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Aspergillus fumigatus is a clinically important fungus with the ability to cause invasive aspergillosis with high mortality rates in immunocompromised patients and chronic pulmonary aspergillosis in immunocompetent individuals. Virulence of mutants has traditionally been assessed using mammalian hosts such as mice and rats and more recently the fruit fly, Drosophila melanogaster, demonstrated the potential to act as an in vivo host suitable for screening Aspergillus mutants. In this study using a larger thermotolerant invertebrate, Galleria mellonella, the virulence of individual gene deletants of Aspergillus fumigatus ( cpcA, sidA, sidC, sidD, sidF and paba,) were compared to the parental and gene-replacement strains, if available. A range of infectious challenges consisting of from 3 ×× 103−−3 ×× 106 spores/larva was followed by observation of larval survival with mean survival time used as a surrogate of microbial pathogenicity. Mutants cpcA, sidA, sidF and paba were avirulent and sidC and sidD showed attenuated virulence. Virulence assessment in G. mellonella correlated closely with the historic data generated using mice and Drosophila. Pre-screening Aspergillus mutants using G. mellonella could significantly reduce the number of mammals required to assess changes in virulence. [ABSTRACT FROM AUTHOR]

Unlabelled: Cryptococcal meningoencephalitis is an urgent global health problem. Induction regimens using 14 days of amphotericin B deoxycholate (dAmB) are considered the standard of care but may not be suitable for resource-poor settings. We investigated the efficacy of conventional and abbreviated regimens of dAmB for cryptococcal meningoencephalitis in both murine and rabbit models of cryptococcal meningoencephalitis. We examined the extent to which immunological effectors contribute to the antifungal effect. We bridged the results to humans as a first critical step to define regimens suitable for further study in clinical trials. There were significant differences in the murine plasma-versus-cerebrum dAmB concentration-time profiles. dAmB was detectable in the cerebrum throughout the experimental period, even following the administration of only three doses of 3 mg/kg. dAmB induced a fungistatic effect in the cerebrum with a 2- to 3-log10 CFU/g reduction compared with controls. The effect of 3 days of therapy was the same as that of daily therapy for 14 days. There was no evidence of increased numbers of CD3(+) CD4(+) or CD3(+) CD8(+) cells in treated mice to account for the persistent antifungal effect of an abbreviated regimen. The administration of dAmB at 1 mg/kg/day for 3 days was the same as daily therapy in rabbits. The bridging studies suggested that a human regimen of 0.7 mg/kg/day for 3 days resulted in nearly maximal antifungal activity in both the cerebrum and cerebrospinal fluid. An abbreviated regimen (3 days of therapy) of dAmB appears to be just as effective as conventional induction therapy for cryptococcal meningoencephalitis., Importance: Cryptococcal meningitis is a significant and neglected infection that is associated with excessive morbidity and mortality. In well-resourced health care settings, induction therapy with at least 2 weeks of amphotericin B deoxycholate (dAmB) is advocated. Multiple clinical studies suggest that dAmB is the drug of choice for cryptococcal meningitis. In many parts of the world where the burden of cryptococcal meningitis is highest, it is infeasible to administer dAmB for prolonged periods. This paper provides the experimental basis for the efficacy of abbreviated regimens of dAmB for cryptococcal meningitis. The concept was explored in two well-validated laboratory animal models of cryptococcal meningitis, and the results were bridged to humans by using a range of mathematical modeling techniques. A 3-day regimen is as effective as the standard 14-day course. An abbreviated regimen is significantly more feasible and may enable better antifungal therapy to be administered to many patients with this frequently lethal disease.

Triazoles are first-line agents for treating aspergillosis. The prevalence of azole resistance in Aspergillus fumigatus is increasing, and cross-resistance is a growing concern. In this study, the susceptibilities of 40 A. fumigatus clinical isolates were tested by using the CLSI method with amphotericin B, itraconazole, voriconazole, posaconazole, and the new triazole isavuconazole. Isavuconazole MICs were higher in strains with reduced susceptibilities to other triazoles, mirroring changes in voriconazole susceptibility. Isavuconazole MICs differed depending on the Cyp51A substitution.

