A Study of CST-2032 and CST-107 in Subjects With Mild Cognitive Impairment or Mild Dementia Due to Parkinson's or Alzheimer's Disease

Inclusion Criteria

• Male or female participants ≥ 50 and ≤ 85 years of age at time of informed consent.
• Diagnosis of mild cognitive impairment OR mild dementia due to either: Parkinson's disease associated with REM sleep behavior disorder (RBD+PD) and positive response to the RBD Single-Question Screen (RBD1Q) and without hallucinations; OR Alzheimer's Disease (AD).
• For participants taking medications: stable dose and regimen for at least 30 days (90 days for anti-psychotic medications) prior to Day -1 and the dose must remain unchanged through the End of Study Visit unless required for management of adverse events (AEs).
• Cognitive decline not primarily caused by vascular, traumatic, or medical problems (alternative causes of cognitive decline are ruled out).
• Adequate visual and auditory abilities and motor skills to perform all aspects of the cognitive and functional assessments.
• Has a spouse or caregiver who can accompany the subject at specified study visits (if required based on cognitive function).
• Montreal Cognitive Assessment (MoCA) score ≥ 14 and ≤ 26.
• Unless confirmed to be azoospermic (vasectomized or secondary to medical cause), males must agree to use a male condom from Day -1 until the End of Study visit when having penile-vaginal intercourse with a woman of childbearing potential who is not currently pregnant. Note: Men with a pregnant or breastfeeding partner must agree to remain abstinent from penile-vaginal intercourse or use a condom during each episode of penile-vaginal penetration until after the End of Study Visit.
• Females of childbearing potential (i.e., not postmenopausal or surgically sterile) who have a male partner must have a negative serum pregnancy test result and must agree to one of the following from start of Screening through 30 days after the last study medication administration: use a highly effective method of birth control; or monogamous relationship with a male partner of confirmed sterility; or practice complete abstinence.
• Females of non-childbearing potential may be enrolled if it is documented that they are postmenopausal.
• Body weight greater or equal to 50 kg and body mass index (BMI) between 18 and 35 kg/m^2, inclusive at Screening.
• Stable medical conditions for 30 days prior to Screening visit (e.g., controlled hypertension, dyslipidemia).
• Willing to follow the protocol requirements and comply with protocol restrictions.
• Capable of providing informed consent and complying with study procedures.
• Able to speak, understand and read English.

Exclusion Criteria

• Participants with poorly controlled hypertension despite lifestyle modifications and/or pharmacotherapy.
• Participants with pulmonary disease, including asthma, or evidence of clinically significant moderate or severe pulmonary symptoms.
• Clinical signs indicating syndromes such as corticobasal degeneration, supranuclear gaze palsy, multiple system atrophy, chronic traumatic encephalopathy, signs of frontotemporal dementia, history of stroke, head injury or encephalitis, cerebellar signs, early severe autonomic involvement, or Babinski sign.
• Current evidence of epilepsy, focal brain lesion, head injury with loss of consciousness or meeting DSM-V diagnostic criteria for psychotic disorders, such as schizophrenia or bipolar disorder, or have unstable concomitant psychiatric symptomatology (participants with psychotic disorders may be enrolled if their condition is effectively managed, i.e., must be receiving stable doses of anti-psychotic medications(s) 90 days prior to randomization and must remain on that dose throughout both treatment periods.)
• Evidence of any significant clinical disorder or laboratory finding (e.g., potassium levels below normal range) that renders the participant unsuitable for receiving an investigational drug including clinically significant or unstable hematologic, moderate and severe impairment of hepatic function (as defined by the National Cancer Institute Organ