Safety and Pharmacokinetics of Single Ascending Doses and Multiple Ascending Doses of CS6253 in Healthy Volunteers

1. Male HVs at least 18 years old.

2. a) Cohort 5 only: Male and female HVs at least 50 years old and if female be of non-childbearing potential, i.e. meet at least one of the following criteria: postsurgical sterilization (hysterectomy or bilateral oophorectomy or tubal ligation) or postmenopausal (amenorrheic for at least 2 years and a serum follicle-stimulating hormone (FSH) > 30 IU/L).

b) If subject is male, must be willing to use acceptable contraception from Day 1 until 30 days after the last dose of study drug.

3. The subject has a body mass index (BMI) within 18-32 kg/m² (inclusive).

4. The subject is in reasonably good health as determined by medical history and physical examination and clinical laboratory tests.

5. The subject is willing and able to speak, read, and understand Spanish and give signed informed consent.

6. The subject must agree to comply with a lumbar catheterization and collection of blood and CSF samples (SAD Cohorts 3-5 only and MAD cohorts).

7. The subject is willing and able to comply with all testing and requirements defined in the protocol.

8. The subject is willing, deemed compliant, and able to remain at the Clinical Research Unit (CRU) for the duration of the confinement period and return for all outpatient visits.

Phase 1B MAD

The eligibility criteria for the Phase 1B MAD study are the same as described for Phase 1A SAD, with the following exceptions:

1. At least 50 years old and female need to be of non-childbearing potential

2. Known to have at least 1 APOE4 allele (homozygous or heterozygous). Note: this criterion applies to on average for the MAD at least 4 APOE4 subjects per cohort

Subjects who meet any of the following criteria will not be enrolled:

1. The subject has any clinically significant deviations from normal in physical examination, ECG, or clinical laboratory tests, as determined by the investigator.

2. The subject has an increased bleeding risk or is treated with anti-coagulation therapies including but not limited to aspirin, coumarin, warfarin and heparin.

3. The subject has had a clinically significant illness within 30 days of check-in, as determined by the investigator.

4. The subject has a history of significant neurological, hepatic, renal, endocrine, cardiovascular, gastrointestinal, pulmonary, or metabolic disease.

5. History of Type 2 diabetes mellitus or hemoglobin A1c (HbA1c) > 7%.

6. Fasting triglycerides > 400 mg/dL

7. Estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73 m2 (Cockcroft-Gault formula)

8. The subject has changed the frequency or dose of chronic medication within the last 8 weeks.

9. The subject has a history of substance abuse or a positive alcohol or urine drug screen at screening or at check-in.

10. The subject has a positive serum hepatitis B surface antigen or positive anti-hepatitis C virus test at the Screening Visit.

11. Have positive test results for, or evidence of active infection with, human immunodeficiency virus type 1 or 2, or hepatitis B, or C.

12. The subject has received an investigational drug within 30 days of Check-in.