First-in-Human Study for the Safety and Evaluation of Two 4R Tau Ligands as Potential PET Radioligands for Imaging Tau Protein in the Brain

This clinical study is being conducted to learn more about two new imaging drugs, called \[18F\]ABBV-964i and \[18F\]ABBV-965i, which are designed to help doctors see changes in the brain related to a condition called Progressive Supranuclear Palsy (PSP). PSP is a rare disease that affects movement, balance, and thinking. These drugs are used with a type of scan called PET (Positron Emission Tomography) to show areas of the brain where a protein called tau builds up. Tau buildup is linked to PSP and other brain diseases. The main goal of this study is to find out if these imaging drugs are safe for people and if they work well to show tau in the brain. The study will also look at how the drugs move through the body and how much radiation they give off. Researchers hope this information will help develop better tools for diagnosing PSP and tracking how it changes over time. Who can join? Adults who are healthy or who have PSP may be able to take part. Participants will have screening tests to make sure they qualify. What does participation involve? People in the study will have PET scans, blood tests, and other safety checks. Some participants will also have an MRI scan. The study is divided into three parts: Part A checks radiation levels in healthy volunteers, Part B looks at how the drugs work in the brain of PSP patients and healthy volunteers, and Part C (optional) repeats scans to see if results are consistent. Why is this important? There is currently no cure for PSP, and better imaging tools could help researchers develop new treatments. By joining this study, participants will help advance research that may improve care for people with PSP and similar conditions in the future.