In vitro susceptibility of varicella zoster virus to adenine arabinoside and hypoxanthine arabinoside

Synthesis of Some Novel Dialkyl Phosphate Derivatives of 3′-Modified Nucleosides as Potential Anti-AIDS Drugs

The reaction of thymidine with diethyl, dipropyl, and dibutyl phosphorochloridates yields novel 5′-(dialkyl phosphates), characterized by spectroscopic and analytical data. These are readily mesylated at the 3′-position. Similar reaction of 3′- O-acetyl and 3′- O-ethyl thymidine with dialkyl phosphorochloridates gives an analogous series of compounds. Lastly, reaction of the anti-AIDS drug AZT with these phosphorylating agents gives the corresponding 3′-azido products. It was hoped that these might act as membrane-soluble pro-drugs of the bio-active free nucleotides of AZT and that the alternative 3′-substituents might also confer similar activity. In fact, none of the compounds studied displayed any anti-HIV activity in vitro. This is attributed to the metabolic stability of the trialkyl phosphate moiety.

Novel Sensitivity of Acyclovir-Resistant Varicella–Zoster Virus to Anti-Herpetic Drugs

Acyclovir-resistant varicella–zoster virus (VZV) selected in the presence of acyclovir was 3–20 times more sensitive to nucleoside analogues with arabinosyl configuration than the parent virus. Their sensitivity in comparison with a thymidine kinase-deficient mutant to anti-herpetic drugs and sensitivity to phosphonoacetic acid suggested that recognition by altered mutants' DNA polymerase might result in their novel sensitivity to nucleoside analogues. Information on the unique sensitivity of these acyclovir-resistant mutants may be useful in designing chemotherapeutic agents against VZV.

Synthesis and anti-HIV Activity of Some Novel Substituted Dialkyl Phosphate Derivatives of AZT and ddCyd

The reaction of thymidine, AZT (Fig. 1, compound 1) and ddCyd (Fig. 1, compound 2) with bis(2,2,2-trichloroethyl) phosphorochloridate gave novel 5′-bis(2,2,2-trichloroethyl) phosphates, characterized by spectroscopic and analytical data. Analogous reactions with bis(2,2,2-trifluoroethyl) phosphorochloridate gave the corresponding AZT and ddCyd derivatives. In both of the ddCyd reactions, by-products were isolated and characterized as O5′, W4-diphosphorylated materials. It was hoped that the 5′-phosphate triesters might act as membrane-soluble pro-drugs of the bio-active free nucleotides of AZT or ddCyd. In fact, all of the 5′-phosphate derivatives of AZT and ddCyd displayed anti-HIV activity in vitro. Surprisingly, the thymidine compound also displayed very slight anti-HIV activity. The striking activity of the AZT and ddCyd derivatives is attributed to the metabolic instability of the substituted trialkyl phosphate moiety.

Synthesis and Evaluation of Some Novel Phosphoramidate Derivatives of 3′-Azido-3′-Deoxythymidine (AZT) as Anti-HIV Compounds

A series of monophosphate triester derivatives of 3′-azido-3′-deoxythymidine (AZT), designed as membrane-soluble pro-drugs of the nucleotide (AZTMP), have been tested for activity against the human immunodeficiency virus (HIV-1). It has been found that when carboxyl-protected, amino-linked amino acids, and alkyl chains, are asymmetrically substituted on the 5′-phosphate a significant antiviral effect is observed. Moreover, the activity of the compounds is profoundly dependent on the structure of the phosphate moiety, and in particular on the nature of the amino acid.

Inhibitory action of acyclovir (ACV) and penciclovir (PCV) on plaque formation and partial cross-resistance of ACV-resistant varicella-zoster virus to PCV

