Biomedical subjects
N Bischofberger
Publications and source records attributed to N Bischofberger.
9-[2-(Phosphonomethoxy)propyl]adenine (PMPA) therapy prolongs survival of infant macaques inoculated with simian immunodeficiency virus with reduced susceptibility to PMPA.
Simian immunodeficiency virus (SIV) infection of newborn rhesus macaques is a useful animal model of human immunodeficiency virus infection for the study of the emergence and clinical implications of drug-resistant viral mutants. We previously demonstrated that SIV-infected infant macaques receiving prolonged treatment with 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) developed viral mutants with fivefold reduced susceptibility to PMPA in vitro and that the development of these mutants was associated with the development of a K65R mutation and additional compensatory mutations in reverse transcriptase (RT). To study directly the virulence and clinical implications of these SIV mutants, two uncloned SIVmac isolates with similar fivefold reduced in vitro susceptibilities to PMPA but distinct RT genotypes, SIVmac055 (K65R, N69T, R82K A158S,S211N) and SIVmac385 (K65R, N69S, I118V), were each inoculated intravenously into six newborn rhesus macaques; 3 weeks later, three animals of each group were started on PMPA treatment. All six untreated animals developed persistently high levels of viremia and fatal immunodeficiency within 4 months. In contrast, the six PMPA-treated animals, despite having persistently high virus levels, survived significantly longer: 5 to 9 months for the three SIVmac055-infected infants and > or = 21 months for the three SIVmac385-infected infants. Virus from only one untreated animal demonstrated reversion to wild-type susceptibility and loss of the K65R mutation. In several other animals, additional RT mutations, including K64R and Y115F, were detected, but the biological role of these mutations is unclear since they did not affect the in vitro susceptibility of the virus to PMPA. In conclusion, this study demonstrates that although SIVmac mutants with the PMPA-selected K65R mutation in RT were highly virulent, PMPA treatment still offered strong therapeutic benefits. These results suggest that the potential emergence of HIV mutants with reduced susceptibility to PMPA in patients during prolonged PMPA therapy may not eliminate its therapeutic benefits.
Postinoculation PMPA treatment, but not preinoculation immunomodulatory therapy, protects against development of acute disease induced by the unique simian immunodeficiency virus SIVsmmPBj.
The fatal disease induced by SIVsmmPBj4 clinically resembles endotoxic shock, with the development of severe gastrointestinal disease. While the exact mechanism of disease induction has not been fully elucidated, aspects of virus biology suggest that immune activation contributes to pathogenesis. These biological characteristics include induction of peripheral blood mononuclear cell (PBMC) proliferation, upregulation of activation markers and Fas ligand expression, and increased levels of apoptosis. To investigate the role of immune activation and viral replication on disease induction, animals infected with SIVsmmPBj14 were treated with one of two drugs: FK-506, a potent immunosuppressive agent, or PMPA, a potent antiretroviral agent. While PBMC proliferation was blocked in vitro with FK-506, pig-tailed macaques treated preinoculation with FK-506 were not protected from acutely lethal disease. However, these animals did show some evidence of modulation of immune activation, including reduced levels of CD25 antigen and FasL expression, as well as lower tissue viral loads. In contrast, macaques treated postinoculation with PMPA were completely protected from the development of acutely lethal disease. Treatment with PMPA beginning as late as 5 days postinfection was able to prevent the PBj syndrome. Plasma and cellular viral loads in PMPA-treated animals were significantly lower than those in untreated controls. Although PMPA-treated animals showed acute lymphopenia due to SIVsmmPBj14 infection, cell subset levels subsequently recovered and returned to normal. Based upon subsequent CD4(+) cell counts, the results suggest that very early treatment following retroviral infection can have a significant effect on modifying the subsequent course of disease. These results also suggest that viral replication is an important factor involved in PBJ-induced disease. These studies reinforce the idea that the SIVsmmPBj model system is useful for therapy and vaccine testing.
Early short-term 9-[2-(R)-(phosphonomethoxy)propyl]adenine treatment favorably alters the subsequent disease course in simian immunodeficiency virus-infected newborn Rhesus macaques.
