Antifungal activity of 2α,3β-functionalized steroids stereoselectively increases with the addition of oligosaccharides

Invasive fungal infections pose a significant problem to the immune-compromised. Moreover, increased resistance to common antifungals requires development of novel compounds that can be used to treat invasive fungal infections. Naturally occurring steroidal glycosides have been shown to possess a range of functional antimicrobial properties, but synthetic methodology for their development hinders thorough exploration of this class of molecules and the structural components required for broad spectrum antifungal activity. In this report, we outline a novel approach to the synthesis of glycoside-linked functionalized 2α,3β-cholestane and spirostane molecules and present data from in vitro screenings of the antifungal activities against human fungal pathogens and as well as mammalian cell toxicity of these derivatives.     

Actividad de la micafungina contra las biopelículas de Candida

BackgroundMost recalcitrant infections are associated to colonization and microbial biofilm development. These biofilms are difficult to eliminate by the immune response mechanisms and the current antimicrobial therapy.AimTo describe the antifungal of micafungin against fungal biofilms based in the scientific and medical literature of recent years.MethodsWe have done a bibliographic retrieval using the scientific terms “micafungin”, “activity”, “biofilm”, “Candida”, “Aspergillus”, “fungi”, “mycos”*, susceptibility, in PubMed/Medline from the National Library of Medicine from 2006 to 2009.ResultsMost current antifungal agents (amphotericin B and fluconazole) and the new azole antifungals have no activity against fungal biofilms. However, micafungin and the rest of echinocandins are very active against Candida albicans, Candida dubliniensis, Candida glabrata, and Candida krusei biofilms but their activities are variable and less strong against Candida tropicalis and Candida parapsilosis biofilms. Moreover, they have not activities against the biofilms of Cryptococcus y Trichosporon.ConclusionsThe activity of micafungin against Candida biofilms gives more strength to its therapeutic indication for candidaemia and invasive candidiasis associated to catheter, prosthesis and other biomedical devices.     

Structure-based rational design,synthesis and antifungal activity of oxime-containing azole derivatives

In an attempt to find novel azole antifungal agents with improved activity and broader spectrum, computer modeling was used to design a series of new azoles with piperidin-4-one O-substituted oxime side chains. Molecular docking studies revealed that they formed hydrophobic and hydrogen-bonding interactions with lanosterol 14α-demethylase of Candida albicans (CACYP51). In vitro antifungal assay indicates that most of the synthesized compounds showed good activity against tested fungal pathogens. In comparison with fluconazole, itraconazole and voriconazole, several compounds (such as 10c, 10e, and 10i) show more potent antifungal activity and broader spectrum, suggesting that they are promising leads for the development of novel antifungal agents.     

Update on Antifungal Resistance and its Clinical Impact

Candida and Aspergillus species are important causes of opportunistic infection in an ever-growing number of vulnerable patients, and these infections are associated with high mortality. This has partly been attributed to the emerging resistance of pathogenic fungi to antifungal therapy, which potentially compromises the management of infected patients. Multi-azole resistance of Aspergillus fumigatus is a current health problem, as well as is the co-resistance of Candida glabrata to both azoles and echinocandins. In most cases, negative clinical consequences of reduced in vitro fungal susceptibility to azoles and/or echinocandins can be traced to acquisition of particular resistance mechanisms. While strategies using antifungal combinations or adjunctive agents that maximize the efficacy of existing antifungals may limit treatment failures, new therapeutic approaches, including antifungal agents with novel mechanisms of action, are urgent. In the meantime, more efforts should be devoted to close monitoring of antifungal resistance and its evolution in the clinical setting.     

Invertebrate models of fungal infection

The morbidity, mortality and economic burden associated with fungal infections, together with the emergence of fungal strains resistant to current antimicrobial agents, necessitate broadening our understanding of fungal pathogenesis and discovering new agents to treat these infections. Using invertebrate hosts, especially the nematode Caenorhabditis elegans and the model insects Drosophila melanogaster and Galleria mellonella, could help achieve these goals. The evolutionary conservation of several aspects of the innate immune response between invertebrates and mammals makes the use of these simple hosts an effective and fast screening method for identifying fungal virulence factors and testing potential antifungal compounds. The purpose of this review is to compare several model hosts that have been used in experimental mycology to-date and to describe their different characteristics and contribution to the study of fungal virulence and the detection of compounds with antifungal properties. This article is part of a Special Issue entitled: Animal Models of Disease.     

