Mutations in MRR1 that confer fluconazole resistance in Candida parapsilosis and Candida albicans confer cross-resistance to manogepix.

OBJECTIVES

Fluconazole resistance has been documented in Candida albicans and Candida parapsilosis, both leading causes of invasive candidiasis, driven in part by mutations in MRR1 that encodes a transcription factor that regulates drug efflux pump expression. A correlation has been observed between susceptibilities to fluconazole and manogepix, the active moiety of fosmanogepix, a promising new antifungal with activity against most Candida species. We aimed to determine whether MRR1-activating mutations driving fluconazole resistance in these species conferred cross-resistance to manogepix.

METHODS

C. albicans and C. parapsilosis clinical isolates and strains engineered to express wild-type or mutant MRR1 alleles, and their derivatives deleted for target drug transporters, were assessed for fluconazole and manogepix susceptibility.

RESULTS

Introducing Mrr1 I283R and A854V substitutions into C. parapsilosis clinical isolate Cp13 increased fluconazole MIC from 0.25 to 16-32 mg/L and increased manogepix MIC from 0.008 to 0.25 mg/L, whereas correcting to MRR1 wild-type sequence in fluconazole-resistant clinical isolates reduced fluconazole MICs from 64, 128, and 32 mg/L to 2, 0.5, and 2 mg/L, respectively, and manogepix MICs from 0.125, 0.25, and 0.125 mg/L to 0.015 mg/L for all. This was dependent upon genes encoding Mdr1B and Cdr1B transporters. In C. albicans, introducing different MRR1-activating mutations into SC5314 increased fluconazole MICs from 0.5 mg/L to 4-16 mg/L and increased manogepix MICs from 0.015 mg/L to 0.06 mg/L. Activating mutations in clinical isolates increased fluconazole MICs from 1-2 mg/L to 32-64 mg/L and manogepix MICs by 2- to 4-fold. MRR1 deletion in resistant isolates restored susceptibility to both drugs.

CONCLUSIONS

Our findings demonstrate that fluconazole and manogepix cross-resistance in C. parapsilosis conferred by MRR1-activating mutations is mediated by Cdr1B and Mdr1B transporters. MRR1-activating mutations conferred cross-resistance, to a lesser degree, in C. albicans, but independent of drug transporters known to be regulated by Mrr1.