Broad susceptibility of Candida auris strains to 8-hydroxyquinolines and mechanisms of resistance

Abstract

The fungal pathogen Candida auris represents a severe threat to hospitalized patients. Its resistance to multiple classes of antifungal drugs and ability to spread and resist decontamination in healthcare settings make it especially dangerous. We screened 1,990 clinically approved and late-stage investigational compounds for the potential to be repurposed as antifungal drugs targeting C. auris and narrowed our focus to five Food and Drug Administration (FDA)-approved compounds with inhibitory concentrations under 10 µM for C. auris and significantly lower toxicity to three human cell lines. These compounds, some of which had been previously identified in independent screens, include three dihalogenated 8-hydroxyquinolines: broxyquinoline, chloroxine, and clioquinol. A subsequent structure-activity study of 32 quinoline derivatives found that 8-hydroxyquinolines, especially those dihalogenated at the C5 and C7 positions, were the most effective inhibitors of C. auris . To pursue these compounds further, we exposed C. auris to clioquinol in an extended experimental evolution study and found that C. auris developed only twofold to fivefold resistance to the compound. DNA sequencing of resistant strains and subsequent verification by directed mutation in naive strains revealed that resistance was due to mutations in the transcriptional regulator CAP1 (causing upregulation of the drug transporter MDR1 ) and in the drug transporter CDR1 . These mutations had only modest effects on resistance to traditional antifungal agents, and the CDR1 mutation rendered C. auris more susceptible to posaconazole. This observation raises the possibility that a combination treatment involving an 8-hydroxyquinoline and posaconazole might prevent C. auris from developing resistance to this established antifungal agent. IMPORTANCE The rapidly emerging fungal pathogen Candida auris represents a growing threat to hospitalized patients, in part due to frequent resistance to multiple classes of antifungal drugs. We identify a class of compounds, the dihalogenated 8-hydroxyquinolines, with broad fungistatic ability against a diverse collection of 13 strains of C. auris . Although this compound has been identified in previous screens, we extended the analysis by showing that C. auris developed only modest twofold to fivefold increases in resistance to this class of compounds despite long-term exposure; a noticeable difference from the 30- to 500-fold increases in resistance reported for similar studies with commonly used antifungal drugs. We also identify the mutations underlying the resistance. These results suggest that the dihalogenated 8-hydroxyquinolines are working inside the fungal cell and should be developed further to combat C. auris and other fungal pathogens. Lohse and colleagues characterize a class of compounds that inhibit the fungal pathogen C. auris . Unlike many other antifungal drugs, C. auris does not readily develop resistance to this class of compounds.

Current Perspectives of Antifungal Therapy: A Special Focus on Candida auris

“…Lohse and their colleague have aimed to develop antifungal agents from a group of FDA-approved compounds [ 124 ]. The selection of these compounds was based on MIC values of <10 µM.…”

“…The selection of these compounds was based on MIC values of <10 µM. Among the hydroxyquinolines tested, clioquinol was more active than others; however, the authors were unable to investigate their mechanisms of action [ 124 ]. In another study, a hydroxyquinoline derivative known as nitroxoline was also active against 35 isolates of C. auris with MIC values ranging from 0.125 to 1 μg/mL.…”

Candida auris Updates: Outbreak Evaluation through Molecular Assays and Antifungal Stewardship—A Narrative Review

“…The antifungal resistance mechanisms identified were diverse: resistance to phagocytosis by macrophages, mutations that explain increased fluconazole and voriconazole resistance ( ERG11 and TAC1B genes), missense substitutions in FKS1 for echinocandin resistance, and the possibility of using the proton pump inhibitor lansoprazole to restore the activity of amphotericin B (AmB) in resistant isolates. Identifying with high precision the antifungal resistance mechanisms could lead to opportunities in the development of novel antifungal drugs against C. auris and could help in tracking the spread of Candida auris between cities and countries by highlighting the genetic relation between strains ( Table 2 ) [ 14 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ].…”