Molecular recognition: identifying compounds and their targets

As a result of gene sequencing and proteomic efforts, thousands of new genes and proteins are now available as potential drug targets. The milieu of these proteins is complex and interactive; thousands of proteins activate, inhibit, and control each other's actions. The effect of blocking or activating a protein in a cell is far-reaching, and can affect whole, as well as adjacent pathways. This network of pathways is dynamic and a cellular response can change depending on the stimulus. In this section, the identification and role of individual proteins within the context of networked pathways, and the regulation of the activity of these proteins is discussed. Diverse chemical libraries, combinatorial libraries, natural products, as well as unnatural natural products that are derived from combinatorial biology (Chiu [2001] Proc. Natl. Acad. Sci. USA. 98:8548-8553), provide the chemical diversity in the search for new drugs to block new targets. Identifying new compounds that can become drugs is a long, expensive, and arduous task and potential targets must be carefully defined so as not to waste valuable resources. Equally important is the selection of compounds to be future drug candidates. Target selectivity in no way guarantees clinical efficacy, as the compound must meet pharmaceutical requirements, such as solubility, absorption, tissue distribution, and lack of toxicity. Thus matching biological diversity with chemical diversity involves something more than tight interactions, it involves interactions of the compounds with a variety host factors that can modulate its activity.