Uptake of T-2307, a novel arylamidine, in Candida albicans

Pharmacodynamics of ATI-2307 in a rabbit model of cryptococcal meningoencephalitis

Cryptococcal meningoencephalitis (CM) is a devastating fungal disease with high morbidity and mortality. The current regimen that is standard-of-care involves a combination of three different drugs administered for up to one year. There is a critical need for new therapies due to both toxicity and inadequate fungicidal activity of the currently available antifungal drugs. ATI-2307 is a novel aryl amidine that disrupts the mitochondrial membrane potential and inhibits the respiratory chain complexes of fungi-it thus represents a new mechanism for direct antifungal action. Furthermore, ATI-2307 selectively targets fungal mitochondria via a fungal-specific transporter that is not present in mammalian cells. It has very potent in vitro anticryptococcal activity. In this study, the efficacy of ATI-2307 was tested in a rabbit model of CM. ATI-2307 demonstrated significant fungicidal activity at dosages between 1 and 2 mg/kg/d, and these results were superior to fluconazole and similar to amphotericin B treatment. When ATI-2307 was combined with fluconazole, the antifungal effect was greater than either therapy alone. While ATI-2307 has potent anticryptococcal activity in the subarachnoid space, its ability to reduce yeasts in the brain parenchyma was relatively less over the same study period. This new drug, with its unique mechanism of fungicidal action and ability to positively interact with an azole, has demonstrated sufficient anticryptococcal potential in this experimental setting to be further evaluated in clinical studies.

Combatting antifungal resistance: Paradigm shift in the diagnosis and management of onychomycosis and dermatomycosis

Antifungal resistance has become prevalent worldwide. Understanding the factors involved in spread of resistance allows the formulation of strategies to slow resistance development and likewise identify solutions for the treatment of highly recalcitrant fungal infections. To investigate the recent explosion of resistant strains, a literature review was performed focusing on four main areas: mechanisms of resistance to antifungal agents, diagnosis of superficial fungal infections, management, and stewardship. The use of traditional diagnostic tools such as culture, KOH analysis and minimum inhibitory concentration values on treatment were investigated and compared to the newer techniques such as molecular methods including whole genome sequencing, and polymerase chain reaction. The management of terbinafine-resistant strains is discussed. We have emphasized the need for antifungal stewardship including increasing surveillance for resistant infection.

Recent Progress in Research on Mitochondrion-Targeted Antifungal Drugs: a Review

Fungal infections, which commonly occur in immunocompromised patients, can cause high morbidity and mortality. Antifungal agents act by disrupting the cell membrane, inhibiting nucleic acid synthesis and function, or inhibiting β-1,3-glucan synthase. Because the incidences of life-threatening fungal infections and antifungal drug resistance are continuously increasing, there is an urgent need for the development of new antifungal agents with novel mechanisms of action. Recent studies have focused on mitochondrial components as potential therapeutic drug targets, owing to their important roles in fungal viability and pathogenesis. In this review, we discuss novel antifungal drugs targeting mitochondrial components and highlight the unique fungal proteins involved in the electron transport chain, which is useful for investigating selective antifungal targets. Finally, we comprehensively summarize the efficacy and safety of lead compounds in clinical and preclinical development. Although fungus-specific proteins in the mitochondrion are involved in various processes, the majority of the antifungal agents target dysfunction of mitochondria, including mitochondrial respiration disturbance, increased intracellular ATP, reactive oxygen species generation, and others. Moreover, only a few drugs are under clinical trials, necessitating further exploration of possible targets and development of effective antifungal agents. The unique chemical structures and targets of these compounds will provide valuable hints for further exploiting new antifungals.

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.

Potential Strategies to Control the Risk of Antifungal Resistance in Humans: A Comprehensive Review

Fungal infections are becoming one of the main causes of morbidity and mortality in people with weakened immune systems. Mycoses are becoming more common, despite greater knowledge and better treatment methods, due to the regular emergence of resistance to the antifungal medications used in clinical settings. Antifungal therapy is the mainstay of patient management for acute and chronic mycoses. However, the limited availability of antifungal drug classes limits the range of available treatments. Additionally, several drawbacks to treating mycoses include unfavourable side effects, a limited activity spectrum, a paucity of targets, and fungal resistance, all of which continue to be significant issues in developing antifungal drugs. The emergence of antifungal drug resistance has eliminated accessible drug classes as treatment choices, which significantly compromises the clinical management of fungal illnesses. In some situations, the emergence of strains resistant to many antifungal medications is a major concern. Although new medications have been developed to address this issue, antifungal drug resistance has grown more pronounced, particularly in patients who need long-term care or are undergoing antifungal prophylaxis. Moreover, the mechanisms that cause resistance must be well understood, including modifications in drug target affinities and abundances, along with biofilms and efflux pumps that diminish intracellular drug levels, to find novel antifungal drugs and drug targets. In this review, different classes of antifungal agents, and their resistance mechanisms, have been discussed. The latter part of the review focuses on the strategies by which we can overcome this serious issue of antifungal resistance in humans.

