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

An update on newer antifungals

INTRODUCTION

Fungal infections constitute a significant global health threat, with an estimated incidence of 6.5 million invasive fungal infections and 2.5 million associated deaths each year. New antifungal agents are being developed to address the challenges of fungal infections management, driven by the evolving fungal epidemiology, the emergence of antifungal resistance, and the limitations of existing treatments.

AREA COVERED

This review provides a thorough overview of the latest developments in novel antifungal agents, highlighting pivotal evidence obtained from clinical trials.

EXPERT OPINION

New antifungal agents hold promising future for difficult-to-treat fungal infections, providing for improved bioavailability, pharmacokinetic properties, adverse events and drug interactions, as well as, spectrum of activity. However, further data is needed before incorporating these agents in everyday clinical practice for the management of invasive fungal infections.

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

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

Antifungal pipeline: New tools for the treatment of mycoses

Fungal infections are becoming an escalating public health challenge, particularly among immunocompromised individuals. The partially limited efficacy of current antifungal treatments, their potential adverse effects, and the increasing problem of resistance emphasize the need for new treatment options. Existing antifungal classes-allylamines, azoles, echinocandins, polyenes, and pyrimidine analogs-face challenges due to their similarity with human cells and rising resistance. New antifungal agents, such as ibrexafungerp, rezafungin, oteseconazole, and miltefosine, offer novel mechanisms of action along with reduced toxicity. While antifungal resistance is a growing global concern, fungal infections in low- and middle-income countries (LMICs) present specific challenges with high rates of opportunistic infections like cryptococcosis and endemic mycoses such as histoplasmosis. The World Health Organization's fungal priority pathogens list highlights the prevalence of these infections in LMICs, where limited access to antifungal drugs and misuse are common. This review provides a comprehensive overview of these new agents and their mechanisms, and explores the challenges and roles of antifungal drugs in LMICs, where the burden of fungal infections is high. Continued research and development are essential to address the rising incidence and resistance of fungal infections globally.

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.

Review of treatment options for a multidrug-resistant fungus: Candida auris

Candida auris is a widely distributed, highly lethal, multidrug-resistant fungal pathogen. It was first identified in 2009 when it was isolated from fluid drained from the external ear canal of a patient in Japan. Since then, it has caused infectious outbreaks in over 45 countries, with mortality rates approaching 60%. Drug resistance is common in this species, with a large proportion of isolates displaying fluconazole resistance and nearly half are resistant to two or more antifungal drugs. In this review, we describe the drug resistance mechanism of C. auris and potential small-molecule drugs for treating C. auris infection. Among these antifungal agents, rezafungin was approved by the US Food and Drug Administration (FDA) for the treatment of candidemia and invasive candidiasis on March 22, 2023. Ibrexafungerp and fosmanogepix have entered phase III clinical trials.

Antifungal resistance, combinations and pipeline: oh my!

Invasive fungal infections are a strong contributor to healthcare costs, morbidity and mortality, especially amongst hospitalized patients. Historically, Candida was responsible for approximately 15% of all nosocomial bloodstream infections. In the past 10 years, the epidemiology of Candida species has altered, with increasing prevalence of resistant species. With rising fungal resistance, especially in Candida spp., the demand for novel antifungal therapies has exponentially increased over the last decade. Newer antifungal agents have become an attractive option for patients needing long-term therapy for infections or those requiring antifungal prophylaxis. Despite advances in coverage of non-Candida pathogens with newer agents, clinical scenarios involving multidrug-resistant fungal pathogens continue to arise in practice. Combination antifungal therapy can lead to a host of side-effects, some of which can be drug limiting. Additional antifungal therapies with enhanced fungal spectrum of activity and decreased rates of adverse effects are warranted. Fosmanogepix, ibrexafungerp, olorofim and rezafungin may help fill some of these gaps in the antifungal armamentarium. This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

New trends in antifungal treatment: What is coming up?

New antifungal agents are needed to overcome limitations of available ones such as poor pharmacokinetic traits, toxicity, drug-drug interactions, limited clinical efficacy, and emerging antifungal resistance. New antifungal drugs belong to well-known families (azoles, polyenes, or beta-d-glucan synthase inhibitors) or to drug families showing completely new mechanisms of action. Some drugs have a head start in terms of potential to reach the clinical setting and are here reviewed.

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.

Recent developments in membrane targeting antifungal agents to mitigate antifungal resistance

Fungal infections cause severe and life-threatening complications especially in immunocompromised individuals. Antifungals targeting cellular machinery and cell membranes including azoles are used in clinical practice to manage topical to systemic fungal infections. However, continuous exposure to clinically used antifungal agents in managing the fungal infections results in the development of multi-drug resistance via adapting different kinds of intrinsic and extrinsic mechanisms. The unique chemical composition of fungal membranes presents attractive targets for antifungal drug discovery as it is difficult for fungal cells to modify the membrane targets for emergence of drug resistance. Here, we discussed available antifungal drugs with their detailed mechanism of action and described different antifungal resistance mechanisms. We further emphasized structure-activity relationship studies of membrane-targeting antifungal agents, and classified membrane-targeting antifungal agents on the basis of their core scaffold with detailed pharmacological properties. This review aims to pique the interest of potential researchers who could explore this interesting and intricate fungal realm.

