Treatment of invasive aspergillosis: Polyenes, echinocandins, or azoles?

Isavuconazole for the treatment of patients with invasive fungal diseases involving the central nervous system

The incidence of invasive fungal diseases (IFDs) with central nervous system (CNS) involvement is increasing due to the rising numbers of immunocompromised individuals, such as patients receiving chemotherapy, transplantation procedures, or immune-modulating therapies. CNS IFDs cause significant morbidity and mortality, and treatments are complicated by difficulties in identifying fungal pathogens and delivering antifungal agents to the CNS. Isavuconazole is a novel triazole with broad-spectrum activity that has shown good blood–brain barrier penetration in animal models. We present a retrospective analysis of isavuconazole in the treatment of patients with CNS IFDs and who either participated in the phase III VITAL or SECURE clinical trials, or were included in a named-patient program. A total of 36 patients were identified, including 27 patients from the clinical trials. Of these patients, 47.2% had hematologic malignancies, while 13.9% had no identifiable underlying conditions. Mucorales, Aspergillus species, and Cryptococcus species accounted for 30.6%, 22.2%, and 13.9% of infections, respectively. The overall survival rate was 80.6% at day 42 and 69.4% at day 84, and at the end of treatment, a complete or partial clinical response was achieved in 58.3% of patients. Isavuconazole exhibited clinical activity in a variety of CNS IFDs.

Fungal Lanosterol 14α-demethylase: A target for next-generation antifungal design

The cytochrome P450 enzyme lanosterol 14α-demethylase (LDM) is the target of the azole antifungals used widely in medicine and agriculture as prophylaxis or treatments of infections or diseases caused by fungal pathogens. These drugs and agrochemicals contain an imidazole, triazole or tetrazole substituent, with one of the nitrogens in the azole ring coordinating as the sixth axial ligand to the LDM heme iron. Structural studies show that this membrane bound enzyme contains a relatively rigid ligand binding pocket comprised of a deeply buried heme-containing active site together with a substrate entry channel and putative product exit channel that reach to the membrane. Within the ligand binding pocket the azole antifungals have additional affinity determining interactions with hydrophobic side-chains, the polypeptide backbone and via water-mediated hydrogen bond networks. This review will describe the tools that can be used to identify and characterise the next generation of antifungals targeting LDM, with the goal of obtaining highly potent broad-spectrum fungicides that will be able to avoid target and drug efflux mediated antifungal resistance.

Blad-Containing Oligomer Fungicidal Activity on Human Pathogenic Yeasts. From the Outside to the Inside of the Target Cell

Blad polypeptide comprises residues 109-281 of Lupinus albus β-conglutin precursor. It occurs naturally as a major subunit of an edible, 210 kDa oligomer which accumulates to high levels, exclusively in the cotyledons of Lupinus seedlings between the 4th and 14th day after the onset of germination. Blad-containing oligomer (BCO) exhibits a potent and broad spectrum fungicide activity toward plant pathogens and is now on sale in the US under the tradename FractureTM. In this work we demonstrate its antifungal activity toward human pathogens and provide some insights on its mode of action. BCO bioactivity was evaluated in eight yeast species and compared to that of amphotericin B (AMB). BCO behaved similarly to AMB in what concerns both cellular inhibition and cellular death. As a lectin, BCO binds strongly to chitin. In addition, BCO is known to possess 'exochitinase' and 'endochitosanase' activities. However, no clear disruption was visualized at the cell wall after exposure to a lethal BCO concentration, except in cell buds. Immunofluorescent and immunogold labeling clearly indicate that BCO enters the cell, and membrane destabilization was also demonstrated. The absence of haemolytic activity, its biological origin, and its extraordinary antifungal activity are the major outcomes of this work, and provide a solid background for a future application as a new antifungal therapeutic drug. Furthermore, its predictable multisite mode of action suggests a low risk of inducing resistance mechanisms, which are now a major problem with other currently available antifungal drugs.