Simian immunodeficiency virus (SIV) infection of newborn macaques is a useful animal model of human pediatric AIDS to study disease pathogenesis and to develop intervention strategies aimed at delaying disease. In the present study, we demonstrate that very early events of infection greatly determine the ultimate disease course, as short-term antiviral drug administration during the initial viremia stage significantly delayed the onset of AIDS. Fourteen newborn macaques were inoculated orally with uncloned, highly virulent SIVmac251. The four untreated control animals showed persistently high virus levels and poor antiviral immune responses; they developed fatal immunodeficiency within 15 weeks. In contrast, SIV-infected newborn macaques which were started on 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) treatment at 5 days of age and continued for either 14 or 60 days showed reduced virus levels and enhanced antiviral immune responses. This short-term PMPA treatment did not induce detectable emergence of SIV mutants with reduced in vitro susceptibility to PMPA. Although viremia increased in most animals after PMPA treatment was withdrawn, all animals remained disease-free for at least 6 months. Our data suggest that short-term treatment with a potent antiviral drug regimen during the initial viremia will significantly prolong AIDS-free survival for HIV-infected infants and adults.
In vitro and in vivo activities of oligodeoxynucleotide-based thrombin inhibitors containing neutral formacetal linkages.
A series of 15-mer oligodeoxynucleotide analogues were synthesized, and their thrombin inhibitory activities in vitro and in vivo were evaluated. These oligodeoxynucleotide analogues share the same sequence (GGTTGGTGTGGTTGG) but have one or more phosphodiester linkages replaced by a neutral formacetal group. The results obtained from monosubstitutions show that no single phosphodiester group is critical for the thrombin inhibitory activity, suggesting that the interaction between the oligodeoxynucleotide and thrombin is based on a multiple-site charge-charge interaction. Analysis of the effects of different phosphodiester replacements indicates that the backside and left side of the chairlike structure formed by the molecule may be involved in binding with thrombin, presumably by having direct contacts with the anion-binding exosite of the enzyme. For the oligodeoxynucleotides containing two noncontiguous formacetal groups, the effect of the disubstitution is the sum of the effects obtained from the corresponding two monosubstitutions. Infusion of an oligodeoxynucleotide containing four formacetal groups into monkeys showed an increased in vivo anticoagulant effect and an extended in vivo half-life compared to the unmodified oligodeoxynucleotide.
N2- and C8-substituted oligodeoxynucleotides with enhanced thrombin inhibitory activity in vitro and in vivo.
2'-Deoxyguanosine (G) analogues carrying various hydrophobic substituents in the N2 and C8 positions were synthesized and introduced through solid-phase synthesis into 15-mer oligodeoxynucleotide, GGTTGGTGTGGTTGG, which forms a chairlike structure consisting of two G-tetrads and is a potent thrombin inhibitor. The effects of the substitutions at N2 and C8 of the G-tetrad-forming G residues on the thrombin inhibitory activity are relatively small, suggesting that these substitutions cause relatively small perturbations on the chairlike structure formed by the oligodeoxynucleotide. Introduction of a benzyl group into N2 of G6 and G11 and naphthylmethyl groups into N2 of G6 increased the thrombin inhibitory activity, whereas other substituents in these positions had almost no effect or decreased the activity. Particularly, the oligodeoxynucleotide carrying a 1-naphthylmethyl group in the N2 position of G6 showed an increase in activity by about 60% both in vitro and in vivo. Substitutions on the N2 position of other G residues had little effect or decreased the activity. Introduction of a relatively small group, such as methyl and propynyl, into the C8 positions of G1, G5, G10, and G14 increased the activity, presumably due to the stabilization of a chairlike structure, whereas introduction of a large substituent group, phenylethynyl, decreased the activity, probably due to the steric hindrance.
Two doses of PMPA protect newborn macaques against oral simian immunodeficiency virus infection.
BACKGROUND: Simple and affordable intervention strategies are needed to reduce the rate of HIV transmission from mother to infant in developing countries. Simian immunodeficiency virus (SIV) infection of newborn rhesus macaques is considered to be a useful model of human pediatric HIV infection. OBJECTIVE: To investigate whether short-term 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) administration can protect newborn rhesus macaques against perinatal SIV infection. DESIGN AND METHODS: Eight newborn macaques were inoculated orally with highly virulent SIVmac within the first 3 days of life. Four of these animals were untreated controls. The other four animals were given one dose of PMPA (30 mg/kg subcutaneously) 4 h before oral SIV inoculation, and were then given a second and final dose of PMPA 24 h later. RESULTS: All four untreated control animals were persistently SIV-positive within 2 weeks after virus inoculation. In contrast, no virus could be detected in the four animals that received two doses of PMPA; these animals were seronegative and healthy at 10 months. CONCLUSIONS: Two doses of PMPA prevented SIV infection of newborn macaques. Our data suggest that short-term administration of PMPA to HIV-infected pregnant women at the onset of labor and to their newborns after delivery may reduce the rate of intrapartum HIV transmission.
