Genetically engineered mouse models for drug discovery: new chemical genetic approaches.
While standard transgenic and knockout mouse technologies have provided a wealth of information for target selection and validation, there have been great advances in using more sophisticated modeling techniques to achieve temporal and spatial regulation of individual genes in adult animals. Recent developments in RNA interference (RNAi) technology in in vivo models promise to further improve upon the static and irreversible features of gene knockouts. Chemical genetic approaches create novel functional alleles of targets and allow fine modulation of protein function in vivo by small molecules, providing the most pharmacologically relevant target validation. Using these advanced models, one can not only ask whether the function of the target is critical for the initiation and maintenance of the disease, but also whether therapies designed to alter the function of the target would be safe and efficacious. In this review, we describe various in vivo tools for target validation in mouse models, discuss advantages and disadvantages of each approach, and give examples of their impact on drug discovery.