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Feline immunodeficiency virus (FIV) is a common infection found in domesticated and wild cats worldwide. Despite the wealth of therapeutic understanding of the disease in humans, considerably less information exists regarding the treatment of the disease in felines. Current treatment relies on drugs developed for the related human immunodeficiency virus (HIV) and includes compounds of the popular non-nucleotide reverse transcriptase (NNRTI) class. This is despite FIV-RT being only 67% similar to HIV-1 RT at the enzyme level, increasing to 88% for the allosteric pocket targeted by NNRTIs. The goal of this project was to try to quantify how well the more extensive pharmacological knowledge available for human disease translates to felines. To this end we screened known NNRTIs and 10 diverse pyrimidine analogs identified virtually. We use this chemo-centric probe approach to (a) assess the similarity between the two related RT targets based on the observed experimental inhibition values, (b) try to identify more potent inhibitors at FIV, and (c) gain a better appreciation of the structure-activity relationships (SAR). We found the correlation between IC 50 s at the two targets to be strong (r 2  = 0.87) and identified compound 1 as the most potent inhibitor of FIV with IC 50 of 0.030 μM ± 0.009. This compared to FIV IC 50 values of 0.22 ± 0.17 μM, 0.040 ± 0.010 μM and >160 μM for known anti HIV-1 RT drugs Efavirenz, Rilpivirine, and Nevirapine, respectively. This knowledge, along with an understanding of the structural origin that give rise to any differences could improve the way HIV drugs are repurposed for FIV., (© 2024 John Wiley & Sons Ltd.)

Feline immunodeficiency virus (FIV) is a veterinary infective agent for which there is currently no efficient drug available. Drugs targeting the lentivirus capsid are currently under development for the treatment of human immunodeficiency virus 1 (HIV-1). Here we describe a lead compound that interacts with the FIV capsid. This compound, 696 , modulates the in vitro assembly of and stabilizes the assembled capsid protein. To decipher the mechanism of binding of this compound to the protein, we performed the first nuclear magnetic resonance (NMR) assignment of the FIV p24 capsid protein. Experimental NMR chemical shift perturbations (CSPs) observed after the addition of 696 enabled the characterization of a specific binding site for 696 on p24. This site was further analyzed by molecular modeling of the protein:compound interaction, demonstrating a strong similarity with the binding sites of existing drugs targeting the HIV-1 capsid protein. Taken together, we characterized a promising capsid-interacting compound with a low cost of synthesis, for which derivatives could lead to the development of efficient treatments for FIV infection. More generally, our strategy combining the NMR assignment of FIV p24 with NMR CSPs and molecular modeling will be useful for the analysis of future compounds targeting p24 in the quest to identify an efficient treatment for FIV.

Specific treatments for the long-life infections by feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are either toxic, expensive or not too effective. Interferon α (IFN-α) is an immunomodulatory molecule which has been shown in vitro to decrease the release of infective particles. The aim of this study was to follow the progress of the clinical score and viral parameters of FeLV- and FIV-naturally infected privately owned cats treated with recombinant human IFN-α (rHuIFN-α, Roferon-A). Twenty-seven FeLV-infected cats (FeLV+) and 31 FIV-infected cats (FIV+) were enrolled in the study. Owners were instructed to orally administer 1 mL/day of 60 IU rHuIFN-α/mL in alternating weeks for four months. Blood samples were taken at the beginning of the study (M0), mid-treatment (M2), end of treatment (M4), and 6-10 months later (M10). Clinical status at these time points improved notably with rHuIFN-α treatment, regardless of the initial severity of the disease, an effect which lasted throughout the study in most animals (15 of the 16 FeLV+ symptomatic cats; 20 of the 22 FIV+ symptomatic cats) improved markedly their clinical situation. In FeLV+ cats plasma antigenemia (p27CA), reverse transcriptase (RT) activity, and proviral load decreased at M2 and M4 but increased again at M10 ("rebound effect"). The level of antigenemia or RT activity was below the detection limits in FIV+ cats, and the effect on proviral load was less marked than in FeLV+ cats. Taken together, these results indicate that rHuIFN-α is a good candidate for treating FeLV+ cats, but the "rebound effect" seen when treatment was discontinued suggests that additional studies should be conducted to clarify its effect on progression of the infection in cats., Competing Interests: The authors declare no conflict of interest.

Feline immunodeficiency virus (FIV) induces opportunistic disease in chronically infected cats, and both prednisolone and cyclosporine A (CsA) are clinically used to treat complications such as lymphoma and stomatitis. However, the impact of these compounds on FIV infection are still unknown and understanding immunomodulatory effects on FIV replication and persistence is critical to guide safe and effective therapies. To determine the immunologic and virologic effects of prednisolone and CsA during FIV infection, FIV-positive cats were administered immunosuppressive doses of prednisolone (2 mg/kg) or CsA (5 mg/kg). Both prednisolone and CsA induced acute and transient increases in FIV DNA and RNA loads as detected by quantitative PCR. Changes in the proportion of lymphocyte immunophenotypes were also observed between FIV-infected and naïve cats treated with CsA and prednisolone, and both treatments caused acute increases in CD4+ lymphocytes that correlated with increased FIV RNA. CsA and prednisolone also produced alterations in cytokine expression that favored a shift toward a Th2 response. Pre-treatment with CsA slightly enhanced the efficacy of antiretroviral therapy but did not enhance clearance of FIV. Results highlight the potential for drug-induced perturbation of FIV infection and underscore the need for more information regarding immunopathologic consequences of therapeutic agents on concurrent viral infections.

A small diverse library of pentathiepin derivatives were prepared to evaluate their efficacy against the nucleocapsid protein function of the feline immunodeficiency virus (FIV) as a model for HIV, using an in vitro cell culture approach. This study led to the development of nanomolar active compounds with low toxicity., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Feline sporotrichosis due to Sporothrix brasiliensis is frequently severe and often correlated to zoonotic transmission. Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV) cause immunodeficiency in cats; no association has been identified with critical cases of sporotrichosis. Moreover, the cytokine profile in Sporothrix-infected cats and a potential impact of retrovirus co-infections on their immunity is unknown. This study assessed immunological parameters in cats with sporotrichosis with and without FIV or FeLV co-infection. FeLV infection was detected by antigen ELISA and by provirus PCR. FIV infection was investigated through ELISA and Western blot. Cytokine transcription (IFN-γ, IL-4, IL-5, IL-6, IL-10, IL-12, TNF-α) was quantified using RT-qPCR and lymphocyte subpopulations (CD4, CD8, CD5 and CD21) were assessed by flow cytometry. Thirty cats with sporotrichosis were recruited to the study, including three FIV-positive and five FeLV-positive (progressive infection) cats. One cat with regressive FeLV infection was excluded from statistics. In comparison to retrovirus-negative cats, FIV-positive cats and FeLV-positive cats had higher IL-10 levels, FeLV-positive cats had lower IL-4 levels and FIV-positive cats had lower IL-12 levels and a lower CD4+/CD8+ ratio. Remarkably, all cats with poor general condition were FeLV (progressive infection) or FIV-positive, but the retrovirus status was not associated with the sporotrichosis treatment length or outcome. The immunological changes and the more severe clinical presentation observed in cats with retrovirus co-infections encourage future prospective studies that address the impact of these changes on prognostic determinants of feline sporotrichosis and the development of new therapy strategies that control disease spread., Competing Interests: The authors have declared that no competing interests exist.

