Differential effects of acyclovir and 9-(1,3-dihydroxy-2-propoxymethyl)guanine on herpes simplex virus and Epstein-Barr virus in a dually infected human lymphoblastoid cell line

We investigated the effects of acyclovir and 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) on a lymphoblastoid cell line dually infected with Epstein-Barr virus and herpes simplex virus (HSV) type 1. The numbers of Epstein-Barr virus genomes were reduced during 70 days of treatment with either drug. Both drugs suppressed HSV replication in a dose-related manner. In the continued presence of the drugs, HSV developed resistance, rapidly to acyclovir and much more slowly to 30 microM DHPG. Analysis of HSV glycoprotein C production and viral DNA showed that treatment with 100 microM DHPG eliminated HSV production, curing the cell line of HSV persistent infection.

Acyclic guanosine analogs as inhibitors of human cytomegalovirus

The acyclic guanosine analogs R- and S-enantiomers of 9-(3,4-dihydroxybutyl)guanine [(R)- and (S)-DHBG], 9-(4-hydroxybutyl)guanine (HBG), and 9-(2-hydroxyethoxymethyl)guanine (ACV) were examined for their effects on human cytomegalovirus (CMV) replication and on CMV DNA synthesis in cell culture as well as for their ability as triphosphates to interact with CMV DNA polymerase. Production of early CMV antigens was not affected. All analogs inhibited CMV DNA synthesis and late viral antigen synthesis. Primary CMV isolates were less susceptible to all tested analogs than was the laboratory strain CMV Ad.169. The triphosphate of ACV was the most potent inhibitor of CMV DNA polymerase, with an observed Ki of 0.0076 microM. The corresponding Ki values of the triphosphates of (R)-DHBG, (S)-DHBG, and HBG were 3.5, 13.0 and 0.23 microM, respectively. All triphosphates of the analogs given above inhibited CMV DNA polymerase in a competitive manner with respect to dGTP. The triphosphates of the analogs also inhibited reactions when the synthetic template poly(dC)oligo(dG)12-18 was used, whereas no inhibition was observed with poly(dA)oligo(dT)12-18. None of the triphosphate analogs supported DNA synthesis in the absence of dGTP, showing that no analog was an alternative substrate to dGTP.

Treatment of cytomegalovirus retinitis in a patient with AIDS with 9-(1,3-dihydroxy-2-propoxymethyl)guanine

Asymptomatic retinal lesions were found on annual ophthalmic examination in a 38-year-old homosexual man with the acquired immune deficiency syndrome (AIDS). The lesions were compatible with cytomegalovirus retinitis and progressed. Treatment with 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) resulted in regression of the lesions and improvement in his overall clinical condition. The retinal lesions in AIDS are reviewed.

Synthesis and antiviral activity of various esters of 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine

The synthesis and in vivo biological activity of a series of mono-O-, di-O-, and N2-acyl derivatives of 9-[(1,3-dihydro-2-propoxy)-methyl]guanine (DHPG) are described.

2'-Nor-2'-deoxyguanosine is an effective therapeutic agent for treatment of experimental herpes keratitis

2'-Nor-2'-deoxyguanosine (2'NDG), previously reported by us to effectively treat acute herpes simplex infections in mice, was used therapeutically to significantly enhance healing of established herpetic corneal lesions and prevent stromal disease in rabbits. Treatment using 0.06% 2'NDG drops (5 times daily) starting 3 days after infection resulted in more rapid healing of corneal epithelial lesions, rapid resolution of conjunctival inflammation, and prevention of stromal clouding compared to placebo-treated animals. In comparative dose-response titrations, the relative potency of 2'NDG to acyclovir was 6.4, which was significant. In addition, soluble ophthalmic inserts were developed for delivery of 2'NDG. Once a day treatment using ophthalmic inserts which released 100 micrograms 2'NDG significantly enhanced corneal and conjunctival healing and prevented stromal disease; 2'NDG eye drops (100 micrograms) delivered once a day were also effective in inhibiting the progression of corneal lesions. These results indicate that 2'NDG may be therapeutically effective in treatment of herpes keratitis, and further suggest that for use as eye drops or in an ophthalmic insert, 2'NDG may be effective even if applied once per day.

