In a series of test tube experiments called assays, compounds are added one at a time to enzymes, cell cultures, or cellular substances grown in a laboratory. The goal is to find which additions show some chemical effect. Some may not work well, but may hint at ways of changing the compound's chemical structure to improve its performance. The latter process alone may require testing dozens or hundreds of compounds. A more high-tech approach is to use computers to simulate an enzyme or other drug target and to design chemical structures that might work against it.
Enzymes work when they attach to the correct site on a cell's membrane.
A computer can show scientists what the receptor site looks like and how one might tailor a compound to block an enzyme from attaching there. Yet a third approach involves testing compounds made naturally by microscopic organisms. Candidates include fungi, viruses and molds, such as those that led to penicillin and other antibiotics. Scientists grow the microorganisms in what they call a fermentation broth, one type of organism per broth. Sometimes 100,000 or more broths are tested to see whether any compound made by a microorganism has a desirable effect.