Design, synthesis, and evaluations of antifungal activity of novel phenyl(2H-tetrazol-5-yl)methanamine derivatives

Fungal infections pose a continuous and serious threat to human health and life. The intrinsic resistance has been observed in many genera of fungi. Many fungal infections are caused by opportunistic pathogens that may be endogenous (Candida infections) or acquired from the environment (Cryptococcus and Aspergillus infections). So, new therapeutic strategies are needed to combat various fungal infections. Fluconazole shows good antifungal activity with relatively low toxicity and is preferred as first line antifungal therapy, but it has suffered from severe drug resistance. So, there is a need to design novel analogues by modification of fluconazole-like structure. A novel series of phenyl(2H-tetrazol-5-yl)methanamine derivatives were synthesized by reaction of α-amino nitrile with sodium azide and ZnCl₂ in presence of isopropyl alcohol. They were evaluated for antifungal activity against Candida albicans and Aspergillus niger and subjected to docking study against 1EA1.     

Benzimidazole tethered pyrrolo[3,4-b]quinoline with broad-spectrum activity against fungal pathogens

Fungal infections caused by Candida and Cryptococcus are particularly dangerous for immunocompromised individuals. In this study, we identified that benzimidazole fused pyrrolo[3,4-b]quinoline compounds have potent antifungal activity against several clinical isolates of pathogenic fungal strains. Specifically, the compound 6a did not show cytotoxicity against mammalian cells at a concentration that inhibits the growth of fungal strains. In addition, the compound 6a also significantly reduced the metabolic activity of fungal cells in the Candida albicans biofilms. Collectively, our results indicate that benzimidazole fused quinoline compounds have a potential to develop as an antifungal agents.     

A Case for Antifungal Stewardship

Purpose of Review

The expanding utilization of limited available antifungal agents has led to a pressing need to implement interventions to ensure appropriate usage. The global emergence of resistant, difficult-to-treat invasive fungal infections among the most vulnerable patient populations is a call to action to develop a multifaceted antifungal stewardship approach.

Recent Findings

Candida species demonstrating multi-drug resistance, including highly resistant Candida auris, are emerging threats. Azole-resistant Aspergillus fumigatus, likely initially originating in the environment, likewise presents a treatment challenge. Routine empiric and prophylactic antifungal use, though effective, further complicates this issue, with the emergence of breakthrough mold infections. Early evidence supports success with antifungal stewardship programs.

Summary

Broad antifungal stewardship approaches that optimize antifungal drug usage, facilitate provider education, and monitor fungal epidemiology are crucial steps to preserve the antifungal armamentarium. Future development of novel diagnostic and treatment strategies will further facilitate management of invasive fungal infections.

     

Design,synthesis, and structure-activity relationship studies of novel triazole agents with strong antifungal activity against Aspergillus fumigatus

The incidence of invasive fungal infections has dramatically increased for several decades. In order to discover novel antifungal agents with broad spectrum and anti-Aspergillus efficacy, a series of novel triazole derivatives containing 1,2,3-benzotriazin-4-one was designed and synthesized. Most of the compounds exhibited stronger in vitro antifungal activities against tested fungi than fluconazole. Moreover, 6m showed comparable antifungal activity against seven pathogenic strains as voriconazole and albaconazole, especially against Aspergillus fumigatus (MIC = 0.25 μg/ml), and displayed moderate antifungal activity against fluconazole-resistant strains of Candida albicans. A clear SAR study indicated that compounds with groups at the 7-position resulted in novel antifungal triazoles with more effectiveness and a broader-spectrum.     