Penciclovir has potent antiviral activity against varicella-zoster virus (VZV). We have characterized the inhibitory effects of penciclovir and acyclovir on the plaque formation of cell-free VZV and cross-resistance of acyclovir-resistant VZV to penciclovir. The apparent effective concentration for 50% plaque reduction (EC50) of penciclovir determined on the third day was significantly lower than that determined on the fourth or fifth day. The size of plaques was smaller in the presence of penciclovir than in the presence of acyclovir. The effective concentrations for 50% reduction of the number of infected cells per plaque were 1.40 and 5.00 micrograms/ml for penciclovir and acyclovir, respectively. Thus penciclovir suppressed spread of infection within developing plaques more efficiently than acyclovir. Five acyclovir-resistant VZV strains with altered DNA polymerase selected by acyclovir were examined for cross-resistance to penciclovir. They were 11- to 18-fold more resistant to ACV than the parent strain, but only 4- to 5-fold more resistant to PCV. Penciclovir-triphosphate carrying the 3'-hydroxyl group of 2'-deoxyribose might have better affinity to the altered viral DNA polymerase than acyclovir-triphosphate without the 3'-hydroxyl group.

Comparison of antiviral assay methods using cell-free and cell-associated varicella-zoster virus

Assay methods for varicella-zoster virus (VZV) susceptibility to acyclovir (ACV) of VZV were compared by using cell-free (CF) and cell-associated (CA) virus of 6 x plaque-purified VZV. The 50% effective doses (ED50) of ACV, as required to reduce virus plaque formation by 50%, were about 8 times higher for CA virus than for CF virus. Also, the ED50 of 1-beta-D-arabinofuranosyl-(E)-5-(2-bromovinyl)uracil (BVaraU) for CA-VZV was higher than for CF-VZV, and fresh clinical isolates of VZV gave higher ACV ED50 values than CF virus. CA virus prepared at various times after CF virus infection showed a gradual increase of the ACV ED50 with time, ranging from the ED50 for CF virus to that for CA virus.

Synthesis and evaluation of some novel phosphate and phosphinate derivatives of araA. Studies on the mechanism of action of phosphate triesters

A number of novel phosphinate and phosphate triester derivatives of the anti-viral nucleoside analogue araA have been prepared. Spectroscopic and analytical data have been collected on both the reagents and the nucleotides. An in vitro assay indicated inhibition of DNA synthesis by mammalian cells, by each of the nucleotide derivatives, in the range 3-30 microM. Inhibition was reduced, but not abolished, for the phosphinates relative to the phosphates. These results are consistent with a mode of action involving release of the free nucleoside araA and the nucleotide araAMP.

Synthesis and biological evaluation of some phosphate triester derivatives of the anti-viral drug AraA

A number of novel phosphate triester derivatives of the anti-viral nucleoside analogue araA have been prepared by a rapid 2-step procedure, not necessitating prior sugar protection. Spectroscopic and lipophilicity data have been collected on these compounds, and they have been assayed with a range of hydrolytic enzymes. The compounds have been found to be highly resistant to hydrolysis at physiological pH, enzymatic or otherwise. An in vitro assay indicated inhibition of DNA synthesis by mammalian cells, by each of these compounds, in the range 3-300 microM. Moreover, the degree of inhibition showed a close correlation to chemical structure; in particular, there was a direct relationship between inhibition of thymidine incorporation and lipophilicity. These results suggest cellular penetration by the phosphate triesters and intracellular hydrolysis, by an unspecified mechanism, to the free nucleotide or nucleoside.

Evaluation of varicella-zoster antiviral drugs by a nucleic acid hybridization assay

A simple nucleic acid hybridization assay was developed for the evaluation of antiviral compounds with activity against varicella-zoster virus. Antiviral-induced reduction in varicella-zoster virus DNA, as measured by hybridization with 32P-labeled probes, correlated with drug-induced inhibition of viral cytopathic effect in cell culture. Three compounds were shown to be more potent than acyclovir at inhibiting varicella-zoster virus in vitro.

Antiviral and antimetabolic activities of neplanocins

Of a series of carbocyclic analogs of adenosine, in which the ribose moiety was replaced by a cyclopentenyl ring, neplanocin A, or (-)-9-[trans-2, trans-3-dihydroxy-4-(hydroxymethyl)cyclopent-4-enyl]adenine proved particularly effective in inhibiting the multiplication of DNA viruses (i.e., vaccinia), (-)RNA viruses (i.e., parainfluenza, measles, and vesicular stomatitis), and double-stranded RNA viruses (i.e., reo) in vitro in cell culture. Depending on the cells used, the MIC of neplanocin A for these viruses ranged from 0.01 to 4 micrograms/ml, and depending on the parameter used to assess toxicity for the host cell, the specificity index of neplanocin A ranged from 50 to 4,000. As postulated before for other adenosine analogs, neplanocin A may owe its antiviral action to inhibition of S-adenosylhomocysteine hydrolase, hence perturbation of transmethylation reactions. In vivo, neplanocin A afforded only marginal protection against a lethal infection of mice with vesicular stomatitis virus.

