Screening of Chemical Libraries for New Antifungal Drugs against Aspergillus fumigatus Reveals Sphingolipids Are Involved in the Mechanism of Action of Miltefosine

Sodium butyrate inhibits the expression of virulence factors in Vibrio cholerae by targeting ToxT protein

Cholera, a diarrheal disease caused by the gram-negative bacterium Vibrio cholerae, remains a global health threat in developing countries due to its high transmissibility and increased antibiotic resistance. There is a pressing need for alternative strategies, with an emphasis on anti-virulent approaches to alter the outcome of bacterial infections, given the increase in antimicrobial-resistant strains. V. cholerae causes cholera by secreting virulence factors in the intestinal epithelial cells. These virulence factors facilitate bacterial colonization and cholera toxin production during infection. Here, we demonstrate that sodium butyrate (SB), a small molecule, had no effect on bacterial viability but was effective in suppressing the virulence attributes of V. cholerae. The production of cholera toxin (CT) was significantly reduced in a standard V. cholerae El Tor strain and two clinical isolates when grown in the presence of SB. Analysis of mRNA and protein levels further revealed that SB reduced the expression of the ToxT-dependent virulence genes like tcpA and ctxAB. DNA-protein interaction assays, conducted at cellular (ChIP) and in vitro conditions (EMSA), indicated that SB weakens the binding between ToxT and its downstream promoter DNA, likely by blocking DNA binding. Furthermore, the anti-virulence efficacy of SB was confirmed in animal models. These findings suggest that SB could be developed as an anti-virulence agent against V. cholerae, serving as a potential alternative to conventional antibiotics or as an adjunctive therapy to combat cholera.

IMPORTANCE

The world has been facing an upsurge in cholera cases since 2021, a similar trend continuing into 2022, with over 29 countries reporting cholera outbreaks (World Health Organization, 16 December 2022, Disease Outbreak News, Cholera-global situation). Treatment of cholera involves oral rehydration therapy coupled with antibiotics to reduce the duration of the illness. However, in recent years, indiscriminate use of antibiotics has contributed to the emergence of antibiotic-resistant strains. In this study, we have addressed the problem of antibiotic resistance by targeting virulence factors. Screening various compounds using in silico methods led to the identification of a small molecule, SB, that inhibits the virulence cascade in V. cholerae. We demonstrated that (i) SB intervened in ToxT protein-DNA binding and subsequently affected the expression of ToxT-regulated virulence genes (ctxAB and tcpA) and (ii) SB is a potential therapeutic candidate for the development of a novel antimicrobial agent.

The GPCR antagonist PPTN synergizes with caspofungin providing increased fungicidal activity against Aspergillus fumigatus

Fungal pathogens pose a serious threat to human health, with Candida and Aspergillus spp. representing some of the most significant opportunistic invaders. Aspergillus fumigatus causes aspergillosis, one of the most prevalent fungal diseases of humans. There is a limited number of drugs available to combat these infections, and antifungal drug resistance is on the rise. In this manuscript, we show 4-[4-(4-Piperidinyl) phenyl]-7-[4-(-(trifluoromethyl) phenyl]-2-naphthalenecarboxylic acid (PPTN), a highly specific antagonist of the human P2Y14 receptor, is a promising antifungal adjuvant against diverse fungal pathogens. PPTN interacts with caspofungin (CAS), ibrexafungerp, voriconazole (VOR), and amphotericin against A. fumigatus CAS- and VOR-resistant clinical isolates, and also CAS against Candida spp and Cryptococcus neoformans. The combination of PPTN and CAS increases cell death in A. fumigatus. In the model yeast Saccharomyces cerevisiae, heterozygous deletion of genes involved in chromatin remodeling results in PPTN hypersensitivity, and in A. fumigatus, PPTN can have increased fungicidal activity when combined with the histone deacetylase inhibitor trichostatin A and the DNA methyltransferase inhibitor 5-azacytidine. Finally, PPTN has reduced toxicity to human immortalized cell lineages and partially clears A. fumigatus conidia infection in A549 pulmonary epithelial cells. Our results indicate that PPTN is a novel adjuvant antifungal drug against fungal diseases caused by A. fumigatus and Candida spp.

