Early-initiated zidovudine therapy prevents disease but not low levels of persistent retrovirus in mice.

An F1 hybrid mouse strain containing the Rfv-3r/s genotype was inoculated with Friend virus complex (FV) and treated with zidovudine (ZDV) intraperitoneally three times daily for 20 days beginning as early as 10 min after initial viral exposure. This strain of mice develops FV-specific neutralizing antibodies that aid in reducing viremia and splenic virus titers but do not prevent splenomegaly and eventual FV-associated death. The virally exposed mice treated with ZDV did not develop splenomegaly or have detectable viremia after the last drug treatment. On day 21, a single animal had demonstrable virus in the spleen as determined by a focal immunoenzyme assay; 57% had detectable virus at 5 weeks, but non displayed splenic virus after 35 weeks. None of the animals died after the 35-week holding period, compared to 38% dying in placebo-treated mice. To detect low levels of the virus, or potentially latent virus, splenocytes were cocultivated with a cell line known to readily propagate FV, and the cells were subsequently passaged four times to amplify replication of the virus. After amplification, a significant increase was seen in the number of mice testing positive for virus. Thus, ZDV treatment initiated early after virus exposure was effective in preventing FV-induced splenomegaly and death, but did not prevent low levels of persistent retrovirus in the mice.

HIV-1 LTR activation model: evaluation of various agents in skin of transgenic mice.

Mice containing the HIV-1 long terminal repeat (LTR) regulating the expression of firefly luciferase reporter gene were investigated for their use as a model for activation of the LTR. As a limited test of this model, a number of different factors were screened for their ability to affect reporter gene activities in the skin. Reporter gene levels were increased in the skin by topical treatment of dimethylsulfoxide, retinoic acid, phorbol ester, ultraviolet light, and hydrogen peroxide, all of which have previously been shown to cause increased HIV production in cultured human cells. Topically applied arachidonic acid, histamine, ethanol, acetone, and methanol did not increase reporter gene activities. A lack of published reports on activation of HIV-1 in human cells by these agents suggests that they do not activate viral expression in human cells, which corroborates with the findings of this report. Minor forms of skin wounding and intraperitoneally administered psoralen plus ultraviolet light also increased reporter gene activities in skin. Control and test treatments could be performed on the same mouse and repetitive samples could be obtained from each treatment area. These transgenic mice might be useful as predictive models for regulation of the LTR in epidermal or dendritic cells.

Effects of zidovudine on Friend virus complex infection in Rfv-3r/s genotype-containing mice used as a model for HIV infection.

Infection with the Friend virus complex (FV) in (B10.A x A/WySn)F1 mice containing the Rfv-3r/s genotype results in several disease manifestations analogous to those seen in patients with acquired immune deficiency syndrome, predominantly high levels of specific antibody and low levels of infectious virus with eventual retroviral disease-induced death of the host. Other immunologic manifestations of FV infection in this murine host included inhibition of percent total T, T-helper, and T-suppressor/cytotoxic cells of total splenic lymphocytes and phytohemagglutinin-induced response of spleen cells. Interleukin-1 production was not affected but the numbers of splenic B cells were increased by the infection. 3'-Azido-3'-deoxythymidine (zidovudine, AZT) administered (a) intraperitoneally three times daily for 24 days beginning 4 h after virus inoculation in doses of 60 to 480 mg/kg/day, (b) in drinking water for 22 days beginning 4 h after virus inoculation in doses of 22 to 216 mg/kg/day, or (c) in drinking water for 29 days beginning 6 days after virus inoculation in doses of 22 to 216 mg/kg/day markedly inhibited FV-induced disease. In the mice receiving early-initiated AZT therapy, FV-induced splenomegaly and hematocrit values were inhibited and infectious centers in the spleen and FV titers in the plasma were reduced to below detectable levels at the higher AZT dosage levels. The percent of total T cells in splenic lymphocytes was increased in the infected, AZT-treated mice. In the intraperitoneal experiment, FV disease-induced death was prevented by treatment with all doses of AZT. Neutralizing antibody to FV was significantly reduced in all AZT-treated groups. Toxicologic manifestations of these AZT treatments included splenic enlargement and reduced hematocrit, although all treated, uninfected mice survived the treatments, gained weight, and displayed no significant effects on enumeration of T and B cells.