Feline immunodeficiency virus (FIV) is a lentivirus that causes immunosuppression through virus-mediated CD4+ T cell depletion in feline species. FIV infection is complicated by virus-induced disease in the nervous system. FIV enters the brain soon after primary infection and is detected as FIV-encoded RNA, DNA, and proteins in microglia, macrophages, and astrocytes. FIV infection activates neuroinflammatory pathways including cytokines, chemokines, proteases, and ROS with accompanying neuronal injury and loss. Neurobehavioral deficits during FIV infection are manifested as impaired motor and cognitive functions. Several treatment strategies have emerged from studies of FIV neuropathogenesis including the therapeutic benefits of antiretroviral therapies, other protease inhibitors, anti-inflammatory, and neurotrophic compounds. Recently, insulin's antiviral, anti-inflammatory, and neuroprotective effects were investigated in models of lentivirus brain infection. Insulin suppressed HIV-1 replication in human microglia as well as FIV replication of lymphocytes. Insulin treatment diminished cytokine and chemokine activation in HIV-infected microglia while also protecting neurons from HIV-1 Vpr protein-mediated neurotoxicity. Intranasal (IN) insulin delivery for 6 weeks suppressed FIV expression in the brains of treated cats. IN insulin also reduced neuroinflammation and protected neurons in the hippocampus, striatum, and neocortex of FIV-infected animals. These morphological and molecular effects of IN insulin were confirmed by neurobehavioral studies that showed IN insulin-treated FIV-infected animals displayed improved motor and cognitive performance compared to sham-treated FIV-infected animals. Thus, FIV infection of the nervous system provides a valuable comparative in vivo model for discovering and evaluating disease mechanisms as well as developing therapeutic strategies for NeuroAIDS in humans.

A diverse library of 5-thieno-, 5-oxo-, and 5-imino-1,2,3-dithiazole derivatives was synthesized and evaluated for efficacy against the feline immunodeficiency virus (FIV) as a model for HIV in cells. Several diverse compounds from this series displayed nanomolar activity and low toxicity, representing a potential new class of compounds for the treatment of FIV and HIV., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Objectives: Feline immunodeficiency virus (FIV) is a lentivirus that induces AIDS-like disease in cats. Some of the antiretroviral drugs available to treat patients with HIV type 1 are used to treat FIV-infected cats; however, antiretroviral therapy (ART) is not used in cats as a long-term treatment. In this study, the effects of long-term ART were evaluated in domestic cats treated initially with the nucleoside transcriptase reverse inhibitor (NTRI) zidovudine (AZT) over a period ranging from 5-6 years, followed by a regimen of the NTRI lamivudine (3TC) plus AZT over 3 years., Methods: Viral load, sequencing of pol (reverse transcriptase [RT]) region and CD4:CD8 lymphocyte ratio were evaluated during and after treatment. Untreated cats were evaluated as a control group., Results: CD4:CD8 ratios were lower, and uncharacterized resistance mutations were found in the RT region in the group of treated cats. A slight increase in viral load was observed in some cats after discontinuing treatment., Conclusions and Relevance: The data strongly suggest that treated cats were resistant to therapy, and uncharacterized resistance mutations in the RT gene of FIV were selected for by AZT. Few studies have been conducted to evaluate the effect of long-term antiretroviral therapy in cats. To date, resistance mutations have not been described in vivo., (© ISFM and AAFP 2015.)

A novel series of fused tetrathiocines were prepared for evaluation of activity against the nucleocapsid protein of the feline immunodeficiency virus (FIV) in an in vitro cell culture approach. The results demonstrated that the compounds display potent nanomolar activity and low toxicity against this key model of HIV infection., (Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.)

Feline immunodeficiency virus (FIV), the causative agent of an acquired immunodeficiency syndrome in cats (feline AIDS), is a ubiquitous health threat to the domestic and feral cat population, also triggering disease in wild animals. No registered antiviral compounds are currently available to treat FIV-infected cats. Several human antiviral drugs have been used experimentally in cats, but not without the development of serious adverse effects. Here we report on the treatment of six naturally FIV-infected cats, suffering from moderate to severe disease, with the antiretroviral compound (R)-9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine ([R]-PMPDAP), a close analogue of tenofovir, a widely prescribed anti-HIV drug in human medicine. An improvement in the average Karnofsky score (pretreatment 33.2 ± 9.4%, post-treatment 65±12.3%), some laboratory parameters (ie, serum amyloid A and gammaglobulins) and a decrease of FIV viral load in plasma were noted in most cats. The role of concurrent medication in ameliorating the Karnofsky score, as well as the possible development of haematological side effects, are discussed. Side effects, when noted, appeared mild and reversible upon cessation of treatment. Although strong conclusions cannot be drawn owing to the small number of patients and lack of a placebo-treated control group, the activity of (R)-PMPDAP, as observed here, warrants further investigation., (© ISFM and AAFP 2014.)

Feline immunodeficiency virus (FIV) is a naturally-occurring, large animal model of lentiviral-induced immunodeficiency syndrome, and has been used as a model of HIV pathogenesis and therapeutic interventions. HIV reservoirs in the form of latent virus remain the primary roadblock to viral eradication and cure, and FIV has been previously established an animal model of lentiviral latency. The goal of this study was to determine whether administration of the histone deacetylase inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA) to aviremic, chronically FIV-infected cats would induce latent viral reactivation in vivo. A proof-of-concept experiment in a Transwell co-culture system demonstrated the ability of SAHA to reactivate latent virus which was replication competent and able to infect naïve cells. Oral SAHA (250mg/m(2)) was administered with food to four asymptomatic, experimentally FIV-infected cats and one uninfected control cat, and a limited pharmacokinetic and pharmacodynamic analysis was performed. A statistically significant increase in cell-associated FIV RNA was detected in the cat with the greatest serum SAHA exposure, and cell-free viral RNA was detected at one time point in the three cats that achieved the highest levels of SAHA in serum. Interestingly, there was a significant decrease in viral DNA burden at 2h post drug administration in the same three cats. Though the sample size is small and the drug response was modest, this study provides evidence that in vivo treatment of FIV-infected cats with the HDACi SAHA can induce viral transcriptional reactivation, which may be dependent upon the concentration of SAHA achieved in blood. Importantly, alternative putative antilatency therapy drugs, and multimodal drug combinations, could be studied in this in vivo system. The FIV/cat model provides a unique opportunity to test novel therapeutic interventions aimed at eradicating latent virus in vivo., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A diverse library of bis[1,2]dithiolo[1,4]thiazines and bis[1,2]dithiolopyrrole derivatives were prepared for evaluation of activity against the nucleocapsid protein of the Feline Immunodeficiency Virus (FIV) as a model for HIV, using an in vitro cell culture approach, yielding nanomolar active compounds with low toxicity., (Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.)