Administration of 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) for prevention of perinatal simian immunodeficiency virus infection in rhesus macaques.
Simian immunodeficiency virus (SIV) infection of newborn macaques is a useful animal model to explore novel strategies to reduce perinatal human immunodeficiency virus (HIV) infection. The availability of two easily distinguishable virus isolates, SIVmac251 and the simian/human immunodeficiency virus chimera SHIV-SF33, allows tracing the source of infection following inoculation with both viruses by different routes. In the present study, we evaluated the efficacy of pre- and postinoculation treatment regimens with 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) to protect newborn macaques against simultaneous oral SIVmac251 and intravenous SHIV-SF33 inoculation. Untreated newborns became persistently infected following virus inoculation. When three pregnant macaques were given a single subcutaneous dose of PMPA 2 hr before cesarean section, their newborns became SIV-infected following SIV and SHIV inoculation shortly after birth. In contrast, when four newborn macaques were inoculated simultaneously with SIV and SHIV, and started immediately on PMPA treatment for 2 weeks, only one animal became persistently SIV-infected; the remaining three PMPA-treated newborns, however, had some evidence of an initial transient virus infection but were seronegative and healthy at 8 months of age. Our data demonstrate that PMPA treatment can reduce perinatal SIV infection and suggest that similar strategies may also be effective against HIV.
Efficacy of the acyclic nucleoside phosphonates (S)-9-(3-fluoro-2-phosphonylmethoxypropyl)adenine (FPMPA) and 9-(2-phosphonylmethoxyethyl)adenine (PMEA) against feline immunodeficiency virus.
The acyclic nucleoside phosphonates (S)-9-(3-fluoro-2-phosphonylmethoxypropyl)adenine (FPMPA) and 9-(2-phosphonylmethoxyethyl)adenine (PMEA) were evaluated for their efficacy and side effects in a double-blind placebo-controlled trial using naturally occurring feline immunodeficiency virus (FIV)-infected cats. This natural retrovirus animal model is considered highly relevant for the pathogenesis and chemotherapy of HIV in humans. Both PMEA and FPMPA proved effective in ameliorating the clinical symptoms of FIV-infected cats, as measured by several clinical parameters including the incidence and severity of stomatitis, Karnofsky's score, immunologic parameters such as relative and absolute CD4+ lymphocyte counts, and virologic parameters including proviral DNA levels in peripheral blood mononuclear cells (PBMC) of drug-treated animals. In contrast with PMEA, FPMPA showed no hematologic side effects at a dose that was 2.5-fold higher than PMEA.
Anti-human immunodeficiency virus activity and cellular metabolism of a potential prodrug of the acyclic nucleoside phosphonate 9-R-(2-phosphonomethoxypropyl)adenine (PMPA), Bis(isopropyloxymethylcarbonyl)PMPA.
Bis(isopropyloxymethylcarbonyl) 9-R-(2-phosphonomethoxypropyl)adenine [bis(POC)PMPA] has been identified as a novel prodrug of PMPA. The anti-human immunodeficiency virus activity of bis(POC)PMPA was >100-fold greater than that of PMPA in both an established T-cell line and primary peripheral blood lymphocytes. This improved efficacy was shown to be due to a rapid intracellular uptake of the prodrug resulting in an increased intracellular accumulation of PMPA diphosphate (PMPApp), the pharmacologically active metabolite. PMPApp levels in bis(POC)PMPA-treated cells exceeded by >1,000-fold the levels seen in cells treated with unmodified PMPA in both resting and activated peripheral blood lymphocytes. Significant differences in the intracellular catabolism of PMPA metabolites were noted between the resting and activated lymphocytes. The half-life for the disappearance of PMPApp, derived from either bis(POC)PMPA or PMPA, was 12 to 15 h in the activated lymphocytes and 33 to 50 h in the resting lymphocytes. This long persistence of PMPApp, particularly in resting lymphocytes, may be unique to the nucleoside phosphonate analogs and indicates that effective levels of the active metabolite can be achieved and maintained with relatively infrequent administration of the parent drug.
Oral administration of a prodrug of the influenza virus neuraminidase inhibitor GS 4071 protects mice and ferrets against influenza infection.
