Drugs in Clinical Development for Fungal Infections

Photoactivated riboflavin inhibits planktonic and biofilm growth of Candida albicans and non-albicans Candida species

Fungal infections caused by Candida species pose a serious threat to humankind. Antibiotics abuse and the ability of Candida species to form biofilm have escalated the emergence of drug resistance in clinical settings and hence, rendered it more difficult to treat Candida-related diseases. Lethal effects of Candida infection are often due to inefficacy of antimicrobial treatments and failure of host immune response to clear infections. Previous studies have shown that a combination of riboflavin with UVA (riboflavin/UVA) light demonstrate candidacidal activity albeit its mechanism of actions remain elusive. Thus, this study sought to investigate antifungal and antibiofilm properties by combining riboflavin with UVA against Candida albicans and non-albicans Candida species. The MIC20 for the fluconazole and riboflavin/UVA against the Candida species tested was within the range of 0.125-2 μg/mL while the SMIC50 was 32 μg/mL. Present findings indicate that the inhibitory activities exerted by riboflavin/UVA towards planktonic cells are slightly less effective as compared to controls. However, the efficacy of the combination towards Candida species biofilms showed otherwise. Inhibitory effects exerted by riboflavin/UVA towards most of the tested Candida species biofilms points towards a variation in mode of action that could make it an ideal alternative therapeutic for biofilm-related infections.

An update on the global treatment of invasive fungal infections

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

Emerging Diagnostics and Therapeutics for Invasive Fungal Infections

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

Novel Approaches in the Management of Mucormycosis

Purpose of Review

Invasive mucormycosis (IM), caused by fungi of the order Mucorales, is one of the deadliest fungal infection among hematologic cancer patients. Its incidence is also increasingly reported in immunocompetent individuals, notably with the COVID-19 pandemic. Therefore, there is an urgent need for novel diagnostic and therapeutic approaches of IM. This review discusses the current advances in this field.

Recent Findings

Early diagnosis of IM is crucial and can be improved by Mucorales-specific PCR and development of lateral-flow immunoassays for specific antigen detection. The spore coat proteins (CotH) are essential for virulence of the Mucorales and may represent a target for novel antifungal therapies. Adjuvant therapies boosting the immune response, such as interferon-γ, anti-PDR1 or fungal-specific chimeric antigen receptor (CAR) T-cells, are also considered.

Summary

The most promising perspectives for improved management of IM consist of a multilayered approach targeting both the pathogen and the host immune system.

Validation and clinical evaluation of an ultra-performance liquid chromatography with ultraviolet detector method for plasma quantification of micafungin

BACKGROUND

Factors associated with interindividual variability in the pharmacokinetics of micafungin have been identified. This variability can cause underexposure and loss of drug efficacy. For this reason, a simple, fast, cost-effective and sensitive ultra-performance liquid chromatography ultraviolet detector (UPLC-UV) method was developed and validated for the quantification of micafungin.

METHODS

The method involves simple plasma precipitation by UPLC with a reversed phase C18 column at 40°C coupled with ultraviolet detection set at a wavelength of 264 nm. The mobile phase consisted of a mixture 42/58 of potassium phosphate 20 mm and acetonitrile.

RESULTS

The method was validated over the concentration range of 0.25-15.0 mg/L and proved to be reliable and reproducible with an average percentage of recoveries of 101.59 ± 3.93% and inter and intraday variation coefficients lower than 15% in all cases. The method was successfully applied in determining 30 samples from 10 patients being treated with micafungin.

CONCLUSIONS

The method proposed could be useful to facilitate the implementation of therapeutic drug monitoring for personalizing micafungin treatment in invasive fungal 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.

New Antifungal Agents with Azole Moieties

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

Development and research progress of anti-drug resistant fungal drugs

With the widespread use of immunosuppressive agents and the increase in patients with severe infections, the incidence of fungal infections worldwide has increased year by year. The fungal pathogens Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus cause a total of more than 1 million deaths each year. Long-term use of antifungal drugs can easily lead to fungal resistance, and the prevalence of drug-resistant fungi is a major global health challenge. In order to effectively control global fungal infections, there is an urgent need for new drugs that can exert effective antifungal activity and overcome drug resistance. We must promote the discovery of new antifungal targets and drugs, and find effective ways to control drug-resistant fungi through different ways, so as to reduce the threat of drug-resistant fungi to human life, health and safety. In the past few years, certain progress has been made in the research and development of antifungal drugs. In addition to summarizing some of the antifungal drugs currently approved by the FDA, this review also focuses on potential antifungal drugs, the repositioned drugs, and drugs that can treat drug-resistant bacteria and fungal infections, and provide new ideas for the development of antifungal drugs in the future.

Evaluation of the Post-Antifungal Effect of Rezafungin and Micafungin against Candida albicans, Candida parapsilosis, and Candida glabrata

BACKGROUND

Rezafungin, a new echinocandin with an extended half-life, exhibits potent activity against Candida spp. Aside from the MIC, specific interactions between antifungal and isolate, including the duration of anti-infective activity, may impact dose interval choices and infection outcome.

OBJECTIVES

We evaluated rezafungin and micafungin post-antifungal effect (PAFE) against C. albicans, C. parapsilosis, and C. glabrata.

