Mixed Results for Aducanumab in Two Phase 3 AD Trials

Damian McNamara

May 28, 2020

High-dose aducanumab, a human monoclonal antibody in development, significantly reduced clinical decline in people with early Alzheimer's disease in one randomized, placebo-controlled phase 3 study but not in another identical study. Aducanumab was associated with favorable changes in activities of daily living and in Alzheimer's disease biomarkers.

The EMERGE and ENGAGE studies compared low-dose and high-dose aducanumab and placebo over 78 weeks. The high-dose EMERGE cohort experienced a 22% improvement in the primary outcome – adjusted mean Clinical Dementia Rating Sum of Box (CDR-SB) scores – compared with baseline.

"We have with EMERGE, in the high-dose group, a positive result," said lead author Samantha Budd Haeberlein, PhD, who presented this research online as part of the 2020 American Academy of Neurology Science Highlights.

In contrast, the low-dose EMERGE group, as well as the low-dose and high-dose cohorts in the ENGAGE study, experienced no statistically significant change in CDR-SB outcomes.

Clinical benefit was associated with the degree of exposure to aducanumab. For example, a protocol adjustment during the study increased the mean dose of aducanumab, a move associated with better outcomes.

"We believe that the difference between the results was largely due to patients' greater exposure to the high dose of aducanumab," Dr. Haerberlein, senior vice president and head of the neurodegeneration development unit at Biogen in Cambridge, Mass., said in an interview.

Although the studies shared an identical design, "because ENGAGE began enrolling first and recruitment remained ahead of EMERGE, more patients in EMERGE were impacted by the protocol amendments, which we believe resulted in a higher number of patients exposed to the highest dose in EMERGE versus ENGAGE," Dr. Haerberlein added.

The EMERGE and ENGAGE studies were conducted at 348 sites in 20 countries. The research included a total of 3,285 participants with mild cognitive impairment caused by Alzheimer's disease or mild Alzheimer's disease dementia.

The mean age was 70 years, about 52% were women, and slightly more than half had a history of taking medication for Alzheimer's disease. The mean Mini-Mental State Exam (MMSE) score was 26 at baseline.

Key Findings

Dr. Haerberlein and colleagues reported that the 22% decrease in CDR-SB scores in the high-dose EMERGE participants was significant (P = .01). No significant difference emerged, however, in the ENGAGE study, where high-dose participants had a 2% decrease at 78 weeks in CDR-SB scores (P = .83).

The high-dose EMERGE regimen was also associated with an 18% improvement in MMSE scores (P < .05). In the ENGAGE study, the high-dose MMSE scores increased a nonsignificant 3% (P = .81).

The researchers reported no significant differences in the low-dose cohorts in both studies regarding CDR-SB or MMSE scores at week 78, compared with baseline.

They also assessed amyloid using PET scans. Levels remained essentially the same throughout both studies in the placebo participants. In contrast, there was a statistically significant, dose- and time-dependent reduction associated with both low- and high-dose aducanumab.

Aducanumab treatment was associated with significant benefits on measures of cognition and function such as memory, orientation, and language, Dr. Haeberlein said. "Patients also experienced benefits on activities of daily living including conducting personal finances; performing household chores such as cleaning, shopping, and doing laundry; and independently traveling out of the home."

Furthermore, reductions in the CSF biomarker phospho-tau in the high-dose EMERGE and ENGAGE cohorts were statistically significant. In contrast, changes in total tau were not significant.

The proportion of patients who experienced an adverse event during EMERGE was similar across groups – 92% of the high-dose group, 88% of the low-dose group, and 87% of the placebo cohort. Similar rates were reported in the ENGAGE high-dose, 90%; low-dose, 90%; and placebo cohorts, 86%.

Adverse events reported in more than 10% of participants included headache, nasopharyngitis, and two forms of amyloid-related imaging abnormalities (ARIA), one of which related to edema (ARIA-E) and the other to hemosiderosis (ARIA-H).

Future Plans

Going forward, the researchers are conducting a redosing study to offer aducanumab to all participants in the clinical trials. Also, Biogen is completing the filing of a Biologics License Application with the Food and Drug Administration and with regulatory agencies in other countries.

Early identification and treatment of Alzheimer's disease remains a priority, Dr. Haeberlein said, because it offers an opportunity to begin health measures like exercise, mental activity, and social engagement; allows people more time to plan for the future; and gives families and loved ones' time to prepare and support each other. From a research perspective, early identification of this population can maximize chances of participation in a clinical trial as well.

Unanswered Questions

"Briefly, while both [studies] were looking at aducanumab's effect on rate of decline across a variety of measures, one statistically showed a positive impact in a subset and the other did not," Richard J. Caselli, MD, said when asked to comment on the EMERGE and ENGAGE findings. "The subset were the mildest affected patients on the highest dose for the longest time."

The main difference between the two studies was that one was adequately powered for this subanalysis and the other was not. Even the underpowered subanalysis showed a beneficial trend, added Dr. Caselli, a neurologist at the Mayo Clinic in Phoenix, Arizona.

Dr. Caselli said these findings raise a number of unanswered questions. For example, is a subanalysis valid? Is the degree of improvement clinically meaningful or meaningful enough to justify the anticipated cost of the drug itself – "likely to be very expensive" plus the "cost and hassle" of monthly IV infusions? Is there enough provider and infusion center capacity going forward? What will the reimbursement from third party payers be like?

Biogen sponsored the EMERGE and ENGAGE studies. Dr. Haeberlein is a Biogen employee. Dr. Caselli had no relevant disclosures.

SOURCE: Haeberlein SB et al. AAN 2020, Abstract 46977.

This story originally appeared on MDedge.com.

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