Establishing a therapeutically beneficial new chemical entity (NCE) can be broadly classified into research (discovery) and development phases. Drug development is generally divided into nonclinical (animal) and clinical (human) testing stages, with regulatory approval of an investigational new drug application separating the two. In contrast, drug discovery does not require regulatory oversight and follows the general path of: target validation —> assay development —> high-throughput screening —> hit to lead —> lead optimization (LO). Promising drug candidates are selected and transitioned from late LO into nonclinical development, although the specific processes for doing so vary between organizations.

By Mike B Bolger, Michael Lawless