Saperconazole therapy in a rabbit model of invasive aspergillosis

Animal Models of Aspergillosis

Aspergillosis is an airborne fungal disease caused by Aspergillus spp., a group of ubiquitous molds. This disease causes high morbidity and mortality in both humans and animals. The growing importance of this infection over recent decades has created a need for practical and reproducible models of aspergillosis. The use of laboratory animals provides a platform to understand fungal virulence and pathophysiology, assess diagnostic tools, and evaluate new antifungal drugs. In this review, we describe the fungus, various Aspergillus-related diseases in humans and animals and various experimental animal models. Overall, we highlight the advantages and limitations of the animal models, the experimental variables that can affect the course of the disease and the reproducibility of infection, and the critical need for standardization of the species, immunosuppressive drugs, route of infection, and diagnostic criteria to use.

Disseminated histoplasmosis (Histoplasma capsulatum) in a pet rabbit: case report and review of the literature

A 2.5-year-old intact male miniature lop rabbit ( Oryctolagus cuniculus) was presented with multiple nodules surrounding the eyes, nose, mouth, and prepuce. Cytological evaluation of the periocular nodules revealed the presence of intracellular (within macrophages) and extracellular yeast organisms. The yeast organisms were approximately 3–5 µm in diameter, round to oval, with a thin clear capsule, and contained an eccentrically placed basophilic crescent-shaped nucleus. The clinical pathological interpretation was granulomatous inflammation with intralesional yeast of a morphology consistent with Histoplasma spp. The rabbit was treated with microsized griseofulvin (25 mg/kg, orally, once a day) for 12 days pending final cytological diagnosis of histoplasmosis. No significant improvement was noted during the treatment period, and humane euthanasia was performed. Postmortem examination revealed the presence of intracellular and extracellular yeast organisms in the small intestine, skin (antebrachium, perioral, palpebral, perianal, and pinnal), penis, penile urethra, rectum, axillary lymph node, and conjunctiva. Postmortem fungal culture yielded Histoplasma capsulatum. Based on clinical and postmortem findings, a definitive diagnosis of disseminated histoplasmosis was made. Disseminated histoplasmosis appears to be unreported in rabbits. Although the treatment used did not provide noticeable improvement, available information on histoplasmosis treatment in other species has been reviewed to provide useful information for future management of this condition in rabbits.

Comparison of galactomannan detection, PCR-enzyme-linked immunosorbent assay, and real-time PCR for diagnosis of invasive aspergillosis in a neutropenic rat model and effect of caspofungin acetate

The performance of different in vitro diagnostic tests for the diagnosis of invasive aspergillosis (IA) was investigated in a transiently neutropenic rat model. Rats were immunosuppressed with cyclophosphamide and then inoculated intravenously with 1.5 x 10(4) CFU Aspergillus fumigatus spores. Animals were then either treated with caspofungin acetate, 1 mg/kg/day for 7 days, or not treated. PCR-enzyme-linked immunosorbent assay (ELISA), real-time PCR, and galactomannan (GM) detection were performed on postmortem blood samples, along with culture of liver, lung, and kidney homogenate. Caspofungin-treated animals showed a decrease in residual tissue burden of A. fumigatus from organ homogenate compared to untreated animals (P < 0.002). PCR-ELISA returned positive results for 11/17 animals treated with antifungal agents and for 10/17 untreated animals. Galactomannan was positive in 8/17 caspofungin-treated animals and 4/17 untreated animals. Real-time PCR was positive in 2/17 treated and 3/17 untreated animals. This study demonstrates that PCR-ELISA is a more sensitive test than either GM detection (P = 0.052) or real-time PCR (P < 0.01) for diagnosis of IA but that any of the three tests may return false-negative results in cases of histologically proven disease. Galactomannan indices from animals treated with antifungal agents showed a trend (P = 0.1) towards higher levels than those of untreated animals, but no effect was observed with PCR-ELISA indices (P = 0.29). GM detection, as previously described, may be enhanced by the administration of caspofungin, but PCR-ELISA appears not to be affected in the same way. We conclude that PCR-ELISA is a more sensitive and reliable method for laboratory diagnosis of IA.