METHODS

Six Candida spp. isolates were tested, including 2 of each species, C. albicans, C. parapsilosis, and C. glabrata. Antifungal susceptibility testing was performed using the CLSI reference broth microdilution method. Antifungal concentrations of 1X, 4X, and 16X the baseline MIC were used for PAFE determinations. Colony counts were performed at T0 (pre-exposure), after the 1-h drug exposure, after the cell wash (T1), and at T2, T4, T8, T12, T24, and T48 hours.

RESULTS

Rezafungin PAFE results were equivalent to micafungin PAFE values for one C. albicans (>14.9 h and both C. glabrata (>40 h) isolates for all concentrations tested. The rezafungin and micafungin PAFEs could not be determined against one C. albicans isolate. Prolonged PAFE results were also noted for rezafungin (range, 18.4 h to >40 h) against both C. parapsilosis isolates at all concentrations, while no micafungin PAFE or a short PAFE (range, 1.8 h to 7.4 h) was observed against these organisms, except at 16X bMIC.

CONCLUSIONS

Rezafungin showed sustained growth inhibition following drug removal and displayed equivalent or longer PAFE values than micafungin against all tested Candida spp.

Novel 1,2,3-Triazole-Coumarin Hybrid Glycosides and Their Tetrazolyl Analogues: Design, Anticancer Evaluation and Molecular Docking Targeting EGFR, VEGFR-2 and CDK-2

This study represents the design and synthesis of a new set of triazole-coumarin-glycosyl hybrids and their tetrazole hybrid analogues possessing various sugar moieties and modified analogues. All the newly synthesized derivatives were screened for their cytotoxic activities against a panel of human cancer cell lines. The coumarin derivatives 10, 13 and 15 derivatives revealed potent cytotoxic activities against Paca-2, Mel-501, PC-3 and A-375 cancer cell lines. These promising analogues were further examined for their inhibitory assessment against EGFR, VEGFR-2 and CDK-2/cyclin A2 kinases. The coumarin-tetrazole 10 displayed broad superior inhibitory activity against all screened enzymes compared with the reference drugs, erlotinib, sorafenib and roscovitine, respectively. The impact of coumarin-tetrazole 10 upon cell cycle and apoptosis induction was determined to detect its mechanism of action. Additionally, it upregulated the levels of casp-3, casp-7 and cytochrome-c proteins and downregulated the PD-1 level. Finally, molecular docking study was simulated to afford better rationalization and gain insight into the binding affinity between the promising derivatives and their targeted enzymes, which could be used as an optimum lead for further modification in the anticancer field.

Antifungal Drugs TDM: Trends and Update

PURPOSE

The increasing burden of invasive fungal infections results in growing challenges to antifungal (AF) therapeutic drug monitoring (TDM). This review aims to provide an overview of recent advances in AF TDM.

METHODS

We conducted a PubMed search for articles during 2016-2020 using "TDM" or "pharmacokinetics" or "drug-drug-interaction" with "antifungal," consolidated for each AF. Selection was limited to English language articles with human data on drug exposure.

RESULTS

More than 1000 articles matched the search terms. We selected 566 publications. The latest findings tend to confirm previous observations in real-life clinical settings. The pharmacokinetic variability related to special populations is not specific but must be considered. AF benefit-to-risk ratio, drug-drug interaction (DDI) profiles, and minimal inhibitory concentrations for pathogens must be known to manage at-risk situations and patients. Itraconazole has replaced ketoconazole in healthy volunteers DDI studies. Physiologically based pharmacokinetic modeling is widely used to assess metabolic azole DDI. AF prophylactic use was studied more for Aspergillus spp. and Mucorales in oncohematology and solid organ transplantation than for Candida (already studied). Emergence of central nervous system infection and severe infections in immunocompetent individuals both merit special attention. TDM is more challenging for azoles than amphotericin B and echinocandins. Fewer TDM requirements exist for fluconazole and isavuconazole (ISZ); however, ISZ is frequently used in clinical situations in which TDM is recommended. Voriconazole remains the most challenging of the AF, with toxicity limiting high-dose treatments. Moreover, alternative treatments (posaconazole tablets, ISZ) are now available.

CONCLUSIONS

TDM seems to be crucial for curative and/or long-term maintenance treatment in highly variable patients. TDM poses fewer cost issues than the drugs themselves or subsequent treatment issues. The integration of clinical pharmacology into multidisciplinary management is now increasingly seen as a part of patient care.

8-hydroxyquinoline and quinazoline derivatives as potential new alternatives to combat Candida spp. biofilm

Often associated to the colonization by Candida spp. biofilm, the catheter-related infections are a serious health problem since the absence of a specific therapy. Hence, the main objective of this work was to evaluate the activity of 8-hydroxyquinoline and quinazoline derivatives on Candida spp. biofilms. A quinazoline derivative (PH100) and an 8-hydroxyquinoline derivative (PH157) were tested against nine strains of C. albicans, C. tropicalis and C. parapsilosis, and their biofilms in polystyrene microtitre plates and on polyurethane central venous catheter. The PH157 compound was incorporated into a film-forming system-type formulation and its capacity to inhibit biofilm formation on catheters was evaluated. The compounds were active against planktonic and sessile cells, as well as against the tested biofilms. PH157 compound performed better than the PH100 compound. The formulation containing PH157 presented results very similar to those of the compound in solution, which indicates that its activity was preserved. Both compounds showed activity against Candida spp. strains and their biofilm, with better PH157 activity. The formulation preserved the action of the PH157 compound, in addition, it facilitates its application on the catheter. The structural modifications that these compounds allow can generate compounds that are even more active, both against planktonic cells and biofilms.

