In Vitro Antifungal Activity of Ibrexafungerp (SCY-078) Against Contemporary Blood Isolates From Medically Relevant Species of Candida: A European Study

Uniqueness of Candida auris cell wall in morphogenesis, virulence, resistance, and immune evasion

Candida auris has drawn global attention due to its alarming multidrug resistance and the emergence of pan resistant strains. C. auris poses a significant risk in nosocomial candidemia especially among immunocompromised patients. C. auris showed unique virulence characteristics associated with cell wall including cell polymorphism, adaptation, endurance on inanimate surfaces, tolerance to external conditions, and immune evasion. Notably, it possesses a distinctive cell wall composition, with an outer mannan layer shielding the inner 1,3-β glucan from immune recognition, thereby enabling immune evasion and drug resistance. This review aimed to comprehend the association between unique characteristics of C. auris's cell wall and virulence, resistance mechanisms, and immune evasion. This is particularly relevant since the fungal cell wall has no human homology, providing a potential therapeutic target. Understanding the complex interactions between the cell wall and the host immune system is essential for devising effective treatment strategies, such as the use of repurposed medications, novel therapeutic agents, and immunotherapy like monoclonal antibodies. This therapeutic targeting strategy of C. auris holds promise for effective eradication of this resilient pathogen.

Clavispora lusitaniae: From a saprophytic yeast to an emergent pathogen

Clavispora lusitaniae has been isolated from different substrates, such as soil, water, fruit, vegetables, plants, and the gastrointestinal tract of animals and humans. However, its importance lies in being isolated from in invasive infections, particularly in pediatric patients with hematologic malignancies. It is an emerging nosocomial pathogen commonly associated with fatal prognosis in immunocompromised hosts. C. lusitaniae has attracted attention in the last decade because of resistance to amphotericin B, 5- flucytosine, and fluconazole. The adaptations of this yeast to the human host may contribute to its pathogenicity. Further study will be needed to understand C. lusitaniae's ability as a potential pathogen. This mini-review highlights the importance of the growing number of invasive disease cases caused by this yeast.

Assessment and Treatment of Vaginitis

Vaginitis is the presenting symptom at millions of office visits each year in the United States. Although treatment of sporadic cases is often straightforward, recurrent cases present both diagnostic and treatment challenges. Molecular diagnostic tests are likely superior to in-office microscopy for most clinicians and most cases. In both recurrent bacterial vaginosis and recurrent vulvovaginal candidiasis, national treatment guidelines recommend an extended treatment duration with one of the first-line agents. In cases in which such treatment is not successful, vaginal boric acid is likely the cheapest and easiest alternative option. New antifungal medications offer additional but limited treatment options. Probiotics are not recommended for prevention of vulvovaginal candidiasis; however, vaginal products containing Lactobacillus crispatus may have promise for recurrent bacterial vaginosis. Trichomoniasis should be treated with a 1-week course of metronidazole; this is the only sexually transmitted infection for which treatment recommendations vary by sex. In cases in which patients do not respond to initial treatment, the diagnosis should be reconsidered, and other potential causes such as desquamative inflammatory vaginitis, genitourinary syndrome of menopause, or vulvodynia should be considered.

Current Perspectives of Antifungal Therapy: A Special Focus on Candida auris

Candida auris is an emerging Candida sp. that has rapidly spread all over the world. The evidence regarding its origin and emerging resistance is still unclear. The severe infection caused by this species results in significant mortality and morbidity among the elderly and immunocompromised individuals. The development of drug resistance is the major factor associated with the therapeutic failure of existing antifungal agents. Previous studies have addressed the antifungal resistance profile and drug discovery for C. auris. However, complete coverage of this information in a single investigation is not yet available. In this review, we have mainly focused on recent developments in therapeutic strategies against C. auris. Based on the available information, several different approaches were discussed, including existing antifungal drugs, chemical compounds, essential oils, natural products, antifungal peptides, immunotherapy, antimicrobial photodynamic therapy, drug repurposing, and drug delivery systems. Among them, synthetic chemicals, natural products, and antifungal peptides are the prime contributors. However, a limited number of resources are available to prove the efficiency of these potential therapies in clinical usage. Therefore, we anticipate that the findings gathered in this review will encourage further in vivo studies and clinical trials.

