A Short-Tandem-Repeat Assay (MmySTR) for Studying Genetic Variation in Madurella mycetomatis

Ibrexafungerp prolongs survival and reduces the eumycetoma grain size in Galleria mellonella infection models of two different causative agents of eumycetoma

OBJECTIVES

Eumycetoma is a neglected tropical fungal disease of the subcutaneous tissue that is currently not treatable with medication only. Standard itraconazole therapy is combined with surgical excision of the lesion. Recently, ibrexafungerp, a novel oral antifungal agent inhibiting 1,3-β-D-glucan synthesis, was approved by the United States Food and Drug Administration (FDA) for the treatment of vulvovaginal candidiasis. In this study we determined the in vitro activity and in vivo efficacy of ibrexafungerp in eumycetoma causative agents.

METHODS

In vitro activity of ibrexafungerp and itraconazole was determined against 30 Madurella and 7 Falciformispora isolates by standardized in vitro susceptibility assays. The in vivo efficacy of ibrexafungerp, itraconazole and the combination of ibrexafungerp and itraconazole was determined by measuring the 10 day survival in M. mycetomatis and F. senegalensis grain models in Galleria mellonella larvae. Grain number and size were determined in Grocott- and haematoxylin and eosin-stained sections.

RESULTS

Ibrexafungerp inhibited the growth of Madurella and Falciformispora species with MICs ranging from 4 to 64 mg/L and from 8 to 32 mg/L, respectively. In G. mellonella larvae, ibrexafungerp was not toxic and prolonged the survival in M. mycetomatis-infected larvae 10 days after infection, but not in F. senegalensis-infected larvae. Combining ibrexafungerp with itraconazole prolonged the survival of M. mycetomatis- and F. senegalensis-infected larvae. Treatment with ibrexafungerp alone and in combination resulted in smaller grains in M. mycetomatis-infected larvae.

CONCLUSIONS

Ibrexafungerp showed in vitro activity and in vivo efficacy against the two most common eumycetoma causative agents.

The performance and costs of XTT, resazurin, MTS and luciferin as viability dyes in in vitro susceptibility testing of Madurella mycetomatis

BACKGROUND

in vitro susceptibility testing for the non-sporulating fungus Madurella mycetomatis is performed with a hyphal suspension as starting inoculum and a viability dye for endpoint reading. Here we compared the performance of four different viability dyes for their use in in vitro susceptibility testing of M. mycetomatis.

METHODS

To compare the reproducibility and the agreement between the viability dyes 2,3-bis-(2-methoxy-4-nitro-5-sulfphenyl)-2H-tetrazolium-5-carboxanilide salt (XTT), resazurin, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt (MTS) and luciferin, the in vitro susceptibilities of 14 genetically diverse M. mycetomatis isolates were determined for itraconazole and amphotericin B. The reproducibility, agreement, price and ease of use were compared.

RESULTS

Each of the four dyes gave highly reproducible results with >85.7% reproducibility. Percentage agreement ranged between 78.9% and 92.9%. Resazurin was the most economical to use (0.0009 €/minimal inhibitory concentration [MIC]) and could be followed in real time. Luciferin omitted the need to transfer the supernatant to a new 96-well plate, but cost 6.07 €/MIC.

CONCLUSION

All four viability dyes were suitable to determine the in vitro susceptibility of M. mycetomatis against itraconazole and amphotericin B. Based on the high reproducibility, high percentage agreement, price and possibility to monitor in real time, resazurin was the most suited for routine in vitro susceptibility testing in the diagnostic laboratory in mycetoma-endemic countries. Because luminescence could be measured directly without the need to transfer the supernatant to a new 96-well plate, luciferin is suitable for drug-screening campaigns.

LAY SUMMARY

To determine the in vitro susceptibility testing in the non-sporulating fungus Madurella mycetomatis, a viability dye is needed for endpoint reading. In this study we tested the viability dyes XTT, resazurin, MTS and luciferin for their use in in vitro susceptibility testing. It appeared that they all could be used but there were differences in time to result and costs associated with them.