Study of antifungal agent caspofungin adsorption to laboratory materials

Treatment of invasive fungal infections with Caspofungin is used as the first-line antifungal agents. The minimum inhibitory concentration value is a test which indicates the degree of sensitivity of a strain regarding a drug. However, no value of minimum inhibitory concentration for caspofungin is available because very variable value is obtained. In this work, we study the link with the adsorption phenomenon of CSF previously described in literature and the lack of minimum inhibitory concentration value. A systematic study of the impact of different parameters on CSF adsorption is reported. The effect of the nature of container material, the aqueous solution pH and the organic solvent proportion was studied. In addition, the possibility of using a coating agent to minimize the adsorption was assayed and evaluated. Results obtained showed the importance of the material used during the manipulation of CSF. The use of acidic pH aqueous solution or the addition of acetonitrile or methanol proportions (50 % and 70 %, respectively) were found efficient to avoid adsorption of CSF on glassware material, which is the relevant strategy for analytical samples of caspofungin. The treatment of HPLC glass vials and 96-well plates with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane reduced the adsorption. The significant adsorption observed in this work especially with plastic materials, questions the results obtained before in different assays and explained the absence of MIC value.

Medicines for Malaria Venture COVID Box: a source for repurposing drugs with antifungal activity against human pathogenic fungi

BACKGROUND

Treatment of mycoses is often ineffective, usually prolonged, and has some side effects. These facts highlight the importance of discovering new molecules to treat fungal infections.

OBJECTIVES

To search the Medicines for Malaria Venture COVID Box for drugs with antifungal activity.

METHODS

Fourteen human pathogenic fungi were tested against the 160 drugs of this collection at 1.0 µM concentration. We evaluated the ability of the drugs to impair fungal growth, their fungicidal nature, and morphological changes caused to cells.

FINDINGS

Thirty-four molecules (21.25%) presented antifungal activity. Seven are antifungal drugs and one is the agricultural fungicide cycloheximide. The other drugs with antifungal activity included antibiotics (n = 3), antimalarials (n = 4), antivirals (n = 2), antiparasitcs (n = 3), antitumor agents (n = 5), nervous system agents (n = 3), immunosuppressants (n = 3), antivomiting (n = 1), antiasthmatic (n = 1), and a genetic disorder agent (n = 1). Several of these drugs inhibited Histoplasma capsulatum and Paracoccidioides brasiliensis growth (15 and 20, respectively), while Fusarium solani was not affected by the drugs tested. Most drugs were fungistatic, but niclosamide presented fungicidal activity against the three dimorphic fungi tested. Cyclosporine affected morphology of Cryptococcus neoformans.

MAIN CONCLUSIONS

These drugs represent new alternatives to the development of more accessible and effective therapies to treat human fungal infections.

Scedosporium and Lomentospora Infections Are Infrequent, Difficult to Diagnose by Histology, and Highly Virulent

OBJECTIVE

To further characterize the histomorphology and clinicopathologic features of colonization and invasive disease by Scedosporium and Lomentospora.

METHODS

We conducted a 20-year retrospective study. Patients with at least 1 histopathology specimen and concurrent culture were included. Clinical features, histopathology, microbiology, and outcomes were analyzed.

RESULTS

Eighteen patients were identified, and all were immunocompromised. Eight patients had colonization, while 10 had invasive disease (pneumonia [n = 3], skin and soft-tissue infections [n = 3], disseminated disease [n = 4]). Scedosporium apiospermum was identified in 15 patients, Lomentospora prolificans in 2 patients, and Scedosporium ellipsoideum in 1 patient. Fungal elements were identified histologically in 11 patients. Granulomatous, suppurative, and necrotizing inflammation with irregular branching hyphae and characteristic microconidia were observed in 9 cases; conidiogenous cells were identified in 4 cases. Seven patients died of invasive disease despite therapy, and 3 recovered after treatment. No deaths were observed in patients with colonization.

CONCLUSIONS

Scedosporium and Lomentospora are rare, virulent opportunistic fungal pathogens. Fungal morphology may overlap with other hyaline molds, but identification of obovoid conidia should allow a diagnosis of non-Aspergillus hyalohyphomycosis and consideration of Scedosporium and Lomentospora. Histopathologic correlation with culture and polymerase chain reaction is critical for diagnosis and treatment.

How urgent is the need for new antifungals?

Introduction: Invasive fungal infection carries a high morbidity, mortality and economic cost. In recent times, a rising incidence of fungal infection and antifungal resistance is occurring which has prompted the development of novel antifungal agents.Areas covered:In this perspective, the authors describe the current status of registered antifungals and their limitations in the treatment of invasive fungal infection. They also go on to describe the new antifungal agents that are in the clinical stage of development and how they might be best utilized in patient care in the future.Expert opinion: The antifungal drug development pipeline has responded to a growing need for new agents to effectively treat fungal disease without concomitant toxicity or issues with drug tolerance. Olorofim (F901318), ibrexafungerp (SCY-078), fosmanogepix (APX001), rezafungin (CD101), oteseconazole (VT-1161), encochleated amphotericin B (MAT2203), nikkomycin Z (NikZ) and ATI-2307 are all in the clinical stage of development and offer great promise in offering clinicians better agents to treat these difficult infections.

