hit compound

A hit compound is the first small spark of hope in a search for a new drug: a molecule that, when tested, actually does something useful against the target. It is a positive blip in a sea of inactive molecules, signalling 'look here, there might be a starting point.'

Defined precisely, it is an early molecule showing confirmed activity against a target in a screening assay. Most hits are still weak, unselective, or chemically awkward, but they prove that the target can be engaged by a small molecule at all.

Hits must be confirmed before they are trusted, because screening throws up many false positives from impurities, aggregation, or assay artifacts. A genuine, reproducible hit that holds up under scrutiny can then be developed into a stronger lead compound.