Activity of 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodouracil against simian varicella virus infections in African green monkeys

Persistence of simian varicella virus DNA in CD4(+) and CD8(+) blood mononuclear cells for years after intratracheal inoculation of African green monkeys

Simian varicella virus (SVV) DNA was detected in blood mononuclear cells (MNCs) of adult African green monkeys 7 days to 23 months after intratracheal inoculation with 10(3) plaque forming units. Infectious virus was not detected in MNCs at 14 months postinfection (p.i.), and electron microscopic (EM) analysis of MNCs from two monkeys 21 months p.i. did not reveal virus particles. Real-time quantitative PCR analysis of DNA from blood MNCs taken at multiple intervals from SVV-infected monkeys M7 and M8 revealed a 10- to 100-fold decrease, but not clearance of SVV DNA in MNCs between 11 and 17 months p.i. Thereafter, the SVV DNA copy number did not decrease further between 17 and 23 months p.i. PCR analysis of MNCs sorted by flow cytometry revealed SVV DNA in T cells (CD4(+), CD8(+)) and B cells (CD20(+)), but not in monocyte-macrophages (CD14(+)), 10 days p.i. At 11 and 23 months p.i., SVV DNA was found exclusively in CD4(+) and CD8(+) T cells. Whether the detection of SVV DNA in CD4(+) and CD8(+) MNCs many months after the resolution of acute varicella reflects continued infection of these cells that began at the time of acute varicella or represents infection acquired by MNCs trafficking through infected tissues is unknown.

Current pharmacological approaches to the therapy of varicella zoster virus infections: a guide to treatment

Varicella zoster virus (VZV), a member of the herpesvirus family, is responsible for both primary (varicella, chickenpox) as well as reactivation (zoster, shingles) infections. In immunocompetent patients, the course of varicella is generally benign. For varicella zoster, post-herpetic neuralgia is the most common complication. In immunocompromised patients (particularly those with AIDS), transplant recipients and cancer patients, VZV infections can be life-threatening. For these patients and also for immunocompetent patients at risk such as pregnant women or premature infants, the current treatment of choice is based on either intravenous or oral aciclovir (acyclovir). The low oral bioavailability of aciclovir, as well as the emergence of drug-resistant virus strains, have stimulated efforts towards the development of new compounds for the treatment of individuals with VZV infections. Among these new compounds, penciclovir, its oral prodrug form famciclovir and the oral pro-drug form of aciclovir (valaciclovir), rank among the most promising. As with aciclovir itself, all of these drugs are dependent on the virus-encoded thymidine kinase (TK) for their intracellular activation (phosphorylation), and, upon conversion to their triphosphate form, they act as inhibitors/alternative substrate of the viral DNA polymerase. Therefore, cross-resistance to these drugs may be expected for those virus mutants that are TK-deficient and thus resistant to aciclovir. Other classes of nucleoside analogues dependent for their phosphorylation on the viral TK that have been pursued for the treatment of VZV infections include sorivudine, brivudine, fialuridine, fiacitabine and netivudine. Among oxetanocins, which are partially dependent on viral TK, lobucavir is now under clinical evaluation. Foscarnet, which does not require any previous metabolism to interact with the viral DNA polymerase, is used in the clinic when TK-deficient VZV mutants emerge during aciclovir treatment. TK-deficient mutants are also sensitive to the acyclic nucleoside phosphonates (i.e. [s]-1-[3-hydroxy-2-phosphonylmethoxypropyl]cytosine; HPMPC); these agents do not depend on the virus-encoded TK for their phosphorylation but depend on cellular enzymes for conversion to their diphosphoryl derivatives which then inhibit viral DNA synthesis. Vaccination for VZV has now come of age. It is recommended for healthy children, patients with leukaemia, and patients receiving immunosuppressive therapy or those with chronic diseases. The protection induced by the vaccine seems, to some extent, to include zoster and associated neuralgia. Passive immuniatin based on specific immunoglobulins does not effectively prevent VZV infection and is therefore restricted to high risk individuals (i.e. immunocompromised children and pregnant women).