The Arylamidine T-2307 as a Novel Treatment for the Prevention and Eradication of Candida tropicalis Biofilms

Candida tropicalis is an emerging pathogen with a high mortality rate due to its virulence factors, including biofilm formation, that has important repercussions on the public health system. The ability of C. tropicalis to form biofilms, which are potentially more resistant to antifungal drugs and the consequent increasing antimicrobial resistance, highlights an urgent need for the development of novel antifungal. The present study analyzed the antibiofilm capacity of the arylamidine T-2307 on two strains of Candida tropicalis. Antimicrobial activity and time-killing assays were performed to evaluate the anticandidal effects of T-2307, the antibiofilm ability on biomass inhibition and eradication was evaluated by the crystal violet (CV) method. Furthermore, in Galleria mellonella infected larvae an increased survival after pre-and post- treatment with T-2307 was observed. The MTT test was used to determine the viability of immortalized human prostate epithelial cells (PNT1A) after exposure to different concentrations of T-2307. Levels of interleukin IL-4, IL-8, IL-10 were quantified after Candida infection of PNT1A cells and treatment. Active doses of T-2307 did not affect the viability of PNT1A cells, and drug concentrations of 0.005 or 0.01 µg mL^-1 inhibited the secretion of inflammatory cytokines. Taken together, these results provide new information on T-2307, indicating this drug as a new and promising alternative therapeutic option for the treatment of Candida infections.

Therapeutic Approaches for Combating Aspergillus Associated Infection

Now-a-days fungal infection emerges as a significant problem to healthcare management systems due to high frequency of associated morbidity, mortality toxicity, drug-drug interactions, and resistance of the antifungal agents. Aspergillus is the most common mold that cause infection in immunocompromised hosts. It's a hyaline mold that is cosmopolitan and ubiquitous in nature. Aspergillus infects around 10 million population each year with a mortality rate of 30-90%. Clinically available antifungal formulations are restricted to four classes (i.e., polyene, triazole, echinocandin, and allylamine), and each of them have their own limitations associated with the activity spectrum, the emergence of resistance, and toxicity. Consequently, novel antifungal agents with modified and altered chemical structures are required to combat these invasive fungal infections. To overcome these limitations, there is an urgent need for new antifungal agents that can act as potent drugs in near future. Currently, some compounds have shown effective antifungal activity. In this review article, we have discussed all potential antifungal therapies that contain old antifungal drugs, combination therapies, and recent novel antifungal formulations, with a focus on the Aspergillus associated infections.

Invasive candidiasis: Investigational drugs in the clinical development pipeline and mechanisms of action

INTRODUCTION

The epidemiology of invasive Candida infections is evolving. Infections caused by non-albicans Candida spp. are increasing; however, the antifungal pipeline is more promising than ever and is enriched with repurposed drugs and agents that have new mechanisms of action. Despite progress, unmet needs in the treatment of invasive candidiasis remain and there are still too few antifungals that can be administered orally or that have CNS penetration.

AREAS COVERED

The authors shed light on those antifungal agents active against Candida that are in late-stage clinical development. Mechanisms of action and key pharmacokinetic and pharmacodynamic properties are discussed. Insights are offered on the potential future roles of the investigational agents MAT-2203, oteseconazole, ATI-2307, VL-2397, NP-339, and the repurposed drug miltefosine.

EXPERT OPINION

Ibrexafungerp and fosmanogepix have novel mechanisms of action and will provide effective options for the treatment of Candida infections (including those caused by multiresistant Candida spp). Rezafungin, an echinocandin with an extended half-life allowing for once weekly administration, will be particularly valuable for outpatient treatment and prophylaxis. Despite this, there is an urgent need to garner clinical data on investigational drugs, especially in the current rise of azole-resistant and multi-drug resistant Candida spp.