Management of invasive candidiasis: A focus on rezafungin, ibrexafungerp, and fosmanogepix

Management of invasive fungal infections is challenging with growing antifungal resistance. Broad antifungal use has resulted in greater intrinsic and acquired resistance among Candida spp. It is important for clinicians to recognize the relationship between host susceptibility, site of infection, Candida resistance profiles, specific drug pharmacokinetics and pharmacodynamics, and the role of novel antifungal agents. This narrative review covers the role of rezafungin, ibrexafungerp, and fosmanogepix in the management of invasive candidiasis (IC). The PubMed Database, Embase, and ClinicalTrials.gov were searched between January 2006 and January 2024 using the following terms: rezafungin, CD101, ibrexafungerp, SCY-078, fosmanogepix, APX001, candidemia, and invasive candidiasis. Review articles, prospective clinical trials, and observational studies published in the English language were reviewed. Studies evaluating pharmacology, pharmacokinetics, efficacy, and safety in animals and humans were also reviewed. Promising data continues to emerge in support of novel drug therapies for IC and candidemia. Rezafungin possesses a unique pharmacodynamic profile that might be advantageous compared to other echinocandins, with a practical, once-weekly dosing interval. Ibrexafungerp, currently approved for vulvovaginal candidiasis, has been studied off-label for use in IC and candidemia, and initial data is encouraging. Lastly, fosmanogepix, a mechanistically novel, investigational antifungal agent, may be a potential future option in the management of IC and candidemia. Future research is needed to evaluate the potential use of these agents among diverse patient populations.

Ibrexafungerp: A narrative overview

Ibrexafungerp (IBX) is a new antifungal drug that recently entered the antifungal landscape. It disrupts fungal cell wall synthesis by non-competitive inhibition of the β-(1,3)-D-glucan (BDG) synthase enzyme. It has demonstrated activity against a range of pathogens including Candida and Aspergillus spp., as well as retaining its activity against azole-resistant and echinocandin-resistant strains. It also exhibits anti-biofilm properties. Pharmacokinetic (PK) studies revealed favorable bioavailability, high protein binding, and extensive tissue distribution with a low potential for CYP-mediated drug interactions. It is characterized by the same mechanism of action of echinocandins with limited cross-resistance with other antifungal agents. Resistance to this drug can arise from mutations in the FKS genes, primarily FKS2 mutations in Nakaseomyces glabrata. In vivo, IBX was found to be effective in murine models of invasive candidiasis (IC) and invasive pulmonary aspergillosis (IPA). It also showed promising results in preventing and treating Pneumocystis jirovecii infections. Clinical trials showed that IBX was effective and non-inferior to fluconazole in treating vulvovaginal candidiasis (VVC), including complicated cases, as well as in preventing its recurrence. These trials positioned it as a Food and Drug Administration (FDA)-approved option for the treatment and prophylaxis of VVC. Trials showed comparable responses to standard-of-care in IC, with favorable preliminary results in C. auris infections in terms of efficacy and tolerability as well as in refractory cases of IC. Mild adverse reactions have been reported including gastrointestinal symptoms. Overall, IBX represents a significant addition to the antifungal armamentarium, with its unique action, spectrum of activity, and encouraging clinical trial results warranting further investigation.

A Mini-Review of In Vitro Data for Candida Species, Including C. auris, Isolated during Clinical Trials of Three New Antifungals: Fosmanogepix, Ibrexafungerp, and Rezafungin

This mini-review summarizes the clinical outcomes and antifungal susceptibility results, where available, for three new antifungals, including fosmanogepix, ibrexafungerp, and rezafungin, against Candida isolates cultured from patients in clinical trials. When reported, most of the data were generated by the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method or by both the CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) methodologies. For fosmanogepix, we summarize the in vitro data for C. auris isolates from 9 patients and for Candida spp. cultured from 20 patients in two clinical trials. Ibrexafungerp has also been evaluated in several clinical trials. From conference proceedings, a total of 176 Candida isolates were evaluated in the FURI and CARES studies, including 18 C. auris isolates (CARES study). However, MIC data are not available for all clinical isolates. Results from the ReSTORE rezafungin phase 3 clinical study also included in vitro results against Candida spp., but no patients with C. auris infections were included. In conclusion, this mini-review summarizes insights regarding clinical outcomes and the in vitro activity of three new antifungals against Candida spp. cultured from patients in clinical trials.

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.