Background: Cryptococcal meningoencephalitis is a lethal infection with relatively few therapeutic options. The optimal dosage of liposomal amphotericin B (LAmB) alone or in combination with flucytosine is not known., Methods: A murine model of cryptococcal meningoencephalitis was used. The fungal density in the brain was determined using quantitative cultures. Pharmacokinetic-pharmacodynamic relationships were determined for LAmB and flucytosine administered alone. The effect of the combination was described using the Greco model and a mathematical model. The results were bridged to humans., Results: Inoculation resulted in hematogenous dissemination and logarithmic growth within the central nervous system. There was histological evidence of multifocal infection throughout the brain. Both LAmB and flucytosine produced a dose-dependent reduction in fungal burden. The effect of the combination of agents in the brain was additive. Bridging studies suggested that a human dosage of LAmB 3 mg/kg/d resulted in a submaximal antifungal effect. Regimens of LAmB 6 mg/kg/d alone, LAmB 3 mg/kg/d plus flucytosine 50 mg/kg/d, and LAmB 3 mg/kg/d plus flucytosine 100 mg/kg/d all resulted in near-maximal antifungal activity., Conclusions: Potential regimens for further study in clinical trials include LAmB 6 mg/kg/d alone, LAmB 3 mg/kg/d plus flucytosine 50 mg/kg/d, and LAmB 3 mg/kg/d plus flucytosine 100 mg/kg/d.

Fluconazole is frequently the only antifungal agent that is available for induction therapy for cryptococcal meningitis. There is relatively little understanding of the pharmacokinetics and pharmacodynamics (PK-PD) of fluconazole in this setting. PK-PD relationships were estimated with 4 clinical isolates of Cryptococcus neoformans. MICs were determined using Clinical and Laboratory Standards Institute (CLSI) methodology. A nonimmunosuppressed murine model of cryptococcal meningitis was used. Mice received two different doses of fluconazole (125 mg/kg of body weight/day and 250 mg/kg of body weight/day) orally for 9 days; a control group of mice was not given fluconazole. Fluconazole concentrations in plasma and in the cerebrum were determined using high-performance liquid chromatography (HPLC). The cryptococcal density in the brain was estimated using quantitative cultures. A mathematical model was fitted to the PK-PD data. The experimental results were extrapolated to humans (bridging study). The PK were linear. A dose-dependent decline in fungal burden was observed, with near-maximal activity evident with dosages of 250 mg/kg/day. The MIC was important for understanding the exposure-response relationships. The mean AUC/MIC ratio associated with stasis was 389. The results of the bridging study suggested that only 66.7% of patients receiving 1,200 mg/kg would achieve or exceed an AUC/MIC ratio of 389. The potential breakpoints for fluconazole against Cryptococcus neoformans follow: susceptible, ≤ 2 mg/liter; resistant, >2 mg/liter. Fluconazole may be an inferior agent for induction therapy because many patients cannot achieve the pharmacodynamic target. Clinical breakpoints are likely to be significantly lower than epidemiological cutoff values. The MIC may guide the appropriate use of fluconazole. If fluconazole is the only option for induction therapy, then the highest possible dose should be used.

Voriconazole is a first-line agent for the treatment of invasive pulmonary aspergillosis. Isolates with elevated voriconazole MICs are increasingly being seen, and the optimal treatment regimen is not defined. We investigated whether the combination of voriconazole with anidulafungin may be beneficial for the treatment of A. fumigatus strains with elevated voriconazole MICs. We used an in vitro model of the human alveolus to define the exposure-response relationships for a wild-type strain (voriconazole MIC, 0.5 mg/liter) and strains with defined molecular mechanisms of triazole resistance (MICs, 4 to 16 mg/liter). All strains had anidulafungin minimum effective concentrations (MECs) of 0.0078 mg/liter. Exposure-response relationships were estimated using galactomannan as a biomarker. Concentrations of voriconazole and anidulafungin were measured using high-performance liquid chromatography (HPLC). The interaction of voriconazole and anidulafungin was described using the Greco model. Fungal growth was progressively inhibited with higher drug exposures of voriconazole. Strains with elevated voriconazole MICs required proportionally greater voriconazole exposures to achieve a comparable antifungal effect. Galactomannan concentrations were only marginally reduced by anidulafungin monotherapy. An additive effect between voriconazole and anidulafungin was apparent. In conclusion, the addition of anidulafungin does not markedly alter the exposure-response relationship of voriconazole. A rise in serum galactomannan during combination therapy with voriconazole and anidulafungin should be interpreted as treatment failure and not attributed to a paradoxical reaction related to echinocandin treatment.

