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Updated: Dec 23, 2025
Development of a 68Gallium-Labeled D-Peptide PET Tracer for Imaging Programmed Death-Ligand 1 Expression
Published on: February 3, 2023
Concurrent Injection of Unlabeled Antibodies Allows Positron Emission Tomography Imaging of Programmed Cell Death
Jun Zhao1, Xiaoxia Wen1, Tingting Li1
1Department of Cancer Systems Imaging and Department of Cancer Biology, The University of Texas MD Anderson Cancer Center, 1881 East Road, 3SCRB4.3636, Houston, Texas 77054, United States.
Abstract:
Purpose: Among the treatment options for pancreatic ductal adenocarcinoma (PDAC) are antibodies against the programmed cell death receptor 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway. Positron emission tomography (PET) has been successfully used to assess PD-1/PD-L1 signaling in subcutaneous tumor models, but orthotopic tumor models are increasingly being recognized as a better option to accurately recapitulate human disease. However, when PET radiotracers have high uptake in the liver and spleen, it can obscure signals from the adjacent pancreas, making visualization of the response in orthotopic pancreatic tumors technically challenging. In this study, we first investigated the impact of radioisotope chelators on the biodistribution of 64Cu-labeled anti-PD-1 and anti-PD-L1 antibodies and compared the distribution profiles of anti-PD-1 and anti-PD-L1 antibodies. We then tested the hypothesis that co-injection of unlabeled antibodies reduces uptake of 64Cu-labeled anti-PD-L1 antibodies in the spleen and thereby permits accurate delineation of orthotopic pancreatic tumors in mice. Procedures: We established subcutaneous and orthotopic mouse models of PDAC using KRAS* murine pancreatic cancer cells with a doxycycline-inducible mutation of KRASG12D. We then (1) compared the biodistribution of 64Cu-labeled anti-PD-1 with 2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (p-SCN-Bn-DOTA) and 2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) used as the chelators in the orthotopic model; (2) compared the biodistribution of [64Cu]Cu-NOTA-anti-PD-1 and [64Cu]Cu-NOTA-anti-PD-L1 in the orthotopic model; and (3) imaged subcutaneous and orthotopic KRAS* tumors with [64Cu]Cu-NOTA-anti-PD-L1 with and without co-injection of unlabeled anti-PD-L1 as the blocking agent. Results: [64Cu]Cu-NOTA-anti-PD-L1 was a promising imaging probe. By co-injection of an excess of unlabeled anti-PD-L1, background signals of [64Cu]Cu-NOTA-anti-PD-L1 from the spleen were significantly reduced, leading to a clear delineation of orthotopic pancreatic tumors. Conclusions: Co-injection with unlabeled anti-PD-L1 is a useful method for PET imaging of PD-L1 expression in orthotopic pancreatic cancer models.
Insights
Co-injecting unlabeled anti-PD-L1 antibodies with PET imaging agents significantly reduces spleen uptake. This technique enables clear visualization of orthotopic pancreatic tumors, improving PD-L1 expression assessment in mouse models.
Area of Science:
- Oncology
- Immunotherapy
- Radiochemistry
Background:
- Pancreatic ductal adenocarcinoma (PDAC) is a challenging cancer with limited treatment options.
- Antibodies targeting the programmed cell death receptor 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway are emerging as a therapeutic strategy for PDAC.
- Positron emission tomography (PET) is a valuable tool for assessing PD-1/PD-L1 signaling, but challenges exist in visualizing orthotopic pancreatic tumors due to high liver and spleen uptake of radiotracers.
Purpose of the Study:
- To investigate the impact of radioisotope chelators on the biodistribution of 64Cu-labeled anti-PD-1 and anti-PD-L1 antibodies.
- To compare the biodistribution profiles of anti-PD-1 and anti-PD-L1 antibodies in orthotopic pancreatic tumor models.
- To test if co-injecting unlabeled antibodies can reduce splenic uptake of 64Cu-labeled anti-PD-L1, thereby improving the delineation of orthotopic pancreatic tumors.
Main Methods:
- Established subcutaneous and orthotopic mouse models of PDAC using KRAS* murine pancreatic cancer cells.
- Compared biodistribution of 64Cu-labeled anti-PD-1 and anti-PD-L1 antibodies using different chelators (DOTA and NOTA) in orthotopic models.
- Imaged tumors with 64Cu-labeled anti-PD-L1, with and without co-injection of unlabeled anti-PD-L1, to assess its effect on spleen uptake and tumor visualization.
Main Results:
- 64Cu-labeled anti-PD-L1, particularly with the NOTA chelator, demonstrated promise as an imaging probe.
- Co-injection of excess unlabeled anti-PD-L1 significantly reduced splenic uptake of the 64Cu-labeled probe.
- This reduction in background signal allowed for clear delineation and visualization of orthotopic pancreatic tumors.
Conclusions:
- Co-injection of unlabeled anti-PD-L1 is an effective strategy to overcome imaging challenges in orthotopic pancreatic cancer models.
- This method enhances PET imaging accuracy for assessing PD-L1 expression in the pancreas.
- The findings support the use of this technique for better monitoring treatment response in preclinical studies of PDAC immunotherapy.