Neutropenia can often be corrected by treatment with granulocyte-colony stimulating factor (G-CSF) and off-label use of commercial human G-CSF (HuG-CSF) is a commonly used treatment for neutropenic animals. However, long-term HuG-CSF treatment can be associated with adverse effects, including neutropenia. Here, feline (Fe) G-CSF was produced in Pichia pastoris, pegylated (Peg) FeG-CSF and tested in cats. A randomized controlled clinical trial was conducted to evaluate the efficacy of PegFeG-CSF compared to FeG-CSF or HuG-CSF in FIV-infected (n=14), FIV-uninfected healthy cats (n=19), and in HuG-CSF-induced neutropenic cats (n=4). Daily FeG-CSF doses induced higher neutrophil production than HuG-CSF after the second week of treatment (P ⩽ 0.002). Weekly doses of PegFeG-CSF induced higher neutrophil counts and showed greater sustained activity than weekly doses of FeG-CSF. PegFeG-CSF provided the most therapeutic and sustainable neutrophil production (P<0.001) in both FIV-uninfected and FIV-infected cats, without the development of neutralizing antibodies. Conversely, all HuG-CSF-treated cats developed neutralizing antibodies, suggesting cross-reactive antibodies to endogenous G-CSF in a majority of the cases with severe neutropenia. Strikingly, when PegFeG-CSF was used to rescue cats with HuG-CSF-induced neutropenia, clinically normal neutrophil numbers returned. Thus, PegFeG-CSF appears to be a superior treatment for neutropenia in feline patients., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Objective: To compare cytotoxic effects and antiviral efficacy of 9 nucleoside reverse transcriptase inhibitors (NRTIs) against FIV in feline peripheral blood mononuclear cells., Sample: Peripheral blood mononuclear cells obtained from 3 specific pathogen-free cats., Procedures: 3 of the 9 NRTIs had not been previously assessed in feline cell lines. Cytotoxic effects were determined by colorimetric quantification of a formazan product resulting from bioreduction of a tetrazolium reagent by viable peripheral blood mononuclear cells; uninfected cells from 1 cat were used in these assays. Cells from all 3 cats were infected with a pathogenic clone of FIV, and in vitro antiviral efficacy of each NRTI was assessed with an FIV p24 antigen capture ELISA., Results: Cytotoxic effects in feline peripheral blood mononuclear cells were observed only at concentrations > 10 μM for all 9 NRTIs. Comparison of the cytotoxic effect at the highest concentration investigated (500 μM) revealed that didanosine and amdoxovir were significantly less toxic than abacavir. All drugs induced a dose-dependent reduction of FIV replication. At the highest concentration investigated (10 μM), there was no significant difference in antiviral efficacy among the test compounds., Conclusions and Clinical Relevance: The evaluated NRTIs had low cytotoxicity against feline peripheral blood mononuclear cells and appeared to be safe options for further in vivo evaluation for the treatment of FIV-infected cats. There was no evidence suggesting that the newly evaluated compounds would be superior to the existing NRTIs for reducing FIV burden of infected cats.

An infectious chimeric feline immunodeficiency virus (FIV)/HIV strain carrying six HIV-like protease (PR) mutations (I37V/N55M/V59I/I98S/Q99V/P100N) was subjected to selection in culture against the PR inhibitor lopinavir (LPV), darunavir (DRV), or TL-3. LPV selection resulted in the sequential emergence of V99A (strain S-1X), I59V (strain S-2X), and I108V (strain S-3X) mutations, followed by V37I (strain S-4X). Mutant PRs were analyzed in vitro, and an isogenic virus producing each mutant PR was analyzed in culture for LPV sensitivity, yielding results consistent with the original selection. The 50% inhibitory concentrations (IC50s) for S-1X, S-2X, S-3X, and S-4X were 95, 643, 627, and 1,543 nM, respectively. The primary resistance mutations, V99(82)A, I59(50)V, and V37(32)I, are consistent with the resistance pattern developed by HIV-1 under similar selection conditions. While resistance to LPV emerged readily, similar PR mutations causing resistance to either DRV or TL-3 failed to emerge after passage for more than a year. However, a G37D mutation in the nucleocapsid (NC) was observed in both selections and an isogenic G37D mutant replicated in the presence of 100 nM DRV or TL-3, whereas parental chimeric FIV could not. An additional mutation, L92V, near the PR active site in the folded structure recently emerged during TL-3 selection. The L92V mutant PR exhibited an IC50 of 50 nM, compared to 35 nM for 6s-98S PR, and processed the NC-p2 junction more efficiently, consistent with increased viral fitness. These findings emphasize the role of mutations outside the active site of PR in increasing viral resistance to active-site inhibitors and suggest additional targets for inhibitor development.

Feline Immnunodeficiency (FIV) and Feline Leukemia (FeLV) viruses are common infectious agents in stray cats and shelter environments. Recombinant feline interferon-ω (rFeIFNω) has shown an antiviral action not only against FIV and FeLV but also against herpesvirus (FHV-1) and calicivirus (FCV). Sixteen naturally infected FIV/FeLV cats were followed during rFeIFNω therapy in order to monitor clinical signs and to correlate with excretion of concomitant viruses (FCV, FHV-1, feline coronavirus (FCoV) and parvovirus (FPV)). Cats were submitted to clinical evaluations and concomitant virus excretion assessement. Comparing D0-D65, 10/16 cats improved clinical scores. Of the 10 cats positive for FHV-1 on D0, 4 were negative and 6 reduced viral loads. Of the 11 FCoV positive cats, 9 reduced viral loads. The 13 FCV positive cats and the FPV positive cat were negative on D65. In conclusion, rFeIFNω improves clinical signs and reduces concurrent viral excretion in naturally infected retroviral cats., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

New large-scale synthetic approach to antiretroviral agent 9-[2-(R)-(phosphonomethoxy)propyl]-2,6-diaminopurine, (R)-PMPDAP, was developed. Reaction of (R)-propanediol carbonate with 2,6-diaminopurine afforded exclusively (R)-9-(2-hydroxypropyl)-2,6-diaminopurine which was subsequently used for introduction of a phosphonomethyl residue using TsOCH(2)P(O)(OiPr)(2) or BrCH(2)P(O)(OiPr)(2) followed by deprotection of ester groups. All minor ingredients and by-products formed during the process were identified and further studied. The final product was obtained in high yield and its high enantiomeric purity (>99%) was confirmed by chiral capillary electrophoretic analysis using β-cyclodextrin as a chiral selector. Antiretroviral activity data of (R)-PMPDAP and its diverse prodrugs against HIV and FIV were investigated. Akin to (R)-PMPDAP, both prodrugs inhibit FIV replication in a selective manner. Compared to the parent molecule, the amidate prodrug was 10-fold less active against FIV in cell culture, whereas the alkoxyalkyl ester prodrug was 200-fold more potent in inhibiting FIV replication in vitro., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The phorbol ester Prostratin may either stimulate or inhibit human immunodeficiency virus-1 (HIV-1) replication. Here we report that Prostratin also exhibits a similar dual action upon feline immunodeficiency virus (FIV) replication in an IL-2-dependent feline CD4(+) T-cell line (MYA-1). While withdrawal of IL-2 halted FIV spread, Prostratin rescued virus production and cell viability, mimicking the functions of the cytokine. Conversely, FIV grew rapidly in the presence of IL-2 and this was inhibited by Prostratin. In contrast to HIV-1, Prostratin mediated inhibition of FIV through means other than blocking virus entry. Co-application of the protein kinase C (PKC) inhibitor Gö6850 with Prostratin reversed both the inhibitory and stimulatory effects, suggesting that PKC is crucial for FIV replication., (Copyright © 2012 Elsevier B.V. All rights reserved.)

