When a biological target for drug discovery programme has been validated, an assay format needs to be developed.
The aim of the assay is to enable characterisation of novel compounds and obtain the potency of these compounds against the target in question. With this information gained from the potency assays and using similar clusters of compounds, a structure activity relationship can be determined (SAR). This will drive the production of future lead compounds for the target and further optimisation. Assay formats have been successfully run as inhibition or activation modes
The type of assay format to use has to be carefully determined on a variety of factors. The primary factor is the choice of target itself and the type of activity that is required to be measured. (for example an GPCR vs. Kinase). Another factor in assay choice depends on the numbers of compounds that will be screened. Libraries of compounds can vary from tens to millions (the latter usually found within big pharmaceutical companies)
Before an assay can used in a screening campaign, it has to be proven to be sensitive with respect to the target, for example known inhibitors are reproducible to literature values. Kinetic parameters have to be determined to ensure that the assay is functioning correctly. The assay has to have a robust signal change to enable detection of activity compared to background noise within the assay. It has to be stable to allow practicable numbers of compounds to be tested within a set timeframe. The cost reagents and labware required is also an important factor, combined with the consumption of the target protein (which can be very time consuming to make and purify).
All these factors have to be balanced when determining the correct assay format to use with the target in question.
There are many different types of assay format available such as biophysical (NMR, SPR), biochemical (purified enzyme assays) and cell based (reporter gene). Typically multiple assay formats are combined together to build a screening sequence or cascade.
The types of technology and techniques used for assay formats range considerably, examples include fluorescence, luminescent, radioactive, and absorbance methods.