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Invasive aspergillosis (IA) due to Aspergillus fumigatus is a deadly infection for which new antifungal therapies are needed. Here, we demonstrate the efficacy of a Gwt1 inhibitor, APX2041, and its prodrug, APX2104, against A. fumigatus. The wild-type, azole-resistant, and echinocandin-resistant A. fumigatus strains were equally susceptible to APX2041 in vitro. APX2104 treatment in vivo significantly prolonged survival of neutropenic mice challenged with the wild-type and azole-resistant strains, revealing APX2104 as a potentially promising therapeutic against IA.

Triazole antifungals are the primary therapeutic option against invasive aspergillosis. However, resistance to azoles has increased dramatically over the last decade. Azole resistance is known to primarily occur due to point mutations in the azole target protein Cyp51A, one of two paralogous 14-α sterol demethylases found in Aspergillus fumigatus. Despite the importance of Cyp51A, little is known about the function of its paralog, Cyp51B, and the behavior of these proteins within the cell or their functional interrelationship. In this study, we addressed two important aspects of the Cyp51 proteins: (i) we characterized their localization patterns under normal growth versus stress conditions, and (ii) we determined how the proteins compensate for each other’s absence and respond to azole treatment. Both the Cyp51A and Cyp51B proteins were found to localize in distinct endoplasmic reticulum (ER) domains, including the perinuclear ER and the peripheral ER. Occasionally, the Cyp51 proteins concentrated in the peripheral ER network of tubules along the hyphal septa and at the hyphal tips. Exposure to voriconazole, caspofungin, and Congo red led to significant increases in fluorescence intensity in these alternative localization sites, indicative of Cyp51 protein translocation in response to cell wall stress. Furthermore, deletion of either Cyp51 paralog increased susceptibility to voriconazole, though a greater effect was observed following deletion of cyp51A, indicating a compensatory response to stress conditions.

Toxoplasma gondii counts among the most consequential food-borne parasites, and although the parasite occurs in a wide range of wild and domesticated animals, farms may constitute a specific and important locus of transmission. If so, parasites in animals that inhabit agricultural habitats might be suspected of harbouring genetically distinct parasite types. To better understand habitat effects pertinent to this parasite's transmission, we compiled and analysed existing genotypic data of 623 samples from animals across a proximity gradient from areas of human settlement to the wilderness in North America. To facilitate such analysis, T. gondii isolates were divided into three groups: (i) from farm-bound animals (with the most limited home ranges on farms); (ii) from free-roaming animals (with wider home ranges on or near farms); and (iii) from wildlife. In addition, parasite genotype distribution in different animal species was analysed. We observed no absolute limitation of any of five major genotypes to any one habitat; however, the frequency of four genotypes decreased across the gradient from the farm-bound group, to the free-roaming group, then the wildlife, whereas a fifth genotype increased along that gradient. Genetic diversity was greater in free-roaming than in farm-bound animals. The genotypic composition of parasites in wildlife differed from those in farm-bound and free-roaming animals. Furthermore, parasite genotypes differed among host species. We conclude that T. gondii genotype distributions are influenced by the spatial habitat and host species composition, and parasite diversity decreases towards areas of human settlement, elucidating facts which may influence transmission dynamics and zoonotic potential in this ubiquitous but regionally variable parasite.

Background Aspergillus fumigatus is the leading cause of invasive aspergillosis (IA), a lethal infection among immunocompromised patients. Guideline-recommended antifungal therapy against IA is a triazole antifungal, with other secondary options including an echinocandin and amphotericin B. Concerns about drug-host toxicity and antifungal resistance have been globally reported, so new, safe, and effective therapeutics are imperative. Methods In vitro, CLSI standards were upheld as we tested APX2041, voriconazole, caspofungin, and amphotericin B against various A. fumigatus strains. In vivo we assessed toxicity and efficacy of APX2104 in immunocompromised mice respectively. Neutropenia was induced with 150 mg/kg of cyclophosphamide on days -2/+3 and 250 mg/kg of cortisone acetate on days -1/+6. Immunocompromised mice were infected in an inhalation chamber via 12 mL of aerosolized spores of A. fumigatus CEA10 at a concentration of 1x109 spores/mL (Day 0). Treatment started day +1 and ended day +7. Results In vitro, APX2041, the active-form of APX2104, has over a 16-fold lower minimum effective concentration (MEC) when compared to voriconazole, caspofungin, and amphotericin B against various A. fumigatus strains, including echinocandin- and azole-resistant strains. In vivo, given preliminary pharmacokinetic data, APX2104 was tested in non-infected immunocompromised mice at 60 mg/kg and 78 mg/kg once per day (QD). Deaths due to toxicity were seen only at a dose of 78 mg/kg, so 60 mg/kg was set as a safe dose for our in vivo efficacy studies. In IA-challenged neutropenic mice, treatment with either posaconazole (20 mg/kg BID) or APX2104 (60 mg/kg QD) equally prolonged survival in 14 of 15 (93%) mice 14 days post-infection (p= 0.985). Untreatment control yielded a survival of 3 of 15 (20%) 14 days post-infection (p= < 0.001). Consistent with our survival studies, H&E and GMS histological samples also demonstrated that APX2104 treatment decreased fungal burden within the lungs of neutropenic mice when compared to the untreated group. Conclusion Future studies will test the efficacy of APX2104 and posaconazole against azole antifungal resistant strains in vivo, as our preliminary findings suggest that APX2104 is a plausible solution to cure IA disease and combat antifungal resistance. Disclosures All Authors: No reported disclosures

