The search for disease-modifying drugs for Alzheimer's disease has been beset with expensive setbacks, such as the recent failure of a Phase III trial of dimebon, a compound for which Pfizer paid Medivation a US$225 million upfront fee for global marketing rights in 2008. This field is challenging to work in for several reasons, which include poorly predictive animal models of Alzheimer's disease and a lack of qualified biomarkers that can predict disease progression and drug response in clinical trials (see the review on page 560). A related problem is the lack of understanding of the natural course of the disorder, which is particularly needed for evaluating potential disease-modifying drugs that might be optimally used before symptoms become readily apparent.
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