Lecanemab: now for the (not that) bad news

A bombshell hit the news yesterday (11/20/22) about a breakthrough treatment for Alzheimer’s disease.  But the drug company announced the same news two months ago in the form of a press release.  Today’s story was merely about a formal presentation of the results at an Alzheimer’s conference that added some important safety data.  Here’s my blog post from September.

The drug is called lecanemab, and as its last three letters indicate, it’s a monoclonal antibody – in this case directed against the beta-amyloid protein.  That’s present in an abnormal, aggregated form in brain cells in Alzheimer’s but not in PSP.  In the trial, the antibody solution was infused intravenously every two weeks for 18 months and compared with a group of participants receiving placebo infusions.  The news was that lecanemab slowed the rate of worsening of Alzheimer’s by 27%.  This is great news from the PSP standpoint because it’s the first time that a monoclonal antibody was shown to slow progression of any neurodegenerative condition, even if it’s a different one.  We call that a “proof of principle.”

Today’s new information on the drug’s safety was most notable for a potentially serious issue called hemorrhagic encephalitis.  That’s where areas of the brain tissue undergo swelling and/or bleeding.  That combination is evidence of inflammation, the equivalent of a very sore arm after a Covid shot.  Among the 898 participants with AD who received active lecanemab over the 18 months of the trial, 13% had swelling, but for the 897 receiving placebo, the figure was 2% – a major difference.   For bleeding, the proportions were 17% for lecanemab and 9% for placebo – a minor difference.  Fortunately, none of those participants suffered important or permanent symptoms from the swelling or bleeding, which in most cases would not even have been suspected without the trial’s routine brain MRIs, and in all cases resolved in a few weeks.  However, one wonders how serious the problem could hypothetically be in a tiny percentage of people — too small a fraction to be detected in the 897 on lecanemab in this study.

The group on active lecanemab was a bit more likely than the placebo group to report a variety of serious side effects unrelated to brain swelling or bleeding: 14% vs 11%; and the lecanemab patients were more likely to drop out of the study because of other, assorted side effects: 7% vs 3%.

Now the FDA and Medicare/Medicaid have to decide if they’ll approve this treatment or if the cost (whatever that might turn out to be) and side effects outweigh the benefit. Or, they may require another large trial first.

So, the takeaway for those with PSP is that it’s possible to modestly slow the rate progression of a neurodegenerative disease with a monoclonal antibody treatment with probably only mild risk. The numbers about the hemorrhagic encephalitis are not to be ignored.  But I think that if a hypothetical treatment for PSP gave similar risk and benefit, and the out-of-pocket cost is affordable, I think the majority of people with PSP would ask where to sign up.

Lecanemab for Alzheimer’s: “Proof of Principle” for PSP

I’m not above plagiarizing myself. What follows is a piece I just wrote for the CurePSP website. It’s pitched at a simpler level than most of my blog posts, but it’s close enough. As I learn more about this drug, I’ll fill in some technical details for you.

Great news for people with Alzheimer’s disease:  A monoclonal antibody for intravenous infusion called “lecanemab” has been found to slow the rate of worsening of early-stage AD by 27%.  The Japanese drug company Eisai, which developed the drug, and the US company Biogen, which is assisting in the testing, jointly announced the news on September 26.  If approved by the FDA, lecanemab would be the first drug available to slow the underlying disease progression in AD rather than merely treating the symptoms, as Aricept and other existing drugs for AD do.

In almost all neurodegenerative diseases, one or more proteins forms clumps called “aggregates” in brain cells.  Lecanemab is an antibody directed against beta-amyloid, which is one of the two proteins that aggregate in AD.  The other such protein is tau, which of course is the one protein that aggregates in PSP and CBD.  In MSA, the protein is alpha-synuclein.  Beta-amyloid protein is not involved in PSP, CBD or MSA.  Two different monoclonal antibodies directed against the tau protein have failed to slow progression in PSP.  Nevertheless, the lecanemab news is welcome for people with PSP, CBD and MSA.  Here’s why:

  • This is the first demonstration that reducing levels of the aggregating protein in a neurodegenerative disease can actually slow the ongoing progression of the condition in humans.  (This has been accomplished in many ways in lab animals, but their artificial versions of human brain diseases are very incomplete models.)  This means that some other way of reducing tau protein in humans with PSP/CBD might work.
  • The two monoclonal antibodies that have failed in PSP were directed against the same end of the tau protein (called the “C-terminal” or “microtubule-binding domain,” if you want to get technical).  Other monoclonal antibodies directed against the other end of tau (the “N-terminal”) might work better, especially as fragments of tau that include the N-terminal now seem to be the bad actors.  Such monoclonal antibodies are in early-phase testing.
  • Until now, it has not been fully clear that in human neurodegenerative diseases, the aggregating protein is what’s causing the loss of brain cells.  Competing theories suggest that something else is damaging the brain cells and the protein aggregation is merely a result of that process rather than its cause.  The lecanemab news suggests that the aggregates themselves are to blame.  This makes future drug development a lot easier and more focused.
  • Although no monoclonal antibody trials are currently in progress for PSP, CBD or MSA, there is a current trial of another way to reduce tau protein.  Rather than destroying protein as antibodies do, this approach prevents the offending protein from being manufactured in the first place.  It’s called “anti-sense oligonucleotide” treatment, and an early-phase safety trial for PSP is under way at several sites in the US and elsewhere.  Trials of other ASOs for other neurodegenerative diseases are planned.

So, we congratulate the AD world on this successful trial, which we hope and expect will be the first of many, and we take heart that this “proof of principle,” as scientists call it, can soon be applied to PSP, CBD and MSA.