Abstract
Rationale: 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 the PD-1/PD-L1 checkpoint blockade therapy. Herein, a novel 68Ga-labeled nanobody tracer, 68Ga-NOTA-Nb109, was designed and developed for specific and noninvasive imaging of PD-L1 expression in the melanoma-bearing mice model. Methods: The nanobody Nb109 was labeled with the radionuclide 68Ga through a NOTA chelator. 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 the stability assay, biodistribution and pharmacokinetics studies as well as positron emission tomography (PET) imaging, autoradiography and immunohistochemical staining studies on the tumor-bearing models with different PD-L1 expression. Results: The tracer 68Ga-NOTA-Nb109 was obtained with the radiochemical yield > 95% and the radiochemical purity > 98% in 10 min. It showed a high specific affinity for PD-L1 with the equilibrium dissociation constant (KD) of 2.9 × 10-9 M. A competitive binding assay indicated a different binding epitope for Nb109 compared with PD-1 and PD-L1 antibody. All the biodistribution, PET imaging, autoradiography and immunohistochemical staining studies revealed that the tracer 68Ga-NOTA-Nb109 specifically accumulated in A375-hPD-L1 tumor with a maximum uptake of 5.0 ± 0.35 %ID/g at 1 h. Conclusion: The tracer 68Ga-NOTA-Nb109 holds great potential for noninvasive PET imaging of the PD-L1 status in tumors and timely evaluating the therapeutic effect of immune checkpoint targeting treatment.
- Animal Imaging
- Molecular Imaging
- Oncology: Melanoma
- PET
- Radiopharmaceuticals
- Immune checkpoints
- Nanobody tracer
- PD-L1
- Positron emission tomography
- Copyright © 2019 by the Society of Nuclear Medicine and Molecular Imaging, Inc.