ABSTRACT
For many decades, the discovery of drugs has depended on screening. From the previous century until the 1960s, chemical compounds and natural products were tested in whole animal assays, and in the case of antibacterial and antitumor testing, the samples were tested in whole cell assays. Although screening was labor intensive and expensive, it was fruitful. A large number of successful drugs such as the cephalosporins, aminoglycosides, tetracyclines, macrolide antibiotics, doxyrubicin, etoposide, and other anticancer agents, steroids and drugs for use in the central nervous system and cardiovascular areas were discovered by screening [1,2]. In many cases, identification of the lead molecule, such as penicillin, cephalosporin, macrolides, captopril, and mevacor, spawned a large number of analogs through chemistry programs [3-7]. A single lead molecule identified in one company has, in many cases, kept several hundred industrial chemists and biologists busy for several years.
