Inclusion Criteria:
* Participants with a weight of at least 50 kilograms (kg) if male or 40 kg if female, and a body mass index (BMI) between 18.0 and 32.0 kg/m² (inclusive) at Screening.
* Participants must be willing and able to read, understand, and sign an informed consent form (ICF) which includes compliance with requirements and restrictions listed in the ICF and in this protocol.
* Participants must be willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures.
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 (for example, surgery of the GI tract that could interfere with the PK of the study medication). Note: prior appendectomy or cholecystectomy is not exclusionary.
* 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 have acute GI symptoms at the time of Screening or admission to the CRU (for example, nausea, vomiting, diarrhea, heartburn).
* Participants whose results from clinical laboratory safety tests are outside the local reference range at Screening or on admission to the CRU.
* Participants who have been dosed with any investigational drug or device in a clinical study within 30 days or 5 half-lives, or time determined by local requirements (whichever is longer) prior to admission to the CRU.
* Male participants who do not agree to refrain from sperm donation from admission to the CRU to 90 days after the last dose of KT-621.
* Male participants (and their partners of childbearing potential) and female participants who do not agree to the contraception requirements as specified in the clinical protocol.
* Female participants who are pregnant, lactating, or breastfeeding, or plan to become pregnant during study participation or within 30 days of the last dose of KT-621.
* Female participants with a positive or undetermined pregnancy result at the Screening visit or at admission to the CRU.