The contribution of animal models of aspergillosis to understanding pathogenesis, therapy and virulence

Animal models of aspergillosis have been used extensively to study various aspects of pathogenesis, innate and acquired host-response, disease transmission and therapy. Several different animal models of aspergillosis have been developed. Because aspergillosis is an important pulmonary disease in birds, avian models have been used successfully to study preventative vaccines. Studies done to emulate human disease have relied on models using common laboratory animal species. Guinea pig models have primarily been used in therapy studies of invasive pulmonary aspergillosis (IPA). Rabbits have been used to study IPA and systemic disease, as well as fungal keratitis. Rodent, particularly mouse, models of aspergillosis predominate as the choice for most investigators. The availability of genetically defined strains of mice, immunological reagents, cost and ease of handling are factors. Both normal and immunosuppressed animals are used routinely. These models have been used to determine efficacy of experimental therapeutics, comparative virulence of different isolates of Aspergillus, genes involved in virulence, and susceptibility to infection with Aspergillus. Mice with genetic immunological deficiency and cytokine gene-specific knockout mice facilitate studies of the roles cells, and cytokines and chemokines, play in host-resistance to Aspergillus. Overall, these models have been critical to the advancement of therapy, and our current understanding of pathogenesis and host-resistance.

Efficacy of caspofungin against central nervous system Aspergillus fumigatus infection in mice determined by TaqMan PCR and CFU methods

We have reported previously that prolonged caspofungin (CAS) dosing enhances survival in a murine model of central nervous system aspergillosis. In this study we determined by quantitative PCR (qPCR) and CFU enumeration whether CAS could reduce fungal burdens, prior to the deaths of untreated animals, and also assessed progressive infection in untreated mice. Mice were infected intracranially and treated for 4 days with CAS (1, 5, or 10 mg/kg of body weight/day) or amphotericin B (AMB) (3 mg/kg/day) starting 1 day postinfection. Fungal burdens in brains and kidneys of untreated controls were determined on days 1, 3, and 5 to assess progressive infection; burdens in treated animals were determined on day 5. qPCR showed higher burdens than CFU enumeration in all comparisons. In untreated animals, qPCR showed transiently increased burdens in brains, while CFU enumeration showed a decrease. qPCR showed increased burdens in kidneys, but CFU enumeration did not. Neither method indicated drug efficacy in the brain. Both methods showed AMB efficacy in the kidneys, and qPCR demonstrated CAS efficacy at all doses. Spearman correlations of qPCR and CFU determination results showed a significant correlation for most untreated groups; results correlated well for kidneys (P < or = 0.03) but not for brains in treated mice. Regression analyses of qPCR and CFU groups indicated different slopes for progressive infection in untreated animals but the same slopes for CAS dose-response efficacy. qPCR appeared to better reflect the progression of untreated infection. The lack of demonstration of efficacy in the brain suggests that longer dosing is necessary to cause burden reduction. These results also suggest that, when there is drug efficacy in a therapeutic study, either method appears to be useful for determining Aspergillus fumigatus burdens.

The future of animal models of invasive aspergillosis

The diagnosis of invasive aspergillosis remains very difficult, coupled with limited treatment options. Animal models have been utilized to evaluate both the diagnosis and treatment of infection and to assess the pathogenicity and virulence of the organism. However, animal models have not been standardized and have been used in only a limited fashion for genomic evaluation in this disease. Extensive efforts are underway to expand significantly the Aspergillus genomic information. Thus, the standardization of animal models of invasive aspergillosis is critical to create a unified platform to enhance evaluation of newer genomic information and allow assessment of pathogenicity and virulence factors. Proposed models, supported by a recently awarded National Institutes of Health/National Institute of Allergy and Infectious Diseases contract, will be developed in close interaction with the extended Aspergillus community (including academia and industry) to answer key questions in this disease. The goal of this work is to provide the framework to evaluate genomic targets in animal models in order to improve the diagnosis and treatment of invasive aspergillosis that will ultimately result in improved outcomes of patients with this frequently fatal infection.

The role of murine models in the development of antifungal therapy for systemic mycoses

Animal testing is crucial to the development of new antifungal compounds. This review describes the role that murine and other animal models have played in the development of three classes of antifungal agents: the polyenes, the triazoles and the echinocandins and the ways in which these models have been either the positive link in the path from in vitro studies to the patient, or have foreclosed later clinical evaluation. Efficacy studies in particular mycoses are discussed, as well as studies designed to determine whether combinations of antifungal drugs may have value over single agents. Copyright 2000 Harcourt Publishers Ltd.

