Has inhibition of Aβ production adequately been tested as therapeutic approach in mild AD? A model-based meta-analysis of γ-secretase inhibitor data.

Purpose: To date, γ-secretase inhibition is the most frequently studied mechanism of reducing Aβ in clinical trials with as yet no therapeutic success for AD patients, as measured by the slowing down of cognitive decline or an improvement in cognitive function. The aims of this investigation were to evaluate whether the amyloid hypothesis has been tested clinically, and to explore whether preclinical data are predictive of clinical Aβ effects.
Methods: A model-based-meta analysis on Aβ levels and drug exposure over time was performed on published and in-house (pre-)clinical data with γ-secretase inhibitors (GSIs; semagacestat, avagacestat, begacestat, PF-3074014, and MK0752).
Results: The clinical data available did not show any significant or robust reduction of CNS Aβ over time at dose levels intended for AD patients. In contrast, these doses resulted in an average increase in plasma Aβ levels over a 24-h interval. A general agreement between preclinical and clinical data was found and allowed for interspecies extrapolations.
Conclusions: More substantially, CNS Aβ-lowering drugs are needed to test whether inhibition of Aβ production is efficacious in mild AD. Predictions based on preclinical data could assist in the selection of drug candidates and trial design.