What should occur at the end of lead optimization?

• A. NDA submission.
• B. Phase 3 trials begin.
• C. A market launch is planned.
• D. A molecule should be selected for testing in humans, moving into drug development.

Answer: (D)

In lead optimization, the aim is to pick a single molecule that best balances potency, selectivity, favorable pharmacokinetics, safety margins, and manufacturability for clinical testing. The endpoint of this stage is choosing that candidate to move into human testing and formal drug development. This isn’t about finishing trials or launching a product yet; it’s about validating enough properties in preclinical work to justify entering clinical studies. The other milestones—regulatory submissions, starting later-phase trials, and market launch—come after this candidate has been shown to be safe and effective in humans through the clinical development program. So the best choice is selecting a molecule for testing in humans, moving into drug development.