Inhibition of SIV and HIV-2 Replication in Cynomolgus Monkeys by (-)9-[4-Hydroxy-2-(Hydroxymethyl)-Butyl]Guanine (H2G)

The antiherpes compound (-)9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine (H2G) has been found to suppress the multiplication of SIVsm and HIV-2 in cynomolgus monkeys. This was seen as a delay in the appearance of viral antigen in serum during the primary infection at drug concentrations of 3×10 mg kg−1 day−1 and higher, when H2G was given subcutaneously. These effects of H2G on SIVsm and HIV-2 replication in monkeys were similar to those observed using the same dose of 3′-azidothymidine (AZT). A complete prevention of HIV-2 infection was observed in one of four animals treated with 3×10 mg kg−1 day−1 of H2G. The enantiomeric mixture (+)H2G at 3×25 mg kg−1 day−1 also delayed the appearance of SIVsm antigen but the (+)enantiomer of H2G at 3×10 mg kg−1 day−1 had no effect on primary SIVsm infection in monkeys, indicating that only the (−)enantiomer (H2G) was inhibitory and that this effect was not influenced by the presence of the (+)enantiomer. No adverse effects on blood chemistry or haematology were observed in monkeys given 25 mg kg−1 day−1 of H2G for 9 weeks or 3×25 mg kg−1 day−1 for 10 days.

Influence of the Infectious Dose of Simian Immunodeficiency Virus on the Acute Infection in Cynomolgus Monkeys and on the Effect of Treatment with 3′-Fluorothymidine

Inoculation of cynomolgus monkeys with simian immunodeficiency virus (SIVSM) results in an acute infection with circulating viral antigen. The time for appearance of the viral antigen peak was dependent on the dose of virus given, a reduced dose of virus resulting in a later peak. 3′-Fluorothymidine (FLT) was given at a dose of 3 × 5mg kg−1 day−1 starting 8 h before virus inoculation and then every 8 h for 10 days. In monkeys inoculated with 500–2500 infectious doses of SIVSM no significant effect of treatment with FLT was seen. When the amount of virus was reduced to 100 infectious doses or less, treatment with FLT resulted in a significant delay in the appearance of viral antigen. At an inoculum of 2–10 infectious doses per monkey, FLT treatment showed a prophylactic effect.

Treatment of Acute SIV infection in cynomolgus Monkeys with 2′,3′-dideoxyinosine (ddl) and 2′,3′-dideoxythymidiene (d4T)

2′,3′-dideoxyinosine (ddl) and 2′,3′-dideoxythymidiene (d4T) have been reported to inhibit the multiplication of human immunodeficiency virus (HIV) in patients, ddl and d4T were administered subcutaneously to cynomolgus monkeys starting 8 h prior to inoculation with 10–50 infectious doses of simian immunodeficiency virus (SIVSM). ddl, at a daily dose of 3 × 3.6 mg kg−1 for 10 days significantly delayed the appearance of SIVSM p24/26 antigen. A significant delay in the appearance of SIVSM p24/26 antigen was also seen when using a daily dose of 3 × 1 mg kg −1 of d4T for 10 days. Neither ddl nor d4T prevented SIVSM infection despite administration prior to virus inoculation.

Effect of Herpesvirus Inhibition on Primary SIV Infection in Cynomolgus Monkeys

Foscarnet and (-)9-[4-hydroxy-2-(hydroxymethyl)butyl] guanine (H2G) have already been shown to inhibit herpesviruses in vitro and also to inhibit viral antigen production in primary SIV infection in monkeys. Attempts have been made to determine if these invivo effects on SIV were due to a direct effect on SIV or were mediated through inhibition of endogenous transactivating herpesviruses. The possible involvement of herpesviruses in primary SIVsm infection in monkeys was studied by the use of various inhibitors of herpesvirus replication. Subcutaneous injections of 3 × 5 mg kg−1 day−1 of aciclovir, 3 × 5 mg kg−1 day−1 of ganciclovir and 3 × 28 mg kg−1 day−1 of phosphonoacetic acid had no effect on primary SIVsm infection in cynomolgus monkeys. These doses of aciclovir, ganciclovir and phosphonoacetic acid are inhibitory to several herpesviruses. The results suggest that the effects of foscarnet and H2G on primary SIVsm infection in monkeys are direct and not mediated through inhibition of a replicating herpesvirus.

Reverse transcriptase and corresponding activity-blocking antibody for monitoring SIVsm infection in macaques

A nonradioactive reverse transcriptase (RT) assay was used to measure RT activity in serum during the viremia peak associated with primary infection and for measuring the generation and maintenance of RT activity-blocking antibody (RTb-ab) titers during and after seroconversion in SIV-infected macaques. The RT assay was compared to an antigen capture immunoassay designed for HIV-2/SIVsm and was found to be approximately 40 times more sensitive in detecting SIVsm in serum from infected macaques. The RT assay detected RT activity in serum corresponding to levels from 3 pg/ml. Earliest detection of viral replication using the RT assay was on day 6-8, with a peak at day 10 (up to 8000 pg/ml). The earliest detection of RTb-ab was seen on day 17-23, with established RTb-ab titers by day 29, followed by increasing titers of 15,000-120,000 by day 62-77. The usefulness of RT and RTb-ab for monitoring the course of SIV infection in monkey models is discussed.

