Safety Study of MT-4666 in Subjects With Alzheimer's Disease

Inclusion Criteria: * Probable Alzheimer's disease consistent with the National Institute on Aging and the Alzheimer's Association Criteria for Diagnosis of Alzheimer's Disease (McKhann et al. 2011). * MMSE score of ≥ 14 and ≤ 24 at the screening and ≥ 12 and ≤ 26 at the baseline. * Modified Hachinski Ischemic Score (mHIS) ≤ 4 at the screening * Appropriate caregiver available * Subject living at home or in facilities who do not require continuous (24-hour) nursing care. Exclusion Criteria: * Diagnosis of any other disease which may cause dementia * Diagnosis of major depressive disorder as defined by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) within last five years * History of or current diagnosis of any psychosis * History of myocardial infarction or unstable angina within six months before screening * History of cerebrovascular disorder within 18 months before screening * complication of hepatic disorder or renal dysfunction