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Chayanika Biswas, Derek Law, Michael Birch, Catriona Halliday, Tania C Sorrell, John Rex, Monica Slavin, Sharon C-A Chen, In vitro activity of the novel antifungal compound F901318 against Australian Scedosporium and Lomentospora fungi, Medical Mycology, Volume 56, Issue 8, November 2018, Pages 1050–1054, https://doi.org/10.1093/mmy/myx161
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Abstract
We determined the in vitro activity of the novel orotomide antifungal, F901318, against 30 Lomentospora prolificans, 20 Scedosporium apiospermum, 7 S. aurantiacum, and 3 S. boydii, isolates in comparison with standard antifungals. Against L. prolificans, F901318 was the most potent compound (MIC90 0.25 μg/ml); the geometric mean MIC (0.26 μg/ml) was significantly lower (23–80-fold) than those of itraconazole, voriconazole, posaconazole, and isavuconazole (all P < .001), and amphotericin B (P < .05). F901318 also had good activity against S. apiospermum, S. aurantiacum, and S. boydii, comparable to that of voriconazole and posaconazole but was more active than isavuconazole for all three species.
There has been a dearth of new drug classes reaching the clinic since the echinocandins in 2001. Limitations of current antifungals include drug toxicity, variable pharmacokinetics and increasing resistance, where resistance to the azoles in Aspergillus fumigatus approaches 30%.1 Further, pathogenic moulds inherently resistant to antifungal drugs are increasingly encountered.2,3
F901318 (F2G Limited, Manchester, UK) is an orotomide antifungal compound that inhibits the fungal pyrimidine biosynthesis enzyme, dihydroorotate dehydrogenase.4 It has potent in vitro activity against Aspergillus species including against azole-resistant strains, and demonstrates favorable pharmacokinetics in mice.4–6 F901318 was also active against Scedosporium species and seven Lomentospora (previously Scedosporium) prolificans isolates.7 Study of larger numbers of Scedosporium/Lomentospora strains from different locales is essential as there are geographic differences in susceptibility patterns.2,8 Here we determined the in vitro activity of F901318 against these fungi in comparison with standard anti-mould agents including isavuconazole. These fungi are the second most common (30%) cause of non-Aspergillus mould infections in Australia3 and are resistant to many current antifungals.
Fifty clinical isolates were studied, comprising 30 L. prolificans and 20 S. apiospermum species complex isolates (10 S. apiospermum sensu stricto, 3 S. boydii, 7 S. aurantiacum), identified as before.9 Three clinical A. fumigatus strains were tested for comparison. Candida parapsilosis ATCC 22019 was the quality control strain and A. fumigatus ATCC 204305, the reference strain.10
F901318 pure substance4 and isavuconazole (ISA) powder (Carbosynth Limited, Berkshire, UK) was provided by F2G Limited. Stock solutions were prepared in DMSO and drug dilutions prepared in RPMI-1640 medium. The drug concentration range tested was 0.008–4 μg/ml for F901318 and 0.03–32 μg/ml for ISA, and susceptibility testing performed according to CLSI M38-A2 methodology.10 MICs read as 100% inhibition of growth after 48 h incubation. Susceptibility to amphotericin B (AMB), itraconazole (ITC), voriconazole (VOR), posaconazole (POS), caspofungin (CAS), micafungin (MFG), and anidulafungin (AFG) was determined using the Sensititre® YeastOne® YO10 system (Trek Diagnostics, Cleveland, OH, USA). MICs (for AMB, azoles) and minimum effective concentrations (MECs; for echinocandins) determined.10 Experiments were performed on two separate occasions.
Geometric mean (GM) MICs/MECs and MIC90/MEC90 values were ascertained for species where at least 10 strains of a species were tested. To establish GM values, the low (<) and high (>) off-scale MIC/MEC values were converted to the next lowest or highest two-fold drug concentrations, respectively.11 Differences between GM MICs were assessed for significance by the Mann–Whitney U-test using Statistical Analysis software SAS version 9.4.