Therapeutic and toxicologic studies in a murine model of invasive pulmonary aspergillosis

Invasive pulmonary aspergillosis remains problematic in immunocompromised patient populations. We studied potential therapeutic options in a murine model of pulmonary aspergillosis in triamcinolone-suppressed DBA/2 mice infected intranasally with conidia from Aspergillus fumigatus. Mice were treated with liposomal-amphotericin B (AmBi; AmBisome), lipid-complexed amphotericin B (ABLC; Abelcet), voriconazole (VCZ), micafungin (MICA), caspofungin (CAS) or deoxycholate amphotericin B (AMBd) given alone or in combination. Monotherapy with AmBi, ABLC, AMBd, CAS or MICA had activity in prolonging survival; however, only AMBd or CAS reduced fungal burden in the lungs and kidneys. Combinations of AmBi plus CAS or MICA prolonged survival, but were not better than monotherapy. VCZ was ineffective and AMBd plus CAS showed a possible antagonism. AmBi or ABLC at higher dosages, or loading-doses of AmBi resulted in reduced survival. Histopathology showed increased incidence of serious renal and mild hepatic toxicity in triamcinolone-treated mice given an amphotericin B regimen compared to no or only triamcinolone (minimal renal changes occurred with CAS or VCZ with or without triamcinolone); suggestive of combined toxicity of triamcinolone and the amphotericin B in AmBi or ABLC. Infected treated mice showed progressive pulmonary disease including abscesses, angioinvasion and abundant intralesional fungi. High loading-doses of AmBi were associated with nephrosis and damage to other tissues. No monotherapy or combination regimen showed superiority for the treatment of pulmonary aspergillosis in corticosteroid suppressed mice and the potential for combined drug toxicity was enhanced in these mice. High dosages of lipid-formulated amphotericin B also proved unsatisfactory. Additional studies are needed to evaluate improved treatment.

The evaluation of in vitro pharmacodynamic properties of amphotericin B, voriconazole and caspofungin against A. fumigatus isolates by the conventional and colorimetric time-kill assays

Aspergillus fumigatus is an opportunistic pathogen responsible for life-threatening infections in immuncompromised patients. Data about the in vitro pharmacodynamics of antifungals against A. fumigatus are limited. In the present study, we investigated the fungicidal activities, at concentrations of 1, 4 and 16 times the minimum inhibitory concentration (MIC), of caspofungin (CAS), amphotericin B (AMB) and voriconazole (VORI) against eight A. fumigatus isolates through the use of time kill and 2,3-Bis [2-methoxy-4-nitro-5-(sulfenylamino) carbonyl-2H-tetrazolium-hydroxide] (XTT) reduction tests. By the conventional time kill test, AMB was fungicidal (≥99.9% reduction in colony forming units; CFU) for all isolates at 4-16 MICs after 48 h incubation. The fungicidal effect for VORI was determined at 4 × MIC for one isolate and at 16 × MIC for four isolates at 48 h of exposure. CAS was also fungicidal at 1 × MIC for one isolate and at 4-16 MICs for two isolates at 48 h. While the percentage of median killing of AMB was found by the time-kill method with XTT as 99% at 4 × MIC and 99.28% at 16 × MIC, that of VORI was 94.5% at 4 × MIC and 92.88% at 16 × MIC after 48 h of incubation. However, a significant increase was observed compared to initial inoculum size with CAS after 48 h. Since the XTT method measures all cellular viability in media, it may give more reliable results about pharmacodynamics of antifungal agents against Aspergillus spp. than the time kill test.

