The genus Aspergillus contains etiologic agents of aspergillosis. The clinical manifestations of the disease range from allergic reaction to invasive pulmonary infection. Among the pathogenic aspergilli, Aspergillus fumigatus is most ubiquitous in the environment and is the major cause of the disease, followed by Aspergillus flavus, Aspergillus niger, Aspergillus terreus, Aspergillus nidulans, and several species in the section Fumigati that morphologically resemble A. fumigatus. Patients that are at risk for acquiring aspergillosis are those with an altered immune system. Early diagnosis, species identification, and adequate antifungal therapy are key elements for treatment of the disease, especially in cases of pulmonary invasive aspergillosis that often advance very rapidly. Incorporating knowledge of the basic biology of Aspergillus species to that of the diseases that they cause is fundamental for further progress in the field.

Increases in the incidence and mortality due to the major invasive fungal infections such as aspergillosis, candidiasis and cryptococcosis caused by the species of Aspergillus, Candida and Cryptococcus, are a growing threat to the immunosuppressed patient population. In addition to the limited armamentarium of the current classes of antifungal agents available (pyrimidine analogs, polyenes, azoles, and echinocandins), their toxicity, efficacy and the emergence of resistance are major bottlenecks limiting successful patient outcomes. Although these drugs target distinct fungal pathways, there is an urgent need to develop new antifungals that are more efficacious, fungal-specific, with reduced or no toxicity and simultaneously do not induce resistance. Here we review several lines of evidence which indicate that the calcineurin signaling pathway, a target of the immunosuppressive drugs FK506 and cyclosporine A, orchestrates growth, virulence and drug resistance in a variety of fungal pathogens and can be exploited for novel antifungal drug development.

Candida species are the third most common cause of pediatric health care-associated bloodstream infection in the United States and Europe. To our knowledge, this report from the International Pediatric Fungal Network is the largest prospective, multicenter observational study dedicated to pediatric and neonatal invasive candidiasis. From 2007 to 2011, we enrolled 196 pediatric and 25 neonatal patients with invasive candidiasis. Non-albicans Candida species predominated in pediatric (56%) and neonatal (52%) age groups, yet Candida albicans was the most common species in both groups. Successful treatment responses were observed in pediatric (76%) and neonatal patients (92%). Infection with Candida parapsilosis led to successful responses in pediatric (92%) and neonatal (100%) patients, whereas infection with Candida glabrata was associated with a lower successful outcome in pediatric patients (55%). The most commonly used primary antifungal therapies for pediatric invasive candidiasis were fluconazole (21%), liposomal amphotericin B (20%) and micafungin (18%). Outcome of pediatric invasive candidiasis was similar in response to polyenes (73%), triazoles (67%) and echinocandins (73%). The most commonly used primary antifungal therapies for neonatal invasive candidiasis were fluconazole (32%), caspofungin (24%) and liposomal amphotericin B (16%) and micafungin (8%). Outcomes of neonatal candidiasis by antifungal class again revealed similar response rates among the classes. We found a predominance of non-albicans Candida infection in children and similar outcomes based on antifungal class used. This international collaborative study sets the foundation for large epidemiologic studies focusing on the unique features of neonatal and pediatric candidiasis and comparative studies of therapeutic interventions in these populations.

Heat shock protein 90 (Hsp90) is a eukaryotic molecular chaperone. Its involvement in the resistance of Candida albicans to azole and echinocandin antifungals is well established. However, little is known about Hsp90's function in the filamentous fungal pathogen Aspergillus fumigatus. We investigated the role of Hsp90 in A. fumigatus by genetic repression and examined its cellular localization under various stress conditions. Failure to generate a deletion strain of hsp90 suggested that it is essential. Genetic repression of Hsp90 was achieved by an inducible nitrogen-dependent promoter (pniiA-Hsp90) and led to decreased spore viability, decreased hyphal growth, and severe defects in germination and conidiation concomitant with the downregulation of the conidiation-specific transcription factors brlA, wetA, and abaA. Hsp90 repression potentiated the effect of cell wall inhibitors affecting the β-glucan structure of the cell wall (caspofungin, Congo red) and of the calcineurin inhibitor FK506, supporting a role in regulating cell wall integrity pathways. Moreover, compromising Hsp90 abolished the paradoxical effect of caspofungin. Pharmacological inhibition of Hsp90 by geldanamycin and its derivatives (17-AAG and 17-DMAG) resulted in similar effects. C-terminal green fluorescent protein (GFP) tagging of Hsp90 revealed mainly cytosolic distribution under standard growth conditions. However, treatment with caspofungin resulted in Hsp90 accumulation at the cell wall and at sites of septum formation, further highlighting its role in cell wall stress compensatory mechanisms. Targeting Hsp90 with fungal-specific inhibitors to cripple stress response compensatory pathways represents an attractive new antifungal strategy.

Calcineurin is important for fungal virulence and a potential antifungal target, but compounds targeting calcineurin, such as FK506, are immunosuppressive. Here we report the crystal structures of calcineurin catalytic (CnA) and regulatory (CnB) subunits complexed with FK506 and the FK506-binding protein (FKBP12) from human fungal pathogens (Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans and Coccidioides immitis). Fungal calcineurin complexes are similar to the mammalian complex, but comparison of fungal and human FKBP12 (hFKBP12) reveals conformational differences in the 40s and 80s loops. NMR analysis, molecular dynamic simulations, and mutations of the A. fumigatus CnA/CnB-FK506-FKBP12-complex identify a Phe88 residue, not conserved in hFKBP12, as critical for binding and inhibition of fungal calcineurin. These differences enable us to develop a less immunosuppressive FK506 analog, APX879, with an acetohydrazine substitution of the C22-carbonyl of FK506. APX879 exhibits reduced immunosuppressive activity and retains broad-spectrum antifungal activity and efficacy in a murine model of invasive fungal infection.

Invasive mold infections (IMIs) are a leading cause of mortality in immunocompromised children, yet there has never been an international epidemiologic investigation of pediatric IMIs. This international, prospective cohort study was performed to characterize the epidemiology, antifungal therapy, and outcomes of pediatric IMIs. Children (≤18 years) with proven or probable IMIs were enrolled between August 2007 and May 2011 at 22 sites. Risk factors, underlying diagnoses, and treatments were recorded. Outcomes were assessed at 12 weeks after diagnosis using European Organization for Research and Treatment of Cancer/Mycoses Study Group response criteria. One hundred thirty-one pediatric patients with IMIs were enrolled; the most common IMI was invasive aspergillosis ([IA] 75%). Children with IA and those with other types of IMIs had similar underlying risk factors, except that children with IMIs caused by non-Aspergillus species were more likely to have received mold-active antifungal agents preceding diagnosis. The most commonly used antifungal classes after diagnosis were triazoles (82%) and polyenes (63%). Combination therapy was used in 53% of patients. Use of combination therapy was associated with an increased risk of adverse events (risk ratio, 1.98; 95% confidence interval, 1.06-3.68; P = .031), although there was no detectable difference in outcome. Although risk factors for IMIs are similar across specific subtypes, preceding antifungal therapy may be an important modifier. Combination antifungal therapy requires further study to determine its true risks and benefits.