Antifungal resistance, combinations and pipeline: oh my!

Potent synergistic effect of natural product-inspired Sinomenine derivatives with fluconazole against azole-resistant Candida albicans

Candida albicans (C. albicans) is the most common cause of invasive Candida infections worldwide. The acquired resistance of C. albicans to fluconazole, a first-line antifungal drug, has been frequently reported, posing significant challenges to treatment. Combination therapy has emerged as an effective strategy to combat drug resistance. In this study, we synthesized a series of sinomenine derivatives and evaluated in vitro synergistic activity against azole-resistant C. albicans. The results demonstrated that compound 3ja exhibited a potent synergistic effect with fluconazole against azole-resistant C. albicans. Mechanism studies revealed that the combination of 3ja and FLC significantly induced reactive oxygen species accumulation, disrupted membrane integrity, altered membrane sterols, and promoted apoptosis in C. albicans.

Antifungal activity of guanidine compounds

Guanidinic compounds are a class of compounds distributed in nature but also synthesized in vitro with a wide variety of applicability. One of the potentials of those molecules is antimicrobial activity. In that sense, although mainly limited to immunocompromised people, fungi pathogens are a cause of concern, even more so after the COVID-19 pandemic. Susceptible groups and increased geographical distribution, besides drug toxicity, resistance, and high costs, made the World Health Organization (WHO) establish a guideline for research and public health politics against different fungi opportunist agents. Our present work evaluated the antifungal activity of 11 guanidine compounds (one of them synthesized for the first time) against six fungi species in the WHO Fungi Priority Pathogens List and their potential for antimicrobial selectivity. The newly synthesized compound, named LQOF-G2-S, was successfully obtained and chemically characterized as spermidine tri-substituted by guanidine moieties in benzylamine-4-bromoaniline groups, and it presented the best antifungal activity and selectivity among the others. It was the only compound active against Candida spp.; however, its activity was more promising against Cryptococcus neoformans, Cryptococcus gattii, and even more against Paracoccidioides brasiliensis and Paracoccidioides lutzii, with a selective index higher than 10. The LQOF-G2-S potential opened up the opportunity to design and evaluate other similar compounds, contributing to finding new effective, less toxic, and more affordable compounds for fungi treatment.

Mono-N-alkylation of Amphotericin B and Nystatin A1 and Its Amides: Effect on the In Vitro Activity, Cytotoxicity and Permeabilization of Model Membranes

Objectives: In 2022, the World Health Organization highlighted the necessity for the development of new antifungal agents. Polyene antibiotics are characterized by a low risk of drug resistance; however, their use is limited by low solubility and severe side effects. Methods: A series of N-alkylated derivatives of amphotericin B and nystatin A1 as well as their N-(2-hydroxyethyl)amides were synthesized. Their antifungal activity was evaluated against various Candida strains and Aspergillus fumigatus using the broth microdilution method. Cytotoxicity was assessed using an MTT assay on human embryonic kidney cells HEK293 and human skin fibroblast cells hFB-hTERT6, as well as a hemolysis assay on erythrocytes. Membrane activity was analyzed by fluorimetric measurement of calcein leakage from model liposomes. Results: Derivatives containing the N-(hydroxyethyl)amino)ethyl fragment (compounds 3 and 4) exhibited relatively high antifungal activity, as did N-(2-hydroxyethyl)amides 5 and 9. Bis-modified compounds 6 and 10 did not outperform their mono-modified analogues in terms of activity or cytotoxicity. The mono-N-alkylated compound 3 showed the highest activity/toxicity ratio, which correlated well with its selectivity for ergosterol-containing model membranes. Discussion: Combining two successful modifications does not necessarily improve the activity/toxicity ratio of polyenes. Further studies can be performed for the optimization of carboxyl group of 3.

Evaluating the Antifungal Potential of Cinnamaldehyde: A Study of its Efficacy against Candida Species