Anti-HIV and Anti-Candidal Effects of Methanolic Extract from Heteropterys brachiata

Nowadays, the HIV pandemic is far from controlled. HIV+/AIDS patients show a serious risk of developing resistance to HIV antiretroviral drugs and to be orally colonized by albicans and non-albicans Candida strains resistant to antifungals. As a consequence, new drugs that possess anti-candidal and anti-HIV effects would represent an alternative in the comprehensive treatment of HIV+/AIDS patients. The present study evaluates the possible anti-HIV and anti-Candida effects of a methanolic extract from Heteropterys brachiata (Hb MeOH), an American tropical plant. The anti-HIV effect of Hb MeOH was tested using a non-radioactive colorimetric method (Lenti RT^® Activity Assay; Cavidi Tech) that uses reverse transcriptase of HIV-1 enzyme as enzymatic target. The anti-candidal effect of HbMeOH extract was evaluated by following a standardized test protocol of microdilution for yeast using the Candida albicans strain ATCC^® 90028. The Hb MeOH at 1 mg/mL concentration shows 38.5% RT-HIV inhibition, while Hb MeOH at 10 mg/mL concentration produced 98% C. albicans growth inhibition. Our findings show that the Hb MeOH possesses a strong anti-candidal activity and moderate anti-HIV effect and suggests that the plant extract could be considered as a potential candidate for HIV/AIDS treatment.

A Review of Characteristics, Properties, Application of Nanocarriers and Analytical Methods of Luliconazole

Luliconazole is an imidazole agent, used for the treatment of fungi infection, especially dermatophytes. The mechanism of action of the drug consisting in inhibits sterol 14α-demethylase which interferes with ergosterol biosynthesis. Due to low aqueous solubility and highly lipophilic, there is a need to develop drug delivery systems (nanocarriers) capable to increase the solubility, permeability, and skin retention of luliconazole, and promote a better therapeutic effect. In this context, this review presents characteristics, properties, nanocarriers, and analytical methods used for luliconazole. From the analyzed studies, the majority reports the use of RP-HPLC techniques for luliconazole determination, but also are cited spectrophotometric UV methods. The luliconazole has been qualitatively and quantitatively analyzed in different matrices, such as raw material and pharmaceutical formulations, however, in this review, only one study was found with the luliconazole quantification biological matrix, demonstrating the lack of studies related to the quantification of the drug in biological matrices. The drug quantification in different matrices by analytical methods is of great importance since they assist in the control of the quality, efficacy, and safety of the medicine.

Preclinical safety evaluation of amphotericin A21: A novel antifungal

Safety studies are essential in drug development. This study evaluates the safety of Amphotericin A21 (AmB-A21), a derivative of amphotericin B with antifungal therapeutic potential. We performed a chronic toxicity study, a targeted organ study and a dermal irritation test. To evaluate chronic toxicity, 18 male adult rats were treated orally with AmB-21 (2 mg/kg) for 26 weeks. The effects on body-weight and animal health were measured, and haematological, clinical chemistry and histopathological tests were conducted on various organs. In the target organ toxicity study, male adult rats received a daily oral dose of AmB-21 (2 mg/kg) for 6 and 17 weeks; testicle histology and testosterone levels were then evaluated. For the dermal irritation study, AmB-21 (200 and 1000 mg/kg) was placed on the skin of adult male rabbits; macroscopic and microscopic studies, as well as haematological and clinical chemistry tests were then conducted. The chronic toxicity study revealed that AmB-21 caused testicle damage, and the testicle-targeted study showed structural alterations and changes in testosterone levels at 17 weeks. However, these alterations were no longer observed 8 weeks after discontinuation of treatment, and the testes showed very similar characteristics to those in the control group. The dermal irritation study showed skin thickening and reddening in rabbits treated with 2000 mg of AmB-A21 after 14 days of exposure. This same group also showed changes in liver enzymes, renal parameters and platelet levels. Based on our results, we consider AmB-21 to be a potential candidate for safe, long-term antifungal treatment given its reduced side effects.

Innovations for prevention and care of oral candidiasis in HIV-infected individuals: Are they available?-A workshop report

Oral candidiasis (OC) is the most prevalent HIV-related oral lesion in patients on combined anti-retroviral therapy (cART) or without cART. Management is challenged in some patients by development of resistance to azole drugs, such as fluconazole. Recent scientific knowledge about OC pathogenesis, the role of OC in the immune reconstitution inflammatory syndrome (IRIS), the relationship of OC with the microbiome, and novelties in OC treatment was discussed in an international workshop format. Literature searches were conducted to address five questions: (a) Considering the pathogenesis of Candida spp. infection, are there any potential therapeutic targets that could be considered, mainly in HIV-infected individuals resistant to fluconazole? (b) Is oral candidiasis part of IRIS in HIV patients who receive cART? (c) Can management of the oral microbiome reduce occurrence of OC in patients with HIV infection? (d) What are the recent advances (since 2015) regarding plant-based and alternative medicines in management of OC? and (e) Is there a role for photodynamic therapy in management of OC in HIV-infected patients? A number of the key areas where further research is necessary were identified to allow a deeper insight into this oral condition that could help to understand its nature and recommend alternatives for care.