We have recently described GS 4071, a carbocyclic transition-state analog inhibitor of the influenza virus neuraminidase, which has potent inhibitory activity comparable to that of 4-guanidino-Neu5Ac2en (GG167; zanamivir) when tested against influenza A virus replication and neuraminidase activity in vitro. We now report that GS 4071 is active against several strains of influenza A and B viruses in vitro and that oral GS 4104, an ethyl ester prodrug which is converted to GS 4071 in vivo, is active in the mouse and ferret models of influenza virus infection. Oral administration of 10 mg of GS 4104 per kg of body weight per day caused a 100-fold reduction in lung homogenate viral titers and enhanced survival in mice infected with influenza A or B viruses. In ferrets, a 25-mg/kg dose of GS 4104 given twice daily reduced peak viral titers in nasal washings and eliminated constitutional responses to influenza virus infection including fever, increased nasal signs (sneezing, nasal discharge, mouth breathing), and decreased activity. Consistent with our demonstration that the parent compound is highly specific for influenza virus neuraminidases, no significant drug-related toxicity was observed after the administration of oral dosages of GS 4104 of up to 800 mg/kg/day for 14 days in nonclinical toxicology studies with rats. These results indicate that GS 4104 is a novel, orally active antiviral agent with the potential to be used for the prophylaxis and treatment of influenza A and B virus infections.
Identification of GS 4104 as an orally bioavailable prodrug of the influenza virus neuraminidase inhibitor GS 4071.
GS 4071 is a potent carbocyclic transition-state analog inhibitor of influenza virus neuraminidase with activity against both influenza A and B viruses in vitro. GS 4116, the guanidino analog of GS 4071, is a 10-fold more potent inhibitor of influenza virus replication in tissue culture than GS 4071. In this study we determined the oral bioavailabilities of GS 4071, GS 4116, and their respective ethyl ester prodrugs in rats. Both parent compounds and the prodrug of the guanidino analog exhibited poor oral bioavailability (2 to 4%) and low peak concentrations in plasma (Cmaxs; Cmax <0.06 microg/ml). In contrast, GS 4104, the ethyl ester prodrug of GS 4071, exhibited good oral bioavailability (35%) as GS 4071 and high Cmaxs of GS 4071 (Cmax = 0.47 microg/ml) which are 150 times the concentration necessary to inhibit influenza virus neuraminidase activity by 90%. The bioavailability of GS 4104 as GS 4071 was also determined in mice (30%), ferrets (11%), and dogs (73%). The plasma of all four species exhibited high, sustained concentrations of GS 4071 such that at 12 h postdosing the concentrations of GS 4071 in plasma exceeded those necessary to inhibit influenza virus neuraminidase activity by 90%. These results demonstrate that GS 4104 is an orally bioavailable prodrug of GS 4071 in animals and that it has the potential to be an oral agent for the prevention and treatment of influenza A and B virus infections in humans.
Antiretroviral efficacy and pharmacokinetics of oral bis(isopropyloxycarbonyloxymethyl)-9-(2-phosphonylmethoxypropyl)adenine in mice.
To overcome the low oral bioavailability of the highly potent and selective antiretroviral agent (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA), a new lipophilic ester derivative, i.e., the bis(isopropyloxycarbonyloxymethyl)-ester [bis(POC)-PMPA], was prepared. The usefulness of bis(POC)-PMPA as an oral prodrug for PMPA was investigated in the intestinal mucosa Caco-2 cell monolayer model. The total transport of bis(POC)-PMPA was 2.7%, whereas it was less than 0.1% for PMPA. Bis(POC)-PMPA was considerably metabolized inside the epithelial cells, since the majority of the compound was recovered after transport in the form of the monoester metabolite [mono(POC)-PMPA]. In contrast, bis(POC)-PMPA was relatively resistant to degradation at the luminal side of the Caco-2 cells. Pharmacokinetic studies with mice showed that the oral bioavailability of bis(POC)-PMPA (calculated from the curves of the concentration of free PMPA in plasma) was 20%. Neither bis(POC)-PMPA nor mono(POC)-PMPA could be recovered in plasma, suggesting the efficient release of the active drug PMPA after oral administration of bis(POC)-PMPA. Severe combined immunodeficient (SCID) mice infected with Moloney murine sarcoma virus (MSV) and treated orally with bis(POC)-PMPA for 5 or 10 days (dosages, 50, 100, or 200 mg of PMPA equivalent per kg of body weight per day) showed a significant delay in MSV-induced tumor appearance and tumor-associated death. The antiviral efficacy of oral bis(POC)-PMPA was related to the dosage and treatment period and was not significantly different from that of subcutaneous PMPA given at an equivalent dose. The favorable pharmacokinetic profile, marked antiviral efficacy, and low toxicity make bis(POC)-PMPA an attractive oral prodrug of PMPA that should be further pursued in clinical studies with patients infected with human immunodeficiency virus or hepatitis B virus.
