Evaluation of ⁶⁸Ga- and ¹⁷⁷Lu-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 68Ga/177Lu-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated DX600 (68Ga/177Lu-HZ20), for the targeting and mapping of ACE2-overexpressing tumors. 68Ga/177Lu-HZ20 was prepared with a routine labeling method. HepG2ACE2+/HepG2WT cell lines were used to evaluate the specificity of 68Ga/177Lu-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 68Ga/177Lu-HZ20 were 88.49 ± 8.57% (n > 10) and 84.71 ± 9.75% (n > 10), with specific activities of (18.74 ± 3.72) × 106 and (17.85 ± 1.62) × 106 GBq/mol, respectively. 68Ga/177Lu-HZ20 showed significant differences in the cellular uptake of HepG2ACE2+/HepG2WT cells and fast clearance in KM mice. Moreover, HepG2ACE2+ tumors were clearly visualized in 68Ga/177Lu-HZ20 micro-PET/SPECT images. Based on micro-PET/CT, the standard uptake value (SUVmax) of HepG2ACE2+ tumors was 0.66 ± 0.02 at 30 min postinjection, IHC confirmed the high expression of ACE2 in HepG2ACE2+ tumors. In PET/CT images, the SUVmean of volunteer 1 was higher than the 18F-FDG value in the same lesion. 68Ga/177Lu-HZ20 was successfully obtained and showed high and specific uptake in tumors overexpressing ACE2. They may serve as paired probes for ACE2-targeting theranostics.