Current and evolving treatment strategies for the Alzheimer disease continuum

The burden of Alzheimer disease (AD) on the US healthcare system is substantial and increasing. AD progresses along a continuum from preclinical disease characterized by normal cognition and abnormal brain biomarkers to mild cognitive impairment and then clinically apparent dementia. Diagnosis early in the AD continuum has benefits for patients and caregivers and appears cost-effective, but often, the clinical diagnosis of AD may be delayed. Currently available biomarkers include β-amyloid positron emission tomography and cerebrospinal fluid tests. Collectively, they are expensive, may lead to adverse effects, are not widely available, and are not suited for primary care. Currently available treatment options, cholinesterase inhibitors and memantine, do not alter disease progression, but can help with some symptoms. Benefits of currently available treatments on cognition are difficult to quantify and are offset by a burden of adverse effects that often go unrecognized. More accurate diagnostic biomarkers and disease-modifying drug therapies are critical unmet needs of patients with AD despite decades of clinical research. Because many phase 3 clinical trials that enrolled patients with symptomatic AD have failed, researchers believe that disease-modifying treatment is more likely to demonstrate benefit when utilized early in the disease continuum. Within the past few years, significant achievements that will advance clinical trials in early AD include the Research Framework to define and stage the AD continuum, FDA guidance on study design in early AD, and development of scales to measure cognition that are suitable for early AD. In October 2019, the AD community was re-invigorated by unexpected news that a Biologics License Application will be submitted for aducanumab to treat AD. This article explores the current state of biomarker-driven drug development across the AD continuum and reviews investigational drugs in phase 2/3 clinical development for AD.