Drug Resistance and Novel Therapeutic Approaches in Invasive Candidiasis

Candida species are the leading cause of invasive fungal infections worldwide and are associated with acute mortality rates of ~50%. Mortality rates are further augmented in the context of host immunosuppression and infection with drug-resistant Candida species. In this review, we outline antifungal drugs already in clinical use for invasive candidiasis and candidaemia, their targets and mechanisms of resistance in clinically relevant Candida species, encompassing not only classical resistance, but also heteroresistance and tolerance. We describe novel antifungal agents and targets in pre-clinical and clinical development, including their spectrum of activity, antifungal target, clinical trial data and potential in treatment of drug-resistant Candida. Lastly, we discuss the use of combination therapy between conventional and repurposed agents as a potential strategy to combat the threat of emerging resistance in Candida.

Emerging Issues in Antifungal Resistance

Invasive fungal diseases continue to cause substantial mortality in the enlarging immunocompromised population. It is fortunate that the field has moved past amphotericin B deoxycholate as the only available antifungal drug but despite new classes of antifungal agents both primary and secondary drug resistance in molds and yeasts abound. From the rise of multiple-drug-resistant Candida auris to the agrochemical selection of environmental azole-resistant Aspergillus fumigatus, it is and will be critical to understand antifungal drug resistance and both prevent and treat it with new strategies and agents.

Promising Drug Candidates and New Strategies for Fighting against the Emerging Superbug Candida auris

Invasive fungal infections represent an expanding threat to public health. During the past decade, a paradigm shift of candidiasis from Candida albicans to non-albicans Candida species has fundamentally increased with the advent of Candida auris. C. auris was identified in 2009 and is now recognized as an emerging species of concern and underscores the urgent need for novel drug development strategies. In this review, we discuss the genomic epidemiology and the main virulence factors of C. auris. We also focus on the different new strategies and results obtained during the past decade in the field of antifungal design against this emerging C. auris pathogen yeast, based on a medicinal chemist point of view. Critical analyses of chemical features and physicochemical descriptors will be carried out along with the description of reported strategies.

Review of T-2307, an Investigational Agent That Causes Collapse of Fungal Mitochondrial Membrane Potential

Invasive infections caused by Candida that are resistant to clinically available antifungals are of increasing concern. Increasing rates of fluconazole resistance in non-albicans Candida species have been documented in multiple countries on several continents. This situation has been further exacerbated over the last several years by Candida auris, as isolates of this emerging pathogen that are often resistant to multiple antifungals. T-2307 is an aromatic diamidine currently in development for the treatment of invasive fungal infections. This agent has been shown to selectively cause the collapse of the mitochondrial membrane potential in yeasts when compared to mammalian cells. In vitro activity has been demonstrated against Candida species, including C. albicans, C. glabrata, and C. auris strains, which are resistant to azole and echinocandin antifungals. Activity has also been reported against Cryptococcus species, and this has translated into in vivo efficacy in experimental models of invasive candidiasis and cryptococcosis. However, little is known regarding the clinical efficacy and safety of this agent, as published data from studies involving humans are not currently available.

The Future of Antifungal Drug Therapy: Novel Compounds and Targets

Fungal infections are a universal problem and are routinely associated with high morbidity and mortality rates in immunocompromised patients. Existing therapies comprise five different classes of antifungal agents, four of which target the synthesis of ergosterol and cell wall glucans. However, the currently available antifungals have many limitations, including poor oral bioavailability, narrow therapeutic indices, and emerging drug resistance resulting from their use, thus making it essential to investigate the development of novel drugs which can overcome these limitations and add to the antifungal armamentarium. Advances have been made in antifungal drug discovery research and development over the past few years as evidenced by the presence of several new compounds currently in various stages of development. In the following minireview, we provide a comprehensive summary of compounds aimed at one or more novel molecular targets. We also briefly describe potential pathways relevant for fungal pathogenesis that can be considered for drug development in the near future.

Novel Antifungal Agents and Their Activity against Aspergillus Species

There is a need for new antifungal agents, mainly due to increased incidence of invasive fungal infections (IFI), high frequency of associated morbidity and mortality and limitations of the current antifungal agents (e.g., toxicity, drug-drug interactions, and resistance). The clinically available antifungals for IFI are restricted to four main classes: polyenes, flucytosine, triazoles, and echinocandins. Several antifungals are hampered by multiple resistance mechanisms being present in fungi. Consequently, novel antifungal agents with new targets and modified chemical structures are required to combat fungal infections. This review will describe novel antifungals, with a focus on the Aspergillus species.

Efficacy of T-2307, a novel arylamidine, against ocular complications of disseminated candidiasis in mice

OBJECTIVES

T-2307, a novel arylamidine, shows broad-spectrum activity against pathogenic fungi, including Candida albicans. Ocular candidiasis is one of the serious complications associated with Candida bloodstream infection and is known to be refractory to conventional antifungal agents. The aim of the present study was to clarify the effectiveness of T-2307 against ocular candidiasis using a mouse model.

