Stability of ganciclovir sodium (DHPG sodium) in 5% dextrose or 0.9% sodium chloride injections

The stability of 9-[(1,3-dihydroxy-2-propoxymethyl]) guanine sodium (ganciclovir sodium, also known as DHPG sodium) in two infusion solutions was studied. Lyophilized ganciclovir sodium 500 mg was reconstituted with sterile water 10 mL to give a theoretical concentration of 50 mg/mL. After reconstitution, 6-mL aliquots of the solution were added to 100 mL of 0.9% sodium chloride injection or 5% dextrose injection in polyvinyl chloride i.v. bags. One sample was withdrawn from each of 10 bags of each solution and analyzed by high-performance liquid chromatography (HPLC). Thirty bags of each solution were then stored under each of the following conditions: at room temperature under laboratory light, at room temperature in the dark, and under refrigeration for up to five days. Single potency assays were performed by HPLC on each of three bags of solution at three and five days after initial dilution of the solutions. The solutions were visually inspected, and the pH of the solutions was measured. All solutions of ganciclovir were stable for at least five days under all storage conditions; mean ganciclovir concentrations did not drop below 98% of initial theoretical values throughout the storage period. No important changes in the pH of the solutions occurred during the study period. Under the conditions of this study, ganciclovir sodium is stable for up to five days when prepared in 5% dextrose injection or 0.9% sodium chloride injection.

Antiviral therapy with ganciclovir for cytomegalovirus retinitis and bilateral exudative retinal detachments in an immunocompromised child

A child with bilateral cytomegalovirus (CMV) retinitis, vitritis, and exudative retinal detachments, who was in remission from stage IV neuroblastoma and status post-chemotherapy and autologous bone marrow transplantation, was treated with ganciclovir. The drug is a new acyclic nucleoside antiviral drug with potent antiCMV activity. There was bilateral retinal reattachment, clearing of vitritis and regression of retinal exudates and hemorrhages, with concomitant resolution of viral shedding in urine and blood, on ganciclovir 7.5 mg/kg per day. There was recurrence of exudative detachments, vitritis and retinitis when the dose was reduced to 2.5 mg/kg per day, and regression of these findings when the dose was again increased to 7.5 mg/kg per day. Despite continued therapy at this dose, a relapse occurred. When the dose of drug was doubled to 15 mg/kg per day, there initially was a partial therapeutic response, followed by a subsequent relapse. No further response was seen when the dose was increased to 19.5 mg/kg per day. This patient was treated with ganciclovir for a total of 192 days. No adverse reactions to ganciclovir were seen. On the last day of drug administration, there were persistent bilateral exudative retinal detachments and progressive optic nerve head involvement with optic disc pallor, despite quiescence of the retinitis.

A human cytomegalovirus mutant resistant to the nucleoside analog 9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine (BW B759U) induces reduced levels of BW B759U triphosphate

We have isolated a human cytomegalovirus mutant that is resistant to the antiviral drug 9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine (BW B759U), yet exhibits wild-type sensitivity to inhibitors of herpesvirus DNA polymerases such as phosphonoformic acid and aphidicolin. Cells infected with the mutant accumulate approximately equal to 1/10th the amount of drug triphosphate as do those infected with the wild-type parent. This reduction in drug triphosphate could not be attributed to altered drug uptake or to reduced stability of the triphosphate, once formed. The induction of normal nucleoside and deoxynucleoside triphosphates and certain cellular nucleoside kinases was comparable in mutant and wild-type virus infections. These results provide strong evidence for the importance of phosphorylation in the selectivity of this antiviral compound and raise the possibility that human cytomegalovirus encodes a nucleoside kinase. The mutant may identify the existence of a cytomegalovirus function whose properties could facilitate genetic analysis of this important pathogen.

