Characterization of Antifungal Activity and Nail Penetration of ME1111, a New Antifungal Agent for Topical Treatment of Onychomycosis

Antidermatophyte activity and PK/PD of ME1111 in a guinea pig model of tinea corporis

Onychomycosis, a superficial fungal infection of the nails, is prevalent in many areas of the world. Topical agents for onychomycosis need to reach the subungual layer and nail bed to exert antifungal activity in the presence of keratin, the major component of the nail. It is difficult to evaluate the efficacy and pharmacodynamics of topical agents for onychomycosis in a non-clinical evaluation system. No consistent animal model has yet been established to predict the efficacy of topical agents for onychomycosis. In this study, we evaluated the pharmacokinetics and pharmacodynamics of ME1111 in a guinea pig model of tinea corporis designed to predict the efficacy of topical medication for onychomycosis in the vicinity of the nail bed. Trichophyton mentagrophytes TIMM1189 was infected on the back skin of guinea pigs, and ME1111 solution (5%, 10%, or 15%) was administered topically, once daily for 14 consecutive days. Following the completion of dosing, segments of skin from the site of infection were excised and cultured. The concentration of ME1111 in the back skin of guinea pigs increased with formulation concentration and correlated with mycological efficacy. We revealed the concentration required for ME1111 to be effective at the site of infection. Further analysis is needed to predict the efficacy of topical agents for onychomycosis by analyzing the relationship between PK/PD around the nail bed and factors such as subungual penetration and permeability.

Regional Differences in Antifungal Susceptibility of the Prevalent Dermatophyte Trichophyton rubrum

In vitro susceptibility testing for Trichophyton rubrum has shown resistance to terbinafine, azoles and amorolfine, locally, but epidemiological cutoffs are not available. In order to assess the appropriateness of current first-line antifungal treatment for T. rubrum in China, we characterized antifungal susceptibility patterns of Chinese T. rubrum strains to nine antifungals and also described the upper limits of wild-type (WT) minimal inhibitory concentrations (MIC) (UL-WT) based on our study and another six studies published during the last decades. Sixty-two clinical isolates originating from seven provinces in China were identified as T. rubrum sensu stricto; all Chinese strains showed low MICs to eight out of nine antifungal drugs. Terbinafine (TBF) showed the lowest MICs of all antifungal classes tested in both the Chinese and global groups, with a 97.5% UL-WT MIC-value of 0.03 mg/L. No non-WT isolates were observed for TBF in China, but were reported in 18.5% of the global group. Our study indicated that TBF was still the most active drug for Chinese T. rubrum isolates, and all strains were within the WT-population. TBF therefore remains recommended for primary therapy to dermatophytosis caused by T. rubrum in China now, but regular surveillance of dermatophytes and antifungal susceptibility is recommended.

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

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

ONYCHOMYCOSIS: A Review of New and Emerging Topical and Device-based Treatments

Onychomycosis is a challenging nail condition to treat. The gold standard treatment relies on long-term systemic therapy, which carries risks of potential side effects and drug interactions. Topical alternatives exist; however, treatment outcomes remain disappointing. In this article, we review newer topical formulations that are approved by the United States Food and Drug Administration, as well as other topical drugs that are still undergoing clinical trials. Lasers and energy-based devices have also been used for the treatment of onychomycosis; however, standardized parameters and clear treatment endpoints have yet to be specified. Currently, device-based therapies are considered as options for improving the cosmetic appearance of nails. The use of lasers to improve the penetration of topical antifungal treatments as possible combination treatments is also reviewed.

Low In Vitro Antifungal Activity of Tavaborole against Yeasts and Molds from Onychomycosis

The in vitro activity of tavaborole, an FDA-approved antifungal drug, was compared to that of four antifungal agents against 170 clinical fungal isolates originating from patients with onychomycosis. Tavaborole had low activity against all isolates compared to itraconazole, terbinafine, and fluconazole, the principal choices for treatment of onychomycosis. Thus, it appears that tavaborole is not a candidate for the treatment of onychomycosis due to Candida species, Aspergillus species, and dermatophytes.