METHODS

We evaluated ocular fungal burden in mice infected with C. albicans that received treatment with antifungal agents [T-2307, liposomal amphotericin B (LAMB) or fluconazole] for 3 consecutive days. We also assessed survival rates of mice after C. albicans infection followed by treatment for 7 consecutive days. In addition, ocular T-2307 concentrations and in vitro effectiveness against C. albicans biofilm formation were evaluated.

RESULTS

The ocular fungal burdens were significantly reduced after T-2307 treatment compared with the control group (no treatment received) and were comparable with those observed following treatment with LAMB or fluconazole in both early- and late-phase treatment experiments. In addition, all of the mice treated with antifungal agents survived for 3 weeks after infection, whereas mice in the control group died within 3 days. The ocular T-2307 trough concentration was maintained above the MIC in the infected mice. An in vitro biofilm inhibition experiment showed that T-2307 suppressed C. albicans biofilm formation at the sub-MIC level, which was comparable with amphotericin B.

CONCLUSIONS

Given these results in experimental disseminated candidiasis, T-2307 may be an effective treatment against the complication of ocular candidiasis.

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.

Hope on the Horizon: Novel Fungal Treatments in Development

The treatment of invasive fungal infections remains challenging due to limitations in currently available antifungal therapies including toxicity, interactions, restricted routes of administration, and drug resistance. This review focuses on novel therapies in clinical development, including drugs and a device. These drugs have novel mechanisms of action to overcome resistance, and some offer new formulations providing distinct advantages over current therapies to improve safety profiles and reduce interactions. Among agents that target the cell wall, 2 glucan synthesis inhibitors are discussed (rezafungin and ibrexafungerp), as well as fosmanogepix and nikkomycin Z. Agents that target the cell membrane include 3 fourth-generation azoles, oral encochleated amphotericin B, and aureobasidin A. Among agents with intracellular targets, we will review olorofim, VL-2397, T-2307, AR-12, and MGCD290. In addition, we will describe neurapheresis, a device used as adjunctive therapy for cryptococcosis. With a field full of novel treatments for fungal infections, the future looks promising.

The Novel Arylamidine T-2307 Selectively Disrupts Yeast Mitochondrial Function by Inhibiting Respiratory Chain Complexes

The novel arylamidine T-2307 exhibits broad-spectrum in vitro and in vivo antifungal activities against clinically significant pathogens. Previous studies have shown that T-2307 accumulates in yeast cells via a specific polyamine transporter and disrupts yeast mitochondrial membrane potential. Further, it has little effect on rat liver mitochondrial function.

The novel arylamidine T-2307 exhibits broad-spectrum in vitro and in vivo antifungal activities against clinically significant pathogens. Previous studies have shown that T-2307 accumulates in yeast cells via a specific polyamine transporter and disrupts yeast mitochondrial membrane potential. Further, it has little effect on rat liver mitochondrial function. The mechanism by which T-2307 disrupts yeast mitochondrial function is poorly understood, and its elucidation may provide important information for developing novel antifungal agents. This study aimed to determine how T-2307 promotes yeast mitochondrial dysfunction and to investigate the selectivity of this mechanism between fungi and mammals. T-2307 inhibited the respiration of yeast whole cells and isolated yeast mitochondria in a dose-dependent manner. The similarity of the effects of T-2307 and respiratory chain inhibitors on mitochondrial respiration prompted us to investigate the effect of T-2307 on mitochondrial respiratory chain complexes. T-2307 particularly inhibited respiratory chain complexes III and IV not only in Saccharomyces cerevisiae but also in Candida albicans, indicating that T-2307 acts against pathogenic fungi in a manner similar to that of yeast. Conversely, T-2307 showed little effect on bovine respiratory chain complexes. Additionally, we demonstrated that the inhibition of respiratory chain complexes by T-2307 resulted in a decrease in the intracellular ATP levels in yeast cells. These results indicate that inhibition of respiratory chain complexes III and IV is a key factor for selective disruption of yeast mitochondrial function and antifungal activity.