Susceptibility of vaccine strains of varicella-zoster virus to antiviral compounds

Using a plaque reduction assay, we determined the 50% effective doses of six antiviral compounds against low- and high-passage viruses of the KMcC and Oka strains of varicella-zoster virus vaccine. The potency, as indicated by the ranges of 50% effective doses (micrograms per milliliter) of the antiviral compounds, in decreasing order was as follows: (E)-5-(2-bromovinyl)-2'-deoxyuridine, 0.0007 to 0.0035; 1-(2'-flouro-2-deoxy-beta-D-arabinofuranosyl)-5-iodocytosine, 0.0063 to 0.0091; aphidicolin, 0.092 to 0.180; acyclovir, 0.79 to 1.81; vidarabine, 0.62 to 2.10; and phosphonoformic acid, 8.18 to 16.4. Susceptibility to the various antiviral compounds was independent of passage level or strain. These data, along with the available in vivo data, indicate that varicella-zoster virus vaccine infections requiring antiviral therapy most probably would be treated as effectively as would natural varicella infections.

Comparative use of adenine arabinoside and adenine arabinoside monophosphate in varicella and disseminated zoster in immunosuppressed patients

Adenine arabinoside monophosphate (ARA AMP) was used in ten immunosuppressed patients suffering from varicella or disseminated zoster, and compared to adenine arabinoside (vidarabine) in ten other similar patients. Good results were obtained with both drugs: the fever stopped suddenly in three or four days and no new vesicles were observed after the third day. ARA AMP is more soluble than vidarabine and is thus easier to handle; it could be an effective treatment of severe varicella-zoster virus infections in immunosuppressed patients.

In vitro susceptibility of varicella-zoster virus to E-5-(2-bromovinyl)-2'-deoxyuridine and related compounds

The in vitro susceptibility of eight strains of varicella-zoster virus (VZV) to E-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) was examined in human embryonic fibroblasts by the following techniques: inhibition of focus formation by either cell-free VZV (4-day assay) or cell-associated VZV (2-day assay), inhibition of viral antigen formation (2-day assay), and inhibition of viral cytopathogenicity (15-day assay). The 50% inhibitory dose (ID50) of BVDU ranged from 0.001 microgram/ml (2-day assay) to 0.01 microgram/ml (15-day assay). BVDU appeared highly selective in its anti-VZV activity since even at concentrations as high as 100 micrograms/ml, BVDU did not markedly affect the viability of the host cells. The ID50 of BVDU for VZV was comparable to that of IVDU (E-5-(2-iodovinyl)-2'-deoxyuridine). Both drugs inhibited the replication of VZV at a much lower concentration than did other antiviral compounds such as iododeoxyuridine, ethyldeoxyuridine, arabinosylcytosine, arabinosyladenine, phosphonoacetic acid, iododeoxycytidine, and acycloguanosine. BVDU and IVDU were virtually inactive against a thymidine kinase-deficient VZV mutant, suggesting that phosphorylation by the viral enzyme is responsible, at least in part, for the selective anti-VZV activity of the compounds.

Comparison of the effects of arabinosyladenine, arabinosylhypoxanthine, and arabinosyladenine 5'-monophosphate against herpes simplex virus, varicella-zoster virus, and cytomegalovirus with their effects on cellular deoxyribonucleic acid synthesis