Synergistic Antifungal Effect of Glabridin and Fluconazole

The incidence of invasive fungal infections is increasing in recent years. The present study mainly investigated glabridin (Gla) alone and especially in combination with fluconazole (FLC) against Cryptococcus neoformans and Candida species (Candida albicans, Candida tropicalis, Candida krusei, Candida parapsilosis and Candida Glabratas) by different methods. The minimal inhibitory concentration (MIC) and the minimal fungicidal concentration (MFC) indicated that Gla possessed a broad-spectrum antifungal activity at relatively high concentrations. After combining with FLC, Gla exerted a potent synergistic effect against drug-resistant C. albicans and C. tropicalis at lower concentrations when interpreted by fractional inhibitory concentration index (FICI). Disk diffusion test and time-killing test confirming the synergistic fungicidal effect. Cell growth tests suggested that the synergistic effect of the two drugs depended more on the concentration of Gla. The cell envelop damage including a significant decrease of cell size and membrane permeability increasing were found after Gla treatment. Together, our results suggested that Gla possessed a synergistic effect with FLC and the cell envelope damage maybe contributed to the synergistic effect, which providing new information for developing novel antifungal agents.     

Design,synthesis, and biological evaluation of 4-chloro-2H-thiochromenes featuring nitrogen-containing side chains as potent antifungal agents

A series of 4-chloro-2H-thiochromenes featuring nitrogen-containing side chains were designed, synthesized and tested in vitro for their antifungal activities. The results of preliminary antifungal tests showed that most target compounds exhibited good inhibitory activities against Candida albicans, Cryptococcus neoformans, Candida tropicalis. Notably, compounds 10e and 10y showed most potent activity in vitro against a variety of fungal pathogens with low MICs. Meanwhile, low cytotoxicity on mammalian cells has been observed for compounds 10e and 10y in the tested concentrations by the MTT assay. Therefore, the 4-chloro-2H-thiochromenes with nitrogen-containing groups provide new lead structures in the search for novel antifungal agents.     

AmBisome,tres retos: infección por Candida auris,infección del sistema nervioso central e infección asociada a biopelículas

The treatment of invasive fungal infections remains a challenge, both for the diagnosis and for the need of providing the appropriate antifungal therapy. Candida auris is a pathogenic yeast that is responsible for hospital outbreaks, especially in intensive care units; it is characterized by a high resistance to the antifungal agents and can become multidrug-resistant. At present, the recommended antifungal agents for the invasive infections with this pathogen are echinocandins, always after carrying out an antifungal susceptibility testing. In case of no clinical response or persistent candidemia, the addition of liposomal amphotericin B or isavuconazole may be considered. Both fungal infection of the central nervous system and that associated with biomedical devices remain rare entities affecting mainly immunocompromised patients. However, an increase in their incidence in recent years, along with high morbidity and mortality, has been shown. The treatment of these infections is conditioned by the limited knowledge of the pharmacokinetic properties of antifungals. A better understanding of the pharmacokinetic and pharmacodynamic parameters of the different antifungals is essential to determine the efficacy of the antifungal agents in the treatment of these infections.     

Synthesis and antifungal activity of substituted 2,4,6-pyrimidinetrione carbaldehyde hydrazones

Opportunistic fungal infections caused by the Candida spp. are the most common human fungal infections, often resulting in severe systemic infections—a significant cause of morbidity and mortality in at-risk populations. Azole antifungals remain the mainstay of antifungal treatment for candidiasis, however development of clinical resistance to azoles by Candida spp. limits the drugs’ efficacy and highlights the need for discovery of novel therapeutics. Recently, it has been reported that simple hydrazone derivatives have the capability to potentiate antifungal activities in vitro. Similarly, pyrimidinetrione analogs have long been explored by medicinal chemists as potential therapeutics, with more recent focus being on the potential for pyrimidinetrione antimicrobial activity. In this work, we present the synthesis of a class of novel hydrazone-pyrimidinetrione analogs using novel synthetic procedures. In addition, structure–activity relationship studies focusing on fungal growth inhibition were also performed against two clinically significant fungal pathogens. A number of derivatives, including phenylhydrazones of 5-acylpyrimidinetrione exhibited potent growth inhibition at or below 10 μM with minimal mammalian cell toxicity. In addition, in vitro studies aimed at defining the mechanism of action of the most active analogs provide preliminary evidence that these compound decrease energy production and fungal cell respiration, making this class of analogs promising novel therapies, as they target pathways not targeted by currently available antifungals.     