FIV establishes a latent infection in peripheral CD4+ T-cells, and the latent FIV promoter is associated with deacetylated, methylated histones, consistent with a restrictive chromatin structure. Here we explored the use of 5 histone-modifying agents - 4 histone deacetylase inhibitors (HDACi) and 1 histone methyltransferase inhibitor (HMTi) - to reactivate latent FIV ex vivo. All compounds tested were able to alter histone lysine residue modifications in feline cells, both globally and at the FIV promoter locally. When latently FIV-infected peripheral CD4+ T-cells were cultured ex vivo in the presence of these inhibitors, viral transcription was significantly activated relative to no treatment controls. Transcriptional reactivation of virus mediated by the HDACi suberoylanilide hydroxamic acid (SAHA) was dose-dependent, detected after as little as 1h of exposure, and resulted in virion formation as evidenced by supernatant reverse transcriptase activity. A synergistic effect was not found when SAHA was combined with HMTi under the conditions tested. At low therapeutically relevant concentrations in primary feline PBMC, SAHA was found to be minimally cytotoxic and non-immune activating. HDACi and HMTi can reactivate latent FIV ex vivo, and SAHA, also known as the anticancer drug Vorinostat, in particular is a promising candidate for in vivo use because of its efficacy, potency, and relative safety. Use of the FIV/cat model of lentiviral latency to explore in vivo treatment with SAHA and other anti-latency therapeutics will allow investigations that are either ethically or logistically not addressable in patients persistently infected with human immunodeficiency virus (HIV-1)., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Feline immunodeficiency virus (FIV) is a member of the retroviridae family of viruses and causes an acquired immunodeficiency syndrome (AIDS) in domestic and non-domestic cats worldwide. Genome organization of FIV and clinical characteristics of the disease caused by the virus are similar to those of human immunodeficiency virus (HIV). Both viruses infect T lymphocytes, monocytes and macrophages, and their replication cycle in infected cells is analogous. Due to marked similarity in genomic organization, virus structure, virus replication and disease pathogenesis of FIV and HIV, infection of cats with FIV is a useful tool to study and develop novel drugs and vaccines for HIV. Anti-retroviral drugs studied extensively in HIV infection have targeted different steps of the virus replication cycle: (1) inhibition of virus entry into susceptible cells at the level of attachment to host cell surface receptors and co-receptors; (2) inhibition of fusion of the virus membrane with the cell membrane; (3) blockade of reverse transcription of viral genomic RNA; (4) interruption of nuclear translocation and viral DNA integration into host genomes; (5) prevention of viral transcript processing and nuclear export; and (6) inhibition of virion assembly and maturation. Despite much success of anti-retroviral therapy slowing disease progression in people, similar therapy has not been thoroughly investigated in cats. In this article we review current pharmacological approaches and novel targets for anti-lentiviral therapy, and critically assess potentially suitable applications against FIV infection in cats.

In in vitro studies, the acyclic nucleoside phosphonate 9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine (PMPDAP) inhibited the replication of feline immunodeficiency virus (FIV). No information about its clinical efficacy is available so far. The aim of this prospective placebo-controlled, double-blinded study was to evaluate the antiviral efficacy of PMPDAP in cats naturally infected with FIV. Twenty cats were randomly assigned to two treatment groups receiving either PMPDAP (25 mg/kg) or placebo twice per week subcutaneously for 6 weeks. The general health status (Karnofsky's score), clinical signs, laboratory, immunological, and surrogate parameters were evaluated. No significant differences were found between PMPDAP- and placebo-treated cats, although cats treated with PMPDAP showed a tendency for improvement in their Karnofsky's score and clinical signs. Haematological side effects were noted in the PMPDAP-treated cats. Thus, PMPDAP may be an option in treating cats if it becomes available for veterinarians, but side effects have been monitored.

Type-I interferons (IFNs) are cytokines that have non-specific antiviral activity, participating mostly in innate defense mechanisms. Their administration has been proposed to treat several viral and immunomediated diseases as an immunomodulatory therapy. Due to its availability, recombinant human interferon-alpha (rHuIFN-α) has been studied in relation to feline retrovirosis, both in vitro and in vivo. However, IFNs are species-specific and antibodies have been shown to develop in response to the high rHuIFN-α doses necessary for an effective therapy. A recombinant feline IFN has been developed, which has been characterized as interferon-omega (rFeIFN-ω), designed to overcome these problems. Nonetheless, very few studies have been undertaken to evaluate its efficacy in cats naturally infected with FIV or FeLV. In an initial study, we here demonstrated that rFeIFN-ω can dramatically improve the clinical condition of infected cats, and induce improvement of hematologic parameters. Minor changes or no change was observed for hypergammaglobulinemia, CD4/CD8 ratio, proviral load, viremia and RT activity, suggesting that the overall effect of IFN was on innate immunity. More studies are needed in order to better understand its in vivo mechanisms., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Domestic cats endure infections by all three subfamilies of the retroviridae: lentiviruses (feline immunodeficiency virus [FIV]), gammaretroviruses (feline leukemia virus [FeLV]), and spumaretroviruses (feline foamy virus [FFV]). Thus, cats present an insight into the evolution of the host-retrovirus relationship and the development of intrinsic/innate immune mechanisms. Tetherin (BST-2) is an interferon-inducible transmembrane protein that inhibits the release of enveloped viruses from infected cells. Here, we characterize the feline homologue of tetherin and assess its effects on the replication of FIV. Tetherin was expressed in many feline cell lines, and expression was induced by interferons, including alpha interferon (IFN-α), IFN-ω, and IFN-γ. Like human tetherin, feline tetherin displayed potent inhibition of FIV and HIV-1 particle release; however, this activity resisted antagonism by either HIV-1 Vpu or the FIV Env and "OrfA" proteins. Further, as overexpression of complete FIV genomes in trans could not overcome feline tetherin, these data suggest that FIV lacks a functional tetherin antagonist. However, when expressed stably in feline cell lines, tetherin did not abrogate the replication of FIV; indeed, syncytium formation was significantly enhanced in tetherin-expressing cells infected with cell culture-adapted (CD134-independent) strains of FIV (FIV Fca-F14 and FIV Pco-CoLV). Thus, while tetherin may prevent the release of nascent viral particles, cell-to-cell spread remains efficient in the presence of abundant viral receptors and tetherin upregulation may enhance syncytium formation. Accordingly, tetherin expression in vivo may promote the selective expansion of viral variants capable of more efficient cell-to-cell spread.

Background: Feline immunodeficiency virus (FIV) is a lentivirus that infects domestic and wild felidae and the course of disease is similar to that of human immunodeficiency virus infection. The thymidine nucleoside analog fozivudine (FZD) tidoxil is a lipid-zidovudine (ZDV) conjugate and member of the family of nucleoside reverse transcriptase (RT) inhibitors (NRTIs)., Hypothesis: FZD administration to cats during acute FIV infection produces antiviral activity with fewer adverse effects than its parent compound ZDV (AZT)., Animals: Male, neutered cats approximately 7 months of age (n = 12)., Methods: FZD (45 mg/kg q12h, n = 6) or placebo (n = 6) was administered PO in a nonblinded trial for 6 weeks to cats infected with the NCSU(1) isolate of FIV. Peripheral blood was collected preinfection and at 2, 4, and 6 weeks postinfection for CBC, evaluation of CD4(+) and CD8(+) cell counts by flow cytometry, and quantification of plasma and cell-associated viremia by real time RT-PCR., Results: Treatment of cats with FZD during the acute stage of FIV infection decreased plasma and cell-associated viremia during the first 2 weeks of infection, but was not protective against FIV, as all cats were infected by 6 weeks., Conclusions: At the dosage used in this study, treatment with FZD results in a short-term decrease in viral load with no adverse effects. Further investigation of FZD is warranted to assess pharmacokinetics, optimal dosage, and to directly compare the antiviral activity of FZD to ZDV in naturally infected cats., (Copyright © 2011 by the American College of Veterinary Internal Medicine.)