Transgenic mice as a chemotherapeutic model for hepatitis B virus infection.

Many transgenic mice carrying either portions of the hepatitis B virus (HBV) genome, or the complete genome, have been developed as models because HBV does not infect any other organisms besides humans and chimpanzees to cause a productive infection and disease. Some of these models have been useful in evaluating chemotherapeutic agents such as interferon-alpha, interleukins-2 and -12, other cytokines and nucleoside analogues for efficacy against HBV. A recently developed transgenic mouse (Guidotti et al., Journal of Virology 69:6158-6169.) which supports the replication of high levels of infectious HBV, provides the opportunity to evaluate the effect of antiviral drugs on various portions of the HBV life cycle in the whole animal. Evaluation of lamivudine, zidovudine and interferon-alpha B/D (IFN-alpha) in this HBV transgenic mouse model are described. Lamivudine and IFN-alpha were highly efficacious in reducing serum HBV DNA. As might be predicted, zidovudine was not efficacious. IFN-alpha was more effective in reducing virus titres in male mice as compared to female mice. This gender difference was not due to lower ability of female mice to express the virus. One anticipates that as this high level HBV transgenic-expressing mouse becomes more fully developed as a chemotherapeutic model, questions about the efficacy of different agents, routes of administration, synergy of antiviral combinations and novel drug therapies will be answered.

Enantiomeric synthesis of D- and L-cyclopentenyl nucleosides and their antiviral activity against HIV and West Nile virus.

Enantiomeric synthesis of D- and L-cyclopentenyl nucleosides and their antiviral activity against HIV and West Nile virus are described. The key intermediate (-)- and (+)-cyclopentenyl alcohols (7 and 15) were prepared from D-gamma-ribonolactone and D-ribose, respectively. Coupling of 7 with appropriately blocked purine and pyrimidine bases via the Mitsunobu reaction followed by deprotection afforded the target L-(+)-cyclopentenyl nucleosides (24-28, 31, 33, and 36). D-(-)-Cyclopentenyl nucleosides (1, 40, 43, and 52-56) were also prepared by a similar procedure for L-isomers from 15. The synthesized compounds were evaluated for their antiviral activity against two RNA viruses: HIV and West Nile virus. Among the synthesized D-(-)-nucleosides, adenine (1, neplanocin A), cytosine (55, CPE-C), and 5-fluorocytosine (56) analogues exhibited moderate to potent anti-HIV activity (EC(50) 0.1, 0.06, and 5.34 microM, respectively) with significant cytotoxicity in PBM, Vero, and CEM cells. Also, cytosine (55) and 5-fluorocytosine (56) analogues exhibited the most potent anti-West Nile virus activity (EC(50) 0.2-3.0 and 15-20 microM, respectively). Among L-(+)-nucleosides, only the cytosine (27) analogue exhibited weak anti-HIV activity (EC(50) 58.9 microM).

Murine retroviral disease-enhancing effects of a pyrimidinone immunomodulator.

(B10.A x A/WySn)F1 mice, infected with the Friend virus (FV) complex, were used as a predictive therapeutic model for AIDS. These infected mice exhibit many of the viral and immunologic manifestations of AIDS. Bropirimine (2-amino-5-bromo-6-phenyl-4[3H]pyrimidinone, ABPP) is an immunomodulating compound which has been shown to inhibit other viral infections. Oral (per os treatment) dosages of ABPP ranging from 50 to 400 mg/kg/day for 3 days resulted in increased numbers of infectious centers in the infected mice and increased splenomegaly and percentage of Ig+ (B cells) in spleens of infected and uninfected mice. Decreased percentages of total Thy-1.2+ (total T) cells and L3T4+ (T-helper) cells were seen in both uninfected and infected mice and a slightly decreased percentage of Ly-2+ (T-suppressor/cytotoxic) cells was observed in spleens of the infected mice. No effect on Ly2+ cells in spleens of uninfected mice was found. Intraperitoneal injection, single or multiple, of 20-200 mg/kg ABPP prior to FV injection resulted in increased spleen weights but had no effect on numbers of infectious centers in the spleens or on FV antibody titers in the plasma. Intraperitoneal treatment of uninfected mice with ABPP resulted in slight or no changes in percentages of Thy-1.2+, L3T4+ and Ly-2+ cells. Mice receiving multiple exposures of ABPP had an increase in percentage of splenic B cells and a depressed response to the T cell mitogen PHA. Treatment with ABPP induced the production of interferon (IFN); however, a state of hyporesponsive IFN production was seen following multiple administrations of ABPP. These data suggest that the immunomodulator ABPP may have an enhancing effect on this retroviral disease.

