Clinical Study Evaluating Efficacy and Safety of T3D-959 in Mild-to-moderate AD Subjects

Inclusion Criteria: * Have a reliable caregiver, an identified adult who, in the opinion of the investigator has sufficient contact to knowledgeably report on the subject's daily cognition, function, behavior, safety, compliance and adherence. Same caregiver(s) must assist the subject throughout the duration of the trial. * Have a clinical diagnosis of mild-to-moderate AD (Stage 4 or 5) according to the NIA-AA (National Institute of Aging - Alzheimer's Association) criteria at screening * Meet criteria for mild-to-moderate cognitive impairment with Mini-Mental State Examination (MMSE) score of 14 through 26 at the screening visit. * Neuroimaging evidence consistent with the diagnosis of AD * Modified Hachinski \</= 4 at screening * Clinical Dementia Rating is 0.5 to 2.0 at screening and Clinical Dementia Rating - Sum of Boxes is ≥ 3 at screening * Visual and auditory acuity adequate for neuropsychological testing * No evidence of hepatic impairment or renal insufficiency Exclusion Criteria: * Have a current diagnosis of a significant psychiatric illness per the Diagnostic and Statistical Manual of Mental Disorders V (DSM-V) * With untreated clinical depression (GDS \>/= 6 at screening and baseline) * Have a current diagnosis of a neurological disease other than AD * With glycosylated hemoglobin (HbA1c) \>/= 7.7 at screening * With a diagnosis of unstable diabetes * With clinically significant thyroid disease at screening TSH \>5 * Have any of the following values at the screening visit: * ALT and/or AST value that is twice the upper limit of normal * Total bilirubin value that exceeds 2 mg/dL * Creatinine level \>1.5 mg/dL in men or \> 1.4 mg/dL in women * Positive urinalysis (other than trace result) unless a cause other than renal impairment * Glomerular filtration rate (GFR) values \<54 mL/min/1.73 m2 * Gamma-glutamyl transpeptidase (GGT) value that is twice the upper limit of normal * Is positive for hepatitis B or anti-hepatitis C virus antibodies at the screening * Have a history of moderate or severe congestive heart failure, NYHA class III or IV * Have experienced a previous cardiovascular event (myocardial infarct, by-pass surgery, or PTCA) within the past 12 months prior to the baseline * Have blood pressure reading at screening that is greater than 160/100 mmHg * Have a clinically significant unstable illness * Have a history of HIV infection * Have a history of alcohol, drug abuse or dependence * Have a history of cancer within 5 years of the screening * Have any surgical or medical condition which may significantly alter the absorption of any drug substance * Females who are pregnant, nursing or of childbearing potential and not practicing effective contraception * Is required to take excluded medications as specified protocol * Have a known or suspected intolerance or hypersensitivity to the study drug, closely related compounds * Resides in hospital or moderate to high dependency continuous care facility * Are non-ambulatory, or wheelchair-bound * Have evidence of clinically relevant pathology that in the investigator's opinion could interfere with the study results or put the subject's safety at risk * History of swallowing difficulties