Interferon-tau (IFN-tau) was initially identified as an ovine pregnancy protein. Produced by the trophoblast, it is important in preventing degradation of the corpus luteum and has been used as an early marker for ovine pregnancy. As a member of the family of type I interferons, IFN-tau has demonstrated promising antiviral activity against human viral infections in vitro. Additionally, it displays high species cross-reactivity despite its absence in humans. To date, IFN-tau has shown efficacy in reducing replication of human immunodeficiency virus, feline immunodeficiency virus, and human papillomavirus. While IFN-tau shares similar antiviral activity to IFN-alpha, the current interferon of choice for treatment of viral infections, it lacks the associated toxicity. This may make IFN-tau an attractive alternative to IFN-alpha for the treatment of viral infections.

Feline immunodeficiency virus (FIV) and human immunodeficiency virus type 1 (HIV-1) proteases (PRs) share only 23% amino acid identity and exhibit distinct specificities yet have very similar 3-dimensional structures. Chimeric PRs in which HIV residues were substituted in structurally equivalent positions in FIV PR were prepared in order to study the molecular basis of PR specificity. Previous in vitro analyses showed that such substitutions dramatically altered the inhibitor specificity of mutant PRs but changed the rate and specificity of Gag cleavage so that chimeric FIVs were not infectious. Chimeric PRs encoding combinations of the I37V, N55M, M56I, V59I, L97T, I98P, Q99V, and P100N mutations were cloned into FIV Gag-Pol, and those constructs that best approximated the temporal cleavage pattern generated by wild-type FIV PR, while maintaining HIV-like inhibitor specificity, were selected. Two mutations, M56I and L97T, were intolerant to change and caused inefficient cleavage at NC-p2. However, a mutant PR with six substitutions (I37V, N55M, V59I, I98P, Q99V, and P100N) was selected and placed in the context of full-length FIV-34TF10. This virus, termed YCL6, had low-level infectivity ex vivo, and after passage, progeny that exhibited a higher growth rate emerged. The residue at the position of one of the six mutations, I98P, further mutated on passage to either P98H or P98S. Both PRs were sensitive to the HIV-1 PR inhibitors lopinavir (LPV) and darunavir (DRV), as well as to the broad-based inhibitor TL-3, with 50% inhibitory concentrations (IC(50)) of 30 to 40 nM, consistent with ex vivo results obtained using mutant FIVs. The chimeras offer an infectivity system with which to screen compounds for potential as broad-based PR inhibitors, define structural parameters that dictate specificity, and investigate pathways for drug resistance development.

FIV is a significant pathogen in the cat and is, in addition, the smallest available natural model for the study of lentivirus infections. Although divergent at the amino acid level, the cat lentivirus has an abundance of structural and pathophysiological commonalities with HIV and thus serves well as a model for development of intervention strategies relevant to infection in both cats and man. The following review highlights both the strengths and shortcomings of the FIV/cat model, particular as regards development of antiviral drugs.

Feline immunodeficiency virus (FIV) is a pathogenic virus that causes an AIDS-like syndrome in the domestic cats. For viral entry and infection, fusion between the virus and the cell membrane is the critical process and this process is mediated by an envelope glycoprotein gp40. We have identified fusion inhibitory peptides from the heptad repeat-2 (HR2) of gp40. Remodeling of the original sequences using alpha-helix-inducible motifs revealed the interactive residues of gp40. Comparative analysis of HR2 peptides derived from four FIV strains demonstrated that the interactive surface of the Shizuoka strain-derived HR2 peptides provides the highest affinity of all the FIV strains examined.

For the entry of lentivirus into target cells, fusion between its viral membrane and cellular membrane is essential. The present study was conducted to examine the inhibitory effect of modified peptides corresponding to heptad repeats (HR) 1 and 2 of feline immunodeficiency virus (FIV) envelope gp40 on the fusion between the viral and cellular membranes. FIV-N36 and FIV-C35 were synthesized as authentic peptides of the N-terminal HR1 domain and C-terminal HR2 domain of FIV gp40, respectively. FIV-C35EK1, FIV-C35EK2, and FIV-C35EK3 were peptides synthesized by modifying FIV-C35 as the X-EE-XX-KK concept to increase their solubility in water and the stability of their alpha-helicity. FIV-C35 and FIV-C35EK1 inhibited the cell membrane fusion mediated by FIV-infected cells and the replication of FIV. FIV-N36, FIV-C35EK2, and FIV-C35EK3 did not show any apparent inhibitory effect. These results indicated that the newly developed membrane fusion inhibitors could facilitate the development of novel anti-lentiviral chemotherapies.

The feline AIDS model for HIV-1 treatment failed in the 1990s, due to structural features resembling protease inhibitor (PI) resistant HIV-1 variants. Widespread drug-resistance to PIs now invokes the possibility of rescuing feline immunodeficiency virus (FIV) as a model for PI treatment. We here analyzed susceptibility of FIV to second generation PIs, lopinavir, atazanavir, and the structurally unrelated non-peptidic PI tipranavir. We found that FIV protease resembles HIV-1 protease drug resistance mutations limiting binding of lopinavir and atazanavir but not tipranavir. All three PIs were found to inhibit FIV replication in a concentration-dependent manner, but only tipranavir inhibited FIV similarly to HIV-1. This drug inhibited FIV synergistically with ritonavir. Inhibition of protease activity was confirmed by Western blot analysis. In molecular docking simulations, tipranavir displayed energetically favorable interactions with the catalytic cavity of the mature dimeric FIV protease. The calculated hydrogen bond network was similar to that found in HIV-1 protease/tipranavir complexes and involved atoms in the protein backbone. We also modeled the interaction of tipranavir with an immature protease monomer, suggesting that inhibition of protease dimerization may be a secondary modality for FIV inhibition by tipranavir. In conclusion, tipranavir is the first FDA-approved non-reverse transcriptase inhibitor of HIV-1 to show anti-FIV properties. The tipranavir response by FIV may 1) support the idea of using FIV as a small animal model for PI-resistant HIV-1, thus expanding access to animal AIDS models; and 2) pave the way for development of novel broad-based inhibitors for treatment of drug resistant HIV-1.

Influences of the cell system on observed EC(50) values of different agents against feline immunodeficiency virus (FIV) were assessed. The activity of various nucleoside reverse transcriptase inhibitors (NRTI) against a lymphotropic FIV strain was evaluated using monocultured thymocytes and a DC-thymocyte coculture. In the second set of experiments activity of carbohydrate binding agents (CBA) towards FIV strains derived from different cell lines (e.g. Crandall feline kidney cells (CRFK) and thymocytes) was compared. We examined three different FIV-based antiviral evaluation systems and obtained marked differences in EC(50) values, especially for CBA entry inhibitors. Our study confirms and extends earlier observed differences between cell systems used for the evaluation of the activity of antivirals towards FIV.

