The exact cause or causes of Alzheimer’s Disease (AD) is uncertain, but much evidence points to the so-called “Amyloid Hypothesis.” This hypothesis is that AD results from the accumulation of amyloid ß peptide (Aß), a collection of amino acids, in the brain. Scientists have successfully immunized mice against the Aß peptide, but this has yet to be shown to be safe and effective among humans. (Previous such drugs have been given initial trials in humans, but had unacceptably high rates of adverse side effects.) A recent study in Sweden tested the safety and immune response of a new drug that may prevent Aß peptide accumulation.
The study was a double-blind, placebo-controlled trial with older adult subjects who had been diagnosed with mild to moderate AD. Participants received either the drug (at one of two doses) or a placebo. Because it was a double-blind design, neither the participants nor those providing the drug or testing the participants knew whether the drug or placebo was being given. In all, 24 participants received 50 µg (micrograms, or .05 milligrams) of the drug, 22 received 150 µg, and 12 received placebo. This study was a Phase I trial, meaning that it is designed to identify a safe dose for the drug and identify potential side effects, rather than to prove the drug’s effectiveness.
Most participants given the experimental drug showed an Aß immune response, suggesting that future study of the drug is worth pursuing. (One participant in the placebo group showed a “response” as well.) There were side effects to the drug, but were of a type and severity typical of effective vaccines, suggesting that the drug is adequately safe for future testing.
There are important caveats to this and any other Phase I study. While the majority of participants in the experimental group had a positive antibody response, it has yet to be established that such a response will prevent dementia, or whether these findings will be repeated in a larger and more diverse sample. This is not a fault of the study, but is the nature of the drug approval process, which (for ethical and logistical reasons) begins with smaller-scale studies designed to identify a safe dose of the drug to be tested. The study did not assess the disease progression of the two groups, just the safety of the drug and the immune response. The authors also acknowledge that this study was funded by the company who manufactures the drug in question and was involved in the design and analysis of the study. Despite these caveats, this study may be an important first step toward finding a vaccine that might delay or prevent AD for many.
Winblad B, Andreasen N, Minthon L, et al. Safety, tolerability, and antibody response of active Aß immunotherapy with CAD106 in patients with Alzheimer’s disease: randomized, double-blind, placebo-controlled, first-in-human study. The Lancet Neurology (2012); 11(7):597-604.