The scopolamine model as a pharmacodynamic marker in early drug development.

Rationale: Drug development is a high-risk and high failure enterprise, and studies that provide an early read on the pharmacodynamic activity of novel compounds could save time and money, increasing the efficiency of the drug development process.

Objective: Preclinical and clinical experiments were designed to examine the utility of the scopolamine-induced cognitive impairment model in predicting pharmacodynamic signals of putatively procognitive compounds, utilizing the acetylcholinesterase inhibitor donepezil for illustration.

Methods/results: In normal healthy rats, scopolamine (0.3 mg/kg) significantly impaired performance on the two-platform water maze and on the T-maze. The deficits in water maze performance were reversed by donepezil at 0.5 and 1.0 mg/kg. There was a trend towards reversal of scopolamine-induced deficits in performance on the T-maze with 1.0 mg/kg donepezil. In normal healthy humans, scopolamine (0.3 and 0.5 mg) reliably impaired performance on the Cognitive Drug Research test battery composite scores (power of attention, continuity of attention, quality of working memory, quality of episodic secondary memory, and speed of memory) in a dose- and time-dependent manner. Donepezil (10 mg) significantly attenuated the scopolamine-induced impairment in cognition on power of attention, continuity of attention, quality of working memory, and speed of memory.

Conclusions: These findings suggest that reversal of scopolamine-induced cognitive impairment is a viable model for predicting pharmacodynamic signals of procognitive compounds in both animals and humans. The utility of the scopolamine-induced cognitive impairment model is discussed and illustrated at various decision points in drug development, with a focus on Go/No Go decisions.