July 29, 2018

Treatment for Alzheimer's or False Alarm?

The most promising treatment of Alzheimer’s disease to date uses monoclonal antibodies to rid the brain of amyloid plaques. These plaques are widely thought to be crucial in the development of Alzheimer’s disease, the form of dementia that afflicts over 5 million Americans—and, unless we find a way to cure or prevent it, will afflict millions more in the coming years. Researchers hope that these drugs will prove to be “disease-modifying,” that they will disrupt the cascade of events that produces the symptoms of the disease. 

So far, the studies of monoclonal antibodies in this setting have been very disappointing: Bapinezumab: 3 failed trials. Solanezumab: 3 failed trials. Crenezumab: 1 failed trial. In the past year, three major pharmaceutical companies, Eli Lilly, AstraZeneca, and Merck, all stopped development of the monoclonal antibodies they were testing against Alzheimer’s disease. Another company, Pfizer, closed its neurodegenerative disease research section entirely. Now we learn that a Phase II trial of the as yet unnamed agent “BAN2401” actually “looks promising.” How promising?

Like its cousins, BAN2401 is a “humanized monoclonal antibody.” That means an antibody that was developed in mice and modified so it wouldn’t be rejected as alien by the human immune system. Now mice don’t normally get Alzheimer’s disease but certain strains have been genetically engineered so that they do. Using the genetically engineered mouse model, a monoclonal antibody was created that binds to amyloid. Today, this chemical is called BAN2401; when it enters the next stage of assessment, it will presumably acquire a name that ends in “zumab” to indicate it is just such a humanized monoclonal antibody. So, what do we know about this nameless entity?

We know that BAN2401 made it through a Phase I trial that tested its safety, tolerability, and pharmacokinetics in 80 people with mild to moderate dementia. We know it then entered Phase II of testing in people aged 50-90 with evidence of amyloid on their PET scans and either mild Alzheimer’s disease or mild cognitive impairment (a condition that is not dementia but often evolves into dementia). Five different dose regimens were administered intravenously and compared to placebo in terms of their effects on cognition and on brain amyloid deposits on PET scan. We know that when the preliminary results were announced last December, no cognitive benefit was reported. But now, after 18 months of study, the final results are in. They were presented at the Alzheimer’s Association International Conference in Chicago this past week.

What we don’t know is how this study will fare when subjected to peer review. We don’t know what the final paper will look like. But here’s what I can glean from the press release by Eisai, the company that collaborated with Biogen to develop and test the drug, and the reports by the news media:

--The amount of amyloid in the brain (as measured by PET scan) decreased with all the doses tested. The more drug, the greater the change. The findings were statistically significant. 

--There was no discernible effect on cognitive function except in the 161 people who were treated with the highest dose of BAN2401. In those 161 people, cognitive function deteriorated over time, just as it did in all the other groups, but it deteriorated less.

--Cognitive function was measured in a way that differs from the way it has been measured in other studies of treatments for Alzheimer’s disease. The researchers used a composite measure made up of several scales, each of which has been individually validated as a way to assess mental status, but only one of which is regularly used to report the outcome of clinical trials of Alzheimer’s drugs. 

--The patients tested included a mix of people with mild dementia and people with mild cognitive impairment (who don’t actually have dementia but aren’t entirely normal either) and the study had no way to determine whether the effectiveness of BAN2401 was any different in the two subgroups.

What does all this mean? The PET scan changes indicate that the monoclonal antibodies were successful in destroying amyloid deposits in the brain. That doesn’t prove that whatever effect the drug had was due to its amyloid-busting, but it’s suggestive. It also indicates that to the extent that the drug was a failure, it wasn’t a failure because it didn’t destroy amyloid. 

How should we interpret the cognitive changes? It’s hard to know, given that the researchers used a non-standard means of measuring clinical decline (a test they called ADCOMS). We cannot, for example, say that BAN2401 is better than one of the other monoclonal antibodies that was deemed a failure since nobody looked at the effect of the other drug on the “ADCOMS.” What we can say is that a 30 percent change in the rate of decline may be statistically significant but clinically, it’s a lot less impressive. Everyone  deteriorated, including those given the highest dose regimen; they just deteriorated a little less. How much of a difference actually occurred depends on the absolute decline: suppose the score went from 100 at baseline to 80 at the end of the study in the controls (I don’t know what the actual numbers are, so this is hypothetical). A 30 percent difference in the rate of decline means that the score in the treated group dropped from 100 to 86.  Is that clinically meaningful? Probably not.

So, no, BAN2401 is not likely to likely to dramatically change the course of Alzheimer’s disease. I hope the FDA does not allow the drug’s manufacturers catapult it into a clinical trial prematurely, before it goes through Phase 3 testing. But it has taught us a few valuable lessons. 

We now know that monoclonal antibodies can be designed that destroy amyloid plaques in the brain. We know that only the highest tolerated dose of the drug has any chance of being clinically useful. We should also realize the importance of studying patients with early dementia and those with MCI separately—it’s possible that using monoclonal antibodies once dementia has set in is too late, and I suppose that it’s also possible that using them before dementia has developed is too early. Finally, the study reminds us of the importance of a uniform methodology in conducting this kind of work. If the test that was previously regarded as the gold standard, the ADAS-Cog, is not the right test to use, then researchers need to agree on that and decide collectively what test to use instead. 

ABC News reported the drug as “giving patients hope” and showing “big promise.” Fortune magazine asserted that “world leaders want to end Alzheimer’s by 2025; a new drug breakthrough means we just might.” Investors are closer to the mark: Eisai’s stock price fell 10 percent after the data were reported.

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