Repurposing the thrombopoietin receptor agonist eltrombopag as an anticryptococcal agent

Immunity to fungi and vaccine considerations

Fungal disease poses a growing threat to public health that our current antifungal therapies are not well equipped to meet. As the population of immunocompromised hosts expands, and ecological changes favor the emergence of fungal pathogens, the development of new antifungal agents, including vaccines, becomes a global priority. Here, we summarize recent advancements in the understanding of fungal pathogenesis, key features of the host antifungal immune response, and how these findings could be leveraged to design novel approaches to deadly fungal disease.

Reductive metabolism of azo dyes and drugs: Toxicological implications

Azo compounds are widely distributed synthetic chemicals in the modern world. Their most important applications are as dyes, but, in addition, several azo compounds are used as pharmaceuticals. Ingested azo compounds can be reduced by the action of bacteria in the gut, where the oxygen tension is low, and the development of microbiome science has allowed more precise delineation of the roles of specific bacteria in these processes. Reduction of the azo bond of an azo compound generates two distinct classes of aromatic amine metabolites: the starting material that was used in the synthesis of the azo compound and a product which is formed de novo by metabolism. Reductive metabolism of azo compounds can have toxic consequences, because many aromatic amines are toxic/genotoxic. In this review, we discuss aspects of the development and application of azo compounds in industry and medicine. Current understanding of the toxicology of azo compounds and their metabolites is illustrated with four specific examples - Disperse Dyes used for dyeing textiles; the drugs phenazopyridine and eltrombopag; and the ubiquitous food dye, tartrazine - and knowledge gaps are identified. SUBMISSION TO: FCT VSI: Toxicology of Dyes.

Combating increased antifungal drug resistance in Cryptococcus, what should we do in the future?

Few therapeutic drugs and increased drug resistance have aggravated the current treatment difficulties of Cryptococcus in recent years. To better understand the antifungal drug resistance mechanism and treatment strategy of cryptococcosis. In this review, by combining the fundamental features of Cryptococcus reproduction leading to changes in its genome, we review recent research into the mechanism of four current anti-cryptococcal agents, coupled with new therapeutic strategies and the application of advanced technologies WGS and CRISPR-Cas9 in this field, hoping to provide a broad idea for the future clinical therapy of cryptococcosis.

Off-label treatments as potential accelerators in the search for the ideal antifungal treatment of cryptococcosis

Cryptococcosis is an opportunistic mycosis that mainly affects immunosuppressed patients. The treatment is a combination of three antifungal agents: amphotericin B, 5-flucytosine and fluconazole. However, these drugs have many disadvantages, such as high nephrotoxicity, marketing bans in some countries and fungal resistance. One of the solutions to find possible new drugs is pharmacological repositioning. This work presents repositioned drugs as an alternative for new antifungal therapies for cryptococcosis. All the studies here were performed in vitro or in animal models, except for sertraline, which reached phase III in humans. There is still no pharmacological repositioning approval for cryptococcosis in humans, though this review shows the potential of repurposing as a rapid approach to finding new agents to treat cryptococcosis.

Novel avenues for identification of new antifungal drugs and current challenges

INTRODUCTION

: Some of otherwise useful fungi are pathogenic to humans, and unfortunately, the number of these pathogens is increasing. In addition to common skin infections, these opportunistic pathogens are able to cause severe, often incurable, systemic mycoses.

AREAS COVERED

: The number of antifungal drugs is limited, especially drugs that can be used for systemic administration, and resistance to these drugs is very common. This review summarizes various approaches to the discovery and development of new antifungal drugs, provides an overview of the most important molecules in terms of basic (laboratory) research and compounds currently in clinical trials, and focuses on drug repurposing strategy, while providing an overview of drugs of other indications that have been tested in vitro for their antifungal activity for possible expansion of antifungal drugs and/or support of existing antimycotics.

EXPERT OPINION

: Despite the limitations of the research of new antifungal drugs by pharmaceutical manufacturers, in addition to innovated molecules based on clinically used drugs, several completely new small entities with unique mechanisms of actions have been identified. The identification of new molecular targets that offer alternatives for the development of new unique selective antifungal highly effective agents has been an important outcome of repurposing of non-antifungal drugs to antifungal drug. Also, given the advances in monoclonal antibodies and their application to immunosuppressed patients, it may seem possible to predict a more optimistic future for antifungal therapy than has been the case in recent decades.