Two dose levels of once-weekly fosravuconazole versus daily itraconazole in combination with surgery in patients with eumycetoma in Sudan: a randomised, double-blind, phase 2, proof-of-concept superiority trial

BACKGROUND

Eumycetoma is an implantation mycosis characterised by a large subcutaneous mass in the extremities commonly caused by the fungus Madurella mycetomatis. Despite the long duration of treatment, commonly a minimum of 12 months, treatment failure is frequent and can lead to amputation. We aimed to compare the efficacy of two doses of fosravuconazole, a synthetic antifungal designed for use in onychomycosis and repurposed for mycetoma, with standard-of-care itraconazole, both in combination with surgery.

METHODS

This phase 2, randomised, double-blind, active-controlled, superiority trial was conducted in a single centre in Sudan. Patients with eumycetoma caused by M mycetomatis, who were aged 15 years or older, with a set lesion diameter (>2 cm and ≤16 cm) requiring surgery were included. There was a limit of 20 female patients in the initial enrolment, owing to preclinical toxicity concerns. Exclusion criteria included previous surgical or medical treatment for eumycetoma; presence of loco-regional lymphatic extension; osteomyelitis, or other bone involvement; pregnancy or lactation; severe concomitant diseases; a BMI under 16 kg/m2; contraindication to use of the study drugs; pre-existing liver disease; lymphatic extension; osteomyelitis; transaminase levels more than two times the laboratory's upper limit of normal, or elevated levels of alkaline phosphatase or bilirubin; or any history of hypersensitivity to any azole antifungal drug. Patients were randomly allocated in a 1:1:1 ratio to 300 mg fosravuconazole weekly for 12 months (group 1); 200 mg fosravuconazole weekly for 12 months (group 2); or 400 mg itraconazole daily for 12 months (group 3) using a random number list with non-disclosed fixed blocks of size 12, with equal allocation to each of the three arms within a block. To ensure masking between groups, placebo pills were used to disguise the difference in dosing schedules. All groups took pills twice daily with meals. In all groups, surgery was performed at 6 months. The primary outcome was complete cure at end of treatment at the month 12 visit, as evidenced by absence of mycetoma mass, sinuses, and discharge; normal ultrasonography or MRI examination of the eumycetoma site; and, if a mass was present, negative fungal culture from the former mycetoma site. The primary outcome was assessed in the modified intention-to-treat (mITT) population (all patients who received one or more treatment dose with one or more primary efficacy assessment). Safety was assessed in all patients who received one or more doses of the study drug. This study is registered with ClinicalTrials.gov (NCT03086226) and is complete.

FINDINGS

Between May 9, 2017, and June 10, 2021, 104 patients were randomly allocated (34 in group 1 and 2, respectively, and 36 in group 3). 86 (83%) of 104 patients were male and 18 (17%) patients were female. After an unplanned second interim analysis, the study was terminated early for futility. Complete cure at 12 months in the mITT population was 17 (50%) of 34 (95% CI 32-68) for group 1, 22 (65%) of 34 (47-80) for group 2, and 27 (75%) of 36 (58-88) in group 3. Neither dose of fosravuconazole was superior to itraconazole (p=0·35 for 200 mg fosravuconazole vs p=0·030 for 300 mg fosravuconazole). 83 patients had a total of 205 treatment-emergent adverse events, and two patients had serious adverse events that led to discontinuation, neither related to treatment.

INTERPRETATION

Treatment with either dose of fosravuconazole was not superior to itraconazole, and the two doses had a numerically lower efficacy. However, fosravuconazole presented no new safety signals, and its lower pill burden and reduced risk of drug-drug interactions compared with the relatively expensive and inaccessible itraconazole suggests further research into effective treatments with a shorter duration and higher cure rate, without the need for surgery are warranted.

FUNDING

Drugs for Neglected Diseases initiative.

Novel Compound MMV1804559 from the Global Health Priority Box Exhibits In Vitro and In Vivo Activity against Madurella mycetomatis

OBJECTIVES

Eumycetoma is a neglected tropical disease (NTD) characterized by subcutaneous lesions and the formation of grains. Attempts to treat eumycetoma involve a combination of antifungal treatment and surgery, although the outcome is frequently disappointing. Therefore, there is a need to identify novel antifungal drugs to treat eumycetoma. In this respect, Medicines for Malaria Venture (MMV) has assembled libraries of compounds for researchers to use in drug discovery research against NTD. Therefore, we screened two MMVOpen compound libraries to identify novel leads for eumycetoma.

