Chemotherapy of varicella zoster virus infections

β-l-1-[5-(E-2-bromovinyl)-2-(hydroxymethyl)-1,3-(dioxolan-4-yl)] uracil (l-BHDU) prevents varicella-zoster virus replication in a SCID-Hu mouse model and does not interfere with 5-fluorouracil catabolism

The alphaherpesvirus varicella-zoster virus (VZV) causes chickenpox and shingles. Current treatments are acyclovir (ACV) and its derivatives, foscarnet and brivudine (BVdU). Additional antiviral compounds with increased potency and specificity are needed to treat VZV, especially to treat post-herpetic neuralgia. We evaluated β-l-1-[5-(E-2-bromovinyl)-2-(hydroxymethyl)-1,3-(dioxolan-4-yl)] uracil (l-BHDU, 1) and 5'-O-valyl-l-BHDU (2) in three models of VZV replication: primary human foreskin fibroblasts (HFFs), skin organ culture (SOC) and in SCID-Hu mice with skin xenografts. The efficacy of l-BHDU in vivo and its drug-drug interactions were previously not known. In HFFs, 200μM l-BHDU was noncytotoxic over 3days, and l-BHDU treatment reduced VZV genome copy number and cell to cell spread. The EC50 in HFFs for l-BHDU and valyl-l-BHDU were 0.22 and 0.03μM, respectively. However, l-BHDU antagonized the activity of ACV, BVdU and foscarnet in cultured cells. Given its similar structure to BVdU, we asked if l-BHDU, like BVdU, inhibits 5-fluorouracil catabolism. BALB/c mice were treated with 5-FU alone or in combination with l-BHDU or BVdU. l-BHDU did not interfere with 5-FU catabolism. In SCID-Hu mice implanted with human skin xenografts, l-BHDU and valyl-l-BHDU were superior to ACV and valacyclovir. The maximum concentration (Cmax) levels of l-BHDU were determined in mouse and human tissues at 2h after dosing, and comparison of concentration ratios of tissue to plasma indicated saturation of uptake at the highest dose. For the first time, an l-nucleoside analog, l-BHDU, was found to be effective and well tolerated in mice.

[Bicyclic furano[2,3-D] derivatives of pyrimidine nucleosides--synthesis and antiviral properties]

The methods of synthesis of furano- and pyrrolo[2,3-dlpyrimidine nucleosides as well as structure activity relationship of obtained compounds towards viruses of varicella zoster, hepatitis C, bovine viral diarrhea and some others are reviewed.

A new class of dual-targeted antivirals: monophosphorylated acyclovir prodrug derivatives suppress both human immunodeficiency virus type 1 and herpes simplex virus type 2

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) and herpes simplex virus type 2 (HSV-2) are responsible for 2 intersecting epidemics in which the disease caused by 1 virus facilitates the transmission of and pathogenesis by the other. Therefore, suppression of one virus infection will affect the other. Acyclovir, a common antiherpetic drug, was shown to directly suppress both viruses in coinfected tissues. However, both antiviral activities of acyclovir are dependent on phosphorylation by the nucleoside kinase activity of coinfecting human herpesviruses.

METHODS

We developed acyclovir ProTides, monophosphorylated acyclovir with the phosphate group masked by lipophilic groups to allow efficient cellular uptake, and investigated their antiviral potential in cell lines and in human tissues ex vivo.

RESULTS

Acyclovir ProTides suppressed both HIV-1 and HSV-2 at median effective concentrations in the submicromolar range in ex vivo lymphoid and cervicovaginal human tissues and at 3-12 micromol/L in CD4(+) T cells. Acyclovir ProTides retained activity against acyclovir-resistant HSV-2.

CONCLUSIONS

Acyclovir ProTides represent a new class of antivirals that suppress both HIV-1 and HSV-2 by directly and independently blocking the key replicative enzymes of both viruses. Further optimization of such compounds may lead to double-targeted antivirals that can prevent viral transmission and treat the 2 synergistic diseases caused by HIV-1 and HSV-2. To our knowledge, the acyclovir ProTides described here represent the first example of acyclic nucleoside monophosphate prodrugs being active against HIV-1.