Opciones terapéuticas frente a especies de Candida resistentes a las equinocandinas

<p><strong>Introducción</strong>: La infección por levaduras del género <em>Candida</em> representa la causa más común de infecciones fúngicas invasivas. Su alta incidencia y la creciente resistencia frente a los azoles y, recientemente, a las equinocandinas ha generado la necesidad de buscar nuevas alternativas farmacológicas. Esta revisión presenta las principales alternativas farmacológicas en estudio frente a <em>Candida</em> resistente a equinocandinas. <strong>Métodos</strong>: Se buscó literatura referente al tema en las bases de datos Bireme, Clinical Key, Embase, Cochrane, Lilacs, Pubmed y Scopus. Se incluyeron 15 artículos en esta revisión. <strong>Resultados</strong>: Se exploran diferentes alternativas, incluyendo el aumento de dosis de las equinocandinas, su combinación con otros medicamentos y nuevos compuestos en estudio. <strong>Conclusión</strong>: A pesar de que las infecciones por <em>Candida</em> resistente a equinocandinas aún representan un desafío, dos alternativas farmacológicas se presentan como promisorias: la combinación con medicamentos existentes como el diclofenaco y nuevos compuestos que se encuentran actualmente en fase II de estudios clínicos.</p><p> </p>

What has changed in the treatment of invasive candidiasis? A look at the past 10 years and ahead

The treatment of invasive candidiasis has changed greatly in the past decade and must continue to evolve if we are to improve outcomes in this serious infection. A review of recent history may provide insights for the future. The morbidity and mortality of invasive candidiasis remain difficult to measure despite an obvious clinical burden. Current treatment guidelines now recommend echinocandins as first-line empirical treatment, with fluconazole as an acceptable alternative for selected patients, reflecting the efficacy demonstrated by echinocandins and increasing resistance observed with fluconazole. The selection of antifungal therapy now must consider not only resistance but also the shift in predominance from Candida albicans to non-albicans species, notably Candida glabrata. The recent emergence of Candida auris has been met with great interest, although the longer-term implications of this phenomenon remain unclear. The broad goal of treatment continues to be administration of safe, efficacious antifungal therapy as soon as possible. Diagnostic methods beyond traditional blood culture present an opportunity to shorten the time to an accurate diagnosis, and earlier treatment initiation based on prophylactic and empirical or pre-emptive strategies seeks to ensure timely therapeutic intervention. In addition, there are novel agents in the antifungal pipeline. These developments, as well as ongoing studies of dosing, toxicity and resistance development, are important items on the current research agenda and may play a role in future changes to the treatment of invasive candidiasis.

The antifungal arsenal: alternative drugs and future targets

Clinically available antifungals for the treatment of invasive fungal infections primarily target either ergosterol in the fungal cell membrane or 1,3-β-D-glucan in the fungal cell wall. These classes include the polyene amphotericin B, the triazoles, and the echinocandins. Although newer antifungals and improved formulations of others have advanced our ability to treat patients with invasive mycoses, these drugs are often limited by toxicities, drug interactions, and the need for intravenous administration. Several investigational agents are currently under development. These include those that also target either ergosterol or 1,3-β-D-glucan, but have advantages over currently available drugs. Among these are the tetrazoles VT-1129, VT-1161, and VT-1598 that are more specific for fungal Cyp51 and less so for mammalian CYP 450 enzymes, the echinocandin CD101 that has an extended half-life, and the glucan synthase inhibitor SCY-078, which is being developed for oral administration. In addition, several agents with novel mechanisms of action are also under development. These include the inositol acyltransferase AX001, the dihydroorotate dehydrogenase inhibitor F901318, and VL-2397, which is similar in structure to the siderophore ferrichrome. In addition to possibly overcoming the limitations of currently available antifungals, these newer agents may be less susceptible to mechanisms of resistance that may render antifungals ineffective. Each of these investigational agents has the potential to improve patient outcomes in the treatment of invasive mycoses.

Antifungal resistance: current trends and future strategies to combat

Antifungal resistance represents a major clinical challenge to clinicians responsible for treating invasive fungal infections due to the limited arsenal of systemically available antifungal agents. In addition current drugs may be limited by drug-drug interactions and serious adverse effects/toxicities that prevent their prolonged use or dosage escalation. Fluconazole resistance is of particular concern in non-Candida albicans species due to the increased incidence of infections caused by these species in different geographic locations worldwide and the elevated prevalence of resistance to this commonly used azole in many institutions. C. glabrata resistance to the echinocandins has also been documented to be rising in several US institutions, and a higher percentage of these isolates may also be azole resistant. Azole resistance in Aspergillus fumigatus due to clinical and environmental exposure to this class of agents has also been found worldwide, and these isolates can cause invasive infections with high mortality rates. In addition, several species of Aspergillus, and other molds, including Scedosporium and Fusarium species, have reduced susceptibility or pan-resistance to clinically available antifungals. Various investigational antifungals are currently in preclinical or clinical development, including several of them that have the potential to overcome resistance observed against the azoles and the echinocandins. These include agents that also target ergosterol and b-glucan biosynthesis, as well as compounds with novel mechanisms of action that may also overcome the limitations of currently available antifungal classes, including both resistance and adverse effects/toxicity.