IMPORTANCE

Invasive fungal infections have a high mortality rate, causing more deaths annually than tuberculosis or malaria. Aspergillus fumigatus is the main etiological agent of aspergillosis, one of the most prevalent and deadly fungal diseases. There are few therapeutic options for treating this disease, and treatment commonly fails due to host complications or the emergence of antifungal resistance. Drug repurposing, where existing drugs are deployed for other clinical indications, has increasingly been used in the process of drug discovery. Here, we show that 4-[4-(4-Piperidinyl) phenyl]-7-[4-(-(trifluoromethyl) phenyl]-2-naphthalenecarboxylic acid (PPTN), a highly specific antagonist of the human P2Y14 receptor, when combined with caspofungin (CAS), ibrexafungerp, voriconazole (VOR), and amphotericin can increase the fungicidal activity against not only A. fumigatus CAS- and VOR-resistant clinical isolates but also CAS against Candida spp.

A Novel Niosomal Gel for Topical Delivery of Miltefosine Against Trichophyton indotineae Dermatophytosis in Animal Model

INTRODUCTION

Dermatophytosis, a cutaneous fungal infection worldwide, is generally localised to the skin's superficial layers and keratinised structures. Although most agents are susceptible to current antifungal drugs available in clinical settings, frequent relapses and failures, especially in cases due to Trichophyton indotineae, have been frequently reported. Therefore, alternative targets and therapeutic approaches are highly required. In the present study, we compared the efficacies of terbinafine with conventional and niosomal forms of miltefosine (MFS) against dermatophytosis in the guinea pig model.

MATERIAL AND METHODS

Initially, 30 guinea pigs were divided into five groups (e.g., untreated control, treated groups by MFS niosomal gel 1%, MFS gel 1%, terbinafine 1% and niosome) and were infected with terbinafine-resistant Trichophyton indotineae and subsequently scored both clinically and mycologically until day 35 of inoculation. MFS was encapsulated into niosomes, elastic vesicles made of non-ionic surfactants that enhance drug delivery through the skin.

RESULTS

Results showed that the MFS niosomal gel 1% significantly reduced lesion scores, mycological evidence of infection and inflammation compared to the untreated control and terbinafine-treated groups (p < 0.05). Moreover, the lesion score in the niosomal gel and terbinafine groups did not differ from the untreated control (p > 0.05). Histopathological analysis confirmed reduced epidermal thickening and fungal burden in treated models with the MFS niosomal gel 1%.

CONCLUSION

The findings highlighted MFS niosomal gel 1% as a potentially effective, targeted therapy for drug-resistant T. indotineae, offering a safer and more effective alternative to topical and oral antifungal treatments. However, further studies are warranted to continue correlating these findings with more clinical outcomes.

The evolution of antifungal therapy: Traditional agents, current challenges and future perspectives

Fungal infections kill more than 3 million people every year. This high number reflects the significant challenges that treating these diseases worldwide presents. The current arsenal of antifungal drugs is limited and often accompanied by high toxicity to patients, elevated treatment costs, increased frequency of resistance rates, and the emergence of naturally resistant species. These treatment challenges highlight the urgency of developing new antifungal therapies, which could positively impact millions of lives each year globally. Our review offers an overview of the antifungal drugs currently available for treatment, presents the status of new antifungal drugs under clinical study, and explores ahead to future candidates that aim to help address this important global health issue.

Milteforan, a promising veterinary commercial product against feline sporotrichosis

Sporotrichosis, the cutaneous mycosis most commonly reported in Latin America, is caused by the Sporothrix clinical clade species, including Sporothrix brasiliensis and Sporothrix schenckii sensu stricto. Due to its zoonotic transmission in Brazil, S. brasiliensis represents a significant health threat to humans and domestic animals. Itraconazole, terbinafine, and amphotericin B are the most used antifungals for treating sporotrichosis. However, many strains of S. brasiliensis and S. schenckii have shown resistance to these agents, highlighting the importance of finding new therapeutic options. Here, we demonstrate that milteforan, a commercial veterinary product against dog leishmaniasis, whose active principle is miltefosine, is a possible therapeutic alternative for the treatment of sporotrichosis, as observed by its fungicidal activity in vitro against different strains of S. brasiliensis and S. schenckii. Fluorescent miltefosine localizes to the Sporothrix cell membrane and mitochondria and causes cell death through increased permeabilization. Milteforan decreases S. brasiliensis fungal burden in A549 pulmonary cells and bone marrow-derived macrophages and also has an immunomodulatory effect by decreasing TNF-α, IL-6, and IL-10 production. Our results suggest milteforan as a possible alternative to treat feline sporotrichosis.

