posted on 2022-12-21, 13:41authored byYingying Zhang, Ying Ding, Ning Li, Sen Wang, Si Zhou, Ruping Li, Hui Yang, Wenliang Li, Jinrong Qu
Programmed cell death protein-1/ligand-1 (PD-1/PD-L1)
checkpoint
blockade is a major breakthrough in cancer therapy, but identifying
patients likely to benefit from this therapy remains challenging.
Immunohistochemistry is not informative about PD-L1 expression heterogeneity
because of the limitations of invasive tissue collection. Noninvasive
SPECT imaging is an approach to patient selection and therapeutic
monitoring by assessing the PD-L1 status throughout the whole body.
Here, we radiolabeled a single-domain PD-L1 antibody with technetium-99m
(99mTc) for immune-SPECT imaging to evaluate its feasibility
of detecting PD-L1 expression. The radiochemical purity of [99mTc]Tc-HYNIC-KN035 was 99.40 ± 0.11% with a specific activity
of 2.68 MBq/μg. [99mTc]Tc-HYNIC-KN035 displayed a
high PD-L1 specificity both in vitro and in vivo and showed a high specific affinity for PD-L1 with
an equilibrium dissociation constant (KD) of 31.04 nM. The binding of [99mTc]Tc-HYNIC-KN035 to
H1975 cells (high expression of PD-L1) was much higher than to A549
cells (low expression of PD-L1). SPECT/CT imaging showed that H1975
tumors were visualized at 4 h post-injection and became clearer with
time. However, mild tumor uptake was observed in A549 tumors and H1975
tumors of the blocking group at all time points. The uptake value
of [99mTc]Tc-HYNIC-KN035 in H1975 tumors was increased
continuously from 9.68 ± 0.91% ID/g at 4 h to 13.31 ± 2.23%
ID/g at 24 h post-injection, which was higher than in A549 tumors
with %ID/g of 4.59 ± 0.76 and 5.54 ± 0.28 at 4 and 24 h
post-injection, respectively. These specific bindings were confirmed
by blocking studies. [99mTc]Tc-HYNIC-KN035 can be synthesized
easily and specifically targeted to PD-L1 in the tumor environment,
allowing PD-L1 expression assessment noninvasively and dynamically
with SPECT/CT imaging.