Structure-guided design and clinical evaluation of ⁶⁸Ga-GP01 for FAP-targeted PET imaging in solid tumors

Fibroblast activation protein (FAP)-targeted radioligands have shown superior performance in detecting FAP-expressing cancers. However, the quinoline-based agent ⁶⁸Ga-FAPI-46 exhibits only moderate in vivo stability and suboptimal pharmacokinetics. To overcome these limitations, a FAP inhibitor, GP01 was designed by introducing N-methyl-benzenesulfonic acid side chain on FAPI-46 with enhanced binding affinity and improved in vivo stability. ⁶⁸Ga-GP01 demonstrated high radiochemical purity, favorable binding energy, and excellent in vitro stability. It specifically bound to FAP on A549-hFAP and U87MG cells, exhibiting greater uptake, enhanced internalization, and slower efflux compared to ⁶⁸Ga-FAPI-46. In vivo PET/CT imaging revealed that ⁶⁸Ga-GP01 accumulated specifically in FAP-positive tumor models, with improved pharmacokinetic behavior and a higher tumor-to-background ratio than ⁶⁸Ga-FAPI-46. Tumor uptake correlated significantly with both ex vivo biodistribution and immunohistochemical FAP expression. Clinical evaluation in 35 patients with solid tumors revealed that ⁶⁸Ga-GP01 has optimal pharmacokinetics, persistent target engagement and promising lesion detection, delivering a low effective dose with no adverse events within 6 h post-injection. Furthermore, in a direct comparison with ¹⁸F-FDG, ⁶⁸Ga-GP01 detected more lesions and achieved higher uptake and tumor-to-background ratios. These data support ⁶⁸Ga-GP01 as a clinically translatable FAP-targeted PET tracer and motivate prospective trials in indications where stromal imaging augments or surpasses metabolic imaging.