Screening

The terminology used in screening

The following terms are used in context with screening:

• HTS: high throughput screening. HTS utilizes the properties single molecules and is often carried out on the interaction molecules.
• UHTS: ultra high throughput screening - more than 100 000samples / day.
• HCS: high content screening. HCS is an approach that utilizes a more complex environment than single molecules. It uses for example high-resolution fluorescence images for analysis of cell based measurements. HCS is sometimes used for lead optimization of HTS.
• Target: Investigative aim, generally a gene or protein.
• Hit: A hit is a substance with a positive result in the screening assay and therefore a possible lead.
• Lead: A lead is a hit that has proven to have specific effect on the target. Lead verification is often done in HCS.
• Hit to lead relation is a means of classifying a screening assay.

Together with combinatorial chemistry or substance libraries the number of testable substances is seemingly infinite. Combinatorial chemistry is also used for lead optimization. The screening process in the pharmaceutical industry is embedded in a line of product development that encompasses basic research via target discovery, target validation, lead verification, clinical research, and scale up production leading to launch of a product. For researchers in a university environment more or less the same is applicable with the publication of the discoveries at the stage of the clinical research.

Several quantitative techniques in fluorescence microscopy have proved their values in screening assays among these are:

• FRET: fluorescence resonant energy transfer
• FLIM: fluorescence lifetime imaging
• FCS: fluorescence correlation spectroscopy
• FRAP: fluorescence recovery after photobleaching
• Time resolve fluorescence
• FP: fluorescence-polarization or anisotropy
• Fluorescence reporters

The accuracy of the measurements depends on the understanding of the biological background on which the measurements are performed. A great variety of fluorescent labels are available for countless of applications. For a quantitative conclusion the quality of the measurements need to be validated, for example by cross checking the signal with a second reference staining.