Repurposing the FDA-approved anticancer agent ponatinib as a fluconazole potentiator by suppression of multidrug efflux and Pma1 expression in a broad spectrum of yeast species

Fungal infections have emerged as a major global threat to human health because of the increasing incidence and mortality rates every year. The emergence of drug resistance and limited arsenal of antifungal agents further aggravates the current situation resulting in a growing challenge in medical mycology. Here, we identified that ponatinib, an FDA-approved antitumour drug, significantly enhanced the activity of the azole fluconazole, the most widely used antifungal drug. Further detailed investigation of ponatinib revealed that its combination with fluconazole displayed broad-spectrum synergistic interactions against a variety of human fungal pathogens such as Candida albicans, Saccharomyces cerevisiae and Cryptococcus neoformans. Mechanistic insights into the mode of action unravelled that ponatinib reduced the efflux of fluconazole via Pdr5 and suppressed the expression of the proton pump, Pma1. Taken together, our study identifies ponatinib as a novel antifungal that enhances drug activity of fluconazole against diverse fungal pathogens.     

An Automated High-Throughput Cell-Based Multiplexed Flow Cytometry Assay to Identify Novel Compounds to Target Candida albicans Virulence-Related Proteins

Although three major classes of systemic antifungal agents are clinically available, each is characterized by important limitations. Thus, there has been considerable ongoing effort to develop novel and repurposed agents for the therapy of invasive fungal infections. In an effort to address these needs, we developed a novel high-throughput, multiplexed screening method that utilizes small molecules to probe candidate drug targets in the opportunistic fungal pathogen Candida albicans. This method is amenable to high-throughput automated screening and is based upon detection of changes in GFP levels of individually tagged target proteins. We first selected four GFP-tagged membrane-bound proteins associated with virulence or antifungal drug resistance in C. albicans. We demonstrated proof-of-principle that modulation of fluorescence intensity can be used to assay the expression of specific GFP-tagged target proteins to inhibitors (and inducers), and this change is measurable within the HyperCyt automated flow cytometry sampling system. Next, we generated a multiplex of differentially color-coded C. albicans strains bearing C-terminal GFP-tags of each gene encoding candidate drug targets incubated in the presence of small molecules from the Prestwick Chemical Library in 384-well microtiter plate format. Following incubation, cells were sampled through the HyperCyt system and modulation of protein levels, as indicated by changes in GFP-levels of each strain, was used to identify compounds of interest. The hit rate for both inducers and inhibitors identified in the primary screen did not exceed 1% of the total number of compounds in the small-molecule library that was probed, as would be expected from a robust target-specific, high-throughput screening campaign. Secondary assays for virulence characteristics based on null mutant strains were then used to further validate specificity. In all, this study presents a method for the identification and verification of new antifungal drugs targeted to fungal virulence proteins using C. albicans as a model fungal pathogen.     

Adaptation to iron deficiency in human pathogenic fungi

Iron is an essential micronutrient for virtually all eukaryotic organisms and plays a central role during microbial infections. Invasive fungal diseases are associated with strikingly high rates of mortality, but their impact on human health is usually underestimated. Upon a fungal infection, hosts restrict iron availability in order to limit the growth and virulence of the pathogen. Here, we use two model yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, to delve into the response to iron deficiency of human fungal pathogens, such as Candida glabrata, Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. Fungi possess common and species-specific mechanisms to acquire iron and to control the response to iron limitation. Upon iron scarcity, fungi activate a wide range of elegant strategies to capture and import exogenous iron, mobilize iron from intracellular stores, and modulate their metabolism to economize and prioritize iron utilization. Hence, iron homeostasis genes represent remarkable virulence factors that can be used as targets for the development of novel antifungal treatments.     

Aspectos actuales de las enfermedades invasoras causadas por Candida y otros hongos levaduriformes

Invasive candidiasis is the most common invasive fungal disease causing an unacceptably high mortality. Candida albicans remains the predominant origin, but an epidemiological shift has been described in the last decades. Some species of Candida have emerged as an important cause of severe candidaemia and can exhibit reduced susceptibility to the current antifungal agents. Candida parapsilosis has been associated with candidaemia in neonates and young adults, whereas Candida glabrata, Candida tropicalis, and Candida krusei are most frequently isolated in blood cultures from older patients (> 65 years). Other yeasts are becoming important causes of invasive mycoses, such as Cryptococcus, Trichosporon, Malassezia, Geotrichum or Saprochaete/Magnusiomyces. Cryptococcosis is more relevant as a cause of meningitis in HIV-infected people, but cryptococcal infections are also a clinical challenge in transplant recipients. Diagnosis remains an important problem, causing unacceptable delays in starting a correct and direct treatment. However, there are some new approaches that can help in the prompt and specific diagnosis of invasive yeast infections, such as in situ hybridisation using PNA-FISH probes, causal agent identification in blood cultures using MALDi-TOF MS, or new and rapid nucleic acids detection assays.     

