PTD802

Myelin is made by cells called oligodendrocytes. These cells are made from special stem cells found in the brain called oligodendrocyte precursor cells (OPCs).

OPCs have a type of receptor called GPR17 on their surface. These receptors can sense signals in the cells’ environment. The GPR17 receptor acts as a ‘brake’ to stop OPCs from turning into oligodendrocytes too quickly. However, researchers have found that there are higher levels of GPR17 in MS lesions.

PTD802 is designed to block the GPR17 receptor. This should release the ‘brake’, allowing OPCs to mature into oligodendrocytes. In doing this, PTD802 has the potential to repair damaged myelin.

PTD802 is designed to be taken by mouth.

PTD802 was developed through Pheno Therapeutics’ programme to make drugs targeting proteins that are important for myelin repair. In January 2025, the biotechnology company Pheno Therapeutics was given approval to begin a Phase 1 clinical trial for PTD802, following promising pre-clinical results. This is the first GPR17 blocker to be tested in humans.

PTD802 has just been approved for testing in a Phase 1 clinical trial, to test the drug in healthy volunteers. The goal of these trials is to assess whether the drug is safe to use in humans. Information on possible side effects is therefore still being gathered.

Current treatments for MS target the immune system to stop further damage to nerve cells and reduce relapses. But we also need to find treatments to repair damaged myelin. PTD802 could work alongside existing MS treatments to slow disease progression.

This is a Phase 1 trial. If it is successful, the drug will still need to go through Phase 2 and Phase 3 trials before it can be made available in the clinic.

Find out more about how treatments are developed.