Stereochemical considerations in the enzymatic phosphorylation and antiviral activity of acyclonucleosides. I. Phosphorylation of 2'-nor-2'-deoxyguanosine

The antiviral compound 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (2'-nor-2'-deoxyguanosine, 2'-NDG) is phosphorylated by the HSV-1-induced thymidine kinase to the monophosphate (2'-NDG-MP) and this is further phosphorylated by cellular kinases to the triphosphate (2'-NDG-TP) which is a potent inhibitor of DNA polymerases. Since phosphorylation of 2'-NDG creates a chiral center in the molecule, it was of interest to examine whether both monophosphate enantiomers were produced by the viral thymidine kinase, whether they both could be further phosphorylated by cellular kinases and, if so, whether the respective triphosphates were equally inhibitory to the DNA polymerases. The time course of the phosphorylation by GMP kinase of a chemically synthesized, racemic 2'-NDG-MP was compared to that of a 2'-NDG-MP preparation obtained by enzymatic phosphorylation of 2'-NDG with HSV-1 thymidine kinase. The results indicated that the two enantiomeric monophosphates were phosphorylated by GMP kinase with different rates and that phosphorylation of 2'-NDG by HSV-1 thymidine kinase gave only one of the isomers, whose structure was determined to be S. Both enantiomeric diphosphates were further phosphorylated to the respective triphosphates and it was shown that, in contrast to the triphosphate obtained from the 2'-NDG-MP prepared by viral thymidine kinase which was a potent inhibitor of HSV-1 DNA polymerase, the triphosphate obtained from the slow-reacting R isomer had little or no inhibitory activity against this enzyme.

Use of intravitreal ganciclovir (dihydroxy propoxymethyl guanine) for cytomegalovirus retinitis in a patient with AIDS

A patient with acquired immune deficiency syndrome with bilateral cytomegalovirus retinitis was treated with intravitreal 200-micrograms/0.1-ml doses of ganciclovir (9-[2-hydroxy-1-(hydroxymethyl) ethoxymethyl]guanine). The ganciclovir serum and intravitreal concentrations were measured with an enzyme-linked immunosorbent assay and pharmacokinetic factors were determined. There was no evidence of systemic absorption of ganciclovir from the eye. The elimination half-life of ganciclovir from the vitreous was estimated to be 13.3 hours. The intravitreal concentration remained above the ID50 of cytomegalovirus for approximately 62 hours after a single injection. Clinically, the patient retained useful vision in his right eye for three months. A total of 28 intravitreal injections were given on an outpatient basis under topical anesthesia and were well tolerated. There was no evidence of retinal toxicity from the drug.

Dihydroxypropoxymethyl guanine in the treatment of AIDS related retinitis due to cytomegalovirus

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Management of viral infections in AIDS patients

Viral infections, predominantly those of the herpes virus family, account for up to 16% of all clinically significant infections in AIDS patients. Acyclovir has provided successful treatment in AIDS patients suffering from severe herpes simplex and herpes zoster virus infections. Preliminary results are presented on newly developed acyclovir analogues. Desciclovir, an oral prodrug of acyclovir which is metabolized to acyclovir in vivo, allows treatment of virus infections per os, where high serum levels are needed, e.g. in Epstein-Barr virus infections. BW B759U, another analogue of acyclovir, has been used for the treatment of life-threatening or sight-threatening cytomegalovirus infections in AIDS patients. More than 80% of the patients treated for retinitis experienced stabilization or clinical improvement. Antiviral efficacy was demonstrated in 73% of the patients. Azidothymidine, a nucleoside analogue of thymidine, has been developed specifically to treat the HIV infection. Its antiviral activity is based on inhibition of reverse transcriptase. Phase I studies have demonstrated that azidothymidine is well tolerated. Its ability to cross the blood brain barrier makes it an attractive candidate for treatment of HIV. Trials to determine efficacy are in progress.

