Table 1.

Desired attributes for successful CNS PET ligands

Structure requirements	PK properties
➢ Structural handle for 18F or 11C labeling	➢ Brain permeable
➢ Amenable for late-stage radiolabeling	➢ No brain permeable radioactive metabolites
Pharmacology	➢ Low non-specific binding (NSB)
➢ Occupy the same binding site for the clinical drug candidate	Safety
➢ High potency (typically low single digit nM to sub-nM)	➢ Safe for clinical dosing, typically at μg scale
➢ High selectivity	➢ Microdosing GLP: single species IV + 14 day observation