Emerging therapeutics: The imidazo[1,2-b]pyridazine scaffold as a novel drug candidate for eumycetoma, a neglected tropical disease.

Mycetoma is a neglected invasive infection endemic in tropical and subtropical regions, presenting as a chronic subcutaneous inflammatory mass that can spread to deeper structures, leading to deformities, disabilities, and potentially mortality. The current treatment of eumycetoma, the fungal form of mycetoma, involves antifungal agents, such as itraconazole, combined with surgical intervention. However, this approach has limited success, with low cure rates and a high risk of recurrence. This study addresses to the urgent need for more effective therapeutics by designing and synthesising 47 diversely pharmacomodulated imidazo [1,2-b]pyridazine derivatives using a simple synthetic pathway with good yields and purity. Of these, 17 showed promising in vitro activity against Madurella mycetomatis, the prime causative agent of eumycetoma, with IC50 ≤ 5 µM and demonstrated significantly lower cytotoxicity compared to standard treatments in NIH-3T3 fibroblasts. Notably, compound 14d exhibited an excellent activity with an IC50 of 0.9 µM, in the same order then itraconazole (IC50 = 1.1 µM), and achieved a favourable selectivity index of 16 compared to 0.8 for itraconazole. These promising results warrant further research to evaluate the clinical potential of these novel compounds as safer, more effective treatments for eumycetoma, thus addressing a profound gap in current therapeutic strategies.

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.

An updated list of eumycetoma causative agents and their differences in grain formation and treatment response.

SUMMARYIn 2023, the World Health Organization designated eumycetoma causative agents as high-priority pathogens on its list of fungal priority pathogens. Despite this recognition, a comprehensive understanding of these causative agents is lacking, and potential variations in clinical manifestations or therapeutic responses remain unclear. In this review, 12,379 eumycetoma cases were reviewed. In total, 69 different fungal species were identified as causative agents. However, some were only identified once, and there was no supporting evidence that they were indeed present in the grain. Madurella mycetomatis was by far the most commonly reported fungal causative agent. In most studies, identification of the fungus at the species level was based on culture or histology, which was prone to misidentifications. The newly used molecular identification tools identified new causative agents. Clinically, no differences were reported in the appearance of the lesion, but variations in mycetoma grain formation and antifungal susceptibility were observed. Although attempts were made to explore the differences in clinical outcomes based on antifungal susceptibility, the lack of large clinical trials and the inclusion of surgery as standard treatment posed challenges in drawing definitive conclusions. Limited case series suggested that eumycetoma cases caused by Fusarium species were less responsive to treatment than those caused by Madurella mycetomatis. However, further research is imperative for a comprehensive understanding.

Protoplast-mediated transformation of Madurella mycetomatis using hygromycin resistance as a selection marker.

Madurella mycetomatis is the main cause of mycetoma, a chronic granulomatous infection for which currently no adequate therapy is available. To improve therapy, more knowledge on a molecular level is required to understand how M. mycetomatis is able to cause this disease. However, the genetic toolbox for M. mycetomatis is limited. To date, no method is available to genetically modify M. mycetomatis. In this paper, a protoplast-mediated transformation protocol was successfully developed for this fungal species, using hygromycin as a selection marker. Furthermore, using this method, a cytoplasmic-GFP-expressing M. mycetomatis strain was created. The reported methodology will be invaluable to explore the pathogenicity of M. mycetomatis and to develop reporter strains which can be useful in drug discovery as well as in genetic studies.

Naphthylisoquinoline alkaloids: novel agents against the causative pathogens of eumycetoma and actinomycetoma-en route to broad-spectrum antimycetomal drugs.