Calcium signaling through calcineurin and its major transcription factor, CrzA, is integral to hyphal growth, stress response, and virulence of the pathogenic fungus Aspergillus fumigatus, the leading etiology of invasive aspergillosis. Dephosphorylation of CrzA by calcineurin activates the transcription factor, but the specific phosphorylation sites and their roles in the activation/inactivation mechanism are unknown. Mass spectroscopic analysis identified twenty phosphorylation sites, the majority of which were specific to filamentous fungi and distributed throughout the CrzA protein, with particular concentration in a serine-rich region N-terminal to the conserved DNA-binding domain (DBD). Site-directed mutagenesis of phosphorylated residues revealed that CrzA activity during calcium stimulation can only be suppressed by a high degree of phosphorylation in multiple regions of the protein. Our findings further suggest that this regulation is not solely accomplished through control of CrzA nuclear import. Additionally, we demonstrate the importance of the CrzA phosphorylation state in regulating growth, conidiation, calcium and cell-wall stress tolerance, and virulence. Finally, we identify two previously undescribed nuclear localization sequences in the DBD. These findings provide novel insight into the phosphoregulation of CrzA which may be exploited to selectively target A. fumigatus.

A majority of emerging infectious diseases in humans are zoonoses. Understanding factors that influence the emergence and transmission of zoonoses is pivotal for their prevention and control. Toxoplasma gondii is one of the most widespread zoonotic pathogens known today. Whereas only a few genotypes of T. gondii dominate in the Northern Hemisphere, many genotypes coexist in South America. Furthermore, T. gondii strains from South America are more likely to be virulent than those from the Northern Hemisphere. However, it is not clear what factor(s) shaped modern-day genetic diversity and virulence of T. gondii Here, our analysis suggests that the rise and expansion of farming in the past 11,000 years established the domestic cat/mouse transmission cycle for T. gondii, which has undoubtedly played a significant role in the selection of certain linages of T. gondii Our mathematical simulations showed that within the domestic transmission cycle, intermediately mouse-virulent T. gondii genotypes have an adaptive advantage and eventually become dominant due to a balance between lower host mortality and the ability to superinfect mice previously infected with a less virulent T. gondii strain. Our analysis of the global type II lineage of T. gondii suggests its Old World origin but recent expansion in North America, which is likely the consequence of global human migration and trading. These results have significant implications concerning transmission and evolution of zoonotic pathogens in the rapidly expanding anthropized environment demanded by rapid growth of the human population and intensive international trading at present and in the future.

