Biomarkers and Surrogate Markers in Drug Development

Animal models provide a good starting point for identifying a compound's safety and efficacy, but do not always mirror results in humans. Early indicators of efficacy in humans are needed to minimize costs and time required for clinical trials, by providing reliable information on whether a novel compound warrants further development. Biomarkers provide early data in humans on whether a compound is reaching its intended target or modifying its intended disease pathway. Unfortunately, biomarkers represent a “wild-west” in drug development; few are fully validated, and research on their utility and what they truly represent is often conflicting. In addition, new biomarkers with unknown parameters are constantly being developed and added to the fray. This chapter reviews the most utilized biomarkers of efficacy, and the most promising new biomarkers being developed, in four major CNS indications: Alzheimer's disease, anxiety disorder, depression, and schizophrenia.