Target site research

A pharmacotectonics concept was illustrated by researchers, in which drug-delivery systems were arranged spatially in tissues to shape concentration fields for potent agents. NGF-releasing implants placed within 1-2 mm of the treatment site enhanced the biological function of cellular targets, whereas identical implants placed mm from the target site of treatment produced no beneficial effect (Mahoney and Saltzman, 1999). Because of some limitations with controlled delivery systems, alternatives such as encapsulation of cells that secrete these factors are discussed in the next section. 

The focus of research in the field of drug targeting is mainly on the selectivity of the DC for the target site (see other chapters in this book), undoubtedly because it is the essential... 

Our goal was to determine the specific target site(s) of action of the aryloxyphenoxypropanoate and cyclohexanedione herbicides. We set two simple criteria as prerequisites for identifying physiological processes as possible target sites. The site of action must be affected (1) rapidly (within minutes) and (2) by low concentrations (lipid metabolism because it seemed most sensitive to these herbicides (11.12). 

Acetolactate synthase (ALS, EC 4.1.3.18) is the first common enzyme in the biosynthetic route to the branched chain amino acids, valine, leucine and isoleucine. It is the primary target site of action for at least three structurally distinct classes of herbicides, the imidazolinones (IM), sulfonylureas (SU), and triazolopyrimidines (TP) (Figure 1). SU and IM were discovered in greenhouse screening programs whereas TP was subsequently targeted as a herbicide. Numerous substitution patterns can be incorporated into the basic structure of all three classes of herbicides to provide crop selectivity as well as broad spectrum weed control. This is amply demonstrated in the seven products based on SU and four based on IM already in the market. A number of others are in various stages of development. The rapid success of ALS inhibitors as herbicidal products has attracted a world-wide research commitment. Not since the photosystem II... 

Encapsulated delivery systems are developed with a specific purpose for each target application. To date, most research has been directed at stabilizing extracted bioactives and delivering the required levels in food. Their ultimate delivery to a target site depends on the core, the material and the methods used for encapsulation as well as the food vehicle used for delivery. Although there have been many technological advances there are still limitations to the use of microencapsulated ingredients in some applications. 

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