This study will test a new medicine, *GSK4172239D*, for people aged 18-50 with **Sickle Cell Disease (SCD)**. SCD is a blood disorder where red blood cells shape like sickles, causing pain and other problems. This study will check if the medicine is safe and how it works in the body. There will be three parts: Screening, Treatment, and Follow-Up. Participants will take either the medicine or a *placebo* (a pill with no medicine) once. The study will last at least 20 days. Some will take the medicine again after eating a high-fat meal to see if food changes how the medicine works.

• The study requires men to use protection or be abstinent to prevent pregnancy.
• Participants must have a body weight over 50 kg (about 110 lbs).
• People with serious health problems or recent medicine use may not join.

Think about the time commitment and if you meet the health criteria before joining. This study helps scientists learn more about treating SCD, but there might be risks since it's a new medicine. Always discuss with your healthcare provider before participating.