Mode of action, toxicity, pharmacokinetics, and efficacy of some new antiherpesvirus guanosine analogs related to buciclovir

9-[4-Hydroxy-3-(hydroxymethyl)butyl]guanine (3HM-HBG), (RS)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine ([+/-]2HM-HBG), and cis-9-(4-hydroxy-2-butenyl)guanine (2EN-HBG), new acyclic guanosine analogs structurally related to buciclovir (BCV [(R)-9-(3,4-dihydroxybutyl)guanine]), were evaluated in parallel with buciclovir as anti-herpes simplex virus (HSV) agents. In cell cultures, replication of different strains of HSV type 1 (HSV-1) and HSV-2 was inhibited at nontoxic drug concentrations. The concentrations giving 50% inhibition of plaque formation were, however, dependent on virus strain and cell type. In most cell types, the order of activity against HSV-1 strains was 3HM-HBG greater than (+/-)2HM-HBG greater than BCV greater than 2EN-HBG, whereas the drugs showed an approximately equivalent activity against HSV-2 strains in different cells. The cytotoxic effects of the drugs were also cell type dependent, the order of activity being BCV greater than 3HM-HBG = (+/-)2HM-HBG greater than 2EN-HBG. At growth-inhibitory concentrations, the guanosine analogs BCV, 3HM-HBG, and (+/-)2HM-HBG showed clastogenic effects in human lymphocytes, mainly because of the induction of chromatid breaks. When evaluated for their anti-HSV effects in systemic HSV-1 infections in mice, the order of activity was BCV = 3HM-HBG greater than (+/-)2HM-HBG greater than 2EN-HBG, and in mice infected systemically with HSV-2, only BCV and 3HM-HBG showed efficacy. The differences between efficacy in vitro and in vivo could be explained in part by differences in kinetics of the drugs in mouse plasma, as the more efficacious drugs, BCV and 3HM-HBG, showed lower clearances and longer half-lives than the less efficacious ones, (+/-)2HM-HBG and 2EN-HBG. When used topically against a cutaneous HSV-1 infection in guinea pigs, 3HM-HBG showed an effect equivalent to that of BCV, whereas (+/-)2HM-HBG and 2EN-HBG were inactive. Mechanistically, the guanosine analogs were characterized by a high affinity for the viral thymidine kinase and a low affinity fo a cellular thymidine kinase and by their inhibition of viral DNA synthesis in infected cells.

Tumor chemosensitivity conferred by inserted herpes thymidine kinase genes: paradigm for a prospective cancer control strategy

The lack of highly exploitable biochemical differences between normal tissues and some tumors can theoretically be circumvented by a strategy utilizing gene insertion prophylactically to create tissue mosaicism for drug sensitivity, thereby ensuring that any tumor arising clonally will differ from part of the normal cell population. Elements of the strategy were tested with neoplastic BALB/c murine cell lines bearing the herpes thymidine kinase gene. Exposure to the herpes thymidine kinase-specific substrate 9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine ablated the clonogenic potential of the cells in vitro, and administration of this drug to BALB/c mice bearing tumors produced by the cell lines uniformly induced complete regression of the tumors. The observed responses to therapy imply that the strategy may prove valuable when the genetic technology needed for its human implementation becomes available.

A515U: a prodrug of acyclovir with increased oral bioavailability

The tolerance and pharmacokinetics of A515U, a xanthine oxidase-activated prodrug of acyclovir have been investigated in healthy volunteers and in two phase-I clinical studies in immunocompromised patients. In all cases the bioavailability of acyclovir following oral administration of A515U was substantially increased over that achieved in the same subjects with oral acyclovir itself. Plasma acyclovir levels were similar to those previously attainable only with intravenous acyclovir. This increase in bioavailability may permit reductions in the frequency of administration and extend the range of herpes virus infections amenable to oral therapy. A515U was very well tolerated, with no significant clinical adverse events being attributed to the drug.