In vitro activity of ibrexafungerp against clinically relevant echinocandin-resistant Candida strains

Invasive candidiasis is a major hospital-acquired infection. Usually, echinocandins are considered first-line treatment. However, resistant phenotypes have emerged. Ibrexafungerp (IBX) is a new antifungal substance with potent anti-Candida activity. We challenged IBX with a library of 192 pheno-/genotypically echinocandin-resistant Candida isolates, focusing on the substance susceptibility, its activity on certain FKS hotspot (HS) mutated strains, and applying WTULs (wild-type upper limits). Therefore, a 9-year-old strain and patient data collection provided by the German National Reference Center for Invasive Fungal Infections were analyzed. Species identification was confirmed through ITS-sequencing. Molecular susceptibility testing was performed by sequencing HS of the FKS gene. Anidulafungin (AND) and IBX EUCAST-broth-microdilution was conducted. The four most common echinocandin-resistance mediating mutations were found in Candida glabrata [112/192 isolates; F659-(43×) and S663-(48×)] and Candida albicans [63/192 isolates; F641-(15×) and S645-(39×)]. Mutations at the HS-start sequence were associated with higher IBX MIC-values (F659 and F641 (MIC 50/90 mg/L: >4/>4 and 2/4 mg/L) in comparison to AND (F659 and F641 (MIC 50/90: 1/4 and 0.25/1 mg/L). MIC-values in HS-center mutations were almost equal [MIC50/90 in S663: 2/4 (AND and IBX); in S645: 0.5/1 (AND) and 0.25/1 (IBX) mg/L]. In total, 61 vs 78 of 192 echinocandin-resistant isolates may be classified as IBX wild type by applying WTULs, whereas the most prominent effect was seen in C. albicans [48% (30/63) vs 70% (44/63)]. IBX shows in vitro activity against echinocandin-resistant Candida and thus is an addition to the antifungal armory. However, our data suggest that this effect is more pronounced in C. albicans and strains harboring mutations, affecting the HS-center.

The Role of Novel Antifungals in the Management of Candidiasis: A Clinical Perspective

Mucosal and invasive candidiasis can be challenging to treat in the setting of drug intolerance, antifungal resistance, drug-drug interactions, or host immune status. Antifungals with novel mechanisms of action and distinct pharmacokinetic/pharmacodynamic properties have been developed in recent years. Rezafungin is an echinocandin with high-tissue penetration and an extended half-life that allows for once-weekly administration, making it a convenient treatment option for invasive candidiasis while obviating the need for central catheter placement. Ibrexafungerp is an oral glucan synthase inhibitor that is active against most echinocandin-resistant Candida species. At present, it is approved for the treatment of acute vulvovaginal candidiasis and is under investigation as an oral step-down therapy following initial treatment with an echinocandin for cases of invasive candidiasis. Oteseconazole is a long-acting tetrazole that exhibits a higher affinity for the fungal enzyme CYP51, resulting in a potentially lower risk of drug-drug interactions and side effects compared to other azoles. It is currently approved for the treatment of recurrent vulvovaginal candidiasis. Fosmanogepix has a novel mechanism of action and potent activity against several Candida strains resistant to other antifungals. Due to its considerable bioavailability and tissue penetration, it holds promise as a potential treatment option in patients with invasive candidiasis, including those with chorioretinitis or meningitis. Results from clinical trials and observational studies will further delineate the role of these agents in the management of candidiasis. As the usage of these novel antifungals becomes widespread, we expect to acquire a greater understanding of their efficacy and potential benefits.

Intra-clade Heterogeneity in Candida auris: Risk of Management

Candida auris has emerged as a significant nosocomial fungal pathogen with a high risk of pathogenicity. Since the initial detection of C. auris in 2009, it gained lots of attention with a recent alert by the Centers for Disease Control and Prevention (CDC) due to its high infectivity and drug resistance. Several studies showed the capability of C. auris to secrete lytic enzymes, germinate, and form a biofilm that eventually results in interactions with the host cells, leading to serious infections. Other studies demonstrated a decrease in susceptibility of C. auris strains to available antifungals, which may be caused by mutations within the target genes, or the drug efflux pumps. However, the contribution of C. auris heterogeneity in pathogenicity and drug resistance is not well studied. Here, we shed light on the factors contributing to the development of heterogeneity in C. auris. These include phenotypic changes, biofilm formation, mechanisms of drug resistance, host invasion, mode of transmission, and expression of virulence factors. C. auris exhibits different phenotypes, particularly aggregative, and non-aggregative forms that play an important role in fungal heterogeneity, which significantly affects drug resistance and pathogenicity. Collectively, heterogeneity in C. auris significantly contributes to ineffective treatment, which in turn affects the fungal pathogenicity and drug resistance. Therefore, understanding the underlying reasons for C. auris heterogeneity and applying effective antifungal stewardship could play a major role in controlling this pathogen.