Candida species exist as commensals in nature, colonizing the mucous membranes, gastrointestinal tract, vagina as well as the skin and usually cause infections in immunocompromised patients. C. albicans are known to be the most prevalent Candida species associated with infections, while there has been a significant surge in the incidence of Non-Candida albicans Candida species (NCAC) recently. The recent occurrences of the antifungal resistance in Candida, especially in NCAC species are quite alarming which raises the need for a safe and efficient alternative antimycotic drug. This study analyses the efficacy of cinnamaldehyde against Candida species, which is known to cause the majority of the fungal infections in humans. Cinnamaldehyde is a natural antimicrobial compound derived from cinnamon and has demonstrated significant antimycotic properties. Antifungal susceptibility profiles of cinnamaldehyde against Candida species were studied by disc diffusion as well as by broth microdilution assays. The mean diameter of the inhibition zone (IZ) formed by direct contact and disc volatilization assays were 61.26 mM and 65.20 mM, respectively. Both the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC) of cinnamaldehyde ranged from 16-256 mg/L with mean MIC of 60.61 mg/L and a mean MFC of 81.94 mg/L. Co-incubation of Candida cells with cinnamaldehyde resulted in the loss of viable cells within 4 hours of incubation. Cinnamaldehyde was found to exhibit both fungistatic and fungicidal properties, making it a potent natural alternative for conventional antifungal agents.

Review of the novel antifungal drug olorofim (F901318)

There is clearly a need for novel antifungal agents, not only concerning spectrum, but also oral bioavailability, tolerability, and drug-drug interactions. There is growing concern for antifungal resistance for current available antifungals, mainly driven by environmental fungicide use or long-term exposure to antifungals, in the setting of mould-active prophylaxis or for chronic antifungal infections, such as chronic pulmonary aspergillosis. Moreover, the incidence of breakthrough infections is increasing, because of the introduction of (mould-active) prophylaxis (1-4). There is emergence of difficult to treat invasive fungal infections, such as those caused by Lomentospora prolificans, cryptic species of Aspergillus, Scedosporium and Coccidioides. Olorofim (F901318) is the first-in class of the orotomides, a novel antifungal class targeting dihydroorotate dehydrogenase (DHODH), a key enzyme in the biosynthesis of pyrimidines. Olorofim shows good in vitro and in vivo activity against Aspergillus species, rare and difficult to treat moulds and endemic dimorphic fungi, including azole- and amphotericin-resistant isolates. It lacks activity against yeasts and the Mucorales species. It is only orally available and shows very promising results in ongoing clinical trials. In this review we will describe the mechanism of action of olorofim, the spectrum of activity in vitro and in vivo, pharmacokinetics, pharmacodynamics, drug-drug interactions, resistance, and clinical outcomes.

The Antifungal Potential of Niclosamide and Structurally Related Salicylanilides

Human mycoses cover a diverse field of fungal diseases from skin disorders to systemic invasive infections and pose an increasing global health problem based on ineffective treatment options, the hampered development of new efficient drugs, and the emergence of resistant fungal strains. Niclosamide is currently applied for the treatment of worm infections. Its mechanisms of action, which include the suppression of mitochondrial oxidative phosphorylation (also known as mitochondrial uncoupling), among others, has led to a repurposing of this promising anthelmintic drug for the therapy of further human diseases such as cancer, diabetes, and microbial infections. Given the urgent need to develop new drugs against fungal infections, the considerable antifungal properties of niclosamide are highlighted in this review. Its chemical and pharmacological properties relevant for drug development are also briefly mentioned, and the described mitochondria-targeting mechanisms of action add to the current arsenal of approved antifungal drugs. In addition, the activities of further salicylanilide-based niclosamide analogs against fungal pathogens, including agents applied in veterinary medicine for many years, are described and discussed for their feasibility as new antifungals for humans. Preliminary structure-activity relationships are determined and discussed. Various salicylanilide derivatives with antifungal activities showed increased oral bioavailabilities when compared with niclosamide. The simple synthesis of salicylanilide-based drugs also vouchsafes a broad and cost-effective availability for poorer patient groups. Pertinent literature is covered until 2024.

In vitro antifungal activity of MMV Pathogen Box® compounds alone or in combination with antifungal drugs against mucormycosis agents

Mucormycosis is a severe fungal infection that demands immediate and decisive intervention upon suspicion. The causative agents of mucormycosis exhibit inherent resistance to echinocandins and voriconazole, and their in vitro susceptibility to terbinafine is highly variable and species-specific. Considering these factors and the limitations of currently available antifungal therapies, the identification of novel antifungals with potent activity against mucormycosis is of paramount importance. This study aims to identify compounds from the MMV Pathogen Box® presenting antifungal activity against selected mucormycosis agents and to evaluate their potential synergistic effects when combined with antifungal drugs. A screening of the Pathogen Box® compounds was conducted, isolated or in combination with sub-inhibitory concentrations of amphotericin B, isavuconazole or posaconazole, against a Rhizopus oryzae strain. Hits from the screenings were further evaluated against eight Mucoralean strains for minimal inhibitory and fungicidal concentration determinations and to confirm synergistic interactions using the checkerboard method. Ultrastructural studies were performed using scanning electron microscopy. MMV675968 exhibited fungicidal activity against a R. oryzae strain. All but one Rhizopus spp. strains presented MIC ≤ 1 μg/mL, with a geometric mean of 0.78 μg/mL observed across all isolates for this compound, which did not change significantly the cellular structure of this fungus. The combination screening with antifungal drugs revealed six additional compounds potentially active against the R. oryzae strain, two of them demonstrated proven synergism through the checkerboard assay. This first study with the MMV Pathogen Box® and Zigomycetes highlights promising new treatment options for mucormycosis in the future.

