In Vitro and In Vivo Antifungal Profile of a Novel and Long-Acting Inhaled Azole, PC945, on Aspergillus fumigatus Infection

Novel antifungals and treatment approaches to tackle resistance and improve outcomes of invasive fungal disease

SUMMARYFungal infections are on the rise, driven by a growing population at risk and climate change. Currently available antifungals include only five classes, and their utility and efficacy in antifungal treatment are limited by one or more of innate or acquired resistance in some fungi, poor penetration into "sequestered" sites, and agent-specific side effect which require frequent patient reassessment and monitoring. Agents with novel mechanisms, favorable pharmacokinetic (PK) profiles including good oral bioavailability, and fungicidal mechanism(s) are urgently needed. Here, we provide a comprehensive review of novel antifungal agents, with both improved known mechanisms of actions and new antifungal classes, currently in clinical development for treating invasive yeast, mold (filamentous fungi), Pneumocystis jirovecii infections, and dimorphic fungi (endemic mycoses). We further focus on inhaled antifungals and the role of immunotherapy in tackling fungal infections, and the specific PK/pharmacodynamic profiles, tissue distributions as well as drug-drug interactions of novel antifungals. Finally, we review antifungal resistance mechanisms, the role of use of antifungal pesticides in agriculture as drivers of drug resistance, and detail detection methods for antifungal resistance.

Pipeline of Novel Antifungals for Invasive Fungal Disease in Transplant Recipients: A Pediatric Perspective

Invasive fungal disease (IFD) remains a significant cause of morbidity and mortality in children undergoing transplantation. There is a growing armamentarium of novel antifungal agents recently approved for use or in late stages of clinical development. The overarching goal of this review is to discuss the mechanisms of action, spectrum of activity, stage of development, and pediatric-specific data for the following agents: encochleated amphotericin B deoxycholate, fosmanogepix, ibrexafungerp, isavuconazole, olorofim, opelconazole, oteseconazole, and rezafungin. Additionally, key drug attributes of these novel agents and their potential future therapeutic roles in pediatric transplant recipients are discussed.

Antifungal Therapies for Aspergillus spp.: Present and Future

Currently available and recommended options for the treatment of pulmonary aspergillosis include the triazoles, echinocandins, and amphotericin B products. These therapies have significant limitations. Only the azoles are available orally, but their use is often limited by toxicities, drug-drug interactions, pharmacokinetic variability, and emerging resistance. While the echinocandins are safe agents and may have a role in combination therapy, they are unproven as monotherapy. Amphotericin B preparations are toxic and require intensive monitoring. Finally, aspergillosis continues to be a disease conferring substantial morbidity and mortality, and clinical trials have not identified a therapeutic approach clearly associated with improved outcomes. As a result, there is a great need for new options in the treatment of invasive aspergillosis. Ideally, such options would be safe, have high oral bioavailability, have favorable pharmacokinetics to sequestered sites and retain activity against azole-resistant isolates. Reassuringly, there is a robust pipeline of novel therapies in development. Rezafungin (a once-weekly dosed echinocandin) and ibrexafungerp (oral agent with same mechanism of action as echinocandins) will likely be reserved for combination therapy or refractory/intolerance scenarios with no other options. Inhaled opelconazole is an attractive option for combination therapy and prophylaxis of pulmonary aspergillosis. Development of an oral form of amphotericin B that avoids nephrotoxicity and electrolyte disturbances is an exciting development. Finally, olorofim and fosmanogepix, two agents with novel mechanisms of action and oral formulations, hold significant potential to challenge the triazole antifungals place as preferred therapies. However, many questions remain regarding these novel agents, and at the time of this writing, none of these agents have been robustly studied in Phase III studies of aspergillosis, and so their promise remains investigational.

Accelerating the understanding of Aspergillus terreus: Epidemiology, physiology, immunology and advances

Aspergillus species encompass a variety of infections, ranging from invasive aspergillosis to allergic conditions, contingent upon the immune status of the host. In this spectrum, Aspergillus terreus stands out due to its emergence as a notable pathogen and its intrinsic resistance to amphotericin-B. The significance of Aspergillus-associated infections has witnessed a marked increase in the past few decades, particularly with the increasing number of immunocompromised individuals. The exploration of epidemiology, morphological transitions, immunopathology, and novel treatment approaches such as new antifungal drugs (PC945, olorofim) and combinational therapy using antifungal drugs and phytochemicals (Phytochemicals: quercetin, shikonin, artemisinin), also using immunotherapies to modulate immune response has resulted in better outcomes. Furthermore, in the context COVID-19 era and its aftermath, fungal infections have emerged as a substantial challenge for both immunocompromised and immunocompetent individuals. This is attributed to the use of immune-suppressing therapies during COVID-19 infections and the increase in transplant cases. Consequently, this review aims to provide an updated overview encompassing the epidemiology, germination events, immunopathology, and novel drug treatment strategies against Aspergillus terreus-associated infections.

Senkyunolide B exhibits broad-spectrum antifungal activity against plant and human pathogenic fungi via inhibiting spore germination and destroying the mature biofilm

BACKGROUND

Aspergillus infection seriously jeopardizes the health and safety of life of immunocompromised patients. The emergences of antifungal resistance highlight a demand to find new effective antifungal drugs. Angelica sinensis is a medicine-food herb and phthalides are its characteristic components. A few of the phthalides have been reported to display satisfactory antifungal activities against plant pathogenic fungi. However, the structure-activity relationships and antifungal action mechanism of phthalides remain to be further explored and elucidated.

RESULTS

The antifungal activities of five natural phthalides and four artificial analogs were investigated, and their structure-activity relationships were preliminarily elucidated in the current study. The benzene ring moiety played an essential role in their antifungal activities; the oxygen-containing substituents on the benzene ring obviously impacted their activities, the free hydroxyl was favorable to the activity. Typical phthalide senkyunolide B (SENB) exhibited broad antifungal activities against human and plant pathogenic fungi, especially, Aspergillus fumigatus. SENB affected the spore germination and hyphae growth of Aspergillus fumigatus via down-regulating phosphatidylinositol-PKC-calcineurin axis and the expression of ENG genes. Moreover, SENB disturbed the oxidation-reduction process in Aspergillus fumigatus to destroy the mature biofilms. In vivo experiments indicated SENB significantly prolonged survival and decreased fungal burden in mouse model of invasive pulmonary aspergillosis.

CONCLUSIONS

Phthalides could be considered as the valuable leads for the development of antifungal drug to cure plant and human disease. © 2023 Society of Chemical Industry.

Invasive pulmonary aspergillosis in the intensive care unit: current challenges and best practices

The prevalence of invasive pulmonary aspergillosis (IPA) is growing in critically ill patients in the intensive care unit (ICU). It is increasingly recognized in immunocompetent hosts and immunocompromised ones. IPA frequently complicates both severe influenza and severe coronavirus disease 2019 (COVID-19) infection. It continues to represent both a diagnostic and therapeutic challenge and can be associated with significant morbidity and mortality. In this narrative review, we describe the epidemiology, risk factors and disease manifestations of IPA. We discuss the latest evidence and current published guidelines for the diagnosis and management of IPA in the context of the critically ill within the ICU. Finally, we review influenza-associated pulmonary aspergillosis (IAPA), COVID-19-associated pulmonary aspergillosis (CAPA) as well as ongoing and future areas of research.