IMPORTANCE

Sporotrichosis is an endemic disease in Latin America caused by different species of Sporothrix. This fungus can infect domestic animals, mainly cats and eventually dogs, as well as humans. Few drugs are available to treat this disease, such as itraconazole, terbinafine, and amphotericin B, but resistance to these agents has risen in the last few years. Alternative new therapeutic options to treat sporotrichosis are essential. Here, we propose milteforan, a commercial veterinary product against dog leishmaniasis, whose active principle is miltefosine, as a possible therapeutic alternative for treating sporotrichosis. Milteforan decreases S. brasiliensis fungal burden in human and mouse cells and has an immunomodulatory effect by decreasing several cytokine production.

Investigating the antifungal potential of genetically modified hybrid chitinase enzymes derived from Bacillus subtilis and Serratia marcescens

Chitinases are glycosyl hydrolase enzymes that break down chitin, an integral component of fungal cell walls. Bacteria such as Bacillus subtilis and Serratia marcescens produce chitinases with antifungal properties. In this study, we aimed to generate hybrid chitinase enzymes with enhanced antifungal activity by combining functional domains from native chitinases produced by B. subtilis and S. marcescens. Chitinase genes were cloned from both bacteria and fused together using overlap extension PCR. The hybrid constructs were expressed in E. coli and the recombinant enzymes purified. Gel electrophoresis and computational analysis confirmed the molecular weights and isoelectric points of the hybrid chitinases were intermediate between the parental enzymes. Antifungal assays demonstrated that the hybrid chitinases inhibited growth of the fungus Fusarium oxysporum significantly more than the native enzymes and also showed fungicidal activity against Candida albicans, Alternaria solani, and Rhizoctonia solani. The results indicate that hybrid bacterial chitinases are a promising approach to engineer novel antifungal proteins. This study provides insight into structure-function relationships of chitinases and strategies for generating biotherapeutics with enhanced bioactive properties. These hybrid chitinases result in a more potent and versatile antifungal agent.

Evolutionary origin and population diversity of a cryptic hybrid pathogen

Cryptic fungal pathogens pose disease management challenges due to their morphological resemblance to known pathogens. Here, we investigated the genomes and phenotypes of 53 globally distributed isolates of Aspergillus section Nidulantes fungi and found 30 clinical isolates-including four isolated from COVID-19 patients-were A. latus, a cryptic pathogen that originated via allodiploid hybridization. Notably, all A. latus isolates were misidentified. A. latus hybrids likely originated via a single hybridization event during the Miocene and harbor substantial genetic diversity. Transcriptome profiling of a clinical isolate revealed that both parental subgenomes are actively expressed and respond to environmental stimuli. Characterizing infection-relevant traits-such as drug resistance and growth under oxidative stress-revealed distinct phenotypic profiles among A. latus hybrids compared to parental and closely related species. Moreover, we identified four features that could aid A. latus taxonomic identification. Together, these findings deepen our understanding of the origin of cryptic pathogens.

Milteforan, a promising veterinary commercial product against feline sporotrichosis

Sporotrichosis, the cutaneous mycosis most commonly reported in Latin America, is caused by the Sporothrix clinical clade species, including Sporothrix brasiliensis and Sporothrix schenckii sensu stricto. In Brazil, S. brasiliensis represents a vital health threat to humans and domestic animals due to its zoonotic transmission. Itraconazole, terbinafine, and amphotericin B are the most used antifungals for treating sporotrichosis. However, many strains of S. brasiliensis and S. schenckii have shown resistance to these agents, highlighting the importance of finding new therapeutic options. Here, we demonstrate that milteforan, a commercial veterinary product against dog leishmaniasis whose active principle is miltefosine, is a possible therapeutic alternative for the treatment of sporotrichosis, as observed by its fungicidal activity in vitro against different strains of S. brasiliensis and S. schenckii, and by its antifungal activity when used to treat infected epithelial cells and macrophages. Our results suggest milteforan as a possible alternative to treat feline sporotrichosis.

Repurposing drugs for fungal infections: advantages and limitations

Tweetable abstract Repurposing existing drugs for fungal infections has demonstrated potential in both in vitro and animal models, but there are still obstacles to overcome for clinical application. #antifungal #drugrepurposing #fungalinfections.

