Objective:

In this study

99m

Tc-labeled PD-L1 nanobody was prepared and its potential as a SPECT/CT imaging agentfor the visualization of tumor PD-L1 ex

pression was performed via a xenograft nude mouse model.

Methods:

The PD-L1 nanobody was radiolabeled with

99m

Tc(CO) 3 (H 2 O) 3 . The radiolabeling yields and stabilities were studied by radio-active instant thin layer chromatography (radio-ITLC) and high performance liquid chromatography (HPLC). Micro-SPECT/CT imaging was performed at 30

90 min after intravenous injection of

99m

Tc-PD-L1 nanobody in HCC827 and A549 as PD-L1 expression positive and negative groups

respectively.

Results:

The radiochemical yield of

99m

Tc-PD-L1 nanobody was above 95%

and was stable within 3 h both in phosphate buffered saline (PBS) and human serum at 37℃. SPECT images of 99m Tc-PD-L1 nanobody in tumor models showed that HCC827 tumor lesions were visualized with high contrast at 30

90 min post-injection

while no obvious radioactive signal could be found in A549 tumor lesions

suggesting that the formed

99m

Tc-PD-L1 nanobody could show the PD-L1 expression in tumors and had favorable specificity invivo. Moreover

the

99m

Tc-PD-L1 was mainly accumulated in kidneys and eliminated from the body through urinary system

while other tissues

including liver

spleen

heart

lung and soft tissues

displayed low accumulation and no obvious radioactivity was found in thyroid and gastrointestinal system

indicating the beneficial biodistribution of

99m

Tc-PD-L1.

Conclusion:

99m

Tc-PD-L1 nanobody was successfully prepared with a high radiochemical purity and stability

and could be used as a tumor- specific ligand for SPECT imaging of tumor PD-L1 expression.