An update on the global treatment of invasive fungal infections

Fungal infections are a serious problem affecting many people worldwide, creating critical economic and medical consequences. Fungi are ubiquitous and can cause invasive diseases in individuals mostly living in developing countries or with weakened immune systems, and antifungal drugs currently available have important limitations in tolerability and efficacy. In an effort to counteract the high morbidity and mortality rates associated with invasive fungal infections, various approaches are being utilized to discover and develop new antifungal agents. This review discusses the challenges posed by fungal infections, outlines different methods for developing antifungal drugs and reports on the status of drugs currently in clinical trials, which offer hope for combating this serious global problem.

Emerging Diagnostics and Therapeutics for Invasive Fungal Infections

Recently, there have been significant advances in the diagnosis and management of invasive fungal infections. Compared with traditional fungal diagnostics, molecular assays promise improved sensitivity and specificity, the ability to test a range of samples (including noninvasive samples, ie, blood), the detection of genetic mutations associated with antifungal resistance, and the potential for a faster turnaround time. Antifungals in late-stage clinical development include agents with novel mechanisms of action (olorofim and fosmanogepix) and new members of existing classes with distinct advantages over existing antifungals in toxicity, drug-drug interactions, and dosing convenience (oteseconazole, opelconazole, rezafungin, ibrexafungerp, encochleated amphotericin B).

A review of prophylactic regimens to prevent invasive fungal infections in hematology patients undergoing chemotherapy or stem cell transplantation

INTRODUCTION

The recent introduction of targeted therapies, including monoclonal antibodies, tyrosine-kinase inhibitors, and immunotherapies has improved the cure rate of hematologic patients. The implication of personalized treatment on primary antifungal prophylaxis will be discussed.

AREAS COVERED

We reviewed the literature for clinical trials reporting the rate of invasive fungal infections during targeted and cellular therapies and stem cell transplant, and the most recent international guidelines for primary antifungal prophylaxis.

EXPERT OPINION

As the use of personalized therapies is growing, the risk of invasive fungal infection has emerged in various clinical settings. Therefore, it is possible that the use of mold-active antifungal prophylaxis would spread in the next years and the risk of breakthrough infections would increase. The introduction of new antifungal agents in the clinical armamentarium is expected to reduce clinical unmet needs concerning the management of primary antifungal prophylaxis and improve outcome of patients.

Epidemiology, Modern Diagnostics, and the Management of Mucorales Infections

Mucormycosis is an uncommon, yet deadly invasive fungal infection caused by the Mucorales moulds. These pathogens are a WHO-assigned high-priority pathogen group, as mucormycosis incidence is increasing, and there is unacceptably high mortality with current antifungal therapies. Current diagnostic methods have inadequate sensitivity and specificity and may have issues with accessibility or turnaround time. Patients with diabetes mellitus and immune compromise are predisposed to infection with these environmental fungi, but COVID-19 has established itself as a new risk factor. Mucorales also cause healthcare-associated outbreaks, and clusters associated with natural disasters have also been identified. Robust epidemiological surveillance into burden of disease, at-risk populations, and emerging pathogens is required. Emerging serological and molecular techniques may offer a faster route to diagnosis, while newly developed antifungal agents show promise in preliminary studies. Equitable access to these emerging diagnostic techniques and antifungal therapies will be key in identifying and treating mucormycosis, as delayed initiation of therapy is associated with higher mortality.

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 chemotherapies and immunotherapies for the future

Human fungal pathogens cause a broad plethora of infections, spanning cutaneous dermatophytoses to invasive infections in immunocompromised hosts. As eukaryotic pathogens are capable of morphotype switching, they present unique challenges both for drug development and the immunological response. Whilst current antifungal therapies are limited to the orally available triazoles, intravenous echonocandins and polyenes, and flucytosine and terbinafine, there has been recent significant progress in the antifungal armamentorium with ibrexafungerp, a novel orally available terpanoid that inhibits 1,3-beta-D-glucan-approved by Food and Drug Administration in 2021, and fosmanogepix, an orally available pro-drug of manogepix, which targets glycosylphosphatidylinositol-anchored protein maturation entering Phase 3 studies for candidaemia. A number of further candidates are in development. There has been significant use of existing immunotherapies such as recombinant interferon-γ and G-CSF for fungal disease in immunocompromised patients, and there are emerging opportunities for monoclonal antibodies targeting TH2 inflammation. Omalizumab, an anti-IgE monoclonal antibody in asthma, is now used routinely for the treatment of allergic bronchopulmonary aspergillosis, and further agents targeting IL-4 and IL-5 are being evaluated. In addition, T-cell CAR therapy is showing early promise for fungal disease. Thus, we are likely to see rapid advances to our approach to the management of fungal disease in the near future.

New Antifungal Agents with Azole Moieties

Fungal conditions affect a multitude of people worldwide, leading to increased hospitalization and mortality rates, and the need for novel antifungals is emerging with the rise of resistance and immunocompromised patients. Continuous use of azole drugs, which act by inhibiting the fungal CYP51, involved in the synthesis of ergosterol, essential to the fungal cell membrane, has enhanced the resistance and tolerance of some fungal strains to treatment, thereby limiting the arsenal of available drugs. The goal of this review is to gather literature information on new promising azole developments in clinical trials, with in vitro and in vivo results against fungal strains, and complementary assays, such as toxicity, susceptibility assays, docking studies, among others. Several molecules are reviewed as novel azole structures in clinical trials and with recent/imminent approvals, as well as other innovative molecules with promising antifungal activity. Structure-activity relationship (SAR) studies are displayed whenever possible. The azole moiety is brought over as a privileged structure, with multiple different compounds emerging with distinct pharmacophores and SAR. Particularly, 1,2,3-triazole natural product conjugates emerged in the last years, presenting promising antifungal activity and a broad spectrum against various fungi.

Invasive Aspergillosis in the Intensive Care Unit

Invasive pulmonary aspergillosis (IPA) is a serious condition resulting in significant mortality and morbidity among patients in intensive care units (ICUs). There is a growing number of at-risk patients for this condition with the increasing use of immunosuppressive therapies. The diagnosis of IPA can be difficult in ICUs, and relies on integration of clinical, radiological, and microbiological features. In this review, we discuss patient populations at risk for IPA, as well as the diagnostic criteria employed. We review the fungal biomarkers used, as well as the challenges in distinguishing colonization with Aspergillus from invasive disease. We also address the growing concern of multidrug-resistant Aspergillosis and review the new and novel therapeutics which are in development to combat this.