Nikkomycin Z-Ready to Meet the Promise?

Nikkomycin Z (NikZ) has fungicidal activity against some fungal species which currently requires patients to endure chronic therapy, sometimes for years. This review highlights reports of NikZ activity against fungal species for which current therapeutics are still inadequate, as a potential roadmap for continuing investigation. The possibility of faster and more complete clinical resolution by using NikZ has attracted scientific attention for decades. NikZ inhibits chitin structure formation, which is important for fungi, but not found in mammals. NikZ raised no safety concerns in a human Phase 1 trial or in extensive toxicology studies. NikZ showed strong clinical benefit in dogs with natural Coccidioides infection. NikZ has protected animals against fatal infections of Candida albicans. NikZ provides high protection in synergistic combination with several agent classes against Candida and Aspergillus species.

Molecular Elucidation of Riboflavin Production and Regulation in Candida albicans, toward a Novel Antifungal Drug Target

Candida albicans is an important fungal pathogen causing common superficial infections as well as invasive diseases with an extremely high morbidity and mortality. Antifungal therapies are limited in efficiency and availability. In this research, we describe the regulation of riboflavin production in C. albicans. Since riboflavin biosynthesis is essential to this organism, we can appreciate that targeting it would be a promising new strategy to combat these fungal infections. We provide evidence that one particular enzyme in the production process, CaRib1, would be most promising as an antifungal drug target, as it plays a central role in regulation and proves to be essential in a mouse model of systemic infection.

Candida albicans is a major cause of fungal infections, both superficial and invasive. The economic costs as well as consequences for patient welfare are substantial. Only a few treatment options are available due to the high resemblance between fungal targets and host molecules, as both are eukaryotes. Riboflavin is a yellow pigment, also termed vitamin B₂. Unlike animals, fungi can synthesize this essential component themselves, thereby leading us to appreciate that targeting riboflavin production is a promising novel strategy against fungal infections. Here, we report that the GTP cyclohydrolase encoded by C. albicansRIB1 (CaRIB1) is essential and rate-limiting for production of riboflavin in the fungal pathogen. We confirm the high potential of CaRib1 as an antifungal drug target, as its deletion completely impairs in vivo infectibility by C. albicans in model systems. Furthermore, the stimulating effect of iron deprivation and PKA activation on riboflavin production seems to involve CaRib1 and the upstream transcription factor CaSef1. Gathering insights in the synthesis mechanism of riboflavin in pathogenic fungi, like C. albicans, will allow us to design a novel strategy and specifically target this process to combat fungal infections.

IMPORTANCECandida albicans is an important fungal pathogen causing common superficial infections as well as invasive diseases with an extremely high morbidity and mortality. Antifungal therapies are limited in efficiency and availability. In this research, we describe the regulation of riboflavin production in C. albicans. Since riboflavin biosynthesis is essential to this organism, we can appreciate that targeting it would be a promising new strategy to combat these fungal infections. We provide evidence that one particular enzyme in the production process, CaRib1, would be most promising as an antifungal drug target, as it plays a central role in regulation and proves to be essential in a mouse model of systemic infection.

Host-pathogen interaction in Candida glabrata infection: current knowledge and implications for antifungal therapy

INTRODUCTION

The opportunistic fungal pathogen Candida glabrata poses a clinical challenge in the successful treatment of invasive Candida infections, owing to its low inherent susceptibility toward azole antifungals and the recent acquisition of coresistance toward azole and echinocandin drugs. Compared to other prevalent Candida bloodstream pathogens, C. glabrata neither exhibits secreted proteolytic activity nor invokes a strong immune response in a variety of host cells and is less virulent. It also does not form true hyphae, and the success of C. glabrata, therefore, as a prevalent human fungal pathogen, appears to be built upon a distinct set of virulence attributes.

AREAS COVERED

The focus of this review is to outline, in brief, the interaction of C. glabrata with the host, deduced from the knowledge gained from different in vitro, ex vivo, and in vivo model systems. In addition, we briefly discuss the current antifungals, antifungal resistance mechanisms, and the development of new antifungal therapies, along with the available information on the host response.

EXPERT OPINION

A detailed understanding of stresses, selection pressures and differential immune responses in the presence and absence of antifungals that C. glabrata encounters in varied niches of the host, is required to design effective antifungal therapy.

A Series of Furan-based Hydrazones: Design, Synthesis, and Evaluation of Antimicrobial Activity, Cytotoxicity and Genotoxicity

Background:

Hydrazones, frequently occurring motifs in many bioactive molecules, have attracted a great deal of interest as potent antimicrobial agents.

Objective:

The aim of this work was to design and synthesize new hydrazone-based antimicrobial agents.