Antifungal susceptibility results and MIC distributions according to species are shown in Table 1. The MICs of standard antifungals for A. fumigatus ATCC 204305 were as expected.12 The F901318 MIC was 0.125 μg/ml for all A. fumigatus isolates. Azole MICs ranged from 0.03–0.5 μg/ml except for ISA (0.5–2 μg/ml).
Fungus . | Antifungal . | Range . | aMIC50/MEC50 . | aMIC90/MEC90 . | aGM MIC/MEC . |
---|---|---|---|---|---|
(no. of isolates) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . |
Scedosporium apiospermum (n=10) | F901318 | 0.12–0.5 | 0.12 | 0.25 | 0.16 |
AMB | 2–16 | 4 | 16 | 6.06 | |
CAS | 0.12–16 | 8 | 16 | 6.03 | |
AFG | 2–16 | 4 | 16 | 6.94 | |
MFG | 4–16 | 16 | 16 | 10.56 | |
ITC | 0.25–1 | 0.5 | 1 | 0.43 | |
VOR | 0.06–0.5 | 0.12 | 0.25 | 0.15 | |
POS | 0.25–1 | 0.5 | 1 | 0.57 | |
ISA | 2–8 | 4 | 8 | 5.28 | |
Scedosporium aurantiacum (n=7) | F901318 | 0.12–0.5 | – | – | – |
AMB | 2–16 | – | – | – | |
CAS | 2–16 | – | – | – | |
AFG | 4–16 | – | – | – | |
MFG | 0.5–16 | – | – | – | |
ITC | 0.12–32 | – | – | – | |
VOR | 0.03–0.25 | – | – | – | |
POS | 0.12–1 | – | – | – | |
ISA | 4–16 | – | – | – | |
Scedosporium boydii (n=3) | F901318 | 0.12–0.25 | – | – | – |
AMB | 4–8 | – | – | – | |
CAS | 8 | – | – | – | |
AFG | 16 | – | – | – | |
MFG | 16 | – | – | – | |
ITC | 0.5 | – | – | – | |
VOR | 0.12 | – | – | – | |
POS | 0.5 | – | – | – | |
ISA | 4–8 | – | – | – | |
Lomentospora prolificans (n=30) | F901318 | 0.12–0.5 | 0.25 | 0.25 | 0.26 |
AMB | 4–16 | 16 | 16 | 11.31 | |
CAS | 4–16 | 8 | 16 | 7.64 | |
AFG | 2–16 | 8 | 16 | 7.29 | |
MFG | 2–16 | 8 | 16 | 8.39 | |
ITC | 32 | 32 | 32 | 32 | |
VOR | 0.5–16 | 8 | 16 | 5.66 | |
POS | 16 | 16 | 16 | 16 | |
ISA | 8–32 | 16 | 16 | 16.76 | |
Aspergillus fumigatus (n=3) | F901318 | 0.12 | – | – | – |
AMB | 0.25–0.5 | – | – | – | |
CAS | 0.008–0.015 | – | – | – | |
AFG | 0.015–0.03 | – | – | – | |
MFG | 0.008–0.015 | – | – | – | |
ITC | 0.06–0.5 | – | – | – | |
VOR | 0.03–0.12 | – | – | – | |
POS | 0.03–0.5 | – | – | – | |
ISA | 0.5–2 | – | – | – |
Fungus . | Antifungal . | Range . | aMIC50/MEC50 . | aMIC90/MEC90 . | aGM MIC/MEC . |
---|---|---|---|---|---|