Progress and challenges in fungal lung disease in cystic fibrosis

PURPOSE OF REVIEW

This review is an overview of the recent progress made for the diagnosis and understanding of fungal lung disease in people with cystic fibrosis (CF), with a focus on Aspergillus fumigatus , the most common filamentous fungus in the CF airway. Currently, the longstanding question of the clinical significance of Aspergillus fumigatus and other fungi in CF respiratory cultures, in the absence of allergy, remains. Clinical criteria and biomarkers are needed to classify fungal lung disease and determine who may warrant therapy.

RECENT FINDINGS

Several retrospective and prospective studies have described the prevalence of A. fumigatus and other fungi in the CF lung and factors contributing to the changes in fungal epidemiology. Selective fungus culture testing for the detection of fungi in CF sputa has been well studied, yet a standardized fungus culture protocol has yet to be defined. Culture-independent molecular studies and other fungal diagnostic testing have been conducted in the CF population, leading to efforts to better understand the clinical role of these tests. Recent works have aimed to determine whether chronic A. fumigatus colonization is associated with lung disease progression measured by FEV 1 percentage predicted, structural lung disease, lung clearance index and respiratory quality-of-life. However, the existing knowledge gaps remain: definition of a fungal respiratory infection, the association between fungal infection and clinical outcomes, and indications for antifungal therapy.

SUMMARY

Significant progress has been made for the detection and diagnosis of fungal lung disease. Yet, the role and impact of A. fumigatus and other fungal infections on respiratory health in people with CF remains to be determined.

Investigational Antifungal Agents for Invasive Mycoses: A Clinical Perspective

Treatment of invasive fungal infections (IFIs) remains challenging, because of the limitations of the current antifungal agents (ie, mode of administration, toxicity, and drug-drug interactions) and the emergence of resistant fungal pathogens. Therefore, there is an urgent need to expand our antifungal armamentarium. Several compounds are reaching the stage of phase II or III clinical assessment. These include new drugs within the existing antifungal classes or displaying similar mechanism of activity with improved pharmacologic properties (rezafungin and ibrexafungerp) or first-in-class drugs with novel mechanisms of action (olorofim and fosmanogepix). Although critical information regarding the performance of these agents in heavily immunosuppressed patients is pending, they may provide useful additions to current therapies in some clinical scenarios, including IFIs caused by azole-resistant Aspergillus or multiresistant fungal pathogens (eg, Candida auris, Lomentospora prolificans). However, their limited activity against Mucorales and some other opportunistic molds (eg, some Fusarium spp.) persists as a major unmet need.

Pharmacodynamics, Mechanisms of Action and Resistance, and Spectrum of Activity of New Antifungal Agents

Several new antifungals are currently in late-stage development, including those with novel pharmacodynamics/mechanisms of action that represent new antifungal classes (manogepix, olorofim, ATI-2307, GR-2397). Others include new agents within established classes or with mechanisms of action similar to clinically available antifungals (ibrexafungerp, rezafungin, oteseconazole, opelconazole, MAT2203) that have been modified in order to improve certain characteristics, including enhanced pharmacokinetics and greater specificity for fungal targets. Many of the antifungals under development also have activity against Candida and Aspergillus strains that have reduced susceptibility or acquired resistance to azoles and echinocandins, whereas others demonstrate activity against species that are intrinsically resistant to most clinically available antifungals. The tolerability and drug–drug interaction profiles of these new agents also appear to be promising, although the number of human subjects that have been exposed to many of these agents remains relatively small. Overall, these agents have the potential for expanding our antifungal armamentarium and improving clinical outcomes in patients with invasive mycoses.

Novel agents in the treatment of invasive fungal infections in solid organ transplant recipients

PURPOSE OF REVIEW

Recipients of solid organ transplants (SOTs) suffer a significant burden of invasive fungal infections (IFIs). The emergence of drug-resistant fungi and toxicities of currently used antifungal agents as well as drug-drug interactions with immunosuppressants make their treatment challenging. This review discusses selected novel antifungal agents in the development pipeline that can currently be used through clinical trials or may be commercially available in the near future.

RECENT FINDINGS

These agents in development have novel pharmacokinetics and pharmacodynamics, expanded spectra of activity and excellent safety profiles.

SUMMARY

The properties of novel antifungal agents have the potential to expand the therapeutic options for IFIs in recipients of SOTs.

Inhaled antifungal therapy: benefits, challenges, and clinical applications

INTRODUCTION

Disease due to pulmonary infection with Aspergillus, and other emerging opportunistic fungi remains a significant unmet need. Existing antifungal medicines are predominantly dosed either orally or systemically, but because of limited exposure to the lung lumen, adverse events, and problematic drug-drug interactions, inhaled treatment could provide an attractive option.

AREA COVERED

This review summarizes 1) the limitations of current antifungal therapy, 2) the beneficial effects of inhaled antifungal agents, 3) the clinical development of inhaled antifungal triazoles (repurposed with an innovative inhalation system or a novel inhaled agent) for the treatment of pulmonary fungal infections, and 4) the difficulties and challenges of inhaled antifungal agent development. Regrettably, details of novel inhaled devices or formulations were not covered.

EXPERT OPINION

Inhaled antifungal treatment could provide an attractive option by shifting the risk benefit ratio of treatment favorably. Preclinical and clinical studies with inhaled antifungal agents (off-label use) are encouraging so far. New inhaled antifungal triazoles are well tolerated in early clinical studies and warrant further clinical development. However, challenges remain and many unaddressed issues including required preclinical studies, appropriate clinical design, pharmacokinetics, delivery system(s) and regulatory process need to be resolved. Early communication with regulatory authorities is therefore recommended.

Novel antifungal agents in clinical trials

Invasive fungal diseases due to resistant yeasts and molds are an important and increasing public health threat, likely due to a growing population of immunosuppressed hosts, increases in antifungal resistance, and improvements in laboratory diagnostics.  The significant morbidity and mortality associated with these pathogens bespeaks the urgent need for novel safe and effective therapeutics.  This review highlights promising investigational antifungal agents in clinical phases of development: fosmanogepix, ibrexafungerp, rezafungin, encochleated amphotericin B, oteseconazole (VT-1161), VT-1598, PC945, and olorofim.  We discuss three first-in-class members of three novel antifungal classes, as well as new agents within existing antifungal classes with improved safety and tolerability profiles due to enhanced pharmacokinetic and pharmacodynamic properties.

Inhaled Antifungal Agents for Treatment and Prophylaxis of Bronchopulmonary Invasive Mold Infections

Pulmonary mold infections are life-threatening diseases with high morbi-mortalities. Treatment is based on systemic antifungal agents belonging to the families of polyenes (amphotericin B) and triazoles. Despite this treatment, mortality remains high and the doses of systemic antifungals cannot be increased as they often lead to toxicity. The pulmonary aerosolization of antifungal agents can theoretically increase their concentration at the infectious site, which could improve their efficacy while limiting their systemic exposure and toxicity. However, clinical experience is poor and thus inhaled agent utilization remains unclear in term of indications, drugs, and devices. This comprehensive literature review aims to describe the pharmacokinetic behavior and the efficacy of inhaled antifungal drugs as prophylaxes and curative treatments both in animal models and humans.