Asymmetric Synthesis of Chiral 1,2-Amino Alcohols and Morpholin-2-ones from Arylglyoxals

Chiral 1,2-amino alcohols are privileged scaffolds with important applications as drug candidates and chiral ligands. Although various methods for the preparation of this structural motif have been reported, these methods are limited because of the use of precious metals and ligands. Here, we report a practical and high yielding synthesis of chiral 1,2-amino alcohols using arylglyoxals and pseudoephedrine auxiliary. This reaction is catalyzed by a Brønsted acid and provides morpholinone products in high yields and selectivities. The morpholine ring was converted into 1,2-amino alcohols in a two-step protocol.

In Vitro Human Onychopharmacokinetic and Pharmacodynamic Analyses of ME1111, a New Topical Agent for Onychomycosis

ME1111 is a novel antifungal agent currently under clinical development as a topical onychomycosis treatment. A major challenge in the application of topical onychomycotics is penetration and dissemination of antifungal agent into the infected nail plate and bed. In this study, pharmacokinetic/pharmacodynamic parameters of ME1111 that potentially correlate with clinical efficacy were compared with those of marketed topical onychomycosis antifungal agents: efinaconazole, tavaborole, ciclopirox, and amorolfine. An ME1111 solution and other launched topical formulations were applied to an in vitro dose model for 14 days based on their clinical dose and administration. Drug concentrations in the deep layer of the nail and within the cotton pads beneath the nails were measured using liquid chromatography-tandem mass spectrometry. Concentrations of ME1111 in the nail and cotton pads were much higher than those of efinaconazole, ciclopirox, and amorolfine. Free drug concentrations of ME1111 in deep nail layers and cotton pads were orders of magnitude higher than the MIC₉₀ value against Trichophyton rubrum (n = 30). Unlike other drugs, the in vitro antifungal activity of ME1111 was not affected by 5% human keratin and under a mild acidic condition (pH 5.0). The in vitro antidermatophytic efficacy coefficients (ratio of free drug concentration to MIC₉₀s against T. rubrum) of ME1111, as measured in deep nail layers, were significantly higher than those of efinaconazole, tavaborole, ciclopirox, and amorolfine (P < 0.05). This suggests that ME1111 has excellent permeation of human nails and, consequently, the potential to be an effective topical onychomycosis treatment.

Morphological Effect of the New Antifungal Agent ME1111 on Hyphal Growth of Trichophyton mentagrophytes, Determined by Scanning and Transmission Electron Microscopy

The effects of ME1111, a novel antifungal agent, on the hyphal morphology and ultrastructure of Trichophyton mentagrophytes were investigated by using scanning and transmission electron microscopy. Structural changes, such as pit formation and/or depression of the cell surface, and degeneration of intracellular organelles and plasmolysis were observed after treatment with ME1111. Our results suggest that the inhibition of energy production by ME1111 affects the integrity and function of cellular membranes, leading to fungal cell death.

Efficacy Coefficients Determined Using Nail Permeability and Antifungal Activity in Keratin-Containing Media Are Useful for Predicting Clinical Efficacies of Topical Drugs for Onychomycosis

