Study Goal: This study, called the PROSPER trial, looks at how well a medication named FNP-223 works to slow down a disease called Progressive Supranuclear Palsy (PSP). Researchers will check if it's safe and how it affects the body over a year.

Who can join: People aged 50-80 with certain types of PSP can join. They need to have had PSP symptoms for 3 years or less. They also need to be able to walk at least 10 steps with little help and have a caregiver who can attend visits.

Who cannot join: People with other brain problems or specific PSP-related genetic issues cannot join. If they have had certain brain scans or tests that show other diseases, they also cannot join.

• The study lasts for 52 weeks (1 year).
• Participants will have regular check-ups to see how they are doing.
• Caregivers need to be available to provide information about the participant's condition.

Participants will be assessed using tools like the PSP Rating Scale (PSPRS) to measure how the disease progresses. This study does involve some tests like brain scans and possibly lumbar punctures (a procedure to get fluid from the spine). All procedures will be discussed with participants before starting.