Drug discovery stages candidate selection

Ultimately rapid methods are needed to obtain data adequate at each stage of drug discovery. At candidate selection level the extrapolation from animals to man, through the integration of pharmacokinetics and pharmacodynamics (PK/PD), becomes crucial for success [62, 63]. Such HT methods are currently being implemented and further developed in the pharmaceutical and biotechnology industry. 

As the compound reaches the late discovery and candidate selection stage, the focus is to determine its major metabolic pathways, metabolic difference between species, and to identify potential pharmacologically active or toxic metabolites. Because of the complexity, comprehensive metabolite characterization studies have been typically conducted at this stage with radiolabeled standard. Identification of circulating metabolites is also important at this stage to explain the pharmacokinetic or the pharmacodynamic profile. An NCE may show efficacy that is inconsistent with what is predicted based upon the known concentration of the parent drug. These inconsistencies could be due to the presence of active metabolites. The knowledge of these metabolites will also dictate how the analysis of samples will be conducted in the development and clinical studies. 

During the early stages of drug discovery, a suitable candidate must be selected from a limited number of structurally related compounds that may have a similar pharmacological profile. At that point, information from in vitro systems would provide important and particularly useful selection criteria. However, results from in vitro models are often not yet available at the early phases of development, or they exist only for a limited number of compounds. Accordingly, there is an urgent need for in silico methods that would allow prediction of the pharmacological properties in humans from the experimental model systems. 

A model for predicting oral bioavailability is an important tool, both in the early phases of drug discovery to select the most promising leads for further optimization, and in the later stages to select candidates for clinical development. The... 

Lipper, R. A. (1999). How can we optimize selection of drag development candidates from many compounds at the discovery stage Modem Drug Discov. 2 55. 

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