Novel Drug for Mild-to-Moderate Alzheimer's Disease Demonstrates Safety and Tolerability at 18-Months

Eisai Co., Ltd. and Biogen Inc. have announced that elenbecestat was generally safe and well tolerated in a Phase II clinical study of the oral BACE (beta amyloid cleaving enzyme) inhibitor elenbecestat conducted in the United States, and the results demonstrated a statistically significant difference in amyloid beta (AB) levels in the brain measured by amyloid-PET (positron emission tomography).

Elenbecestat, discovered by Eisai, has been jointly developed by Eisai and Biogen since March 2014. The two companies are currently conducting two global Phase III clinical studies (MISSION AD1/2) in early Alzheimer's disease

A numerical slowing of decline in functional clinical scales of a potentially clinically important difference was also observed, although this effect was not statistically significant. This study, a Phase II study of 70 patients, is the first study of a BACE inhibitor to show a statistically significant difference in amyloid beta in the brain while also suggesting a delay of clinical symptom decline in exploratory endpoints.

The study is a multicenter, randomized, double-blind, placebocontrolled parallel-group 18-month Phase II clinical study in patients with mild cognitive impairment (MCI) due to Alzheimer's disease, or mild to moderate dementia due to Alzheimer's disease with confirmed amyloid pathology by PET screening. Seventy patients were randomized to four treatment arms receiving elenbecestat (5, 15, or 50 mg) or placebo daily.

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During the study period, more than half the patients in the elenbecestat 5 mg and 15 mg arms were switched to the 50 mg arm for three months or more. The 50 mg treatment arm plus the group switched to the 50 mg arm are hereafter referred to as "50 mg total arm" (38 subjects) with a mean duration of approximately 11 months on 50 mg per day.

Elenbecestat demonstrated acceptable safety and tolerability profile through 18 months of study drug administration. In the elenbecestat 50 mg total arm, the six most common adverse events observed were contact dermatitis, upper respiratory infection, headache, diarrhea, fall, and dermatitis. No serious adverse reactions suggestive of hepatic toxicity were observed in this study.

In addition to the safety objectives, the study assessed AB in the brain at 18 months as measured by amyloid PET as well as efficacy in terms of clinical symptoms, which were exploratory objectives in this study.

The elenbecestat 50 mg total arm demonstrated a statistically significant difference in AB levels in the brain as measured by amyloid PET compared with placebo (35 subjects participated in this longitudinal amyloid PET assessment). This is the first time in which a significant effect in AB in the brain using a BACE inhibitor was confirmed in a clinical study of patients with mild cognitive impairment (MCI) through moderate Alzheimer's dementia.

CDR-SB (Clinical Dementia Rating Sum of Boxes) was an exploratory endpoint to assess efficacy in terms of clinical symptoms. The study showed numerically less decline in CDR-SB for the elenbecestat 50 mg total arm as compared to placebo of a potentially clinically important difference, 41 subjects participated in this assessment, which was not statistically significant. Further, a similar magnitude and direction of differential in decline was observed in a post-hoc analysis of ADCOMS, Eisai's newly developed assessment scale (Alzheimer's Disease Composite Score) in the elenbecestat 50 mg total arm as compared to placebo. The study was not powered to show statistical significance compared to placebo on clinical symptoms.

Eisai plans to present detailed results of the study at a future medical meeting.

"It is highly encouraging that this study confirmed elenbecestat's treatment effect in reducing amyloid in the brain and suggested a slowing of clinical decline. Eisai and Biogen will continue to work together to advance the ongoing Phase III program (MISSION AD) in order to contribute a new potential treatment option to Alzheimer's disease patients as soon as possible," said Lynn Kramer, MD, Chief Clinical Officer and Chief Medical Officer, Neurology Business Group, Eisai.

"Biogen is heartened by the safety and tolerability results of this study of elenbecestat," said Alfred Sandrock, M.D., Ph.D., executive vice president and chief medical officer at Biogen. "We remain committed to research in Alzheimer's, an area of significant unmet need with a devastating impact on those living with the disease, their families, friends, and society."

By inhibiting BACE, a key enzyme in the production of Aβ peptides, elenbecestat reduces amyloid beta production, which is thought to lead to a reduction in amyloid plaque formations caused by the aggregation of toxic oligomers and protofibrils in the brain. Currently, two global Phase III clinical studies (MISSION AD1/2) of elenbecestat in early Alzheimer’s disease including mild cognitive impairment (MCI) due to AD/Prodromal AD and the early stages of mild AD are underway. In addition, the U.S. Food and Drug Administration (FDA) has granted Fast Track designation for the development of elenbecestat, a process allowing priority reviews by the FDA for drugs deemed as having potential to treat serious conditions and tackle key unmet medical needs.

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