Valaciclovir:development, clinical utility and potential

Valaciclovir (Valtrex, Zelitrex), the L-valine ester of aciclovir, increases aciclovir bioavailability by 3- to 5-fold over that achievable with oral aciclovir. It addresses many unmet needs of currently available anti-herpesvirus therapies. Valaciclovir extends the efficacy of aciclovir in the treatment of herpes zoster and genital HSV infections, using less frequent dose regimens but retaining the highly acceptable safety profile established for aciclovir. The potential for valaciclovir in CMV prophylaxis has now been proven, and further refining to identify the optimal dose regimen is ongoing. After oral administration, valaciclovir is rapidly absorbed and extensively converted to aciclovir and L-valine, the essential amino acid. The mode of action and spectrum of antiviral activity of valaciclovir are thus identical to aciclovir. The bioavailability of aciclovir after valaciclovir, characterised from studies in healthy adult volunteers, is similar in a wide range of patient populations, including the elderly, those with advanced HIV disease, patients with impaired liver or renal function, or undergoing bone marrow transplantation. No clinically significant drug interactions with valaciclovir have so far been identified. Dosage reductions in clinical use of valaciclovir are only necessary when renal function is severely impaired. In controlled clinical trials in herpes zoster, valaciclovir (1000 mg three times daily) is superior to aciclovir in speeding the resolution of zoster-associated pain and post-herpetic neuralgia. It is as effective as aciclovir in hastening rash healing. In patients with ophthalmic zoster, no differences were evident between valaciclovir and aciclovir treatment on zoster-associated pain or the occurrence of ocular complications. The safety profiles of valaciclovir, aciclovir and placebo were not different in this study programme. In a series of controlled, randomised trials of valaciclovir, aciclovir and placebo for the acute treatment of genital HSV infections in approximately 3000 patients, twice daily valaciclovir was proven as effective as the standard 5 times daily aciclovir regimen in resolving the clinical signs and symptoms of lesional disease. Early patient-initiated valaciclovir therapy (500 mg twice daily) of recurrent genital herpes episodes was shown significantly to increase the chance of prevention of vesicular or ulcerative lesions, a valuable clinical advantage not prospectively proven for aciclovir. When used for periods of up to one year, valaciclovir (500 mg once daily) effectively suppresses genital herpes recurrences. Long-term studies of valaciclovir for HSV suppression, evaluating doses of up to 1000 mg daily in approximately 3000 patients, about 25% of whom were HIV seropositive (CD+ > 100 cells/microl), revealed a highly acceptable clinical tolerability profile for valaciclovir that did not differ from aciclovir or placebo. There were no cases resembling thrombotic microangiopathy in these long-term studies. The aciclovir safety heritage and pharmacokinetic rationale for the development of valaciclovir have been realised through the clinical research programmes in the zoster and HSV indications. Further studies in these and related areas, including CMV prophylaxis, are in progress and aim to expand further the clinical potential of valaciclovir in the future.

Oral brivudin in comparison with acyclovir for improved therapy of herpes zoster in immunocompetent patients: results of a randomized, double-blind, multicentered study

Brivudin [(E)-5-(2-bromovinyl)-2'-deoxyuridine] is a nucleoside analogue with a high and selective antiviral activity against varicella-zoster virus (VZV) and herpes simplex virus type 1 (HSV-1). The double-blind, randomized study presented here compared efficacy and safety of oral brivudin 1 x 125 mg and acyclovir 5 x 800 mg, both for 7 days, in 1227 immunocompetent patients with herpes zoster. Main results were as follows: brivudin was superior to acyclovir in accelerating the "time to last formation of new vesicles" (primary parameter; risk ratio(ITT): 1.13, P=0.014). Equivalent effects of brivudin and acyclovir were observed for the secondary parameters "time to first crust" (RR(ITT): 0.93, P=0.004), "time to full crusting" (risk ratio(ITT): 1.03, P<0.001), and "time to loss of crusts" (RR(ITT): 0.95, P=0.002). The incidence of potentially treatment-related adverse events was similar under brivudin (7.7%) and acyclovir (10.0%). In conclusion, brivudin proved to be more effective than acyclovir in terminating vesicle formation, the parameter which reflects the end of viral replication, thus confirming, in the clinical setting, the greater in vitro antiviral activity of brivudin. Compared with acyclovir, brivudin provides a similar safety profile and a significant improvement in efficacy.