Future Directions for Clinical Respiratory Fungal Research

There has been a growing appreciation of the importance of respiratory fungal diseases in recent years, with better understanding of their prevalence as well as their global distribution. In step with the greater awareness of these complex infections, we are currently poised to make major advances in the characterization and treatment of these fungal diseases, which in itself is largely a consequence of post-genomic technologies which have enabled rational drug development and a path towards personalized medicines. These advances are set against a backdrop of globalization and anthropogenic change, which have impacted the world-wide distribution of fungi and antifungal resistance, as well as our built environment. The current revolution in immunomodulatory therapies has led to a rapidly evolving population at-risk for respiratory fungal disease. Whilst challenges are considerable, perhaps the tools we now have to manage these infections are up to this challenge. There has been a welcome acceleration of the antifungal pipeline in recent years, with a number of new drug classes in clinical or pre-clinical development, as well as new focus on inhaled antifungal drug delivery. The "post-genomic" revolution has opened up metagenomic diagnostic approaches spanning host immunogenetics to the fungal mycobiome that have allowed better characterization of respiratory fungal disease endotypes. When these advances are considered together the key challenge is clear: to develop a personalized medicine framework to enable a rational therapeutic approach.

The Antifungal Pipeline: Fosmanogepix, Ibrexafungerp, Olorofim, Opelconazole, and Rezafungin

The epidemiology of invasive fungal infections is changing, with new populations at risk and the emergence of resistance caused by the selective pressure from increased usage of antifungal agents in prophylaxis, empiric therapy, and agriculture. Limited antifungal therapeutic options are further challenged by drug-drug interactions, toxicity, and constraints in administration routes. Despite the need for more antifungal drug options, no new classes of antifungal drugs have become available over the last 2 decades, and only one single new agent from a known antifungal class has been approved in the last decade. Nevertheless, there is hope on the horizon, with a number of new antifungal classes in late-stage clinical development. In this review, we describe the mechanisms of drug resistance employed by fungi and extensively discuss the most promising drugs in development, including fosmanogepix (a novel Gwt1 enzyme inhibitor), ibrexafungerp (a first-in-class triterpenoid), olorofim (a novel dihyroorotate dehydrogenase enzyme inhibitor), opelconazole (a novel triazole optimized for inhalation), and rezafungin (an echinocandin designed to be dosed once weekly). We focus on the mechanism of action and pharmacokinetics, as well as the spectrum of activity and stages of clinical development. We also highlight the potential future role of these drugs and unmet needs.

Advances in anti-fungal therapies

Anti-fungal therapies remain sub-optimal, and resistant pathogens are increasing. New therapies are desperately needed, especially options that are less toxic than most of the currently available selection. In this review, I will discuss anti-fungal therapies that are in at least phase I human trials. These include VT-1161 and VT-1598, modified azoles with a tetrazole metal-binding group; the echinocandin rezafugin; the novel β-1,3-d-glucan synthase inhibitor ibrexafungerp; fosmanogepix, a novel anti-fungal targeting Gwt1; the arylamidine T-2307; the dihydroorotate inhibitor olorofim; and the cyclic hexapeptide ASP2397. The available data including spectrum of activity, toxicity and stage of clinical development will be discussed for each of these so clinicians are aware of promising anti-fungal agents with a strong likelihood of clinical availability in the next 5–7 years.

Identification of Thiazoyl Guanidine Derivatives as Novel Antifungal Agents Inhibiting Ergosterol Biosynthesis for Treatment of Invasive Fungal Infections

Invasive fungal infections (IFIs) are fatal infections, but treatment options are limited. The clinical efficacies of existing drugs are unsatisfactory because of side effects, drug-drug interaction, unfavorable pharmacokinetic profiles, and emerging drug-resistant fungi. Therefore, the development of antifungal drugs with a new mechanism is an urgent issue. Herein, we report novel aryl guanidine antifungal agents, which inhibit a novel target enzyme in the ergosterol biosynthesis pathway. Structure-activity relationship development and property optimization by reducing lipophilicity led to the discovery of 6h, which showed potent antifungal activity against Aspergillus fumigatus in the presence of serum, improved metabolic stability, and PK properties. In the murine systemic A. fumigatus infection model, 6h exhibited antifungal efficacy equivalent to voriconazole (1e). Furthermore, owing to the inhibition of a novel target in the ergosterol biosynthesis pathway, 6h showed antifungal activity against azole-resistant A. fumigatus.

Novel antifungal agents in clinical trials

Invasive fungal diseases due to resistant yeasts and molds are an important and increasing public health threat, likely due to a growing population of immunosuppressed hosts, increases in antifungal resistance, and improvements in laboratory diagnostics.  The significant morbidity and mortality associated with these pathogens bespeaks the urgent need for novel safe and effective therapeutics.  This review highlights promising investigational antifungal agents in clinical phases of development: fosmanogepix, ibrexafungerp, rezafungin, encochleated amphotericin B, oteseconazole (VT-1161), VT-1598, PC945, and olorofim.  We discuss three first-in-class members of three novel antifungal classes, as well as new agents within existing antifungal classes with improved safety and tolerability profiles due to enhanced pharmacokinetic and pharmacodynamic properties.

Investigational Agents for the Treatment of Resistant Yeasts and Molds

Purpose of Review

This review summarizes the investigational antifungals in clinical development with the potential to address rising drug resistance patterns. The relevant pharmacodynamics, spectrum of activity, preclinical studies, and latest clinical trial data are described.

Recent Findings

Agricultural and medicinal antifungal use has been selected for inherently drug-resistant fungi and acquired resistance mechanisms. The rates of fungal infections and immunocompromised populations continue to grow as few new antifungals have hit the market. Several agents with the potential to address the emergence of multidrug-resistant (MDR) molds and yeasts are in clinical development.

Summary

Evolved formulations of echinocandins, polyenes, and triazoles offer less toxicity, convenient dosing, and greater potency, potentially expanding these classes’ indications. Ibrexafungerp, olorofim, oteseconazole, and fosmanogepix possess novel mechanisms of actions with potent activity against MDR fungi. Successful clinical development is neither easy nor guaranteed; thus, perpetual efforts to discover new antifungals are needed.

1,2,4-Triazole: A Privileged Scaffold for the Development of Potent Antifungal Agents - A Brief Review

Over the past decades, a tremendous rise in invasive fungal infection diseases attributed to the yeast Candida albicans in immunocompromised individuals poses a seriously challenging issue. Another concern is the emergence of multi-drug resistant pathogens to the existing medicines due to their overuse and misuse. It was recently reported that 25-55% of the mortality rate is caused by invasive infection. Despite a large variety of drugs being available to treat invasive candidiasis, only two of them contain a 1,2,4-triazole core, namely Fluconazole and itraconazole, which are efficient in treating infection induced by fungal Candida species. Moreover, long-term therapy associated with azole medications has led to an increase in azole resistance as well as a high risk of toxicity. Despite numerous outstanding achievements in antifungal drug discovery, development of novel, safer and potent antifungal agents while overcoming the resistance problem associated with the current drugs is becoming the main focus of medicinal chemists. Therefore, this review outlines the breakthroughs in medicinal chemistry research regarding 1,2,4- triazole-based derivatives as potential antifungal agents in the past decade. In addition, the structureactivity relationship of these compounds is also discussed.

