High-throughput screening of a collection of known pharmacologically active small compounds for identification of Candida albicans biofilm inhibitors

Abstract

Candida albicans is the most common etiologic agent of systemic fungal infections with unacceptably high mortality rates. The existing arsenal of antifungal drugs is very limited and is particularly ineffective against C. albicans biofilms. To address the unmet need for novel antifungals, particularly those active against biofilms, we have screened a small molecule library consisting of 1,200 off-patent drugs already approved by the Food and Drug Administration (FDA), the Prestwick Chemical Library, to identify inhibitors of C. albicans biofilm formation. According to their pharmacological applications that are currently known, we classified these bioactive compounds as antifungal drugs, as antimicrobials/antiseptics, or as miscellaneous drugs, which we considered to be drugs with no previously characterized antifungal activity. Using a 96-well microtiter plate-based high-content screening assay, we identified 38 pharmacologically active agents that inhibit C. albicans biofilm formation. These drugs were subsequently tested for their potency and efficacy against preformed biofilms, and we identified three drugs with novel antifungal activity. Thus, repurposing FDA-approved drugs opens up a valuable new avenue for identification and potentially rapid development of antifungal agents, which are urgently needed.

Fig 1

Primary screening. (A) The initial hits were identified by screening compounds from the Prestwick Chemical Library that inhibit biofilm formation. C. albicans strain SC5314 was grown in the presence of 20 μM each compound in a 96-well microtiter plate for 24 h at 37°C, and the extent of biofilm formation was estimated using the XTT colorimetric assay. The experiment was performed in duplicate, and the results are expressed as the percentage of biofilm inhibition. (B) The hits were classified into three classes: antifungals, antiseptics, and miscellaneous agents.

Fig 2

Effect of representative antifungal drugs on prevention of C. albicans biofilm formation (open circles) and against preformed biofilms (closed circles).

Fig 3

Effect of representative antiseptic drugs on prevention of C. albicans biofilm formation (open circles) and against preformed biofilms (closed circles).

Fig 4

Effect of representative miscellaneous drugs on prevention of C. albicans biofilm formation (open circles) and against preformed biofilms (closed circles).