2'-nor-cGMP, a new cyclic derivative of 2'NDG, inhibits HSV-1 replication in vitro and in the mouse keratitis model

The present study examined the antiherpetic effect of 2'-nor-cGMP, a new cyclic phosphate derivative of 2'NDG, in vitro and in the mouse keratitis model. The 50% inhibitory dose (ID50) was determined with HSV-1 RE strain in Vero cell monolayers for 2'-nor-cGMP (6.9 mcg./ml), 2'NDG (.06 mcg/ml), and trifluridine (F3T) (.72 mcg/ml). Balb C mice underwent bilateral ocular inoculation with HSV-1 RE strain, and then were treated with different therapeutic regimens. The antiviral efficacy of each drug was evaluated by ocular virus titers, clinical grading of epithelial keratitis, and histological evaluation of stromal keratitis. 2'-nor-cGMP was the most effective drug (P = .0001) in reducing ocular viral titers. Both 2'-nor-cGMP and 2'NDG were significantly more effective (P = .0001) than F3T in reducing epithelial keratitis, and as effective as F3T in reducing stromal keratitis.

Chemotherapy of herpesvirus infections

The following paper is intended to review those nucleoside analogs currently licensed for the treatment of herpetic diseases. Potentially efficacious congeners also will be considered. The mechanism of action, preclinical and clinical efficacy, and the problems associated with the use of each nucleoside analog will be described.

Comparative efficacy of three 2'-fluoropyrimidine nucleosides and 9-(1,3-dihydroxy-2-propoxymethyl)guanine (BW B759U) against pseudorabies and equine rhinopneumonitis virus infection in vitro and in laboratory animals

The three 2'-fluoropyrimidine nucleosides 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (FIAC), 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU), and 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-methyluracil (FMAU), showed high activity in RK13 monolayers against equine rhinopneumonitis virus, (EHV-1, IC50 range 0.02-0.18 microM), Aujeszky's disease virus (SHV-1, pseudorabies, IC50 range 0.25-7 microM) and infectious bovine rhinotracheitis virus (1BR, BHV-1, IC50 range 0.1-3 microM). The activity of these compounds was compared with 9-(1,3-dihydroxy-2-propoxymethyl)guanine (BW B759U, DHPG) in two laboratory animal disease models: EHV-1-induced hepatitis in hamsters and SHV-1-induced encephalitis in mice. All the compounds, provided from 3 to 5 h pre-infection for 5 days, were effective in preventing EHV-1 mortality (at 3-5 mg/kg per day) and in significantly reducing SHV-1 mortality (at 60 mg/kg per day). While FIAU had the greatest activity in vitro, FMAU tended to be more potent in vivo. The reasons for these differences between relative in vitro and in vivo activities are briefly discussed.

Anti-herpes simplex virus (HSV) effect of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) in rabbit cornea

The anti-herpes simplex virus (HSV) effect and cytotoxicity of a new nucleoside analogue, 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) in rabbit cornea were studied. In tests of the anti-HSV effect of DHPG, even 0.03% ointment, given 5 times per day for 2 days, prevented lesion formation. The preventive effect of DHPG was much stronger than that of acyclovir (ACV) or 5-iodo-2'-deoxyuridine (IDU). In tests on the therapeutic effect of DHPG against dendritic ulcers, 0.3% ointment, given 5 times per day for 4 days, had a dramatic therapeutic effect. The effect was stronger than that of 3% ACV or 0.5% IDU ointment. Application of 0.3%, 1% or 3% DHPG ointment to normal rabbit corneas, 5 times per day for 2 weeks resulted in no histopathological abnormalities. The above results show that DHPG is superior to ACV or IDU for treatment of HSV infections.

