The Alzheimer’s field begins 2021 with a glimmer of good news: Donanemab, a monoclonal antibody that recognizes a pyroglutamated form of Aβ, slowed cognitive decline in people with early AD. That was the upshot of the topline results of the Phase 2 TRAILBLAZER-ALZ study, announced by Eli Lilly & Company on January 10. In addition to stemming cognitive decline, the monoclonal also wiped out Aβ plaques, lowering them into the range seen in healthy volunteers.
- Donanemab slowed decline on the Integrated Alzheimer's Disease Rating Scale by a third.
- The drug reduced Aβ plaques into the normal range.
- A larger Phase 2 trial is ongoing.
“It’s a good day for the field,” said Eric Siemers of Siemers Integration, LLC, who worked at Lilly when the trial began but has since retired. “We now have one more monoclonal antibody signaling in the right direction.”
Cynthia Lemere of Brigham and Women’s Hospital in Boston welcomed the news. “Lilly’s Phase 2 positive findings lend further support to the amyloid hypothesis and validate Aβ as a therapeutic target for early-stage AD,” she wrote (full comment below).
Donanemab is unique among the cadre of anti-Aβ monoclonal antibodies developed so far. Rather than latching onto a specific amino acid epitope within the original peptide, donanemab recognizes Aβ(p3-42), an enzymatically modified form of Aβ adorned with pyroglutamate at its N-terminus. This form of Aβ is only found within amyloid plaques (Dec 2012 news; Jul 2014 news).
In a Phase 1b trial, the antibody had demonstrated prowess at plaque removal (Aug 2018 conference news; Dec 2019 conference news). This spurred Lilly to test whether banishing Aβ plaques would also slow cognitive decline in people with AD.
In 2017, the Phase 2 TRAILBLAZER-ALZ began enrolling people in the early symptomatic phase of AD. Participants had to score between 20 and 28 on the mini-mental state examination, and have had memory loss stretching back at least six months. The trial enrolled participants with evidence of amyloid plaques, whose neurofibrillary tangle accumulation fell within a low-to-medium range, defined by an SUVR of 1.15 to 1.36 by flortaucipir PET. Mark Mintun of Eli Lilly told Alzforum that using tau PET in this way helped select participants who were in the process of decline, but at an early enough stage to make them still likely to benefit from this treatment. The trial was initially designed as a combination study, testing the effectiveness of donanemab alone or in combination with Lilly’s BACE1 inhibitor, LY3202626, but in 2018 Lilly discontinued this latter portion.
The topline results disclosed yesterday are based on data from 272 participants randomized 1:1 to receive placebo or donanemab for 76 weeks. People in the treatment arm received 700 mg of donanemab once a month for the first three doses, then 1400 mg monthly thereafter. Notably, participants were switched to placebo once their plaque load dipped into the normal range, i.e. falling below 25 centiloids for two consecutive measures or below 11 centiloids at any one measure.
The trial met its primary endpoint, slowing decline on the Integrated Alzheimer’s Disease Rating Scale in the donanemab group by 32 percent relative to placebo. Developed by scientists at Eli Lilly, the iADRS tests both cognition and function, and is essentially a combination of the ADAS-Cog13 and the ADCS-iADL (Wessels et al., 2015). The company disclosed no numeric results of secondary clinical outcomes, but did claim that participants in the donanemab group trended better than those on placebo on every secondary measure.
Confirming findings from earlier trials, donanemab cleared amyloid plaques. In the treatment group, amyloid plummeted by an average of 84 centiloids, from 108 to 24. Anything less than 25 centiloids is considered within the normal range of amyloid accumulation. Lilly scientists did not say how many participants dropped below this threshold and were therefore switched to placebo.
Consistent with the Phase 1 data, donanemab did trigger amyloid-related imaging abnormalities—edema (ARIA-E), which occurred in 27 percent of treated participants, including 6 percent in whom it was symptomatic.
Lilly is currently enrolling participants into an open-label extension, which will continue to study safety, cognition, Aβ and tau deposition, while also validating the accuracy of home video-based cognitive assessments.