Miltefosine repositioning: A review of potential alternative antifungal therapy

Fungal infections are a global health problem with high mortality and morbidity rates. Available antifungal agents have high toxicity and pharmacodynamic and pharmacokinetic limitations. Moreover, the increased incidence of antifungal-resistant isolates and the emergence of intrinsically resistant species raise concerns about seeking alternatives for efficient antifungal therapy. In this context, we review literature data addressing the potential action of miltefosine (MFS), an anti-Leishmania and anticancer agent, as a repositioning drug for antifungal treatment. Here, we highlight the in vitro and in vivo data, MFS possible mechanisms of action, case reports, and nanocarrier-mediated MFS delivery, focusing on fungal infection therapy. Finally, many studies have demonstrated the promising antifungal action of MFS in vitro, but there is little or no data on antifungal activity in vertebrate animal models and clinical trials, so have a need to develop more research for the repositioning of MFS as an antifungal therapy.

Evolutionary origin, population diversity, and diagnostics for a cryptic hybrid pathogen

Cryptic fungal pathogens pose significant identification and disease management challenges due to their morphological resemblance to known pathogenic species while harboring genetic and (often) infectionrelevant trait differences. The cryptic fungal pathogen Aspergillus latus, an allodiploid hybrid originating from Aspergillus spinulosporus and an unknown close relative of Aspergillus quadrilineatus within section Nidulantes, remains poorly understood. The absence of accurate diagnostics for A. latus has led to misidentifications, hindering epidemiological studies and the design of effective treatment plans. We conducted an in-depth investigation of the genomes and phenotypes of 44 globally distributed isolates (41 clinical isolates and three type strains) from Aspergillus section Nidulantes. We found that 21 clinical isolates were A. latus; notably, standard methods of pathogen identification misidentified all A. latus isolates. The remaining isolates were identified as A. spinulosporus (8), A. quadrilineatus (1), or A. nidulans (11). Phylogenomic analyses shed light on the origin of A. latus, indicating one or two hybridization events gave rise to the species during the Miocene, approximately 15.4 to 8.8 million years ago. Characterizing the A. latus pangenome uncovered substantial genetic diversity within gene families and biosynthetic gene clusters. Transcriptomic analysis revealed that both parental genomes are actively expressed in nearly equal proportions and respond to environmental stimuli. Further investigation into infection-relevant chemical and physiological traits, including drug resistance profiles, growth under oxidative stress conditions, and secondary metabolite biosynthesis, highlight distinct phenotypic profiles of the hybrid A. latus compared to its parental and closely related species. Leveraging our comprehensive genomic and phenotypic analyses, we propose five genomic and phenotypic markers as diagnostics for A. latus species identification. These findings provide valuable insights into the evolutionary origin, genomic outcome, and phenotypic implications of hybridization in a cryptic fungal pathogen, thus enhancing our understanding of the underlying processes contributing to fungal pathogenesis. Furthermore, our study underscores the effectiveness of extensive genomic and phenotypic analyses as a promising approach for developing diagnostics applicable to future investigations of cryptic and emerging pathogens.

Antifungal Development and the Urgency of Minimizing the Impact of Fungal Diseases on Public Health

Fungal infections are a major public health problem resulting from the lack of public policies addressing these diseases, toxic and/or expensive therapeutic tools, scarce diagnostic tests, and unavailable vaccines. In this Perspective, we discuss the need for novel antifungal alternatives, highlighting new initiatives based on drug repurposing and the development of novel antifungals.

Antifungal activity of miltefosine against both azole-susceptible and -resistant Aspergillus strains

Miltefosine, an alkylphosphocholine, has been approved recently for the treatment of visceral leishmaniasis. Miltefosine has shown promise as a treatment for paracoccidioidomycosis, and has mixed activity against other fungi and yeast. There are limited data on the in-vitro activity of miltefosine against azole-resistant and -susceptible Aspergillus spp. As such, the aim of this study was to determine the in-vitro activity of miltefosine against Aspergillus strains. Miltefosine was tested against 108 azole-susceptible and -resistant Aspergillus strains isolated from Iran and other countries using the broth microdilution method. Miltefosine was found to be effective against azole-resistant Aspergillus isolates, with minimum inhibitory concentrations (MICs) ranging from 1.562 to 6.25 µg/mL. MIC₅₀ and MIC₉₀ were 1.562 and 3.125 µg/mL, respectively. Miltefosine had a higher geometric mean MIC (2.459 µg/mL) for wild-type Aspergillus isolates than itraconazole (0.220 µg/mL) and voriconazole (0.298 µg/mL). No significant difference was found between miltefosine MICs for azole-resistant Aspergillus isolates and azole-susceptible Aspergillus isolates (P>0.05). Miltefosine appears to have good in-vitro activity against azole-resistant Aspergillus strains, according to these findings. Furthermore, the findings suggest that miltefosine could be used to treat infections caused by azole-resistant Aspergillus spp.

