Kathryn E. Follis

Prevention of SIV Infection in Macaques by (R)-9-(2-Phosphonylmethoxypropyl)adenine

The efficacy of pre- and postexposure treatment with the antiviral compound (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) was tested against simian immunodeficiency virus (SIV) in macaques as a model for human immunodeficiency virus (HIV). PMPA was administered subcutaneously once daily beginning either 48 hours before, 4 hours after, or 24 hours after virus inoculation. Treatment continued for 4 weeks and the virologic, immunologic, and clinical status of the macaques was monitored for up to 56 weeks. PMPA prevented SIV infection in all macaques without toxicity, whereas all control macaques became infected. These results suggest a potential role for PMPA prophylaxis against early HIV infection in cases of known exposure.

Post-exposure chemoprophylaxis (PECP) against SIV infection of macaques as a model for protection from HIV infection.

We report that simian immunodeficiency virus (SIV) infection in macaques is a valuable animal model for studying post‐exposure chemoprophylaxis (PECP). PECP with the acyclic nucleoside reverse transcriptase inhibitors 9‐(2‐phosphonylmetho‐xyethyl)adenine (PMEA) and (R)‐9‐(2‐phosphonylmethoxypropyl)adenine (PMPA) at early viral infection can provide long‐term protection against subsequent heterologous SIV challenge. Eight macaques previously treated with PECP (called PECP macaques) and four naive controls were challenged intravenously with the most virulent form of SIV, SIVPBj14. All controls showed signs of SIVPBj14‐induced acute disease syndrome on days 6 and 7 post‐inoculation (PI). One had a fatal viral infection and two surviving controls had persistent infection and decreased CD4+cell count. Virologic studies of the three surviving controls revealed SIV in multiple lymphoid tissues and peripheral blood mononuclear cells (PBMCs) at necropsy. In contrast, the PECP macaques showed none to mild signs of acute disease syndrome at day 9 PI and exhibited only transient SIV infection in PBMCs between weeks 1 and 8 PI. In virologic studies of five PECP macaques necropsied, two macaques were SIV‐negative and the other three were SIV‐positive only in either lymph node or bone marrow. Three SIVPBj14‐challenged PECP macaques, that were randomly reserved for a follow‐up study for>4.0 years PI showed extremely low to undetectable levels of PBMC‐associated viremia and normal to increased levels of CD4+ and CD8+ cell counts throughout the study. Our results indicate that early PECP could activate immune responses to protect against subsequent infection with heterologous challenge virus.

Comparison of the efficacy of AZT and PMEA treatment against acute SIVmne infection in macaques

The antiretroviral drugs azidothymidine (AZT) and 9‐(‐2‐phosphonylmethoxyethyl) adenine (PMEA) were individually tested for prevention of simian immunodeficiency virus (SIVmne) infection in macaques (Macaca fascicularis). Macaques were pretreated with either drug before inoculation with SIVmne, and drug treatment was continued for four weeks. The virus, antibody, and clinical status of the macaques was monitored for up to 36 weeks following inoculation. While AZT prophylaxis resulted in reduced virus load in some macaques, PMEA prophylaxis was highly efficacious in preventing acute SIVmne infection.

In vitro screening for antiretroviral agents against simian immunodeficiency virus (SIV).

Simian immunodeficiency virus (SIV), which causes an acquired immunodeficiency syndrome in macaques, is a lentivirus that is morphologically, antigenically, genetically, and biologically similar to the human immunodeficiency virus (HIV). Because of these similarities, the SIV model represents a unique opportunity for in vitro and in vivo testing of antiretroviral agents. Since antiretroviral agents may exhibit different properties in different cells in vitro, more than one cell line may be necessary to evaluate the efficacy and modes of action of an antiretroviral agent. Initially we tested ten cell lines for their permissiveness to five SIV isolates. One B-cell line (AA-2) and one T-cell line (HuT 78) were selected to test antiretroviral agents since both were extremely permissive for SIVmac251, an isolate with a high rate of infectivity. Using this optimized in vitro testing protocol, we screened ten antiretroviral agents for their ability to inhibit SIV replication. Six of the compounds completely inhibited SIV viral antigen expression. Based on the selectivity index, 3-azido-3-dideoxythymidine, 3-azido-2,3-dideoxyuridine, and 3-fluoro-3-deoxythymidine appear to be the most efficacious antiretroviral agents against SIVmac251. Several different assays for determining viral antigen inhibition were conducted and the results of these assays were comparable. Our results demonstrate that the SIV in vitro model is a valuable screening tool for determining the efficacy and toxicity of new antiretroviral agents.

Inhibitory effects of heterogeneous dextran sulphate compounds on simian type D retrovirus in vitro

Nine heterogeneous dextran sulphate compounds were tested in vitro for their ability to inhibit a type D simian retrovirus (SRV-2) known to cause simian acquired immunodeficiency syndrome (SAIDS). Dextran sulphate, a sulphated polysaccharide, is available commercially in a variety of molecular weights ranging from 5000 (5K) to 500000 (500K). Of the four 500K compounds tested, three completely blocked replication and infectivity of SRV-2. Of the remaining five compounds tested, only three completely inhibited the virus. Cytotoxic effects also varied even among compounds of the same mol. wt. All nine compounds were further tested in combination with azidothymidine (AZT) or dideoxycytidine (ddC) for possible additive, synergistic or antagonistic effects at reduced concentrations of both drugs. Six dextran sulphate compounds showed slight additive or synergistic effects with AZT, while no effects were seen with ddC. The results suggest that the antiretroviral activity of dextran sulphate depends on the particular chemical preparation of the compound and is not entirely dependent on mol. wt. Thus, it is important to be aware of the inhibitory and cytotoxic variability in heterogeneous dextran sulphate compounds when considering the potential use of this drug, either alone or in combination, as an antiretroviral agent in vivo.