Start from the destination
Mature teams do not optimize blindly toward "better." They write a candidate profile (or target product profile) up front: the explicit list of criteria a molecule must meet to be declared a candidate. It states the minimum potency, the required selectivity margins, the solubility and permeability thresholds, the metabolic stability and projected human half-life, the clean safety panel, and the synthesizability. This turns a vague quest into a checklist.
Trading properties wisely
Potency–property balance is the daily art of optimization. Because properties are coupled, almost every design choice is a trade. The discipline is to know which gauges are thresholds (must clear a bar, no extra credit) versus which are maximize (genuinely better the higher they go).
- Identify the non-negotiables. A reactive-metabolite alert or a strong hERG signal is usually a hard stop, not a trade.
- Find which property is limiting. At any moment one gauge is usually the bottleneck; spend your cycles there, not on the gauge that is already fine.
- Use efficiency, not raw potency, as the compass. Trading a little potency for a big gain in LipE almost always moves the series forward.
- Use property MPO scores carefully. A weighted score can rank analogues, but never let it hide a single red flag the profile calls fatal.
Knowing when you have a candidate
Candidate selection is the moment a molecule clears every line of the profile and the team commits it to expensive preclinical development. You rarely pick a single hero in isolation; good practice is to carry two or three diverse molecules — often from different scaffolds — so that if one fails in tox or formulation, you are not back to zero. This is direct insurance against attrition, the brutal rate at which molecules fail downstream.
Step back and the whole track tells one story: a hit becomes a lead, cycles driven by efficiency metrics raise potency without bloat, ADMET and safety gates are cleared along the way, and a written profile tells you the destination and when you have arrived. That disciplined balancing act — property-based, honest, and patient — is what lead optimization is.