Candidate drug: a compound (small molecule, antibody, etc.) with strong therapeutic potential and whose activity and specificity have been optimised.

The point of departure for fundamental researchers (fundamental and academic research) consists in identifying and validating therapeutic targets likely to be involved in a given disease.
Once the target has been identified, characterised and validated by a series of biological tests, it is necessary to identify the substances capable of acting on the target (activation, inhibition) appropriately. Active molecules are identified by screening and are called “hits”. Then new tests are performed to measure their dose-effect and physicochemical properties.

Computer modelling of the chemical structure of the hits and their interaction with the target permits designing new derivatives that undergo new tests to measure the therapeutic potential of these molecules and their capacity to be administered to human beings.

Medicinal chemistry thus optimises the activity of these molecules on the target and their behaviour in vivo (toxicity, bioavailability, etc.). Thus lead molecules are obtained.

After several cycles of optimisation (exchanges between modelling, chemical synthesis and biological tests), the substance presenting optimal characteristics is chosen as a candidate drug. This substance is then subjected to a new series of tests, and preclinical and clinical trials.