Antifungal and antiviral chemotherapy

Fungal and viral infections are difficult to treat, since fungal infections commonly rebound after suppression by the antifungal agent and current antiviral drugs are only virustatic, allowing the virus to reassert its pathogenicity if not eliminated by the host defenses. In addition, fungal infections commonly are associated with significant biofilms, retarding drug penetration, and the fluid nature of the oral cavity does not promote drug-fungus contact for long periods of time. Both mycotic and viral pathogens are developing sophisticated methods to elude the toxic effects of drugs intended to eliminate their existence. The drug therapy of oral fungal and viral infections is therefore limited but occasionally successful (more with fungal than viral infections) and is often relegated to palliative care. The specter of drug resistance and its promotion by prolonged, repetitive and frivolous use must always be foremost in the clinician's mind.

Structure-activity relationships of (E)-5-(2-bromovinyl)uracil and related pyrimidine nucleosides as antiviral agents for herpes viruses

A series of (E)-5-(2-bromovinyl)uracil analogues and related nucleosides was synthesized, and their antiviral activities were evaluated. (E)-5-(2-Bromovinyl)-2'-deoxy-L-uridine (L-BVDU, 2), 1-(beta-L-arabinofuranosyl)-(E)-5-(2-bromovinyl)uracil (L-BVAU, 4), (E)-5-(2-bromovinyl)-1-(2-deoxy-2-fluoro-beta-L-ribofuranosyl)uracil (L-FBVRU, 8) and (E)-5-(2-bromovinyl)-1-(2-deoxy-2-fluoro-beta-L-arabinofuranosyl)urac il (L-FBVAU, 10) were synthesized via appropriate 5-iodouracil analogues from L-arabinose. D- and L-Oxathiolane and -dioxolane derivatives 13, 16, 20, 21, and 29-34 were prepared by glycosylation reaction of the oxathiolane and dioxolane intermediates with silylated uracil analogues using TMSI as the coupling agent. The synthesized compounds were evaluated in cell cultures infected with the following viruses: varicella zoster virus (VZV), Epstein Barr virus (EBV), and herpes simplex virus types 1 and 2 (HSV-1 and HSV-2). Among the tested compounds, beta-L-CV-OddU (29), beta-L-BV-OddU (31), and beta-L-IV-OddU (33) exhibited potent in vitro antiviral activity against VZV with EC(50) values of 0.15, 0. 07, and 0.035 microM, respectively, and against EBV with EC(50) values of 0.49, 0.59, and 3.91 microM, respectively.

Synthesis and antiviral activity of 6-benzoyl-benzoxazolin-2-one and 6-benzoyl-benzothiazolin-2-one derivatives

The synthesis and antiviral activity of an original series of 6-benzoyl-benzoxazolin-2-one and 6-benzoyl-benzothiazolin-2-one derivatives are described. Several compounds were found to have a selective inhibitory activity against human cytomegalovirus (HCMV) and varicella-zoster virus (VZV) in vitro, being inactive against a variety of other DNA and RNA viruses. 6-(3-fluorobenzoyl)benzoxazolin-2-one, 6-(3-fluorobenzoyl)benzothiazolin-2-one, 6-(3-bromobenzoyl)benzothiazolin-2-one, 6-(3-iodobenzoyl)benzothiazolin-2-one, 3-methyl-6-(3-fluorobenzoyl)benzothiazolin-2-one, 3-benzyl-6-benzoyl-benzothiazolin-2-one, 3-benzyl-6-(3-fluorobenzoyl)benzothiazolin-2-one and 3-benzoyl-6-(3-fluorobenzoyl)benzothiazolin-2-one were the most active of the series against HCMV and VZV with a selectivity index (CC50/IC50) ranging from 10 to 20. They displayed similar activity against thymidine kinase competent (TK+) and deficient (TK-) VZV strains, and also proved to be active against clinical HCMV isolates that were resistant to ganciclovir (GCV). Time-of-addition experiments revealed a site of interaction with the HCMV replicative cycle that may be close or similar to that of GCV and cidofovir (HPMPC). The compounds showed poor, if any, activity against herpes simplex virus type 1 (HSV-1) and HSV-2, and were not inhibitory against human immunodeficiency virus and other DNA and RNA viruses. Therefore, these compounds may represent a novel lead for the development of specific HCMV and VZV drugs.