Respiratory pharmacology. Antiviral agents

In summary, there are numerous clinically useful antiviral agents currently available, with many more investigational drugs on the horizon. The future of antiviral chemotherapy looks bright, and the principles behind successful therapy will remain the same. It is hoped that with the advent of effective therapy, improved rapid viral diagnosis and early treatment of patients will be possible to maximize beneficial effects.

Human pharmacokinetics of the antiviral drug DHPG

The pharmacokinetics of the antiviral drug 9-[2-hydroxy-1-(hydroxymethyl) ethoxymethyl]guanine (DHPG) were examined in six patients receiving 2.5 or 5.0 mg/kg every 8 or 12 hours for human cytomegalovirus (HCMV) pneumonitis or retinitis. Biexponential decay with a mean distribution t1/2 of 0.23 hours and terminal t1/2 of 2.53 hours was observed. Total clearance correlated well with and exceeded creatinine clearance by a factor of 2.4. Mean volume of the central compartment was 15.26 L/1.73 m2 and the volume of distribution at steady state was 32.8 L/1.73 m2. Peak (model predicted) and trough plasma concentrations were 4.75 to 6.20 micrograms/ml and less than 0.25 to 0.63 microgram/ml, respectively, in patients receiving 2.5 mg/kg. Peak concentrations are well above those needed to inhibit HCMV at the 50% level (ID50) and troughs are near this ID50. Cerebrospinal fluid concentrations of DHPG indicate a penetration of 24% to 67%. No accumulation of DHPG was apparent in these patients. However, dosage reduction is necessary in renal insufficiency. Neutropenia occurred in one patient. The plasma concentration profile of DHPG suggests potential beneficial activity against HCMV.

Mutation within the herpes simplex virus DNA polymerase gene conferring resistance to (R)-9-(3,4-dihydroxybutyl)guanine

Five herpes simplex virus mutants known or presumed to contain mutations in their DNA polymerase genes conferring resistance to acyclovir and arabinosyladenine also proved to exhibit some degree of resistance to (R)-9-(3,4-dihydroxybutyl)guanine (buciclovir). For one mutant, a buciclovir resistance mutation was mapped to a region of the viral DNA polymerase gene proposed to encode the deoxynucleoside 5'-triphosphate binding domain. These data implicate the viral polymerase as a target of buciclovir action that contributes to its antiviral selectivity.

Synthesis and anti-herpes-virus activity of acyclic 2'-deoxyguanosine analogues related to 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine

Several "sugar" modified acyclic nucleoside analogues related to 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (DHPG, 2) were synthesized and evaluated for antiviral activity. The preparation generally involved the condensation of the acetoxymethyl ether of alcohols 6c-g and 10-12a with diacetylguanine to give adducts 7c-g and 14-16, which were then deprotected to afford analogues 9c-g and 17-19. Alternatively, alcohols 12a and 13a were converted to iodides via their tosylates 12b and 13b and then reacted with the sodium salt of guanine to afford, after deprotection, analogues 22 and 23. A crossed aldol-Cannizzaro reaction on aldehyde 27 readily afforded 28, which was deprotected to give analogue 29. An in vitro assay against HSV-1 showed that all compounds tested were less active than DHPG, though several were good substrates for the viral thymidine kinase. The more promising acyclic nucleosides 9c, 19, and 29 were evaluated in a mouse encephalitis model and proved ineffective at preventing death at a dose of 20 mg/kg.

In vitro and in vivo activities of phosphate derivatives of 9-(1,3-dihydroxy-2-propoxymethyl)-guanine against cytomegaloviruses

The anti-cytomegalovirus activities of four phosphate derivatives of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) were evaluated against human, monkey and murine viruses. The 5'-mono-, 3'5'-bis(mono-), and 3',5'-cyclic monophosphate and 5'-homophosphonate forms of DHPG inhibited virus plaque formation at 1-15 microM. The cyclic phosphate and homophosphonate were more active than the other compounds against murine cytomegalovirus (MCMV) in vitro. In an in vivo MCMV infection model, DHPG homophosphonate and DHPG were equally effective at reducing mortality at greater than or equal to 10 mg/kg. The cyclic phosphate was active at 10-20 mg/kg but toxic at greater than or equal to 40 mg/kg. The phosphorylation of DHPG phosphate and DHPG phosphonate, as well as the inhibition of human cytomegalovirus DNA polymerase by their respective triphosphates, were also examined.

