target-based screening

Target-based screening is the opposite strategy to phenotypic screening: you pick one specific molecule you believe matters in disease — say, a particular enzyme — purify or isolate it, and test compounds directly against that single target. It is like deciding in advance that the lock you care about is the front door, and testing keys only on that door.

Here the biological hypothesis comes first: the target is chosen because there is evidence (from genetics, biology, or prior drugs) that modulating it will help patients. Compounds are screened against the isolated target in a defined assay — often a biochemical assay with purified protein, sometimes a cell-based assay engineered to report on that one target — so any hit's mechanism of action is known from the start.

The advantage is clarity: you know exactly what a hit does, which makes optimization, selectivity work, and safety reasoning much more direct. The risk is that everything rides on the target hypothesis being correct — a beautifully potent inhibitor of a target that turns out not to drive the disease is a dead end no matter how good the chemistry.