Radioiodinated compound FJR01: a novel P2X7R-targeted SPECT tracer for visualizing glioma-associated microglia/macrophages in a rat glioblastoma model.

Abstract

The P2X7 receptor (P2X7R) is an imaging biomarker of glioblastoma-associated microglia/macrophages (GAMMs), yet no SPECT tracer is currently available for GAMM imaging. Guided by the high-affinity P2X7R scaffold JNJ-64413739 and molecular docking, we designed two radioiodination-ready analogues, FJR01 and FJR02. Compounds were screenedusing homogenates from cell lines stably expressing mouse or human P2X7R; FJR01 was prioritised (hP2X7R,= 8.8 nM). Radioiodination afforded [I]FJR01 in high radiochemical yield (95%) with excellent stability. In normal mice, biodistribution showed high brain uptake and rapid clearance. In a rat C6 glioma model,SPECT demonstrated focal tumour accumulation, which was corroborated byautoradiography; immunofluorescence confirmed P2X7R expression in GAMMs. Histopathology (H&E) and mouse-to-human dosimetry supported a favourable safety profile and the clinical translation potential of [I]FJR01. In addition, [I]FJR01 is well suited as a probe for competitive binding assays to screen next-generation P2X7R-targeted ligands.