1. How does high-throughput screening work?
Primary screening: millions of known compounds are inserted at high concentrations (e.g. 20-50 mM) into wells (e.g. containing cells, proteins). Generally a binary result indicates activity or lack thereof. Secondary/confirmatory screening: active compounds are re-diluted, plated, and screened. Approximately ~500 compounds may be deemed “hits.” Further testing: anywhere from 0 to 2 compounds are determined to be active.
2. Why are there limited data for other coronaviruses?
Funding for public health research is limited, so screening is limited to vital threats. As a result, there is an abundance of data regarding SARS and MERS, but less about other coronaviruses, such as the common cold.
3. Why do we rely so much on high-throughput screening? Why not test against live cells?
Whole cell screening is expensive and difficult. High-throughput screening can be automated and pipelined by robots. In contrast, whole cell screening requires several days of work by an experienced operator. The process generates several terabytes of data, which are evaluated by multiple software packages (compensating for systematic effects, selecting cell boundaries, detecting dyes, etc). High-content imaging is hard.