Near-Infrared Phospha-Rhodamine Probe for Confocal and Multiphoton Imaging of P2X7 Receptor Expression

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Abstract The P2X7 receptor (P2X7R) is an ATP-gated cation channel that plays an important role in inflammatory signaling, cancer progression, and immune regulation. Yet pharmacological tools that enable direct visualization of P2X7 receptor (P2X7R) expression in live biological systems remain limited. We report a near-infrared fluorescent P2X7R probe generated by conjugating the selective antagonist AZD9056 to a sulfonated phospha-rhodamine fluorophore. The resulting probe retains favorable photophysical properties after ligand conjugation, including absorption and emission beyond 700 nm, aqueous solubility, and sufficient brightness for fluorescence imaging. In a YO-PRO-1 dye-uptake assay, the conjugate preserved antagonistic activity at P2X7R, consistent with retained receptor engagement. Confocal microscopy revealed receptor-associated labeling in P2X7R-expressing cells, as evidenced by antibody colocalization and control experiments. The phospha-rhodamine scaffold also enabled multiphoton excitation, allowing visualization of probe-labeled cells and imaging in ex vivo mouse skin with low background and good photostability. Together, these results establish a small-molecule near-infrared probe for fluorescence imaging of P2X7R from single cells to intact tissue and highlight phospha-rhodamine fluorophores as useful scaffolds for targeted receptor imaging.

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