Immune checkpoint inhibitors targeting the programmed cell death-1 (PD-1) and its ligand, PD-L1, have proven to be efficient cancer therapies in a subset of patients. Although patients with expression of PD-L1 in their tumor microenvironement tend to respond better, such information is not always used in treatment decision. Expression of PD-L1 is typically assessed via immunohistochemical detection in a tumor biopsy. However, this method does not take into account the expression heterogeneity within the lesion or throughout the body. To visualize whole-body PD-L1 expression by PET imaging, we developed a Nanobody-based radio-immunotracer targeting PD-L1 site-specifically labeled with gallium-68. The cysteine-tagged Nanobody was site-specifically conjugated with a maleimide (mal)-NOTA chelator and radiolabeling was tested at different Nanobody concentrations and temperatures. Affinity and specificity of the tracer, referred to as [68Ga]Ga-NOTA-mal-hPD-L1 Nb, were assayed by surface plasmon resonance and on PD-L1POS or PD-L1NEG 624-MEL cells. Xenografted athymic nude mice bearing 624-MEL PD-L1POS or PD-L1NEG tumors were injected with the tracer and ex vivo biodistribution was performed 1 h 20 min post-injection. Ideal 68Ga-labeling conditions were found at 50°C for 15 minutes. 68GaGa-NOTA-mal-hPD-L1 Nb was obtained in 80 ± 5% DC-RCY with a RCP > 99% and was stable in injection buffer and human serum up to 3 h (> 99% RCP). The in vitro characterization showed that the NOTA-functionalized Nb retained its affinity and specificity. Ex vivo biodistribution revealed a tracer uptake of 2.26 ± 0.59%IA/g in the positive tumors as compared with 0.42 ± 0.04%IA/g in the negative tumors. Low background uptake was measured in the other organs and tissues, except for the kidneys and bladder due to the expected excretion route of Nbs. The data obtained shows that the site-specifically 68Ga-labeled NOTA-mal-hPD-L1 Nb is a promising PET radio-immunotracer due its ease of production, stability and specificity for PD-L1.
Originele taal-2English
StatusPublished - 8 sep 2021
EvenementVIB Nanobodies conference - Tour & Taxis, Brussels, Belgium
Duur: 8 sep 202110 sep 2021


ConferenceVIB Nanobodies conference
Internet adres


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