Metabolism of desciclovir, a prodrug of acyclovir, in humans after multiple oral dosing

Desciclovir (DCV), a prodrug of the antiherpetic agent acyclovir (ACV), is converted in humans to ACV, presumably by xanthine oxidase. Further metabolism of these two compounds was investigated in six human volunteers given 250 mg DCV orally every eight hours for ten days plus one dose on day 11. The mean percent dose recovered in urine (24 hr) on days 2, 5, and 10 as carboxy-DCV (2%) and as carboxy-ACV (14%) along with recoveries of DCV (6%) and ACV (62%) gave a mean total of 84% cleared over a 24-hour period at steady state. Carboxyl metabolites were not found in the plasma of these same subjects at peak DCV concentration on dose day 11. The ratios of DCV and ACV to their corresponding carboxyl metabolites in urine were 4:1 and 3:1, respectively, suggesting that there is little or no difference in the efficiency of these two substrates for oxidation to their carboxylic acid metabolites.

Antiviral effect of 9-(1,3-dihydroxy-2-propoxymethyl)guanine against cytomegalovirus infection in a guinea pig model

The antiviral activity of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) against guinea pig cytomegalovirus (GPCMV) was evaluated in guinea pig cell cultures and in Hartley guinea pigs. The 50% effective dose of DHPG against GPCMV replication in cell cultures was 71 microM. Ultrastructural studies revealed that DHPG inhibited the formation of viral cores and the production of nucleocapsids, enveloped virions and dense bodies, but the drug did not prevent the formation of virus induced intranuclear tubular structures. In vivo, guinea pigs inoculated intraperitoneally with GPCMV were treated with DHPG, 25 mg/kg subcutaneously, twice daily. Treatment was initiated 24 h after infection and continued for 7 days. During the acute infection, the average body weights of DHPG-treated, virus infected guinea pigs were approximately 14% lower than the sham-treated counterparts on day 10, 11 and 13 post-virus inoculation. Virus infectivity titers were higher in the lungs of DHPG-treated guinea pigs on day 10 than the sham-treated ones. Although there was no significant difference on histopathologic lesions in the spleen, liver and lungs of the drug-treated and the sham-treated guinea pigs, DHPG treated animals appeared to have fewer virus-induced lesions or inclusions in the kidneys and salivary glands than the sham-treated ones. In addition, virus infectivity titers in the salivary gland of DHPG treated guinea pigs were consistently lower than the sham-treated animals.

Retinal toxicity of ganciclovir in vitrectomy infusion solution

The authors investigated the retinal toxicity of the antiviral agent ganciclovir after its addition to vitrectomy infusion fluid in rabbit eyes. Intravitreal infusion of the drug in concentrations up to 30 micrograms/ml produced no electroretinographic or histologic changes suggestive of retinal toxicity. Ganciclovir in vitrectomy infusion fluid has potential therapeutic benefit in viral retinitis (particularly in cytomegalovirus retinitis) associated with vitreous traction or rhegmatogenous retinal detachment. Based on the median inhibitory doses of ganciclovir against various herpes group viruses and the results of this study, a concentration of 30 micrograms/ml or less of the drug is recommended for vitrectomy infusion solution.

Intravitreal injection of liposome-encapsulated ganciclovir in a rabbit model

The authors determined the intravitreal clearance of liposome-encapsulated ganciclovir. Liposome-encapsulated ganciclovir (84.1 micrograms/0.1 ml) was injected into the vitreous cavity of New Zealand rabbits, which were killed at 24 hours and 7, 14, and 28 days after injection. Total ganciclovir concentrations in the vitreous, up to 28 days, were higher than ID50 (50% inhibitory dose) for different clinical and laboratory strains of viruses belonging to the herpes simplex family.