Utilization of transgenic mice replicating high levels of hepatitis B virus for antiviral evaluation of lamivudine.

A recently developed transgenic mouse strain which expresses high levels of hepatitis B virus (HBV) was studied as a model for evaluation of potential chemotherapeutic agents. Lamivudine ([-]2'-deoxy-3'-thiacytidine), known to reduce hepatitis B viremia in human patients, and zidovudine (3'-azido-3'-deoxythymidine), previously shown to be ineffective for HBV infections in man, were used in parallel in this transgenic animal model. Orally administered lamivudine at dosages of 100, 50, and 25 mg/kg per day given once a day for 21 days significantly decreased serum and liver HBV DNA titers in a dose-responsive manner. Zidovudine (approximately 22 mg/kg per day) administered in the drinking water for 21 days was not effective in reducing these HBV parameters as compared to transgenic placebo-treated controls. The serum HBV DNA titers rebounded to high levels 1 week after cessation of lamivudine treatment. Male and female mice responded in a similar manner to these therapies. The results using this transgenic mouse model were similar to what would be predicted from treatment of HBV-infected human patients with lamivudine and zidovudine, and indicate these mice may be useful as a small animal chemotherapeutic model for study of potential HBV inhibitors.

Effect of imexon treatment on Friend virus complex infection using genetically defined mice as a model for HIV-1 infection.

Imexon (4-imino-1,4-diazobicyclo-3.1.0-hexan-2-one) was moderately effective in the treatment of a retroviral infection in a genetically defined murine model. The animal model consisted of a Friend virus complex (FV) infection in a hybrid mouse strain, (B10.A x A/WySn)F1, which has similarities with acquired immune deficiency syndrome (AIDS). Intraperitoneal imexon initiated 1 or 3 days after FV inoculation and continued through 13 days after inoculation significantly reduced splenomegaly, splenic cell-free virus titers and viral RNA. Viral infectious centers/10(6) splenocytes and FV titers in the plasma were reduced, though not to a statistically significant level. The effect of imexon on survival was not statistically significant which suggested that the antiviral effects were only transiently effective. Phytohemagglutinin-induced blastogenesis and percent of total T cells, T helper cells and T suppressor/cytotoxic cells in the spleens were increased, and the percentage of B cells decreased by imexon treatment of both FV-infected and uninfected mice. The splenic natural killer cell activity and interleukin-1 production were not markedly affected. Virus specific neutralizing antibody developed in both imexon- and placebo-treated FV-infected mice, although titers were lower in the imexon-treated animals.

Elucidation of mode of retroviral-inhibitory effects of imexon through use of immune competent and severe combined immune deficiency (SCID) mice.

Mice infected with various tumor retroviruses have been used as models for evaluating therapeutic substances for the treatment of some cancers, and more recently, for human immunodeficiency virus (HIV) infection, the causative agent of acquired immune deficiency syndrome (AIDS). Consequently, there is a need to determine the ability of biological response modifiers (BRMs) to specifically reduce virus-infected cells, as compared to their non-specific anti-proliferative effects. To address this need, a BRM, imexon, was evaluated in this study using three strains of mice having different Friend virus (FV)-specific immunological capabilities. The first strain, (B10.A x A/WySn)F1, was genetically capable of producing FV-specific neutralization and cytotoxic antibodies, the second, Balb/c, was not, and the third, SCID mice, lacked functional T and B cell immunity. Imexon treatment reduced virally-induced splenomegaly in all 3 strains; however, the concentration of splenic viral infectious centers (IC) were not affected. Since imexon was efficacious in reducing splenomegaly in SCID mice, the mode of action was concluded to not require functional T or B cell immunity. The observation that imexon did not affect splenic IC titers also suggested that imexon did not specifically eliminate virally infected cells, but may have functioned by other mechanisms. This study also demonstrated the use of various mouse strains as a strategy for delineating the modes of action of BRMs against murine retroviral infections.