Effectiveness of postinoculation (R)-9-(2-phosphonylmethoxypropyl) adenine treatment for prevention of persistent simian immunodeficiency virus SIVmne infection depends critically on timing of initiation and duration of treatment.
(R)-9-(2-Phosphonylmethoxypropyl)adenine (PMPA), an acyclic nucleoside phosphonate analog, is one of a new class of potent antiretroviral agents. Previously, we showed that PMPA treatment for 28 days prevented establishment of persistent simian immunodeficiency virus (SIV) infection in macaques even when therapy was initiated 24 h after intravenous virus inoculation. In the present study, we tested regimens involving different intervals between intravenous inoculation with SIV and initiation of PMPA treatment, as well as different durations of treatment, for the ability to prevent establishment of persistent infection. Twenty-four cynomolgus macaques (Macaca fascicularis) were studied for 46 weeks after inoculation with SIV. All mock-treated control macaques showed evidence of productive infection within 2 weeks postinoculation (p.i.). All macaques that were treated with PMPA for 28 days beginning 24 h p.i. showed no evidence of viral replication following discontinuation of PMPA treatment. However, extending the time to initiation of treatment from 24 to 48 or 72 h p.i. or decreasing the duration of treatment reduced effectiveness in preventing establishment of persistent infection. Only half of the macaques treated for 10 days, and none of those treated for 3 days, were completely protected when treatment was initiated at 24 h. Despite the reduced efficacy of delayed and shortened treatment, all PMPA-treated macaques that were not protected showed delays in the onset of cell-associated and plasma viremia and antibody responses compared with mock controls. These results clearly show that both the time between virus exposure and initiation of PMPA treatment as well as the duration of treatment are crucial factors for prevention of acute SIV infection in the macaque model.
Adenosine A1 receptor agonists as clinically viable agents for treatment of ischemic brain disorders.
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Effects of (R)-9-(2-phosphonylmethoxypropyl)adenine monotherapy on chronic SIV infection in macaques.
(R)-9-(2-Phosphonylmethoxypropyl)adenine (PMPA) acts as a reverse transcriptase inhibitor of retroviruses and has been shown to be effective against acute simian immunodeficiency virus (SIV) infection in macaques. To study its efficacy at different stages of infection, we tested PMPA in cynomolgus macaques (Macaca fascicularis) that had been chronically infected with SIVMne for at least 19 weeks before treatment was begun. PMPA was administered subcutaneously in a single daily dose of either 30 or 75 mg/kg body weight for 28 days. Within < or = 2 weeks of treatment, PMPA in both dosing regimens reduced SIV levels by >99% in the plasma or peripheral blood mononuclear cells; in some macaques SIV levels were reduced to below the lower quantitation limit. At a dose of 30 mg/kg/day PMPA was well tolerated, causing no side effects while increasing the mean CD4+ cell counts in animals that received this dose. Thus PMPA seems to be a promising agent for use against retroviral infections.
Influenza neuraminidase inhibitors possessing a novel hydrophobic interaction in the enzyme active site: design, synthesis, and structural analysis of carbocyclic sialic acid analogues with potent anti-influenza activity.
The design, synthesis, and in vitro evaluation of the novel carbocycles as transition-state-based inhibitors of influenza neuraminidase (NA) are described. The double bond position in the carbocyclic analogues plays an important role in NA inhibition as demonstrated by the antiviral activity of 8 (IC50 = 6.3 microM) vs 9 (IC50 > 200 microM). Structure-activity studies of a series of carbocyclic analogues 6a-i identified the 3-pentyloxy moiety as an apparent optimal group at the C3 position with an IC50 value of 1 nM for NA inhibition. The X-ray crystallographic structure of 6h bound to NA revealed the presence of a large hydrophobic pocket in the region corresponding to the glycerol subsite of sialic acid. The high antiviral potency observed for 6h appears to be attributed to a highly favorable hydrophobic interaction in this pocket. The practical synthesis of 6 starting from (-)-quinic acid is also described.
Viral dynamics of primary viremia and antiretroviral therapy in simian immunodeficiency virus infection.
Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus.