Activities of the triazole SCH 51048 against Coccidioides immitis in vitro and in vivo

Nikkomycin Z against Disseminated Coccidioidomycosis in a Murine Model of Sustained-Release Dosing

Nikkomycin Z (nikZ) is a chitin synthase inhibitor. Efficacy against Coccidioides has been demonstrated in animal models of pulmonary or brain infection. Its short half-life in mice and in humans would necessitate divided daily dosing. We assayed nikZ efficacy in disseminated coccidioidomycosis (in a reduction of CFU design) and whether sustained release might be useful. Mice were challenged intravenously with low or high arthroconidial inocula. Fluconazole, clinically the most commonly used anticoccidioidal drug, was compared (gavage) at high dose to a dose range of nikZ administered intraperitoneally or, to mimic sustained release, administered continuously in drinking water. Therapy was given for 5 days. In vitro, both fluconazole and nikZ inhibited the isolate studied; nikZ was fungicidal. Oral nikZ therapy gave similar results to intraperitoneal nikZ and sterilized infection in most animals after low-inoculum challenge. In both challenges, oral nikZ produced greater reduction of CFU in organs (lung, liver, and spleen) than fluconazole. Oral nikZ doses of ≥200 mg/kg of body weight/day were particularly effective in all organs and were well tolerated. This efficacy occurred even though, after severe challenge, mice had reduced water intake, resulting in ingesting less than the desired dose, particularly initially after infection. This study shows, for the first time, efficacy of nikZ against disseminated coccidioidomycosis. Efficacy was shown after challenges producing different levels of severity of disease. This study also suggests the likely benefits of developing an extended release formulation supplying continuous systemic concentrations of nikZ.

Efficacy of nikkomycin Z in murine CNS coccidioidomycosis: modelling sustained-release dosing

OBJECTIVES

Meningitis is the most feared coccidioidomycosis complication. Nikkomycin Z (nikZ) is a chitin synthase inhibitor. A concern is short half-life, necessitating multiple dose/day regimens. We simulated extended release, providing nikZ in drinking water. Extended release would enhance convenience, and adherence, for patients.

METHODS

Coccidioides posadasii was injected intracerebrally into mice. Twelve day treatments began on Day 3. Fluconazole was given 100 mg/kg once daily (gavage); designed doses of nikZ 30, 100 or 300 mg/kg/day in drinking water. On Day 30 post-treatment, survivors were euthanized, brain cfu quantitated and cfu in other organs assessed.

RESULTS

nikZ was stable in drinking water. Survival was 11%, 50%, 70%, 90% and 100% in untreated controls, fluconazole and nikZ 30, 100 and 300 mg/kg/day, respectively ; nikZ 300 mg/kg/day was superior (P ≤ 0.01) to fluconazole. Brains were sterilized in 0%, 20%, 86%, 89% and 80% of mice, respectively; nikZ 100 or 300 mg/kg/day was superior (P ≤ 0.01) to fluconazole. Clearance of infection in other organs was similar. All decreased drinking after infection, causing nikZ mice to ingest less than the desired dose in early therapy; despite this, they recovered sufficiently to resume pre-infection drinking and designed drug intakes. Thus, when sickest, even less than the designed dose was sufficient to enable recovery.

CONCLUSIONS

This efficacy supports the development of sustained-release nikZ. Decreased intake wouldn't be a factor in humans, receiving drug via extended-release pill or continuous IV infusion. In prior studies (twice daily nikZ) of murine coccidioidal meningitis, results were inferior, suggesting sustained release may provide both convenience and superior outcomes.

Large-Scale Evaluation of In Vitro Amphotericin B, Triazole, and Echinocandin Activity against Coccidioides Species from U.S. Institutions

Large-scale testing of Coccidioides isolates has not been performed, and the frequency of clinical isolates with elevated amphotericin B or triazole MICs has not been evaluated. Coccidioides isolates (n = 581) underwent antifungal susceptibility testing. Elevated MIC values were observed for fluconazole (≥16 μg/ml, 37.3% of isolates; ≥32 μg/ml, 7.9% of isolates), itraconazole (≥2 μg/ml, 1.0% of isolates), posaconazole (≥1 μg/ml, 1.0% of isolates), and voriconazole (≥2 μg/ml, 1.2% of isolates). However, mold-active triazoles exhibited low MICs for the majority of isolates tested. Additional correlation with patient outcomes to determine the relevance of elevated MICs in Coccidioides isolates is needed.

Whole glucan particles as a vaccine against systemic coccidioidomycosis

We reported previously that yeast-derived whole glucan particles (WGPs), with or without conjugation to BSA, used as a vaccine protected against systemic aspergillosis in mice. Here, we examined their utility as a potential vaccine against coccidioidomycosis. WGPs were prepared from Saccharomyces cerevisiae; conjugation with BSA (WGP-BSA) was done using 1-cyano-4-dimethylaminopyridinium tetrafluoroborate-mediated conjugation. Heat-killed S. cerevisiae (HKY) was used as a positive-control vaccine. CD-1 mice were vaccinated with WGPs or WGP-BSA, HKY or PBS once weekly, beginning 21 days prior to infection. Mice were infected intravenously with arthroconidia of Coccidioides posadasii. In the low-mortality study, 50 % of PBS-treated controls died. Only WGP-BSA at 0.6 mg per dose induced significant protection compared with PBS treatment. All surviving mice were infected in all three organs examined. Those given WGP-BSA at 0.6 mg per dose had fewer c.f.u. in liver and lungs (P = 0.04), and those given WGPs at 6 mg per dose had fewer in lungs (P < 0.02), compared with PBS. In the high-mortality study, 90 % of PBS mice died. Vaccination with HKY, and WGPs or WGP-BSA at 6 or 12 mg per dose significantly prolonged survival (P ≤ 0.05). No surviving mice were free of infection. HKY and WGP-BSA at 12 mg per dose reduced c.f.u. in the liver and lungs (P < 0.05) and WGP-BSA at 6 mg per dose reduced c.f.u. in the lungs (P < 0.05); unconjugated WGPs did not reduce infection. WGPs or WGP-BSA acted as a vaccine that protected against mortality caused by coccidioidomycosis. Thus, WGP protection against coccidioidomycosis and aspergillosis provides the basis for development of a pan-fungal vaccine.

Posaconazole (Noxafil, SCH 56592), a new azole antifungal drug, was a discovery based on the isolation and mass spectral characterization of a circulating metabolite of an earlier lead (SCH 51048)

Posaconazole (SCH 56592) is a novel triazole antifungal drug that is marketed in Europe and the United States under the trade name 'Noxafil' for prophylaxis against invasive fungal infections. SCH 56592 was discovered as a possible active metabolite of SCH 51048, an earlier lead. Initial studies have shown that serum concentrations determined by a microbiological assay were higher than those determined by HPLC from animals dosed with SCH 51048. Subsequently, several animals species were dosed with (3)H-SCH 51048 and the serum was analyzed for total radioactivity, SCH 51048 concentration and antifungal activity. The antifungal activity was higher than that expected based on SCH 51048 serum concentrations, confirming the presence of active metabolite(s). Metabolite profiling of serum samples at selected time intervals pinpointed the peak that was suspected to be the active metabolite. Consequently, (3)H-SCH 51048 was administered to a large group of mice, the serum was harvested and the metabolite was isolated by extraction and semipreparative HPLC. LC-MS/MS analysis suggested that the active metabolite is a secondary alcohol with the hydroxyl group in the aliphatic side chain of SCH 51048. All corresponding monohydroxylated diastereomeric mixtures were synthesized and characterized. The HPLC retention time and LC-MS/MS spectra of the diastereomeric secondary alcohols of SCH 51048 were similar to those of the isolated active metabolite. Finally, all corresponding individual monohydroxylated diasteriomers were synthesized and evaluated for in vitro and in vivo antifungal potencies, as well as pharmacokinetics. SCH 56592 emerged as the candidate with the best overall profile.

Experimental animal models of coccidioidomycosis

Experimental models of coccidioidomycosis performed using various laboratory animals have been, and remain, a critical component of elucidation and understanding of the pathogenesis and host resistance to infection with Coccidioides spp., as well as to development of more efficacious antifungal therapies. The general availability of genetically defined strains, immunological reagents, ease of handling, and costs all contribute to the use of mice as the primary laboratory animal species for models of this disease. Five types of murine models are studied and include primary pulmonary disease, intraperitoneal with dissemination, intravenous infection emulating systemic disease, and intracranial or intrathecal infection emulating meningeal disease. Each of these models has been used to examine various aspects of host resistance, pathogenesis, or antifungal therapy. Other rodent species, such as rat, have been used much less frequently. A rabbit model of meningeal disease, established by intracisternal infection, has proven to model human meningitis well. This model is useful in studies of host response, as well as in therapy studies. A variety of other animal species including dogs, primates, and guinea pigs have been used to study host response and vaccine efficacy. However, cost and increased needs of animal care and husbandry are limitations that influence the use of the larger animal species.

Comparison of itraconazole and fluconazole treatments in a murine model of coccidioidal meningitis

Coccidioidal meningitis (CM) is a devastating disease that requires long-term therapy and for which there is little hope of a cure. A model was used to compare the efficacies of itraconazole and fluconazole. CD-1 mice were infected intrathecally with 30 to 36 viable arthroconidia of Coccidioides. Oral therapy with cyclodextrin (control) or itraconazole or fluconazole at 10, 25, or 50 mg/kg of body weight twice daily (BID) was given for 12 days, from day 3 of infection. Treatment with both antifungals at all doses prolonged survival compared with that of the control treatment (P < 0.01 to 0.0001). At 50 mg/kg, itraconazole and fluconazole were equivalent, whereas itraconazole at 10 or 25 mg/kg prolonged survival compared to that achieved with fluconazole at these dosages (P < 0.05 and 0.01, respectively). Early histologic analysis (10 days of treatment) with 50 mg/kg BID itraconazole or fluconazole showed suppression of CM in all five animals per group; in quantitative cultures, three of three animals from each group had no detectable infection in the brain, spinal cord, or a site of secondary infection, the lungs. In contrast, four of seven controls showed mild to severe meningitis, with arteritis detected in three animals. In a short-term organ clearance study, 5 days of treatment with 10 or 50 mg/kg BID itraconazole or fluconazole reduced the tissue burdens in the brain and spinal cord compared to the tissue burdens in the controls (P < 0.02 to 0.0003). Fluconazole at 10 mg/kg did not reduce the fungal burden in secondary sites, the lungs and kidneys, whereas this itraconazole dose was more effective in clearing the fungi from both organs (P < 0.05 and P < 0.001, respectively). At 50 mg/kg, itraconazole and fluconazole were equivalent in clearing the fungi from the brain and kidney, but itraconazole was superior to fluconazole in clearing the fungi from the spinal cord and lungs (P < 0.05). Thus, both itraconazole and fluconazole were effective at controlling CM, but neither eliminated Coccidioides from tissues. Overall, itraconazole was more efficacious on an mg/kg basis; at high doses they were similarly effective.

Importance of antifungal drug-resistance: clinical significance and need for novel therapy

The incidence of fungal infections has increased dramatically over the past few decades due to the increase in the members of the population susceptible to such infections. This population includes individuals undergoing chemotherapy for cancer, those enduring long-term treatment with antibacterial agents, those receiving immunosuppressive drugs following transplantations, or those immunosuppressed due to diseases, such as AIDS, or malignancies. Newer antifungal agents, namely the triazoles, have aided in both the treatment of fungal infections and in the prevention of disease in susceptible individuals. However, resistance to the azoles, as well as to the polyenes, has resulted in clinical failures. Only a few potential antifungal targets have been exploited to date and there is a critical need for the discovery and development of novel antifungal agents that will result in improved therapy in this ever-expanding patient population. An increased intensity in the study of fungal pathogens at the molecular level holds the key to such advances.

[Treatment and prophylaxis of opportunistic infections in the course of HIV disease: a state of the art in 2004. Part 2: Viral, fungal and bacterial infections]

Remarkable progress has been made in antiretroviral therapeutics, as well as in the prophylaxis and treatment of opportunistic infections, since the beginning of the AIDS epidemic. The patient's life expectancy and quality of life have consequently improved, thanks to better management of opportunistic diseases. The introduction of protease inhibitors-containing regimen (i.e. highly active antiretroviral therapy or HAART), since 1996, has drastically reduced the incidence of opportunistic infections by restoring immunity. The large panel of antiretroviral drugs responsible for frequent sustained viral and immune responses has thus allowed a new definition of guidelines for the prophylaxis and treatment of opportunistic infections. A better use of prophylactic drugs should help to reduce the risk of drug-related toxicity and pharmaceutical interactions. It should also decrease the cost of HIV management and eventually increase compliance to treatment and quality of life.

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.

Murine models of blastomycosis, coccidioidomycosis, and histoplasmosis

Animal models have contributed much to the knowledge of fungal infections and their corresponding therapeutic treatments. This is true for animal models of the primary fungal pathogens, Blastomyces dermatitidis, Coccidioides immitis, and Histoplasma capsulatum. This review gives a brief background of human diseases associated with these organisms and describes the development, details, and utility of murine models of blastomycosis, as well as coccidioidomycosis and histoplasmosis.

Activity of the triazole SCH 56592 against disseminated murine coccidioidomycosis

SCH 56592 (SCH) is a new triazole antifungal with a broad spectrum of activity. In vitro susceptibility testing against five strains of Coccidioides immitis revealed MICs from 0.39 to 3.13 microg/ml and minimal fungicidal concentrations from 1.56 to 3.13 microg/ml. A murine model of systemic coccidioidomycosis was established in female CD-1 mice. Groups received either no treatment or oral therapy with fluconazole at 10 or 100 mg/kg of body weight; itraconazole at 10 or 100 mg/kg; SCH at 0.5, 2, 10, or 25 mg/kg; or its methylcellulose diluent alone. Therapy began 2 days postinfection and continued once daily for 19 days. Surviving mice were euthanized 49 days postinfection, and infectious burdens were determined by culture. All drugs were superior to no-treatment or diluent-treatment controls (P < 0.001) in prolonging survival but were not significantly different from one another. Itraconazole at 100 mg/kg was superior to fluconazole in reduction of CFU in the spleen, liver, and lung (P < 0.01 to 0.001). SCH at 0.5 mg/kg was superior to either fluconazole or itraconazole at 10 mg/kg in reduction of CFU in all three organs (P < 0.05 to 0.001). SCH at 2 mg/kg was not significantly different from itraconazole at 100 mg/kg in all three organs. SCH at 10 and 25 mg/kg was superior to either dose of fluconazole or itraconazole in all three organs (P < 0.05 to 0.001). In terms of reduction of CFU, SCH was > or = 200-fold as potent as fluconazole and > or = 50-fold as potent as itraconazole. There was a clear dose-responsive relationship for SCH in each of the organs. It is noteworthy that SCH effected cures (no detectable C. immitis in any organ) in 1 of 9, 6 of 10, or 9 of 9 surviving mice in animals given 2, 10, or 25 mg/kg, respectively. Neither fluconazole nor itraconazole cured any survivor. SCH has potent, fungicidal activity in vivo against C. immitis. It should be considered for clinical trials in patients with coccidioidomycosis.

In vitro studies of activities of the antifungal triazoles SCH56592 and itraconazole against Candida albicans, Cryptococcus neoformans, and other pathogenic yeasts

We investigated the effects of various assay conditions on the activities of two antifungal drugs, SCH56592 and itraconazole, against seven species of fungi by the broth macrodilution testing procedure proposed by the National Committee for Clinical Laboratory Standards (NCCLS). For both drugs, which are insoluble in water, the concentration and type of solubilizing agent produced differences in drug activity. Starting inoculum size differences from 10(2) to 10(5) yeast cells per ml resulted in approximately a fourfold effect on the MIC of both drugs, but other significant differences were not observed with variations in synthetic medium composition, pH, buffering reagent, or incubation temperature. Under standardized conditions of reference method M27-T with 1% polyethylene glycol as the solubilizing agent, median MICs of SCH56592 and itraconazole of 60 and 125 mg/ml, respectively, were demonstrated for 110 strains (12 to 23 strains for each of seven species). Broth microdilution results were typically severalfold higher than broth macrodilution results. We conclude that the NCCLS standard reference method can be applied without modification to the testing of SCH56592 and itraconazole, but particular attention to solubilizing the agents is critical to obtaining consistent results.

Efficacies of two novel azole derivatives each containing a morpholine ring, UR-9746 and UR-9751, against systemic murine coccidioidomycosis

UR-9746 and UR-9751 are novel azole derivatives each containing a morpholine ring. They were examined for both in vitro and in vivo activities against Coccidioides immitis. In vitro, UR-9746 and UR-9751 were active, with MICs of 25 and 3.1 micrograms/ml, respectively, against C. immitis Silveira; minimum fungicidal concentrations were > 100 micrograms/ml, the highest concentration tested, for both compounds. Antifungal activity in serum showed the desirable characteristic of remaining severalfold above the MIC at all times. Against systemic murine coccidioidomycosis, UR-9746 and UR-9751 prolonged survival at dosages of > or = 10 mg/kg/day and showed increased reduction of infectious burden in the spleens, livers, and lungs of treated mice with escalating dosage. Both compounds lacked observable toxicity and on a milligram-per-kilogram of body weight basis were > or = 10-fold superior to fluconazole in prolonging survival and clearing infection with C. immitis.