SANTA CRUZ, Calif.—In the search for new drugs, it is sometimes beneficial to go back to basics. In the case of antifungals research, this includes the use of halo assays where potential drugs are touched to plated yeast and researchers look for open halos that indicate cell death. Looking to take this assay to the next step, researchers at University of California, Santa Cruz and colleagues at other institutes developed a high-throughput yeast halo assay to screen chemical libraries for possible antifungal activity.

 

As they reported in the Journal of Natural Products, the basic set up involves the transfer of compounds from a 384-well plate using automated array pins onto agar plates confluent with yeast. The presence of halos is then determined using optical density readings with a plate reader.

 

Initially, the researchers screened 3104 compounds from the NCI's Diversity, Mechanistic, and Natural Product libraries and detected 46 hits—a hit rate of 1.5 percent that compares favorably with published rates. Of these compounds, they noted several known fungal toxins, but the majority did not have known molecular targets in yeast. They then randomly selected 22 compounds from Diversity library and measured their IC₂₀ values in liquid culture. They found a good correlation between halo size and IC₂₀ value.

 

The researchers then screened in-house extracts of marine sponges and sponge-derived fungi cultures and identified one compound—crambescidin 800—that had been previously noted for its ability to inhibit HIV-1 and cytotoxicity toward some cancer cell lines. The assay offers the potential of renewed vigor in antifungal generation, a field that the authors suggest has yielded few surprises in the last three decades.