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.
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.