Acyclic nucleosides as antiviral compounds

Acyclovir is an effective drug for the treatment of HSV and VZV infections, which after phosphorylation to the triphosphate, inhibits viral DNA polymerase. Acyclovir has low oral bioavailability, therefore prodrugs have been developed, and the L-valyl ester, valaciclovir, recently has been licensed for the treatment of shingles. Ganciclovir is used against CMV, and famciclovir, a lipophilic prodrug of penciclovir, is marketed for shingles. The acyclic nucleoside phosphonates are active against thymidine kinase-resistant viral strains. Promising analogs are PMEA (in clinical trial for the treatment of AIDS) and (S)-HPMPC (good in vivo activity against HSV, VZV, CMV, and EBV). Oligonucleotides incorporating acyclic nucleosides at the 3'-and 5'-ends, or constituted of amino acyclic nucleosides, are resistant to cleavage by nucleases and may be useful in antisense and/or antigene therapy. HEPT is active against HIV-1: It binds in a hydrophic pocket on reverse transcriptase, rather than in the polymerase active site. Some acyclic nucleosides are potent inhibitors of purine and pyrimidine nucleoside phosphorylase. These compounds may have a therapeutic niche in combination therapy with antiviral and anticancer nucleosides, and in the treatment of diseases involving the T-cell.

Comparative activity of selected antiviral compounds against clinical isolates of varicella-zoster virus

Sixteen freshly isolated varicella-zoster virus (VZV) strains were evaluated in vitro, in parallel with two reference strains expressing a functional thymidine kinase (TK+) (Oka and YS) and two thymidine kinase-deficient mutants (TK-) (07-1 and YS-R), for their susceptibility to a broad range of antiviral compounds. The following compounds were included: acyclovir (ACV), brivudine (BVDU), sorivudine (BVaraU), other BVDU congeners such as BTDU, CTDU, CVDC and CVDU, ganciclovir (GCV), FIAC, araT, araA, araC, foscarnet (PFA), phosphonoacetic acid (PAA), the acyclic nucleoside phosphonates HPMPC, cHPMPC, HPMPA, cHPMPA, HPMPc3A, PMEA and PMEDAP, the N7-isomeric acyclic nucleoside analogue N7AP, penciclovir (PCV), compounds 882C87 and H2G and two oxetanocin derivatives OXT-A and OXT-G. Fourteen of the 16 clinical isolates displayed the following order of decreasing selectivity against VZV: BVaraU > BVDU > CVDU approximately CVDC > H2G > N7AP approximately CTDU approximately BTDU approximately OXT-G approximately 882C87 > ACV > FIAC approximately araT > HPMPC approximately cHPMPC approximately HPMPA approximately HPMPc3A approximately cHPMPA > PCV approximately GCV approximately OXT-A > PMEDAP approximately PMEA > PFA approximately PAA approximately araA > araC. Two VZV strains (isolated from the cerebrospinal fluid of an AIDS patient) that were shown to have a truncated TK were clearly resistant to all the compounds that need the viral TK for their phosphorylation, while sensitivity to the acyclic nucleoside phosphonates, PFA, PAA, OXT-A and araA, remained unchanged. A slight (5- and 10-fold) increase was noted in the 50% inhibitory concentration of N7AP and OXT-G, respectively, for the TK- VZV strains as compared to the TK+ VZV strains. Ganciclovir and FIAC also showed a marked decrease in their activity against these two strains, but this was not as pronounced as for the other viral TK-dependent drugs. From our results, it appears that although acyclic nucleoside phosphonates may not have as favourable a therapeutic index as drugs requiring the viral TK, they should be considered for the treatment of TK- VZV life-threatening infections that are resistant to the viral TK-dependent drugs.