(no. of isolates) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . |
Scedosporium apiospermum (n=10) | F901318 | 0.12–0.5 | 0.12 | 0.25 | 0.16 |
AMB | 2–16 | 4 | 16 | 6.06 | |
CAS | 0.12–16 | 8 | 16 | 6.03 | |
AFG | 2–16 | 4 | 16 | 6.94 | |
MFG | 4–16 | 16 | 16 | 10.56 | |
ITC | 0.25–1 | 0.5 | 1 | 0.43 | |
VOR | 0.06–0.5 | 0.12 | 0.25 | 0.15 | |
POS | 0.25–1 | 0.5 | 1 | 0.57 | |
ISA | 2–8 | 4 | 8 | 5.28 | |
Scedosporium aurantiacum (n=7) | F901318 | 0.12–0.5 | – | – | – |
AMB | 2–16 | – | – | – | |
CAS | 2–16 | – | – | – | |
AFG | 4–16 | – | – | – | |
MFG | 0.5–16 | – | – | – | |
ITC | 0.12–32 | – | – | – | |
VOR | 0.03–0.25 | – | – | – | |
POS | 0.12–1 | – | – | – | |
ISA | 4–16 | – | – | – | |
Scedosporium boydii (n=3) | F901318 | 0.12–0.25 | – | – | – |
AMB | 4–8 | – | – | – | |
CAS | 8 | – | – | – | |
AFG | 16 | – | – | – | |
MFG | 16 | – | – | – | |
ITC | 0.5 | – | – | – | |
VOR | 0.12 | – | – | – | |
POS | 0.5 | – | – | – | |
ISA | 4–8 | – | – | – | |
Lomentospora prolificans (n=30) | F901318 | 0.12–0.5 | 0.25 | 0.25 | 0.26 |
AMB | 4–16 | 16 | 16 | 11.31 | |
CAS | 4–16 | 8 | 16 | 7.64 | |
AFG | 2–16 | 8 | 16 | 7.29 | |
MFG | 2–16 | 8 | 16 | 8.39 | |
ITC | 32 | 32 | 32 | 32 | |
VOR | 0.5–16 | 8 | 16 | 5.66 | |
POS | 16 | 16 | 16 | 16 | |
ISA | 8–32 | 16 | 16 | 16.76 | |
Aspergillus fumigatus (n=3) | F901318 | 0.12 | – | – | – |
AMB | 0.25–0.5 | – | – | – | |
CAS | 0.008–0.015 | – | – | – | |
AFG | 0.015–0.03 | – | – | – | |
MFG | 0.008–0.015 | – | – | – | |
ITC | 0.06–0.5 | – | – | – | |
VOR | 0.03–0.12 | – | – | – | |
POS | 0.03–0.5 | – | – | – | |
ISA | 0.5–2 | – | – | – |
Abbreviations: MIC, minimum inhibitory concentration; MEC, minimum effective concentration; AMB, amphotericin B; AFG, anidulafungin; CAS, caspofungin; ISA, isavuconazole; ITC, itraconazole; MFG, micafungin; POS, posaconazole; VOR, voriconazole.
MIC/MECs of F901318 and isavuconazole determined by the CLSI M38-A2 reference method 10. MICs/MECs of the remaining antifungal agents determined using the Sensititre® YeastOne® Y010 panel as described in the Methods.
aThe MIC50/MEC50, MIC90/MEC90 and GM MICs/MECs values were ascertained for species where at least 10 isolates, respectively were tested.
