Research Study Investigating How Well NDec Works in People With Sickle Cell Disease

This study examines how well a new, potential medicine called NDec works and is tolerated in people with sickle cell disease. NDec is a combination of two medicines (decitabine-tetrahydrouridine). Both medicines are new for the treatment of sickle cell disease. Participants who are not taking Hydroxyurea (HU) will get NDec, NDec and placebo, or placebo. Participants who are on HU treatment before joining the study will get NDec, NDec and placebo, or continue on HU. Which treatment participants get is decided by chance. Participants getting NDec and/or Placebo will get capsules to take twice weekly. The study will last for about a year.