A 68 Ga‐Substituted Keggin Phosphotungstate as an Intrinsically Radiolabeled Inorganic PET Tracer for Cell Tracking

ABSTRACT Polyoxometalates (POMs) offer unique physicochemical properties for radiopharmaceutical design, yet their integration with clinically relevant radionuclides remains largely unexplored. Here we report the isolation and comprehensive solid‐state and solution characterization of the gallium‐substituted Keggin phosphotungstate cesium salt, Cs 4 [Ga(H 2 O)PW 11 O 39 ]·8H 2 O ( CsGaPW 11 ), including single‐crystal and powder X‐ray diffraction, multinuclear NMR ( 31 P, 71 Ga, 183 W), IR spectroscopy, ESI‐MS, elemental analysis, and TGA. The radiolabeled analogue Cs 68 GaPW 11 (45–55 MBq, >96% radiochemical purity) was synthesized in under 60 min, dictated by the 68 min half‐life of 68 Ga, and retained full structural integrity after radioactive decay. In CHO‐K1 cells, Cs 68 GaPW 11 shows higher cellular uptake than 68 GaCl 3 and 68 Ga‐oxine, with radioactivity progressively shifting from the cell membrane to the intracellular compartment over 60 min. Together with low cytotoxicity (>90% viability at 100 µM), these findings identify the membrane‐permeable Keggin anion as a viable inorganic platform for PET cell tracking.