This is the first stage of preclinical research. “Optimization” refers to a series of steps whereby a drug is made better, usually in a series of experiments in which the original molecule is chemically tweaked.
Each new drug made is tested to see if it is more effective than the original, or has other more desirable properties. Is it less likely to cause harm? Better able to get into the part of the body that needs it? More potent so that less drug will be needed to get the same effect?
Each new series of compounds is tested until the developer decides that he or she has the “optimal” compound selected — the one with the best chance of working with the lowest chance of side effects. This compound is called the “development candidate.” One or more development candidates may be brought forward.