Oteseconazole: a long-awaited diversification of the antifungal arsenal to manage recurrent vulvovaginal candidiasis (RVVC)

INTRODUCTION

Recurrent vulvovaginal candidiasis (RVVC) affects women worldwide and has far-reaching implications for a patient's quality of life. For decades, maintenance treatment using the azole antifungal fluconazole was the preferred treatment. Although efficient in controlling the symptoms, the development of azole resistance and high rates of recurrence after therapy cessation have emerged as significant limitations. Nevertheless, persistent efforts have delivered novel treatment options. Oteseconazole (VT-1161), marketed as VIVJOA, is an oral, tetrazole antifungal with unprecedented specificity toward the fungal lanosterol 14α-demethylase.

AREAS COVERED

We reviewed literature data on oteseconazole with a focus on the management of RVVC.

EXPERT OPINION

Therapeutic options for RVVC are limited, and novel, innovative approaches are needed to treat this debilitating condition. These therapies need to be well-tolerated and prevent RVVC recurrence. The available clinical data show excellent safety and efficacy, with an unprecedentedly low recurrence rate. However, we believe health-care providers should be mindful to monitor for the development of resistance, as this may result in treatment failure. Further, the availability and cost may, like for most novel drugs, affect the widespread clinical implementation of VIVJOA. Altogether, we are convinced that VIVJOA is a significant advance in RVVC management.

Ibrexafungerp for the Treatment of Vulvovaginal Candidiasis: Design, Development and Place in Therapy

Vulvovaginal candidiasis (VVC) is experienced by an estimated 75% of women at least once in their lifetime and is recurrent, defined as three or more infections per year (RVVC) in 5-9%. Candida albicans is the most common causative agent, but up to 19% of infections may be related to non-albicans species. Available treatment options for VVC have consisted of oral and topical azoles (except for topical nystatin, a polyene). Oral polyenes are not absorbed and therefore not effective for VVC. Fluconazole is the only oral medication FDA approved for VVC. None of these treatments are FDA approved for RVVC. Ibrexafungerp, a triterpenoid fungicidal agent, was FDA approved in 2021, becoming the first oral non-azole agent for VVC. Ibrexafungerp reaches concentrations up to 9-fold higher in vaginal tissues versus plasma. In Phase 2 clinical trials, ibrexafungerp had a clinical cure rate comparable to fluconazole at day 10, but significantly better at day 25. In Phase 3 clinical trials, ibrexafungerp had both a higher clinical and mycologic cure rate versus placebo at both days 10 and 25. In December 2022, Ibrexafungerp received FDA approval for once monthly dosing to decrease the incidence of RVVC. This approval was based on data from the CANDLE STUDY, which showed 65.4% resolution of symptoms and culture negative success through week 24, compared to 53.1% of placebo. Ibrexafungerp provides an alternative oral option for treatment of acute, severe VVC. It is the only FDA approved antifungal for RVVC. Currently, the population likely to benefit from this drug are those with azole allergy, non-albicans or azole resistant albicans species, or other azole contraindications such as drug interactions (like statins or tricyclics). Side effects are mostly gastrointestinal and mild in nature. Ibrexafungerp, like fluconazole, should be used with caution in women who are or may become pregnant.

Candidiasis and Other Emerging Yeasts

Purpose of Review

The review presents a comprehensive and updated information on the contemporary status of invasive candidiasis (IC), other emerging yeast infections, and the challenges they present in terms of at-risk population, specific virulence attributes, and antifungal susceptibility profile.

Recent Findings

With the advancement in medical field, there has been parallel expansion of vulnerable populations over the past two decades. This had led to the emergence of a variety of rare yeasts in healthcare settings, both Candida and non-Candida yeast causing sporadic cases and outbreaks. The advancements in diagnostic modalities have enabled accurate identification of rare Candida species and non-Candida yeast (NCY) of clinical importance. Their distribution and susceptibility profile vary across different geographical regions, thus necessitating surveillance of local epidemiology of these infections to improve patient outcomes.

Summary

The challenges in management of IC have been complicated with emergence of newer species and resistance traits. C. tropicalis has already overtaken C. albicans in many Asian ICUs, while C. auris is rising rapidly worldwide. Recent genomic research has reclassified several yeasts into newer genera, and an updated version of MALDI-TOF MS or ITS sequencing is necessary for accurate identification. Having a knowledge of the differences in predisposing factors, epidemiology and susceptibility profile of already established pathogenic yeasts, as well as new emerging yeasts, are imperative for better patient management.