Phosphorylation of nucleoside analogs by equine herpesvirus type 1 pyrimidine deoxyribonucleoside kinase

Replication of equine herpesvirus type 1 (EHV-1) was sensitive to 9-(1,3-dihydroxy-2-propoxymethyl)guanine(DHPG) but relatively resistant to E-5-(2-bromovinyl)-2'-deoxyuridine (BVDU). Likewise, plaque formation by EHV-1 was inhibited by DHPG, but not by BVDU. Plaque formation by a thymidine kinase-negative (tk-) mutant of EHV-1 was not inhibited by DHPG. In order to investigate biochemical mechanisms determining the differential sensitivity of EHV-1 to these drugs, the EHV-1-encoded thymidine kinase enzyme activity (TK)1 was partially purified from EHV-1-infected cells and analyzed. The EHV-1-induced enzyme utilized both ATP and CTP as phosphate donors and differed in relative electrophoretic mobility from the TKs of mock-infected and HSV-1-infected cells. Phosphorylation of 3H-dThd by the EHV-1 TK was inhibited by AraT, IdUrd, BVDU, and DHPG. The EHV-1 TK phosphorylated 125I-dCyd and 3H-ACV. The results indicate that EHV-1 encodes a pyrimidine deoxyribonucleoside kinase with broad nucleoside substrate specificity. These observations suggest that the failure of BVDU to inhibit EHV-1 replication is not attributable to an inability of the EHV-1 TK to phosphorylate BVDU, but may result from the incapacity of the viral TK to convert BVDU monophosphate to the triphosphate or from lack of inhibitory effect of BVDU triphosphate on viral DNA polymerase reactions.

Kaposi's sarcoma of the conjunctiva and CMV-retinitis in AIDS

The number of AIDS patients is still increasing. In 30-50% of these patients ocular lesions occur, which are of diagnostic and prognostic significance. If the life-span of AIDS patients lengthens in the future, adequate treatment of the ocular conditions will become increasingly important. The two most important ocular manifestations AIDS are CMV-retinitis and Kaposi's sarcoma of the conjunctiva. DHPG, a new virustatic for human cytomegalovirus, appears promising as treatment for the severe CMV-retinitis, which leads rapidly to blindness. Two case histories illustrate the preliminary results obtained with DHPG treatment. Kaposi's sarcoma of the conjunctiva is relatively benign is AIDS and can be treated successfully by surgical excision, radiotherapy, cryotherapy or local injections of cytostatics.

Treatment of cytomegalovirus retinopathy in patients with acquired immunodeficiency syndrome. Use of the experimental drug 9-[2-hydroxy-1-(hydroxymethyl)ethoxymethyl]guanine

Cytomegalovirus (CMV) retinopathy, a relentlessly progressive disease that results in permanent blindness, is the most common opportunistic infection of the eye in patients with the acquired immunodeficiency syndrome. Twenty patients with the acquired immunodeficiency syndrome with CMV retinopathy were treated with a new, experimental, antiviral drug, 9-[2-hydroxy-1-(hydroxymethyl)ethoxymethyl]guanine (BW B759U), in dosages ranging from 5.0 to 14.0 mg/kg/d for a ten- to 20-day course. In 19 patients (95%), treatment halted the progression of infection and decreased retinal opacification, hemorrhage, and vasculitis. Vision remained stable in most cases. Six patients received no additional treatment. Fourteen patients received continued treatment with a lower maintenance dosage. Retinal disease reactivated in all patients who did not receive maintenance therapy immediately after initial treatment, indicating persistence of live virus despite drug therapy. Reactivation of disease also developed in four (40%) of ten patients receiving continuous, uninterrupted maintenance therapy for longer than three weeks. Reversible neutropenia, requiring cessation of treatment, developed in five (25%) of 20 patients on initial treatment and five (36%) of 14 patients receiving maintenance therapy. Rhegmatogenous retinal detachment was a late complication in four patients. BW B759U appears to be useful in the management of CMV retinopathy by reducing or delaying visual loss.

Ophthalmoscopic and histologic findings in cytomegalovirus retinitis treated with BW-B759U

Recent reports have suggested a role for BW-B759U in the treatment of cytomegalovirus retinitis. The present study presents the ophthalmoscopic features in three treated patients, and examines the microscopic findings in the eyes of the first patient ever treated with BW-B759U for cytomegalovirus retinitis. Ophthalmoscopic findings of improvement on drug therapy included remission of perivascular infiltration, stabilization of the extent of the retinal area involved, and development of a pigmented chorioretinal scar in the involved area. Relapses occurred with cessation of therapy, and repeated courses of therapy were required. One patient developed a rhegmatogenous detachment with retinal breaks in an atrophic area of treated retinitis. Electron microscopic examination of the eyes of one patient disclosed the persistence of cytomegalovirus inclusions in retinal cells despite previous drug therapy. These findings suggest a virostatic action for BW-B759U.