Modulation of Virulence-Associated Traits in Aspergillus fumigatus by BET Inhibitor JQ1

Aspergillus fumigatus is a disease-causing, opportunistic fungus that can establish infection due to its capacity to respond to a wide range of environmental conditions. Secreted proteins and metabolites, which play a critical role in fungal-host interactions and pathogenesis, are modulated by epigenetic players, such as bromodomain and extraterminal domain (BET) proteins. In this study, we evaluated the in vitro and in vivo capability of the BET inhibitor JQ1 to modulate the extracellular proteins and virulence of A. fumigatus. The abundance of 25 of the 76 extracellular proteins identified through LC-MS/MS proteomic analysis changed following JQ1 treatment. Among them, a ribonuclease, a chitinase, and a superoxide dismutase were dramatically downregulated. Moreover, the proteomic analysis of A. fumigatus intracellular proteins indicated that Abr2, an intracellular laccase involved in the last step of melanin synthesis, was absent in the JQ1-treated group. To investigate at which level this downregulation occurred and considering the ability of JQ1 to modulate gene expression we checked the level of ABR2, Chitinase, and Superoxide dismutase mRNA expression by qRT-PCR. Finally, the capacity of JQ1 to reduce the virulence of A. fumigatus has been proved using Galleria mellonella larvae, which are an in vivo model to evaluate fungal virulence. Overall, the promising activity exhibited by JQ1 suggests that A. fumigatus is sensitive to BET inhibition and BET proteins may be a viable target for developing antifungal agents.

A Histoplasma capsulatum Lipid Metabolic Map Identifies Antifungal Targets

Lipids play a fundamental role in fungal cell biology, being essential cell membrane components and major targets of antifungal drugs. A deeper knowledge of lipid metabolism is key for developing new drugs and a better understanding of fungal pathogenesis. Here, we built a comprehensive map of the Histoplasma capsulatum lipid metabolic pathway by incorporating proteomic and lipidomic analyses. We performed genetic complementation and overexpression of H. capsulatum genes in Saccharomyces cerevisiae to validate reactions identified in the map and to determine enzymes responsible for catalyzing orphan reactions. The map led to the identification of both the fatty acid desaturation and the sphingolipid biosynthesis pathways as targets for drug development. We found that the sphingolipid biosynthesis inhibitor myriocin, the fatty acid desaturase inhibitor thiocarlide, and the fatty acid analog 10-thiastearic acid inhibit H. capsulatum growth in nanomolar to low-micromolar concentrations. These compounds also reduced the intracellular infection in an alveolar macrophage cell line. Overall, this lipid metabolic map revealed pathways that can be targeted for drug development.

Identification of Promising Antifungal Drugs against Scedosporium and Lomentospora Species after Screening of Pathogen Box Library

Fungal infections have been increasing during the last decades. Scedosporium and Lomentospora species are filamentous fungi most associated to those infections, especially in immunocompromised patients. Considering the limited options of treatment and the emergence of resistant isolates, an increasing concern motivates the development of new therapeutic alternatives. In this context, the present study screened the Pathogen Box library to identify compounds with antifungal activity against Scedosporium and Lomentospora. Using antifungal susceptibility tests, biofilm analysis, scanning electron microscopy (SEM), and synergism assay, auranofin and iodoquinol were found to present promising repurposing applications. Both compounds were active against different Scedosporium and Lomentospora, including planktonic cells and biofilm. SEM revealed morphological alterations and synergism analysis showed that both drugs present positive interactions with voriconazole, fluconazole, and caspofungin. These data suggest that auranofin and iodoquinol are promising compounds to be studied as repurposing approaches against scedosporiosis and lomentosporiosis.