How fezolinetant is processed in men with prostate cancer taking hormone therapy

Inclusion Criteria:

* Participant is born male, inclusive of all gender ideologies.
* Male participant must agree to use contraception with female partner(s) of childbearing potential (including breastfeeding partner) throughout the treatment period and for 30 days after final fezolinetant administration.
* Male participant must agree to remain abstinent or use a condom with pregnant partner(s) for the duration of the pregnancy throughout the investigational period and for 30 days after final study intervention administration.
* Male participant must not donate sperm during the treatment period and for 30 days after final study intervention administration.
* Participant agrees not to participate in another interventional study while participating in the present study.
* Participant has a body mass index (BMI) range of 18.5 to 30.0 kg/m\^2 inclusive and weighs at least 50 kg at screening.

Inclusion Criteria for Participants with Prostate Cancer:

* Participant is diagnosed with histologically or cytologically confirmed adenocarcinoma of the prostate.
* Participant must be receiving concurrent gonadotropin-releasing hormone (GnRH) agonist or antagonist therapy for a minimum of 3 months prior to study intervention on day 1 and be planning to continue on the therapy for the duration of the study.
* Participant has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 at screening.
* Participant is receiving concurrent and stable enzalutamide, apalutamide or bicalutamide for at least 3 months prior to study intervention on day 1, which must be continued throughout the study.
* Participant has at least 6-month life expectancy.

Inclusion Criteria for Healthy Participants:

* Participant is healthy and has no clinically significant medical conditions based on the physical examination, electrocardiograms (ECGs) and protocol-defined clinical laboratory tests at screening or on day -1.

Exclusion Criteria:

* Participant has had major surgery (e.g., requiring general anesthesia) within 90 days before screening, or will not have fully recovered from surgery, or has surgery planned during the time the participant is expected to participate in the study or within 5 half-lives (approximately 2 days) after the last dose of study drug administration or end-of-study visit (ESV), whichever is longer.
* Participant has/had febrile illness or symptomatic, viral, bacterial (including upper respiratory infection) or fungal (noncutaneous) infection within 28 days prior to day -1.
* Participant has a history of drug or alcohol abuse according to Diagnostic and Statistical Manual (American Psychiatric Association), Fifth Edition (DSM-5) criteria within 2 years before screening.
* Participant has a history of unexplained syncope, cardiac arrest, unexplained cardiac arrhythmias or torsades de pointes, structural heart disease or a family history of long QT syndrome.
* Participant has a gastrointestinal disorder affecting absorption.
* Participant has present exposure or history of participation in a study of the study intervention (fezolinetant) or previous exposure to fezolinetant within 28 days prior to day -1.
* Participant has received any investigational therapy within 90 days or 5 half-lives, whichever is longer, prior to screening
* Participant tests positive for alcohol at screening or on day -1.
* Participant has a positive serology test for hepatitis A virus (HAV) antibodies (immunoglobulin M (IgM)), hepatitis B (HBc) antibodies, hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) antibodies or antibodies to human immunodeficiency virus (HIV) type 1 and/or type 2 at screening.
* Participant tests positive for drugs of abuse (e.g., amphetamines, barbiturates, benzodiazepines, cocaine, opiates and cannabinoids) at screening or on day -1.
* Participant has a positive result for Severe Acute Respiratory Syndrome Coronavirus-2 (novel coronavirus causing COVID-19 disease) (SARS-CoV-2) test at screening or on day -1.
* Participant has creatinine \> 1.5 x upper limit of normal (ULN) or estimated glomerular filtration rate (eGFR) \< 60 mL/min/1.73 m\^2 using the Modification of Diet in Renal Disease formula at the screening visit.
* Participant has active liver disease, jaundice, or elevated liver aminotransferase (ATs) (alanine aminotransferase (ALT) or aspartate aminotransferase (AST)), elevated total bilirubin (TBL) or direct bilirubin (DBL), or elevated alkaline phosphatase (ALP) at screening. A participant with mildly elevated ALT or AST up to \< 1.5 x ULN can be enrolled if TBL and DBL are normal. Participant with mildly elevated ALP (up to \< 1.5 x ULN) can be enrolled if cholestatic liver disease is excluded and no cause other than fatty liver is diagnosed. Participant with Gilbert's syndrome with elevated TBL may be enrolled as long as DBL, hemoglobin and reticulocytes are normal.
* Participant has any condition which makes the participant unsuitable for study participation.
* Participant regularly consumes \> 200 mg of caffeine per day.
* Participant has smoked, used tobacco-containing products or nicotine or nicotine-containing products (e.g., electronic vapes) within 6 months prior to screening or the participant tests positive for cotinine at screening or day -1.
* Participant has had significant blood loss, donated \>/=1 unit (450 mL) of whole blood or donated plasma within 7 days prior to day -1 and/or received a transfusion of any blood or blood products within 60 days.
* Participant has a history of consuming \> 10 units of alcoholic beverages per week within 3 months prior to screening (note: 1 unit = 350 mL of beer, 150 mL of wine, 45 mL of spirits/hard liquor).
* Participant has used any drugs of abuse (e.g., amphetamines, barbiturates, benzodiazepines, cocaine, opiates and cannabinoids) within 3 months prior to day -1.

Exclusion Criteria for Participants with Prostate Cancer:

* Participant has a history of malignancy within 2 years before screening except for prostate cancer. Exception: squamous and basal cell carcinoma of the skin, or other malignancy that is considered cured with minimal risk of recurrence are allowed, upon agreement by the sponsor's medical monitor.
* Participant has had surgery or chemotherapy treatment, immunotherapy or other targeted therapy for prostate cancer within the last 3 months prior to signing informed consent. Radiotherapy is allowed.
* Participant plans to initiate treatment with chemotherapy during the study.
* Participant has a medical condition or chronic disease (including history of neurological \[including cognitive\], hepatic, renal, cardiovascular, gastrointestinal, pulmonary \[e.g., moderate asthma\]) or malignancy that could confound interpretation of the study outcome.
* Participant has known metastases in the liver or any hepatic disorder that could affect drug metabolism deemed clinically significant.
* Participant uses a prohibited therapy or is not willing to wash out such drugs.
* Participant has used any inducer of metabolism (e.g., barbiturates and rifampin) within 28 days prior to day -1.
* Participant uses any concomitant medication that is an inhibitor of CYP1A2, CYP2C9 or CYP2C19 within 7 days prior to day -1.

Exclusion Criteria for Healthy Participants:

* Participant has any history or evidence of any clinically significant cardiovascular, gastrointestinal, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal and/or other major disease or malignancy.
* Participant has used any prescribed or nonprescribed drugs (including vitamins and natural and herbal remedies, e.g., St. John's Wort) in the 28 days prior to study intervention administration (i.e., 45 mg fezolinetant) on day 1, except for occasional use of acetaminophen or paracetamol (up to 2 g/day) and topical dermatological products (including corticosteroid products).
* Participant has a mean pulse \< 40 or \> 90 bpm; mean systolic blood pressure (SBP) \> 160 mmHg; mean diastolic blood pressure (DBP) \> 100 mmHg (measurements taken in triplicate after participant has been resting in the supine position for at least 5 minutes; pulse will be measured automatically) on day -1. If the mean blood pressure exceeds the limits above, 1 additional triplicate may be taken.
* Participant has a mean corrected QT interval by Fridericia's correction formula (QTcF) of \> 450 msec on day -1.
* Participant is an employee of Astellas, the study-related contract research organization (CROs) or the clinical unit.