MK-6884

MK-6884 is a small molecule positron emission tomography (PET) tracer developed for in vivo imaging of the M4 subtype of muscarinic acetylcholine receptors (M4R) in the brain. It is labeled with carbon-11 ([11C]) and binds selectively to an allosteric site on M4R. The compound acts as a positive allosteric modulator (PAM), enhancing binding of the receptor’s natural ligand acetylcholine; conversely, higher acetylcholine concentrations also increase MK-6884 binding. This cooperative interaction allows MK-6884 to serve as a sensitive biomarker for target engagement by M4 PAMs and to probe neuropathological changes in diseases such as Alzheimer’s disease. The tracer has been used in both preclinical and clinical studies to quantify M4R availability and assess pharmacodynamic effects of cholinergic drugs[1][2][6].