Methods:

4-[2-((5-Arylfuran-2-yl)methylene)hydrazinyl]benzonitrile derivatives (1-10) were obtained via the reaction of 4-cyanophenylhydrazine hydrochloride with 5-arylfurfurals. Compounds 1-10 were evaluated for their antimicrobial effects using a broth microdilution method. Their cytotoxic effects on NIH/3T3 mouse embryonic fibroblast cell line were determined using XTT assay. The most effective antimicrobial agents were investigated for their genotoxic effects using Ames MPF assay. In silico docking and Absorption, Distribution, Metabolism and Excretion (ADME) studies were also performed using Schrödinger’s Maestro molecular modeling package.

Results:

The antifungal effects of the compounds were more significant than their antibacterial effects. Compound 5 bearing 3-nitrophenyl moiety was the most potent antifungal agent against Candida albicans, Trichoderma harzianum and Fusarium species, whereas compound 10 bearing 4- chloro-2-nitrophenyl moiety was the most effective antifungal agent on Aspergillus ochraceus. According to XTT and Ames MPF assays, these compounds were neither cytotoxic nor genotoxic at the concentrations tested. Docking studies suggested that these compounds showed good affinity to the active site of lanosterol 14α-demethylase (CYP51) (PDB code: 5V5Z) and interacted with the key residues such as Hem601 and Cys470. Based on in silico ADME studies, the compounds are expected to have high oral bioavailability.

Conclusion:

According to the in vitro and in silico studies, compounds 5 and 10 stand out as potential orally bioavailable antifungal agents for further studies.

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.

Antifungal drugs: What brings the future?

The high burden and growing prevalence of invasive fungal infections (IFIs), the toxicity and interactions associated with current antifungal drugs, as well as the increasing resistance, ask for the development of new antifungal drugs, preferably with a novel mode of action. Also, the availability of oral or once-weekly alternatives would enable ambulatory treatment resulting in an improved patient's comfort and therapy adherence. However, only one new azole and two new posaconazole-formulations were marketed over the last decade. This review focuses on the antifungal drugs in the pipeline undergoing clinical evaluation. First, the newest azole, isavuconazole, with its improved safety profile and reduction in DDIs, will be discussed. Moreover, there are two glucan synthase inhibitors (GSIs) in the antifungal pipeline: rezafungin (CD101), a long-acting echinocandin with an improved stability that enables once weekly administration, and SCY-078, an orally available GSI with efficacy against azole- and echinocandin resistant isolates. A new oral formulation of amphotericin B will also be presented. Moreover, the first representative of a new antifungal class, the orotomides, with a broad spectrum and no cross-resistance with current antifungal classes, will be discussed. Finally, an overview of other antifungals that are still in earlier clinical development phases, is provided.

Dihydroorotate dehydrogenase inhibitors in anti-infective drug research

Pyrimidines are essential for the cell survival and proliferation of living parasitic organisms, such as Helicobacter pylori, Plasmodium falciparum and Schistosoma mansoni, that are able to impact upon human health. Pyrimidine building blocks, in human cells, are synthesised via both de novo biosynthesis and salvage pathways, the latter of which is an effective way of recycling pre-existing nucleotides. As many parasitic organisms lack pyrimidine salvage pathways for pyrimidine nucleotides, blocking de novo biosynthesis is seen as an effective therapeutic means to selectively target the parasite without effecting the human host. Dihydroorotate dehydrogenase (DHODH), which is involved in the de novo biosynthesis of pyrimidines, is a validated target for anti-infective drug research. Recent advances in the DHODH microorganism field are discussed herein, as is the potential for the development of DHODH-targeted therapeutics.

Extended Dosing Regimens for Fungal Prophylaxis

Invasive fungal diseases carry high morbidity and mortality in patients undergoing chemotherapy for hematological malignancies or allogeneic hematopoietic stem cell transplantation. In order to prevent these life-threatening infections, antifungal chemoprophylaxis plays an important role in daily clinical practice. Broad-spectrum antifungal triazoles are widely used but exhibit disadvantages such as relevant drug-drug interactions. Therefore, amphotericin B products or echinocandins can be an alternative in selected patient populations. As these compounds are available as intravenous formulations only, there is growing interest in extended dosing regimens. Although not approved for these agents, this strategy is a rational option, as these compounds have properties suitable for this strategy, including dose-proportional pharmacokinetics, prolonged elimination half-life, and a large therapeutic window. As the use of extended dosing regimens in antifungal prophylaxis is expanding in clinical practice, we reviewed the pharmacokinetic and pharmacodynamic rationale for this strategy, animal model data, dose escalation studies, and clinical trials supporting this concept.

Chromatographic methods for echinocandin antifungal drugs determination in bioanalysis

The increase of fungal resistance to drugs, such as azole family, gave rise to the development of new antifungals. In this context, echinocandins emerged as a promising alternative for antifungal therapies. Following the commercialization of caspofungin in 2001, echinocandins became the first-line therapy for invasive candidiasis in different patient populations. The quantification of these drugs has gained importance since pharmacokinetic/pharmacodynamic and resistance studies are a paramount concern. This fact has led us to exhaustively examine the methodologies used for the analysis of echinocandins in biological fluids, which are mainly based on LC coupled to different detection techniques. In this review, we summarize the analytical methods for the quantification of echinocandins focusing on sample treatment, chromatographic separation and detection methods.