Background: Treatment of feline immunodeficiency virus (FIV) infection has been hampered by the absence of a specific combination antiretroviral treatment (ART). Integrase strand transfer inhibitors (INSTIs) are emerging as a promising new drug class for HIV-1 treatment, and we evaluated the possibility of inhibiting FIV replication using INSTIs., Methods: Phylogenetic analysis of lentiviral integrase (IN) sequences was carried out using the PAUP* software. A theoretical three-dimensional structure of the FIV IN catalytic core domain (CCD) was obtained by homology modeling based on a crystal structure of HIV-1 IN CCD. The interaction of the transferred strand of viral DNA with the catalytic cavity of FIV IN was deduced from a crystal structure of a structurally similar transposase complexed with transposable DNA. Molecular docking simulations were conducted using a genetic algorithm (GOLD). Antiviral activity was tested in feline lymphoblastoid MBM cells acutely infected with the FIV Petaluma strain. Circular and total proviral DNA was quantified by real-time PCR., Results: The calculated INSTI-binding sites were found to be nearly identical in FIV and HIV-1 IN CCDs. The close similarity of primate and feline lentivirus IN CCDs was also supported by phylogenetic analysis. In line with these bioinformatic analyses, FIV replication was efficiently inhibited in acutely infected cell cultures by three investigational INSTIs, designed for HIV-1 and belonging to different classes. Of note, the naphthyridine carboxamide INSTI, L-870,810 displayed an EC50 in the low nanomolar range. Inhibition of FIV integration in situ was shown by real-time PCR experiments that revealed accumulation of circular forms of FIV DNA within cells treated with L-870,810., Conclusion: We report a drug class (other than nucleosidic reverse transcriptase inhibitors) that is capable of inhibiting FIV replication in vitro. The present study helped establish L-870,810, a compound successfully tested in human clinical trials, as one of the most potent anti-FIV agents ever tested in vitro. This finding may provide new avenues for treating FIV infection and contribute to the development of a small animal model mimicking the effects of ART in humans.

RNA interference (RNAi) is a process in which double-stranded RNA induces the post-transcriptional sequence-specific degradation of homologous messenger RNA. The present study was carried out to apply the RNAi technology to inhibit the replication of feline immunodeficiency virus (FIV). Four small interfering RNAs (siRNAs) homologous to the FIV gag gene were synthesized and transfected into a feline fibroblastic cell line chronically infected with FIV (CRFK/FIV). These synthetic siRNAs efficiently inhibited the replication of FIV. Next, we examined the effect of retroviral vector-mediated transfer of FIV-specific short hairpin RNA (shRNA) on the replication of FIV in a feline T-cell line chronically infected with FIV (FL4). The retroviral vector-mediated transfer of FIV-specific shRNA was shown to markedly inhibit the replication of FIV in the FL4 cells. These results provide useful information for the development of RNAi-based gene therapy strategy to control FIV infection.

By using a genetic screen, we have isolated a mammalian cell line that is resistant to infection by retroviruses that are derived from the murine leukemia virus, human immunodeficiency virus type 1, and feline immunodeficiency virus. We demonstrate that the cell line is genetically recessive for the resistance, and hence it is lacking a factor enabling infection by retroviruses. The block to infection is early in the life cycle, at the poorly understood uncoating stage. We implicate the proteasome at uncoating by completely rescuing the resistant phenotype with the proteasomal inhibitor MG-132. We further report on the complementation cloning of a gene (MRI, modulator of retrovirus infection) that can also act to reverse the inhibition of infection in the mutant cell line. These data implicate a role for the proteasome during uncoating, and they suggest that MRI is a regulator of this activity. Finally, we reconcile our findings and other published data to suggest a model for the involvement of the proteasome in the early phase of the retroviral life cycle.

Several animal models for the study of HIV/AIDS have been established and characterized and have been widely used to study the pathogenesis of HIV/AIDS as well as vaccine development. The purpose of this study was to review the literature and identify the animal models most frequently used for the evaluation of drugs, drug combinations, plant extracts and drug-plant combinations. Four of these animal models were evaluated namely the SIV model due to its similarities in pathogenesis of disease to humans, the FIV and the LP-BM5 model due to wide availability and the SCID murine model that combines components of both systems. The pathogenesis of disease in each model, application in the evaluation of drugs, drug combinations and plant extracts as well as the inherent advantages and disadvantages of each model are discussed. The LP-BM5 murine AIDS (MAIDS) model with its in vitro equivalent was identified as the animal model, although not identical to HIV/AIDS, most suitable for the rapid and cost effective initial screening of drugs, drug combinations, plant extracts and drug-plant combinations.

P59 is the Trp-rich 20-mer peptide ((767)L-G(786)), partial sequence of the membrane-proximal external region (MPER) of the FIV gp36. It has potent antiviral activity, possibly due to a mechanism that inhibits the fusion of the virus with the cell membranes. In the hypothesis that a lipophilic tail could enhance the adhesion of P59 to the membrane so improving its antiviral activity, we synthesized its lipoylated analogue lipo-P59. Fluorescence, CD and NMR investigations in membrane mimicking environments (such as SDS and DPC micelles) were aimed to assess the potential of the lipo-P59 lipophilic tail to affect the biophysical and conformational behaviour of the peptide. In vitro inhibitory assays using lymphoid cell cultures to check the antiviral activity of peptides were also performed. The data show that the biophysical properties and the conformational preferences of the peptides are not dramatically affected by the hydrophobic tail, suggesting that the lipopeptide is capable of preserving all the biophysical peculiarities. Similarly, antiviral experimental data show that the membrane-anchored lipo-P59 peptide is also effective in inhibiting virus replication. Moreover, the lipophilic tail allows P59 to preserve its antiviral activity even in conditions in which the non lipoylated peptide is devoid of activity. In accordance with the unusual high Trp presence, the peptides confirm the preference to be positioned on the membrane interface. Furthermore, the data point out a peculiarity of interaction of the peptides with SDS as compared with DPC.

Feline immunodeficiency virus (FIV) is a naturally occurring pathogen that causes an AIDS-like syndrome in domestic cats and is a valuable model system by which criteria for antiviral vaccines and drugs development can be tested. The cell-entry step of the lentivirus life cycle is regarded as a promising target for the development of new generation inhibitors. We have previously described potent in vitro anti-FIV activity associated with a synthetic octapeptide, termed C8 (Ac-Trp-Glu-Asp-Trp-Val-Gly-Trp-Ile-NH2), containing the Trp-rich motif of FIV transmembrane glycoprotein, which shares a common structural framework with the corresponding molecule of HIV and appears to play a similar role in cell entry. In this report, in an attempt to develop simpler potential fusion inhibitors to be tested in vivo, we describe further studies focused on synthetic peptide analogues of C8. Since C8 inhibitory activity is dependent upon the Trp motif, we systematically replaced these residues with bulky and/or aromatic natural and unnatural amino acids, in order to develop a rational structure-activity relationship. Furthermore, the amino acids located between the Trp residues, which are not crucial for inhibitory activity, were replaced by simple alkyl spacers of appropriate length. Design, NMR structural analysis, in vitro anti-FIV activity in lymphoid cell cultures, and serum stability of these new analogues are reported. The final results indicate that a simpler hexapeptide (Ac-Nal2-Ape-Nal2-Ape-Nal2-Ile-NH2; Nal2 = 3-naphthalen-2-yl-L-alanine, Ape = 5-aminopentanoic acid), almost entirely made up of unnatural amino acid residues, has markedly increased enzymatic stability, while maintaining strong antiviral potency in vitro.