Onychomycosis is difficult to treat topically due to the deep location of the infection under the densely keratinized nail plate. In order to obtain an in vitro index that is relevant to the clinical efficacy of topical anti-onychomycosis drugs, we profiled five topical drugs: amorolfine, ciclopirox, efinaconazole, luliconazole, and terbinafine, for their nail permeabilities, keratin affinities, and anti-dermatophytic activities in the presence of keratin. Efinaconazole and ciclopirox permeated full-thickness human nails more deeply than luliconazole. Amorolfine and terbinafine did not show any detectable permeation. The free-drug concentration of efinaconazole in a 5% human nail keratin suspension was 24.9%, which was significantly higher than those of the other drugs (1.1-3.9%). Additionally, efinaconazole was released from human nail keratin at a greater proportion than the other drugs. The MICs of the five drugs for Trichophyton rubrum were determined at various concentrations of keratin (0-20%) in RPMI 1640 medium. The MICs of ciclopirox were not affected by keratin, whereas those of efinaconazole were slightly increased and those of luliconazole and terbinafine were markedly increased in the presence of 20% keratin. Efficacy coefficients were calculated using the nail permeation flux and MIC in media without or with keratin. Efinaconazole showed the highest efficacy coefficient, which was determined using MIC in media with keratin. The order of efficacy coefficients determined using MIC in keratin-containing media rather than keratin-free media was consistent with that of complete cure rates in previously reported clinical trials. The present study revealed that efficacy coefficients determined using MIC in keratin-containing media are useful for predicting the clinical efficacies of topical drugs. In order to be more effective, topical drugs have to possess higher efficacy coefficients.

Evaluation of the Efficacy of ME1111 in the Topical Treatment of Dermatophytosis in a Guinea Pig Model

The treatment of dermatophytoses, including onychomycosis, has come a long way over the past few decades with the introduction of oral antifungals (e.g., terbinafine and itraconazole). However, with these advancements in oral therapies come several undesirable effects, such as kidney and liver toxicity, along with drug-drug interactions. Consequently, there is a need for new topical agents that are effective against dermatophytosis. ME1111 is a topical antifungal under development. In this study, thein vivoefficacy of ME1111 was compared to that of ciclopirox in the topical treatment of dermatophytosis caused byTrichophyton mentagrophytesusing a guinea pig model. Animals were treated with the topical antifungals starting at 3 days postinfection, with each agent being applied once daily for seven consecutive days. After the treatment period, the clinical and mycological efficacies were evaluated. The data showed that both antifungals demonstrated significant clinical and mycological efficacies; however, ME1111 showed clinical efficacy superior to that of ciclopirox (46.9% and 25.0%, respectively, with aPvalue of <0.001). The potent efficacy of ME1111 could be attributed to its properties, such as low keratin binding.

Multilaboratory Evaluation of In Vitro Antifungal Susceptibility Testing of Dermatophytes for ME1111

ME1111 is a novel small molecule antifungal agent under development for the topical treatment of onychomycosis. Standardization of the susceptibility testing method for this candidate antifungal is needed. Toward this end, 8 independent laboratories determined the interlaboratory reproducibility of ME1111 susceptibility testing. In addition, we subsequently identified 2 strains as quality control (QC) isolates for the method. In the reproducibility study, 5 blinded clinical strains each of Trichophyton rubrum, Trichophyton mentagrophytes, and Epidermophyton floccosum were tested, while the QC study tested 6 blinded T. rubrum or T. mentagrophytes ATCC strains. Testing was performed in frozen microtiter panels according to the Clinical and Laboratory Standards Institute (CLSI) M38-A2 methodology. In the reproducibility study, 9 of 15 clinical strains showed interlaboratory agreement of >90% at the 80% inhibition endpoint, with a range of agreement of 76.2% to 100%. In the QC study, 4 of the 6 ATCC strains showed interlaboratory agreement of >90%. ME1111 demonstrated excellent interlaboratory agreement when tested against dermatophytes. Based on this data, the CLSI Subcommittee on Antifungal Susceptibility Tests approved the susceptibility testing of ME1111 against dermatophytes according to M38-A2 methodology, which stipulates RPMI 1640 as the test medium, an inoculum size of 1 to 3 × 10(3) CFU/ml, and an incubation time and temperature of 96 h at 35°C. The MIC endpoint should be 80% inhibition compared with the growth control. T. rubrum ATCC MYA-4438 and T. mentagrophytes ATCC 28185 were selected as QC isolates, with an acceptable range of 0.12 to 1 μg/ml for the two strains.