Relationship between anti-fungal effects and lung exposure of PC945, a novel inhaled antifungal agent, in Aspergillus fumigatus infected mice: Pulmonary PK-PD analysis of anti-fungal PC945

PC945 is a novel antifungal agent, optimised for inhaled treatment. In this study, the relationship between antifungal effects of PC945 and its exposure in the lungs was investigated in Aspergillus fumigatus intranasally infected, temporarily neutropenic mice. Mice were given prophylactic PC945 intranasally once daily (0.56 µg/mouse) on either Day -7 to 0 (8 doses) or Day -1 to 0 (2 doses). Lung tissue, plasma and bronchoalveolar lavage (BAL) fluid were collected 24 or 72 h post A. fumigatus inoculation for biomarker and pharmacokinetic analyses. BAL cell pellets and supernatants were prepared separately by centrifugation. 8 prophylactic doses of PC945 were found to demonstrate significantly stronger antifungal effects (lung fungal burden and galactomannan (GM) in BAL and plasma) than prophylaxis with 2 doses. PC945 concentrations were below the limit of detection in plasma but readily measured in lung extracts. The concentrations were much higher after extended prophylaxis (709 and 312 ng/g of lung) than short prophylaxis (301 and 195 ng/g of lung) at 24 and 72 h post last dose, respectively, suggesting PC945 accumulation in whole lung after repeat dosing although it was likely to be a mixture of dissolved and undissolved PC945, meaning that the data should be interpreted with caution. Interestingly, low concentrations of PC945 were detected in BAL supernatant (6.6 and 1.9 ng/ml) whereas high levels of PC945 were measured in BAL cell pellets (626 and 406 ng/ml) at 24 and 72 h post last dose, respectively, in extended prophylaxis. In addition, the PC945 concentrations in BAL cells showed a statistically significant correlation with measured anti-fungal activities. These observations will be pursued, and it is intended that BAL cell concentrations of PC945 be measured in future clinical studies rather than standard measurement in BAL itself. Thus, PC945's profile makes it an attractive potential prophylactic agent for the prevention of pulmonary fungal infections.

Allergic Diseases Caused by Aspergillus Species in Patients with Cystic Fibrosis

Aspergillus spp. are spore forming molds; a subset of which are clinically relevant to humans and can cause significant morbidity and mortality. A. fumigatus causes chronic infection in patients with chronic lung disease such as asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF). In patients with CF, A. fumigatus infection can lead to allergic disease, such as allergic bronchopulmonary aspergillosis (ABPA) which is associated with high rates of hospitalizations for acute exacerbations and lower lung function. ABPA results from T_H2 immune response to Aspergillus antigens produced during hyphal growth, marked by high levels of IgE and eosinophil activation. Clinically, patients with ABPA experience difficulty breathing; exacerbations of disease and are at high risk for bronchiectasis and lung fibrosis. Oral corticosteroids are used to manage aspects of the inflammatory response and antifungal agents are used to reduce fungal burden and lower the exposure to fungal antigens. As the appreciation for the severity of fungal infections has grown, new therapies have emerged that aim to improve treatment and outcomes for patients with CF.

Safety and nonclinical and clinical pharmacokinetics of PC945, a novel inhaled triazole antifungal agent

PC945 is a novel antifungal triazole formulated for nebulized delivery to treat lung Aspergillus infections. Pharmacokinetic and safety profiles from nonclinical studies and clinical trials in healthy subjects, and subjects with mild asthma were characterized. Toxicokinetics were assessed following daily 2-hour inhalation for 14 days. Potential for drug-drug interactions was evaluated using pooled human liver microsomes. Clinical safety and pharmacokinetics were assessed following (a) single inhaled doses (0.5-10 mg), (b) 7-day repeat doses (5 mg daily) in healthy subjects; (c) a single dose (5 mg) in subjects with mild asthma. Cmax occurred 4 hours (rats) or immediately (dogs) after a single dose. PC945 lung concentrations were substantially higher (>2000-fold) than those in plasma. PC945 only inhibited CYP3A4/5 substrate metabolism (IC50 : 1.33 µM [testosterone] and 0.085 µM [midazolam]). Geometric mean Cmax was 322 pg/mL (healthy subjects) and 335 pg/mL (subjects with mild asthma) 4-5 hours (median tmax ) after a single inhalation (5 mg). Following repeat, once daily inhalation (5 mg), Day 7 Cmax was 951 pg/mL (0.0016 µM) 45 minutes after dosing. Increases in Cmax and AUC0-24h were approximately dose-proportional (0.5-10 mg). PC945 administration was well tolerated in both healthy subjects and subjects with mild asthma. Treatment-emergent adverse events were mild/moderate and resolved before the study ended. No clinically significant lung function changes were observed. PC945 pharmacokinetics translated from nonclinical species to humans showed slow absorption from lungs and low systemic exposure, thereby limiting the potential for adverse side effects and drug interactions commonly seen with systemically delivered azoles.

PC945, a Novel Inhaled Antifungal Agent, for the Treatment of Respiratory Fungal Infections

Disease due to pulmonary Aspergillus infection remains a significant unmet need, particularly in immunocompromised patients, patients in critical care and those with underlying chronic lung diseases. To date, treatment using inhaled antifungal agents has been limited to repurposing available systemic medicines. PC945 is a novel triazole antifungal agent, a potent inhibitor of CYP51, purpose-designed to be administered via inhalation for high local lung concentrations and limited systemic exposure. In preclinical testing, PC945 is potent versus Aspergillus spp. and Candida spp. and showed two remarkable properties in preclinical studies, in vitro and in vivo. The antifungal effects against Aspergillus fumigatus accumulate on repeat dosing and improved efficacy has been demonstrated when PC945 is dosed in combination with systemic anti-fungal agents of multiple classes. Resistance to PC945 has been induced in Aspergillus fumigatus in vitro, resulting in a strain which remained susceptible to other antifungal triazoles. In healthy volunteers and asthmatics, nebulised PC945 was well tolerated, with limited systemic exposure and an apparently long lung residency time. In two lung transplant patients, PC945 treated an invasive pulmonary Aspergillus infection that had been unresponsive to multiple antifungal agents (systemic ± inhaled) without systemic side effects or detected drug–drug interactions.

Fungal sensitization and positive fungal culture from sputum in children with asthma are associated with reduced lung function and acute asthma attacks respectively

BACKGROUND

Sensitization to thermotolerant fungi, including filamentous fungi and Candida albicans, is associated with poor lung function in adults with severe asthma. Data in children are lacking. Environmental exposure to fungi is linked with acute severe asthma attacks, but there are few studies reporting the presence of fungi in the airways during asthma attacks.