Suppression of murine retroviral disease by 2',3'-didehydro-2',3'-dideoxythymidine (D4T).

The thymidine analog, 2',3'-didehydro-2',3'-dideoxythymidine (D4T), and 3'-azido-3'-deoxythymidine (AZT) were evaluated for activity against Friend virus complex (FV) in Mus dunni cells using a focal immunoenzyme assay. The 50% effective doses were, respectively, 1.2 and 0.1 microM for the two compounds; the 50% cytotoxic doses using trypan blue dye exclusion were 25.4 and > 100 microM. Four FV inhibition experiments with D4T were run in F1 hybrid mice containing the Rfv-3r/s genotype. This mouse strain allows the study of treatment effects on development of specific neutralizing antibodies and on splenomegaly, splenic and plasma virus titers, and splenic viral RNA. In the first experiment, D4T was given by oral gavage (p.o.) three times daily (t.i.d.) for 14 days beginning 4 h post-virus inoculation. All dosages used (187.5, 375, 750 mg/kg/day) significantly inhibited all viral parameters. Other experiments used D4T p.o. twice daily, with dosages of 46.9, 93.8, 187.5 and 375 mg/kg/day or four times daily with a dose of 375 mg/kg/day. No significant disease inhibition was seen using the twice daily treatment schedule, but efficacy was apparent using the four times daily treatment. The final experiment repeated the initial study, extending the t.i.d. treatments to 25 days and using dosages of 46.9, 93.8, 187.5 and 375 mg/kg/day. All but the lowest dose reduced each virus parameter. None of the D4T treatment regimens caused death in toxicity controls, although moderate host weight loss or less weight gain was seen, and variable hematocrit decreases occurred, particularly in mice receiving the highest drug dosage. Inhibition of natural killer (NK) cell activity also was seen in these same animals, but in infected mice, FV-induced decrease in NK cell activity was prevented by D4T treatment. Virus-specific neutralizing antibodies developed in all infected, treated animals. These data indicate D4T has potential as a possible candidate for anti-human immunodeficiency virus evaluations in the clinic.

Inhibition of influenza virus infections in immunosuppressed mice with orally administered peramivir (BCX-1812).

Experiments were run to determine the effect of oral gavage treatment with the cyclopentane influenza virus neuraminidase inhibitor peramivir (BCX-1812, RWJ-270201) in influenza A (H1N1) virus-infected mice that had their immune system suppressed by cyclophosphamide (CP) therapy or in severe combined immune deficient (SCID) mice. Treatment of CP-immunosuppressed mice with peramivir using doses of 100, 10, or 1mg/kg/day was begun 2.5 or 8 days post-virus exposure and continued twice daily for 3 or 5 days. The 5-day therapy was more effective than the 3-day treatment, as seen by significantly increased survivor numbers, lessened decline in arterial oxygen saturation, reduced lung consolidation, and inhibition of lung virus titers. Infected SCID mice were also responsive to peramivir therapy begun 8 days after virus exposure and continued for 5 days, although antiviral effects did not include prevention of death and were dependent upon the viral challenge dose received. These data indicate that peramivir may have potential for treatment of influenza virus-infected immunosuppressed patients.

Influence of virus strain, challenge dose, and time of therapy initiation on the in vivo influenza inhibitory effects of RWJ-270201.

