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Olorofim Susceptibility Testing of 1,423 Danish Mold Isolates Obtained in 2018-2019 Confirms Uniform and
Karen Marie Thyssen Astvad1, Karin Meinike Jørgensen1, Rasmus Krøger Hare1
1Unit of Mycology, Statens Serum Institut, Copenhagen, Denmark.
Abstract:
Olorofim is a novel antifungal drug in phase 2 trials. It has shown promising in vitro activity against various molds, except for Mucorales. Initially, we observed a broad range of EUCAST MICs for Aspergillus fumigatus Here, we explored the MIC variability in more detail and prospectively investigated the susceptibility of contemporary clinical mold isolates, as population data are needed for future epidemiological cutoff (ECOFF) settings. Fifteen A. fumigatus isolates previously found with low/medium/high MICs (≤0.002 to 0.25 mg/liter) were tested repeatedly and EUCAST MICs read in a blinded fashion by three observers. pyrE, encoding the olorofim target enzyme dihydroorotate dehydrogenase (DHODH), was sequenced. A total of 1,423 mold isolates (10 Aspergillus species complexes [including 1,032 A. fumigatus isolates] and 105 other mold/dermatophyte isolates) were examined. Olorofim susceptibility (modal MIC, MIC50, MIC90, and wild-type upper limits [WT-ULs] [species complexes with ≥15 isolates]) was determined and compared to that of four comparators. MICs (mg/liter) were within two 2-fold dilutions (0.016 to 0.03) for 473/476 determinations. The MIC range spanned four dilutions (0.008 to 0.06). No significant pyrE mutations were found. Modal MIC/WT-UL97.5 (mg/liter) values were 0.03/0.06 (A. terreus and A. flavus), 0.06/0.125 (A. fumigatus and Trichophyton rubrum), and 0.06/0.25 (A. niger and A. nidulans). The MIC range for Scedosporium spp. was 0.008 to 0.25. Olorofim susceptibility was similar for azole-resistant and -susceptible isolates of A. fumigatus but reduced for A. montevidensis and A. chevalieri (MICs of >1). With experience, olorofim susceptibility testing is robust. The testing of isolates from our center showed uniform and broad-spectrum activity. Single-center WT-ULs are suggested.
Insights
Olorofim demonstrates robust antifungal activity against a wide range of molds, with consistent minimum inhibitory concentrations (MICs) observed in susceptibility testing. This study establishes reliable wild-type upper limits for epidemiological cutoff (ECOFF) settings.
Area of Science:
- Clinical Mycology
- Antifungal Drug Development
- Antimicrobial Susceptibility Testing
Background:
- Olorofim is a novel antifungal agent undergoing phase 2 clinical trials.
- Initial studies indicated promising in vitro activity against molds, with variability noted for Aspergillus fumigatus.
- Population data on antifungal susceptibility are crucial for establishing epidemiological cutoff (ECOFF) values.
Purpose of the Study:
- To investigate the minimum inhibitory concentration (MIC) variability of olorofim against Aspergillus fumigatus.
- To prospectively determine the susceptibility of contemporary clinical mold isolates to olorofim.
- To provide population data for future ECOFF settings.
Main Methods:
- Repeatedly tested 15 Aspergillus fumigatus isolates with varying MICs using blinded EUCAST methodology.
- Sequenced the pyrE gene, encoding the target enzyme dihydroorotate dehydrogenase (DHODH).
- Examined 1,423 mold isolates (including 10 Aspergillus species complexes and other molds/dermatophytes) for susceptibility.
- Determined olorofim susceptibility parameters (modal MIC, MIC50, MIC90, wild-type upper limits [WT-ULs]).
Main Results:
- Olorofim MICs showed high reproducibility, with most determinations within two 2-fold dilutions.
- No significant pyrE mutations were identified in tested isolates.
- Established modal MIC/WT-UL97.5 values for several species complexes, including Aspergillus fumigatus (0.06/0.125 mg/liter).
- Olorofim demonstrated broad-spectrum activity, with reduced susceptibility noted only for Aspergillus montevidensis and Aspergillus chevalieri.
Conclusions:
- Olorofim susceptibility testing is robust and reproducible with experience.
- The drug exhibits uniform and broad-spectrum antifungal activity against a diverse range of clinical mold isolates.
- The study suggests single-center WT-ULs for epidemiological surveillance and ECOFF development.
