Study to Evaluate the Safety, Tolerability, and Pharmacokinetics of GSK3915393 in Healthy Participants and to Evaluate the Interaction Between GSK3915393 and Grapefruit Juice and Itraconazole

Inclusion Criteria

• Between 18 and 50 years of age inclusive, at the time of signing the informed consent.
• Healthy participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and cardiac monitoring.
• Negative coronavirus disease of 2019 (COVID-19) test on admission.
• Body weight >=40 kilograms (kg) and body mass index (BMI) within the range 18.5-29.9 kilograms per square meter (kg/m^2) (inclusive).
• Male or females: No restrictions for male participants. A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies: Is a woman of non-childbearing potential (WONCBP) OR Is a woman of childbearing potential (WOCBP) and using an acceptable contraceptive method from 30 days prior to first dose until follow up visit. The investigator should evaluate the potential for contraceptive method failure (e.g., noncompliance, recently initiated in relationship to the first dose of study intervention). A WOCBP must have a negative highly sensitive pregnancy test (serum) at screening and on admission to the clinical unit. The investigator is responsible for review of medical history, menstrual history, and recent sexual activity to decrease the risk for inclusion of a woman with an early undetected pregnancy.
• Capable of giving signed informed consent.

Exclusion Criteria

• History or current evidence of cardiovascular, respiratory, hepatic, renal, gastrointestinal (Irritable bowel syndrome [IBS], Gastroesophageal reflux disease [GERD], nausea, vomiting or dysphagia), endocrine, hematological, neurological, or psychiatric disorders capable of significantly altering the absorption, metabolism, or elimination of drugs; constituting a risk when taking the study treatment; or interfering with the interpretation of data.
• Current evidence of active infection.
• Participants with signs/symptoms suggestive of COVID-19 (i.e. fever, cough, etc) within the past 14 days prior to screening and admission to clinical unit.
• Participants with known COVID-19 positive contacts in the past 14 days prior to screening and admission to clinical unit.
• Any history of suicidal behavior within the past 6 months or any history of attempted suicide in a participant's lifetime.
• Alanine transaminase (ALT) >1.5 times upper limit of normal (ULN).
• Bilirubin >1.5 times ULN (isolated bilirubin >1.5 times ULN is acceptable if bilirubin is fractionated and direct bilirubin 450 milliseconds (msec) at screening.
• Any clinically relevant abnormality on the screening medical assessment, laboratory examination, or electrocardiogram.
• History of QTc prolongation, symptomatic cardiac arrhythmias or cardiac arrest.
• For Part C only, history of liver toxicity resulting from drug administration.
• For Part C only, history of intolerance to itraconazole.
• History of sensitivity to any of the study medication, or components thereof or a history of drug or other allergy that, in the opinion of the investigator or GlaxoSmithKline Medical Monitor, contraindicates their participation.
• Use of any immunosuppressive medications within 6 months prior to entry.
• Unable to refrain from the use of prescription or non-prescription drugs, including vitamins, probiotics, antacids, herbal and dietary supplements (including Saint [St] John's Wort) within 7 days (or 14 days if the drug is a potential enzyme inducer) or 5 half- lives (whichever is longer) prior to the first dose of study medication for each dosing, unless in the opinion of the Investigator and GlaxoSmithKline Medical Monitor the medication will not interfere with the study procedures or compromise participant safety. (Paracetamol is acceptable at a dose of no more than 500 milligrams [mg] at a time and no more than 2 grams [g] per day).
• Participants who have received a COVID-19 vaccine within 7 days of admission (or readmission) to the clinical unit or who are demon