Lonafarnib synergizes with azoles against Aspergillus spp. and Exophiala spp

Farnesylation, which is catalyzed by farnesyltransferase, promotes membrane association of the modified protein and protein-protein interactions, and plays an important role in a number of physiological processes of pathogenic fungi, including stress response, environmental adaption and virulence. Lonafarnib is an orally bioavailable nonpeptide tricyclic farnesyltransferase inhibitor with excellent pharmacokinetic and safety profile. In the present study, we investigated the in vitro activities of lonafarnib alone or combined with azoles, including itraconazole, voriconazole, and posaconazole, against 22 strains of Aspergillus spp. and 18 strains of Exophiala dermatitidis via broth microdilution checkerboard technique. Lonafarnib alone was inactive against all isolates tested. However, synergistic effects between lonafarnib and itraconazole were observed in 86% Aspergillus strains and 94% E. dermatitidis strains. In addition, lonafarnib/posaconazole combination also exhibited synergism against 59% of Aspergillus strains and 100% E. dermatitidis strains. However, synergistic effects of lonafarnib/voriconazole were only observed in 32% Aspergillus strains and 28% E. dermatitidis strains. The effective working ranges of lonafarnib were 2-4 μg/ml and 1-4 μg/ml against Aspergillus isolates and E. dermatitidis isolates, respectively. No antagonism was observed in all combinations. This study demonstrated that lonafarnib could enhance the in vitro antifungal activity of itraconazole, posaconazole and voriconazole against Aspergillus spp. and E. dermatitidis, suggesting that azoles, especially itraconazole and posaconazole, combined with farnesyltransferase inhibitor might provide a potential strategy to the management of Aspergillus and Exophiala infections. However, further studies are warranted to elucidate the underlying mechanism and to investigate the potential of reliable and safe application in clinical practice.