[11C]MK-6884 Positron Emission Tomography (PET) Tracer Validation Trial (MK-6884-001)

Inclusion Criteria:

Part I, II and III:

- Male, or non-pregnant and non-breast feeding female of 18 to 55 years of age (Part I)
or 55 to 85 years of age (Parts II and III); in addition:

- Male participant who is sexually active with females of childbearing potential
must be willing to use a condom from the first dose of study drug until 3 months
post the last dose of study drug

- Female participant with reproductive potential must have serum β-human chorionic
gonadotropin (β-hCG) test result consistent with non-pregnant state at screening
and agree to use two acceptable methods of birth control beginning at screening
visit, during study and until 2 weeks after the last dose of study drug

- Female participant of non-childbearing potential must be post-menopausal female
(participant has been without menses for at least 1 year and has a follicle
stimulating hormone [FSH] level in the postmenopausal range at screening), or
surgically sterile female (status post hysterectomy, oophorectomy, or tubal
ligation)

- Body Mass Index (BMI) ≤35 kg/m^2, with height ≤195 cm and weight ≤136 kg

- In good health (Part I) or generally healthy (Parts II and III) based on medical
history, physical examination, vital sign measurements and electrocardiogram (ECG)

- Nonsmoker and/or has not used nicotine or nicotine-containing products for at least
approximately 3 months

Part II Only:

- Willing to allow placement of an arterial catheter in the radial artery

- Mini Mental Status Examination (MMSE) score ≥27

- No history of subjective memory or other cognitive complaints

- No objective evidence of memory or cognitive impairment

Part III Only:

- Moderate to severe AD as defined by:

- MMSE score ≤20

- Meets National Institute of Neurological and Communicative Diseases and
Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA)
criteria for probable AD

- Meets Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-V)
criteria for AD

- Rosen-Modified Hachinski score ≤4

- Screening magnetic resonance imaging (MRI) scan consistent with a diagnosis of AD

- Clear history of cognitive and functional decline over ≥1 year

- On a stable dose of one of protocol-defined acetylcholinesterase inhibitors (AChEIs)
(i.e., donepezil and rivastigmine) for symptomatic treatment of AD. Dose must be
stable for at least the last 4 weeks before screening

- Has a reliable trial partner/caregiver who is able to accompany the participant to all
clinic visits, if needed, and able to provide information to study investigator/staff
via telephone contact

Exclusion Criteria:

Part I, II and III:

- Mentally or legally incapacitated, has significant emotional problems at the time of
screening visit or expected during the conduct of the trial or has a history of
clinically significant psychiatric disorder of the last 5 years, except (for Part III
only) for psychiatric disorders associated with AD

- History of clinically significant endocrine, gastrointestinal, cardiovascular,
hematological, hepatic, immunological, renal, respiratory, genitourinary or major
neurological abnormalities or diseases, unless (for Part II and III only) adequately
controlled through a stable medication regimen

- History of cancer

- History of significant multiple and/or severe allergies or has had an anaphylactic
reaction or significant intolerability to prescription or non-prescription drugs or
food. For Part II, this includes any known allergy to lidocaine which may be used as
an anesthetic for the placement of the arterial catheter

- Has positive test result for hepatitis B surface antigen, hepatitis C antibodies or
human immunodeficiency virus (HIV)

- Has had major surgery or donated or lost 1 unit of blood (approximately 500 mL) within
4 weeks prior to screening

- Has participated in another investigational trial within 4 weeks of screening

- Corrected QT (QTc) interval ≥470 msec (for males) or ≥480 msec (for females)

- Is unable to refrain from or anticipates the use of any medication, including
prescription and non-prescription drugs or herbal remedies, beginning approximately 2
weeks prior to administration of the initial dose of study drug and throughout the
study.

- Consumes >3 servings of alcohol a day

- Consumes >6 caffeine servings a day

- Is currently a regular or recreational user of cannabis, any illicit drugs or has a
history of drug (including alcohol) abuse within approximately 3 months

- Has participated in a PET research study or other study involving administration of a
radioactive substance or ionizing radiation within 12 months prior to screening or has
undergone an extensive radiological examination within this period

- Suffers from claustrophobia or an inability to tolerate confinement in small places
and would be unable to undergo MRI or PET scanning

Part II Only:

- Has been administered an AChEI within the prior 3 months or will require administration
of an AChEI during study

Part III Only:

- Has been administered galantamine within the prior 7 days or will require
administration of galantamine during study

- History within 2 years prior to screening, or current evidence of any neurological or
neurodegenerative disorder other than AD that is associated with transient or
sustained alterations in cognition

- History within 2 years prior to screening, or current evidence of a psychotic disorder
or a major depressive disorder

Part II and III Only:

- Has or is suspected to have implanted or embedded metal objects, or fragments in the head
or body that would present a risk during the MRI scanning procedure