Fungus . | Antifungal . | Range . | aMIC50/MEC50 . | aMIC90/MEC90 . | aGM MIC/MEC . |
---|---|---|---|---|---|
(no. of isolates) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . |
Scedosporium apiospermum (n=10) | F901318 | 0.12–0.5 | 0.12 | 0.25 | 0.16 |
AMB | 2–16 | 4 | 16 | 6.06 | |
CAS | 0.12–16 | 8 | 16 | 6.03 | |
AFG | 2–16 | 4 | 16 | 6.94 | |
MFG | 4–16 | 16 | 16 | 10.56 | |
ITC | 0.25–1 | 0.5 | 1 | 0.43 | |
VOR | 0.06–0.5 | 0.12 | 0.25 | 0.15 | |
POS | 0.25–1 | 0.5 | 1 | 0.57 | |
ISA | 2–8 | 4 | 8 | 5.28 | |
Scedosporium aurantiacum (n=7) | F901318 | 0.12–0.5 | – | – | – |
AMB | 2–16 | – | – | – | |
CAS | 2–16 | – | – | – | |
AFG | 4–16 | – | – | – | |
MFG | 0.5–16 | – | – | – | |
ITC | 0.12–32 | – | – | – | |
VOR | 0.03–0.25 | – | – | – | |
POS | 0.12–1 | – | – | – | |
ISA | 4–16 | – | – | – | |
Scedosporium boydii (n=3) | F901318 | 0.12–0.25 | – | – | – |
AMB | 4–8 | – | – | – | |
CAS | 8 | – | – | – | |
AFG | 16 | – | – | – | |
MFG | 16 | – | – | – | |
ITC | 0.5 | – | – | – | |
VOR | 0.12 | – | – | – | |
POS | 0.5 | – | – | – | |
ISA | 4–8 | – | – | – | |
Lomentospora prolificans (n=30) | F901318 | 0.12–0.5 | 0.25 | 0.25 | 0.26 |
AMB | 4–16 | 16 | 16 | 11.31 | |
CAS | 4–16 | 8 | 16 | 7.64 | |
AFG | 2–16 | 8 | 16 | 7.29 | |
MFG | 2–16 | 8 | 16 | 8.39 | |
ITC | 32 | 32 | 32 | 32 | |
VOR | 0.5–16 | 8 | 16 | 5.66 | |
POS | 16 | 16 | 16 | 16 | |
ISA | 8–32 | 16 | 16 | 16.76 | |
Aspergillus fumigatus (n=3) | F901318 | 0.12 | – | – | – |
AMB | 0.25–0.5 | – | – | – | |
CAS | 0.008–0.015 | – | – | – | |
AFG | 0.015–0.03 | – | – | – | |
MFG | 0.008–0.015 | – | – | – | |
ITC | 0.06–0.5 | – | – | – | |
VOR | 0.03–0.12 | – | – | – | |
POS | 0.03–0.5 | – | – | – | |
ISA | 0.5–2 | – | – | – |
Fungus . | Antifungal . | Range . | aMIC50/MEC50 . | aMIC90/MEC90 . | aGM MIC/MEC . |
---|---|---|---|---|---|
(no. of isolates) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . | (μg/ml) . |
Scedosporium apiospermum (n=10) | F901318 | 0.12–0.5 | 0.12 | 0.25 | 0.16 |
AMB | 2–16 | 4 | 16 | 6.06 | |
CAS | 0.12–16 | 8 | 16 | 6.03 | |
AFG | 2–16 | 4 | 16 | 6.94 | |
MFG | 4–16 | 16 | 16 | 10.56 | |
ITC | 0.25–1 | 0.5 | 1 | 0.43 | |
VOR | 0.06–0.5 | 0.12 | 0.25 | 0.15 | |
POS | 0.25–1 | 0.5 | 1 | 0.57 | |
ISA | 2–8 | 4 | 8 | 5.28 | |
Scedosporium aurantiacum (n=7) | F901318 | 0.12–0.5 | – | – | – |
AMB | 2–16 | – | – | – | |
CAS | 2–16 | – | – | – | |
AFG | 4–16 | – | – | – | |
MFG | 0.5–16 | – | – | – | |
ITC | 0.12–32 | – | – | – | |
VOR | 0.03–0.25 | – | – | – | |
POS | 0.12–1 | – | – | – | |
ISA | 4–16 | – | – | – | |
Scedosporium boydii (n=3) | F901318 | 0.12–0.25 | – | – | – |
AMB | 4–8 | – | – | – | |
CAS | 8 | – | – | – | |
AFG | 16 | – | – | – | |
MFG | 16 | – | – | – | |
ITC | 0.5 | – | – | – | |
VOR | 0.12 | – | – | – | |
POS | 0.5 | – | – | – | |
ISA | 4–8 | – | – | – | |
Lomentospora prolificans (n=30) | F901318 | 0.12–0.5 | 0.25 | 0.25 | 0.26 |
