Lead compounds drug-receptor interactions

Drug metabolism has been recognized as one of the key factors in the discovery of new chemical entities. A lead compound needs to not only interact with the target enzyme/receptor but also remain over a certain threshold concentration at the site of action for a defined period to produce the desired therapeutic effect. Drug metabolism together with absorption, distribution and excretion are among the factors that influence the final time-concentration relationship of drugs and therefore the potential efficacy of the compound [1],... 

The next step is the screening of thousands of these compounds to hnd lead compounds or potential drug molecules that bind with receptors and modulate disease pathways. When an interaction happens, it is referred to as a hit. ... 

The effect of a given adrenomimetic drug on a particular type of effector cell depends on the receptor selectivity of the drug, the response characteristics of the effector cells, and the predominant type of adrenoceptor found on the cells. For example, the smooth muscle cells of many blood vessels have only or predominantly a-adrenoceptors. The interaction of compounds with these adrenoceptors initiates a chain of events in the vascular smooth muscle cells that leads to activation of the contractile process. Thus, norepinephrine and epinephrine, which have high affinities for a-adrenoceptors, cause the vascular muscle to contract and the blood vessels to constrict. Since bronchial smooth muscle contains p2-adrenoceptors, the response in this tissue elicited by the action of p2-adrenoceptor agonists is relaxation of smooth muscle cells. Epinephrine and isoproterenol, which have high affinities for p2-adrenoceptors, cause relaxation of bronchial smooth muscle. Norepinephrine has a lower affinity for p2-adrenoceptors and has relatively weak bronchiolar relaxing properties. 

As a lead compound is optimized, enhancing the features of the pharmacophore in order to elicit a more energetic therapeutic interaction with the receptor is important. So too is modifying toxicophores to lessen or eliminate side effects. In addition to these pharmacodynamic and toxicodynamic considerations, pharmacokinetic considerations need to be addressed. The goal here is to modify the metabophore where possible to minimize the drug s metabolism in the liver and its rapid excretion by the kidneys, thereby giving the molecule a greater chance to exert its desired pharmacodynamic effects. 

The pharmacophore concept plays a very important role in guiding the drug discovery process. Pharmacophore models help medicinal chemists gain an insight into the key interactions between ligand and receptor when the receptor structure has not been determined experimentally. A pharmacophore can be used as a basis for the alignment rules in 3D-QSAR analysis for the lead compound optimization... 

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