Bioassays for Drug Discovery
The first biological assays involved measuring the effect of a chemical substance on a living organism. The results of these experiments are essential for assessing potential activity, toxicity and side effects of drugs. Projects can be divided into those with known molecular targets and those with a defined phenotypic effect in a cell or tissue based assay. Setting up a bioassay that is suitable for discovering initial hits involves the following steps:
Known Molecular target projects
- Express and purify the protein target from a suitable expression system in bacterial, mammalian, yeast or insect cells.
- Characterise the protein in terms of protein folding, functional effects ie enzyme activity etc
- Analyse the structure of the protein via crystallography or other biophysical techniques, if possible.
- Develop an assay which enables quantitative measurement of the activity for which the target protein is essential. This may involve measuring enzyme activity and kinetics, receptor binding or more downstream functions of the target. The main assay to be used for compound screening activities needs to be highly reproducible; validated with any available known tool compounds; work robustly with compounds in solvents such as DMSO; and amenable to medium thoughput assay formats ie 96/ 384 well automated assay systems. The DDC screening group can support this development.
Targets where the cellular/tissue effects are known, but the molecular target is not defined
It can be acceptable to progress projects where a desirable cellular or tissue effect is observed but the defined molecular target is not known. In this case a different assay path is likely such as:
- Characterise the biology of the cellular effect and its link to the disease of interest. Ideally this will implicate the effect in a human based cellular/tissue system.
- Develop an assay using a readily accessible, appropriate and amenable cell line or primary culture to quantitatively measure the desired biological effect e.g. levels of cytokines, calcium flux etc.
- As above, this assay needs to be highly reproducible, validated with any available known tool compounds, work robustly with compounds in solvents such as DMSO and ameanable to medium thoughput assay formats ie 96/ 384 well automated assay systems.The DDC screening group can support this development.