Mycetoma is a devastating neglected tropical infection of the subcutaneous tissues. It is caused by fungal and bacterial pathogens recognized as eumycetoma and actinomycetoma, respectively. Mycetoma treatment involves diagnosing the causative microorganism as a prerequisite to prescribing a proper medication. Current therapy of fungal eumycetoma causative agents, such as Madurella mycetomatis, consists of long-term antifungal medication with itraconazole followed by surgery, yet with usually unsatisfactory clinical outcomes. Actinomycetoma, on the contrary, usually responds to treatment with co-trimoxazole and amikacin. Therefore, there is a pressing need to discover novel broad-spectrum antimicrobial agents to circumvent the time-consuming and costly diagnosis. Using the resazurin assay, a series of 23 naphthylisoquinoline (NIQ) alkaloids and related naphthoquinones were subjected to in vitro screening against two fungal strains of M. mycetomatis and three bacterial strains of Actinomadura madurae and A. syzygii. Seven NIQs, mostly dimers, showed promising in vitro activities against at least one strain of the mycetoma-causative pathogens, while the naphthoquinones did not show any activity. A synthetic NIQ dimer, 8,8'''-O,O-dimethylmichellamine A (18), inhibited all tested fungal and bacterial strains (IC50 = 2.81-12.07 µg/mL). One of the dimeric NIQs, michellamine B (14), inhibited a strain of M. mycetomatis and significantly enhanced the survival rate of Galleria mellonella larvae infected with M. mycetomatis at concentrations of 1 and 4 µg/mL, without being toxic to the uninfected larvae. As a result, broad-spectrum dimeric NIQs like 14 and 18 with antimicrobial activity are considered hit compounds that could be worth further optimization to develop novel lead antimycetomal agents.

Sandalwood Oils of Different Origins Are Active In Vitro against Madurella mycetomatis, the Major Fungal Pathogen Responsible for Eumycetoma.

In the search for new bioactive agents against the infectious pathogen responsible for the neglected tropical disease (NTD) mycetoma, we tested a collection of 27 essential oils (EOs) in vitro against Madurella mycetomatis, the primary pathogen responsible for the fungal form of mycetoma, termed eumycetoma. Among this series, the EO of Santalum album (Santalaceae), i.e., East Indian sandalwood oil, stood out prominently with the most potent inhibition in vitro. We, therefore, directed our research toward 15 EOs of Santalum species of different geographical origins, along with two samples of EOs from other plant species often commercialized as "sandalwood oils". Most of these EOs displayed similar strong activity against M. mycetomatis in vitro. All tested oils were thoroughly analyzed by GC-QTOF MS and most of their constituents were identified. Separation of the sandalwood oil into the fractions of sesquiterpene hydrocarbons and alcohols showed that its activity is associated with the sesquiterpene alcohols. The major constituents, the sesquiterpene alcohols (Z)-α- and (Z)-ß-santalol were isolated from the S. album oil by column chromatography on AgNO3-coated silica. They were tested as isolated compounds against the fungus, and (Z)-α-santalol was about two times more active than the ß-isomer.

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.

The synthetic synergistic cinnamon oil CIN-102 is active against Madurella mycetomatis, the most common causative agent of mycetoma.

Mycetoma is a devastating neglected tropical infection of the subcutaneous tissue and most commonly caused by the fungus Madurella mycetomatis. Treatment of mycetoma consists of a combination of a long term antifungal treatment with itraconazole and surgery. However, treatment is associated with low success rates. Therefore, there is a need to identify novel treatments for mycetoma. CIN-102 is a synthetic partial copy of cinnamon oils with activity against many pathogenic bacteria and fungi. In this study we determined the in vitro activity of CIN-102 against 21 M. mycetomatis isolates and its in vivo efficacy in a M. mycetomatis infected Galleria mellonella larval model. In vitro, CIN-102 was active against M. mycetomatis with MICs ranging from 32 µg/mL to 512 µg/mL. 128 µg/mL was needed to inhibit the growth in 50% of tested isolates. In vivo, concentrations below the MIC of 40 mg/kg and 80 mg/kg CIN-102 prolonged larval survival, but higher concentrations of CIN-102 did not.

Addressing the most neglected diseases through an open research model: The discovery of fenarimols as novel drug candidates for eumycetoma.

