PET Imaging of Tumor PD-L1 Expression with a Highly Specific Nonblocking Single-Domain Antibody.

Abstract

Although immunotherapy through programmed death 1/programmed death ligand 1 (PD-1/PD-L1) checkpoint blockade has shown impressive clinical outcomes, not all patients respond to it. Recent studies have demonstrated that the expression level of PD-L1 in tumors is one of the factors that correlate with PD-1/PD-L1 checkpoint blockade therapy. Herein, a 68Ga-labeled single-domain antibody tracer, 68Ga-NOTA-Nb109, was designed and developed for specific and noninvasive imaging of PD-L1 expression in a melanoma-bearing mouse model. Methods: The single-domain antibody Nb109 was labeled with the radionuclide 68Ga through a NOTA chelator. An in vitro binding assay was performed to assess the affinity and binding epitope of Nb109 to PD-L1. The clinical application value of 68Ga-NOTA-Nb109 was evaluated by a stability assay; by biodistribution and pharmacokinetics studies; and by PET imaging, autoradiography, and immunohistochemical staining studies on tumor-bearing models with differences in PD-L1 expression. Results:68Ga-NOTA-Nb109 was obtained with a radiochemical yield of more than 95% and radiochemical purity of more than 98% in 10 min. It showed a highly specific affinity for PD-L1, with an equilibrium dissociation constant of 2.9 × 10-9 M. A competitive binding assay indicated Nb109 to have a binding epitope different from that of PD-1 and PD-L1 antibody. All biodistribution, PET imaging, autoradiography, and immunohistochemical staining studies revealed that 68Ga-NOTA-Nb109 specifically accumulated in A375-hPD-L1 tumor, with a maximum uptake of 5.0% ± 0.35% injected dose/g at 1 h. Conclusion:68Ga-NOTA-Nb109 holds great potential for noninvasive PET imaging of the PD-L1 status in tumors and for timely evaluation of the effect of immune checkpoint targeting treatment.

• Authors: Gaochao Lv, Xiaorong Sun, Ling Qiu, Yan Sun, Ke Li, Qingzhu Liu, Qi Zhao, Songbing Qin, Jianguo Lin
• Journal: Journal of nuclear medicine : official publication, Society of Nuclear Medicine (J Nucl Med) Vol. 61 Issue 1 Pg. 117-122 (01 2020) ISSN: 1535-5667 [Electronic] United States
• PMID: 31253743 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2020 by the Society of Nuclear Medicine and Molecular Imaging.

Chemical References

• B7-H1 Antigen
• CD274 protein, human
• Epitopes
• Gallium Radioisotopes
• Radiopharmaceuticals
• Single-Chain Antibodies

Topics

• Animals
• B7-H1 Antigen (analysis, metabolism)
• Cell Line, Tumor
• Epitopes (chemistry)
• Female
• Gallium Radioisotopes (chemistry)
• Gene Expression Regulation
• Humans
• Immunohistochemistry
• Immunotherapy
• MCF-7 Cells
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Neoplasm Transplantation
• Neoplasms (diagnostic imaging)
• Positron-Emission Tomography
• Protein Binding
• Protein Domains
• Radiopharmaceuticals (chemistry, pharmacokinetics, pharmacology)
• Single-Chain Antibodies (chemistry)
• Tissue Distribution