First-in-human Study of Orally Administered KT-621 in Healthy Adult Participants

Inclusion Criteria: * Participants aged 19 to 55 years (inclusive) at the time of consent, with a weight of at least 50 kg if male or 40 kg if female, and a body mass index (BMI) between 18.0 and 30.0 kg/m² (inclusive) at Screening. * Evidence of a personally signed and dated informed consent document indicating that the participant has been informed of all pertinent aspects of the study. * Participants must be willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures. * Male participants (and their partners of childbearing potential) and female participants must agree to the contraception requirements as specified in the clinical protocol. * Female participants may not be pregnant, lactating, or breast-feeding or plan to become pregnant (including ova donation) within 30 days of last study drug administration. * Female participants must have a negative result for pregnancy test at Screening and on admission to the CRU. Exclusion Criteria: * Participants who have a clinically relevant history of respiratory, gastrointestinal (GI), renal, hepatic, hematological, lymphatic, endocrinological, neurological, cardiovascular, psychiatric, musculoskeletal, genitourinary, immunological, dermatological, ophthalmological, or connective tissue diseases or disorders. * Participants who have a clinically relevant surgical history (eg, surgery of the GI tract that could interfere with the PK of the trial medication) Note: prior appendectomy or cholecystectomy is not exclusionary. * Participants with a history of alcohol or substance abuse within the previous 5 years. * Participants who have any known factor, condition, or disease that might interfere with treatment compliance, study conduct or interpretation of the results such as drug or alcohol dependence or psychiatric disease. * Participants who test positive for alcohol and drugs of abuse at Screening and on admission to the CRU. * Participants who have acute GI symptoms at the time of Screening or admission to the CRU (eg, nausea, vomiting, diarrhea, heartburn). * Participants whose results from clinical laboratory safety tests are outside the local reference range at Screening and on admission to the CRU. * Participants who have previously received KT-621 in another cohort in this study. * Participants who have been dosed with any investigational drug or device in a clinical study within 30 days or 5 half-lives (whichever is longer) of KT-621/placebo administration.