METHODS

A total of 400 compounds from the COVID Box and the Global Health Priority Box were screened in vitro at 100 µM and 25 µM against the most common causative agents of eumycetoma, namely Madurella mycetomatis and Falciformispora senegalensis, and the resulting IC50 and MIC50 values were obtained. Compounds with an IC50 < 8 µM were identified for possible in vivo efficacy studies using an M. mycetomatis grain model in Galleria mellonella larvae.

RESULTS

Out of the 400 compounds, 22 were able to inhibit both M. mycetomatis and F. senegalensis growth at 100 µM and 25 µM, with compounds MMV1593278, MMV020335, and MMV1804559 being selected for in vivo testing. Of these three, only the pyrazolopyrimidine derivative MMV1804559 was able to prolong the survival of M. mycetomatis-infected G. mellonella larvae. Furthermore, the grains in MMV1804559-treated larvae were significantly smaller compared to the PBS-treated group.

CONCLUSION

MMV1804559 shows promising in vitro and in vivo activity against M. mycetomatis.

The combination of manogepix and itraconazole is synergistic and inhibits the growth of Madurella mycetomatis in vitro but not in vivo

Mycetoma is a neglected tropical disease commonly caused by the fungus Madurella mycetomatis. Standard treatment consists of extensive treatment with itraconazole in combination with surgical excision of the infected tissue, but has a low success rate. To improve treatment outcomes, novel treatment strategies are needed. Here, we determined the potential of manogepix, a novel antifungal agent that targets the GPI-anchor biosynthesis pathway by inhibition of the GWT1 enzyme. Manogepix was evaluated by determining the minimal inhibitory concentrations (MICs) according to the CLSI-based in vitro susceptibility assay for 22 M. mycetomatis strains and by in silico protein comparison of the target protein. The synergy between manogepix and itraconazole was determined using a checkerboard assay. The efficacy of clinically relevant dosages was assessed in an in vivo grain model in Galleria mellonella larvae. MICs for manogepix ranged from <0.008 to >8 mg/l and 16/22 M. mycetomatis strains had an MIC ≥4 mg/ml. Differences in MICs were not related to differences observed in the GWT1 protein sequence. For 70% of the tested isolates, synergism was found between manogepix and itraconazole in vitro. In vivo, enhanced survival was not observed upon admission of 8.6 mg/kg manogepix, nor in combination treatment with 5.7 mg/kg itraconazole. MICs of manogepix were high, but the in vitro antifungal activity of itraconazole was enhanced in combination therapy. However, no efficacy of manogepix was found in an in vivo grain model using clinically relevant dosages. Therefore, the therapeutic potential of manogepix in mycetoma caused by M. mycetomatis seems limited.

Short Tandem Repeat DNA Profiling Using Perylene-Oligonucleotide Fluorescence Assay

We report an amplification-free genotyping method to determine the number of human short tandem repeats (STRs). DNA-based STR profiling is a robust method for genetic identification purposes such as forensics and biobanking and for identifying specific molecular subtypes of cancer. STR detection requires polymerase amplification, which introduces errors that obscure the correct genotype. We developed a new method that requires no polymerase. First, we synthesized perylene-nucleoside reagents and incorporated them into oligonucleotide probes that recognize five common human STRs. Using these probes and a bead-based hybridization approach, accurate STR detection was achieved in only 1.5 h, including DNA preparation steps, with up to a 1000-fold target DNA enrichment. This method was comparable to PCR-based assays. Using standard fluorometry, the limit of detection was 2.00 ± 0.07 pM for a given target. We used this assay to accurately identify STRs from 50 human subjects, achieving >98% consensus with sequencing data for STR genotyping.

Epidemiological cut-off values for itraconazole and ravuconazole for Madurella mycetomatis, the most common causative agent of mycetoma

BACKGROUND

Eumycetoma is a neglected tropical disease. It is a chronic inflammatory subcutaneous infection characterised by painless swellings which produce grains. It is currently treated with a combination of itraconazole and surgery. In an ongoing clinical study, the efficacy of fosravuconazole, the prodrug of ravuconazole, is being investigated. For both itraconazole and ravuconazole, no clinical breakpoints or epidemiological cut-off values (ECV) to guide treatment are currently available.

OBJECTIVE

To determine tentative ECVs for itraconazole and ravuconazole in Madurella mycetomatis, the main causative agent of eumycetoma.