METHODS

We investigated the association between fungal sensitization and/or positive fungal sputum culture and markers of asthma severity in children with chronic and acute asthma. Sensitization was determined using serum-specific IgE and skin prick testing against a panel of five fungi. Fungal culture was focused towards detection of filamentous fungi from sputum samples.

RESULTS

We obtained sensitization data and/or sputum from 175 children: 99 with chronic asthma, 39 with acute asthma and 37 controls. 34.1% of children with chronic asthma were sensitized to thermotolerant fungi compared with no children without asthma (p =< 0.001). These children had worse pre-bronchodilator lung function compared with asthmatics without sensitization including a lower FEV₁ /FVC ratio (p < .05). The isolation rate of filamentous fungi from sputum was higher in children with acute compared with chronic asthma.

CONCLUSIONS

Fungal sensitization is a feature of children with chronic asthma. Children sensitized to thermotolerant fungi have worse lung function, require more courses of systemic corticosteroids and have greater limitation of activities due to asthma. Asthma attacks in children were associated with the presence of filamentous fungi positive sputum culture. Mechanistic studies are required to establish whether fungi contribute directly to the development of acute asthma.

The role of antifungals in the management of patients with severe asthma

In patients with asthma, the inhalation of elevated amounts of fungal spores and hyphae may precipitate the onset of asthma or worsen control to the extent of being life-threatening. Sensitisation to fungi, especially Aspergillus fumigatus, is found in 15% to 48% of asthmatics in secondary care and is linked to worse asthma control, hospitalisation, bronchiectasis and fixed airflow obstruction, irrespective of whether allergic bronchopulmonary aspergillosis (ABPA) is diagnosed. ABPA represents a florid response to the presence of Aspergillus spp. but up to 70% of patients with severe asthma exhibit sensitisation to different fungi without meeting the diagnostic criteria for ABPA. The presence of persistent endobronchial colonisation with fungi, especially A. fumigatus, is linked to significantly higher rates of radiological abnormalities, lower post-bronchodilator FEV1 and significantly less reversibility to short acting bronchodilators. The therapeutic benefit for antifungal intervention in severe asthma is based on the assumption that reductions in airway fungal burden may result in improvements in asthma control, lung function and symptoms (especially cough). This contention is supported by several prospective studies which demonstrate the effectiveness of antifungals for the treatment of ABPA. Significantly, these studies confirm lower toxicity of treatment with azoles versus high dose oral corticosteroid dosing regimens for ABPA. Here we review recent evidence for the role of fungi in the progression of severe asthma and provide recommendations for the use of antifungal agents in patients with severe asthma, airways fungal infection (mycosis) and fungal colonisation. Documenting fungal airways colonisation and sensitisation in those with severe asthma opens up alternative therapy options of antifungal therapy, which may be particularly valuable in low resource settings.

The Triazole Ring as a Privileged Scaffold for Putative Antifungals: Synthesis and Evaluation of a Series of New Analogues

The significant antifungal activity of a series of novel 1,2,4-triazole derivatives against different strains of Candida albicans, Candida krusei and Aspergillus fumigatus, compared to the commercial fungicides ketoconazole and itraconazole, is reported. Systemic mycosis and invasive fungal infections, whether from immunodeficiency or hospital-acquired infection, have been on an upward trend for several years. The 1,2,4-triazole ring substituted with other aromatic and heteroaromatic systems plays an important role in the field of antifungal drug discovery and development. Thus, an extensive series of 29 triazoles, substituted in different positions with a variety of aromatic rings, has been designed, synthesized, and evaluated for their fungicidal activity. Almost all the agents tested in vitro showed high activity against all examined fungal strains. It is noteworthy that, in the case of A. fumigatus, all the examined compounds achieved equal or higher antifungal activity than ketoconazole, but less activity than itraconazole. Among all the derivatives studied, the dichlorourea analogue and bromo-substituted triazole stand out as the most promising compounds. Quantitative structure-activity relationship (QSAR) models were built for a systematic structure-activity relationship (SAR) profile to explain and potentially explore the potency characteristics of 1,2,4-triazole analogues.

Anti-fungal activity of a novel triazole, PC1244, against emerging azole-resistant Aspergillus fumigatus and other species of Aspergillus

Objectives

The growing emergence of azole-resistant Aspergillus fumigatus strains worldwide is a major concern for current systemic antifungal treatment. Here we report antifungal activities of a novel inhaled triazole, PC1244, against a collection of multi-azole-resistant A. fumigatus strains.

Methods

MICs of PC1244 were determined for A. fumigatus carrying TR₃₄/L98H (n = 81), TR₄₆/Y121F/T289A (n = 24), M220 (n = 6), G54 (n = 11), TR₅₃ (n = 1), TR₄₆³/Y121F/T289A (n = 2), G448S (n = 1), G432C (n = 1) and P216S (n = 1) resistance alleles originating from either India, the Netherlands or France. The effects of PC1244 were confirmed in an in vitro model of the human alveolus and in vivo in temporarily neutropenic, immunocompromised mice.

Results

PC1244 exhibited potent inhibition [geometric mean MIC (range), 1.0 mg/L (0.125 to >8 mg/L)] of growth of A. fumigatus strains carrying cyp51A gene mutations, showing much greater potency than voriconazole [15 mg/L (0.5 to >16 mg/L)], and an effect similar to those on other azole-susceptible Aspergillus spp. (Aspergillus flavus, Aspergillus terreus, Aspergillus tubingensis, Aspergillus nidulans, Aspergillus niger, Aspergillus nomius, Aspergillus tamarii) (0.18–1 mg/L). In TR₃₄/L98H and TR₄₆/Y121F/T289A A. fumigatus-infected in vitro human alveolus models, PC1244 achieved superior inhibition (IC₅₀, 0.25 and 0.34 mg/L, respectively) compared with that of voriconazole (IC₉₀, >3 mg/L and >10 mg/L, respectively). In vivo, once-daily intranasal administration of PC1244 (0.56–70 μg/mouse) to the A. fumigatus (AF91 with M220V)-infected mice reduced pulmonary fungal load and serum galactomannan more than intranasal posaconazole.

Conclusions

PC1244 has the potential to become a novel topical treatment of azole-resistant pulmonary aspergillosis.

In vitro antifungal activity of a novel topical triazole PC945 against emerging yeast Candida auris

Objectives

Management of Candida auris infection is difficult as this yeast exhibits resistance to different classes of antifungals, necessitating the development of new antifungals. The aim of this study was to investigate the susceptibility of C. auris to a novel antifungal triazole, PC945, optimized for topical delivery.

Methods

A collection of 50 clinical isolates was obtained from a tertiary care hospital in North India. Nine isolates from the UK, 10 from a CDC panel (USA) and 3 from the CBS-KNAW culture collection (Japanese and South Korean isolates) were also obtained. MICs (azole endpoint) of PC945 and other triazoles were determined in accordance with CLSI M27 (third edition). Quality control strains were included [Candida parapsilosis (ATCC 22019) and Candida krusei (ATCC 6258)].