Tetrazole hybrids with potential anticancer activity

Cancer is one of the main causes of death throughout the world. The anticancer agents are indispensable for the treatment of various cancers, but most of them currently on the market are not specific, resulting in series of side effects of chemotherapy. Moreover, the emergency of drug-resistance towards cancers has already increased up to alarming level in the recent decades. Therefore, it's imperative to develop novel anticancer candidates with excellent activity against both drug-susceptible and drug-resistant cancers, and low toxicity as well. Tetrazole is the bioisoster of carboxylic acid, and its derivatives demonstrated promising anticancer activity. Hybridization of tetrazole with other anticancer pharmacophores may provide novel candidates with anticancer potency. The present review described the anticancer activity of tetrazole hybrids, and the structure-activity relationship (SAR) is also discussed to provide an insight for rational designs of tetrazole anticancer candidates with higher efficiency.

APX001 Pharmacokinetic/Pharmacodynamic Target Determination against Aspergillus fumigatus in an In Vivo Model of Invasive Pulmonary Aspergillosis

APX001, the prodrug of APX001A, is a first-in-class antifungal agent that has a potent activity against Aspergillus fumigatus The goal of current study was to determine the pharmacodynamic (PD) index and target of APX001 in an immunocompromised murine model of invasive pulmonary aspergillosis against 6 A. fumigatus isolates. Minimum effective concentration (MEC) values ranged from 0.03 to 0.06 mg/liter. Dose fractionation was performed against isolate AF293 using total doses of APX001 ranging from 81 to 768 mg/kg of body weight/day fractionated into every 3-, 6-, and 8-h regimens over a 96-h treatment duration. Efficacy was assessed by A. fumigatus quantitative PCR (qPCR) of conidial equivalents from lung homogenates. Nonlinear regression analysis using the Hill equation demonstrated that the 24-h area under the concentration-time curve (AUC)/MEC ratio was the pharmacokinetic (PK)/PD index that best correlated with efficacy (coefficient of determination [R ²] = 0.79). Treatment studies with the remaining strains utilized regimens of 40 to 1,536 mg/kg of APX001 administered every 3 h for a 96-h duration. Exposure-response relationships for all strains were similar, and the median free drug AUC/MEC PK/PD targets for stasis and 1-log-kill endpoints were 47.6 and 89.4, respectively. The present studies demonstrated in vitro and in vivo APX001A/APX001 potency against A. fumigatus These results have potential relevance for clinical dose selection and evaluation of susceptibility breakpoints.

The fungal cell wall as a target for the development of new antifungal therapies

In the past three decades invasive mycoses have globally emerged as a persistent source of healthcare-associated infections. The cell wall surrounding the fungal cell opposes the turgor pressure that otherwise could produce cell lysis. Thus, the cell wall is essential for maintaining fungal cell shape and integrity. Given that this structure is absent in host mammalian cells, it stands as an important target when developing selective compounds for the treatment of fungal infections. Consequently, treatment with echinocandins, a family of antifungal agents that specifically inhibits the biosynthesis of cell wall (1-3)β-D-glucan, has been established as an alternative and effective antifungal therapy. However, the existence of many pathogenic fungi resistant to single or multiple antifungal families, together with the limited arsenal of available antifungal compounds, critically affects the effectiveness of treatments against these life-threatening infections. Thus, new antifungal therapies are required. Here we review the fungal cell wall and its relevance in biotechnology as a target for the development of new antifungal compounds, disclosing the most promising cell wall inhibitors that are currently in experimental or clinical development for the treatment of some invasive mycoses.

Synthesis and Spectroscopic Identification of Certain Imidazole-Semicarbazone Conjugates Bearing Benzodioxole Moieties: New Antifungal Agents

During the last three decades the extent of life-threatening fungal infections has increased remarkably worldwide. Synthesis and structure elucidation of certain imidazole-semicarbazone conjugates 5a–o are reported. Single crystal X-ray analysis of compound 5e unequivocally confirmed its assigned chemical structure and the (E)-configuration of its imine double bond. Compound 5e crystallized in the triclinic system, P-1, a = 6.3561 (3) Å, b = 12.5095 (8) Å, c = 14.5411 (9) Å, α = 67.073 (4)°, β = 79.989 (4)°, γ =84.370 (4)°, V = 1048.05 (11) ų, Z = 2. In addition, DIZ and MIC assays were used to examine the in vitro antifungal activity of the title conjugates 5a–o against four fungal strains. Compound 5e, bearing a 4-ethoxyphenyl fragment, showed the best MIC value (0.304 µmol/mL) against both C. tropicalis and C. parapsilosis species, while compounds 5c (MIC = 0.311 µmol/mL), 5k, and 5l (MIC = 0.287 µmol/mL) exhibited the best anti-C. albicans activity.

Candidemia in the cancer patient: diagnosis, treatment, and future directions

INTRODUCTION

The presence of Candida species in the blood is known as candidemia and may constitute a medical emergency for patients with cancer. Despite advances in diagnosis and treatment of this fungal infection, mortality remains unacceptably high. Areas covered: This paper reviews recent advances in molecular diagnostics to detect species of Candida as well as novel antifungal agents that have been developed to address candidiasis. We also review prophylaxis strategies to prevent candidiasis in high-risk cancer patients. Expert commentary: We draw from our own experiences treating candidemia in the cancer patient and review novel diagnostic strategies involving molecular resonance and mass spectroscopy. We also explore novel chemoprophylaxis and treatment options, including new drugs such as rezafungin and SCY-078. We also look ahead, to examine how this condition will be managed in the years ahead.

