Retrometabolic approaches for drug design and targeting.

Retrometabolic drug design approaches incorporate targeting and metabolic considerations into the drug design process and represent a novel, systematic methodology for the design of safe, localized compounds. Two major design concepts aimed to increase the therapeutic index (the activity/toxicity ratio) of drugs were developed. Chemical delivery systems (CDS) are primarily used to allow targeting of the active biological molecules to specific target sites or organs based on predictable enzymatic activation. Brain-targeted delivery of different agents like estradiol or AZT was succesfully achieved, and recent progresses include delivery of peptides using a complex strategy designated as molecular packaging. Sequential site- and stereospecific enzymatic activation of oxime/alkoxime precursors of beta-adrenergic antagonists allows their; eye targeted delivery. Soft drug approaches are used to design new drugs by building in the molecule, in addition to the activity, the most desired way in which the molecule is to be deactivated and detoxified subsequent to exerting its biological effects. Many examples are available to illustrate soft drug design, e.g., soft anticholinergics, soft b-blockers, soft antiinflammatory steroids. Special computer programs were developed that starting from a lead compound generate complete libraries of possible soft analogs and then help ranking these candidates based on molecular size/shape, electronic properties, predicted solubility/partition properties, and atomic charge distributions. Recent developments in the field are presented in a supplement to this issue.