The pharmacokinetics and toxicity profile of stampidine (STAMP, DDE-113, HI-113, N-[p-(4-bromophenyl)-2',3'-didehydro-3'-deoxy-5'-thymidylyl]-L-alanine methyl ester, CAS 217178-62-6) were studied in beagle dogs and feline immunodeficiency virus-infected domestic cats. Therapeutic plasma concentrations of STAMP 3-4 logs higher than its IC50 value can be achieved after its p.o. administration to dogs as well as cats at the 100 mg/kg nontoxic dose level. In accordance with its safety profile in rodent species, a 4- to 7-week STAMP treatment course with twice daily administration of hard gelatin capsules containing 25-100 mg/kg (50-200 mg/kg/ day) STAMP was very well-tolerated by dogs and cats at cumulative dose levels as high as 8.4 g/kg. Except for the sporadic occurrence of nausea and vomiting after its administration and elevation of serum ALT levels in some of the cats, STAMP therapy was not associated with any clinical or laboratory evidence of toxicity. No STAMP-related toxic lesions were found in any of the organs from STAMP-treated cats or dogs. These findings encourage the further development of stampidine for possible clinical use in HIV-infected persons.

The hematological and virological effects of recombinant human granulocyte colony-stimulating factor (rHuG-CSF) were evaluated in feline immunodeficiency virus (FIV)-infected cats. Six age-matched, FIV-infected cats used in this cross-over study were injected subcutaneously with 5 microg/kg of rHuG-CSF daily for 3 weeks, while six control cats received a placebo. Five of six rHuG-CSF-treated cats had significant increases in neutrophil counts that peaked on days 11-21 of treatment. All rHuG-CSF-treated cats exhibited an increase in myeloid:erythroid ratios of the bone marrow cells without significant changes in lymphocyte, CD4 counts, CD4/CD8 ratios, RBC counts, FIV antibody titers, and FIV loads in peripheral blood, and without clinical and hematological toxicities. Five of six rHuG-CSF-treated cats developed antibodies to rHuG-CSF by 14-21 days of treatment, which correlated with decreasing neutrophil counts and increasing neutralizing antibodies to rHuG-CSF. Three cats re-treated with rHuG-CSF rapidly developed neutralizing antibodies to rHuG-CSF, while one cat also developed neutralizing antibodies to recombinant feline G-CSF (rFeG-CSF). Overall, rHuG-CSF treatment increased neutrophil counts in FIV-infected cats without affecting the infection status of cats. However, long-term use of rHuG-CSF is not recommended in cats because of the neutralizing antibody production to rHuG-CSF that affects the drug activity. In addition, a preliminary finding suggests that repeated treatment cycle can also induce cross-neutralizing antibodies to rFeG-CSF, which may potentially affect the homeostasis of endogenous FeG-CSF.

In the fight against the human HIV, new targets are being explored, such as the proteins involved in the process of fusion of the virus with the host cell. Recently, the first generation of fusion inhibitors (enfuvirtide), targeting gp41 (virus envelope glycoprotein 41), has become commercially available. However, this promising class of drugs has to be improved in respect of their efficacy and bioavailability. Considering the strong homologies between HIV and FIV (feline immunodeficiency virus), as well as the highly conserved structure of the transmembrane envelope protein among species, FIV represents a relevant model of pre-screening studies for HIV. Taking into account (i) sequence homologies between the ectodomain of HIV gp41 and FIV gp36 (envelope glycoprotein 36), (ii) structural data available for gp41 and (iii) the fact that synthetic peptides derived from gp36 are effective inhibitors of FIV infection, we designed several peptides derived from gp36 sequence. We checked that these peptides had the same structural features as the corresponding peptides from gp41 HIV by CD, analytical ultracentrifugation and 1H-2H (hydrogen-deuterium) exchange combined with MS. By combining this latter technique with surface-plasmon-resonance assays, we identified the amino acid residues of the C-terminal region of the ectodomain of gp36 that are critical for interaction with the N-terminal region. This gave clues for therapy and vaccines against FIV, thus providing helpful data for treatments against HIV.

Cellular activation plays an important role in retroviral replication. Previously, we have shown that CD4(+)CD25(+) T cells by the virtue of their partially activated phenotype represent ideal candidates for a productive feline immunodeficiency virus (FIV) infection. In the present study, we extended our previous observations with regard to FIV replication in CD4(+)CD25(+) and CD4(+)CD25(-) cells under different stimulation conditions. Both CD4(+)CD25(+) and CD4(+)CD25(-) cells remain latently infected in the absence of IL-2 or concanvalinA (ConA), respectively; harboring a replication competent provirus capable of reactivation several days post-infection. While CD4(+)CD25(+) cells require low levels of exogenous IL-2 and virus inputs for an efficient FIV replication, CD4(+)CD25(-) T cells can only be productively infected in the presence of either high concentrations of IL-2 or high virus titers, even in the absence of mitogenic stimulation. Interestingly, while high virus input activates CD4(+)CD25(-) cells to replicate FIV, it induces apoptosis in a high percentage of CD4(+)CD25(+) T cells. High IL-2 concentrations but not high virus inputs lead to surface upregulation of CD25 and significant cellular proliferation in CD4(+)CD25(-) cells. These results suggest that CD4(+)CD25(+) and CD4(+)CD25(-) T cells have different activation requirements which can be modulated by both viral and cytokine stimuli to reach threshold activation levels in order to harbor a productive FIV infection. This holds implications in vivo for CD4(+)CD25(+) and CD4(+)CD25(-) cells to serve as potential reservoirs of a productive and latent FIV infection.

Parietaria diffusa M. et K., Urtica dioica L. (Urticaceae) and Sambucus nigra L. (Caprifoliaceae) are plants usually used in popular medicine of central Italy for treating numerous diseases, first of all Herpes zoster. Several plant products have been described as potential antiviral agents, with special attention being devoted to those having retroviruses as etiological agents, including acquired immunodeficiency syndrome (AIDS), in which a retrovirus, the designated human immunodeficiency virus HIV, has been clearly identified as the primary cause of this disease. The present study proposes a preliminary screening of the antiviral activity of Parietaria diffusa, Sambucus nigra and Urtica dioica preparation against the feline immunodeficiency virus (FIV) infection. The feline immunodeficiency virus is a widespread lentivirus of domestic cats sharing numerous biological and pathogenic features with the human immunodeficiency virus (HIV). FIV infection in cats has therefore been proposed as an animal model for AIDS studies with respect to pathogenesis, chemotherapy, and vaccine development [Pedersen, N.C., 1993. Feline immunodeficiency virus infection. In: Levy, J.A. (Ed.), The Retroviridae. Plenum Press, New York; Bendinelli, M., Pistello, M., Lombardi, S., Poli, A., Garzelli, C., Matteucci, D., Ceccherini-Nelli, L., Malvaldi, G., Tozzini, F., 1995. Feline immunodeficiency virus: an interesting model for AIDS studies and an important cat pathogen. Clinical Microbiology Revue 8, 87-112; North, T.W., LaCasse, R.A., 1995. Testing anti-HIV drugs in the FIV model. Nature Medicine 1, 410-411; Matteucci, D., Pistello, M., Mazzetti, P., Giannechini, S., Isola, P., Merico, A., Zaccaro, L., Rizzati, A., Bendinelli, M., 2000. AIDS vaccination studies using feline immunodeficiency virus as a model: immunisation with inactivated whole virus suppresses viraemia levels following intravaginal challenge with infected cells but non-following intravenous challenge with cell-free virus. Vaccine 18, 119-130]. Early studies showed that some of them presented antiviral activity against infection of FIV as assayed by syncytia formation using feline kidney Crandell cells (CrFK).