The anti-Aspergillus drug pipeline: Is the glass half full or empty?

Aspergillosis has emerged as important human mycoses, in view of the ever expanding population at risk. The emergence of resistance to the most commonly used drugs for aspergillosis, the azoles, the mediocre activity, and frequent toxicity of the current antifungal armamentarium, support the need for development of novel antifungals for treatment of this disease. In this minireview, we describe recent efforts by small drug companies and University research labs to develop novel therapies for invasive aspergillus infections. We specifically discuss four small-molecule antifungals (T-2307, E1210/APX001, ASP2397, and F901318) with novel modes-of-action, which are currently entering phase I clinical trials. In addition, we provide a nonexhaustive discussion of some interesting, yet early developments in the quest for improved therapeutic strategies such as (i) novel formulations of amphotericin B including AMB nanoparticle suspensions and AMB-arabinogalactan or AMB-PEG conjugates that show low toxicity and high efficacy in preclinical animal models, (ii) repurposed drugs that synergize with existing antifungals (clozafimine, trichostatin A, MGCD290, geldanamycin, tacrolimus, cyclosporin), (iii) natural products (psoriasin, humidimycin), and (iv) immunotherapy using adoptive transfer of activated immune cells with antifungal activity. We argue that despite the plethora of candidates, the extremely low success rates of drug development leading to clinically useful drugs reinforces the need for continued clinical reliance on mainstream antifungals and their improved derivatives.

New Horizons in Antifungal Therapy

Recent investigations have yielded both profound insights into the mechanisms required by pathogenic fungi for virulence within the human host, as well as novel potential targets for antifungal therapeutics. Some of these studies have resulted in the identification of novel compounds that act against these pathways and also demonstrate potent antifungal activity. However, considerable effort is required to move from pre-clinical compound testing to true clinical trials, a necessary step toward ultimately bringing new drugs to market. The rising incidence of invasive fungal infections mandates continued efforts to identify new strategies for antifungal therapy. Moreover, these life-threatening infections often occur in our most vulnerable patient populations. In addition to finding completely novel antifungal compounds, there is also a renewed effort to redirect existing drugs for use as antifungal agents. Several recent screens have identified potent antifungal activity in compounds previously indicated for other uses in humans. Together, the combined efforts of academic investigators and the pharmaceutical industry is resulting in exciting new possibilities for the treatment of invasive fungal infections.

What's new in antifungals: an update on the in-vitro activity and in-vivo efficacy of new and investigational antifungal agents

PURPOSE OF REVIEW

Despite the availability of new antifungals and improved antifungal formulations, there is a continued need for the development of new drugs to treat invasive fungal infections. In high-risk populations, including heavily immunocompromised patients, those with multiple comorbidities, and patients in intensive care settings, invasive fungal infections remain a significant problem, and are associated with high morbidity and mortality. In addition, concerns of increasing antifungal resistance to available agents further highlight the need for new drugs to treat these infections.

RECENT FINDINGS

Recent studies have reported potent in-vitro activity for several investigational agents, including both yeasts and moulds. This in-vitro activity has also translated into in-vivo efficacy in animal models of various invasive fungal infections, including those caused by isolates that are resistant to clinically available agents. These agents include those with mechanisms of action similar to available agents and those that target fungi by novel means.

SUMMARY

Several new antifungal agents are currently in various stages of development. This is promising, as there is a continued need for new agents to treat invasive fungal infections. Which ones will receive approval for clinical use and their impact in patients with these infections remain unknown.

A complex game of hide and seek: the search for new antifungals

Fungal infections directly affect millions of people each year. In addition to the invasive fungal infections of humans, the plants and animals that comprise our primary food source are also susceptible to diseases caused by these eukaryotic microbes. The need for antifungals, not only for our medical needs, but also for use in agriculture and livestock causes a high demand for novel antimycotics. Herein, we provide an overview of the most commonly used antifungals in medicine and agriculture. We also present a summary of the recent progress (from 2010-2016) in the discovery/development of new agents against fungal strains of medical/agricultural relevance, as well as information related to their biological activity, their mode(s) of action, and their mechanism(s) of resistance.

T-2307, a novel arylamidine, is transported into Candida albicans by a high-affinity spermine and spermidine carrier regulated by Agp2

OBJECTIVES

T-2307, a novel arylamidine, exhibits potent broad-spectrum activities against pathogenic fungi, particularly Candida albicans. We previously reported that T-2307 uptake was mainly mediated by a saturable high-affinity carrier at the MIC for C. albicans. Since we hypothesized that the potent anticandidal activity arose from accumulation via the high-affinity carrier, we characterized the specificity and kinetic features of the carrier.

