Evaluating methodological constraints in PET imaging of neuropeptide Y2 receptors with N-[11C]-methyl-(R)-JNJ-31020028 in brains of C57BL/6J mice

Abstract

Background

The Neuropeptide Y (NPY) system regulates mood, stress, and feeding behavior and plays a central role in neuropsychiatric and metabolic disorders. It exerts its effects primarily through a family of G-protein-coupled NPY receptors (NPYR), comprising the Y1, Y2, Y4, and Y5 subtypes. Among these, the Y2 receptor (NPY2R) has emerged as a promising imaging target through its involvement in mood regulation, anxiety, and feeding behavior. This study evaluated the in vivo performance of the selective NPY2R antagonist PET tracer N-[¹¹C]methyl-(R)-JNJ-31020028 in mice, focusing on tracer metabolism, brain uptake, and blood–brain barrier transport via P-glycoprotein (P-gp).

Results

In vitro, N-methyl-(R)-JNJ-31020028 showed nanomolar affinity and selectivity for the murine NPY2R with no observable interaction with mY1, mY4, and mY5. In vivo, brain percent injected dose per cc (%ID/cc), peaked within the first 5 min after injection and declined rapidly. Tariquidar pretreatment increased brain uptake more than threefold at 15 min post administration, particularly in hippocampus, thalamus, and striatum, but differences disappeared at 60 min. Radiometabolite analysis revealed rapid peripheral metabolism, and absence of intact tracer in the brain at 60 min in vehicle-treated mice. In plasma, the parent fraction was unaffected by tariquidar, while it was significantly higher in the brain with P-gp inhibition. Metabolite-corrected brain-to-plasma concentration ratios (K_p,brain) confirmed negligible tracer uptake without P-gp blockade.

Conclusions

N-[¹¹C]methyl-(R)-JNJ-31020028 binds selectively to NPY2R but undergoes rapid metabolism and strong P-gp–mediated efflux at the murine blood–brain barrier. Reliable data interpretation requires early imaging and metabolite correction. For preclinical NPY2R-PET, pharmacological P-gp inhibition may be essential, and future tracers should be optimized for improved metabolic stability.