Itraconazole is used for the prevention and treatment of infections caused by Aspergillus fumigatus. An understanding of the pharmacodynamics of itraconazole against wild-type and triazole-resistant strains provides a basis for innovative therapeutic strategies for treatment of infections. An in vitro model of the human alveolus was used to define the pharmacodynamics of itraconazole. Galactomannan was used as a biomarker. The effect of systemic and airway administration of itraconazole was assessed, as was a combination of itraconazole administered to the airway and systemically administered 5FC. Systemically administered itraconazole against the wild type induced a concentration-dependent decline in galactomannan in the alveolar and endothelial compartments. No exposure-response relationships were apparent for the L98H, M220T, or G138C mutant. The administration of itraconazole to the airway resulted in comparable exposure-response relationships to those observed with systemic therapy. This was achieved without detectable concentrations of drug within the endothelial compartment. The airway administration of itraconazole resulted in a definite but submaximal effect in the endothelial compartment against the L98H mutant. The administration of 5FC resulted in a concentration-dependent decline in galactomannan in both the alveolar and endothelial compartments. The combination of airway administration of itraconazole and systemically administered 5FC was additive. Systemic administration of itraconazole is ineffective against Cyp51 mutants. The airway administration of itraconazole is effective for the treatment of wild-type strains and appears to have some activity against the L98H mutants. Combination with other agents, such as 5FC, may enable the attainment of near-maximal antifungal activity.

Background: Voriconazole is a first-line agent for the treatment of invasive pulmonary aspergillosis (IPA). There are increasing reports of Aspergillus fumigatus isolates with reduced susceptibility to voriconazole., Methods: An in vitro dynamic model of IPA was developed that enabled simulation of human-like voriconazole pharmacokinetics. Galactomannan was used as a biomarker. The pharmacodynamics of voriconazole against wild-type and 3 resistant strains of A. fumigatus were defined. The results were bridged to humans to provide decision support for setting breakpoints for voriconazole using Clinical Laboratory Standards Institute (CLSI) and European Committee of Antimicrobial Susceptibility Testing (EUCAST) methodologies., Results: Isolates with higher minimum inhibitory concentrations (MICs) required higher area under the concentration time curves (AUCs) to achieve suppression of galactomannan. Using CLSI and EUCAST methodologies, the AUC:MIC values that achieved suppression of galactomannan were 55 and 32.1, respectively. Using CLSI and EUCAST methodologies, the trough concentration:MIC values that achieved suppression of galactomannan were 1.68 and 1, respectively. Potential CLSI breakpoints for voriconazole are ≤ 0.5 mg/L for susceptible and >1 mg/L for resistant. Potential EUCAST breakpoints for voriconazole are ≤1 mg/L for susceptible and >2 mg/L for resistant., Conclusions: This dynamic model of IPA is a useful tool to address many remaining questions related to antifungal treatment of Aspergillus spp.

Hematogenous Candida meningoencephalitis (HCME) is a serious infection in premature neonates. Anidulafungin is an echinocandin antifungal agent with potent activity against Candida spp., but its efficacy and optimal regimens for human neonates with HCME are not known. A well-validated rabbit model of HCME was used to define pharmacokinetic-pharmacodynamic (PK-PD) relationships of anidulafungin. A mathematical model was fitted to the entire data set. The experimental data were bridged to humans. A population PK model was fitted to the data from human neonates receiving anidulafungin receiving a loading dose of 3 mg/kg, followed by 1.5 mg/kg/day. Monte Carlo simulations were performed to identify candidate anidulafungin regimens for humans. All untreated rabbits succumbed by ≤96 h postinoculation. The PK of anidulafungin was linear with dose-dependent penetration into the cerebrum. Anidulafungin exerted a rapid antifungal effect that was apparent in the first dosing interval. Near-maximal antifungal activity was observed with dosages of 10 to 20 mg/kg/day. The bridging studies suggested that the current regimen of first 3 mg/kg, followed by 1.5 mg/kg/day, is suboptimal. Higher dosages were associated with progressively greater antifungal effect. Anidulafungin is effective for the treatment of experimental HCME. Higher dosages than those currently used for clinical care are required for maximal antifungal effect.