A larger placebo-controlled Phase 2 study, TRAILBLAZER-ALZ-2, began in June of last year. The 18-month trial will enroll 500 participants with early AD but, unlike its predecessor, will not exclude participants with high levels of neurofibrillary tangle accumulation. Mintun told Alzforum that the boost in statistical power gained from the larger trial allows the inclusion of participants with more advanced disease.
The larger trial will also move participants to placebo once their amyloid drops into the normal range. Mintun said that because donanemab’s target—pyroglutamated Aβ—resides specifically within Aβ plaques, there is no need to continue dosing once that target is gone. What about if amyloid creeps back up? Mintun said that given the slow, decades-long process of amyloid accumulation that occurs during the preclinical phase of AD, this is unlikely to happen within the course of an 18-month trial. Therefore, there are no plans, either within the placebo-controlled portion of the trial or in an extension phase, to switch plaque-cleared participants back to donanemab.
How does this compare to BAN2401 aka lecanemab—an antibody that recognizes Aβ protofibrils found in both plaques and oligomers? In a large Phase 2 trial, lecanemab also virtually wiped out plaques (Jul 2018 conference news). However, participants were off drug for anywhere between nine and 60 months before starting an open-label extension study. During that time, plaques remained at bay but cognition started to slide, suggesting that even in the absence of full-blown plaques, continued dosing of BAN2401 was necessary to maintain cognition (Dec 2019 conference news). This could be due to lecanemab’s binding to toxic oligomers, scientists have proposed. Unlike lecanemab, donanemab is not thought to bind oligomers. However, Siemers suggested donanemab may indirectly get rid of other toxic Aβ species by removing their reservoir, i.e. plaques. Whether draining this Aβ swamp is sufficient to hold off cognitive decline for years to come remains to be seen.
In its press release, Lilly referred to the second donanemab Phase 2 trial as “pivotal” (see press release). Does that imply positive results could be used to apply for regulatory approval, sans Phase 3? Mintun said both TRAILBLAZER-ALZ trials were designed as registration-level studies. “We believe that if both studies reinforce each other and describe a clearly efficacious drug, that would be compelling evidence,” Mintun said. Lilly will discuss data available thus far with regulators, including the FDA, to determine next steps.
Donanemab’s development path is slim compared to what Lilly did with solanezumab, an anti-Aβ antibody binding mostly Aβ monomers. Lilly ran three large Phase 3 trials of that antibody. If donanemab’s 32 percent slowing of decline sounds familiar, Lilly’s solanezumab ordeal may be the reason. The first two trials—Expedition 1 and 2—tested solanezumab in people with mild to moderate AD, without PET to select amyloid-positive participants. Both trials missed their primary endpoint, but a secondary analysis of participants with mild AD found solanezumab had slowed their progression by 34 percent (Siemers et al., 2015; Aug 2015 news). Lilly then ran a third Phase 3 trial—Expedition 3—that included only people with mild AD who had amyloid accumulation. In a blow, that trial missed its primary endpoint, with solanezumab slowing decline on the ADAS-Cog by only 11 percent, which was not statistically significant (Dec 2016 conference news; Jan 2018 news).
Mintun said that despite the glimmer of hope offered by the post hoc analyses of Expedition 1 and 2, all three Expedition trials fell short of their primary endpoints. In this initial Phase 2 trial, donanemab met the primary endpoint.—Jessica Shugart
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- CTAD: Solanezumab Seen to Nudge AD Ever so Slightly
- End of the EXPEDITION: Solanezumab Results Published
- Wessels AM, Siemers ER, Yu P, Andersen SW, Holdridge KC, Sims JR, Sundell K, Stern Y, Rentz DM, Dubois B, Jones RW, Cummings J, Aisen PS. A Combined Measure of Cognition and Function for Clinical Trials: The Integrated Alzheimer's Disease Rating Scale (iADRS). J Prev Alzheimers Dis. 2015 Dec 1;2(4):227-241. PubMed.
- Siemers ER, Sundell KL, Carlson C, Case M, Sethuraman G, Liu-Seifert H, Dowsett SA, Pontecorvo MJ, Dean RA, Demattos R. Phase 3 solanezumab trials: Secondary outcomes in mild Alzheimer's disease patients. Alzheimers Dement. 2015 Aug 1; PubMed.