Failing trials for Alzheimer’s treaments based on the “amyloid hypothesis” are leaving scientists and pharmaceutical companies searching for better theories. The pharmaceutical company Merck terminated its Alzheimer’s late-stage trial of the drug verubecestat after an independent study found that it had no chance of working. Eli Lilly ended the clinical trial of its Alzheimer’s drug solanezumab, after patients taking it demonstrated no signs of improvement compared to those taking a placebo. Pfizer and Johnson & Johnson likewise ceased testing bapineuzumab.
The amyloid hypothesis predicts that because Alzheimer’s patients have an unusual buildup of the protein amyloid in their brains, drugs that prevent or remove the amyloid should slow the onset of dementia. Although many research studies have shown reversed or reduced memory loss in lab animals such as rats, which have been bred with human genes as a model for Alzheimer’s, none of these successes has yet been replicated in humans. Other large clinical trials targeting amyloid are still underway to test more powerful anti-amyloid drugs or retest previously failed drugs in patients with less advanced Alzheimer’s. Scientists believe the remaining trials will either affirm the amyloid hypothesis or kill it for good.