The influenza virus neuraminidase inhibitor RWJ-270201 (cyclopentane carboxylic acid, 3-[cis-1-(acetylamino)-2-ethylbutyl]-4[(aminoiminomethyl)amino]-2-hydroxy-[cis, 2S, 3R, 4R]) was significantly inhibitory to an infection in mice induced by influenza A/NWS/33 (H1N1) virus when oral gavage (p.o.) treatment with 10 mg/kg per day was delayed at least 60 h after virus exposure. Treatment was 5 mg/kg twice daily for 5 days. Viral challenge doses of influenza A/Shangdong/09/93 (H3N2) virus ranging from the LD(70) to the LD(100) did not affect the marked antiviral efficacy of 12.5 mg/kg of RWJ-270201 administered p.o. twice daily for 5 days beginning 4 h pre-virus exposure; infection by an approximate 2 LD(100) dose (10(8) cell culture infectious doses/ml) was only weakly inhibited by the same treatment as seen by significant increase in mean day to death. Murine infections induced by influenza A/Bayern/57/93 (H1N1) and B/Lee/40 viruses were significantly inhibited by 100, 10, and 1 mg/kg per day of RWJ-270201 using the above treatment regimen; influenza A/PR/8/34 (H1N1) virus infections in mice were only moderately inhibited, the antiviral effects using this virus being lessening of arterial oxygen decline, reduced lung consolidation, and inhibition of lung virus titers primarily at the higher dosages.

Immunomodulator effects on the Friend virus infection in genetically defined mice.

The disease induced by the Friend virus complex (FV) in F1 hybrid mice containing the Rfv-3r/s genotype in the presence of H-2a/a was used to evaluate a variety of immunomodulating substances. In these genetically defined mice, the FV disease results in splenomegaly, early production of high titers of cell-associated and plasma virus, high levels of splenic viral RNA, increased hematocrit, and eventual death. As the disease progresses, reduced levels of infectious virus correlate with development of specific antibody; reduction in T cell populations, increase in B cells, and decrease in T-cell function also occur. The following immunomodulators were evaluated, listed in the order of their ability to inhibit the FV disease: imexon > MVE-2 > human recombinant IFN-alpha A/D > AS101 > ampligen > AM-3 = oxamisole > ImuVert > bropirimine. In fact, bropirimine, used with certain treatment regimens, appeared to enhance the FV disease. These data suggest that certain immunomodulators may have potential value in the treatment of HIV disease, but also indicate that caution should be exercised in their clinical use.

Importance of primer selection in the application of PCR technology to the diagnosis of bovine leukemia virus.

The polymerase chain reaction (PCR) was used to detect bovine leukemia virus in bovine blood samples. When applied to leucocytes extracted from the blood samples, the standard method of DNA extraction gave good correlation with agar gel immunodiffusion, but a method in which 5 microliters of blood was the starting material was unreliable. Selection of the primers was important, and differences in results were observed when the PCR method was applied to blood samples from different geographic areas. The sensitivity varied from 50% to 90%, depending on the primer set applied to the gag gene of proviral nucleic acid. This variation was based on geographic origin of the cattle, suggesting an influence of viral strain. In some areas, more than 1 primer may needed to optimize results.

Staphylococcosis of turkeys. 1. Portal of entry and tissue colonization.

Staphylococcus aureus and various coagulase-negative staphylococci were isolated from turkeys with staphylococcosis. Virulent S. aureus adhered well (averaged more than 100 bacteria per tissue cell) in vitro to cells from tissues of the respiratory tract but did not adhere well (averaged fewer than 12 bacteria per tissue cell) to cells from tissues of the alimentary tract. Some avirulent coagulase-negative staphylococci also adhered well to cells from the respiratory tissues. Lungs and livers of turkeys became colonized with virulent S. aureus following experimental aerosol exposure. Tracheas, livers, and hock joints of some market-age turkeys were naturally colonized with S. aureus and various species of coagulase-negative staphylococci.

Early detection of bovine leukemia virus in cattle by use of the polymerase chain reaction.

A study was performed to determine whether experimentally induced bovine leukemia virus (BLV) infection in cattle could be detected earlier by use of polymerase chain reaction (PCR) amplification of genomic DNA extracted from leukocytes than by use of conventional agar-gel immunodiffusion (AGID). The PCR primers were designed to amplify a 375-base-pair region of the proviral gag gene. Five cows were identified that were BLV-negative on the basis of AGID and PCR results. At day 0, these cows were inoculated IM with blood pooled from 3 naturally infected cows. Blood samples were taken on days 0, 1, and 7, and every 2 weeks thereafter until 3 months after inoculation. Three of the cows were BLV-positive by AGID test results 3 weeks after inoculation, and the remaining 2 seroconverted at 5 weeks. In contrast, all 5 cows were BLV-positive by PCR results 7 days after inoculation and remained positive for the duration of the study. Five cows that were BLV-positive by AGID test and PCR results on day 0 and from which samples were obtained at the same times as those from the other 5 cows, remained BLV-positive by results of both tests during the course of the study. Results indicate that under experimental conditions, BLV infection in cattle can be detected as much as 2 to 4 weeks earlier by use of PCR than by use of the AGID test.

