated on Vero cell monolayers. Mice treated with saline or a white petroleum jelly were used as controls.

RESULTS

A-5021 eyedrops significantly suppressed both corneal epithelial and stromal lesions at all concentrations used. Clinical scores on the epithelium and stroma treated with 0.1% A-5021 were equivalent to those with 3% acyclovir treatment. When compared with the non-drug-treated control mice, virus titers in the eyeballs and trigeminal ganglia in A-5021- and acyclovir-treated mice were significantly less than those in controls.

CONCLUSIONS

A-5021 eyedrops, which are easily applied onto the affected cornea, ameliorated clinical scores and suppressed virus growth. It is a promising alternative treatment of herpetic keratitis.

Main adult herpes virus infections of the CNS

Herpes viruses are widely involved in human infectious diseases, and some are life threatening, such as CNS infections. These manifestations vary according to the type of virus involved and the immune status of the patient. This article will review the clinical manifestations (encephalitis, myelitis, meningitis and postinfectious encephalomyelitis), the diagnostic strategies and the presently used drugs (acyclovir, valacyclovir, ganciclovir, valgancyclovir, foscarnet and cidofovir). The review will also discuss drugs that are currently in the pipeline and that could be used in the future.

Synthesis and biological activity of tricyclic analogues of 9-{[cis-1′,2′-bis(hydroxymethyl)cycloprop-1′-yl]methyl}guanine

The base moiety of the potent antiherpetic agent 9-[[cis-1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]guanine 3 was transformed into that of the tricyclic 3,9-dihydro-9-oxo-6-R-5H-imidazo[1,2-a]purine system. The tricyclic analogues 5a-d were evaluated for their activity against herpes viruses as well as for cytostatic activity against HSV-1 thymidine kinase (TK) gene-transduced human osteosarcoma tumor cells. Marked activity was found against VZV. The 6-phenyl-substituted fluorescent analogues 5c and d were comparable to that of parent 3 in activity against the VZV strain YS and were 3-fold less active against the VZV strain OKA. The compounds 5a-d also showed marked activity against HSV-1 (KOS) and HSV-2 (G)-against the former generally approximately comparable to that of acyclovir 1a and one order of magnitude lower than 3; against the latter comparable to that of 1a and approximately 6- to 30-fold lower than that of 3. The most pronounced cytostatic activity (5-fold lower than that of 3) was exhibited by compounds 5c and d. Tricyclic analogues with pseudosugar moieties are intrinsically bio-active.

Synthesis of phosphonate analogues of the antiviral cyclopropane nucleoside A-5021

A series of phosphonate analogues of the antiviral cyclopropane nucleoside A-5021 were synthesized from (1S*, 7R*)-3,5-dioxa-4,4-diphenylbicyclo[5. 1.0]octane-l-methanol by a 10-step process. In contrast to the potent antiherpetic activity of A-5021, they were all devoid of antiviral activity.

Acyclic/carbocyclic guanosine analogues as anti-herpesvirus agents

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus [i.e. herpes simplex virus type 1 (HSV-1), and type 2 (HSV-2), varicella-zoster virus (VZV) and/or human cytomegalovirus (HCMV)] infections. In recent years, several new guanosine analogues have been developed, including the 3-membered cyclopropylmethyl and -methenyl derivatives (A-5021 and synguanol) and the 6-membered D- and L-cyclohexenyl derivatives. The activity of the acyclic/carbocyclic guanosine analogues has been determined against a wide spectrum of viruses, including the HSV-1, HSV-2, VZV, HCMV, and also human herpesviruses type 6 (HHV-6), type 7 (HHV-7) and type 8 (HHV-8), and hepatitis B virus (HBV). The new guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) were found to be particularly active against those viruses (HSV-1, HSV-2, VZV) that encode for a specific thymidine kinase (TK), suggesting that their antiviral activity (at least partially) depends on phosphorylation by the virus-induced TK. Marked antiviral activity was also noted with A-5021 against HHV-6 and with D- and L-cyclohexenyl G against HCMV and HBV. The antiviral activity of the acyclic/carbocyclic nucleoside analogues could be markedly potentiated by mycophenolic acid, a potent inhibitor of inosine 5'-monophosphate (IMP) dehydrogenase. The new carbocyclic guanosine analogues (i.e. A-5021 and D- and L-cyclohexenyl G) hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also an antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transduced by the viral (HSV-1, VZV) TK gene.

The anti-herpesvirus activity of (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)-cycloprop-1'-yl]methyl]guanine is markedly potentiated by the immunosuppressive agent mycophenolate mofetil

Mycophenolic acid (MPA), the active form of the immunosuppressive agent mycophenolate mofetil (MMF), was found to markedly potentiate the anti-herpesvirus activity of the novel anti-herpesvirus agent A-5021, (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]guanine. For example, at a concentration of 1 microg/ml MPA, the activity of A-5021 against HSV-1, HSV-2 and TK(-) HSV-1 increased by a factor of 130, 14 and > or = 189, respectively. Exogenously added guanosine reversed this potentiating effect, suggesting that a depletion of the endogenous dGTP pools enhanced the inhibitory effect of the 5'-triphosphate metabolite of A-5021 on the viral DNA polymerase. The combined effect of A-5021 and MPA on the growth of uninfected Vero cells was additive rather than synergistic. The combination of topically applied MMF (5%) with 0.05% A-5021 (a subactive concentration) completely protected against HSV-1-induced cutaneous lesions in hairless mice, whereas therapy with either compound used alone had no protective effect. These findings may have implications for those transplant recipients that receive MMF as (part of) their immunosuppressive therapy and that develop intercurrent herpesvirus infections for which they need treatment.

Anti-herpesvirus activity of (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)-cycloprop-1'-yl]methyl] x guanine (A-5021) in vitro and in vivo

The novel nucleoside analog (1S',2R')-9-[[1',2'-bis(hydroxymethyl)cycloprop-1-yl]methyl]guanine (A-5021) was previously shown to be a potent inhibitor of the replication of herpes simplex virus type 1 and 2 (HSV-1 and HSV-2) and varicella zoster virus (VZV), both in vitro and in vivo (J. Med. Chem. 41, 1284-1298; Antimicrob. Agents Chemother. 42, 1666-1670). Here we demonstrate that A-5021 is also a potent inhibitor of Epstein-Barr virus (EBV) and human herpes virus 6 (HHV-6A and HHV-6B), but that the compound lacks activity against HHV-8. A-5021, in comparison to acyclovir, was also assessed for protective activity against HSV-1-induced mortality in SCID mice. The compounds were administered at 50 mg/kg per day by subcutaneous injection for four consecutive days and treatment was initiated at either 2 h, 1 or 2 days post infection (p.i.). When administered from day 0 to 4 p.i., A-5021 conferred complete protection against the infection (as assessed at 22 days p.i.), whereas acyclovir delayed virus induced mortality by only 5 days. When treatment was begun on day 1 or 2, A-5021 still afforded marked protection against the infection, whereas acyclovir was virtually devoid of any activity under these conditions. Our data underline that A-5021 may offer great promise for the treatment of herpesvirus infections.

Guanosine analogues as anti-herpesvirus agents

Several guanosine analogues, i.e. acyclovir (and its oral prodrug valaciclovir), penciclovir (in its oral prodrug form, famciclovir) and ganciclovir, are widely used for the treatment of herpesvirus (i.e. HSV-1, HSV-2, VZV and HCMV) infections. In recent years, several new guanosine analogues have been developed, including the 3-membered (cyclopropyl) sugar derivative A-5021 and the 6-membered D- and L-cyclohexenyl derivatives. Prominent features shared by all guanosine analogues are the following. They depend for their phosphorylation on the virus-encoded thymidine kinase (TK), which makes them particularly effective against those viruses (HSV-1, HSV-2 and VZV) that encoded for such TK. They are also active against HCMV, whether or not they are subject of phosphorylation by the HCMV-induced UL97 protein kinase. Their antiviral activity can be markedly potentiated by mycophenolic acid, an IMP dehydrogenase inhibitor, and they hold great promise, not only as antiviral agents for the treatment of herpesvirus infections, but also as antitumor agents for the combined gene therapy/chemotherapy of cancer, provided that (part of) the tumor cells have been transfected by the viral TK gene.