Requirement for Ergosterol in V-ATPase Function Underlies Antifungal Activity of Azole Drugs

Ergosterol is an important constituent of fungal membranes. Azoles inhibit ergosterol biosynthesis, although the cellular basis for their antifungal activity is not understood. We used multiple approaches to demonstrate a critical requirement for ergosterol in vacuolar H⁺-ATPase function, which is known to be essential for fungal virulence. Ergosterol biosynthesis mutants of S. cerevisiae failed to acidify the vacuole and exhibited multiple vma ⁻ phenotypes. Extraction of ergosterol from vacuolar membranes also inactivated V-ATPase without disrupting membrane association of its subdomains. In both S. cerevisiae and the fungal pathogen C. albicans, fluconazole impaired vacuolar acidification, whereas concomitant ergosterol feeding restored V-ATPase function and cell growth. Furthermore, fluconazole exacerbated cytosolic Ca²⁺ and H⁺ surges triggered by the antimicrobial agent amiodarone, and impaired Ca²⁺ sequestration in purified vacuolar vesicles. These findings provide a mechanistic basis for the synergy between azoles and amiodarone observed in vitro. Moreover, we show the clinical potential of this synergy in treatment of systemic fungal infections using a murine model of Candidiasis. In summary, we demonstrate a new regulatory component in fungal V-ATPase function, a novel role for ergosterol in vacuolar ion homeostasis, a plausible cellular mechanism for azole toxicity in fungi, and preliminary in vivo evidence for synergism between two antifungal agents. New insights into the cellular basis of azole toxicity in fungi may broaden therapeutic regimens for patient populations afflicted with systemic fungal infections.     

Novel hybrids of fluconazole and furanones: design, synthesis and antifungal activity

During our efforts to develop new antifungal agents, a number of hybrid molecules containing furanones and fluconazole pharmacophores were designed and synthesized. The new chemical entities thus synthesized were tested for their potential as antifungal agents against various fungal strains and it was observed that the compounds with general structure 7 were potent inhibitors of Candida albicans ATCC 24433, Candida glabrata ATCC 90030, Candida tropicalis ATCC 750 and Candida neoformans ATCC 34664 while the fluconazole analogues 12 exhibited antifungal activity against Candida albicans ATCC 24433 and Candida glabrata ATCC 90030. The structure-activity relationship for these compounds is discussed. The synthetic strategies used in the present work have potential to prepare a large number of compounds for further refinement of structures to obtain molecules suitable for development as antifungal drugs.     

1,2,3-Triazole Derivatives as an Emerging Scaffold for Antifungal Drug Development against Candida albicans: A Comprehensive Review

Candida infections are most prominent among fungal infections majorly target immunocompromised and hospitalized patients and cause significant morbidity and mortality. Candida albicans is the notorious and most prevalent among all pathogenic Candida strains. Its emerging resistance toward available antifungal agents making it hard to tackle and emerging as global healthcare emergency. Simultaneously, 1,2,3-triazole nucleus is a privileged scaffold that is gaining importance in antifungal drug development due to being a prominent bioactive linker and isostere of triazole based antifungal class core 1,2,4-triazole. Numerous reports have been updated in scientific literature in last few decades related to utilization of 1,2,3-triazole nucleus in antifungal drug development against Candida albicans. Present review will shed light on various preclinical studies focused on development of 1,2,3-triazole derivatives targeting Candida albicans along with brief highlight on clinical trials and newly approved drugs. Structure-activity relationship has been precisely discussed for each architect along with future perspective that will help medicinal chemists in design and development of potent antifungal agents for tackling infections derived from Candida albicans.