Madurella mycetomatis, the main causative agent of eumycetoma, is highly susceptible to olorofim

Abstract

Objectives Eumycetoma is currently treated with a combination of itraconazole therapy and surgery, with limited success. Recently, olorofim, the lead candidate of the orotomides, a novel class of antifungal agents, entered a Phase II trial for the treatment of invasive fungal infections. Here we determined the activity of olorofim against Madurella mycetomatis, the main causative agent of eumycetoma. Methods Activity of olorofim against M. mycetomatis was determined by in silico comparison of the target gene, dihydroorotate dehydrogenase (DHODH), and in vitro susceptibility testing. We also investigated the in vitro interaction between olorofim and itraconazole against M. mycetomatis. Results M. mycetomatis and Aspergillus fumigatus share six out of seven predicted binding residues in their DHODH DNA sequence, predicting susceptibility to olorofim. Olorofim demonstrated excellent potency against M. mycetomatis in vivo with MICs ranging from 0.004 to 0.125 mg/L and an MIC90 of 0.063 mg/L. Olorofim MICs were mostly one dilution step lower than the itraconazole MICs. In vitro interaction studies demonstrated that olorofim and itraconazole work indifferently when combined. Conclusions We demonstrated olorofim has potent in vitro activity against M. mycetomatis and should be further evaluated in vivo as a treatment option for this disease.

In vitro susceptibility testing for black grain eumycetoma causative agents

“…All combinations appeared to be indifferent according to the calculated Fractional inhibitory concentration index (FICI) and interaction ratio's (IR) (Table 4 ). 35 , 37 This indifference was confirmed in vivo in Galleria mellonella larvae. Treatment with a combination of itraconazole and terbinafine did not enhance larval survival compared with treatment with itraconazole or terbinafine alone.…”

“…The echinocandins inhibit 1,3-β-glucan synthesis (Figure 2 ). As can be seen in Table 3 , the most common causative agent, M. mycetomatis , has low MICs for the azoles (median MIC50 0.03 µg/ml) 17 , 28 , 32 , 37 and olorofim (MIC50 0.016 µg/ml), 35 slightly higher MICs for amphotericin B (MIC50 0.5 µg/ml) 17 and terbinafine (MIC50 8 µg/ml) 32 , 37 and is not inhibited by 5-flucytosine 17 and the echinocandins. 40 The lowest MICs were obtained for ravuconazole, 28 the drug currently clinically investigated.…”

“…These included the azoles ketoconazole, itraconazole, posaconazole, ravuconazole, isavuconazonium (isovuconazole), eberconazole, luliconazole, miconazole, bitertanol and difenoconazole; the benzimidazoles fenbendazole and carbendazim; and the strobilurins azoxystrobin and trifloxystrobin. Two of the potent hits obtained from these screenings were olorofim 35 and the fenarimol EPL-BS1246. 34 For the fenarimols, 35 additional analogues were screened and an additional 4 potent fenarimols were identified: EPL-BS0178, EPL-BS0495, EPL-BS0800 and EPL-BS1025.…”

DHODH and cancer: promising prospects to be explored

“…Moreover, DHODH inhibitors exhibited efficacy against virus, including respiratory syncytial virus [ 109 ], rotavirus [ 110 ], foot-and-mouth disease virus infection [ 111 ], flavivirus which contains dengue virus, Zika virus, and Japanese encephalitis virus [ 112 ], and notably, against RNA viruses including newly emerged coronavirus SARS-CoV-2 [ 113 ]. DHODH inhibitors are also found to be effective against oomycete phytophthora infestans [ 114 ], schistosomiasis [ 115 , 116 ], invasive fungal infections [ 117 ], eumycetoma [ 118 ], and malaria [ 119 – 122 ].…”

Review of the Novel Investigational Antifungal Olorofim

“…The MIC values for olorofim were lower than those observed for clinically available antifungal agents, including amphotericin B, itraconazole, voriconazole, and posaconazole, especially against L. prolificans, where the MIC ranges for the clinically available agents ranged from 0.5 μg/mL to more than 16 μg/mL, and most isolates demonstrated frank resistance to these clinically available antifungals. Olorofim has also been reported to have activity against Microascus and Scopulariopsis species (which frequently have reduced susceptibility to the azoles), as well as Acremonium species, Paecilomyces variotii (which has reduced susceptibility to voriconazole), Purpureocillium lilacinum (which is intrinsically resistant to amphotericin B), Talaromyces marneffei, the endemic and thermally dimorphic fungi Blastomyces dermatitidis , Coccidioides species, Histoplasma capsulatum [ 33 , 37 ], and Madurella mycetomatis (the main causative agent of eumycetoma) [ 42 ].…”