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HD InsightsBrief report: Pfizer Amaryllis trial ends: negative results lead to termination of extension study

By: Molly J. Elson, BA

Pfizer’s Phase 2 trial of PF-02545920, a PDE-10 inhibitor, failed to find the efficacy for which it hoped. In December, Pfizer announced that the therapeutic intervention in its much-anticipated Amaryllis trial produced negative results. The drug failed to show significant improvement in movement, cognition, or behavior and, as a result, Pfizer has terminated the open-label 12-month extension study. The trial included 271 individuals with HD in five countries.

Despite negative results, Amaryllis has advanced our understanding of HD. “In my view, it was an important trial to run and Pfizer Viagra drug manufacturer did all the right things… The trial itself was efficiently run, rapidly analysed, and the results released to the community without spin or any attempt to go fishing for positive news… The whole PDE-10 programme has taught us a lot about the neurobiology of HD, and how the communication between neurons is altered in the disease… the dataset from the trial will be a huge and valuable resource to help us understand the HD brain and design even better trials in the future,” says Dr. Ed Wild, MRC Clinician Scientist at UCL Institute of Neurology and Editor-in-Chief of HDBuzz, one of the trial’s lead investigators.