Prevention of simian immunodeficiency virus, SIVsm, or HIV-2 infection in cynomolgus monkeys by pre- and postexposure administration of BEA-005

OBJECTIVE

To study the possibilities and limitations of postexposure treatment to prevent the establishment of infection after accidental exposure to HIV.

DESIGN AND METHODS

The effect of 2,3'-dideoxy-3'-hydroxymethyl cytidine (B1 A-005) was investigated on acute simian immunodeficiency virus (SIV) and HIV-2 infections in macaques in pre- and postexposure treatment experiments.

RESULTS

Postexposure treatment with BLA-005 (3 x 10 mg/kg) for as short as 3 days prevented infection with SIVsm after intravenous or rectal inoculation. Infection with HIV-2 could also be blocked by postexposure BFA-005 treatment.

CONCLUSION

This study shows that therapeutic intervention can block early systemic and mucosal infections with SIV and HIV-2. Further evaluation is ongoing.

Comparison of the sensitivities of primary isolates of HIV type 2 and HIV type 1 to antiviral drugs and drug combinations

The sensitivity of primary isolates of HIV-2 to the antiretroviral drugs 3'-azido-3'-deoxythymidine (AZT), 2',3'-dideoxyinosine (ddI), and 3'-fluoro-3'-deoxythymidine (FLT) was measured in vitro in PBMCs and compared to that of primary isolates of HIV-1. HIV-2 isolates showed a similar sensitivity to the drugs compared to HIV-1 isolates. Both the relative and the absolute potencies of the three drugs were similar for inhibition of HIV-1 or HIV-2 replication. The effect of combinations of the antiviral drugs was also studied. The combinations of AZT plus FLT, AZT plus ddI, and FLT plus ddI showed synergistic inhibition of three primary HIV-2 isolates, similar to that previously shown for primary HIV-1 isolates. These results indicate that primary isolates of HIV-2 from untreated persons show a level of sensitivity to antiviral nucleoside analogs similar to that shown by HIV-1 isolates, and are also synergistically inhibited by drug combinations shown to be synergistic against HIV-1. Therapeutic regimes with nucleoside analogs used clinically against HIV-1 infection may therefore also be similarly useful against infection with HIV-2.

An animal model for antilentiviral therapy: effect of zidovudine on viral load during acute infection after exposure of macaques to simian immunodeficiency virus

We analyzed the kinetics of the virological and immunological events that occurred in four AZT-treated cynomolgus macaques during the acute infection that followed their exposure to the simian immunodeficiency virus (SIVmac251) grown on monkey PBMCs in a cell-free stock solution. These events included changes in the CD4+ and CD8+ T lymphocyte subsets, p27 antigenemia, infectious serum virus, and cell-associated virus loads. The kinetics of these changes proved strikingly similar to those reported in human HIV-1 infection. Four other SIV-exposed macaques were treated with placebo instead of AZT. We demonstrated that AZT does not prevent SIV infection, even when administered before SIV inoculation. However, the peaks of p27 antigenemia and of serum and cellular viremia were significantly smaller and occurred significantly later in the monkeys given AZT than in those given placebo.

Prevention of HIV-2 and SIV infections in cynomolgus macaques by prophylactic treatment with 3'-fluorothymidine

The aim of this study was to determine the usefulness of human immunodeficiency virus type 2 (HIV-2) for in vivo evaluation of antiviral drugs in monkeys and to study if prophylactic treatment with 3'-fluorothymidine (FLT) could prevent infection against a low challenge dose of HIV-2 or simian immunodeficiency virus (SIV). Protection against infection was assessed by virus isolation and polymerase chain reaction (PCR) on monkey peripheral blood mononuclear cells (PBMC) as well as by antibody and viral antigen assays. Prophylactic treatment with FLT 3 x 5 mg/kg/day, starting 8 h prior to virus inoculation, prevented HIV-2 infection in 3 of 8 monkeys. In another experiment 2 of 4 monkeys resisted 2-10 monkey infectious doses (MID50) of SIV with the same prophylactic treatment. All control animals (HIV-2 n = 8, SIV n = 4) became infected. Thus, FLT treatment prevented HIV-2 and SIV infection in 5 of 12 animals.

Early appearance of simian immunodeficiency virus (SIV) antigen and antibodies as variables in evaluating antiviral drugs in macaques

SIV infection in macaques has become an important animal model for HIV-1 infection in humans. An antibody assay was therefore developed and compared to a commercially available antigen assay with respect to their usefulness to monitor the course of simian immunodeficiency virus (SIV) infection in cynomolgus monkeys. A peptide, JB6T, consisting of 21 amino acids with the sequence NSWGCAFRQVCHTTVPWVNDS corresponding to a segment in the env protein of human immunodeficiency virus (HIV) type 2 was used as antigen in an enzyme-linked immunosorbent assay (ELISA). JB6T was found to detect IgG and IgM antibodies to viral antigens with high specificity. The earliest anti-SIV IgM antibodies were detected at days 13-16, with a maximum at day 20 and subsequently the levels fell. Specific IgG antibody levels increased at day 16-20 after SIV infection and reached a plateau at day 60. The commercially available HIV-1 p24/26 antigen test could, due to cross-reactivity, be employed to detect SIV antigen delay, peak and duration.