Unexpected effects of azole transporter inhibitors on antifungal susceptibility in Candida glabrata and other pathogenic Candida species.

Yohsuke Nagayoshi,Shigeru Kohno,Shigeki Nakamura,Koichi Izumikawa,Shintaro Shimamura,Takahiro Takazono,Taiga Miyazaki,Shunsuke Yamauchi,Asuka Minematsu,Hironobu Nakayama,Hiroshi Mukae,Katsunori Yanagihara,Ilse D Jacobsen

doi:10.1371/journal.pone.0180990

Yohsuke Nagayoshi, Shigeru Kohno + Show 11 more

Open Access

https://doi.org/10.1371/journal.pone.0180990

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Abstract

The pathogenic fungus Candida glabrata is often resistant to azole antifungal agents. Drug efflux through azole transporters, such as Cdr1 and Cdr2, is a key mechanism of azole resistance and these genes are under the control of the transcription factor Pdr1. Recently, the monoamine oxidase A (MAO-A) inhibitor clorgyline was shown to inhibit the azole efflux pumps, leading to increased azole susceptibility in C. glabrata. In the present study, we have evaluated the effects of clorgyline on susceptibility of C. glabrata to not only azoles, but also to micafungin and amphotericin B, using wild-type and several mutant strains. The addition of clorgyline to the culture media increased fluconazole susceptibility of a C. glabrata wild-type strain, whereas micafungin and amphotericin B susceptibilities were markedly decreased. These phenomena were also observed in other medically important Candida species, including Candida albicans, Candida parapsilosis, Candida tropicalis, and Candida krusei. Expression levels of CDR1, CDR2 and PDR1 mRNAs and an amount of Cdr1 protein in the C. glabrata wild-type strain were highly increased in response to the treatment with clorgyline. However, loss of Cdr1, Cdr2, Pdr1, and a putative clorgyline target (Fms1), which is an ortholog of human MAO-A, or overexpression of CDR1 did not affect the decreased susceptibility to micafungin and amphotericin B in the presence of clorgyline. The presence of other azole efflux pump inhibitors including milbemycin A4 oxime and carbonyl cyanide 3-chlorophenylhydrazone also decreased micafungin susceptibility in C. glabrata wild-type, Δcdr1, Δcdr2, and Δpdr1 strains. These findings suggest that azole efflux pump inhibitors increase azole susceptibility but concurrently induce decreased susceptibility to other classes of antifungals independent of azole transporter functions.

Highlights

The pathogenic fungus Candida glabrata is the second most common cause of candidemia and is relatively resistant to azole antifungal agents [1]
A recent study discovered that the monoamine oxidase A (MAO-A) inhibitor clorgyline inhibits the activity of azole efflux pumps, such as Cdr1, Cdr2, and Mdr1, leading to increased azole susceptibility in C. glabrata and Candida albicans [5]
We examined whether the azole transporter inhibitor clorgyline affects susceptibility to micafungin and amphotericin B in main Candida species including C. glabrata, C. albicans, C. parapsilosis, C. tropicalis, and C. krusei, which account for about 95% of clinical isolates of Candida species [23]

Summary

Introduction

The pathogenic fungus Candida glabrata is the second most common cause of candidemia and is relatively resistant to azole antifungal agents [1]. A key mechanism of azole-resistance is the reduction in the intracellular drug concentration, which is achieved by activation of azole transporters, such as Cdr and Cdr (formerly denoted Pdh1) [2,3,4]. Inhibition of these transporters is one effective way for combating azole-resistance. A recent study discovered that the monoamine oxidase A (MAO-A) inhibitor clorgyline inhibits the activity of azole efflux pumps, such as Cdr, Cdr, and Mdr, leading to increased azole susceptibility in C. glabrata and Candida albicans [5]. It has been reported that polyene susceptibility is attenuated in azole-resistant isolates [11]

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