AMB | 4–16 | 16 | 16 | 11.31 | |
CAS | 4–16 | 8 | 16 | 7.64 | |
AFG | 2–16 | 8 | 16 | 7.29 | |
MFG | 2–16 | 8 | 16 | 8.39 | |
ITC | 32 | 32 | 32 | 32 | |
VOR | 0.5–16 | 8 | 16 | 5.66 | |
POS | 16 | 16 | 16 | 16 | |
ISA | 8–32 | 16 | 16 | 16.76 | |
Aspergillus fumigatus (n=3) | F901318 | 0.12 | – | – | – |
AMB | 0.25–0.5 | – | – | – | |
CAS | 0.008–0.015 | – | – | – | |
AFG | 0.015–0.03 | – | – | – | |
MFG | 0.008–0.015 | – | – | – | |
ITC | 0.06–0.5 | – | – | – | |
VOR | 0.03–0.12 | – | – | – | |
POS | 0.03–0.5 | – | – | – | |
ISA | 0.5–2 | – | – | – |
Abbreviations: MIC, minimum inhibitory concentration; MEC, minimum effective concentration; AMB, amphotericin B; AFG, anidulafungin; CAS, caspofungin; ISA, isavuconazole; ITC, itraconazole; MFG, micafungin; POS, posaconazole; VOR, voriconazole.
MIC/MECs of F901318 and isavuconazole determined by the CLSI M38-A2 reference method 10. MICs/MECs of the remaining antifungal agents determined using the Sensititre® YeastOne® Y010 panel as described in the Methods.
aThe MIC50/MEC50, MIC90/MEC90 and GM MICs/MECs values were ascertained for species where at least 10 isolates, respectively were tested.
F901318 exhibited potent in vitro activity against Scedosporium/Lomentospora isolates. Notably, it was the most active compound against all 30 L. prolificans isolates (MIC90 0.25 μg/ml, MIC range 0.125–0.5 μg/ml). The GM MIC of 0.26 μg/ml for F901318 was 23–80-fold (Table 1) lower than those of the azoles (all P < .001) and 40-fold lower than that of AMB (P < .05). Additionally, the F901318 MIC90 value was 32–128-fold lower than those for ITC, VOR, POS, and ISA (Table 1). Of the azoles, VOR exhibited the lowest GM MIC (5.66 μg/ml) against L. prolificans with a broad MIC range where two strains had MICs of 0.5 μg/ml and 1.0 μg/ml, respectively. The MIC distribution of all agents against L prolfiicans illustrates the greater activity of F901318 (Fig. 1).
GM MICs of F901318 against S. apiospermum and the MIC range against S. aurantiacum and S. boydii were similar to those of L. prolificans (Table 1), and for all compounds, the susceptibility profiles of the three species were similar. Overall, GM MICs for F901318 were similar to those of POS, VOR, and ITC but were up to 32-fold lower than those of ISA (Table 1), The next most active agent against Scedosporium species was VOR (GM MICs 0.11–0.125 μg/ml) followed by POS (GM MICs 0.37–0.55 μg/ml). Compared with AMB, F901318 was more active against all three species. For all Scedosporium and Lomentospora strains, GM MICs of AMB were highest for L. prolificans (11.31 μg/ml) (Table 1).
MICs for ISA ranged between 2 and 32 μg/ml and were highest for L. prolificans (GM MIC 16.76 μg/ml; Table1) followed by S. apiospermum (GM MIC 5.28 μg/ml). MICs of the echinocandins were high and comparable for CAS, AFG, and MFG. A single S. apiospermum isolate had a CAS MIC of 0.125 μg/ml.