Pharmacokinetics and antiviral activity of a novel isonucleoside, BMS-181165, against simian varicella virus infection in African green monkeys

A novel nucleoside analog BMS-181165 with potent activity against varicella-zoster virus was tested for efficacy in a simian varicella virus infection in African green monkeys. BMS-181165 was effective in preventing the development of a rash, decreasing the development of viremia and preventing death in infected monkeys when administered orally at 4, 16 or 64 mg/kg/day. The compound is well orally absorbed in monkeys, between 44 to 50% oral bioavailability, and may prove of value in therapy of varicella-zoster infections in humans.

Prevalence and distribution of latent simian varicella virus DNA in monkey ganglia

We used polymerase chain reaction to analyze the prevalence and distribution of latent simian varicella virus (SVV) in ganglionic and nonganglionic tissues from nine African green monkeys experimentally infected with SVV. Primers specific for three different regions of the SVV genome were used for amplification. SVV DNA sequences were detected in trigeminal ganglia from seven of nine monkeys and in thoracic ganglia from seven of nine monkeys. Analysis of DNA from nonneuronal tissues of three monkeys and from adrenal glands of nine monkeys revealed the presence of SVV-specific sequences in the adrenal gland of one monkey. The results indicate that, like human varicella, SVV becomes latent primarily in ganglia at multiple levels of the neuraxis, and more than one region of the SVV genome is present in latently infected ganglia. SVV latency in primates may be a useful model for varicella latency in humans.

Evaluation of infrequent dosing regimens with (S)-1-[3-hydroxy-2-(phosphonylmethoxy)propyl]-cytosine (S-HPMPC) on simian varicella infection in monkeys

(S)-1-[3-Hydroxy-2-(phosphonylmethoxy)propyl]cytosine (S-HPMPC) was able to prevent simian varicella infection in African green monkeys inoculated intratracheally with virus. A dose of 50 mg/S-HPMPC/kg administered intravenously was shown to prevent the development of rash, reduce viremia and protect the monkeys from death. The 50 mg/kg dose was effective when treatments initiated on day 2 post-infection (p.i.) was given as ten daily doses of 5 mg/kg, as 10 mg/kg administered on five days on an alternate-day schedule, as two 25 mg/kg doses given on day 2 and on day 7 p.i., or as a single injection of 50 mg/kg on day 2. The single 50 mg/kg dose was also effective when treatment was delayed until four days p.i., but was ineffective when treatment was delayed until six days p.i. The 50 mg/kg dose was not effective when given orally by gavage. No evidence of toxicity was noted in daily clinical examinations, or in frequent hematology and clinical chemistry tests performed during the clinical evaluation of the infection.

Simian varicella virus DNA in dorsal root ganglia

Clinical, pathological, immunological, and virological evidence suggests that simian varicella virus (SVV) infection of primates is the counterpart of varicella-zoster virus infection of humans. To determine whether these two viruses share similarities in their properties during latency, we analyzed ganglia and brain of an African green monkey experimentally infected with SVV for the presence of viral nucleic acid using the polymerase chain reaction technique. We detected SVV DNA in dorsal root ganglia but not in brain of this monkey, which demonstrated no apparent clinical signs of SVV infection. Our results suggest that SVV becomes latent in monkey ganglia and that latency can develop in the absence of clinical varicella (chickenpox). These studies provide an animal model system to study varicella virus latency.

Inhibition of simian varicella virus infection of monkeys by 1-(2-deoxy-2- fluoro-1-beta-D-arabinofuranosyl)-5-ethyluracil (FEAU) and synergistic effects of combination with human recombinant interferon-beta

1-(2-Deoxy-2-fluoro-1-beta-D-arabinofuranosyl)-5-ethyluracil (FEAU) has been shown to be a highly effective inhibitor of Simian varicella virus infection in African green monkeys. Administration of FEAU by either intravenous injection or gavage at doses as low as 1 mg/kg/day prevented the development of rash and reduced viremia. The effective dose could be further reduced to 0.2 mg/kg/day when administered in combination with a sub-effective dose of human recombinant interferon-beta. No evidence of toxicity was seen in monkeys treated for 10 days with FEAU doses of 10 mg/kg/day when they were monitored by hematology and clinical chemistry tests and by clinical observations.