Results

Seventy-four percent of isolates tested showed reduced susceptibility to fluconazole (≥64 mg/L). PC945 (geometric mean MIC = 0.058 mg/L) was 7.4-fold and 1.5-fold more potent than voriconazole and posaconazole, respectively (both P < 0.01). PC945 MIC values correlated with those of voriconazole or posaconazole, and only three isolates were found to be cross-resistant between PC945 and other azoles. ERG11 sequence analysis revealed several mutations, but no correlation could be established with the MIC of PC945. Tentative epidemiological cut-off values (ECOFFs) evaluated by CLSI’s ECOFF Finder (at 99%) with 24 h reading of MICs were 1, 4 and 1 mg/L for PC945, voriconazole and posaconazole, respectively. MIC values for quality control strains of all triazoles were in the normal ranges.

Conclusions

PC945 was found to be a more potent inhibitor than posaconazole, voriconazole and fluconazole of C. auris isolates collected globally, warranting further laboratory and clinical evaluations.

A comprehensive overview of the medicinal chemistry of antifungal drugs: perspectives and promise

The emergence of new fungal pathogens makes the development of new antifungal drugs a medical imperative that in recent years motivates the talents of numerous investigators across the world. Understanding not only the structural families of these drugs but also their biological targets provides a rational means for evaluating the merits and selectivity of new agents for fungal pathogens and normal cells. An equally important aspect of modern antifungal drug development takes a balanced look at the problems of drug potency and drug resistance. The future development of new antifungal agents will rest with those who employ synthetic and semisynthetic methodology as well as natural product isolation to tackle these problems and with those who possess a clear understanding of fungal cell architecture and drug resistance mechanisms. This review endeavors to provide an introduction to a growing and increasingly important literature, including coverage of the new developments in medicinal chemistry since 2015, and also endeavors to spark the curiosity of investigators who might enter this fascinatingly complex fungal landscape.

New and Promising Chemotherapeutics for Emerging Infections Involving Drug-resistant Non-albicans Candida Species

Fungal infections are a veritable public health problem worldwide. The increasing number of patient populations at risk (e.g. transplanted individuals, cancer patients, and HIV-infected people), as well as the use of antifungal agents for prophylaxis in medicine, have favored the emergence of previously rare or newly identified fungal species. Indeed, novel antifungal resistance patterns have been observed, including environmental sources and the emergence of simultaneous resistance to different antifungal classes, especially in Candida spp., which are known for the multidrug-resistance (MDR) profile. In order to circumvent this alarming scenario, the international researchers' community is engaged in discovering new, potent, and promising compounds to be used in a near future to treat resistant fungal infections in hospital settings on a global scale. In this context, many compounds with antifungal action from both natural and synthetic sources are currently under clinical development, including those that target either ergosterol or β(1,3)-D-glucan, presenting clear evidence of pharmacologic/pharmacokinetic advantages over currently available drugs against these two well-known fungal target structures. Among these are the tetrazoles VT-1129, VT-1161, and VT-1598, the echinocandin CD101, and the glucan synthase inhibitor SCY-078. In this review, we compiled the most recent antifungal compounds that are currently in clinical trials of development and described the potential outcomes against emerging and rare Candida species, with a focus on C. auris, C. dubliniensis, C. glabrata, C. guilliermondii, C. haemulonii, and C. rugosa. In addition to possibly overcoming the limitations of currently available antifungals, new investigational chemical agents that can enhance the classic antifungal activity, thereby reversing previously resistant phenotypes, were also highlighted. While novel and increasingly MDR non-albicans Candida species continue to emerge worldwide, novel strategies for rapid identification and treatment are needed to combat these life-threatening opportunistic fungal infections.

Efficacy of Voriconazole against Aspergillus fumigatus Infection Depends on Host Immune Function

Antifungal therapy can fail in a remarkable number of patients with invasive fungal disease, resulting in significant morbidity worldwide. A major contributor to this failure is that while these drugs have high potency in vitro, we do not fully understand how they work inside infected hosts. Here, we used a transparent larval zebrafish model of Aspergillus fumigatus infection amenable to real-time imaging of invasive disease as an in vivo intermediate vertebrate model to investigate the efficacy and mechanism of the antifungal drug voriconazole. We found that the ability of voriconazole to protect against A. fumigatus infection depends on host innate immune cells and, specifically, on the presence of macrophages. While voriconazole inhibits fungal spore germination and growth in vitro, it does not do so in larval zebrafish. Instead, live imaging of whole, intact larvae over a multiday course of infection revealed that macrophages slow down initial fungal growth, allowing voriconazole time to target and kill A. fumigatus hyphae postgermination. These findings shed light on how antifungal drugs such as voriconazole may synergize with the immune response in living hosts.

Antifungal synergy of a topical triazole, PC945, with a systemic triazole against respiratory Aspergillus fumigatus infection

Invasive pulmonary Aspergillosis is a leading cause of morbidity and mortality in immunosuppressed patients and treatment outcomes using oral antifungal triazoles remain suboptimal. Here we show that combining topical treatment using PC945, a novel inhaled triazole, with systemic treatment using known triazoles demonstrated synergistic antifungal effects against Aspergillus fumigatus (AF) in an in vitro human alveolus bilayer model and in the lungs of neutropenic immunocompromised mice. Combination treatment with apical PC945 and either basolateral posaconazole or voriconazole resulted in a synergistic interaction with potency improved over either compound as a monotherapy against both azole-susceptible and resistant AF invasion in vitro. Surprisingly there was little, or no synergistic interaction observed when apical and basolateral posaconazole or voriconazole were combined. In addition, repeated prophylactic treatment with PC945, but not posaconazole or voriconazole, showed superior effects to single prophylactic dose, suggesting tissue retention and/or accumulation of PC945. Furthermore, in mice infected with AF intranasally, 83% of animals treated with a combination of intranasal PC945 and oral posaconazole survived until day 7, while little protective effects were observed by either compound alone. Thus, the combination of a highly optimised topical triazole with oral triazoles potentially induces synergistic effects against AF infection.

Fungal Lanosterol 14α-demethylase: A target for next-generation antifungal design

The cytochrome P450 enzyme lanosterol 14α-demethylase (LDM) is the target of the azole antifungals used widely in medicine and agriculture as prophylaxis or treatments of infections or diseases caused by fungal pathogens. These drugs and agrochemicals contain an imidazole, triazole or tetrazole substituent, with one of the nitrogens in the azole ring coordinating as the sixth axial ligand to the LDM heme iron. Structural studies show that this membrane bound enzyme contains a relatively rigid ligand binding pocket comprised of a deeply buried heme-containing active site together with a substrate entry channel and putative product exit channel that reach to the membrane. Within the ligand binding pocket the azole antifungals have additional affinity determining interactions with hydrophobic side-chains, the polypeptide backbone and via water-mediated hydrogen bond networks. This review will describe the tools that can be used to identify and characterise the next generation of antifungals targeting LDM, with the goal of obtaining highly potent broad-spectrum fungicides that will be able to avoid target and drug efflux mediated antifungal resistance.