The Trp-rich motif (TrpM) of the transmembrane glycoprotein (TM) of lentiviruses is an attractive domain on which to design new potential cell entry peptide inhibitors. We recently demonstrated that an octapeptide reproducing the TrpM of feline immunodeficiency virus (FIV), designated C8, broadly inhibited this virus in vitro and that the retroinverso analogue of this peptide (riC8) was almost as inhibitory and exhibited features suggestive of a much increased stability. Here, we demonstrated that riC8 is indeed highly stable, maintaining its concentration unchanged for at least 24 h in cat serum in vitro. Furthermore, once inoculated into cats, riC8 produced no major acute toxic effects and exhibited satisfactory pharmacokinetic properties. Finally, we report the results of a short-term monotherapy experiment in chronically FIV-infected cats showing that riC8 is well tolerated and also has substantial antiviral activity in vivo. In particular, the mean viral load of riC8-treated animals declined progressively with increasing time of treatment, whereas that of control animals given C8 or solvent alone did not. These results provide the first evidence that clinically useful inhibition of virus replication with a small peptide derived from a functional domain of the TM of a lentivirus can be achieved in vivo.

Background: The protease inhibitor, TL-3, demonstrated broad efficacy in vitro against FIV, HIV and SIV (simian immunodeficiency virus), and exhibited very strong protective effects on early neurologic alterations in the CNS of FIV-PPR infected cats. In this study, we analyzed TL-3 efficacy using a highly pathogenic FIV-C isolate, which causes a severe acute phase immunodeficiency syndrome, with high early mortality rates., Results: Twenty cats were infected with uncloned FIV-C and half were treated with TL-3 while the other half were left untreated. Two uninfected cats were used as controls. The general health and the immunological and virological status of the animals was monitored for eight weeks following infection. All infected animals became viremic independent of TL-3 treatment and seven of 20 FIV-C infected animals developed severe immunodepletive disease in conjunction with significantly (p < or = 0.05) higher viral RNA loads as compared to asymptomatic animals. A marked and progressive increase in CD8+ T lymphocytes in animals surviving acute phase infection was noted, which was not evident in symptomatic animals (p < or = 0.05). Average viral loads were lower in TL-3 treated animals and of the 6 animals requiring euthanasia, four were from the untreated cohort. At eight weeks post infection, half of the TL-3 treated animals and only one of six untreated animals had viral loads below detection limits. Analysis of protease genes in TL-3 treated animals with higher than average viral loads revealed sequence variations relative to wild type protease. In particular, one mutant, D105G, imparted 5-fold resistance against TL-3 relative to wild type protease., Conclusions: The findings indicate that the protease inhibitor, TL-3, when administered orally as a monotherapy, did not prevent viremia in cats infected with high dose FIV-C. However, the modest lowering of viral loads with TL-3 treatment, the greater survival rate in symptomatic animals of the treated cohort, and the lower average viral load in TL-3 treated animals at eight weeks post infection is indicative of a therapeutic effect of the compound on virus infection.

In vivo tests were performed to assess the influence of the protease inhibitor TL-3 on feline immunodeficiency virus (FIV)-induced central nervous system (CNS) deficits. Twenty cats were divided into four groups of five animals each. Group 1 received no treatment, group 2 received TL-3 only, group 3 received FIV strain PPR (FIV-PPR) only, and group 4 received FIV-PPR and TL-3. Animals were monitored for immunological and virological status, along with measurements of brain stem auditory evoked potential (BAEP) changes. Groups 1 and 2 remained FIV negative, and groups 3 and 4 became virus positive and seroconverted by 3 to 5 weeks postinoculation. No adverse effects were noted with TL-3 only. The average peak viral load for the virus-only group 3 animals was 1.32 x 10(6) RNA copies/ml, compared to 6.9 x 10(4) copies/ml for TL-3-treated group 4 cats. Group 3 (virus-only) cats exhibited marked progressive delays in BAEPs starting at 2 weeks post virus exposure, which is typical of infection with FIV-PPR. In contrast, TL-3-treated cats of group 4 exhibited BAEPs similar to those of control and drug-only cats. At 97 days postinfection, treatments were switched; i.e., group 4 animals were taken off TL-3 and group 3 animals were treated with TL-3. BAEPs in group 3 animals returned to control levels, while BAEPs in group 4 animals remained at control levels. After 70 days on TL-3, group 3 was removed from the drug treatment regimen. Delays in BAEPs immediately increased to levels observed prior to TL-3 treatment. The findings show that early TL-3 treatment can effectively eliminate FIV-induced changes in the CNS. Furthermore, TL-3 can counteract FIV effects on the CNS of infected cats, although continued treatment is required to maintain unimpaired CNS function.

Feline immunodeficiency virus (FIV) provides a valuable animal model by which criteria for the development of HIV-1 inhibitors can be explored. Previous studies had shown that a synthetic 8-mer peptide modeled on the tryptophan-rich motif of the ectodomain of the viral transmembrane glycoprotein (TM) is a potent inhibitor of FIV The observation that inhibition efficiency varied somewhat depending on FV strain prompted the present study in which we investigated whether changes in the surface (SU) glycoprotein can affect virus susceptibility to TM-derived peptide inhibitors. This was done by examining how effectively selected entry inhibitors blocked the infectivity of well characterized variants and molecular clones of the prototype isolate of FIV The results have shown that substitutions in the SU can indeed modulate virus susceptibility to TM-derived entry inhibitors. Interestingly, we also observed a parallelism between reduced susceptibility to entry inhibitors and broad resistance to antibody-mediated neutralization.

WHI-07 [5-bromo-6-methoxy-5,6-dihydro-3'-azidothymidine-5'-(p-bromophenyl)-methoxy alaninyl phosphate] is a novel dual-function aryl phosphate derivative of zidovudine with potent anti-human immunodeficiency virus (HIV) and spermicidal activities. WHI-07 was active against the feline immunodeficiency virus (FIV). This study evaluated whether topical application of WHI-07 as a single agent and in combination with an organometallic vanadium complex, vanadocene dithiocarbamate (VDDTC), via a nontoxic gel microemulsion can block vaginal as well as rectal transmission of feline AIDS (FAIDS) by chronically FIV-infected feline T cells in the natural host model. Genital transmission of FIV was monitored in recipient cats by the appearance of viral antibodies to FIV Gag proteins and by virus isolation of blood leukocytes as measured by FIV reverse transcriptase activity and FIV-specific PCR. Microbicidal activity was considered effective when the treated cats did not show evidence of FIV infection for up to 18 weeks postchallenge. An aggregate analysis of 46 specific-pathogen-free cats revealed that a single dose of the infected cell inoculum efficiently transmitted FIV infection when delivered into the vagina (100%) or rectum (66%). Pretreatment of the vagina or rectum with 2% WHI-07 alone or in combination with 0.25% VDDTC significantly (P = 0.004) protected cats from genital transmission by the highly infectious inoculum (7 million FIV(Bangston)-infected feline T cells). Collectively, using the vaginal and rectal transmucosal model for FAIDS, our studies demonstrated that WHI-07 either alone or in combination with a vanadocene has clinical potential for the development of a dual-function anti-HIV microbicide for sexually active women.

We described the antiviral activity of an octapeptide corresponding to a Trp-rich domain of feline immunodeficiency virus (FIV) transmembrane glycoprotein. To overcome the limited enzymatic stability of short peptides, the retroinverso analogue was prepared and tested for inhibitory activity of FIV in the presence or absence of normal cat serum. Differently from the unmodified peptide, the retroinverso analogue maintains strong inhibitory activity in serum. NMR studies showed that it displays crucial conformational features believed to be important for antiviral activity.