Prospects for neurodegenerative and psychiatric disorder drug discovery.

The discovery of CNS-active drugs has, to a major extent, resulted from clinical serendipity. Once targets for such compounds were identified, conventional mechanism-based approaches were used to identify new chemical entities for the treatment of neurological and psychiatric disorders. Most of these have, however, failed to display any greater efficacy than existing psychotherapeutics and may, in fact, be less efficacious because of side effect liabilities. Among the reasons for this lack of success in drug discovery include a lack of fundamental knowledge regarding the causes of CNS disorders, the absence of biomarkers for diagnosing and monitoring these conditions, a paucity of animal models that are congruent with the human disease state and the increasing likelihood that CNS conditions are multifactorial in their etiology. These challenges force the inclusion of a Phase IIa proof of concept trial as a component of the drug discovery program. Unlike other therapeutic areas, serendipity is a major factor in the CNS translational medicine interface requiring a close collaboration between preclinical and clinical scientists trained to appreciate unusual behavioral phenotypes. When combined with conventional target-based drug discovery technologies, this increases the likelihood of identifying truly novel drugs for the treatment of CNS disorders.