A Study of ATH-1017 in Mild to Moderate Alzheimer's Disease

Key Inclusion Criteria: * Age 55 to 85 years * Mild-to-moderate AD dementia subjects, MMSE 14-24, CDR 1 or 2 at Screening * Clinical diagnosis of dementia, due probably to AD, by Revised National Institute on Aging-Alzheimer's Association criteria (McKhann, 2011) * Reliable and capable support person/caregiver * Treatment-free or receiving stable acetylcholinesterase inhibitor (AChEI) treatment, defined as: * Treatment-naïve, OR * Subjects are on a stable, approved dose of an AChEI (except for donepezil at 23 mg PO) for at least 3 months before Screening OR * Subjects who received an AChEI in the past and discontinued 4 weeks prior to Screening Key Exclusion Criteria: * History of significant neurologic disease, other than AD, that may affect cognition, or concurrent with the onset of dementia * History of unexplained loss of consciousness, and epileptic fits (unless febrile) * Subject has atypical variant presentation of AD, if known from medical history, particularly non-amnestic AD * History of brain MRI scan indicative of any other significant abnormality * Hearing test result considered unacceptable for auditory ERP P300 assessment * Diagnosis of severe major depressive disorder even without psychotic features * Significant suicide risk * History within 2 years of Screening, or current diagnosis of psychosis * Myocardial infarction or unstable angina within the last 6 months * Clinically significant (in the judgment of the investigator) cardiac arrhythmia (including atrial fibrillation), cardiomyopathy, or cardiac conduction defect (note: pacemaker is acceptable) * Subject has either hypertension (supine diastolic blood pressure \> 95 mmHg), or symptomatic hypotension in the judgment of the investigator * Clinically significant ECG abnormality at Screening * Renal insufficiency (serum creatinine \> 2.0 mg/dL) * Hepatic impairment with alanine aminotransferase or aspartate aminotransferase \> 2 times the upper limit of normal, or Child-Pugh class B and C * Malignant tumor within 3 years before Screening * Memantine in any form, combination or dosage within 4 weeks prior to Screening * Donepezil at 23 mg PO * The subject has received active amyloid or tau immunization (i.e., vaccination for Alzheimer's disease) at any time, or passive immunization (i.e., monoclonal antibodies for Alzheimer's disease) within 6 months of Screening