In Vivo Pharmacokinetics and Pharmacodynamics of APX001 against Candida spp. in a Neutropenic Disseminated Candidiasis Mouse Model

APX001 is the prodrug of APX001A, which is a first-in-class small molecule with a unique mechanism of action that inhibits the fungal enzyme Gwt1 in the glycosylphosphatidylinositol (GPI) biosynthesis pathway. The goal of the present study was to determine which pharmacokinetic/pharmacodynamic (PK/PD) index and magnitude best correlated with efficacy in the murine disseminated candidiasis model for Candida albicans (n = 5), C. glabrata (n = 5), and C. auris (n = 4). MIC values ranged from 0.002 to 0.03 mg/liter for C. albicans, from 0.008 to 0.06 mg/liter for C. glabrata, and from 0.004 to 0.03 mg/liter for C. auris Plasma APX001A pharmacokinetic measurements were performed in mice after oral administration of 4, 16, 64, and 256 mg/kg of body weight APX001. Single-dose pharmacokinetic studies exhibited maximum plasma concentration (C_max) values of 0.46 to 15.6 mg/liter, area under the concentration-time curve (AUC) from time zero to infinity (AUC_0-inf) values of 0.87 to 70.0 mg · h/liter, and half-lives of 1.40 to 2.75 h. A neutropenic murine disseminated candidiasis model was utilized for all treatment studies, and drug dosing was by the oral route. Dose fractionation was performed against C. albicans K1, with total doses ranging from 4 to 1,024 mg/kg/day of APX001 fractionated into regimens of dosing every 3, 6, 8, and 12 h for a 24-h treatment duration. Nonlinear regression analysis was used to determine which PK/PD index best correlated with efficacy on the basis of the reduction in the number of CFU/kidney at 24 h. The 24-h free-drug AUC/MIC ratio (fAUC_0-24/MIC) was the PK/PD index that best correlated with efficacy (coefficient of determination [R²] = 0.88). Treatment studies with the remaining strains utilized regimens of 1 to 256 mg/kg of APX001 administered every 6 h for a 24-h duration with C. albicans and a 96-h study duration with C. glabrata and C. auris The dose required to achieve 50% of the maximum effect (ED₅₀) and stasis fAUC/MIC targets were as follows: for C. albicans, 3.67 ± 3.19 and 20.60 ± 6.50, respectively; for C. glabrata, 0.38 ± 0.21 and 1.31 ± 0.27, respectively; and for C. auris, 7.14 ± 4.54 and 14.67 ± 8.30, respectively. The present studies demonstrated in vitro and in vivo APX001A and APX001 potency, respectively, against C. albicans, C. glabrata, and C. auris. These results have potential relevance for clinical dose selection and evaluation of susceptibility breakpoints. The identification of a lower AUC/MIC ratio target for C. glabrata suggests that species-specific susceptibility breakpoints should be explored.

Amino Acid Metabolism and Transport Mechanisms as Potential Antifungal Targets

Discovering new drugs for treatment of invasive fungal infections is an enduring challenge. There are only three major classes of antifungal agents, and no new class has been introduced into clinical practice in more than a decade. However, recent advances in our understanding of the fungal life cycle, functional genomics, proteomics, and gene mapping have enabled the identification of new drug targets to treat these potentially deadly infections. In this paper, we examine amino acid transport mechanisms and metabolism as potential drug targets to treat invasive fungal infections, including pathogenic yeasts, such as species of Candida and Cryptococcus, as well as molds, such as Aspergillus fumigatus. We also explore the mechanisms by which amino acids may be exploited to identify novel drug targets and review potential hurdles to bringing this approach into clinical practice.

The synthesis, antifungal and apoptotic effects of triazole-oxadiazoles against Candida species

In search of potent and safe antifungal agents, herein, we report the synthesis, characterization and biological activities of triazole-oxadiazole compounds. The structural verification of the molecules was carried out by ¹H NMR, ¹³C NMR and mass spectral data. The in vitro antifungal and apoptotic activity were investigated against C. albicans, C. parapsilosis, C. krusei and C. glabrata. The compounds namely N-(4-nitrophenyl)-2-[(5-(2-((4-methyl-4H-1,2,4-triazol-3-yl)thio)ethyl)-1,3,4-oxadiazol-2-yl)thio]acetamide (4e) and N-(6-fluorobenzothiazol-2-yl)-2-[(5-(2-((4-methyl-4H-1,2,4-triazol-3-yl)thio)ethyl)-1,3,4-oxadiazol-2-yl)thio]acetamide (4i) were detected as the most potent compounds against C. albicans and C. glabrata (MIC₉₀ = 62.5 μg/mL). According to studies on their mechanism of action, it was confirmed that compound 4i has apoptotic effect on four Candida via Annexin V-PI with flow cytometry. The MTT assay revealed that all compounds were determined to be non-toxic against healthy cells in the tested concentrations.