Micro-PET study of 68Ga-HZ20 in the rhACE2-intraperitoneal liver model
To investigate the targeting ability of the 68Ga-HZ20 probe in different tissues and organs, we chose to perform PET imaging studies after in situ injection of different doses of rhACE2 in the liver of KM mice. PET imaging showed clear probe uptake in the liver, and the uptake was rhACE2 dose dependent (Fig. 4A, Fig. S7). Compared with the control group, the rhACE2 injection group showed a higher SUVmax value at the liver injection site, and the SUVmax obtained 15 min after probe injection was 0.43±0.02, 0.52±0.02 and 0.76±0.01, respectively (Fig. 4B). Similarly, the target ratio of liver to muscle in the rhACE2 injection group was significantly higher than that in the blank control group, and the ratio in the 0.4 nmol rhACE2 injection group was higher than that in the 0.2 nmol rhACE2 injection group and reached the highest rate at 60 min, at 1.3±0.20, 2.54±0.27 and 3.95±0.52, respectively (Fig. 4C). After probe injection for 150 min, the liver was sampled for γ counter measurement. Consistent with the PET imaging results, % ID/g in the liver also depended on rhACE2 injection doses, which were 0.24± 0.01, 0.32±0.01, and 0.37±0.02 (Fig. 4D). The correlation analysis between rhACE2 and SUVmax showed the highest correlation 60 min after injection of the probe, and the R2 was 0.9994 (Fig. 4E). There was almost no expression of ACE2 in the liver tissue, but rhACE2 injection artificially increased the protein levels (Fig. 4F).