Intracranial Aspergilloma in Immunocompetent Patients Successfully Treated with Radical Surgical Intervention and Antifungal Therapy – Case Series

Introduction: Aspergillosis of the central nervous system is an uncommon infection, mainly occurring in immunocompromised patients with a high mortality. Surgical excision of the intracranial lesion combined with oral voriconazole has been proposed to improve the outcome in immunocompromised patients. Itraconazole has been considered not to be effective because of poor penetration into the brain tissue. We report the long-term outcome of 3 cases of intracranial aspergilloma in immunocompetent patients who were successfully treated with radical surgery combined with oral itraconazole. Materials and Methods: This is a retrospective study in which chronic invasive intracranial aspergilloma was successfully treated in 3 apparently immunocompetent patients and followed-up for more than 5 years. Results: Near complete or radical surgical removal of this localised chronic invasive intracranial aspergilloma whenever possible is the definitive treatment. When combined with the oral antifungal drug itraconazole, the management regimen is effective in achieving near complete long-term cure of more than 5 years. Oral itraconazole 200 mg twice daily should be given for a prolonged period of at least 6 months. Conclusion: In chronic invasive intracranial aspergilloma in an immunocompetent patient, it was suggested that radical excision of the intracranial aspergilloma combined with oral antifungal drug belonging to triazole group that can be either itraconazole or voriconazole given for a period of 6 months was likely to improve the long-term outcome. Key words: Central nervous system aspergillosis, Aspergilloma, Itraconazole, Voriconazole

Contribution of galactofuranose to the virulence of the opportunistic pathogen Aspergillus fumigatus

The filamentous fungus Aspergillus fumigatus is responsible for a lethal disease called invasive aspergillosis that affects immunocompromised patients. This disease, like other human fungal diseases, is generally treated by compounds targeting the primary fungal cell membrane sterol. Recently, glucan synthesis inhibitors were added to the limited antifungal arsenal and encouraged the search for novel targets in cell wall biosynthesis. Although galactomannan is a major component of the A. fumigatus cell wall and extracellular matrix, the biosynthesis and role of galactomannan are currently unknown. By a targeted gene deletion approach, we demonstrate that UDP-galactopyranose mutase, a key enzyme of galactofuranose metabolism, controls the biosynthesis of galactomannan and galactofuranose containing glycoconjugates. The glfA deletion mutant generated in this study is devoid of galactofuranose and displays attenuated virulence in a low-dose mouse model of invasive aspergillosis that likely reflects the impaired growth of the mutant at mammalian body temperature. Furthermore, the absence of galactofuranose results in a thinner cell wall that correlates with an increased susceptibility to several antifungal agents. The UDP-galactopyranose mutase thus appears to be an appealing adjunct therapeutic target in combination with other drugs against A. fumigatus. Its absence from mammalian cells indeed offers a considerable advantage to achieve therapeutic selectivity.

Clustering of invasiveAspergillus ustuseye infections in a tertiary care hospital: A molecular epidemiologic study of an uncommon species

Aspergillus infections are being increasingly recognized as an important cause of morbidity and blindness. We report here the first cluster of Aspergillus ustus endophthalmitis cases which occurred in a large tertiary care hospital during the period October 2003 to June 2004. In three of the cases, the patients required enucleation following cataract surgery, while the fourth involved a fatal infection in a pediatric patient hospitalized for osteopetrosis. Patient charts from the four cases were reviewed retrospectively and indicated that postoperative signs of fungal endophthalmitis developed in the patients 1-11 weeks after surgery. The molecular characterization of the isolates and their epidemiological relatedness were evaluated by Random Amplification of Polymorphic DNA (RAPD). A source investigation of this mini outbreak was performed by environmental sampling, but no isolates of A. ustus were recovered from these studies. All A. ustus strains isolated from three patients with fungal endophthalmitis had the same RAPD pattern suggesting a common source. The strain from the pediatric patient differed from the ophthalmic isolates in five electrophoretic loci. The latter was included solely as an outbreak, unrelated control to evaluate the discriminatory power of the molecular typing method employed in the analysis of the ophthalmic strains. These cases illustrate the potential for uncommon species like A. ustus to cause high morbidity and mortality in some clinical settings. Aspergillus ustus endophthalmitis is a serious and devastating complication of ocular surgery. It is unknown whether ongoing hospital construction may have contributed to this cluster of cases. Random amplification of polymorphic DNA may give valuable clues about the clonality of A. ustus strains.