Eumycetoma is a chronic infectious disease characterized by a large subcutaneous mass, often caused by the fungus Madurella mycetomatis. A combination of surgery and prolonged medication is needed to treat this infection with a success rate of only 30%. There is, therefore, an urgent need to find more effective drugs for the treatment of this disease. In this study, we screened 800 diverse drug-like molecules and identified 215 molecules that were active in vitro. Minimal inhibitory concentrations were determined for the 13 most active compounds. One of the most potent compounds, a fenarimol analogue for which a large analogue library is available, led to the screening of an additional 35 compounds for their in vitro activity against M. mycetomatis hyphae, rendering four further hit compounds. To assess the in vivo potency of these hit compounds, a Galleria mellonella larvae model infected with M. mycetomatis was used. Several of the compounds identified in vitro demonstrated promising efficacy in vivo in terms of prolonged larval survival and/or reduced fungal burden. The results presented in this paper are the starting point of an Open Source Mycetoma (MycetOS) approach in which members of the global scientific community are invited to participate and contribute as equal partners. We hope that this initiative, coupled with the promising new hits we have reported, will lead to progress in drug discovery for this most neglected of neglected tropical diseases.

Amphotericin B and terbinafine but not the azoles prolong survival in Galleria mellonella larvae infected with Madurella mycetomatis.

Mycetoma is a tropical neglected disease characterized by large subcutaneous lesions in which the causative organisms reside in the form of grains. The most common causative agent is Madurella mycetomatis. Antifungal therapy often fails due to these grains, but to identify novel treatment options has been difficult since grains do not form in vitro. We recently used Galleria mellonella larvae to develop an in vivo grain model. In the current study, we set out to determine the therapeutic efficacy of commonly used antifungal agents in this larval model. Pharmacokinetics of ketoconazole, itraconazole, voriconazole, posaconazole, amphotericin B, and terbinafine were determined in the hemolymph of G. mellonella larvae. Antifungal therapy was given either therapeutically or prophylactic on three consecutive days in therapeutically equivalent dosages. Survival was monitored for 10 days and colony-forming units (cfu) and melanization were determined on day 3. Measurable concentrations of antifungal agents were found in the hemolymph of the larvae. None of the azole antifungal agents prolonged survival when given therapeutically or prophylactically. Amphotericin B and terbinafine did prolong survival, even at concentrations below the minimal inhibitory concentration of M. mycetomatis. The cfu and melanization did not differ between any of the treated groups and phosphate-buffered saline (PBS) treated groups. Grains were still present in surviving larvae but appeared to be encapsulated. This study demonstrated for the first time a comparison between the efficacy of different antifungal agents toward grains of M. mycetomatis. It appeared that amphotericin B and terbinafine were able to prolong larval survival.

The in vitro antifungal activity of sudanese medicinal plants against Madurella mycetomatis, the eumycetoma major causative agent.

Eumycetoma is a debilitating chronic inflammatory fungal infection that exists worldwide but it is endemic in many tropical and subtropical regions. The major causative organism is the fungus Madurella mycetomatis. The current treatment of eumycetoma is suboptimal and characterized by low cure rate and high recurrence rates. Hence, an alternative therapy is needed to address this. Here we determined the antifungal activity of seven Sudanese medicinal plant species against Madurella mycetomatis. Of these, only three species; Boswellia papyrifera, Acacia nubica and Nigella sativa, showed some antifungal activity against M. mycetomatis and were further studied. Crude methanol, hexane and defatted methanol extracts of these species were tested for their antifungal activity. B. papyrifera had the highest antifungal activity (MIC50 of 1 ug/ml) and it was further fractionated. The crude methanol and the soluble ethyl acetate fractions of B. papyrifera showed some antifungal activity. The Gas-Liquid-Chromatography hybrid Mass-Spectrophotometer analysis of these two fractions showed the existence of beta-amyrin, beta-amyrone, beta-Sitosterol and stigmatriene. Stigmatriene had the best antifungal activity, compared to other three phytoconstituents, with an MIC-50 of 32 µg/ml. Although the antifungal activity of the identified phytoconstituents was only limited, the antifungal activity of the complete extracts is more promising, indicating synergism. Furthermore these plant extracts are also known to have anti-inflammatory activity and can stimulate wound-healing; characteristics which might also be of great value in the development of novel therapeutic drugs for this chronic inflammatory disease. Therefore further exploration of these plant species in the treatment of mycetoma is encouraging.

Last generation triazoles for imported eumycetoma in eleven consecutive adults.