Successful treatment of murine cytomegalovirus disease does not prevent latent virus infection

9-(1,3-Dihydroxy-2-propoxymethyl)guanine (DHPG), a nucleoside analogue, inhibits the replication of human and murine cytomegalovirus (MCMV) in cell culture. We studied the effects of treatment with DHPG on acute MCMV infection in mice and assessed the impact of drug therapy on the eventual development of latent viral infection. In virus-susceptible Balb/c mice, DHPG treatment limited dissemination of virus infection and prevented death. In sublethal infection of both Balb/c and virus-resistant C3H/St mice, DHPG prevented recovery of infectious virus from visceral organs, including the spleen. Despite these effects of drug treatment on virus replication during acute infection, latent MCMV could be reactivated in vivo by immunosuppression and in vitro by spleen explantation in virtually all mice. These results indicate that successful treatment of MCMV infection and marked suppression of viral replication do not prevent establishment of viral latency.

Galactosylated poly(L-lysine) as a hepatotropic carrier of 9-beta-D-arabinofuranosyladenine 5'-monophosphate

D-Galactopyranosyl residues were coupled to poly(L-lysine) and the antiviral agents arabinofuranosyladenine 5'-monophosphate (ara-AMP) and acyclovir were conjugated with this glycosylated polymer. In mice the ara-AMP conjugate accomplished a selective drug delivery to liver cells.

Intraocular 9-([2-hydroxy-1-(hydroxymethyl) ethoxy] methyl) guanine levels after intravitreal and subconjunctival administration

Clearance studies in rabbits following intravitreal injection of 400 micrograms of 9-([2-Hydroxy-1-(hydroxymethyl)ethoxy]methyl) guanine demonstrated levels of the antiviral at 60 hours above the in vitro ID50 for several strains of human cytomegalovirus. Intravitreal administration of this new antiviral may have therapeutic application in the treatment of acute retinal necrosis and cytomegalovirus retinitis complicating acquired immune deficiency syndrome (AIDS).

Water soluble complexes of the antiviral drugs, 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine and acyclovir: the role of hydrophobicity in complex formation

We investigated water-soluble complexes of various ligands with the antiviral drugs, 9-[(2-hydroxyethoxy)methyl]guanine (acyclovir) and 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (DHPG). For comparison, we also examined the "parent" compounds, guanine and guanosine, as substrates for complex formation. Using the phase-solubility technique, we measured formation constant (K1) values at 23 degrees C in pH 7 buffer. For a single substrate, formation constants with different ligands varied in the order: caffeine greater than pyridoxine approximately cytidine greater than nicotinamide greater than sucrose. With caffeine as the ligand, formation constants with different substrates varied in the order: guanine greater than guanosine approximately acyclovir greater than DHPG. The largest formation constant observed was 58 M-1 (for guanine-caffeine), and the smallest formation constant was 0.29 M-1 (for DHPG-sucrose). Examining the literature for formation constant data on compounds related to DHPG, and comparing literature data with our own, reveals a significant correlation between formation constants and ligand hydrophobicity. For 41 substrate-ligand pairs, least squares linear regression analysis of log K1 values versus various parameters reflecting donor-acceptor abilities (e.g., substrate and ligand HOMO and LUMO values, or substrate oxidation potentials) failed to significantly correlate. We conclude that ligand hydrophobicity is a general determinant of water soluble complex formation, but not necessarily the exclusive or dominant controlling factor for all complexes. Charge-transfer interactions are not important determinants of complex formation for the substrate-ligand combinations that we have considered.