Cellular bilayer models can be used to simulate many biological compartments. Here, we describe a cell culture model of the human alveolus that enables the study of early invasive pulmonary aspergillosis. The cellular bilayer is constructed with human alveolar epithelial cells and human pulmonary artery endothelial cells. The cells are grown on a semipermeable polyester membrane. This model can be used to study the pathogenesis, immunobiology and pharmacology of invasive pulmonary aspergillosis.

Candida glabrata is a leading cause of disseminated candidiasis. The echinocandins are increasingly used as first-line agents for the treatment of patients with this syndrome, although the optimal regimen for the treatment of invasive Candida glabrata infections in neutropenic patients is not known. We studied the pharmacokinetics (PK) and pharmacodynamics (PD) of micafungin, anidulafungin, and caspofungin in a neutropenic murine model of disseminated Candida glabrata infection to gain further insight into optimal therapeutic options for patients with this syndrome. A mathematical model was fitted to the data and used to bridge the experimental results to humans. The intravenous inoculation of Candida glabrata in mice was followed by logarithmic growth throughout the experimental period (101 h). A dose-dependent decline in fungal burden was observed following the administration of 0.1 to 20 mg/kg of body weight every 24 h for all three agents. The exposure-response relationships for each drug partitioned into distinct fungistatic and fungicidal components of activity. Surprisingly, the average human drug exposures following currently licensed regimens were predicted to result in a fungistatic antifungal effect. Higher human dosages of all three echinocandins are required to induce fungicidal effects in neutropenic hosts.

Background: Posaconazole is a triazole with anti-Aspergillus activity. However, little is known about the utility of posaconazole as primary therapy for invasive pulmonary aspergillosis., Methods: An in vitro model of the human alveolus was used to study the impact of minimum inhibitory concentrations (MIC) on exposure-response relationships. The pharmacokinetic-pharmacodynamic relationships of posaconazole were examined in an inhalational murine model of invasive pulmonary aspergillosis. A mathematical model was fitted to the entire data set. This model was then used to describe the relationship between drug exposure, quantified in terms of the area under the concentration time curve to MIC (AUC:MIC) and the observed antifungal effect., Results: The posaconazole MIC was an important determinant of exposure-response relationships and accounted for a portion of the observed variance. Murine pharmacokinetics were linear for dosages 1-20 mg/kg/day. There was a dose-dependent decline in serum galactomannan concentrations, with near-maximal suppression following 20 mg/kg/day. The murine pharmacokinetic-pharmacodynamic data were well described by the mathematical model. An AUC:MIC ratio of 167 was associated with half-maximal antifungal effect., Conclusions: These results provide the experimental foundation for the selection of candidate posaconazole regimens for the primary treatment of invasive pulmonary aspergillosis in profoundly neutropenic hosts.

The pharmacodynamic and pharmacokinetic (PK-PD) properties of amphotericin B (AmB) formulations against invasive pulmonary aspergillosis (IPA) are not well understood. We used an in vitro model of IPA to further elucidate the PK-PD of amphotericin B deoxycholate (DAmB), liposomal amphotericin B (LAmB) and amphotericin B lipid complex (ABLC). The pharmacokinetics of these formulations for endovascular fluid, endothelial cells, and alveolar cells were estimated. Pharmacodynamic relationships were defined by measuring concentrations of galactomannan in endovascular and alveolar compartments. Confocal microscopy was used to visualize fungal biomass. A mathematical model was used to calculate the area under the concentration-time curve (AUC) in each compartment and estimate the extent of drug penetration. The interaction of LAmB with host cells and hyphae was visualized using sulforhodamine B-labeled liposomes. The MICs for the pure compound and the three formulations were comparable (0.125 to 0.25 mg/liter). For all formulations, concentrations of AmB progressively declined in the endovascular fluid as the drug distributed into the cellular bilayer. Depending on the formulation, the AUCs for AmB were 10 to 300 times higher within the cells than within endovascular fluid. The concentrations producing a 50% maximal effect (EC50) in the endovascular compartment were 0.12, 1.03, and 4.41 mg/liter for DAmB, LAmB, and ABLC, respectively, whereas, the EC50 in the alveolar compartment were 0.17, 7.76, and 39.34 mg/liter, respectively. Confocal microscopy suggested that liposomes interacted directly with hyphae and host cells. The PK-PD relationships of the three most widely used formulations of AmB differ markedly within an in vitro lung model of IPA.