Emerging Antifungal Targets and Strategies

Despite abundant research in the field of antifungal drug discovery, fungal infections remain a significant healthcare burden. There is an emerging need for the development of novel antifungals since those currently available are limited and do not completely provide safe and secure protection. Since the current knowledge regarding the physiology of fungal cells and the infection mechanisms is greater than ever, we have the opportunity to use this for the development of novel generations of antifungals. In this review, we selected and summarized recent studies describing agents employing different antifungal mechanisms. These mechanisms include interference with fungal resistance, including impact on the efflux pumps and heat shock protein 90. Additionally, interference with virulence factors, such as biofilms and hyphae; the impact on fungal enzymes, metabolism, mitochondria, and cell wall; and antifungal vaccines are explored. The agents investigated belong to different classes of natural or synthetic molecules with significant attention given also to plant extracts. The efficacy of these antifungals has been studied mainly in vitro with some in vivo, and clinical studies are needed. Nevertheless, there is a large quantity of products employing novel antifungal mechanisms that can be further explored for the development of new generation of antifungals.

Repurposing Eltrombopag as an Antimicrobial Agent Against Methicillin-Resistant Staphylococcus aureus

Because of the excessive use of antibiotics, methicillin-resistant Staphylococcus aureus (MRSA) has become prevalent worldwide. Moreover, the formation of S. aureus biofilms often cause persistence and relapse of infections. Thus, the discovery of antibiotics with excellent antimicrobial and anti-biofilm activities is urgently needed. In the present study, eltrombopag (EP), a classic thrombopoietin receptor agonist, exhibited potential antimicrobial activity against S. aureus and its biofilms. Through our mechanistic studies, EP was found to interfere with proton motive force in S. aureus. The in vivo anti-infective efficacy of EP was further confirmed in the wound infection model, thigh infection model and peritonitis model by MRSA infection. In addition, the cytotoxicity of EP against mammalian cells and the in vivo toxicity of EP in animal models were not observed at the tested concentrations. Collectively, these results indicate that EP could be considered a potential novel antimicrobial agent against recalcitrant infections caused by MRSA.

A Unique Dual-Readout High-Throughput Screening Assay To Identify Antifungal Compounds with Aspergillus fumigatus

Treatment of invasive mold infections is limited by the lack of adequate drug options that are effective against these fatal infections. High-throughput screening of molds using traditional antifungal assays of growth is problematic and has greatly limited our ability to identify new mold-active agents. Here, we present a high-throughput screening platform for use with Aspergillus fumigatus, the most common causative agent of invasive mold infections, for the discovery of novel mold-active antifungals. This assay detects cell lysis through the release of the cytosolic enzyme adenylate kinase and, thus, is not dependent on changes in biomass or metabolism to detect antifungal activity. The ability to specifically detect cell lysis is a unique aspect of this assay that allows identification of molecules that disrupt fungal cell integrity, such as cell wall-active molecules. We also found that germinating A. fumigatus conidia release low levels of adenylate kinase and that a reduction in this background allowed us to identify molecules that inhibit conidial germination, expanding the potential for discovery of novel antifungal compounds. Here, we describe the validation of this assay and proof-of-concept pilot screens that identified a novel antifungal compound, PIK-75, that disrupts cell wall integrity. This screening assay provides a novel platform for high-throughput screens with A. fumigatus for the identification of anti-mold drugs.

IMPORTANCE Fungal infections caused by molds have the highest mortality rates of human fungal infections. These devastating infections are hard to treat and available antifungal drugs are often not effective. Therefore, the identification of new antifungal drugs with mold activity is critical. Drug screening with molds is challenging and there are limited assays available to identify new antifungal compounds directly with these organisms. Here, we present an assay suitable for use for high-throughput screening with a common mold pathogen. This assay has exciting future potential for the identification of new drugs to treat these fatal infections.

Antifungal Drug Repurposing

Control of fungal pathogens is increasingly problematic due to the limited number of effective drugs available for antifungal therapy. Conventional antifungal drugs could also trigger human cytotoxicity associated with the kidneys and liver, including the generation of reactive oxygen species. Moreover, increased incidences of fungal resistance to the classes of azoles, such as fluconazole, itraconazole, voriconazole, or posaconazole, or echinocandins, including caspofungin, anidulafungin, or micafungin, have been documented. Of note, certain azole fungicides such as propiconazole or tebuconazole that are applied to agricultural fields have the same mechanism of antifungal action as clinical azole drugs. Such long-term application of azole fungicides to crop fields provides environmental selection pressure for the emergence of pan-azole-resistant fungal strains such as Aspergillus fumigatus having TR34/L98H mutations, specifically, a 34 bp insertion into the cytochrome P450 51A (CYP51A) gene promoter region and a leucine-to-histidine substitution at codon 98 of CYP51A. Altogether, the emerging resistance of pathogens to currently available antifungal drugs and insufficiency in the discovery of new therapeutics engender the urgent need for the development of new antifungals and/or alternative therapies for effective control of fungal pathogens. We discuss the current needs for the discovery of new clinical antifungal drugs and the recent drug repurposing endeavors as alternative methods for fungal pathogen control.