Evaluation of <superscript>68</superscript> Ga- and <superscript>177</superscript> Lu-Labeled HZ20 Angiotensin-Converting Enzyme 2-Targeting Peptides for Tumor-Specific Imaging.

Angiotensin-converting enzyme 2 (ACE2) is closely related to tumor formation. We developed the radiolabeled peptide pair 68 Ga/ 177 Lu-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated DX600 ( 68 Ga/ 177 Lu-HZ20), for the targeting and mapping of ACE2-overexpressing tumors. 68 Ga/ 177 Lu-HZ20 was prepared with a routine labeling method. HepG2 ACE2+ /HepG2 WT cell lines were used to evaluate the specificity of 68 Ga/ 177 Lu-HZ20. Pharmacokinetics, biodistribution, and micro-PET/CT and -SPECT/CT imaging were performed, and radiation dosimetry was estimated. Immunohistochemistry (IHC) staining was performed to assess the expression of ACE2 in tumors. The radiolabeling yields of 68 Ga/ 177 Lu-HZ20 were 88.49 ± 8.57% ( n > 10) and 84.71 ± 9.75% ( n > 10), with specific activities of (18.74 ± 3.72) × 10 6 and (17.85 ± 1.62) × 10 6 GBq/mol, respectively. 68 Ga/ 177 Lu-HZ20 showed significant differences in the cellular uptake of HepG2 ACE2+ /HepG2 WT cells and fast clearance in KM mice. Moreover, HepG2 ACE2+ tumors were clearly visualized in 68 Ga/ 177 Lu-HZ20 micro-PET/SPECT images. Based on micro-PET/CT, the standard uptake value (SUVmax) of HepG2 ACE2+ tumors was 0.66 ± 0.02 at 30 min postinjection, IHC confirmed the high expression of ACE2 in HepG2 ACE2+ tumors. In PET/CT images, the SUVmean of volunteer 1 was higher than the 18 F-FDG value in the same lesion. 68 Ga/ 177 Lu-HZ20 was successfully obtained and showed high and specific uptake in tumors overexpressing ACE2. They may serve as paired probes for ACE2-targeting theranostics.