Simufilam (PTI-125), 100 mg, for Mild-to-moderate Alzheimer's Disease Patients

INCLUSION CRITERIA: 1. Informed consent form (ICF) signed by the subject or legally acceptable representative. 2. Patient has a caregiver or legal representative responsible for administering the drug and recording the time. 3. Ages ≥ 50 and ≤ 85 years 4. Clinical diagnosis of dementia due to possible or probable AD consistent with criteria established by a workgroup of the National Institute on Aging and the Alzheimer's Disease Association. 5. If female, postmenopausal for at least 1 year 6. Patient living at home, senior residential setting, or an institutional setting without the need for continuous (i.e. 24-h) nursing care 7. General health status acceptable for participation in the study 8. Fluency (oral and written) in English or Spanish 9. If receiving memantine, rivastigmine, galantamine or an AChEI, receiving a stable dose for at least 3 months (90 days) before screening. If receiving donepezil, receiving any dose lower than 23 mg once daily. Multiple medications are allowed. 10. The patient is a non-smoker for at least 3 years. 11. The patient or legal representative must agree to comply with the drawing of blood samples for the PK assessments, laboratory assessments and SavaDx. 12. MMSE-2 score ≥ 16 and ≤ 26 at screening, OR if \> 26, must have evidence of AD pathology such as a prior CSF total tau/Aβ42 ratio ≥ 0.28, an amyloid positive PET scan or hippocampal volume loss consistent with AD. EXCLUSION CRITERIA: 1. Anything that in the opinion of the Investigator would preclude participation in a 2-year study. 2. BMI \< 18.5 3. Positive urine drug screen. 4. Positive HIV, HCV or HbsAg screen. 5. Suicidality on C-SSRS 6. Exposure to an experimental drug other than simufilam, experimental biologic or experimental medical device within 3 months before screening 7. A medical condition that would interfere with a lumbar puncture 8. Residence in a skilled nursing facility and requiring 24 h care. 9. Clinically significant laboratory test results 10. Clinically significant untreated hypothyroidism (if treated, thyroid-stimulating hormone level and thyroid supplementation dose must be stable for at least 6 months before screening) 11. Insufficiently controlled diabetes mellitus, including requiring insulin or metformin \>1000 mg/day. 12. Renal insufficiency (serum creatinine \> ULN and clinically significant in the opinion of PI and/or Sponsor OR eGFR \<60 ml/min/m2 as estimated by either the MDRD or CKD-EPI equation) 13. Malignant tumor within 3 years before screening (except squamous and basal cell carcinoma or cervical carcinoma in situ or localized prostate cancer or localized stage 1 bladder cancer) 14. History of ischemic colitis or ischemic enterocolitis 15. Unstable medical condition that is clinically significant in the judgment of the investigator 16. Alanine transaminase (ALT) or aspartate transaminase (AST) \> ULN or total bilirubin \> ULN and clinically significant in the opinion of PI and/or Sponsor. 17. History of myocardial infarction or unstable angina within 6 months before screening 18. History of more than 1 myocardial infarction within 5 years before screening 19. Clinically significant cardiac arrhythmia (including atrial fibrillation), cardiomyopathy, or cardiac conduction defect (patients with a pacemaker are acceptable) 20. Symptomatic hypotension, or uncontrolled hypertension 21. Clinically significant abnormality on screening electrocardiogram (ECG), including but not necessarily limited to a confirmed QTc (Fridericia correction method) value ≥ 450 msec for males or ≥ 470 msec for females. 22. Stroke within 18 months before screening, or history of a stroke concomitant with onset of dementia 23. History of brain tumor or other clinically significant space-occupying lesion on CT or MRI 24. Head trauma with clinically significant loss of consciousness within 12 months before screening or concurrent with the onset of dementia 25. Onset of dementia secondary to cardiac arrest, surgery with general anesthesia, or resuscitation 26. Specific degenerative CNS disease diagnosis other than AD (e.g., Huntington's disease, Creutzfeld-Jacob disease, Down's syndrome, Frontotemporal Dementia, Parkinson's disease) 27. Wernicke's encephalopathy 28. Active acute or chronic CNS infection 29. Donepezil 23 mg or greater QD currently or within 3 months prior to randomization 30. Discontinued AChEI \< 30 days prior to randomization 31. Antipsychotics; low doses are allowed only if given for sleep disturbances, agitation and/or aggression, and only if the subject has received a stable dose for at least 3 months before randomization 32. Tricyclic antidepressants and monoamine oxidase inhibitors; all other antidepressants are allowed only if the subject has received a stable dose for at least 3 months before randomization 33. Anxiolytics or sedative-hypnotics, including barbiturates (unless given in low doses for benign tremor); low doses of benzodiazepines and zolpidem are allowed only if given for insomnia/sleep disturbance, and only if the subject has received a stable dose for at least 3 months before randomization 34. Immunosuppressants, including systemic corticosteroids, if taken in clinically immunosuppressive doses (Steroid use for allergy or other inflammation is permitted.) 35. Antiepileptic medications if taken for control of seizures 36. Chronic intake of opioid-containing analgesics 37. Sedating H1 antihistamines 38. Nicotine therapy (all dosage forms including a patch), varenicline (Chantix), or similar therapeutic agent within 30 days before screening 39. Clinically significant illness within 30 days of enrollment 40. History of significant neurological, hepatic, renal, endocrine, cardiovascular, gastrointestinal, pulmonary, or metabolic disease 41. Loss of a significant volume of blood (\> 450 mL) within 4 weeks prior to the study 42. COVID-19 infection within 3 months