Micro-PET study of 68Ga-HZ20 in the rhACE2-intraperitoneal spleen model
RhACE2 was injected in situ into the spleen of KM mice, and PET imaging showed significant aggregation of the68Ga-HZ20 probe in the 0.4 nmol rhACE2 injection group (Fig. 5A, Fig. S7). Comparing SUVmax in PET images revealed that the difference in probe uptake in the spleen between the 0.2 nmol rhACE2 injection group and the control group was small, while that in the 0.4 nmol rhACE2 injection group was significantly higher than that of the other two groups, and the SUVmax at 15 min after probe injection was 0.28± 0.03, 0.28±0.01 and 0.58±0.01, respectively (Fig. 5B). Similarly, the splenic muscle target ratio was significantly higher in the 0.4 nmol rhACE2 injection group than in the 0.2 nmol and control groups, with 60 min ratios of 1.25±0.20, 1.30±0.14 and 4.13±0.05, respectively (Fig. 5C). After 60 min of probe injection, the spleen was sampled forex vivo imaging, and PET showed that the probe had a high uptake in the spleen in the 0.4 nmol group and a small amount of uptake in the 0.2 nmol group, especially at the injection site of rhACE2 (Fig. 5D). After ex vivo imaging, the spleen tissue was measured by a γ counter to analyze probe uptake more accurately, and the results showed that the % ID/g in the rhACE2 injection group was significantly higher than that in the control group, which was 0.41±0.01, 0.53±0.01 and 0.86±0.03, respectively (Fig. 5E). The correlation analysis between rhACE2 and SUVmax showed the highest correlation 45 min after probe injection, and the R2was 0.9095 (Fig. 5F). Similarly, there was almost no expression of ACE2 in the spleen, and rhACE2 aggregation in the spleen tissue was observed in the injection group, but the rhACE2 content was significantly lower than that of other model groups with the same dose, although the analysis results may be due to the small volume of the spleen and the leakage of rhACE2 during surgery (Fig. 5G).