Progression of Aleutian disease in natural and experimentally induced infections of mink.

OBJECTIVE: To study temporal changes in amounts of viral DNA in blood leukocytes over long periods, and to determine whether severity of the disease is greater in experimentally induced, compared with natural, infection. ANIMALS: 18 naturally and 6 experimentally infected black mink; 26 naturally infected brown mink. PROCEDURE: Polymerase chain reaction amplification to detect viral DNA in blood and counter-immune electrophoresis to detect serum antibody were performed at regular intervals. RESULTS: In naturally infected black mink, amounts of viral DNA were initially high, but after the appearance of antibody, viral DNA fluctuated and, in some instances, was undetectable. In other mink, small amounts of viral DNA were infrequently detected during the course of the infection. Amounts of viral DNA in leukocytes in late stages of the disease correlated with renal lesions in brown mink, but black mink had more severe lesions associated with smaller amounts of viral DNA. Severity of the disease was not enhanced in experimentally inoculated black mink. CONCLUSIONS: After infection, leukocyte viral DNA is initially present in large amounts, but, in most mink, decreases markedly in association with the appearance of antibody. There is no difference in the progression and severity of the disease between black mink infected experimentally or naturally. Transmission of the disease may be enhanced by use of contaminated toenail clippers for blood collection.

Resistance to Friend leukemia virus in transgenic mice expressing the native Fv-4 gene.

Fv-4 is a truncated ecotropic retrovirus gene that codes for an envelope protein under control of a cellular promoter. It confers resistance to ecotropic murine leukemia viruses. Transgenic mice were derived using the native Fv-4 gene as the construct for microinjection. Two founder mice were derived. In both founder lines, there was no detectable expression of the transgene or resistance to Friend murine leukemia virus (FrMLV) in hemizygotes. In one line, the resistance was observed in homozygotes with Fv-4 RNA formation in the thymus but not in the spleen or in other tissues. In the other founder line, a homozygous male was identified. Double integrants, derived from breeding this homozygous male to homozygous females from the other founder line, were also resistant. These results indicate that the native gene confers the resistance in homozygous transgenic mice or double integrants derived from different founders but not hemizygotes.

Prions and transmissible spongiform encephalopathy (TSE) chemotherapeutics: A common mechanism for anti-TSE compounds?

No validated treatments exist for transmissible spongiform encephalopathies (TSEs or prion diseases) in humans or livestock. The search for TSE therapeutics is complicated by persistent uncertainties about the nature of mammalian prions and their pathogenic mechanisms. In pursuit of anti-TSE drugs, we and others have focused primarily on blocking conversion of normal prion protein, PrP(C), to the TSE-associated isoform, PrP(Sc). Recently developed high-throughput screens have hastened the identification of new inhibitors with strong in vivo anti-TSE activities such as porphyrins, phthalocyanines, and phosphorthioated oligonucleotides. New routes of administration have enhanced beneficial effects against established brain infections. Several different classes of TSE inhibitors share structural similarities, compete for the same site(s) on PrP(C), and induce the clustering and internalization of PrP(C) from the cell surface. These activities may represent a common mechanism of action for these anti-TSE compounds.

Ethical issues in transgenics.

The arguments of critics and concerns of the public on generating transgenic cloned animals are analyzed for the absence or presence of logical structure. Critics' arguments are symbolically compared with "genetic trespassing," "genetic speeding," or "going the wrong way," and responses are provided to these arguments. Scientists will be empowered to participate in the public discussion and to engage the critics on these issues as they consider thoughtful, plausible responses to their concerns. Temporary moratoriums are recognized as a plausible approach to dealing with possible concerns of new scientific advancements.