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).