A Phase 2 Study to Evaluate the Safety and Efficacy of BEY2153 in Patients with Early Alzheimer's Disease

Inclusion Criteria: * Male and female adults at the age of ≥ 55 to ≤ 85 at the time of informed consent * Patients diagnosed according to the NIA-AA 2024 Criteria for Diagnosis with Mild Cognitive Impairment (MCI) or diagnosed with mild Alzheimer's disease * CDR-GS 0.5-1.0 at Screening * MMSE ≥ 20 at Screening * Amyloid-positive at amyloid PET scan * Patients who are capable of understanding information provided and can voluntarily sign written informed consent form Exclusion Criteria: * Subjects diagnosed with cognitive impairment due to causes other than substrate causes such as brain lesions, psychiatric disorders, or Alzheimer's disease (e.g., stroke, Parkinson's disease, Lewy body disease, vascular dementia) * Subjects with any of the following cardiovascular diseases at Screening \* Cerebrovascular disease within the past 6 months (cerebral infarction, cerebral hemorrhage, transient ischemic attack, etc.) * Myocardial infarction or unstable angina pectoris within the past 6 months * New York Heart Association (NYHA) Class II congestive heart failure * QTcF ≥450 msec or clinically significant electrocardiogram (ECG) abnormalities * Patients with malignant tumors * Patients with medical conditions that can affect cognitive decline such as hypothyroidism, vitamin B12 or folate deficiency, niacin deficiency, etc. * Patients with a history of alcohol related disorders within the past 6 months * Patients with a positive HIV antibody test result at Screening * Patients with a positive HBs antigen or HCV antibody test at Screening * Patients with active bacterial infections who have received antibiotics within 7 days prior to Screening. * Patients with a history of hypersensitivities to any of the components of investigational product * Patients who have been hospitalized or treated for suicidal behavior within 5 years prior to Screening or whose C-SSRS results at Screening indicate serious suicidal ideation or behavior * Patients who have received treatment for Alzheimer's disease (e.g., Lecanemab) within 6 months prior to Screening * Patients expected to require the administration of a long-acting benzodiazepine (BDZ) for the treatment of sleep disorders at Screening * Any of the following laboratory test values at Screening: * Serum Creatinine \>1.5×ULN or eGFR (MDRD) \<40 mL/min/1.73 m2 * Any of the following: AST, ALT \>3×ULN, or Total bilirubin \>2xULN * Women who test positive for pregnancy at Screening, or women and men of childbearing potential who are planning to become pregnant, or who do not agree to use adequate contraception\* during the study and for 4 weeks after the end of study drug administration \*Adequate contraception: complete abstinence, hormonal contraceptives with no known drug interactions \[Levonorgestrel intrauterine system (IUS) (Mirena), Medroxyprogesterone\], surgical sterilization (including vasectomy, bilateral salpingectomy and ligation). However, intermittent abstinence (e.g., using ovulation timing, symptothermal method, or post-ovulation) or external ejaculation are not considered adequate contraception. * Pregnant or lactating women or women who are tested positive for pregnancy at Screening * Patients treated with other IP within 4 weeks prior to screening * Patients who are considered ineligible for study participation for other reasons based on the judgment of the investigator \[Extension Study\] Inclusion Criteria: * Patients who completed the 26-week visit in the Main Study * Patients who provided written consent to participate in the Extension Study Exclusion Criteria: * Subjects who have dropped out of the Main Study * Patients who, in the investigator's judgement, are not suitable for participation in Extension Study * Any of the following laboratory test values at Baseline: * Serum Creatinine \>1.5×ULN or eGFR (MDRD) \<40 mL/min/1.73 m2 * Any of the following: AST, ALT \>3×ULN, or Total bilirubin \>2xULN