Comparison of the modes of antiviral action of 2'-nor-deoxyguanosine and its cyclic phosphate, 2'-nor-cyclic GMP

The metabolisms of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (2'NDG) and its cyclic phosphate, 9-[(2-hydroxy-1,3,2-dioxophosphorinan-5-yl) oxymethyl]guanine P-oxide (2'-nor-cGMP), were compared in cultures of primary rabbit kidney cells infected with herpes simplex virus type 1 (HSV-1). 2'-Nor-cGMP was taken up by the cells essentially intact, after which it was opened to the acyclic monophosphate and phosphorylated further, ultimately to the triphosphate. Formation of the triphosphate was independent of HSV thymidine kinase expression, unlike what is observed with 2'NDG. In addition, there was a direct correlation between the antiviral activity of 2'NDG and the level of triphosphate formed in HSV-1-infected cells, whereas such a correlation was absent with 2'-nor-cGMP. In vivo experiments indicated that only a small percentage of free 2'NDG was formed in the bloodstream of mice after oral administration of 2'-nor-cGMP. Incubation of 2'-nor-cGMP with crude extracts of HSV-1-infected or uninfected HeLa cells resulted in the direct production of 2'NDG triphosphate. The possibility that the triphosphate of 2'NDG produced from 2'-nor-cGMP was the enantiomer of the triphosphate made from 2'NDG by viral and cellular kinases was investigated and disproved. Taken together, these data indicate that (i) 2'-nor-cGMP does not act simply as a prodrug of 2'NDG, (ii) 2'-nor-cGMP does not require viral thymidine kinase for its activity, and (iii) 2'-nor-cGMP may have an additional, triphosphate-independent mode of action.

Inhibition of herpes simplex virus-induced DNA polymerases and cellular DNA polymerase alpha by triphosphates of acyclic guanosine analogs

The triphosphates of the antiherpes acyclic guanosine analogs (R)- and (S)-enantiomers of 9-(3,4-dihydroxybutyl)guanine [BCVTP and (S)-DHBGTP], 9-(4-hydroxybutyl)guanine (HBGTP), and 9-(2-hydroxyethoxymethyl)guanine (ACVTP) were investigated for their effects on partially purified DNA polymerases of herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2) as well as cellular DNA polymerase alpha of calf thymus and Vero cells. The triphosphates of the four analogs were all competitive inhibitors when dGTP was the variable substrate with both the viral and the cellular DNA polymerases with activated calf thymus DNA or poly(dC)oligo(dG)12-18 as template. No inhibition was observed with deoxythymidine 5'-triphosphate as substrate and poly(dA)oligo(dT)12-18 as template. All analogs were preferential inhibitors of the viral DNA polymerases. Ordering the compounds according to their decreasing binding affinities, as reflected by their increasing inhibition constants for the viral DNA polymerases, gave ACVTP greater than HBGTP greater than BCVTP greater than (S)-DHBGTP. The DNA polymerase from the HSV-1 mutant, CI(101)P2C5, resistant to ACV, showed a stronger decrease in sensitivity for ACVTP and HBGTP than for BCVTP compared to the effects on DNA polymerase from the wild-type strain CI(101). The analogs were not able to support DNA synthesis in the absence of the competing substrate dGTP. A decrease in the ability of calf thymus DNA to serve as primer template for HSV-2 DNA polymerase was observed after preincubation with the triphosphates of the acyclic guanosine analogs. The analogs showed a progressive inhibition of the HSV-2 DNA polymerase activity with incubation time, and the inhibition could be reversed by high concentrations of dGTP both with and without addition of fresh enzyme or fresh template. However, no reversion was obtained when fresh enzyme or template was added if dGTP was omitted. The data indicate that these analogs inhibited the DNA polymerases by a similar mechanism and that the inhibition was reversible.