Invasive aspergillosis (IA), caused by the filamentous fungal pathogen Aspergillus fumigatus, is a major cause of death among immunocompromised patients. The cyclic AMP/protein kinase A (PKA) signaling pathway is essential for hyphal growth and virulence of A. fumigatus, but the mechanism of regulation of PKA remains largely unknown. Here, we discovered a novel mechanism for the regulation of PKA activity in A. fumigatus via phosphorylation of key residues within the major catalytic subunit, PkaC1. Phosphopeptide enrichment and tandem mass spectrometry revealed the phosphorylation of PkaC1 at four sites (S175, T331, T333, and T337) with implications for important and diverse roles in the regulation of A. fumigatus PKA. While the phosphorylation at one of the residues (T333) is conserved in other species, the identification of three other residues represents previously unknown PKA phosphoregulation in A. fumigatus. Site-directed mutagenesis of the phosphorylated residues to mimic or prevent phosphorylation revealed dramatic effects on kinase activity, growth, conidiation, cell wall stress response, and virulence in both invertebrate and murine infection models. Three-dimensional structural modeling of A. fumigatus PkaC1 substantiated the positive or negative regulatory roles for specific residues. Suppression of PKA activity also led to downregulation of PkaC1 protein levels in an apparent novel negative-feedback mechanism. Taken together, we propose a model in which PkaC1 phosphorylation both positively and negatively modulates its activity. These findings pave the way for future discovery of fungus-specific aspects of this key signaling network., IMPORTANCE Our understanding of signal transduction networks in pathogenic fungi is limited, despite the increase in invasive fungal infections and rising mortality rates in the immunosuppressed patient population. Because PKA is known to be essential for hyphal growth and virulence of A. fumigatus, we sought to identify fungus-specific regulatory mechanisms governing PKA activity. In this study, we identify, for the first time, a novel mechanism for the regulation of PKA signaling in which differential phosphorylation of the PkaC1 catalytic subunit can lead to either positive or negative regulation of activity. Furthermore, we show that inactivation of PKA signaling leads to downregulation of catalytic subunit protein levels in a negative-feedback mechanism distinct from expression patterns previously reported in the yeasts. Our findings represent a divergence in the regulation of PKA signaling in A. fumigatus, which could potentially be exploited as a target and also open the avenue for discovery of fungus-specific downstream effectors of PKA.

Histone deacetylases (HDACs) play an important role in regulation of gene expression through histone modifications. Here we show that the Aspergillus fumigatus HDAC HdaA is involved in regulation of secondary metabolite production and is required for normal germination and vegetative growth. Deletion of the hdaA gene increased the production of several secondary metabolites but decreased production of gliotoxin whereas over-expression hdaA increased production of gliotoxin. RT-PCR analysis of 14 nonribosomal peptide synthases indicated HdaA regulation of up to nine of them. A mammalian cell toxicity assay indicated increased activity in the over-expression strain. Neither mutant affected virulence of the fungus as measured by macrophage engulfment of conidia or virulence in a neutropenic mouse model.

With respect to fungal pathogenesis and virulence, fungal secondary metabolites are primary virulence factors in several fungus-plant interactions. This chapter explores the current state of knowledge on the production of secondary metabolites by the opportunistic human pathogen Aspergillus fumigatus. Several types of secondary metabolites have been isolated from A. fumigatus in vitro cultures, including fumitremorgins, verruculogen, fumigaclavines, fumagillin, helvolic acid, and gliotoxin, among other, less-studied compounds. Importantly, gliotoxin has been detected in the serum of patients with invasive pulmonary aspergillosis (IPA) and in experimental murine models of IPA. Overexpression of the nonribosomal peptide synthetase (NRPS) ftmA in A. fumigatus AF293.1 and A. nidulans resulted in accumulation of brevianamide F, the likely precursor of fumitremorgin biosynthesis. Like many other A. fumigatus-produced secondary metabolites, the potential role of helvolic acid in aspergillosis is unknown. Production of secondary metabolites is an energetically costly process involving many enzymatic steps. In fungi, signals generated in response to the environment are typically relayed through DNA-binding Cys2His2 zinc-finger proteins, including CreA for carbon signaling, AreA for nitrogen signaling, and PacC for pH signaling. Insight into signaling pathways linking growth, development, and secondary metabolism came from a key study in A. nidulans showing heterotrimeric G-protein activation simultaneously inhibits sporulation and production of the mycotoxin sterigmatocystin while promoting vegetative growth. Fungal secondary metabolites are important biomolecules with significant biological activities.

Bioactive small molecules are critical in Aspergillus species during their development and interaction with other organisms. Genes dedicated to their production are encoded in clusters that can be located throughout the genome. We show that deletion of hdaA , encoding an Aspergillus nidulans histone deacetylase (HDAC), causes transcriptional activation of two telomere-proximal gene clusters—and subsequent increased levels of the corresponding molecules (toxin and antibiotic)—but not of a telomere-distal cluster. Introduction of two additional HDAC mutant alleles in a Δ hdaA background had minimal effects on expression of the two HdaA-regulated clusters. Treatment of other fungal genera with HDAC inhibitors resulted in overproduction of several metabolites, suggesting a conserved mechanism of HDAC repression of some secondary-metabolite gene clusters. Chromatin regulation of small-molecule gene clusters may enable filamentous fungi to successfully exploit environmental resources by modifying chemical diversity.