MATERIALS AND METHODS

Minimal inhibitory concentrations (MICs) for itraconazole and ravuconazole were determined in 131 genetically diverse clinical M. mycetomatis isolates with the modified CLSI M38 broth microdilution method. The MIC distributions were established and used to determine ECVs with the ECOFFinder software. CYP51A sequences were sequenced to determine whether mutations occurred in this azole target gene, and comparisons were made between the different CYP51A variants and the MIC distributions.

RESULTS

The MICs ranged from 0.008 to 1 mg/L for itraconazole and from 0.002 to 0.125 mg/L for ravuconazole. The M. mycetomatis ECV for itraconazole was 1 mg/L and for ravuconazole 0.064 mg/L. In the wild-type population, two CYP51A variants were found for M. mycetomatis, which differed in one amino acid at position 499 (S499G). The MIC distributions for itraconazole and ravuconazole were similar between the two variants. No mutations linked to decreased susceptibility were found.

CONCLUSION

The proposed M. mycetomatis ECV for itraconazole is 1 mg/L and for ravuconazole 0.064 mg/L.

Genomics and metagenomics of Madurella mycetomatis, a causative agent of black grain mycetoma in Sudan

Madurella mycetomatis is one of the main causative agents of mycetoma, a debilitating neglected tropical disease. Improved understanding of the genomic diversity of the fungal and bacterial causes of mycetoma is essential to advances in diagnosis and treatment. Here, we describe a high-quality genome assembly of M. mycetomatis and results of the whole genome sequence analysis of 26 isolates from Sudan. We demonstrate evidence of at least seven genetically diverse lineages and extreme clonality among isolates within these lineages. We also performed shotgun metagenomic analysis of DNA extracted from mycetoma grains and showed that M. mycetomatis reads were detected in all sequenced samples with the average of 11,317 reads (s.d. +/- 21,269) per sample. In addition, 10 (12%) of the 81 tested grain samples contained bacterial reads including Streptococcus sp., Staphylococcus sp. and others.

Madurella mycetomatis grains within a eumycetoma lesion are clonal

Eumycetoma is a neglected tropical infection of the subcutaneous tissue, characterized by tumor-like lesions and most commonly caused by the fungus Madurella mycetomatis. In the tissue, M. mycetomatis organizes itself in grains, and within a single lesion, thousands of grains can be present. The current hypothesis is that all these grains originate from a single causative agent, however, this hypothesis was never proven. Here, we used our recently developed MmySTR assay, a highly discriminative typing method, to determine the genotypes of multiple grains within a single lesion. Multiple grains from surgical lesions obtained from 11 patients were isolated and genotyped using the MmySTR panel. Within a single lesion, all tested grains shared the same genotype. Only in one single grain from one patient, a difference of one repeat unit in one MmySTR marker was noted relative to the other grains from that patient. We conclude that within these lesions the grains originate from a single clone and that the inherent unstable nature of the microsatellite markers may lead to small genotypic differences.

Screening the pandemic response box identified benzimidazole carbamates, Olorofim and ravuconazole as promising drug candidates for the treatment of eumycetoma

Eumycetoma is a chronic subcutaneous neglected tropical disease that can be caused by more than 40 different fungal causative agents. The most common causative agents produce black grains and belong to the fungal orders Sordariales and Pleosporales. The current antifungal agents used to treat eumycetoma are itraconazole or terbinafine, however, their cure rates are low. To find novel drugs for eumycetoma, we screened 400 diverse drug-like molecules from the Pandemic Response Box against common eumycetoma causative agents as part of the Open Source Mycetoma initiative (MycetOS). 26 compounds were able to inhibit the growth of Madurella mycetomatis, Madurella pseudomycetomatis and Madurella tropicana, 26 compounds inhibited Falciformispora senegalensis and seven inhibited growth of Medicopsis romeroi in vitro. Four compounds were able to inhibit the growth of all five species of fungi tested. They are the benzimidazole carbamates fenbendazole and carbendazim, the 8-aminoquinolone derivative tafenoquine and MMV1578570. Minimal inhibitory concentrations were then determined for the compounds active against M. mycetomatis. Compounds showing potent activity in vitro were further tested in vivo. Fenbendazole, MMV1782387, ravuconazole and olorofim were able to significantly prolong Galleria mellonella larvae survival and are promising candidates to explore in mycetoma treatment and to also serve as scaffolds for medicinal chemistry optimisation in the search for novel antifungals to treat eumycetoma.