METHODS

The MICs of T-2307 for C. albicans strains were evaluated in the presence and absence of potential competitive substrates. The cells were exposed to [(14)C]T-2307, [(14)C]spermine or [(14)C]spermidine in the presence of unlabelled T-2307, pentamidine, propamidine, or competitive substrates if necessary, and the radioactivity in the cells was measured. C. albicans gene deletion was performed using a one-step PCR-based technique.

RESULTS

Coapplication with exogenous spermine or spermidine decreased the antifungal activity and uptake of T-2307 in C. albicans strains. T-2307 competitively inhibited spermine and spermidine uptake with inhibition constants similar to its Km for the high-affinity carrier. The comparison of MICs and kinetic values between T-2307 and other diamidine compounds suggested that the different antifungal properties could be partially attributable to the variations in their affinity with the carrier. Studies of gene deletion mutants revealed that T-2307 was transported into C. albicans by a high-affinity spermine and spermidine carrier regulated by Agp2.

CONCLUSIONS

Uptake of T-2307 via the high-affinity spermine and spermidine carrier regulated by Agp2 could contribute to its potent antifungal activity. Further investigation is required to identify the high-affinity carrier for potential targeting with novel therapies.

Synergistic combinations of antifungals and anti-virulence agents to fight against Candida albicans

Candida albicans, one of the pathogenic Candida species, causes high mortality rate in immunocompromised and high-risk surgical patients. In the last decade, only one new class of antifungal drug echinocandin was applied. The increased therapy failures, such as the one caused by multi-drug resistance, demand innovative strategies for new effective antifungal drugs. Synergistic combinations of antifungals and anti-virulence agents highlight the pragmatic strategy to reduce the development of drug resistant and potentially repurpose known antifungals, which bypass the costly and time-consuming pipeline of new drug development. Anti-virulence and synergistic combination provide new options for antifungal drug discovery by counteracting the difficulty or failure of traditional therapy for fungal infections.

The novel arylamidine T-2307 demonstrates in vitro and in vivo activity against echinocandin-resistant Candida glabrata

OBJECTIVES

Candida species are major causes of invasive mycoses in immunocompetent and immunocompromised hosts. Treatment options are limited in the setting of antifungal resistance and increased rates of echinocandin-resistant Candida glabrata have been reported. The novel arylamidine T-2307 demonstrates potent in vitro antifungal activity against Candida species. Our objective was to evaluate the in vitro and in vivo activity of T-2307 against resistant C. glabrata.

METHODS

In vitro activity was determined against 42 clinical C. glabrata isolates, including 17 echinocandin-resistant strains. Neutropenic ICR mice were inoculated intravenously with an echinocandin-resistant C. glabrata isolate (T-2307; caspofungin MICs ≤0.008 and 0.5 mg/L, respectively). Therapy with vehicle control, T-2307 (0.75, 1.5, 3 or 6 mg/kg subcutaneously once daily) or caspofungin (1 or 10 mg/kg intraperitoneally once daily) began 1 day post-challenge. Kidneys were collected on day 8 and fungal burden was assessed by counting cfu.

RESULTS

T-2307 demonstrated potent in vitro activity against C. glabrata (geometric mean MIC 0.0135 mg/L), which was maintained against echinocandin-resistant isolates (geometric mean MIC 0.0083 mg/L). T-2307 also demonstrated in vivo efficacy in mice infected with echinocandin-resistant C. glabrata. Significant reductions in fungal burden were observed at each dosage level of T-2307 compared with control. Reductions in fungal burden were also observed with high-dose caspofungin.

CONCLUSIONS

T-2307 demonstrated potent in vitro activity against C. glabrata, including echinocandin-resistant isolates, which translated into in vivo efficacy against invasive candidiasis caused by an echinocandin-resistant C. glabrata strain. These results demonstrate the potential for T-2307 as therapy against echinocandin-resistant Candida.

