Overall, investigation of the P2Y family receptors has been challenging due to the absence of potent, selective, and high-specific-radioactivity PET radioligands. Recently, a highly potent (IC50 = 10 nM) P2Y1R antagonist (compound 18) was identified and radiolabeled with [18F] ([18F]18) as shown in Figure 8. Although [18F]18 exhibited fast in vivo metabolism, its high potency and unique allosteric binding mode has provided an opportunity to investigate it as a potential PET tracer for mapping the P2Y1 receptor.256 Additionally, highly potent, selective, and high specific radioligand [32P]MRS2500 has been used successfully to measure human P2Y1 receptor expression in Sf9 insect cell membrane.257
