Micro-PET study of 68Ga-HZ20 in the rhACE2 intratumoral model
Intratumoral injection of rhACE2 and micro-PET imaging in A549 tumor-bearing mice showed that 68Ga-HZ20 accurately tracked rhACE2 in tumors (Fig. 3A, Fig. S6). Consistent with the western blot results, no expression of ACE2 in the A549 tumor was detected by micro-PET imaging with 68Ga-HZ20. In contrast, the probe uptake of the rhACE2-injected group increased with increasing injection dose. Comparing SUVmax in PET imaging in different injection groups also yielded consistent results, and SUVmax at tumor sites reached 0.3±0.08, 0.6±0.07, 0.75±0.03 and 0.94±0.03, respectively, 30 min after probe injection (Fig. 3B). To further investigate the specificity of the probe, the SUVmax ratio of tumor to muscle was analyzed, and the results showed that when the injection group was treated with the same dose of rhACE2 protein, the ratio increased with time. At all time points, the ratio correlated with the rhACE2 injection dose. At 240 min after probe injection, the ratios were 0.88±0.54, 4.59±0.32, 6.22±1.56, and 7.13±0.54, respectively (Fig. 3C). After 240 min of probe injection, the tumor was sampled for ex vivo imaging (Fig. 3D), and consistent results with those of in vivo imaging were observed. γ-counting analysis after ex vivo imaging of tumor tissues showed that the % ID/g of the 0.4 nmol rhACE2 injection group was up to 1.22±0.08, and there were significant differences among rhACE2 doses (Fig. 3E). The correlation analysis between rhACE2 and SUVmax showed the highest correlation 30 min after probe injection, and the R2 was 0.9176 (Fig. 3F). rhACE2 protein bands were validated in the tumor after rhACE2 injection (Fig. 3G).