Fig 1. Screening a library of 1,280 pharmacologically active compounds identifies molecules that potentiate the activity of caspofungin against an echinocandin-resistant clinical isolate.

A) The LOPAC¹²⁸⁰ Navigator library was screened at 25 μM in RPMI medium in the presence or absence of 8 μg/mL caspofungin to identify compounds that enhance the efficacy of caspofungin against an echinocandin-resistant C. albicans clinical isolate (CaLC990). Growth was measured by absorbance at 600 nm after 96 hours at 30°C. A compound was classified as a hit if it inhibited growth by 90% in combination with caspofungin compared to growth with the LOPAC compound alone. Optical densities were normalized relative to the no compound control for wells with LOPAC compound alone, or to the caspofungin-only control for wells with caspofungin and LOPAC compound. Data was displayed as a heat map using Java TreeView 1.1.6, see color bar. B) Compounds identified as ‘weak hits’ (inhibited growth by 80–90% in combination with caspofungin compared to growth with the LOPAC compound alone) were rescreened at 50 μM of the LOPAC compound and analyzed as in A). C) Compounds that were toxic on their own (inhibited growth by greater than 70% in the absence of caspofungin) were rescreened at 12.5 μM and analyzed as in A). D) A dose response assay was used to quantify the impact of lead compounds on caspofungin resistance. Shown are the four compounds that best reduced the growth of the resistant strain in combination with caspofungin, and that have not previously been implicated in drug resistance. Assays were performed in RPMI medium in the presence or absence of a fixed concentration of caspofungin (8 μg/mL), as indicated. Data was analyzed after 96 hours at 30°C and normalized as in Part A.