Current approaches to the discovery of novel inhaled medicines

Inhaled administration is underutilised because the drug discovery process is viewed as challenging, risky, and expensive. However, unmet medical need continues to grow, and significant opportunities exist to discover novel inhaled medicines delivering the required lung concentrations while minimising systemic exposure. This profile could be achieved by a combination of properties, including lung retention and low oral bioavailability. Property-based rules exist for orally administered compounds, but there has been limited progress defining in silico predictors to guide the discovery of novel inhaled drugs. Recently, the use of informative cell- and tissue-based screens has greatly facilitated the identification of compounds with optimal characteristics for inhaled delivery. Here, we address opportunities for novel inhaled drugs, and the key challenges and uncertainties hampering progress.

Sterol Composition of Clinically Relevant Mucorales and Changes Resulting from Posaconazole Treatment

Mucorales are fungi with increasing importance in the clinics. Infections take a rapidly progressive course resulting in high mortality rates. The ergosterol biosynthesis pathway and sterol composition are of interest, since they are targeted by currently applied antifungal drugs. Nevertheless, Mucorales often exhibit resistance to these drugs, resulting in therapeutic failure. Here, sterol patterns of six clinically relevant Mucorales (Lichtheimia corymbifera, Lichtheimia ramosa, Mucor circinelloides, Rhizomucor pusillus, Rhizopus arrhizus, and Rhizopus microsporus) were analysed in a targeted metabolomics fashion after derivatization by gas chromatography-mass spectrometry. Additionally, the effect of posaconazole (POS) treatment on the sterol pattern of R. arrhizus was evaluated. Overall, fifteen different sterols were detected with species dependent variations in the total and relative sterol amount. Sterol analysis from R. arrhizus hyphae confronted with sublethal concentrations of posaconazole revealed the accumulation of 14-methylergosta-8,24-diene-3,6-diol, which is a toxic sterol that was previously only detected in yeasts. Sterol content and composition were further compared to the well-characterized pathogenic mold Aspergillus fumigatus. This work contributes to a better understanding of the ergosterol biosynthesis pathway of Mucorales, which is essential to improve antifungal efficacy, the identification of targets for novel drug design, and to investigate the combinatorial effects of drugs targeting this pathway.

In Vitro and In Vivo Efficacy of a Novel and Long-Acting Fungicidal Azole, PC1244, on Aspergillus fumigatus Infection

The antifungal effects of the novel triazole PC1244, designed for topical or inhaled administration, against Aspergillus fumigatus were tested in a range of in vitro and in vivo studies. PC1244 demonstrated potent antifungal activities against clinical A. fumigatus isolates (n = 96) with a MIC range of 0.016 to 0.25 μg/ml, whereas the MIC range for voriconazole was 0.25 to 0.5 μg/ml. PC1244 was a strong tight-binding inhibitor of recombinant A. fumigatus CYP51A and CYP51B (sterol 14α-demethylase) enzymes and strongly inhibited ergosterol synthesis in A. fumigatus with a 50% inhibitory concentration of 8 nM. PC1244 was effective against a broad spectrum of pathogenic fungi (MIC range, <0.0078 to 2 μg/ml), especially Aspergillus terreus, Trichophyton rubrum, Candida albicans, Candida glabrata, Candida krusei, Cryptococcus gattii, Cryptococcus neoformans, and Rhizopus oryzae. PC1244 also proved to be quickly absorbed into both A. fumigatus hyphae and bronchial epithelial cells, producing persistent antifungal effects. In addition, PC1244 showed fungicidal activity (minimum fungicidal concentration, 2 μg/ml) which indicated that it was 8-fold more potent than voriconazole. In vivo, once-daily intranasal administration of PC1244 (3.2 to 80 μg/ml) to temporarily neutropenic, immunocompromised mice 24 h after inoculation with itraconazole-susceptible A. fumigatus substantially reduced the fungal load in the lung, the galactomannan concentration in serum, and circulating inflammatory cytokine levels. Furthermore, 7 days of extended prophylaxis with PC1244 showed in vivo effects superior to those of 1 day of prophylactic treatment, suggesting accumulation of the effects of PC1244. Thus, PC1244 has the potential to be a novel therapy for the treatment of A. fumigatus infection in the lungs of humans.

In Vivo Biomarker Analysis of the Effects of Intranasally Dosed PC945, a Novel Antifungal Triazole, on Aspergillus fumigatus Infection in Immunocompromised Mice

PC945 is a novel triazole optimized for lung delivery, and the objective of this study is to determine the effects of intranasally dosed PC945 on Aspergillus fumigatus infection and associated biomarkers in immunocompromised mice. PC945, posaconazole, or voriconazole was administered intranasally once daily on days 0 to 3 (early intervention) or days 1 to 3 (late intervention) postinfection in temporarily neutropenic A/J mice infected intranasally with A. fumigatus, and bronchoalveolar lavage fluid (BALF) and serum were collected on day 3. The effects of extended prophylaxis treatment (daily from days −7 to +3 or days −7 to 0) were also compared with those of the shorter treatment regimens (days −1 to +3 or days −1 and 0). Early and late interventions with PC945 (2.8 to 350 μg/mouse; approximately 0.11 to ∼14 mg/kg of body weight) were found to inhibit lung fungal loads and to decrease the concentrations of galactomannan (GM) in both BALF and serum as well as several biomarkers in BALF (interferon gamma [IFN-γ], interleukin-17 [IL-17], and malondialdehyde) and serum (tumor necrosis factor alpha [TNF-α] and IL-6) in a dose-dependent manner and were >3- and >47-fold more potent than intranasally dosed posaconazole and voriconazole, respectively. Furthermore, extended prophylaxis with low-dose PC945 (0.56 μg/mouse; 0.022 mg/kg) was found to inhibit fungal loads and to decrease the concentrations biomarkers more potently than did the shorter treatment regimens. Thus, PC945 dosed intranasally once daily showed potent antifungal effects, and the effects of PC945 accumulated upon repeat dosing and were persistent. Therefore, PC945 has the potential to be a novel inhaled therapy for the treatment of A. fumigatus infection in humans.

Drugs currently under investigation for the treatment of invasive candidiasis

INTRODUCTION

The widespread implementation of immunosuppressants, immunomodulators, hematopoietic stem cell transplantation and solid organ transplantation in clinical practice has led to an expanding population of patients who are at risk for invasive candidiasis, which is the most common form of fungal disease among hospitalized patients in the developed world. The emergence of drug-resistant Candida spp. has added to the morbidity associated with invasive candidiasis and novel therapeutic strategies are urgently needed. Areas covered: In this paper, we explore investigational agents for the treatment of invasive candidiasis, with particular attention paid to compounds that have recently entered phase I or phase II clinical trials. Expert opinion: The antifungal drug development pipeline has been severely limited due to regulatory hurdles and a systemic lack of investment in novel compounds. However, several promising drug development strategies have recently emerged, including chemical screens involving Pathogen Box compounds, combination antifungal therapy, and repurposing of existing agents that were initially developed to treat other conditions, all of which have the potential to redefine the treatment of invasive candidiasis.