In a single line of human foreskin fibroblasts, minimum inhibitory concentrations (MICs) and the minimum intracellular virus inactivation concentrations (MIICs) of arabinosyladenine, arabinosylhypoxanthine, and arabinosyladenine 5'-monophosphate were assayed for a number of recent isolates of herpes simplex virus types 1 and 2 (HSV-1, HSV-2), varicella-zoster virus (VZV), and cytomegalovirus (CMV). (The term MIIC is used here to describe the selective qualitative intracellular inhibition of the virus inoculum in the primary tissue cultures. The inoculum is not recoverable in subcultures free of antiviral agent.) MICs and MIICs of each of the antiviral agents were readily obtained for each strain of HSV-1, HSV-2, and VZV tested, but all seven strains of CMV tested were much more resistant. At the endpoint, there was little variation in the MICs or MIICs among strans of the same virus. Final MIC results for HSV-1 and HSV-2 were complete after 3 days of incubation; CMV and VZV results required as long as 6 days. The MIC for each herpesvirus increased with incubation, but at the endpoint the MIC and MIIC were approximately equal. VZV was most susceptible to each drug, followed by HSV-1 and HSV-2. The latter two viruses were quite similar. There was no difference in antiviral susceptibilities among any of the strains of HSV-1, HSV-2, VZV, or CMV tested. The toxicities of arabinosyladenine, arabinosylhypoxanthine, and arabinosyladenine 5'-monophosphate were simultaneously compared by using both microscopic cytotoxicity and inhibition of uptakes of [14C]thymidine into cellular deoxyribonucleic acid and of 14C-labeled amino acids into protein. The selective inhibition of each antiviral agent against viral and cellular deoxyribonucleic acid polymerases was confirmed. Simultaneous assays of antiviral and anticellular activities of antiviral agents may be useful in projecting further in vivo experiments.

In vitro susceptibility of varicella-zoster virus to acyclovir

The in vitro susceptibility of five strains of varicella-zoster virus to acyclovir was examined by the plaque-reduction method in human diploid lung cells. The 50% effective doses of acyclovir ranged from 2.06 microM to 6.28 microM in a 7-day assay, with a mean of 3.65 microM. Irreversible inhibition of plaque formtation was achieved by drug doses exceeding the 50% effective dose for plaque reduction but nontoxic to the cells. Studies on the relative in vitro susceptibility of varicella-zoster virus and herpes simplex virus types 1 and 2 to acyclovir suggested that varicella-zoster virus is two- to eightfold less susceptible to the drug. The antiviral potency of acyclovir for varicella-zoster virus in vitro was compared with that of several other nucleoside analogs. Analysis of the metabolism of acyclovir in varicella-zoster virus-infected WI-38 cells revealed that, as with herpes simplex virus types 1 and 2, the formation of the triphosphate forms of the drug is specific to viral infection.

Effect of 5-iodo-5'-amino-2',5'-dideoxyuridine on varicella-zoster virus in vitro

The antiviral effect of the nucleoside analog 5-iodo-5'-amino-2',5'-dideoxyuridine (AIU) was tested with three isolates of varicella-zoster virus (VZV). AIU concentrations of 10 to 800 muM (3.5 to 288 mug/ml) reduced the number of plaques produced by VZV-infected cells and cell-free VZV from approximately 30 to 95%. Smaller plaque size was also observed in the presence of AIU. AIU was less effective than arabinofuranosylthymine in reducing VZV-induced plaques since as little as 5 mug of arabinofuranosylthymine per ml completely blocked plaque formation by cell-free VZV. Toxicity assays with human diploid embryo fibroblast cells were also carried out. Drug concentrations as high as 800 muM were not toxic to human diploid embryo fibroblast cells as determined by radiolabeling of cell deoxyribonucleic acid, ribonucleic acid, and protein.