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.

Clinical Uses of Inhaled Antifungals for Invasive Pulmonary Fungal Disease: Promises and Challenges

The role of inhaled antifungals for prophylaxis and treatment of invasive fungal pneumonias remains undefined. Herein we summarize recent clinically relevant literature in high-risk groups such as neutropenic hematology patients, including those undergoing stem cell transplant, lung and other solid transplant recipients, and those with sequential mold lung infections secondary to viral pneumonias. Although there are several limitations of the available data, inhaled liposomal amphotericin B administered 12.5 mg twice weekly could be an alternative method of prophylaxis in neutropenic populations at high risk for invasive fungal pneumonia where systemic triazoles are not tolerated. In addition, inhaled amphotericin B has been commonly used as prophylaxis, pre-emptive, or targeted therapy for lung transplant recipients but is considered as a secondary alternative for other solid organ transplant recipients. Inhaled amphotericin B seems promising as prophylaxis in fungal pneumonias secondary to viral pneumonias, influenza, and SARS CoV-2. Data remain limited for inhaled amphotericin for adjunct treatment, but the utility is feasible.

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.

Severe Fungal Asthma: A Role for Biologics and Inhaled Antifungals

Allergic asthma has traditionally been treated with inhaled and systemic glucocorticosteroids. A continuum of allergic fungal airways disease associated with Aspergillus fumigatus colonization and/or atopic immune responses that encompasses fungal asthma, severe asthma with fungal sensitization and allergic bronchopulmonary aspergillosis is now recognized along a phenotypic severity spectrum of T2-high immune deviation lung disease. Oral triazoles have shown clinical, anti-inflammatory and microbiologic efficacy in this setting; in the future inhaled antifungals may improve the therapeutic index. Humanized monoclonal antibody biologic agents targeting T2-high disease also show efficacy and promise of improved control in difficult cases. Developments in these areas are highlighted in this overview.

Review of current and future therapeutics in ABPA

Allergic bronchopulmonary aspergillosis is an allergic pulmonary condition caused by hypersensitivity to antigens of Aspergillus sp. found most commonly in patients with underlying asthma or cystic fibrosis. Host factors which alter the innate and adaptive immune responses to this abundant airborne fungus contribute to the development of chronic airway inflammation, bronchiectasis, and fibrosis. Traditionally, treatment has focussed on reducing fungal burden and immune response to fungal antigens. However, a significant proportion of patients continue to suffer recurrent exacerbations with progressive lung damage, and the side effect burden of existing treatments is high. New treatments including novel antifungal agents, monoclonal antibodies against aspects of the adaptive immune response as well as targeted immunotherapies may be better tolerated and achieve improved outcomes but have not yet been studied in large-scale randomised control trials.

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.

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.

New Perspectives in the Diagnosis and Management of Allergic Fungal Airway Disease

Allergy to airway-colonising, thermotolerant, filamentous fungi represents a distinct eosinophilic endotype of often severe lung disease. This endotype, which particularly affects adult asthma, but also complicates other airway diseases and sometimes occurs de novo, has a heterogeneous presentation ranging from severe eosinophilic asthma to lobar collapse. Its hallmark is lung damage, characterised by fixed airflow obstruction (FAO), bronchiectasis and lung fibrosis. It has a number of monikers including severe asthma with fungal sensitisation (SAFS) and allergic bronchopulmonary aspergillosis/mycosis (ABPA/M), but these exclusive terms constitute only sub-sets of the condition. In order to capture the full extent of the syndrome we prefer the inclusive term allergic fungal airway disease (AFAD), the criteria for which are IgE sensitisation to relevant fungi in association with airway disease. The primary fungus involved is Aspergillus fumigatus, but a number of other thermotolerant species from several genera have been implicated. The unifying mechanism involves germination of inhaled fungal spores in the lung in the context of IgE sensitisation, leading to a persistent and vigorous eosinophilic inflammatory response in association with release of fungal proteases. Most allergenic fungi, including Alternaria and Cladosporium species, are not thermotolerant and cannot germinate in the airways so only act as aeroallergens and do not cause AFAD. Studies of the airway mycobiome have shown that A. fumigatus colonises the normal as much as the asthmatic airway, suggesting it is the tendency to become IgE-sensitised that is the critical triggering factor for AFAD rather than colonisation per se. Treatment is aimed at preventing exacerbations with glucocorticoids and increasingly by the use of anti-T2 biological therapies. Anti-fungal therapy has a limited place in management, but is an effective treatment for fungal bronchitis which complicates AFAD in about 10% of cases.