Effect of antiviral agents on replication of herpes simplex virus type 1 in brain cultures

An in vitro tissue culture system consisting of reaggregated embryonic brain cells was used to evaluate the inhibition of herpes simplex type 1 (HSV-1) by several antiviral compounds. The efficacy of acyclovir, vidarabine, bromovinyldeoxyuridine, and 9-(1,3-dihydroxy-2-propoxymethyl) guanine in HSV-1-infected Vero cell monolayer cultures was compared with that seen with brain cell aggregates. At a mean 50% inhibitory dose with Vero cells, acyclovir showed a 99% reduction of virus titer in brain cell aggregates. Vidarabine and 9-(1,3-dihydroxy-2-propoxymethyl) guanine gave a dose-dependent reduction in virus titer with Vero cells; however, in aggregate cultures treated with the same drugs a dose-dependent decrease at 24 h was followed by an increase to a point of no inhibition at 72 h postinfection. Pretreatment of brain cell aggregates with a hybrid human leukocyte interferon (Le IF-AD) reduced virus titers at 48 h postinfection but did not maintain this reduction at 72 h. In contrast, infected Vero cell monolayer cultures demonstrated a dose-dependent reduction in virus titers with Le IF-AD. Postinfection treatment with Le IF-AD did not reduce plaque formation in Vero cells but was effective in reducing virus titer in HSV-1-infected brain cell aggregates at 48 h postinfection. Antiviral concentrations of up to 200 micrograms or 200,000 IU/ml for interferon did not appear morphologically toxic to brain cells. Antiviral therapy of HSV-1-infected brain cell aggregates may more closely mimic in vivo responses than monolayer cultures.

Metabolic activation of 9([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine in human lymphoblastoid cell lines infected with Epstein-Barr virus

9-([2-Hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine (BW B759U) is more potent and has a more prolonged inhibitory effect against Epstein-Barr virus (EBV) in vitro than does acyclovir (ACV). To assess the mechanism of this difference, we first compared the extent of phosphorylation of the two drugs in superinfected Raji cells. BW B759U is phosphorylated to levels 100-fold higher than is ACV. In addition, lower levels of phosphorylation of BW B759U and ACV were observed in uninfected Raji cells. Studies on the kinetics of formation of BW B759U triphosphate in superinfected Raji cells indicated that drug-phosphorylating activity was detected as early as 3 h after superinfection; this activity was steadily maintained for the first 7 h, followed by a burst of activity between 7 and 10 h and a doubling of phosphorylation between 10 and 25 h. During the superinfection cycle, the pool sizes of deoxyribonucleoside and ribonucleoside triphosphates were increased and reached their maxima at 10 h after infection. The maximal amount of triphosphorylated drug in a virus producer cell, P3HR-1 (LS), was obtained at 21 h after drug treatment. During long-term drug treatment, approximately 44 and 77% reduction in EBV genome copies per cell was observed on days 3 and 7, respectively. In a separate experiment, after treatment of P3HR-1 (LS) cells with BW B759U for 36 h, 4.2 pmol of BW B759U triphosphate per 10(6) cells was achieved. After the cells were released into drug-free medium, drug triphosphate was rapidly decreased to 11% of the original level in 1 day. Thereafter, the decrease was slow but steady, down to 0.22 pmol/10(6) P3HR-1 cells by 5 days. We calculated that 0.22 pmol of BW B759U triphosphate per 10(6) cells represents a cellular concentration of 0.22 microM, which is theoretically enough to inhibit EBV replication. This is based upon a comparison with the 50% effective dose of BW B759U (0.05 microM) for inhibition of genome replication and a Ki of 0.08 microM for BW B759U triphosphate inhibition of EBV DNA polymerase.