Characterization of an Epstein-Barr virus-induced DNA polymerase

The addition of iododeoxyuridine to P3HR-I cell cultures led to a large increase in both Epstein-Barr virus (EBV)-induced DNA polymerase activity and early antigen-positive cells. This EBV-induced DNA polymerase was separated from the cellular alpha- and beta-polymerases by sequential column chromatography on Sepharose 6B, DEAE-cellulose, and phosphocellulose, resulting in partial purification of about 320-fold. The partially purified-EBV DNA polymerase could be distinguished from the cellular DNA polymerases by its activation by salts, its catalytic properties, and its degree of sensitivity to N-ethylmaleimide, phosphonoacetic acid, araATP, and araCTP. The viral polymerase showed properteis similar to those reported for other herpesvirus DNA polymerases. The enzyme exhibited optimal activity for copying activated calf DNA in the presence of 50 mH (NH4)2SO4 and was resistant to 150 mM (NH4)2SO4. It utilized with high efficiency template-primer poly(dC)-oligo(dG)12-18 or poly(dA)-oligo(dT)12-18, but failed to copy poly(rA)-oligo(dT)10 and oligo(dT)10, indicating that this enzyme has characters distinct from DNA polymerase gamma, reverse transcriptase, and terminal deoxynucleotidyl transferase. Phosphonacetic acid inhibited not only EBV DNA polymerase, but also, to a lesser degree, the cellular polymerase alpha. AraATP did not severely inhibit viral activity, whereas the polymerase alpha was inhibited most effectively. Both EBV polymerase and polymerase alpha were inhibited at a comparable level by araCTP.

Combined antiviral effects of interferon, adenine, arabinoside, hypoxanthine arabinoside, and adenine arabinoside-5'-monophosphate in human fibroblast cultures

Adenine arabinoside and human interferon are currently being evaluated in clinical trials against herpes- and poxvirus infections. Interferon production is also a normal antiviral response. It is therefore important to examine the combined actions of interferon and antiviral arabinosides for possible synergy or antagonism. We have examined the antiviral activities of human fibroblast interferon, adenine arabinoside, hypoxanthine arabinoside, and adenine arabinoside 5'-monophosphate individually, using plaque inhibition of vaccinia and herpes simplex type 2 viruses in human skin fibroblast cultures. By combining doses of interferon and arabinosides that, acting alone, give intermediate degrees of plaque inhibition, we were able to compare the combined antiviral activity with that calculated from the activity of each inhibitor alone, assuming that the activities are statistically independent. Our results show that the plaque-inhibitory activities of interferon and the arabinosides tested are statistically independent. The results also show that the arabinosides do not destabilize the antiviral state previously induced by interferon, and that interferon pretreatment does not interfere with subsequent arabinoside action in infected cells. We have also found that arabinosides do not affect the induction of interferon synthesis by either Newcastle disease virus or double-stranded ribonucleic acid, and are not themselves interferon inducers.

Antiviral activity of arabinosyladenine and arabinosylhypoxanthine in herpes simplex virus-infected KB cells: selective inhibition of viral deoxyribonucleic acid synthesis in the presence of an adenosine deaminase inhibitor

The antiviral activity of the fraudulent nucleoside arabinosyladenine (ara-A) against herpes simplex virus (HSV) type 1 was increased nearly 20-fold by the adenosine deaminase inhibitor, coformycin. The combination of ara-A plus coformycin was 90 times more potent in blocking HSV replication than was arabinosylhypoxanthine (ara-H). In suspension culture both drugs were more active than they were in monolayer culture. Deoxyribonucleic acid (DNA) synthesis also was inhibited by the nucleosides. Depending upon the species of DNA examined, ara-A was 8 to 15 times more active in the presence of coformycin, and the combination was 35 to 70 times more potent than ara-H. Both drugs inhibited total DNA synthesis to the same extent in uninfected and HSV-infected KB cells. In contrast, viral DNA synthesis was three to six times more susceptible to inhibition than was cellular DNA synthesis. Inhibition of viral DNA synthesis was more pronounced in suspension culture than in monolayer culture. However, the method of cell propagation did not alter the degree to which the drugs inhibited DNA synthesis in uninfected KB cells. An index has been derived to quantitate the extent of the selective inhibition of viral or cellular DNA synthesis. Fifty percent inhibitory concentrations of a drug were calculated for uninfected KB DNA synthesis and viral DNA synthesis and expressed as a ratio. The logarithm of this ratio was termed the selective index and was positive if viral DNA synthesis was inhibited preferentially or negative if uninfected KB DNA synthesis was more strongly inhibited. Data from experiments performed in monolayer culture gave positive selective index values of 0.3, 0.5, and 0.4 for ara-A plus coformycin, ara-A, and ara-H, respectively. Values of 0.7 and 0.6 were obtained from suspension culture data for ara-A plus coformycin and ara-H, respectively. Considered collectively, the data presented in this communication establish that coformycin increased the potency of ara-A but did not increase its selectivity.