LAUSR

ABSTRACT The purinergic receptor P2X ligand‐gated ion channel 7 (P2X7 receptor) is a promising imaging target to detect neuroinflammation. Herein, we report development of a potent iodinated radiotracer for P2X7 receptor, [123I]TZ6019. The radiosynthesis of [123I]TZ6019 was accomplished by allylic‐tin precursor iodination using [123I]NaI with good radiochemical yield of 85% and high radiochemical purity of > 99%. Human embryonic kidney 293 (HEK‐293) cell line stably transfected with the human P2X7 receptor was used to characterize the binding affinity of TZ6019 by fluorescence, radioactive competitive, and saturation binding assays. A radioligand competitive binding assay with [123I]TZ6019 demonstrated that the nonradioactive compound TZ6019 has an IC50 value of 9.49 ± 1.4 nM, and the known P2X7 receptor compound GSK1482160 has an IC50 value of 4.30 ± 0.86 nM, consistent with previous reports. The radioligand saturation binding assay and competitive assay revealed that [123I]TZ6019 specifically bound to the human P2X7 receptor with high affinity (Ki = 6.3 ± 0.9 nM). In vitro autoradiography quantification with brain slices collected from 9‐month old P301S tau transgenic mice along with wild type controls, revealed higher binding of [123I]TZ6019 (35% increase) in the brain of P301S transgenic mice (n = 3, p = 0.04) compared to wild type controls. The immunofluorescence microscopy confirmed that expression of P2X7 receptor was colocalized with astrocytes in the tauopathy P301S transgenic mice. [123I]TZ6019 has specific binding for P2X7 receptor and has great potential to be a radiotracer for screening new compounds and quantifying expression of P2X7 receptor in neuroinflammation related diseases.