Efficacies of two new antifungal agents, the triazole ravuconazole and the echinocandin LY-303366, in an experimental model of invasive aspergillosis

The efficacy of ravuconazole, a new triazole antifungal agent, and the echinocandin LY-303366 were evaluated in an immunosuppressed, temporarily leukopenic rabbit model of invasive aspergillosis. Oral therapy with ravuconazole at a dosage of 30 mg/kg of body weight per day or the echinocandin LY-303366, given intravenously in a dosage of 5 or 10 mg/kg, was begun 24 h after a lethal or sublethal challenge, and results were compared with those for amphotericin B therapy and untreated controls. Prophylaxis was also studied with LY-303366 given at a dosage of 5 or 10 mg/kg/day 48 h before lethal or sublethal challenge. Ravuconazole eliminated mortality, cleared aspergillus antigen from the serum, and eliminated Aspergillus fumigatus organisms from tissues of both lethally and sublethally challenged immunosuppressed animals with invasive aspergillosis. Although LY-303366, at both doses, prolonged survival and reduced aspergillus antigenemia, it did not eliminate aspergillus organisms from organ tissues. The half-lives of ravuconazole and LY-303366 in rabbits were 13 and 12.5 h, respectively, and no accumulation of either drug was seen after 6 days of treatment. Although LY-303366 showed activity in this rabbit model of invasive aspergillosis, ravuconazole was the more active agent, comparable to amphotericin B. Additional studies are needed to determine the potential of ravuconazole for use in the treatment of this infection.

Efficacy of UK-109496, a new azole antifungal agent, in an experimental model of invasive aspergillosis

The efficacy of UK-109496, a new azole antifungal agent, was evaluated in an immunosuppressed, temporarily leukopenic rabbit model of invasive aspergillosis. Oral therapy with UK-109496 at a dosage of 10 or 15 mg/kg of body weight every 8 h was begun 24 h after a lethal or sublethal challenge, and results were compared with those for amphotericin B therapy and untreated controls. UK-109496 eliminated mortality and also reduced the tissue burden of Aspergillus fumigatus 10- to 100-fold in liver and kidney tissues and to a lesser degree in lung tissue, and at the higher dose, no viable organisms were recovered from brain tissue from these animals. Both dosages of UK-109496 decreased or eliminated circulating antigen. The half-life of UK-109496 in rabbits was 2.5 to 3 h, and no accumulation of drug was seen even after 15 doses in either uninfected or infected animals. Thus, UK-109496 shows activity in this rabbit model of invasive aspergillosis. Additional studies are needed to determine the potential of the drug for use in the treatment of this infection.

Efficacy of oral saperconazole in systemic murine aspergillosis

Saperconazole is a fluorinated bis-triazole. Groups of ten 5-week-old female CD-1 mice were infected intravenously with 5.5 x 10(7) Aspergillus conidia. Saperconazole, dissolved in hydroxypropyl-beta-cyclodextrin (HPBC), was given orally twice a day for 11 days, beginning 1 day post-infection, at 50, 100 or 200 mg kg-1 day-1. At day 18 post-infection, survivors were killed and residual infection quantified in the kidneys. With Aspergillus fumigatus isolate 10AF, 70% given no therapy, 100% given daily oral HPBC and 40% given intraperitoneal amphotericin B at 3.3 mg kg-1 three times a week for 2 weeks died, whereas all mice given saperconazole survived. Each saperconazole regimen prolonged survival compared to untreated or HPBC treated mice (P < 0.01). Saperconazole at 200 mg kg-1 day-1 reduced colony forming units of aspergillus in kidneys more than 1000-fold compared to untreated or HPBC treated mice (P < 0.001) and saperconazole regimens were superior to amphotericin B therapy (P < 0.01). In another study of the same design with A. fumigatus isolate 15AF, 90% of untreated and 20% of mice treated with saperconazole at 50 mg kg-1 day-1 died; all others survived. Any saperconazole regimen prolonged survival (P < 0.001). Residual infection was also significantly reduced by all saperconazole regimens (P < 0.01). With Aspergillus terreus isolate 4AT, 80% of untreated mice, 50% of mice treated with saperconazole at 50 mg kg-1 day-1 and 10% of mice treated at 200 mg kg-1 day-1 died. Any saperconazole regimen prolonged survival (P < 0.05). Saperconazole at 100 and 200 mg kg-1 day-1 also reduced residual infection (P < 0.001). No adverse effects were noted in any study. Thus, saperconazole was efficacious in vivo against different Aspergillus isolates.

Efficacy of itraconazole solution in a rabbit model of invasive aspergillosis

The efficacy of an itraconazole-cyclodextrin solution against Aspergillus fumigatus was assessed in an immunosuppressed, temporarily leukopenic rabbit model of invasive aspergillosis and compared with that of amphotericin B. Oral itraconazole solution at dosages of 20 and 40 mg/kg/day improved survival as compared with that of controls. Itraconazole (40 mg/kg/day) not only improved survival and reduced antigen levels but also significantly eradicated A. fumigatus from tissues and was as effective as amphotericin B in these studies. The higher dose of itraconazole produced higher levels in serum, which correlated with improved efficacy of the drug. This itraconazole-cyclodextrin solution was well absorbed and was effective in the treatment of experimental invasive aspergillosis; it demonstrates the potential of this class of agents in improving therapy for invasive aspergillosis.