BACKGROUND: Optimal management of eumycetoma, a severely debilitating chronic progressive fungal infection of skin, disseminating to bone and viscera, remains challenging. Especially, optimal antifungal treatment and duration are ill defined. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a monocentric retrospective study of 11 imported cases of eumycetoma treated by voriconazole or posaconazole for at least 6 months. Response to treatment was assessed through evolution of clinical and magnetic resonance imaging (MRI). (1→3) ß-D-glucan (BG) and positron emission tomography using [18F] fluorodeoxyglucose (PET/CT) results were also assessed. Identified species were Fusarium solani complex (n = 3); Madurella mycetomatis, (n = 3), and Exophiala jeanselmei, (n = 1). Moreover, two coelomycetes and one phaeohyphomycetes strains without species identification were retrieved. Serum BG and PET/CT were abnormal in 7/8 and 6/6 patients tested, respectively. Patients received last generation azoles for a mean duration of 25.9±18 months. Complete response (major clinical and MRI improvement) was observed in 5/11 patients, partial response (minor MRI improvement or stable MRI findings) in 5 and failure (MRI evidence of disease progression) in one, with a 73±39 [6-132] months mean follow-up. Relapse occurred in 2 patients after treatment discontinuation. Optimal outcome was associated with fungal species, initiation of last generation triazole therapy (<65 months since first symptoms), negative serum BG and PET/CT normalization. CONCLUSIONS/SIGNIFICANCE: MRI, PET/CT and serum BG appear as promising tools to assess optimal time of antifungal treatment for eumycetoma.

Madurella mycetomatis is highly susceptible to ravuconazole.

The current treatment of eumycetoma utilizing ketoconazole is unsatisfactory because of high recurrence rates, which often leads to complications and unnecessary amputations, and its comparatively high cost in endemic areas. Hence, an effective and affordable drug is required to improve therapeutic outcome. E1224 is a potent orally available, broad-spectrum triazole currently being developed for the treatment of Chagas disease. E1224 is a prodrug that is rapidly converted to ravuconazole. Plasma levels of E1224 are low and transient, and its therapeutically active moiety, ravuconazole is therapeutically active. In the present study, the in vitro activity of ravuconazole against Madurella mycetomatis, the most common etiologic agent of eumycetoma, was evaluated and compared to that of ketoconazole and itraconazole. Ravuconazole showed excellent activity with MICs ranging between ≤ 0.002 and 0.031 µg/ml, which were significantly lower than the MICs reported for ketoconazole and itraconazole. On the basis of our findings, E1224 with its resultant active moiety, ravuconazole, could be an effective and affordable therapeutic option for the treatment of eumycetoma.

In vitro antifungal activity of isavuconazole against Madurella mycetomatis.

Currently, therapy of black-grain mycetoma caused by Madurella mycetomatis consists of extensive debridement of the infected tissue combined with prolonged antifungal therapy with ketoconazole or itraconazole. In the present study, the in vitro activity of the new triazole isavuconazole toward M. mycetomatis was evaluated. Isavuconazole appeared to have high activity against M. mycetomatis, with MICs ranging from ≤0.016 to 0.125 µg/ml. Due to its favorable pharmacokinetics, isavuconazole could be a promising antifungal agent in the treatment of mycetoma.

New species of Madurella, causative agents of black-grain mycetoma.

A new species of nonsporulating fungus, isolated in a case of black-grain mycetoma in Sudan, is described as Madurella fahalii. The species is characterized by phenotypic and molecular criteria. Multigene phylogenies based on the ribosomal DNA (rDNA) internal transcribed spacer (ITS), the partial ß-tubulin gene (BT2), and the RNA polymerase II subunit 2 gene (RPB2) indicate that M. fahalii is closely related to Madurella mycetomatis and M. pseudomycetomatis; the latter name is validated according to the rules of botanical nomenclature. Madurella ikedae was found to be synonymous with M. mycetomatis. An isolate from Indonesia was found to be different from all known species based on multilocus analysis and is described as Madurella tropicana. Madurella is nested within the order Sordariales, with Chaetomium as its nearest neighbor. Madurella fahalii has a relatively low optimum growth temperature (30°C) and is less susceptible to the azoles than other Madurella species, with voriconazole and posaconazole MICs of 1 µg/ml, a ketoconazole MIC of 2 µg/ml, and an itraconazole MIC of >16 µg/ml. Since eumycetoma is still treated only with azoles, correct species identification is important for the optimal choice of antifungal therapy.