F901318 is a novel compound with established activity against Aspergillus spp.4,6 The results herein extend its promise as an antifungal agent to Scedosporium/Lomentospora fungi, with particular clinical relevance in regions where infections due to these pathogens are relatively common.3
As a “quality check" all three clinical A. fumigatus isolates had low F901318 MICs (0.125 μg/ml) athough these were twofold higher than the modal MIC of 0.062 μg/ml in wild-type A. fumigatus strains in the Netherlands.5 Buil et al. employed the EUCAST broth microdilution (E.Def 9.2)13 and not the CLSI M38-A2, method, but the two methodologies generally produce comparable susceptibility results for moulds.14
The key finding of our study was that F901318 exhibited potent in vitro activity against all three species of Scedosporium and L. prolificans. In particular, F901318 was the only agent to show low MICs (0.125–0.5 μg/ml) against a relatively large number (n = 30) of L. prolificans isolates (Fig. 1). One study reported F901318 MICs of ≤0.25 μg/ml for this species but for only seven strains.7 While in vivo efficacy data of F901318 against invasive scedosporiosis have not been published, the MICs of F901318 for Scedosporium and Lomentospora spp. were similar to those for A. fumigatus where F901318 has potent activity in animal models.4,6 Importantly, our data also suggests that F901318 susceptibility results are generalizable across countries.
In contrast, none of the other antifungals had appreciable in vitro activity against L. prolificans. GM MIC values of ITC, POS, VOR, and ISA were >20-fold higher than that of F901318. VOR was the next most active agent but the GM MIC was ∼threefold less than that reported in the United States (5.66 μg/ml vs. >16 μg/ml).7 VOR MICs varied widely, and others have observed MICs as low as 0.06 μg/ml.15 Hence, susceptibility testing of all clinical isolates is recommended to guide therapy.2,16 Current guidelines recommend using combination voriconazole and terbinafine to treat L. prolificans infections based on demonstration of synergy in vitro.17,18 F901318 is a potentially effective alternative for use as a single agent to treat such infections. It also had good in vitro activity against the major Scedosporium species, with comparable activity to that of VOR and POS but up to 32-fold more active than ISA.
ISA demonstrated little in vitro activity against L. prolificans (MIC90 16 μg/ml) (Fig. 1), similar to results of one study.19 However, as with VOR and POS, there may be synergistic interactions with terbinafine.20 Among Scedosporium spp., S. aurantiacum was the least susceptible to ISA. As before,7 neither AMB nor the echinocandins demonstrated good activity against Scedosporium or Lomentospora spp. However, in another study, micafungin was moderately active against Scedosporium spp.16 Clinical trials are required to ascertain the role of echinocandins, including in combination with other drugs in the treatment of scedosporiosis.
In summary, the results of testing a large panel of Australian Scedosporium and L. prolificans isolates against F901318 support the conduct of clinical studies of this agent, especially for L. prolificans infection, where the activity of approved antifungals is poor.
Funding
There was no funding received for this study.
Acknowledgments
The authors thank Professor Wieland Meyer and Ms. Krystyna Maszewska from the Molecular Mycology Research Laboratory, Westmead Insitute for Medical Research for donating a subset of the isolates. We also thank Ms. Daneeta Hennessy for assistance with statistical data analysis. T.C.S. is a Sydney Medical School Foundation Fellow.
Declaration of Interest
D.L., M.B., and J.R. are employees of F2G Limited and each has stock options in this company. T.C.S, M.S., and S.C.A.C. are on the advisory boards for MSD Australia, Gilead Sciences Inc., and have received untied research grants from MSD Australia, Pfizer Australia and Gilead Sciences. C.H. has received untied research grants from MSD Australia.