Development\nof [<sup>68</sup>Ga]Ga/[<sup>177</sup>Lu]Lu-DOTA-NI-FAPI-04 Containing\na Nitroimidazole Moiety as New FAPI\nRadiotracers with Improved Tumor Uptake and Retention

Fibroblast activation protein (FAP), which is overexpressed\nin\ncancer-associated fibroblasts (CAFs), represents a promising target\nfor cancer diagnosis and therapy. Hypoxia is a common feature of solid\ntumors. A bivalent agent, DOTA-NI-FAPI-04 (<b>1</b>), was developed\nby incorporating hypoxia-sensitive nitroimidazole (NI) into the FAP-targeting\nagent FAPI-04. Compound <b>1</b> exhibited a strong FAP binding\naffinity with an IC<sub>50</sub> of 7.44 nM. Radiolabeled [<sup>68</sup>Ga]Ga-<b>1</b> and [<sup>177</sup>Lu]Lu-<b>1</b> demonstrated\nenhanced <i>in vitro</i> cell uptake. <i>In vivo</i> positron emission tomography/computed tomography (PET/CT) imaging\nshowed that [<sup>68</sup>Ga]Ga-<b>1</b> displayed significantly\nhigher specific uptake and retention in U87MG tumor-bearing mice compared\nto [<sup>68</sup>Ga]Ga-FAPI-04 (SUV<sub>avg</sub>: 7.87 vs 1.99% ID/mL\nat 120 min). Biodistribution studies confirmed superior tumor uptake\nof [<sup>68</sup>Ga]Ga-<b>1</b> (48.15 vs 5.72% ID/g at 120\nmin). Similarly, [<sup>177</sup>Lu]Lu-<b>1</b> exhibited higher\ntumor uptake than [<sup>177</sup>Lu]Lu-FAPI-04 (50.75 vs 20.48% ID/g\nat 120 min). These preliminary results suggest that a nitroimidazole-containing\nbivalent-targeting agent, [<sup>68</sup>Ga]Ga/[<sup>177</sup>Lu]Lu-<b>1</b>, is a promising candidate for tumor theranostics.