Cell surface changes in the Candida albicans mitochondrial mutant goa1Δ are associated with reduced recognition by innate immune cells

We have previously characterized several fungal-specific proteins from the human pathogen Candida albicans that either encode subunits of mitochondria Complex I (CI) of the electron transport chain (ETC) or regulate CI activity (Goa1p). Herein, the role of energy production and cell wall gene expression is investigated in the mitochondria mutant goa1Δ. We show that downregulation of cell wall-encoding genes in the goa1Δ results in sensitivity to cell wall inhibitors such as Congo red and Calcofluor white, reduced phagocytosis by a macrophage cell line, reduced recognition by macrophage receptors, and decreased expression of cytokines such as IL-6, IL-10 and IFN-γ. In spite of the reduced recognition by macrophages, the goa1Δ is still killed to the same extent as control strains. We also demonstrate that expression of the epithelial cell receptors E-cadherin and EGFR is also reduced in the presence of goa1Δ. Together, our data demonstrate the importance of mitochondria in the expression of cell wall biomolecules and the interaction of C. albicans with innate immune and epithelial cells. Our underlying premise is thatmitochondrial proteins such as Goa1p and other fungal-specific mitochondrial proteins regulate critical functions in cell growth and in virulence. As such, they remain as valid drug targets for antifungal drug discovery.

Antifungal activity of azole compounds CPA18 and CPA109 against azole-susceptible and -resistant strains of Candida albicans

OBJECTIVES

In this study we investigated the in vitro fungistatic and fungicidal activities of CPA18 and CPA109, two azole compounds with original structural features, alone and in combination with fluconazole against fluconazole-susceptible and -resistant Candida albicans strains.

METHODS

Antifungal activities were measured by MIC evaluation and time-kill studies. Azole binding analysis was performed by UV-Vis spectroscopy. Hyphal growth inhibition and filipin and propidium iodide staining assays were used for morphological analysis. An analysis of membrane lipids was also performed to gauge alterations in membrane composition and integrity. Synergism was calculated using fractional inhibitory concentration indices (FICIs). Evaluation of cytotoxicity towards murine macrophages was performed to verify selective antifungal activity.

RESULTS

Even though their binding affinity to C. albicans Erg11p is comparable to that of fluconazole, CPA compounds are active against resistant strains of C. albicans with a mutation in ERG11 sequences and/or overexpressing the ABC transporter genes CDR1 and CDR2, which encode ATP-dependent efflux pumps. Moreover, CPA18 is fungistatic, even against the two resistant strains, and was found to be synergistic with fluconazole. Differently from fluconazole and other related azoles, CPA compounds induced marked changes in membrane permeability and dramatic alterations in membrane lipid composition.

CONCLUSIONS

Our outcomes suggest that CPA compounds are able to overcome major mechanisms of resistance in C. albicans. Also, they are promising candidates for combination treatment that could reduce the toxicity caused by high fluconazole doses, particularly in immunocompromised patients.

T-2307 causes collapse of mitochondrial membrane potential in yeast

T-2307, an arylamidine compound, has been previously reported to have broad-spectrum in vitro and in vivo antifungal activities against clinically significant pathogens, including Candida species, Cryptococcus neoformans, and Aspergillus species, and is now undergoing clinical trials. Here we investigated the mechanism of action of T-2307 using yeast cells and mitochondria isolated from yeast and rat liver. Nonfermentative growth of Candida albicans and Saccharomyces cerevisiae in glycerol medium, in which yeasts relied on mitochondrial respiratory function, was inhibited at 0.001 to 0.002 μg/ml (0.002 to 0.004 μM) of T-2307. However, fermentative growth in dextrose medium was not inhibited by T-2307. Microscopic examination using Mitotracker fluorescent dye, a cell-permeant mitochondrion-specific probe, demonstrated that T-2307 impaired the mitochondrial function of C. albicans and S. cerevisiae at concentrations near the MIC in glycerol medium. T-2307 collapsed the mitochondrial membrane potential in mitochondria isolated from S. cerevisiae at 20 μM. On the other hand, in isolated rat liver mitochondria, T-2307 did not have any effect on the mitochondrial membrane potential at 10 mM. Moreover, T-2307 had little inhibitory and stimulatory effect on mitochondrial respiration in rat liver mitochondria. In conclusion, T-2307 selectively disrupted yeast mitochondrial function, and it was also demonstrated that the fungal mitochondrion is an attractive antifungal target.

In vitro and in vivo antimalarial activities of T-2307, a novel arylamidine

T-2307, a novel arylamidine, has been shown to exhibit broad-spectrum antifungal activities against clinically significant pathogens. Here, we evaluated the in vitro and in vivo antimalarial activity of T-2307. The 50% inhibitory concentrations (IC₅₀s) of T-2307 against Plasmodium falciparum FCR-3 and K-1 strains were 0.47 and 0.17 μM, respectively. T-2307 at 2.5 to 10 mg/kg of body weight/day exhibited activity against blood stage and liver stage parasites in rodent malaria models. In conclusion, T-2307 exhibited in vitro and in vivo antimalarial activity.