Transcriptomic meta-analysis to identify potential antifungal targets in Candida albicans

BACKGROUND

Candida albicans is a fungal pathogen causing human infections. Here we investigated differential gene expression patterns and functional enrichment in C. albicans strains grown under different conditions.

METHODS

A systematic GEO database search identified 239 "Candida albicans" datasets, of which 14 were selected after rigorous criteria application. Retrieval of raw sequencing data from the ENA database was accompanied by essential metadata extraction from dataset descriptions and original articles. Pre-processing via the tailored nf-core pipeline for C. albicans involved alignment, gene/transcript quantification, and diverse quality control measures. Quality assessment via PCA and DESeq2 identified significant genes (FDR < = 0.05, log2-fold change > = 1 or <= -1), while topGO conducted GO term enrichment analysis. Exclusions were made based on data quality and strain relevance, resulting in the selection of seven datasets from the SC5314 strain background for in-depth investigation.

RESULTS

The meta-analysis of seven selected studies unveiled a substantial number of genes exhibiting significant up-regulation (24,689) and down-regulation (18,074). These differentially expressed genes were further categorized into 2,497 significantly up-regulated and 2,573 significantly down-regulated Gene Ontology (GO) IDs. GO term enrichment analysis clustered these terms into distinct groups, providing insights into the functional implications. Three target gene lists were compiled based on previous studies, focusing on central metabolism, ion homeostasis, and pathogenicity. Frequency analysis revealed genes with higher occurrence within the identified GO clusters, suggesting their potential as antifungal targets. Notably, the genes TPS2, TPS1, RIM21, PRA1, SAP4, and SAP6 exhibited higher frequencies within the clusters. Through frequency analysis within the GO clusters, several key genes emerged as potential targets for antifungal therapies. These include RSP5, GLC7, SOD2, SOD5, SOD1, SOD6, SOD4, SOD3, and RIM101 which exhibited higher occurrence within the identified clusters.

CONCLUSION

This comprehensive study significantly advances our understanding of the dynamic nature of gene expression in C. albicans. The identification of genes with enhanced potential as antifungal drug targets underpins their value for future interventions. The highlighted genes, including TPS2, TPS1, RIM21, PRA1, SAP4, SAP6, RSP5, GLC7, SOD2, SOD5, SOD1, SOD6, SOD4, SOD3, and RIM101, hold promise for the development of targeted antifungal therapies.

The top 10 papers on the treatment of invasive fungal infections, 2018-2023

Background

Invasive fungal infections are responsible for a large number of infections in hospitalized patients annually and are responsible for high morbidity and mortality. Familiarity with novel agents or strategies in this area can be challenging.

Objectives

To identify the top 10 manuscripts on the treatment of invasive fungal infections from 2018 to 2023.

Design

Modified Delphi consensus-building technique.

Methods

A three-stage consensus-building approach was used comprised of (1) identifying relevant articles; (2) voting by a panel of experts to establish consensus on the importance of these articles; and (3) finalizing the list of top articles by a small group. Members of the Southeastern Research Group Endeavor network served as content experts. Publications from 2018 to 2023 were evaluated if articles met the following inclusion criteria: (1) published between 2018 and 2023, (2) contained content related to fungal infections, and (3) included an actionable intervention.

Results

A total of 6518 potential publications were assessed. After applying inclusion and exclusion criteria, 82 articles were reviewed. The top 10 publications related to invasive fungal infections, selected by a panel of experts, are summarized in this manuscript and include publications related to the treatment of invasive aspergillosis, candidiasis, and cryptococcosis.

Conclusion

This article highlights the selected publications and may serve as a key resource for teaching and training. Clinicians may also employ these reported interventions to identify new opportunities to optimize antifungal therapeutic strategies within one's institution.