Recent Antifungal Pipeline Developments against Candida auris: A Systematic Review

The alarming spread and impact of multidrug-resistant Candida auris infections alongside the limited therapeutic options have prompted the development of new antifungals. These promising agents are currently in different stages of development, offering novel dosing regimens and mechanisms of action. A systematic search in MEDLINE, EMBASE, Web of Science, and Scopus up to 27 June 2022 was conducted to find relevant articles reporting data of in vitro activity and in vivo efficacy of investigational antifungals against C. auris. These included new additions to existing antifungal classes (rezafungin and opelconazole), first-in-class drugs such as ibrexafungerp, manogepix/fosmanogepix, olorofim and tetrazoles (quilseconazole, oteseconazole and VT-1598), as well as other innovative agents like ATI-2307, MGCD290 and VL-2397. From 592 articles retrieved in the primary search, 27 met the eligibility criteria. The most studied agent was manogepix/fosmanogepix (overall MIC₉₀: 0.03 mg/L), followed by ibrexafungerp (overall MIC₉₀: 1 mg/L) and rezafungin (overall MIC mode: 0.25 mg/L), while VT-1598 and ATI-2307 were the least explored drugs against C. auris. All these compounds demonstrated significant improvements in survival and reduction in tissue fungal burden on neutropenic animal models of candidemia due to C. auris. Continual efforts towards the discovery of new treatments against this multidrug-resistant fungus are essential.

EUCAST Ibrexafungerp MICs and Wild-Type Upper Limits for Contemporary Danish Yeast Isolates

Ibrexafungerp is a novel triterpenoid antifungal that inhibits glucan synthase and thus fungal cell wall synthesis. We examined the in vitro activity against contemporary clinical yeast, investigated inter-laboratory and intra-laboratory variability, suggested wild-type upper-limit values (WT-UL), and compared in vitro activity of ibrexafungerp to five licensed antifungals. Susceptibility to ibrexafungerp and comparators was investigated prospectively for 1965 isolates (11,790 MICs) and repetitively for three QC strains (1764 MICs) following the EUCAST E.Def 7.3.2 method. Elevated ibrexafungerp/echinocandin MICs prompted FKS sequencing. Published ibrexafungerp EUCAST MIC-distributions were retrieved and aggregated for WT-UL determinations following EUCAST principles. Ibrexafungerp MICs were ≤2 mg/L except against C. pararugosa, Cryptococcus and some rare yeasts. Modal MICs (mg/L) were 0.06/0.125/0.25/0.5/0.5/0.5/0.5/1/2 for C. albicans/C. dubliniensis/C. glabrata/C. krusei/C. parapsilosis/C. tropicalis/S. cerevisiae/C. guilliermondii/C. lusitaniae and aligned within ±1 dilution with published values. The MIC ranges for QC strains were: 0.06–0.25/0.5–1/0.125–0.5 for CNM-CL-F8555/ATCC6258/ATCC22019. The WT-UL (mg/L) were: 0.25/0.5/1/1/2 for C. albicans/C. glabrata/C. krusei/C. parapsilosis/C. tropicalis. Adopting these, non-wild-type rates were 0.3%/0.6%/0%/8%/3% for C. albicans/C. glabrata/C. krusei/C. parapsilosis/C. tropicalis and overall lower than for comparators except amphotericin B. Five/six non-wild-type C. albicans/C. glabrata were echinocandin and Fks non-wild-type (F641S, F659del or F659L). Eight C. parapsilosis and three C. tropicalis non-wild-type isolates were echinocandin and Fks wild-type. Partial inhibition near 50% in the supra-MIC range may explain variable MICs. Ibrexafungerp EUCAST MIC testing is robust, although the significance of paradoxical growth for some species requires further investigation. The spectrum is broad and will provide an oral option for the growing population with azole refractory infection.

Postantifungal Effect of Antifungal Drugs against Candida: What Do We Know and How Can We Apply This Knowledge in the Clinical Setting?

The study of the pharmacological properties of an antifungal agent integrates the drug pharmacokinetics, the fungal growth inhibition, the fungicidal effect and the postantifungal activity, laying the basis to guide optimal dosing regimen selection. The current manuscript reviews concepts regarding the postantifungal effect (PAFE) of the main classes of drugs used to treat Candida infections or candidiasis. The existence of PAFE and its magnitude are highly dependent on both the fungal species and the class of the antifungal agent. Therefore, the aim of this article was to compile the information described in the literature concerning the PAFE of polyenes, azoles and echinocandins against the Candida species of medical interest. In addition, the mechanisms involved in these phenomena, methods of study, and finally, the clinical applicability of these studies relating to the design of dosing regimens were reviewed and discussed. Additionally, different factors that could determine the variability in the PAFE were described. Most PAFE studies were conducted in vitro, and a scarcity of PAFE studies in animal models was observed. It can be stated that the echinocandins cause the most prolonged PAFE, followed by polyenes and azoles. In the case of the triazoles, it is worth noting the inconsistency found between in vitro and in vivo studies.